Injection Mold

In modern industrial production, mold is an important technology used in shaping products (including metal products and nonmetal products) for all of the industries. Meanwhile, it is the ‘magnifying glass of efficiency and profit’ to the raw material and equipment, because the value of the final product made in the mold is often tens of, even hundreds of times as valuable as that of the mold itself.

The mold industry is the basic industry of the national economy, and it is called ‘the mother of industry’. Every aspect of human life such as clothes, food, housing, and transportation is closely connected with the mold industry. Therefore, the level of injection mold technology has been a significant symbol to measure a country’s developing level of mechanical industry.

And mold can be divided into two kinds of them: mold for metal products and nonmetal products.
The metal products mold include cold-press mold, pressing mold, forging mold, press casting mold, precise casting mold, stamping tool, punch tool, and dust metallurgy mold, etc. These kinds of mold have extensive apply-cation in electrode-cranial products, automobiles, aviation instruments, and other metal products.
The nonmetal products include plastic injection mold, ceramic mold, rubber mold, glass mold, food mold, and ornament mold. These kinds of molds have extensive apply cation in our lives, at this page we are talking about injection mold. this is the most papular modern technology which used in our life everywhere.

An injection mold used to form a plastic product using the injection molding process. A standard injection mould is made of a stationary or injection side containing one or more cavities and a moving or ejection side.

The resin, or raw material for injection moulding, is usually in pellet form and is melted by heat and shearing forces shortly before being injected into the mould. The channels through which the plastic flows toward the chamber will also solidify, forming an attached frame. This frame is composed of the sprue, which is the main channel from the reservoir of molten resin, parallel with the direction of the nozzle, and runners, which are perpendicular to the direction of the nozzle and are used to convey molten resin to the gate(s), or point(s) of the gate and feeding the molten material into the mold cavity. The sprue and runner system can be cut off and recycled after molding. Some moulds are designed such that it is automatically stripped from the part through the action of the mould. For example, the submarine gate or banana gate, if using hot runner systems then there will be no runners.

The quality of the injection molded part depends on the quality of the mould, the care taken during the moulding process, and upon details of the design of the part itself. It is essential that the molten resin is at just the right pressure and temperature so that it flows easily to all parts of the mold. The parts of the injection mold must also come together extremely precisely, otherwise small leakages of molten plastic can form, a phenomenon known as flash. When filling a new or unfamiliar mould for the first time, where shot size for that particular mould is unknown, a technician should reduce the nozzle pressure so that the mold fills, but does not flash. Then, using that now-known shot volume, pressure can be raised without fear of damaging the mould. Sometimes factors such as venting, temperature, and resin moisture content, can affect the formation of flash as well.

Injection Mold Material

Traditionally, molds have been very expensive to manufacture therefore they were usually only used in mass production where thousands of parts are being produced. Injection Molds are typically constructed from hardened steel or aluminum. The choice of material to build a mold is primarily one of economics. Steel molds generally cost more to construct, but their longer lifespan will offset the higher initial cost over a higher number of parts made in the mold before wearing out. Aluminum molds can cost substantially less, and when designed and machined with modern computerized equipment, can be economical for moulding hundreds or even tens of parts.

Requirements for the injection mold

ejection system

An ejection system is needed to eject the molded part from the cavity at the end of the molding cycle. Ejector pins built into the moving half of the mold usually accomplish this function. The cavity is divided between the two mold halves in such a way that the natural shrinkage of the molding causes the part to stick to the moving half. When the mold opens, the ejector pins push the part out of the mold cavity.

cooling system

A cooling system is required for the mold. This consists of an external pump connected to passageways in the mold, through which water is circulated to remove heat from the hot plastic. Air must be evacuated from the mold cavity as the polymer rushes in. Much of the air passes through the small ejector pin clearances in the mold. In addition, narrow air vents are often machined into the parting surface; only about 0.03 mm (0.001 in.) deep and 12 to 25 mm (0.5 to 1.0 in.) wide, these channels permit air to escape to the outside but are too small for the viscous polymer melt to flow through.

All of the information we referred from Wikipedia, but we sort out together for easy to read, if you want to know more, please go to injection mold Wikipedia.


Co-injection molding(or sandwich molding) a process that creates a skin and core material arrangement in a molded part. The skin material is injected first into the mold cavity, and is immediately followed by a core material. As the skin material flows into the cavity, the material next to the cavity walls freezes and material flows down a center channel. When the core material enters it displaces the skin material in the center of the channel by pushing the skin ahead. As it flows ahead it continues to freeze on the walls producing the skin layer

Machine Based Co-Injection molding

The Co-Injection process requires two injection/processing units. The units generally inject material through a manifold located at the end of the injection barrels. The manifold ports the two melt streams into a centrally located nozzle. The machine controls the injection units to achieve a skin-core-skin flow sequence through the manifold into the mold. Last skin flow is needed to clear the short nozzle section of core material and to seal the gate area with skin. This arrangement can be used on any single or multiple cavity, conventional cold runner mold.

Mold Based Co-Injection

This same process can be achieved on a hot runner mold by utilizing a hot runner system from hot runner Corporation. This system, sometimes identified as “Mold Based Co-Injection”, still utilizes two injection units. The two melt streams are directed into the mod via separate channels. These two channels remain separate until they reach the gate area of the part. At this point they flow through a nozzle arrangement similar to the normal co-injection manifold.

Co-Injection Benefits

  • Lower Cost Parts
  • Higher Strength Core
  • Sound Absorption Core
  • Reduced Cooling Time for Lower Temperature Core
  • Improved Aesthetic Qualities
  • Combined Property Characteristics


  • Foamed Core for reduced weight and noise transmission
  • Glass filled cores for improved physical properties
  • Low cost core for cost savings.
  • High gloss skin material over structural core material for combination of aesthetic and structural properties.
  • Post Consumer Recycled material in core. Environmental friendly.
  • Post Industrial recycled Material in core
  • Reground painted parts recycled into core.

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Flexible Gating Advantages, Dependable Reproduction, Economical Process, Easy to Maintain, Fast Molding Cycle, Decreased Tool Wear

SINCERE TECH is mold manufacturer china company that provides plastic mold making and plastic injection molding solutions to industries of the world, started since 2005 we specially make plastic molds for the customer, after 2016 we have bought a plastic injection molding company to mold the molded part for our world customers.

Our advanced manufacturing facilities include a wide range of thermoplastic injection molding solutions for many types of plastic parts, including processes for Hot Runner mold Systems and Cold Runner mold Systems.

Insulated Runner Molds: Hot Runner System With A Twist

Insulated runner systems are inexpensive alternatives to traditional hot runners, where the mold is not heated, but the runner channels are extremely thick and stay molten during continuous cycling.

This feature provides the flexible gating advantages of hot runner switch out the added cost of the manifold and drops of a heated hot runner system.

Properly designed insulated runners, with thermally controlled gate, offer several advantages over hot runner mold systems, including:

  • Dependable reproduction – no “dead spots” in mold
  • Uniform temperature distribution – thermal insulation forms through melt deposited at the wall
  • Economical process for continuous operation of uniform cycles without extended interruptions
  • Easy to maintain – quick to clean
  • Fast production color changes
  • Molds are less expensive to build and to maintain than hot runners
  • Minimal heat loss – thermal equilibrium reached quickly
  • Low energy input on startup – reduces energy cost
  • More consistent volume of polymer per part
  • Faster molding cycles
  • Elimination of runner scrap — less regrind

    Mold manufacturer China

    Mold manufacturer China

  • Improved part finish
  • Decreased tool wear

However, as with hot runners, the insulated runner system also has disadvantages when compared to cold runner systems. The increased level of technology required to manufacture and operate the mold results in:

  • More complicated mold design
  • Higher mold costs
  • More difficult start-up procedures
  • Possible thermal degradation of the polymer melt
  • More difficult color changes than with cold runners

For a quote or more information about how we can help your project, please call us or send us an email, we will quote you in 24 hours.


