overmoolding insert molding

In the plastics industry, injection molding is a significant process that is used to produce a large volume of plastic parts or products. This technique involves the use of a mold, usually of steel-made metal, that has an interior pattern that resembles the intended design of the part or product. The material, usually inserted after melting into a liquified or molten hot plastic state, is forced into a die cavity, eventually cooled, and then released to create thousands of similar pieces by applying high pressure.

Due to high production accuracy, almost all large-scale plastic products on the market today are fabricated through injection molding techniques. The process has many benefits, such as low cost per part production, short time per part manufacturing, accommodating several materials, and high accuracy of the final part meeting exact tolerance requirements.

These include overmolding vs. insert molding techniques. Although both are interchangeably used, there are clear distinctions between them. This blog post specifically provides key details about two techniques: overmold vs. insert mold processes, by highlighting their differences, applications, and situations to choose between the two.

insert molding

Insert Molding: How Does It Work?

Both overmolding and insert molding techniques involve injection molding. In the process, metal parts are placed into a mold cavity, and then plastic is injected. These metal inserts are placed in the mold by hand or with the help of industrial robots used in automated processes. Once the mold is in position, the mold is closed, and a plastic material is injected over the metal inserts to create a single, unbroken part.

These features enable easy assembling and disassembling of the parts without any effect on the quality or appearance. For instance, heat-set threaded inserts are used in the plastic parts to reduce the likelihood of thread damage during assembly.

In addition, insert molding may sometimes even reduce the need for secondary fasteners. This technique involves the direct incorporation of required metal components into the mold to form a strong, single component that increases the mechanical stability of the part and minimizes the chances of part breakage. If you want to know more about insert molding, please go to what is insert molding page.

Why should one opt for Insert Molding?

Insert molding is an adaptive manufacturing process to produce high-strength plastic components. Let’s discuss its extensive use cases:

Reduced Assembly Costs: An injection molding machine is capable of producing thousands of parts in a minimal time frame, and this makes it economical for large batch parts production. In contrast to CNC machining, sheet metal fabrication, or 3D additive manufacturing techniques, where the assembly can become a significant problem, insert molding can minimize or even remove the need for additional assembly and tooling requirements, which will lead to further cost optimization of projects.

Enhanced Part Performance: Plastic parts are typically not as durable as their metal counterparts, but plastic has its benefits, including being cheaper, easier to mold into different shapes, and lighter in weight. Insert-molded products normally entail durability due to the combination of plastic (a substrate on which metal is inserted) and metals (insert both materials). This ensures that the intended part being inserted has the necessary strength and stiffness. Moreover, the plastic matrix helps reduce the overall weight of parts. Furthermore, insert molding imparts in parts the ability to resist cyclical loads and other loads.

Disadvantages of Insert Molding

Despite its several benefits, insert molding also comes with certain limits that product manufacturers must consider: These common drawbacks include;

insert molding vs overmolding

Multiple Manufacturing Technologies: Insert molding may need to be done in two phases in general. Metal-forming processes such as CNC machining may be used when manufacturing custom-designed inserts rather than off-the-shelf parts. These methods are generally costlier per part than fully injection-molded processes. While it is possible to reduce the cost of manufacturing metal inserts by employing techniques such as metal die casting or metal injection molding (MIM), Despite this, the cost of manufacturing parts with metal inserts is still higher than that of parts made entirely out of plastic.

Increased Part Complexity: When producing products that have to have metal inserts made to order, it’s essential to have a deep understanding of both metal and plastic manufacturing. Product designers must know the DFM rules of both technologies and how to combine them into one part that functions as required. This can add to the design and manufacturing time and cost of the product.

An Overview of the Overmolding Process?

Overmolding is a subcategory of insert molding, which is the process of molding one plastic material directly onto a formed part. In this process, the first part is molded by injection molding, and then it is placed in the second mold for the overmolded material. This technique enables the use of two or more plastics in the production of a single product, giving the product both utility and beauty.

