Two-shot Molding Guide

 

 

What is Two-shot Molding

Two-shot injection molding is a multi-material injection molding process. The molded plastic part can be a combination of two different materials or a combination of different colors of the same material.

Two-shot molding can also be called 2k injection molding, double shot molding, multiple injection molding (sequential injection molding).

When Is The Use of Two-shot Molding?

ㆍProduct function requirements

For example, power switches, phone buttons, keyboard indicators, car switches, etc. Portion with an LED capable of transmitting light.

ㆍImprove the handle feeling

Some handheld products require the use of rubber in hand-held parts, which makes the hand feel more comfortable. For example, walkie-talkie housing, power tool handle, wrench, screwdriver handle, toothbrush handle, thermos, etc.

ㆍEnhance beauty

For example, some plastic parts have a logo. If you use two-shot injection molding, you don’t have to worry about it being erased.

ㆍA localized area of the product that needs to be plated

In the plastic range, only ABS and PSUsurfaces can be plated. If it is necessary to plate a part or a single side of the product, the plating area should be injected into the ABS. Areas that do not require plating are injected with other materials such as PC.

7 Suggestions for Product Design

 

Two-shot molding frees the designer’s creativity. However, the following factors should also be noted in the product design process.

No.1

Choose the right material. The figure below shows the compatibility of different plastics.

1 ) The core material can use low viscosity materials to reduce the injection pressure.

2) Consider from the perspective of environmental protection. The recycled material can be used as a core material.

3) Optimize the product according to the characteristics of different materials. For thick parts, the finished skin layer uses soft materials. The core material uses hard or foamed plastic to reduce weight.

No.2

If the material is not chemically compatible, the two materials can be integrated by mechanical interlocking.

No.3

Maintain proper draft angle, uniform wall thickness and smooth transition lines.

No.4

The surface of the part should be flush or slightly lower than any adjacent substrate surface.

No.5

The surface of the substrate is textured to improve the adhesion of the two materials.

No.6

The mass ratio of the two materials should not be too large. Factors such as material forming time and injection pressure should be considered.

No.7

By increasing the contact area of the two parts, the weld strength of the two materials can be enhanced.

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9 Suggestions for Two-shot Molding

 

 

 

No.1

The hard plastic is molded for the first time, and the soft plastic is molded for the second time. Transparent for the first time, non-transparent for the second time. The plastic with high molding temperature is molded for the first time, and the plastic with low molding temperature is used for the second molding.

No.2

Before the official production, test the mold to produce a complete product.

No.3

Identify all possible defects in the process and eliminate them before the mold is manufactured.

No.4

Consider the shrinkage of the two materials.In general, shrinkage is determined by the material that is first formed.

No.5

A second injection can only be made after the first injection has been completely completed.

No.6

Consider the molded position, to prevent damage in the process.

No.7

Allow the edge of the first injection molded part to be too large. This ensures a higher pressure during the second injection.

No.8

Ensure that the parameters of the injection unit provide the required pressure, flow rate and cooling capacity.

No.9

Ensure that the structural strength of the first molded part can withstand the injection pressure of the second molding.

6 Suggestions for Maintenance of Two-shot Mold

No.1

Check for loose or damaged fastening parts of the double shot mold. The solution is to find parts of the same specification for replacement.

No.2

After the mold has been used for a long time, the cutting edge must be cleaned and ground. After grinding, the surface of the cutting edge must be demagnetized, otherwise it will easily block the material.

No.3

Elastic parts such as springs of the two-shot mold are most susceptible to damage during use. Breakage and deformation usually occur.

No.4

The method adopted is to replace, and the specifications and model of the spring must be paid attention to during the replacement process.

No.5

Two-shotmold punch during use prone to breakage or bending. Damage to the punch and the sleeve is generally replaced with parts of the same specification. The parameters of the punch mainly include the working part size, the mounting part size, and the length size.

No.6

Check the pressure plate, top plate and other parts of the double shot mold. During maintenance, check the accessories of each part and whether there is any damage, and repair the damaged parts. Pneumatic ejector check for air leaks, and specific measures taken.

