There are very similar between plastic overmolding and 2k injection molding (2 shot injection molding) but they have some key differences. see below for the different between those two molding process.

Plastic over molding is using normal single nozzle injection molding machine to produce the two different type of plastic parts in one (or two different color of plastic parts in one solid part), over molding process means move the first part (substrate part) or melt inserts (insert molding) to the subsequent mold (over mold) and mold to get the final part. Overmold can be used to add a soft-touch grip to a tool handle, or to create a product with multiple colors or textures.

2K injection molding, also known as two-component injection molding, 2 shot injection molding or dual-injection molding, It is using the 2K injection molding machine injecting two or three materials (colors) simultaneously into the same mold. Unlike overmolding, both materials are injected at the same time, and they will be fully bonded together once the molding process is completed. 2k molding process is complex but fast, efficient, and high quality.

Compare to plastic overmoulding and 2k injection molding, 2k injection molding has high quality and high production efficiency, but since the 2k injection molding machine is too expensive, so sometimes use over-molding to replace it, on the other hand, overmoulding cost is high than 2K injection molding cost, but plastic over molding can use any normal injection molding machine to produce the over moulded parts, so for low volume of 2 color molding.

Plastic over molding has more advantages, and some of parts can only be done by plastic over molding process, but for the high volume of 2 color molded parts using 2K molding process will be the best. Both overmoulding and 2K injection molding have their own advantages and disadvantages, depending on the requirement of the final product.

Both over molding and 2K injection molding can be used to create products with multiple materials or layers, but the key difference is that in overmoulding, two materials are molded separately, and then combined together, while in 2K injection molding, two materials are molded together in the same process.

Blow is the relation to plastic overmolding and 2k injection molding.

What is overmolding?

Plastic Overmolding is an operation in which two or more mediums (substances) are merged to form an ending molded product, plastic over-molding needs to make two separate molds, one is substrate (first mold), the second mold is called over mold (usually a TPE material for the second mold), but if the substrate is metal parts or brass parts, this type of over molding we normally call insert molding, and insert molding only need one mold to finish the process.

The plastic over molding materials majorly used are thermoplastics (TPE) and rubber, or the same material but different colors. During over molding, the activity that happens is either mechanical or chemical which leaves the two substances bonded.



Plastic Overmolding process is producing the molded part (substrate) from the first mold and move it to another related over mold, the substance can be used to combine the surface molded with the molding substrate. The molded material can otherwise be put back to the surface it was extracted from and the overmolding substance added. Types of over molding include two shot sequential over molding, insert over molding or multi-shot injection molding.

Two shot sequential plastic overmolding is where the molding machine injects the first plastic resin into a first mold cavity (both molds in one molding machine), once formed then move the molded part to the second over mold immediately and close the mold and injecting second material, using the first component as an insert for the second shot using a different material or color, requires special injection machine which has the two injection units.

Insert over-molding uses a pre-molded insert placed into the mold before injecting the second material, if it the inserts are metal or brass, then we call metal insert molding, this overmolding process which we used a lot, Multi-shot injection molding injects multiple plastic resin into the mold cavity during the same injection molding cycle.

Overmolding cost

The cost of over moulding can vary widely depending on a number of factors, including the materials being used, the size and complexity of the finished product, and the quantity being produced. In this article, below take take a look at those various factors that can impact the cost of overm oulding, as well as some tips for minimizing costs and maximizing efficiency in the overmolding process.


One of the primary drivers of overmolding cost is the materials being used. The cost of the overmold and the insert can vary significantly depending on the type of material being used. Some materials, such as plastic and rubber (TPE or TPU material), are relatively inexpensive, while others, such as metals and exotic polymers (copper inserts, stainless steel etc.), can be much more expensive.

Size and Complexity

The size and complexity of the finished product can also impact the cost of overmolding. Larger, more complex products may require more material and more processing time, which can drive up the cost. In addition, products with more intricate or detailed features may require more advanced molding techniques, which can also increase the cost.


