Overmolding Injection Molding

Inox Cast Overmolding Injection Molding

Providing you your exact type of overmolding injection molding is our objective. Manufacturing and supplying overmolding injection molding and its related products are our line of work since 1997. That means we are expert enough to handle such large purchasing and importing products.

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Inox Cast intends to fulfill the needs and desires of our loyal customers. We made our offered overmolding injection mold more reliable and in outstanding performance. This type of injection molding can form a lot of styles and designs according to the demands of our customers.

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Overmolding Injection Molding: The Ultimate FAQ Guide

I know you are probably looking for more information about Overmolding injection molding.

A reason this guide will answer all your questions on Overmolding injection molding.

So, keep reading to learn more..

1. What Is Overmolding Injection Molding?

Overmolding injection molding is a multi-step injection process that aims at bringing two or multiple materials together to form one component.

The substrate is the first material or shot which will subsequently receive the overmolds you want to inject.

These overmolds are thermoplastic for flexibility and also enhance softness once you mold them on the main substrate.

overmolding injection molding

Overmolding injection molding improves products safety, ergonomics, and overall product functionality such as sound absorption and electrical insulation.

2. When Should You Choose Overmolding Injection Molding?

Overmolding injection molding may have unique requirements that are important to always consider during the molding process.

Choosing overmolding injection molding has the following benefits. They include;

Provides Enhanced Product Flexibility

Overmolding injection molding provides a flexible area of grip on a rigid substrate.

This not only makes it easy to use the product but also provides comfort.

Improves The Product Performance And Quality

Using overmolding injection molding to design different products helps improve the product’s performance.

For instance, the use of thermoplastic such as TPE provides a non-slip grip and provides a soft surface to the products you will be molding.

More so, thermoplastic materials such as TPE improve the quality of products thus increasing shelf life as it acts as an environmental barrier.

It provides a shield from noise, vibration, and even shock making it suitable for the overmolding process.

Reduces The Cost Of Parts

Overmolding injection molding reduces the need for any secondary operations which results in a reduction in labor costs and time consumption.

The overmolding injection molding process gradually reduces the number of stages during the manufacturing of the product.

For instance, there is less need for painting, coating, and priming which are secondary operations.

Improves Product Ergonomics

Overmolding injection molding helps improve products ergonomics.

This increases the comfortability levels of the products when the product reaches the end-users.

For instance, the rubber grip on toothbrushes, tools, and other handheld objects improves the grip of these objects.

Improves The Safety Of The Products

Overmolding injection molding provides a safe grip while using different objects in wet or dry environments.

Thermoplastic materials used on the main substrate reduce vibration damping.

For instance, if you use rubber between substrates, it will eliminate the vibration of the elements you are using such as pumps.

Improves Product Functionality.

Sound absorption, electrical insulation, and water absorption seal are some of the functionalities that overmolding injection molding aids.

Overmolding injection molding provides sealing from water in case you are using electrical devices or any other devices that require insulation.

Regardless of the sealing, these products are always flexible for usage.

Reduced Need For Adhesives And Fasteners

Overmolding injection molding eliminates the need for using fasteners and adhesives on products.

For instance, a toothbrush contains a two-side plastic handle to provide a firm grip eliminating the need for adhesives.

3. What Are the Disadvantages of Overmolding Injection Molding?

Overmolding injection molding as a process also has its drawbacks. Some of the disadvantages of overmolding injection molding include;

• The initial cost of starting up the overmolding injection molding is high from designing, testing, and also tooling.
• Overmolding injection molding involves a series or multiple production processes.

You will require much time to produce products since this process involves multiple steps.

• With overmolding injection molding, you will require extra tools since it’s a two-step process.
• There is a high chance of the molds debonding from the main substrate.

Any changes in the optimal temperature range results in delamination of the overmolds materials.

To carb these you can use mechanical interlocks for backup in case there is no sufficient temperature during the overmolding injection molding process.