For example, overmolding allows for the combination of different Shore hardnesses, providing a soft touch layer on top of a rigid base for better grip and feel. Also, the use of multiple colors in an overmolded part can give it a competitive edge since it is not easily seen in other products. This technique is widely applied to the grips of tools like screwdrivers, power drills, and toothbrushes since both the comfort of the grip and the product’s appearance are essential factors.

Why choose the overmolding process?

Overmolding offers a range of benefits that make it a versatile and advantageous process.

Increased Material Flexibility: Overmolding enables the use of different materials in a single part, and this makes it possible to have different properties in the same part. This process improves the product’s looks, feel, and usability, which is advantageous to both the product and the consumer.

Elimination of Adhesives: Overmolding is a process where two or more different materials are joined together through an injection mold, thus replacing the need for adhesives or other joining techniques. This not only strengthens the final part but also cuts the assembly costs.

Integrated Seals: Overmolding makes it possible to bond soft seals directly onto molded parts. For instance, in electronics enclosures with IP ratings, an overmolded seal is cheaper and more efficient than fitting an o-ring groove. This integration enhances the performance of the part and the structural stability of the whole system.

Limitations of overmolding

Overmolding, despite its numerous benefits, comes with certain drawbacks:

Complex Process: Overmolding is a two-shot process, which means that the part cycle time and the cost are higher than in single-part molding. Also, it calls for the application of two tools or a two-shot mold that is quite expensive to produce. However, these are some of the challenges that one can face when using overmolding, but it can be cheaper than manufacturing two different injection-molded parts and then joining them.

Debonding Risk: The problem of delamination or distortion may occur when two different materials are bonded in an injection mold because the temperatures may not be ideal for the given material combination. This may require the use of mechanical interlocks in order to achieve a secure connection where heat alone is not enough.

If you want to know more about overmolding, please go to the overmolding page to check this out.

Industrial Uses of Overmolding vs Insert Molding

Both overmolding and insert molding are widely used for applications requiring high-quality and stringent products. Nevertheless, all these techniques have similar uses, and they are employed to manufacture numerous parts and products.

Automotive Industry

Both insert molding and overmolding play a vital role in manufacturing numerous automotive parts that contain metal, rubber, or plastic, such as batteries, knobs, dash panels, motors, and handles.

Cosmetic Industry

These techniques are indispensable in the cosmetics industry for producing custom-made items and their containers with the use of various colors and surface treatments of cosmetic items such as perfume flacons, cosmetic brushes, and compacts.

Consumer Products

In the case of household products, insert mold and overmold play a central role in manufacturing items such as toothbrush holders, containers, and cell phone cases. They also reinforce items such as patio chairs and step stools, which are usually found in multiple colors or materials.

Electrical Appliances:

The use of insert molding cannot be overemphasized, particularly in the electrical industry, where wires are coated with rubber insulation. This process helps to stop electrical conduction and increase safety levels. Insert molding also makes electrical appliances safer to handle by providing a proper place for insulators to be installed.

Sincere Tech is one of the top 10 plastic injection molding companies in China that specializes in creating unique products for different sector., With the help of the technical knowledge and skills that the company has gained over the years, the company offers its services at affordable prices. Whether for consumer products, home appliances, or car accessories, you can rely on these processes for quality production.

overmolding vs insert molding

Conclusion: Selecting Between Overmolding, Insert Molding, and Injection Molding

Overmolding and insert molding are the different techniques that fall under the injection molding process, which is a popular and efficient method of manufacturing consumer goods. As for the cost, injection molding is generally considered to be the most cost-effective method compared to other methods such as CNC machining and 3D printing per part.

Overmolding could be an optimal choice if:

  • Your part’s surface has different electrical or thermal properties.
  • It is essential to increase the level of shock absorption or decrease the level of vibrations.
  • It is necessary to produce a part from multi-colored plastic.
  • Your part must offer a comfortable, non-stick surface that the other part can easily grip.

Opt for insert molding when:

  • The substrate can be in the form of wires, electronic components, or circuit boards.
  • It is preferred not to have to spend the money on a two-shot mold or a 2K, which is more complicated.
  • You have to tap this part and install threaded inserts.