The quantity of products being produced can also affect the cost of overmolding. In general, the cost of overmolding decreases as the quantity increases, due to the economies of scale. This is because the fixed costs of setting up the overmolding process, such as the cost of the mold and the setup time, are spread out over a larger number of products. As a result, it’s often more cost-effective to produce a larger quantity of products in a single run, rather than producing smaller quantities in multiple runs.

Minimizing Costs

There are a number of steps that can be taken to minimize the cost of overmolding, including: Selecting the most cost-effective materials: As mentioned above, the cost of the materials can have a significant impact on the overall cost of overmolding. By carefully selecting the most cost-effective materials, it’s possible to reduce the cost of the finished product.

Optimizing the design: The design of the finished product can also impact the cost of overmolding. By simplifying the design and minimizing the number of features and details, it’s possible to reduce the amount of material and processing time required, which can help to lower the cost. Increasing the quantity:

As mentioned above, the cost of overmolding tends to decrease as the quantity increases. By producing a larger quantity of products in a single run, it’s possible to take advantage of economies of scale and reduce the overall cost.

Advantages of plastic over molding

  1. Compare to 2k injection molding, plastic over molding is more easy to make, you can use a normal injection molding machine to make 2 or 3 different colors in one molded part, or make two or three different materials in one ending part.
  2. For some small quantity of two-color molding parts projects, you do you not need to invert or hire 2k injection molding machine, use over molding process is the best and low cost to meet customers requirement.
  3. It increases the design diversity and also exalts the end product towards many materials composition.
  4. Reduced assembly costs, there are less secondary activities or processes carried out on the end products. This reduces any cost of labour. Also, after manufacture, no more costs are incurred.
  5. The parts have a high level of stability and constitution since after being left to mechanically inter-lock they become one.
  6. Product over molded using plastics have high resistance to vibrations and shock due to the plastic resins having been structured perfectly.
  7. The plastic molding components are more reliable because there is no bonding at the manufacturing stage.
  8. The end products are of desired quality such as firm components and eye-catching designs.

    Metal insert overmolding

    Metal insert overmolding

Disadvantage of over moulding

  1. Since over molding process is moving the first molded substrate part to another over mold, so the tolerance is not as good as the 2k injection molding process.
  2. the production capacity is not as efficient as 2k injection molding, because working on the over molding you need use robot or manual jobs to put the substrate into the over-mold, this will take time and the molding parameter sometimes is not stable, especially two or more substrates in one over mold, this will cause more issue and increased the waste rate, and this waste is double (substrate and over mold).
  3. With over molding, there are less available choices in terms of plastic compatibility. Some materials may not bond well together, or may not be able to withstand the high temperatures and pressures of the injection molding process.
  4. There are no secondary practices carried out on the end products of over molding. Activities and adjustments come to a full stop when the molding material becomes cold.
  5. In cases where products are scarce, it is expensive to run such an operation. Sincere you need use person to put the substrate into over mold, so the cycle time is increased and the production cost is increased accordingly.
  6. overmoulding process normally requires two molds, one for substrate and one for overmold, so there will be more initial mold cost at first.
  7. Overmoulding is a more complex process than traditional injection molding, requiring precise coordination between the two injection systems and proper design of the mold.
  8. In the event of an issue with the overmoulding process, it can be more difficult to troubleshoot and fix problems with overmolding than with traditional injection molding.

What is 2k injection molding? (Two-shot injection)

2k injection molding or 2 shot injection molding is a manufacturing process used when referring to molding two materials/colors into one plastic part. This plastic molding technology blends two materials or two different colours materials into one ending plastic part by using 2k injection molding machine.

2K injection molding

2K injection molding

The chemical bonding process involved in this process takes place because they are able to merge two or more material into one part. When using 2k injection molding technology process, the material selection will be the key point factor to the success of the project or not.

This is an industrial activity that entails directing two totally opposite polymers into a ready product.

Differences between the 2K injection molding and over molding

Over molding is for some small scale production volume compared to the 2k injection which is majorly large production scale.

With the over molding process, for another process to happen, the material used to mold must get cold to be removed whereas.