• Overmolding injection molding is suitable for large production of parts to balance the costs, otherwise, the cost itself is very high.

4. How Does Insert Injection Molding Compare to Overmolding Injection Molding?

Both insert injection molding and overmolding injection molding falls under injection molding which is a manufacturing process of different products.

These make them subsets of injection molding.

Ideally, they undergo the same molding processes thermoplastic injection onto a mold cavity on the main substrate.

Both insert injection molding and overmolding injection molding cuts the assembly cost which means the machine can produce a wide range of products in a day.

insert injection molding

However, there are distinctive differences between these two subsets of injection molding.

Insert injection molding occurs when a part is made to fit into a bigger molded component.

You will then deposit the thermoplastic resin into the part resulting in the final product molded part.

This method is most suitable for a wide range of production of products mostly used in many industries such as automotive.

Overmolding injection molding involves molding thermoplastic resin onto the main substrate. The layers of molds you are adding onto the substrate molds firmly form one single end product. A good example is a toothbrush.

over molding injection molding

Insert injection molding eliminates the need to use fasteners because it fixes the parts firmly into a single bonded assembly.

Overmolding injection molding eliminates the need to use adhesives thus increasing the shelf-life of the molded products.

Overmolding injection molding is normally a two-step process. These processes include curing and molding the main substrate forming a layer on the substrate.

For insert injection molding is not normally a two-step however, it results in molding a layer on the original product.

Insert injection molding tends to take more time to form on the product since they are developed separately.

Insert injection molding involves a full product encapsulation, unlike overmolding injection molding which has partial encapsulation.

Overmolding injection molding takes lesser time because these two products are not developed separately.

More so, molding occurs directly of the thermoplastic onto the substrate.

This process though requires all instructions followed to the latter by the operators.

Overmolding injection molding involves adding a plastic mold onto a plastic substrate.

For insert injection molding, it involves adding plastic molding around a non-plastic substrate.

5. What Are the Key Stages in Overmolding Injection Molding?

The key stages in overmolding injection molding help in analyzing the design, tools, and efficiency of the products you will be producing.

The following are the key stages in overmolding injection molding. They include;

• Injection

Normally in this section, the heated overmold will be injected into the mold. Gates and runners ensure molds are filled well.

• Cooling

Once the molds fill up, it’s left to cool down at a certain temperature which makes the molten materials solidify.

Part thickness and type of resin determine greatly time needed for cooling the mold.

• Plasticizing the resin
• Upon cooling, the formed plastic resin will be drawn from the hooper
• Ejection

At this stage, the ejector releases the formed resin onto the part for bonding.

6. How Do You Choose Best Materials for Overmolding Injection Molding Process?

Choosing the best materials for the overmolding injection molding process can sometimes be a difficult task.

There are countless combinations that you can opt for depending on your preference.

The different materials you use for the over molding injection molding process have different properties thus resulting in different benefits.

For instance, you will get materials with high safety features, provide flexibility, and also provide enough grip on the products.

These different features will accommodate the need of different clients purchasing these products.

Therefore, to choose the best materials for over molding injection molding you should look out for;

Hardness

The over molding injection molding process can be sometimes hard depending on the type of materials you are using.

It’s therefore important to choose a material that will be able to stand up to the magnitude of toughness during the over molding injection molding process.

It’s also important to constantly check whether the material is bending.

Any bending of the material will affect the gripping of the product once you complete the over molding injection molding.

Bending of the materials results in the two materials detaching from each other.

Thickness

Material thickness is another aspect to consider during over molding injection molding. Normally, material thickness greatly attributes to the performance of the products you are making.

There are cases when over molding injection molding is suitable for vibration dampening and only a thicker material will perform these features effectively.

Thick materials not only feel soft but also provide excellent absorption of vibrations which a thinner material cannot perform these functionalities.

Temperature

Different materials have great features such as flexibility, however, those materials do not have the capability of withstanding certain levels of temperature.