When the decision has been made to use injection molding for a certain application, the next choice is between insert molding, overmolding, or conventional injection molding. It is important to provide a clear definition of the product application to be able to make a proper choice. All these processes have their own special benefits suitable for various products. Deciding which method is right for your particular product is not always easy; therefore, it is advisable to consult a professional.

Speaking to a SincereTech representative can be helpful due to over a decade of the company’s experience in manufacturing. We can assist you in the decision-making process of your project and determine which process—insert molding, overmolding, or standard injection molding—will be most beneficial for your project.


Q1. What is the process of TPE overmolding?

TPE overmolding is a process where TPE is injected into an existing substrate or a plastic part to form a chemical bond with the material in order to increase its durability and usefulness.

Q2. Is 2K injection molding the same as insert molding?

No, Insert molding involves placing an additional part on the substrate, while 2K injection molding involves injecting multiple materials into multiple-cavity molds for the production of intricate parts for vehicles.

Q3. What plastic types are suitable for overmolded?

The most commonly engineered plastics suitable for overmolding processes include high-density polyethylene (HDPE), PEEK resin, Delrin or acetal, polymethyl methacrylate acrylic, commonly known as PMMA, ABS, nylon, and PBTR. These plastics have different characteristics that make them suitable for different overmolding processes across industries like automotive and consumer products.

Q4. Overmolding vs. Insert Molding:  Which One Costs More?

Overmolding, however, provides economical scalability at higher production rates for companies, which in turn increases the overall profitability of a company through decreased tooling and assembly costs. Further, it helps with faster production of parts in large-volume runs. If you are going to produce intricate prototypes or low-volume parts, this cost differential becomes apparent due to the requirements of two parts.

Injection moulding service
precision plastic injection molding

What is precision plastic injection molding?

Precision Plastic Injection Molding is tight tolerance requirement plastic injection molding parts. Normally tolerance on the plastic molding part is around 0.05-0.1mm, if the part tolerance requirement is about 0.01-0.03mm, that means this is precision plastic injection molding, to make high precision plastic injection molding parts, the first thing is making the precision injection mold, all of the mold components must have tolerance within 0.005-0.01mm.

This is min requirement for high precision plastic injection mold after mold is completed finished, then take mold trial to verify the dimension according to 2D drawing requirement, to trial the mold and make stable tolerance.

High Precision plastic injection mold is number one key point to making high precision plastic injection molding parts, but not limited to this, you still need use high precision injection molding machine to produce the part, by this two min requirement we can make sure that we can make precision injection molded plastics continually, there are few issues that we make still need to know for the high precision plastic injection molding.

Precision Plastic Injection Molding

Plastic precision Connector-overmolding

Question I:

The determination of the structure of the precision plastic mold is the key, and the overall structure is the embodiment of the final effect of the product: the determination of the overall structure of the mold, the determination of the gate system, the determination of the ejection system and the determination of the water transportation system, and others should be conducive to the post-processing orientation of the product.

Question II:

What about the feeding problem? First of all, we will choose a reasonable injection scheme according to the structure, weight, volume, and cost of the product, which can meet the requirements of customers as well as the requirements of quality.

Second, we will design in strict accordance with the injection design standards: the layout of the runner should be uniform, especially the size of the cross load surface of the main and sub runner, the shape and size of the gate.

Question III:

What about the ejection problem? Firstly, we will determine the ejection mode according to product orientation and structure. Secondly, we will evaluate the ejection balance and coexist with other systems, such as interference with water transportation and recycling marks, date clock, etc.

Question IV:

The design of the water channel system is based on four requirements (the cooling line should be as balanced as possible. The water cooling line shall not interfere with other mechanisms. The water channel equipment shall meet the customer’s standards and be easy to install. Each water channel line shall be displayed with identification numbers or marks (in and out).

 Question V:

How to ensure the manufacturing accuracy of the mold and the accuracy of the molding products to get precision injection molding, this mainly depends on the manufacturing accuracy of the mold cavity, the insert, and the mold core size. The accuracy of the mold cavity number or the accuracy of the parting line will directly affect the size of the product. Firstly, we need to make the manufacturing process plan and flow chart.