Molding Flash or burrs

Cold Runner Mold: Plastic Injection Molding, Simple Part Design, Limited Production Runs, Low Maintenance, Change Production Color, Low-Cost Mold

What is cold runner mold

A cold runner mold is a type of injection molding tool where the plastic material is cooled in a separate channel or “runner” before it reaches the individual cavities of the mold. The plastic resin is injected into the cold runner system, where it solidifies before being directed into the cavities to form the final parts. The term “cold” refers to the fact that the runner system is not heated, unlike a “hot runner” mold. Cold runner molds are often used for producing large numbers of small, simple parts and are relatively low-cost to produce.

SINCERE TECH ( provides plastic injection mold solutions to industries of all types and sizes.

Our state-of-the-art mold building facilities include high-speed CNC Milling and mirror EDM Machining for many types of complex specialty injection molds, including insert molds, gas-assist injection molding, 2K mold, multiple cavities mold and unscrewing molds. We can build molds from small to big (25 ton) for both hot runner mold systems and cold runner mold systems.

Cold Runner Molds: Efficient and Economical

Each system has it’s advantages and disadvantages. Choosing the correct system depends on the requirements of the part to be produced. A few of the considerations include:Cold runner mold

  • Part complexity
  • Color requirements
  • Physical characteristics of the material
  • Type of material – virgin or “regrind”
  • Color changes during the production run

Cold runner systems are best used:

  • When the parts produced are of simple design,
  • For limited production runs, or
  • When a rapid change in production colour is needed

In a cold runner mold, the runner (excess material retained in the feed channels) is cooled and ejected with the part. Every cycle, apart, and a runner is produced.

There are two major types of cold runner molds:

  • A two-plate cold runner mold is the easiest and least expensive type of mold to produce. Two plate molds have a single parting plane, and the mold splits into two halves at the plane. Because the runner system must be in line with the parting plane, the part can only be gated on its perimeter.
  • A three-plate cold runner mold differs from a two plate in that it has two parting planes, and the mold splits into three sections every time the part is ejected. This feature provides greater flexibility of design, allowing gating to be placed in the most efficient locations. Since the mold has two parting planes, the runner system can be located on one, and the part on the other, for easier separation.

Cold Runner Mold Systems: The advantages & disadvantages

There are many significant advantages to using a cold runner mold system:

  • Simple, lower-cost mold design and construction
  • Considerably less expensive than a hot runner system
  • Moulds require less maintenance
  • Easier to set up and operate
  • Colour changes are easy – all plastic in the mould is ejected with each cycle

While it is a less expensive process that hot runner systems, there are a few disadvantages to cold runner systems that need to be considered, including:

  • Waste plastic generated
  • Runner material must be either disposed of or
    reground and reprocessed
  • Additional steps in the manufacturing process
  • Regrind will increase variations in the injection 
    molding process
  • Regrinding could decrease the plastic’s strength characteristics and mechanical properties

Is your project ready for molding parts yet? Welcome to send us your requirement for quotation, we will provide you with the best solution base on your part design?

hot runner with manifold

What is hot runner mold

A hot runner mold is a type of injection molding system that uses heated material feed channels, or “hot runners,” to maintain the temperature of the plastics as it flows through the injection mold. This allows for a more consistent and efficient molding process, as the plastic does not have to be reheated between shots so the cycle time will be reduced and will save the waste runner materials ( sometimes has no any runner with hot runner systems). Hot runner systems are commonly used in the production of large quantities of plastic parts, such as in the automotive and consumer goods industries, or used in the stack mold.

DONGGUAN SINCERE TECH CO.LTD(SINCERE TECH) provides plastic injection mould solutions to industries of all types and sizes. For almost 20 years DST has designed, built, and worked on almost every type of mold existing in the plastic industry.

We are experienced in building custom plastic molds for a variety of hot runner mold systems, from hot runner manufacturers like:

  • Husky hot runner systems
  • Synventive hot runner systems
  • Kona hot runner systems
  • DME hot runner systems
  • Mold-Masters hot runner systems
  • INCOE hot runner systems
  • HOSCO hot runner systems

Our state-of-the-art mold building facilities include High precision CNC machines, automatic CMM measurement machine, and Two heads of EDM Machines to create many types of custom molds, including complex specialty injection molds, insert molds, unscrewing molds, overmolding, hot runner mold, cold runner mold, stack mold, gas-assisted injection molds, double injection molds (2k molding), etc. We can build molds for both cold runner systems and hot runner systems.

Hot Runner Molding: Efficient High Production

Each system offers advantages and disadvantages. Choosing the system to employ depends on the requirements of the part to be produced. A few of the considerations include:

Hot runner mold structure

Hot runner mold structure

  • Type of material to use – virgin or “regrind”
  • Colour changes during the production run
  • Single or multiple design production
  • Part complexity
  • Colour requirements
  • Physical characteristics of the material

The primary difference between the two systems is that the hot runner eliminates the excess material retained in the feed channels of a cold runner mold. This feature reduces the number of production steps required and saves in material and energy costs.

Furthermore, mostly hot runners use 100% virgin resins; no reprocessed or “re-grind” material is added. This is an important feature for specific applications where regrinding can cause the material to yellow, or detracts from the material properties, such as clarity in light pipe or lens production, where long-lasting transparency is a specific requirement.

Hot runner molding systems normally inject melted material directly into the individual mold cavity. Hot runner is almost always used for large volume production of thermoplastic injection molded parts, or multiple part production using multi-cavity molds and stack-molding technology.

Hot runner molds are two plate molds with a heated runner system inside one half of the mold. A hot runner system is divided into two parts:

  • The manifold has channels that convey the plastic on a single plane, parallel to the parting line, to a point above the cavity
  • The drops, situated perpendicular to the manifold, convey the plastic from the manifold to the part

Hot-Runner Systems: The advantages and disadvantages

Primary advantages of hot runner systems include:

  • Shorter, faster cycle times – most of them have no runners to cool
  • Smaller machines – reduced shot volume into runners
  • Automated processing – runners do not need to be separated from the parts
  • Gates at the best position for economical design
  • Elimination of runners means
  • Materials cost savings – no runner to regrind or reprocess
  • Least expensive cost/piece
  • Reduction of energy costs
  • No runners to remove or regrind
  • Reduces the possibility of contamination
  • Lower injection pressures
  • Lower clamping pressure
  • Consistent heat within the cavity
  • Shorter cooling time
  • Shot size reduced
  • Cleaner molding process
  • Eliminates nozzle freeze

There are, however, a few disadvantages to hot runner mold systems that need to be considered:

  • Hot runner molds are more complex and expensive to build than cold runner molds
  • Higher initial start-up costs than for cold runner systems
  • Complex initial setup prior to running the mold
  • Higher maintenance costs – more susceptible to:
    • Breakdowns
    • Leakage
    • Heating element failure
    • Wear caused by filled materials
  • Risk of thermal damage to sensitive materials
  • Elaborate temperature control required
  • The colors change is more complex than the cold runner, sometime you will spend lots of time and cost to clean up the hot runner systems, especially for transparency and white color parts.

Hot Runner Molds: Applications & Possibilities

Hot-runner systems are almost always used when large runs have to be manufactured in highly automated production. Additionally, technological advances enable us to build molds with gates positioned to yield the best quality molded parts.