Conclusion

Two-shot molding increases the added value and productivity of the product. At the same time, plastics are becoming more and more colorful.

Correspondingly, the cost of two-shot molding is higher. Master the design points and avoid risks in advance. Avoid cost waste.

If you have any questions about two-shot injection molds, please contact us directly. Get a free quote.

Insert Molding VS. Overmolding: What’s the Difference?

 

 

There are various sub-processes within injection molding that add further capabilities to this already versatile technology. This article will explore insert molding vs overmolding and the advantages of each.

Injection molding is a broad term used to describe one of the most important processes in the manufacturing industry. It’s a process that requires a mold, typically made of metal with a cavity in the shape of the desired part. Molten plastic is injected into the mold and ejected. The process repeats to produce thousands of identical parts. It’s safe to assume that every large-volume plastic part on the market has come from an injection molding machine because the benefits of using injection molding for production are numerous. These benefits include low cost per part, short cycle times, extensive materials, and compatible, in-tolerance parts.

Various sub-processes add further capabilities to this already versatile technology. This article will specifically explore insert molding vs. overmolding and the advantages of each.

What is Insert Molding?

Insert molding is a subset of injection molding techniques similar to overmolding where metal components are placed into a mold cavity before the actual plastic injection. The insert is precisely positioned inside the mold either manually or by a robotic arm. The mold then closes, and plastic is molded over the insert, creating a single part.

One of the most common applications for insert molding is the creation of metal attachment features for fasteners. Fasteners enable assemblies to be securely assembled and disassembled without product damage. Heat-set threaded inserts are molded into plastic to reduce the risks of thread damage during installation.

Insert molding can also eliminate the need for fasteners by including the necessary metal parts in the mold, thus firmly securing the parts into a single bonded component.

Why Choose Insert Molding?

Insert molding is a versatile process that has numerous benefits, some of which are listed below.

Reduced Assembly Cost – An injection molding machine can create thousands of parts per day. Such economies of scale can significantly reduce the cost of the individual parts. In a typical CNC machining, sheet metal, or additive manufactured part, any required assembly can be a major bottleneck. Insert molding can be used to eliminate assembly and thus maximize cost savings.

Part Performance – In general, plastic parts are less robust than their metal counterparts. However, plastic offers other benefits such as reduced cost, superior design flexibility, and lighter weight. Combining both metal and plastic materials into one part can capitalize on the benefits of both. Metal inserts can be used where strength and stiffness are required and the remainder of the part can be made of plastic to reduce weight. Moreover, plastic parts do not fare well against wear and tear and metal inserts add an element of durability to parts to withstand any kind of cyclical loading.

What are the Disadvantages of Insert Molding?

Despite the many benefits of insert molding, a few disadvantages need to be considered before choosing to use this sub-process.

Multiple Manufacturing Technologies – Insert molding can involve a 2-step manufacturing process. If the inserts are a custom design and not off-the-shelf parts, they will need to be manufactured using a metal forming process like CNC machining. These metal forming techniques are often significantly more expensive per part than similar, fully injection-molded processes. In some cases, the metal parts can be manufactured via die casting or MIM (metal injection molding). This can reduce the overall cost of the metal inserts but cannot eliminate the insert molded unit’s increased cost because parts with metal inserts will typically cost more than a part that is only plastic.

Increased Part Complexity – If a custom-made metal insert is required, the designer must be aware of both technologies’ design for manufacturability (DFM) principles and understand how best to integrate these technologies into a single practical part.

What is Overmolding?

Overmolding is essentially a type of insert molding. However, overmolding vs. insert molding is, as the name suggests, plastic is molded over another molded part. The first component is made inside an injection mold, and it is then placed into a second mold to add the over-molded material. This technique combines multiple plastics for either practical or aesthetic purposes. For example, one might use different durometer plastics to mold a softer plastic over a more rigid one to make a part easier to grip. Using multiple colored plastics in an over molded part can also distinguish the product from other brands. Overmolding is regularly used on the handles of tools like screwdrivers, power drills, or toothbrushes.