Each completed manufacturing process must be fully inspected and the data inspection list must be recorded in the datasheet. After the manufacturing is completed, the workpiece shall be processed and maintained.

The design of the parting line of plastic mold is also an important part. If the design is not reasonable, the part is not easy to demoulding or even damage the mold. Here are the design principles for the parting line of mold

It is convenient to eject out the plastic part and simplify the structure of the plastic mold. After the demoulding direction is selected, the position of the parting line should make the plastic part fall done without any interference, like sliders, etc.

For the plastic part with high coaxiality accuracy, the parting line should be selected at the position where two diameters can be placed on the lower mold or upper mold at the same time.

When the precision plastic injection molding along the height direction is required to be high, the half overflow cavity should be used. If the transverse flash is formed at the parting line, it is easy to ensure the height precision, while the non-overflow cavity is not easy to ensure.

When the radial dimension accuracy is high, the influence of flash thickness on the accuracy of the plastic part should be considered, as shown in the figure. If the vertical parting of plastic parts is easy to ensure, the horizontal profile is difficult to control due to the thickness of the flash, which affects the accuracy of plastic parts.

Ensure the appearance of the plastic part, it shall be easy to clean the flash and not easy to damage the appearance. The flash produced by the parting surface as shown in the figure shall be easy to clean and not easy to damage the appearance of the plastic part.

It is convenient for the manufacture of plastic mold and the processing of forming parts. The improved parting surface makes the processing concentricity of plastic mold low, easy to manufacture and the flash does not damage the appearance of plastic parts.

Ensure the strength of the formed parts, for example, when determining the parting surface, avoid the thin wall and sharp corner of the formed parts.

In addition to the design elements of general molds, the following points should also be considered in the design of precision injection molds:

  •  Adopt proper mold dimension tolerance;
  •  Prevent forming shrinkage error;
  •  Prevent deformation of injection part;
  •  Prevent the deformation of demoulding;
  •  The manufacturing error of the die/mold is minimized;
  •  Prevent the error of mould precision;
  •  Maintain mold accuracy.

Prevent the error of mold precision; classification of processing molds in plastic mold factory and requirements of various points for attention

There are many kinds of plastic injection molds, which can be roughly divided into ten categories. According to different requirements of a part material, physical and chemical properties, mechanical strength, dimensional accuracy, surface finish, service life, economy, etc, different types of injection mold are selected.

The plastic mould with high precision needs to be processed by a high precision CNC machine, and the material and molding process of the mould have strict requirements. Mould technology is also needed to design and analyze.

Some of the parts have special requirements during molding, so advanced technologies such as hot runner, gas-assisted injection molding, nitrogen cylinder, etc. are needed for plastic mold.

Plastic mold manufacturers shall have CNC machine tools, EDM machine tools, wire cutting machine tools, and CNC profiling milling equipment, high-precision grinder, high-precision three coordinate measuring instruments, computer design, and related software, etc.

In general, large metal stamping dies (such as automobile cover part die) should consider whether the machine tool has a blank holder mechanism, even edge lubricant, multi-position progressive, etc. In addition to the punching tonnage, the punching times, feeding device, machine tool and die protection device should be considered.

The plastic mold manufacturing capacity and process of the above are not possessed and mastered by every enterprise. When choosing a cooperative plastic mold manufacturer, we must know its processing ability, not only look at the hardware equipment, but also combine the management level, manufacturing experience, and technical force.

For the same set of mould, there is sometimes a big gap in the quotation of different mould manufacturers. You should not pay more than the value of the mold, but also should not be less than the cost of the mold. Plastic mold manufacturers, like you, want to make a reasonable profit in business, ordering a set of molds with a much lower price will be the beginning of trouble. You should start with your own requirements and measure them comprehensively.

If you have a plastic parts that needs precision injection molding manufacturing services, you are welcome to contact us, Sincere Tech is customized precision plastic injection molding company in China. We offer precision injection molds and molding services to customers all over the world.