The whole over molding injection molding process requires heat for the molding process to be effective.

It’s therefore important to choose materials that can withstand extreme temperature and still maintain the original functionalities.

This should be the case for both the substrate materials and overmold materials.

Friction

Different materials used in over molding injection molding have different levels of friction.

Friction levels normally determine the ability of these two materials to move against each other and the effects of the friction on the materials.

Ideally, each of these materials you are using has different friction coefficients.

Friction coefficiency and the surface texture of the material are the key determinants of the bonding of these two materials.

It will be easier for these two materials to bond if the rate of friction and surface texture is high.

Bonding

The whole idea of over molding injection molding is to mold two materials together through bonding.

There are cases where these two materials will not bond easily requiring you to force this material to bond.

To achieve this, you can either undercut or ident one material to allow bonding to the substrate material.

7. When Should You Use Over Molding Injection Molding Process?

Overmolding injection molding is suitable when manufacturing most plastic parts which feature a rubber handle.

For instance, the overmolding injection molding process of making a toothbrush involves a two-shot process.

This process involves coming up with a base layer that makes the handle and later molding a rubber layer on top of the handle.

This whole process improves grip making the toothbrush less slippery while in use.

You should also opt for overmolding injection molding if you are considering large production of parts within a set period.

These will cut out on the overall costs of production and labor too.

With overmolding injection molding, the tooling expense may shoot up unlike for standard injection molding.

The shooting of these is a result of the needed extra materials you will require to make the overmold layer and the substrate material.

8. What Should You Consider for Both Part and Mold Design of Overmolding Injection Molding?

The following are the most general considerations for both part and mold design of overmolding injection molding.

Part Design Considerations

To prevent wrappage, ensure the thermoplastic (TPE) thickness is equal to or less than the thickness of the main substrate.

You should avoid deep, inventable blind pockets or ribs at all costs

The use of a radius of 0.5mm especially around the corners reduces localized stresses.

To reduce wall flow, the transition between wall thickness should be a gradual process.

To obtain the best mold cycle time, ensure the wall substrate thickness and that of the overmold are as uniform as possible.

For instance, a wall thickness ranging from 0.060’’ to 0.120’’ provides the strongest bond between the overmold and the substrate walls.

If there is a need to use thick thermoplastic (TPE) in the part, it should be cored out to reduce cycle time and minimize shrinkage problems.

Mold Design Considerations

It’s important to provide adequate cooling to the thermoplastic (TPE) through proper molding cooling techniques to ensure low cycle time.

Gates should be placed at the thickest TPE wall section

Avoid large gates at all costs instead, use small TPE injection gates to obtain the best TPE.

9. What Are the Common Overmolding Injection Molding Defects?

In overmolding injection molding, you will constantly experience a different set of defects. Some of these defects include;

• Short shot: This occurs as a result of incomplete filling of the molten materials into the cavities.

After cooling you will notice incomplete compartments of the overmold material.

Possible causes of short shot include;

• Poor venting
• Fewer injection pressures
• Inadequate materials
• Low filling speed

Ways of eliminating these defects include;

• Increase the injecting speed
• Increase the shot size
• Increase in the injecting pressure
• Flashing of the overmold: flashing of the overmold occurs when excess mold spews out and appears as a layer at the edge of the product.

This means the overmold overflowed past the required areas on the products.

Possible causes of flash defect include;

• Substrate shrinkage
• Poot shutoff design
• Inadequate machine tonnage

Ways of eliminating this defect include;

• Check for substrate sinks and re-cut tool.
• Increase tonnage
• Re-cut tool to obtain full shutoff
• Discoloration: this occurs when you receive your product with the overmold but contains a different color from what you expected.

This defect affects the final appearance of your product but not necessarily the functionality.