Why Choose Overmolding?

Overmolding is a versatile process that has numerous benefits:

Increased Material Flexibility – Overmolding allows designers to leverage the benefits of multiple types of materials to create complex parts with different properties, add visual complexity, or add haptics.

No Adhesives Required – Overmolding allows different materials to be fused in the mold, thus eliminating the need for glues or other permanent bonding methods. This increases the part’s overall durability and reduces assembly costs.

Embedded Seals – Overmolding offers the option of molding soft seals into parts. An example would be an electronics enclosure that needs to be IP rated. Usually, the part will have a groove into which an o-ring can be installed later. However, it is far more cost-efficient and robust to permanently mold the seal as an integral component.

What are the Disadvantages of Overmolding

Despite the many benefits of overmolding, a few disadvantages need to be considered before deciding to use this process.

Multi-Step Process – Overmolded parts are made in a two-step process. This increases part cycle time and is thus more expensive than molding a single part with no overmolding. This also requires two tools or a complex two-shot mold with increased upfront costs. However, when the alternative is to create two separate injection-molded parts and then assemble them after the fact, overmolding becomes a value-added solution.

Debonding – Bonding two different materials together in an injection mold runs the risk of delamination. This typically happens if the temperatures are not in the optimal range for the specific material combination. In some cases, mechanical interlocks may be required when materials cannot be reliably bonded together using heat.

Conclusion: Choosing Between Insert Molding, Overmolding, or Injection Molding

Injection molding, which includes the sub-processes of insert molding and overmolding, is a versatile and low-cost manufacturing production process that is used in the large majority of consumer products. Injection molding often results in the lowest cost per part when compared to other manufacturing techniques like CNC machining and even 3D printing.

Once injection molding is chosen for a specific application, the next step is often whether to use insert molding, overmolding, or just stick with plain injection molding. When trying to weigh the advantages of the processes, it is important to accurately define the product application. Each of these processes has specific use cases that are suited to different product types. It can be difficult to gauge which process will best suit your particular product, so it’s good to get expert advice early on. Contact WIT and We will help steer your design decisions in the right direction so that you can choose between insert molding vs. overmolding or just injection molding.

Difference between Thermoset & Thermoplastic Injection Molding

 

 

Thermoplastics and thermosetting plastics are two separate classes of polymers that are widely used in the process of injection molding to create products of various types. Both these categories of plastics possess different properties and characteristics. Hence, choosing the right category of polymer, between the two, is of paramount importance to achieve the expected results when used in applications.  Most of the injection molding service providers usually receive a question from their clients about the differences between thermoplastic and thermoset molding process. Here, in this post, let’s see thermoset & thermoplastic injection molding comparison.

Defining Thermoplastic and Thermosets

Before we go deeper into the topic, it is important to understand the two terms thermoset and thermoplastic. Let’s first find out what are thermosets and thermoplastics.

What are Thermosets?

Thermoset plastics “set” after they cure and are generally stronger than thermoplastic materials. Initially, the polymer is a liquid or soft solid, which becomes rigid later when cured. Owing to their high mechanical and physical strength, resistance to heat, corrosion, and mechanical creep, thermosets are used in a variety of applications. A few amongst the common thermoset materials used in the injection molding process include alkyds, epoxy, phenolic, polyimides, thermoset polyester, and so on.

What are Thermoplastics?

In contrast to thermoset, thermoplastics liquefy and become pliable when heat is applied. Thermoplastic polymers can be reheated and reprocessed many times, which is impossible when it comes to thermosets. Usually stored in the form of pellets prior to the molding process, these categories of polymers can withstand multiple re-shaping without causing any damage to the material. They possess high strength, shrink-resistance, flexibility, high-Impact resistance, and chemical resistant, among others. A few amongst the common thermoset materials used in the injection molding process include ABS, nylon, PET, polypropylene, polyethylene and TPE, among others.

Difference between Thermoset & Thermoplastic Injection Molding

The way thermosets are molded differs with respect to thermoplastics in several aspects and both the categories require varied treatment during the injection molding process. Let’s check a few differences when molding thermosets and thermoplastics.