Hot runner molds are sometimes connected to needle valve nozzles, which are activated with precise computer-controlled timing. This allows for a number of advanced processes, including:

  • In-Mold Decoration – lamination with a colored film coating
  • Multi-Cavity Molds – cavities with different geometries and/or volumes
    • Parts that belong together produced in one mold
    • Injection valve opening and closing can be adjusted to the conditions of each individual cavity
    • Injection pressure and holding pressure may be adjusted  independently of each other
  • Controlled Volume Balancing – a weld line can be shifted into a non-critical area of the molded part
  • Stack Molding – two or more mold bases in production simultaneously creating multiple parting lines
Injection moulding service

We are a China injection molding/mold company that provides the Custom injection mould and injection moulding manufacturing services for Variety plastic products over the world. We offer part design, mold design, mold making, massive production, painting, plating, silk-screen, printing, and assembly, all in one-stop services.

Do you know the name of the process by which most plastic solid materials are produced? It is called Injection moulding. It is one of the best molding processes to make millions of injection molding parts in a very short time. However, The initial injection mold tooling cost is pretty high than other machining methods, but this injection tooling cost will be recovered by the large production later, and this process has less or even no waste rate.

Injection molding (or Injection Moulding) is a manufacturing technology for producing products from plastics. Injecting the molten plastic resin at high pressure into an injection mould, which the mold is made according to the desired part shape, the part shape was created by a designer using some CAD design software ( such as UG, Solidworks, etc), The mould is made by a mould company (or mold maker) from metal material or aluminum, and precision-machined to form the features of the desired part by some high technical machines like CNC machine, EDM machine, lather machine, grinding machine, wire-cutting machine, etc, step by step to make final mould cavity base on exactly desired part shape and size, which we called an injection mold.

The injection molding process is widely used for producing a variety of plastic products, from the smallest component to the big bumpers of cars. It is the most common technology to produce molding products on the world today, with some commonly made products including food containers, buckets, storage bins, house cooking equipment, outdoor furniture, automotive components, medical components, molding toys, more and more.

If you want to run your business with injection molding, below some basic information you may need to know

1. Types of Injection Molding

2. Injection molding equipment

    2.1. Injection molding machine

  • 2.1.1 Horizontal or vertical machines
  • 2.1.2 Clamping unit

3. Injection Mold

    3.1. Cold runner mold

  • 3.1.1. Two plate mold
  • 3.1.2. Three plate mold

  3.2. Hot runner mold

4. Injection Molding Process

Types of Injection Molding – Basically 7 types of injection molding process as below

Injection molding equipment

Injection molding machine

Injection molding machine, American normally called injection press (or press), press our custom made injection mold in the machine. The injection machine is rated by tonnage, which indicates the amount of clamping force that the press can generate. This clamping force keeps the mold closed during the injection molding process. There are Various specifications of injection molding machines from less than 5 tons to 6000 tons, or even bigger.


Horizontal Injection-molding-machine

Horizontal or vertical machines

There are normally two types of injection molding machines, Horizontal & vertical molding machines,

This means molding machines fasten the mold in either a horizontal or vertical position. The majority is horizontally injection molding machines but vertical machines are used in some niche applications such as cable insert moldinginsert molding or some special molding process requirement, there are some injection machines can produce two colors, three or four colors molded parts at one step, we call double-shot injection molding machine or 2K injection molding machine (more color will be 3K or 4K molding machine),

Clamping unit

Machines are classified primarily by the type of driving systems they use: hydraulic, electric, or hybrid. Hydraulic presses have historically been the only option available to molders until Nissei introduced the first all-electric machine in 1983. The electric press, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have higher accuracy, however, the machines are more expensive. Hybrid injection molding machines take advantage of the best features of both hydraulic and electric systems. Hydraulic machines are the predominant type in most of the world, with the exception of Japan.

Injection Mold- Types of injection molds

Simply explain the injection mold is custom made of desired part shape by cutting the steel or aluminum, and produce the mold that can be used in the injection molding machine, which we called injection mold or plastic injection mold, go to our plastic molding section to know more about plastic injection mold manufacturing, but to make injection mould actually is not easy, you need to have a professional team (mold maker, mold designer) and mold manufacturing equipment like CNC machines, EDM machines, wire-cutting machines, etc

There are two main types of injection moldscold runner mold (two plate and three plate designs) and hot runner mold (the more common of the runner-less molds). The significant difference is the presence of sprue and runner with every molded part in the cold runner type. This extra molded component must be separated from the desired molded part, the hot runner basically does not have any runner waste of have small runner waste.

Cold runner mold

Developed to provide for injection of thermoset material either directly into the cavity or through sprue and a small sub-runner and gate into the mold cavity, there are basically two types of the cold runner which mostly used in the mold industry, two plate mold and Three plate mold.

two plate cold runner mold

two-plate cold runner mold

Two plate mold

The conventional two-plate mold consists of two halves fastened to the two platens of the molding machine’s clamping unit. When the clamping unit is opened, the two mold halves open, as shown in (b). The most obvious feature of the mold is the cavity, which is usually formed by removing metal from the mating surfaces of the two halves. Molds can contain a single cavity or multiple cavities to produce more than one part in a single shot. The figure shows a mold with two cavities. The parting surfaces (or parting line in a cross-sectional view of the mold) is where the mold opens to remove the part(s).

In addition to the cavity, there are other features of the mold that serve indispensable functions during the molding cycle. The mold must have a distribution channel through which the polymer melt flows from the nozzle of the injection barrel into the mold cavity. The distribution channel consists of (1) a sprue, which leads from the nozzle into the mold; (2) runners, which lead from the sprue to the cavity (or cavities); and (3) gates that constrict the flow of plastic into the cavity. There are one or more gates for each cavity in the mold.

Three plate cold runner mold

Three-plate cold runner mold

Three plate mold

The two-plate mold is the most common mold in injection molding. An alternative is a three-plate mold. There are advantages to this mold design. First, the flow of molten plastic is through a gate located at the base of the cup-shaped part, rather than at the side. This allows more even distribution of melt into the sides of the cup. In the side gate design in the two-plate the plastic must flow around the core and join on the opposite side, possibly creating a weakness at the weld line. Second, the three-plate mold allows more automatic operation of the molding machine. As the mold opens, it divides into three plates with two openings between them. This forces the disconnection of runner and parts, which drop by gravity (with possible assistance from blown air or a robotic arm) into different containers beneath the mold.

Hot Runner Mold

Hot runner molding has parts that are physically heated. These types of molding help transfer the molten plastic quickly from the machine directly feeding into the mold cavity. It can also be known as the runner-less mold. The hot runner system is very useful for some of the high volumes of products, that will save huge production costs by using the hot runner mold system. The sprue and runner in a conventional two-plate or three-plate mold represent waste material. In many instances they can be ground and reused; however, in some cases, the product must be made of “virgin” plastic (original raw plastic material) or there is multiple cavity mold ( such as 24 cavities, 48 cavities. 96 cavities, 128 cavities or even more cavities mold). The hot-runner mold eliminates the solidification of the sprue and runner by locating heaters around the corresponding runner channels. While the plastic in the mold cavity solidifies, the material in the sprue and runner channels remains molten, ready to be injected into the cavity in the next cycle.

Type of hot runner system.

Basically there are two types of hot runner systems, one is cal hot sprue mold (without the manifold plate and hot runner plate) and one is hot runner mold (with the manifold plate and hot runner plate).

Hot sprue mold (without the manifold plate and hot runner plate) is using the hot nozzle (sprue) feeding the material into the mold cavity directly or indirectly.

hot runner mold (with the manifold plate and hot runner plate) means the hot runner system has the hot runner plate, manifold plate, and sub-hot runner sprue. The below pictures are simple explaining for two types of hot runner systems.