Possible causes of discoloration defect include;

• Inadequate mixing of the masterbatch
• Lack of proper thermal stability of the colorant
• Overmolds of different types from the previous run

Ways of eliminating discoloration defects include;

• Ensure there is even mixing of the masterbatch molds
• Ensure adequate thermal stability of the colorant
• Ensure the hooper, nozzle, and mold are well cleaned.

10. What Are the Applications of Overmolding Injection Molding?

There are so many occasions we encounter products that have undergone overmolding injection molding.

The following are some of the applications of overmolding injection molding. They include;

Surgical Devices

In the medical industry, overmolding injection molding is most applicable for products safety and also object precision.

There is a great need to keep medical equipment clean and sterile which is determined by the kind of material you use for overmold and the substrate.

Some medical devices made using overmolding injection molding include dilators, syringes, and needles.

Hardware Tools

Screwdrivers, hammers, and blades among others are some of the equipment that is formed through overmolding injection molding.

This process enhances the grip of this equipment making work easy.

The most common overmold you can you, in this case, is plastic, it serves the purpose well.

Cookware

The overmolding injection molding process is also suitable while making most kitchenware equipment.

From cookware, utensils, and also food holding containers.

The most common overmold material is plastic as it helps in insulation and improves the grip of the cookware.

Household Items

Effective gripping, ease of use, and ease of cleaning are some of the features that overmolding injection molding provides.

For example, toothbrushes, reusable food containers, and shampoo containers are among the items that are a result of overmolding injection molding.

11. What Is Double Shot Molding?

Double shot molding is also known as two-shot, double-injection, or multi-shot molding. Double-shot molding involves the addition of overmold materials such as thermoplastic elastomer to a plastic substrate.

This results in improved handling characteristics, aesthetics, grip, and impact resistance.

Multi-barrel injection molding machine performs the task of adding all the additional materials.

The type of bonding you achieve mainly depends on the kind of materials you use for your overmold and substrate. The bonding will either be chemical or mechanical.

12. Are There Different Types of Overmolding Techniques?

Yes, there exist different types of overmoding techniques.

These techniques help to bring out a clear description of how the overmolding injection molding process works.

These techniques include;

Multiple Material Molding

Multiple material molding is also known as two-shot molding(2K).

With this process, there is a strong bond formation of the overmolded parts forming a strong mold on the substrate which protects it from harsh environmental conditions.

It contains subsets of two types of cavities, cavity 1 and cavity 2.

The first cavity is for setting the substrate while the second cavity is for molding the molding materials on the substrate.

This technique offers very low cycle time, low costs, and also superior part quality.

For multiple material molding, it provides two molding options you can opt for. They include;

• Thermoplastic over the thermoplastic substrate
• Elastomer over the thermoplastic substrate

Insert Molding

Insert molding is one of the most common overmolding techniques.

It’s most suitable if you work with plastic materials such as an elastomer or rigid plastic materials.

To carry out insert molding first place and position the substrate inside the injection molding.

From there you can add the secondary overmold materials such as thermoplastic into the injection mold and let it cool off.

After cooling then you can remove the part from the injected mold.

The benefit of using elastomers during insert molding is to enhance bonding between overmold material and the substrate material.

Rotary And Shuttle Molding

This over molding technique involves the insertion of a substrate which you can use horizontal insertion into the B cavity.

The table will be rotated into the nest station where thermoplastic material (TPE)is injected.

After injection, the table will move to a rotary unit where ejection of these two components occurs.

Injection Molding

This technique is also known as the dual-injection technique.

This process is different from the rest of the techniques because you will not be infecting an overmold into a substrate that is already in place.

But rather you should inject the substrate and the overmold material all in the same state since they exist in a molten state.

overmolding injection molding

This condition enhances adhesion and also improves the quality of the overmolding process.

Other Molding Techniques:

PLA Injection Molding

Multi Shot Injection Molding

2k Injection Molding

Prototype Injection Molding

Precision Injection Molding

For all your Overmolding injection molding or other techniques, contact us now.