Where and How They’re Used

The differences inherent to thermosets and thermoplastics make them uniquely suited for differing applications.

Appliance fabrication may require a thermoset such as epoxy — the material’s high-impact resistance, microbial resistance, and general inert properties are ideal in the kitchen and cooling environment. Conversely, a thermoplastic such as polyethylene makes a great packaging film, since the material shrinks and conforms to the packaging when heated.

As a general rule, thermosets are often affiliated with manufacturing and utilities — appliances, electrical applications, and anything else involving heat that may otherwise warp thermoplastics. Thermoplastics, on the other hand, are broadly diverse and used in everything from aerospace fabrication to consumer goods and toys. The nature of the polymer used depends on the final application.

 

Now that you know how thermoset injection molding differs with respect to thermoplastic injection molding. With the information provided in the post, you would be able to make a judgment on the type of polymer category you should opt to produce molded parts. However, just knowing the differences between the materials won’t be enough, instead you would need an injection molding service provider who can mold your parts as per the right specifications provided. Partner with leading injection molding companies like WIT MOLD who own a comprehensive working knowledge regarding thermoplastic vs thermoset molding.

What Is Thermoset Molding?

 

Many people are not aware of the advantages of thermoset materials. This guide describes the thermoset molding process and how it can benefit you.

*Thermoset Molding

Thermoset molding is an irreversible molding process by which malleable forms of plastic are forced into a heated mold and formed into their final shape.

Thermoplastic molding is the reverse process where heated material is injected into a cool mold. The material is then cooled to maintain the final shape of the part.

*Why Use Thermoset Molding?

Thermoset materials are generally stronger than thermoplastic materials due to the catalysts that are added to the base compound that cause chemical reactions at the molecular level, forming a harder, irreversible final form. Thermoset plastics cannot be re-melted, only ground and recycled as filler for different applications.

Thermoset molded products have electrical and thermal insulation properties, which make them ideal for electrical and electronic applications. They are resistant to corrosion and have high impact strength, depending on the resin, and are cost competitive with engineered thermoplastics. Using thermoset molding allows producers to maintain tighter tolerances during the molding process compared to similar thermoplastic materials.

*Pros of Thermoset Injection Molding

Injection molded pieces may be the best fit for a piece for several reasons:

Many different types of materials may be used in injection molding, including thermoplastic and thermosetting resins, polymers, and elastomers. This offers the engineer a great deal of control over which blend of materials will yield the best outcome, especially when needing to meet specific property requirements.

Fantastic for high-volume runs.

Precision and low waste. Because of the specific tooling and material mix, there is less waste with injection-molded parts than with other processes.

Short cooling time – Injection molded pieces cool quickly, reducing the time required to release the injected piece from the mold.

*Cons of Thermoset Injection Molding

While injection molding is a fantastic process for the reasons mentioned above, there are certain limitations and drawbacks. A few of these drawbacks include:

Tooling costs – These costs can be significant as precision crafted molds are required.

Flash – Flash is unavoidable when injection molding thermosets. Once the part has been created and ejected from the mold, an automated or manual next step is necessary to remove the flash (excess material). Flash isn’t an issue with thermoplastics due to the higher viscosity of the liquid plastic.

Part size – The size of the piece being created definitely matters when it comes to the molding process. Typically, smaller part sizes (0.1 lbs to 6 lbs) are injection molded, while larger parts are transfer or compression molded. The volume of the order will also dictate which molding process will be the best fit for the project. Compression molding would likely be used for larger parts with a low (or high) volume, while transfer molding would be used for medium to high volume projects. Injection molding would be ideal for high volume runs with smaller pieces.

 

WIT offers Custom Plastic Molding services. If you are interested in it, please contact us now!

Two-shot molding vs. overmolding: What you need to know

Injection molding is a popular manufacturing process that’s ideal for quickly creating precise parts with intricate shapes, all without leaving behind a lot of material waste. Common applications include packaging, automotive dashboards, mechanical parts like gears, and even popular kids’ toys.