Advantages and Disadvantages of Cold Runner Molding

There are a few, amazing advantages of cold runner molding such as:

  1. Cold runner molding is cheaper and easier to maintain.
  2. You are able to quickly change colors.
  3. It has a faster cycle time.
  4. It is more flexible than hot runner molding.
  5. The gate locations can easily be changed or fixed.

Although there are many advantages, there are also some disadvantages. The disadvantages of cold runner molding are:

  1. You have to have thicker dimensions compare to the hot runner mold.
  2. You can only use certain types of nozzles, fittings, and manifolds.
  3. Cold runner molding can result in slower production time when you remove sprues and runners.
  4. You must manually separate the runner and parts after molding.
  5. You may waste the plastic materials if you do not reset after each run.

If you want to know more information, please go to the cold runner mold page to check more detail.

Advantages and Disadvantages of Hot Runner Molding

Hot runner molding has a few advantages such as:

  1. Hot runner molding has a very quick cycle time.
  2. You can save production costs by using hot runner molding.
  3. Less pressure is needed to inject the molding.
  4. You have more control over the hot runner molding.
  5. Hot runner molding can fit a wide variety of gates.
  6. multiple cavities mold can be easily done by using the hot runner system.

The disadvantages to using hot runner moldings are:

  1. It is more expensive to make the hot runner mold than cold runner mold.
  2. It is difficult to maintain and fix the hot runner mold.
  3. You are not able to use hot runner molding on materials that are thermally sensitive.
  4. You will need to get your machines inspected more often than cold runner molding machines.
  5. It is hard to change the colors to the hot runner mold system.

Want to know more information, welcome to the hot runner mold section to know more.

Injection Molding Processing?

Injection molding

Injection molding

Injection molding is one of the best ways to shape plastic products by injecting a thermoplastic material, During the process of injection molding, the plastic material in the injection molding machine and use the melt system of the injection unit to melt the plastics into the liquid, then use high pressure injecting the liquid material into a mold (custom manufacturing mold) which assembled in that injection molding machine. The mold is made up of any metal such as steel or aluminum. The molten form is then allowed to cool down and set it into a solid form.

The plastic material thus formed is then ejected out of the plastic mold. The actual process of plastic molding is just an expansion of this basic mechanism. The plastic is let into a barrel or chamber under gravity or force-fed. As it moves down, the increasing temperature melts the plastic resin. Then, the molten plastic is forcibly injected into the mold under the barrel with an appropriate volume. As the plastic cools, it solidifies. The injection molded parts like this has a reverse shape than that of the mold. A variety of shapes both 2D and 3D can be produced by the process.

The process of plastic molding is cheap due to the simplicity involved and the quality of the plastic material is modifiable by changing the factors involved in the custom injection molding process: – The pressure of injection can be changed to change the hardness of the final product. – The thickness of the mold also governs the quality of the article produced. – The temperature for melting and cooling determine the quality of the plastic formed. ADVANTAGES The major advantage of injection molding is that it is very cost-effective and fast. Apart from this, unlike the cutting processes, this process rules out any undesired sharp edges. Also, this process produces smooth and finished products that require no further finishing. Check below for the detail advantages and disadvantages.

Advantages of injection moulding

Although injection molding is used by many different companies, and there is no doubt this is one of the most popular methods to produce the injection molding products, there are some of the advantages of using them such as:

  • Precision and aesthetics – because in this injection moulding process you can make your plastic part with any shape and surface finished ( texture and high gloss finishing), some of the special surface finishing still can meet by the secondary surface finishing process, injection moulding part is the repeatability of their shapes and dimensions.
  •  Efficiency and speed – a single production process, even for the most complex products, lasts from a few to several dozen seconds,
    The possibility of full automation of the production process – which in the case of companies dealing with the production of plastic components translates into low production effort and the possibility of mass production.
  • Ecology – because compared to metalworking, we are dealing with a significant reduction in the number of technological operations, less direct energy and water consumption and low emissions of compounds harmful to the environment.

Plastics are materials that, although known relatively recently, have even become indispensable in our lives, and thanks to increasingly modern production processes from year to year they will contribute even more to saving energy and other natural resources.

Disadvantages of injection molding

  • The high cost of injection molding machines and often the cost of tooling (molds) that equals it resulting in extended depreciation time and high costs of starting production.
  • Due to the above, injection technology is only cost-effective for mass production.
  • The need for high qualifications of technical supervision employees who must know the specifics of injection molding processing.
  • The need for high technical requirements for injection mold making
  • The need to maintain narrow tolerances of processing parameters.
  • A long time of preparation of the production due to the labor-intensive implementation of the injection molds.

Injection Molding Cycle Time

The basic injection cycle time is including Mold close – injection carriage forward –plastics filling time – metering – carriage retracts – holding pressure – cooling time – mold open – eject part(s)

The mold is closed shut by the injection molding machine, and the melted plastics is forced by the pressure of the injection screw to inject into the mold. The cooling channels then assist in cooling the mold and the liquid plastics become solid into the desired plastic part. The cooling system is one of the most important parts in the mold, inappropriate cooling can result in distorted molding products and the cycle time will be increased, this will increase the injection molding cost as well.

Injection Molding

Molding trial

When the injection plastic mold has been made by mold maker, the first thing we need to do the mold trial, this is the only way to check the mold quality if made according to custom requirement or not, to trial the mold we normally fill the plastics the molding step by step, use short shot filling at the first and increase the material weight little by little until the mold is 95 to 99% full. After meeting this status a small amount of holding pressure will be added and holding time increased until the gate freeze off has been occurred, then holding pressure is increased until the molding part is free of sink marks and part weight has been stables. Once the part is good enough and has passed any specific technical tests, a machine parameter sheet needs to be recorded for massive production in the future.

Plastic Injection Molding Defects

Injection molding is a complex technology and problems may happen every time. A new custom made of an injection mold has some issue is very normal, to solve the mold issue we need to fix and test the mold several times, normally two or three times trial can completely solve all o issue, for some of the cases only need one-time mold trial can be approved the samples. and finally, all of the issues are solved completely. Below are most of the injection molding defects and the troubleshooting skills to solve those issues.

Issue No. I: Short shot defects- What is a short shot issue?

Injecting material into the cavity, molten material does not completely fill the cavity, resulting in the product lacking material. This is called Short Molding or Short Shot as shown in the picture, there are lots of reason to cause the short shot issues,