With 2K injection molding it is different. The polymer is usually still hot and flexible; hence more operations can still be carried out.

Once an object is made using over-molding it is locked mechanically with the other substances whereas it forms a chemical bond that entails its molecules bonding in 2k injection molding.

The 2K injection molding procedure can house diverse ideas such as the use of many different materials thus high-quality end product, opposed to the 2K injection molding procedure, the over molding activity can have some compatibility issues more so plastics.

When over molding, you are restricted to over-molding a metal with a plastic a few cases of a plastic and a plastic.

While in 2K injection molding there is a wide range of materials that can act as the molding substance or be molded on.

Advantages of 2K injection molding

2K injection molding offers a number of advantages over traditional single-material injection molding. Some of these advantages include:

  • Greater design flexibility: 2K injection molding allows for greater design flexibility as it allows for the use of two different materials in the same part, which can open up new possibilities for product design.
  • Reduced assembly costs: By using 2K injection molding, manufacturers can eliminate the need for secondary operations such as bonding or fastening, which can reduce assembly costs and improve overall efficiency.
  • Increased efficiency: 2K injection molding allows for the integration of multiple functions into a single part, which can increase efficiency and reduce the overall number of parts required for a product.
  • Better bonding: 2K injection molding allows for better bonding between the overmold and substrate materials, which can improve the overall strength and durability of the finished product.
  • More versatile material options: 2K injection molding allows for the use of different materials in the same part, which can provide more options for manufacturers to choose from depending on the specific application or product requirements.
  • Greater control over surface finish: 2K injection molding allows greater control over surface finish and can make it possible to achieve a more consistent and high-quality finish compared to overmolding.
  • Possibility of creating a more complex geometric shapes: 2K injection molding allows for the creation of more complex geometric shapes, since it allows for the use of two different materials.
  • Greater dimensional accuracy: 2K injection molding process can provide greater dimensional accuracy compared to overmolding process.

However, it’s worth noting that 2K injection molding can be more complex and challenging than traditional injection molding. It requires precise coordination between the two injection systems and it is more expensive than traditional injection molding. It also require specialized equipment, which can increase the costs of the process.

2K plastic molding

2K plastic molding

Disadvantages of 2K injection molding

There are also several disadvantages that 2K injection molding has compared to overmolding and traditional mold:

  • Higher cost: 2K injection molding can be more expensive due to the specialized equipment ( need 2 color injection molding machines) and expertise required for the process, as well as the need for two different materials.
  • More complex process: 2K injection molding is a more complex process than overmolding and traditional molding, which can lead to higher setup costs, longer lead times, and the need for specialized expertise.
  • Materials compatibility: 2K injection molding requires that the overmold and substrate materials are compatible with each other and that they can bond well. This can limit the materials that can be used and may require extensive testing to ensure proper compatibility.
  • Possibility of defects: 2K injection molding process is complex, which means that there is a higher risk of defects or quality issues, this requires high technical team on the 2K mold manufacutring and molding process.
  • Higher requirements of precision: 2K injection molding requires higher precision in terms of the design and measurements of the mold, which can be more challenging and time-consuming to achieve.
  • Limited design options: Some design options may not be feasible due to the requirements of the 2K injection molding process.
  • Higher maintenance: 2K injection molding equipment can require more maintenance compared to traditional overmolding equipment.
  • More difficult to troubleshoot: In the event of an issue with the process, it can be more difficult to troubleshoot and fix problems with 2K injection molding than with traditional injection molding.


You may have question when do you need to use over molding and when should you use 2k injection molding process, there is some simple suggestion,

  1. If the quantity is not so high, maybe only a few thousand or ten thousand, then use over molding process, this will save some mold cost for you.
  2. If you need over a half million of parts, then 2K injection molding is the best process to save cost for you.
  3. some of the parts only can use over molding and some of parts can be done by double injection molding process only, this is depending on the part structure, if you can not sure about this, you are welcome to send your data to [email protected], we can check this for you and offer you a price for your reference.

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