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What is Injection Moulding

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 process may require practice for efficiency.

Plastic Injection moulding

Injection moulding (or Injection Molding) 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 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. Injection molding is very 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
    • 2.2 Injection mold
  • 3 Injection molding process
    • 3.1 Injection Molding Cycle
    • 3.2 Molding trial
    • 3.3 Molding defects

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 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 insert 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),

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

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 https://www.plasticmold.net/injection-mold/ to know more about injection mold, 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

Injection Molding process

Injection molding is one of the ways to shape plastic objects by injecting a thermoplastic material, in liquid or plasticized form, into a specially designed mold. However, before the production of plastic components begins, a suitable mass must be formed which in the initial phase is in the form of granules or a special cut. Only after heating up it changes its consistency which allows it to be injected under high pressure into a closed mold. The next step is heating or cooling the mold; it depends on the type of material used in production.

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 part 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 MoldingMolding trial

When the injection mold has been made by moldmaker, 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.

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 normal, to solve the mold issue we need to fix and test the mold several times (normally 3 or 4 times) and finally all of the issues are solved completely.

What is Injection molding Processing?

Injection molding

Injection molding

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 plastic into the liquid, then use high pressure injecting the liquid material into a 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 retrieved 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. Then, the molten plastic is forcibly injected into the mold under the barrel with an appropriate shape. 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

The popularity of this method that allows plastic shaping has undoubtedly been influenced by many of its advantages:

  •  Precision and aesthetics – because in this injection moulding process there is very little or no share of finishing and high quality of finished products, as well as 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 plastic 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.

Due to the specific properties of plastics, injection molding 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.

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