short shot

Fault Analysis and Method for Correction the defects

  1. Improper selection of injection molding machine – When choosing plastic injection machines, the maximum shot weight of the plastic injection machine must be bigger than the weight of the product. During verification, the total injection volume (including the plastic product, runner and trimming) shall not be more than 85% of the plasticizing capacity of the machine.
  2. Insufficient supply of material -The bottom of the feed position might have “bridging the hole” phenomena. The shot stroke of the injection plunger should be added to increase the supply of material.
  3. Poor flow factor of raw material – improve mold injection system, for example, by proper design of runner location, by enlarging gates, runner and feeder size, and by using a bigger nozzle, etc. In the meantime, the additive can be added to the raw material to improve the flow rate of the resin or change the material with a better flow rate.
  4. Overdose of using the lubricant – Reduce the lubricant and adjust the gap between barrel and injection plunger to recover the machine, or fix the mold so that is no need any lubricant during the molding process
  5. Cold foreign substances blocked the runner – This issue is normally happened to hot runner systems, dismount and clear the nozzle of hot runner tip, or enlarge the cold material cavity and runner cross-section area.
  6. Improper design of injection feeding system – When designing the injection system, pay attention to gates balance, product weight of each cavity should be in proportion of gates size, so as to make each cavity can be full filled simultaneously and gates should be positioned in thick walls. A balanced separate runners scheme can also be adopted. If the gate or runner is small, thin, or long, the molten material pressure will be reduced too much during running and the flow rate is blocked, which will result in the poor filling. To solve this problem, the cross-sections of the gate and runner should be enlarged and use multiple gates when necessary.
  7. Lack of venting – Check if there is cold-slug well or if the position of cold-slug well is correct. For mold with a deep cavity or deep ribs, venting slots or venting grooves should be added at positions of short molding (end of feeding area). Basically, there is always have venting grooves on the parting line, venting grooves size can be 0.02-0.04mm and 5-10mm width, 3mm close to the sealing area, and venting opening should be at the end of filling the position. When using raw materials with excessive moisture and volatile content, a large amount of gas (air) will also be generated, causing the air trap in the mold cavity. In this case, raw material should be dried and cleared in volatile substances. In addition, during the injection process operation, poor venting can be addressed through increasing mold temperature, low injection speed, reducing injection system obstruction and reducing mold clamping force, and enlarging gaps between molds. But the short shot issue happens to the deep ribs area, to release the air out, you need to add venting insert to solve this air trap and short shot issues.
  8. The mold temperature is too low – Before starting molding production, mold should be heated up to the required temperature. In the beginning, should connect all of the cooling channels and check if the cooling line is working well, especially for some special material, like PC, PA66, PA66+GF, PPS, etc, the perfect cooling design is the must for those special plastics material.
  9. Molten material temperature is too low – In proper molding process window, the temperature of the material is in the proportion of filling length, low-temperature molten material is poor in fluidity and the filling length is shortened. It should be noted that after the feed barrel is heated to the required temperature, it should stay constant for a while before start molding production. In case that low-temperature injection must be used to prevent molten material being resolved, the injection cycle time can be prolonged to overcome short shot, if you have professional molding operator he should know this very well
  10. Nozzle temperature is too low – When open mold, the nozzle should be part away from the mold spure to reduce the influence of mold temperature on the nozzle temperature and keep the nozzle temperature within the range of the molding process requires.
  11. Insufficient injection pressure or holding pressure –  Injection pressure is close to a positive proportion to the filling distance. The injection pressure is too low, the filling distance is short, and the cavity cannot be fully filled, increasing the injection pressure and holding pressure can improve this issue
  12. Injection speed is too slow – Mold filling speed is directly related to injection speed. If injection speed is too low, filling of molten material is slow while slow-flowing molten is easy to cool hence the flow properties further decrease and result in short injection. For this reason, the injection speed should be enhanced properly.
  13. Plastic product design is not reasonable – If the wall thickness is out of proportion to the length of the plastic product and the product shape is very complex and the forming area is large, melt material is easily blocked at the thin wall of the product and leading to insufficient filling. Therefore, when designing the shape and structure of the plastic products, note that wall thickness is in direct relation to melting limit filling length. During injection molding, product thickness should range between 1-3mm and 3-6mm for large products. Generally, it is not good for injection molding if the wall thickness is over 8mm or less than 0.4mm, so this kind of thickness should be avoided in design.

Issue No. II: Trimming (Flashing or burrs) Defects

I. What is the flashing or Burrs?

When extra plastic melt material is a force out of mold cavity from the mold joint and forming thin sheet, trimming is generated, if the thin sheet is big in size, it is called flashing.

Molding Flash or burrs

Molding Flash or burrs

II. Fault Analysis and Method for Correction

  1. Mold clamping force is not sufficient. Check whether the booster is over pressurizing and verify whether the product of the projected area of the plastic part and the forming pressure exceeds the clamping force of the equipment. Forming pressure is the average pressure in the mold, normally is 40Mpa. If the calculation product is larger than the mold clamping force, it indicates that the clamping force is insufficient or the injection positioning pressure is too high. In this case, the injection pressure or the section area of the injection gate size should be reduced, pressure keeping and pressurization time can also be shortened, or reduce injection plunger stroke, or reduce the number of injection cavity or use mold injection machine with larger tonnage.
  2. Material temperature is too high. The temperature of feed barrel, nozzle and mold should be decreased properly and reduce the injection cycle. For melts of low viscosity, like polyamide, it is difficult to solve overflow flashing defects by simply changing injection molding parameters. To solve this issue completely, fix the mold is the best way, like do better mold fitting and make the parting line and shot off area more precisely.
  3. Mold defect. Mold defect is the main reason for overflow flashing. The mold must be carefully examined and re-verified the mold parting line to ensure the pre-centering of mold. Check whether the parting line fits well, whether the gap between sliding parts in the cavity and core is out of tolerance, whether there is adhesion of foreign matter on the parting line, whether the mold plates are flat and whether there is bending or deformation, whether the distance between mold pate is adjusted to fit the thickness of the mold, whether the surface mold block is damaged, whether the pull rod is deformed unevenly, and whether the venting slot or grooves is too large or too deep.
  4. Improper of the molding process. If injection speed is too high, injection time is too long, injection pressure in the mold cavity is unbalanced, mold filling speed is not constant, or overfeeding of material, overdosage of lubricant can lead to flashing, therefore corresponding measures should be taken according to the specific situation during operation.

Issue No. III. Welding Line (Joint Line) Defects

I. What is the welding line defect?

Welding line

Welding line

When filling the mold cavity with molten plastic material, if two or more flows of molten material have cooled down in advance before confluence t the joint area, the flows will not be able to totally integrate and a liner is produced at the confluence, thereby a welding line is formed, also called joint line

II. Fault Analysis and Method for Correction

  1. Material temperature is too low. Low-temperature molten material flows are poor in confluence performance and the welding line is easily formed. If welding marks appear at the same position of both interior and exterior of a plastic product, usually it is inappropriate welding caused by the low temperature of the material. To address this problem, feeding barrel and nozzle temperature can be properly increased or the injection cycle can be prolonged to increase the material temperature. In the meantime, the coolant flow inside the mold should be regulated to properly increase mold temperature. Generally, the strength of the plastic product welding line is relatively low, if the position of the mold with the welding line can be partially heated to partially increase the temperature at the welding position, the strength at the welding line can be enhanced. When low-temperature injection molding process is used for special needs, injection speed and injection pressure can be increased to improve confluence performance, a small dosage of lubricant can also be added to the raw material formula to increase molten flow performance.
  2. Mold Defect. The fewer numbers of the gate should be adopted and the position of the gate should be reasonable to avoid inconsistent filling speed and interruption of molten flow. Where possible, one point gate should be adopted. To prevent low-temperature molten material generates welding mark after injected into the mold cavity, mold temperature and add more cold well in the mold
  3. Poor mold venting solution. Check whether the venting slot is blocked by solidified plastic or other substance at first (especially happened to some glass fiber material), and check whether there is a foreign substance at the gate. If there still are carbonation spots after removing the extra blocks, add venting groove at the flow convergence in the mold, or change the gate location, reduce mold clamping force to increase venting intervals to speed up the convergence of material flows. In terms of the molding process, reducing material temperature and mold temperature, shortening high-pressure injection time, decreasing injection pressure can be taken.
  4. Improper use of release agents. In injection molding, usually, a small quantity of release agent is evenly applied at the thread and other position not easy to demould. In principle, the use of the release agent should be reduced as far as possible. In the massive production should never use a release agent.
  5. The structure of plastic products is not reasonably designed. If the wall of the plastic product is too thin or the thickness differs greatly, or there are too many inserts, it will cause poor welding. When designing a plastic product, it shall be ensured that the thinnest part of the product must be greater than the minimum wall thickness allowed during forming. In addition, reduce the number of inserts and make the wall thickness to be uniform as possible.
  6. The welding angle is too small. Each kind of plastic has its own limit welding angle. When two flows of molten plastic converge, the welding mark will appear if the converging angle is smaller than the limit welding angle and will disappear if the converging angle is bigger than the limit welding angle. Usually, the limit welding angle is around 135 degrees.
  7. Other causes. Different degree of poor welding can be caused by use of raw material with excessive moisture and volatile content, oil stains in the mold that are not cleaned up, cold material in mold cavity or uneven distribution of fiber filler in the molten material, unreasonable design of mold cooling system, fast solidification of the melt, low temperature of the insert, small nozzle hole, insufficient plasticizing capacity of the injection machine, or large pressure loss in the plunger or barrel of the machine. To solve these problems, different measures, such as pre-drying of raw materials, regular cleaning of mold, changing the design of mold cooling channel, controlling the flow of cooling water, increasing the temperature of inserts, replacing nozzles with larger apertures, and using injection machines with larger specifications, can be taken in the process of operation.