 

Many different processes fall under the umbrella of injection molding, including two-shot molding and overmolding. These two processes are similar but have a few key distinctions — here’s what engineers and designers need to know:

 

What is two-shot molding?

Two-shot molding, also known as dual-shot, multi-shot, or double-shot molding is a subcategory of injection molding that allows engineers to create multi-material or multi-colored parts without adding extra assembly steps.

 

The two-shot injection molding process is best understood in terms of the different layers of materials or colors that are created by the injection molding machine. The first material is injected into a mold to create the substrate, around which the other material or materials will be molded. The substrate solidifies and cools before being transferred — by hand, robot arm, or rotary plane — to the other chamber of the mold.

 

From there, the mold opens and the side with the substrate rotates 180° to meet the other mold chamber and injection molding nozzle. Once the substrate is in place, the second material is injected and bonds with the substrate to form a firm hold.  Once the second layer cools, the final part is ejected.

 

Engineers should know that two-shot injection molding can be sped up or slowed down based on how the substrate is transferred to the other chamber of the mold. Hand and robot arm transfers take longer than a rotary plane, but rotary platen molding is more expensive and generally only an efficient option for high volume production runs.

 

Additionally, it’s critical that molds are made out of materials that will easily bond together and that the molds align correctly to prevent deformities in the part.

 

Advantages and disadvantages of two-shot molding

Two-shot plastic injection molding is an excellent technique for efficient and cost-effective manufacturing. This process also produces highly durable end parts and components.

 

From a design standpoint, two-shot molding offers designers a lot of flexibility because this process can create complex geometries and accommodate multiple colors, making for more aesthetically pleasing parts.

 

Further, since one machine makes the whole part and no post-processing is required, engineers can dramatically reduce manufacturing time, which in turn keeps costs low. However, it’s worth noting that the initial two-shot mold costs can be high and the two-shot molding machine is more expensive than a standard injection molding machine. Luckily, these costs are often offset by labor savings and assembly costs on large production runs.

 

What is overmolding?

Overmolding, like two-shot molding, is a multi-shot injection molding process that produces a single end product from two or more different thermoplastics. This process is ideal for engineers who want to build strong, functional, aesthetically pleasing parts that won’t separate over time.

 

To start the overmolding process, an engineer injection molds a substrate out of the more rigid overmold material. Then, the substrate is placed in an overmold tool or overmold cavity within the same tool. The molten overmolding material is then ejected into, onto, or around the substrate. After the molten material cools, the substrate and overmold are chemically or mechanically bonded. The entire overmolding process can take as little as 30 seconds.

 

Product teams must keep in mind that all thermoplastics used in the overmolding process must be chemically or thermally compatible with one another. Compatibility generally is not an issue with metal substrates because they can be used with any plastic overmold, but product teams can encounter compatibility issues when overmolding plastic with plastic. If the substrate and overmold aren’t compatible, the end product might be deformed or poorly bound.

 

However, if two plastics with less-than-ideal compatibility must be used, teams can design mechanical bonding features into the part after the fact, though this is likely to result in higher costs.

 

Advantages and disadvantages of overmolding

Overmolding and two-shot injection molding share many of the same advantages. They’re both ideal for quickly creating durable, reliable, and vibration-resistant parts with complex geometries, but overmolding is best suited for low-volume production runs.

 

Compared to two-shot molding, overmold designs are also easier to make because engineers can use any standard injection molding machine to conduct this process.

 

In terms of disadvantages, the tolerances of parts made via overmolding are often inferior to those that can be achieved with two-shot injection molding. It’s also important to remember that plastic compatibility requirements can constrain designers.

 

Choosing between two-shot molding and overmolding

Two-shot molding and overmolding are both simple and effective processes for creating durable parts made of two or more materials or two or more colors. To choose between the two, engineers should consider the size of their production run.

 

Two-shot molding usually only makes sense for larger production runs, whereas overmolding is better for low volume production runs. Still, teams must do their due diligence and evaluate all critical considerations of each potential manufacturing process against their specific project requirements to ensure they’re making the right choice.