Issue No. IV: Warp Distortion – What is warp distortion?

Due to internal shrinkage of the product is inconsistent, the internal stress is different and distortion occurs.

Warp Distortion

Warp Distortion

Fault Analysis and Method for Correction

1. The molecular orientation is unbalanced. In order to minimize warp distortion caused by diversification of molecular orientation, create conditions to reduce the flow orientation and relax orientation stress, the most effective method is to reduce molten material temperature and mold temperature. When this method is used, it is better to combine with heat treatment of the plastic parts, otherwise, the effect of reducing molecular orientation diversification is often of short duration. The method of heat treatment is: after demoulding, keep the plastic product at a high temperature for some time and then cool to room temperature gradually, in this way, the orientation stress in the plastic product can be largely eliminated.

2. Improper cooling. When designing a plastic product structure, the cross-section of each position should be consistent. Plastic must keep in the mold for a sufficient time for cooling and forming. For the design of a mold cooling system, cooling pipelines should be at positions where the temperature is easy to rise and the heat is relatively concentrated, as for the positions easily cool down, gradual cooling should be adopted to ensure balanced cooling of each position of the product.

Warpage issue

Warpage issue

3. The gating system of mold is not properly designed. When determining the gate position, be aware that the molten material shall not directly impact the core, and be sure the stress on both sides of the core is the same. For large flat rectangular plastic parts, membrane gate or multi-point gate shall be used for resin raw materials with wide molecular orientation and shrinkage, and side gate shall not be used; for ring parts, disk gate or wheel gate shall be used, and side gate or pinpoint gate shall not be used; for housing parts, the straight gate shall be used, and side gate shall not be used as far as possible.

4. Demolding and venting system is not properly designed. In-mold design, draft angle, position, and the number of ejectors should be reasonably designed to improve mold strength and positioning accuracy. For small and medium-sized molds, anti warping molds can be designed and made according to warping behavior. In respect of mold operation, ejection speed or ejection stroke should be properly reduced.

5. Improper operation process. The process parameter shall be adjusted according to the actual situation.

Issue No. V: Sink Mark Defects – What is the sink mark?

Sink marks are unevenly shrinking of the surface caused by the inconsistent wall thickness of the plastic product.

Sink marks

Sink marks

Fault Analysis and Method for Correction

  1. The injection molding condition is not properly controlled. Properly increase injection pressure and speed, increase molten material compression density, prolong injection and pressure keeping time, compensate the sinking of the molten, and increase the buffering capacity of injection. However, the pressure should not be too high, otherwise, the convex mark will appear. If sink marks are around the gate, prolong the pressure keeping time can eliminate the sink marks; if sink marks are at the thick wall, prolong the cooling time of the plastic product in the mold; if sinks around insert are caused by partial shrinkage of molten, the main reason is that the temperature of the insert is too low, try to increase the temperature of the insert to eliminate the sink marks; if sink marks are caused by insufficient material feeding, increase the material. Besides all of this, the plastic product must be fully cooled in the mold.
  2. Mold defects. According to the actual situation, properly enlarge gate and runner cross-section, and the gate should be at a symmetrical position, feed inlet should be in the thick wall. If sink marks appear away from the gate, the cause usually is that flow of molten material is not smooth at some position of the mold, which hampers the transmission of pressure. To solve this problem, enlarge the injection system size to allow the runner to extend to the position of the sink marks. For products with thick walls, wing type gate is preferred.
  3. Raw material cannot meet molding requirements. For plastic products with high finish standards, resin with low shrinkage shall be used or the appropriate dosage of lubricant can also be added to the raw material.
  4. Improper design of product structure. The wall thickness of the product shall be uniform, if the wall thickness differs a lot, the structure parameter of the injection system or the wall thickness shall be adjusted.

    sink marks defects

    sink marks defects

Issue No. VI: Flow Mark-What is Flow Mark?

Flow mark is a linear trace on the surface of a molding product that shows the flow direction of molten material.

Flow mark

Flow mark

Fault Analysis and Method for Correction

  1. Ring shape flow mark on the surface of the plastic part with the gate as the center caused by poor flow motion. To address this kind of flow marks, increase the temperature of mould and nozzle, increase injection rate and filling speed and prolong pressure keeping time, or add a heater at the gate to raise the temperature around the gate. Appropriately expand the gate and runner area can also work, while the gate and runner section is preferably circular, which can guarantee the best filling. However, if the gate is in the weak area of the plastic part, it shall be square. In addition, a large cold-slug well should be set at the bottom of the injection port, and at the end of the runner; the greater the influence of material temperature on the flow performance of the melt, the more attention should be paid to the size of the cold-slug well. The cold-slug well must be set at the end of the melt flow direction from the injection port.
  2. Whirl flow marks on the surface of the plastic part caused by the unsmooth flow of molten material in the runner. When the molten material flows from the runner with a narrow section to the cavity with a larger section or the mold runner is narrow and the finish is poor, the material flow is easy to form turbulence, resulting in whirl flow mark on the surface of the plastic part. To address this kind of flow marks, reduce injection speed appropriately, or control the injection speed in slow-fast-slow mode. Gate of mold shall be in the thick wall and preferably in the form of handle type, fan type, or film type. Runner and gate can be enlarged to reduce material flow resistance.
  3. Cloud-like flow marks on the surface of the plastic part caused by volatile gas. When ABS or other copolymerized resin are used, if the processing temperature is high, the volatile gas produced by resin and lubricant will form cloud-like ripple marks on the surface of the product. In order to solve this problem, it is necessary to reduce the temperature of mold and barrel, improve the venting of mold, reduce the material temperature and filling speed, enlarge the gate section properly, and consider changing the type of lubricant or reducing the use of lubricant.

Issue No. VII: Glass fiber streaks – What is Glass fiber streaks

Surface Appearance: Plastic molding products with glass fiber have various surface defects, such as dim and dreary in color, coarse in texture, and metal bright spots, etc. these are especially obvious in the convex part of the material flow area, close to the joint line where the fluid meets again.

Physical cause

If the injection temperature and the mold temperature is too low, the material containing glass fiber tend to solidify fast on the mold surface, and the glass fiber will not be melt in the material again. When two flows meet, the orientation of glass fiber is in the direction of each flow, which will lead to irregular surface texture at the intersection, resulting in the formation of joint seams or flow lines.

This type of defect is more obvious if the molted material is not fully mixed in the barrel, for example, if the stroke of the screw is too long, it will cause the under mixed material is also injected.

Causes related to process parameter and improvements can be taken:

  1. Injection speed is too low: increase injection speed, consider use multi-step injection method like slow-fast mode.
  2. The temperature of mold is low: increase mold temperature could improve the glass fiber streaks
  3. Molten material temperature is too low: increase barrel temperature and increase screw back pressure to improve.
  4. The temperature of molten material varies a lot: if the molten material is not fully mixed, increase screw back pressure, reduce screw speed, and use the longer barrel to shorten stroke.

Issue No. VIII: Ejector marks – What is Ejector marks

Surface Appearance: Stress whitening and stress rising phenomena found on the side of the product which is facing the nozzle, i.e. where the ejector rod is located on the ejector side of the mold.

Physical cause

If the demoulding force is too high or the surface of the ejector rod is relatively small, the surface pressure here will be very high, causing deformation and eventually causing whitening at the ejection area.

Causes related to process parameter and improvements can be taken:

  1. Holding pressure is too high: decrease pressure keeping pressure
  2. holding pressure time is too long: shorten pressure keeping time
  3. holding pressure switch time is too late: advance the pressure keeping switch
  4. Cooling time is too short: increasing the cooling time

Causes related to mold design and improvements can be taken:

  1. The draft angle is no enough: increase the draft angle according to specification, especially in the area of the ejector mark.
  2. The surface finish is too rough: mold shall be well polished on the demolding direction.
  3. A vacuum is formed on the ejection side: install an air valve in the cor


Due to the specific properties of plastics, injection moulding is a very complex technological process; unlike the seemingly related process of the metal die casting, it is not a mechanical process but a mechanical-physical one. In the injection molding process, a molded piece is obtained. It is characterized not only by a specific shape but also by a specific structure resulting from the flow of the plasticized material in the mold and the course of its solidification. Because these processes occur in the form of injection, the designer of this tool must take into account, in addition to typically mechanical issues, also issues related to the physical nature of the material transformation. Constructing a rationally working form requires at the same time from the designer a thorough knowledge of the technical capabilities of the injection molding machine, because it is a machine with extremely rich possibilities provided by its equipment and numerous work programs.

If you want to know more please go to our other plastic mold page, if you are looking for injection molding services, you are welcome to send us your requirement for a quotation.

If you have a new project or current project that needs a China injection molding company to support you, we are happy to support, please call us or send us an email.

plastic cup mold

When you have a project then you may need plastic injection molded parts, the first thing you need to do is finding a plastic mold company to make mold & molded parts, but before start this I think you need to check injection molding cost and mold cost in advance for investment budget, multi cavity injection molding will be one of the best way to save unit production cost, but not suitable for all of project, below are some suggestions on how to save injection molding cost, there have both advantages and disadvantages, by reading this you could choose the one base on your project requirement.

What is multi cavity injection molding

Multi-cavity injection molding is typically used when high volume production of identical parts is needed. It allows for the efficient production of multiple parts in a single cycle, which can significantly increase production rates and reduce the cost per part. Additionally, using a multi-cavity mold can also help to reduce the overall cost of the mold itself.

Multiple cavity mold means the number of cavities greater than one, which means that has more than one part in an injection mold, It is usually professional to say cavity, One cavity or two cavities, for examples 8 cavities mold means one molding cycle to mold 8 parts with the 99% same part feature, dimension, shape, size, etc.

Some examples of products that may be produced using multi-cavity injection molding include automotive parts, electronic components, toys, and household items. It is also commonly used in the production of medical devices, personal care products and packaging.

24 multiple cavity mold

24 multiple cavity mold

When do we need multi cavity mold?

There are some factors to make decisions before starting to make your plastic mould.
1, the size of the product,
2, the number of the product requirement
3, the size of the machine, if you only buy plastic molded parts then you do not need to care about this point, you plastic molding supplier we check this.

If the size of the product is small, such as the computer keyboard button, usually make 24 or 48 cavities, you must say why not make 30 or 40, this is because for the balance mold layout and material filling balance, especially when you use cold runner mold. so normally multi-cavity mold is 4, 8, 16, 24, 48, 96 cavities are better options.
When we make multiple cavity mold and the cavities are more than 24, we normally suggest making hot runner mold, one part per hot-drop, at least to use 6 hot runners to the cold runner, which means four cavities per hot drop. this could save the cycle time and keeping the best quality of injection molding parts.

The advantages of multi-cavity mold

The reason we make multi-cavity mold, the question is simple, we need to save production unit cost for each plastic molded parts, multi-cavity molds have several advantages over single-cavity molds in injection molding:

  1. Increased production efficiency: By producing multiple identical parts in a single cycle, multi-cavity molds can significantly increase production rates and reduce the overall production time.
  2. Reduced cost per part: Multi-cavity molds can produce multiple identical parts at a lower cost per part than single-cavity molds.
  3. Reduced tooling costs: Since multi-cavity molds require only one tool, the overall cost of the mold is typically lower than that of multiple single-cavity molds.
  4. Better consistency: By producing multiple identical parts in a single cycle, multi-cavity molds can improve the consistency of the final product, reducing the need for rework or scrap.
  5. Reduced labor costs: Multi-cavity molds require less labor to operate than multiple single-cavity molds, as the operator only needs to monitor one machine.
  6. Reduced material consumption: By producing multiple parts in a single cycle, multi-cavity molds can also reduce the amount of raw material required to produce the final product.
  7. Improve part quality: Due to the consistency in the process and the precision of the machinery, multi-cavity molds can produce parts with tighter tolerances and better surface finish.

The disadvantages of multi-cavity mold

We all know that all of the customers prefer the multiple cavity mould since this can save lots of production cost, but there are other factors you need to think about before making decision, because make plastic mold is not cheaper, make multi-cavity mould is more expensive than single cavity mold, some times double or even 3 times expensive than single cavity or two-cavity mold, for example if you make 24 cavity mold, then you at least us 6 hot runner drops for the mold, the pure hot runner cost is around USD 5400 ( YUDO brand), if use China local brand of hot runner still need USD 3000, and this cost some times is enough to make 2 cavities cold runner mold, since there are many cavities in one mold, the mold manufacturing cost is high than the less cavity mold as well, this is another cost, so total cost is two or three times more is not surprised, below listed some disadvantages while use multi cavity mold:

  1. Higher initial cost: The initial cost of a multi-cavity mold can be higher than that of a single-cavity mold, especially for complex designs.
  2. Greater complexity: Multi-cavity molds are more complex than single-cavity molds and require more precise machining and design. This can lead to longer lead times for tooling and increased risk of defects.
  3. Higher maintenance costs: Due to the complexity of the mold and the increased number of moving parts, multi-cavity molds may require more maintenance and repairs than single-cavity molds.
  4. Greater risk of defects: With multiple cavities, the risk of defects is greater, as a problem in one cavity can affect multiple parts.
  5. Increased cycle time: Multi-cavity molds have longer cycle times than single-cavity molds as the machine has to fill multiple cavities at once.
  6. Greater potential for warpage: Multi-cavity molds have to be designed to account for the potential warpage that can occur during the cooling phase of the injection molding process.
  7. Increased risk of sink marks: As the material cools it will shrink, if the mold design is not optimized for multi-cavity, sink marks may appear on the surface of the parts.
  8. Increased risk of flash: Flash is the excess material that is extruded from the mold. Multi-cavity molds can be more prone to flash than single-cavity molds as the pressure and flow rate of the material is increased to fill multiple cavities.

When do you need multiple cavity mold

There is some simple suggestion when do you need to single cavity mold (may 2cavities at fist), when you should make the multi-cavity mold, like 8 cavity mold, 16 cavity mold or more. When you are sure that you will need the plastic parts more than one million or at least 0.5 million, then go to 8 or more mold cavities will surely save cost for you, you may need to pay more cost on plastic mold manufacturing, but compare the production cost you are going to save, this injection mold cost is insignificant, because you will save 10 times more than this injection mold cost.
If you are not sure how many plastic moulding parts needed at the first, or this is depending on your business market sell, then we suggest use the 2 cavity mold at first, because this can save the plastic mold cost for you in advance, after you open your market, and the requirement of injection molded parts increased, you still can save injection molding cost by making new multiple cavity mold, you use the existing mold to produce the parts at the same time and  make new multi-cavity mold, this will not have a delay as well, after the multiple cavity mold finished then you only need to run this multi-cavity mould, but if the quantity requirements are not so high, then you use the currently molds to produce, so you still have good profits with less investment (compare to make multi-cavity mold at first beginning).

What do you think? by reading above I assume you have the idea on how to save injection molding cost for your project.

If you have any project in hands that need to make injection mold for your business, you are welcome to contact us, we will give you some good suggestions and ideas, to help you spend min investment on plastic mold cost and open your market rapidly.

Sincere tech is plastic mold manufacturer in China, we make custom single cavity molds, multiple cavity molds, hot runner mold, cold runner mold, overmolding, 2k injection molding and more, you can call us or send us an email for a quote

Plastic molding technology

Plastic molding technologyPlastic molding technology continues evolving with the market and with the advances in science. Plastic molding is the process used in producing plastic components for a variety of industries.

When plastic resin materials are heated the resin will flow, and can then be injected into a mold. A plastic mold consists of two halves referred to as the “A” side (cavity side) and the “B” side (core side). The “A” side is where the molten plastic enters the mold, and the “B” side contains the ejector system which removes the parts from the mold.

Plastic Molding Includes Many Terms and Components

Plastic molds are required to have many components in order to make high-quality plastic parts. Below is some of the terminology used to describe the components and processes that are required when producing injection molded parts:

  • Sprue – this connects the nozzle of the injection molding machine to the main runner, or cavity
  • Runner – this component conveys the melted plastic from the sprue to the gate and into the part
  • Gates – these are the openings that allow the molten plastic to be injected into the cavities of the mold
  • Cold Runner mold – this design involves the plastic entering into the “sprue” and then traveling through the “runner” where it then enters the part cavities through the various “gates.”
  • Hot Runner mold – this design is an assembly of heated components used to inject molten pPlastic moldslastic into the cavities of the mold. Hot Runner mold usually makes mold more expensive to manufacture but allow savings by reducing plastic waste and reducing the cycle time.

When observing plastic molding products, you will often see a line running between different sides of the finished plastic part. Here are some descriptions of why parts have a specific appearance:

  • The Parting Line – this occurs anywhere there are any two pieces of mold that meet.

There are also several configurations of plastic molds. These configurations are described as


  • The Two Plate Mold – consists of one parting line where the mold splits into two halves.  The sprue, runners, gates, and cavities are all on the same side of the mold.
  • The Three Plate Mold – has a runner plate in between a moving half and a fixed half.  These molds will have two parting lines and are used because of their flexibility in gating locations.
  • An Unscrewing Mold – is what is used when there is a requirement for male or female threads on a plastic component
  • The Action Mold – these consist of a mechanical cam action incorporated in their design, when a hole, slot, undercut or thread is needed that is not perpendicular to the parting line.
  • The MUD Unit Mold– these are standard frameworks for toolsets (u-frame), which allow for custom-machined tooling inserts to be made for specific components.

Large Plastic Molding Runs Cost Less 

Plastic injection molding offers many industries a huge number of benefits.  In large runs, molding is much cheaper than when machining the parts individually. The over-all manufacturing speed is much faster with this approach as well. This is one of the many reasons there are so many different types of injection molding processes. Some of these include:

Cold runner mold

Insert Molding – This is the process of putting a metal insert into a mold and then molding plastic around the insert.  Since multiple parts are manufactured together – this eliminates the need for a secondary assembly operation.

OverMolding – This is the process of over-molding, and the production of injection molded parts that seamlessly combines a rigid plastic with a rubber-like elastomer.

Family Molding – This is a process that utilizes a mold that contains various shapes of cavities to mold all the plastic components for one completed part.  Family molds are used when the different plastic components are made from the same material.

Injection Molding CleanRoom – This is the process used primarily for medical components. It is the injection molding process that is performed in a cleanroom environment in order to protect the parts from any contaminants.

When considering having plastic parts custom designed and molded – SINCERE TECH is the ideal partner for your plastic component or device.

SINCERE TECH is your single-source solution for your device by providing mold building, design, and engineering, injection molding as well as injection molding cleanroom and any secondary operations that may be required to complete your project. contact us now to know more information

There are normally two ways to do plastic mold polishing:

1. Do it in-house.

When we do the mold polishing in-house we could keep the time control.  And will be easy to communicate with your polishing department to keep the high-quality polishing job, this will prevent the issue happened by the over-polishing jobs.

2. Do it outsource.

  • You still can take control of the lead time easier by scheduling the polishing to an outside polishing company. Especially for some multiple cavities molds, because they have many polishing workers and can work on polishing cavities separately.
  • But when meet some issue that will be difficult to discuss with each other, if your polishing supplier is close to you, that will be much easy, you can go over there in minutes and explain to themPlastic mold polishing

Final suggestion to handle the mould polishing works

1. For some surface if your customer needs texture surface to cavity side, you can work this use EDM machine to make surface texture directly, This is my favourite method, because almost all the works are finished by EDM jobs, the advantage on this is when the draft angle is very small and cavity side need some textured surface, use EDM you will never get any scratch issue, and this will be the only way to prevent the quality, we have been done this many times, at the first beginning we used the old way ( polishing and then texture), the was scratch issue on some area and never solved, finally we made a new cavity and made with texture by EDM machine, the result was perfect.

2. For some mold the cavity side needs high gloss polishing surface, which means this is high gloss plastic molding parts, so EDM machining is not possible to get mirror polishing surface even EDM machine can get the high gloss surface, but for some requirement are too high to meet, in this case we have to do the high polishing jobs, the best way to solve this is outsource, to find the professional polishing company to manage this hard task.

Tips to improve your plastic mold polishing

  • Cleanliness. Keep your polishing area away from grinding dust and chips. Do not allow it to become a disorganized mess of loose stones and accessories.
  • Separate your stones. It is amazing that people dump a 220 gritstone in a box or can with a 600 grit stone. Sometimes they even mix up polishing sticks with different grits of the diamond. Let’s see, if you think you are polishing with a fine finish diamond and you get a coarser diamond piece mixed in, what do you think will be the result?
  • Move your polishing area away from grinders and bead blasting equipment. For some reason, many shops just keep polishing away, right next to the surface grinders. All it takes is one stray piece of grinding grit to ruin your finish.
  • Use a microscope. Even though it is disheartening to see your work under a microscope, this is the only way to see the tiny scratches and imperfections. Plus, you can avoid rolling edges and damaging critical molding details
  • Don’t use unskilled help to do skilled work. Polishing is an art that takes a lot of time to learn. Don’t expect everyone to have the same ability when it comes to fine finishes or detail. Yet this often happens when owners view polishing as a nuisance.
  • Make a chart of the diamond paste colors. For some reason, some shops never write down which diamond is which grit and moldmakers are left trying to figure out the same problem over and over again. Figure it out and make a copy near the diamond compound!
  • Don’t think that “cross-hatching” is some kind of religion. Sometimes you see people who think you must only polish in one direction for each grit. Horizontal with a 400 grit and vertical with a 600 grit, for example. You can and should go back and forth in any direction you need to, just make sure you end up with the lines in the direction of the ejection-draw polish it. Your speed will dramatically increase once you get over this misconception.

Hope this information is helping you on how to do better mold polishing, in this case, you could have a better idea on your project what kind of surface will be the best option, any question welcome to send us an email