Injection molding is a popular rapid prototyping process used to create metallic or plastic parts with intricate shapes and designs. For example, it is a process suitable for making products such as automotive dashboards, mechanical parts, and ever-popular toys because of its mass production property.
Injection molding is a popular process amongst many engineers. However, there are many sub-processes under it. One very important process used in making different products is the two-shot molding. This article will introduce two-shot molding and its advantages and disadvantages. It will also show how it differs from popular process overmolding.
What is Two-Shot Molding?
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It is a plastic molding manufacturing process used in making multiple materials of multiple colours. It goes by many names, such as dual-shot, multi-shot, or double-shot molding, and involves creating these products using a machine that can perform two injections in one cycle.
Two-shot injection molding creates different layers of materials or colors by using the steps below. The first material, e.g., plastic, is injected into an injection mold to create the substrate. It is then allowed to cool and transferred to another chamber in the same mold. Once in place, the second material is injected with the substrate, allowed to cool, and ejected.
Two-Shot Molding Products Driving in Daily Life
There are many products made by the two-shot molding process in daily life. Common examples include power tool grips, hinges, airtight seals, and gaskets.
Difference Between Two-Shot Molding and Overmolding
It’s often confused with another plastic molding manufacturing process called overmolding. Both processes are undoubtedly similar as they produce a single end product from different materials. However, they are different. Their difference starts with how overmolding works. While reading this, kindly compare it to how two-shot molding works.
What is Overmolding?
Overmolding involves injecting a substrate into an injection mold to form a more rigid structure. The other material known as the overmold is then ejected around or into the substrate. On cooling, the substrate and overmold undergo mechanical or chemical bonding depending on their compatibility.
Other differences between overmolding and two-shot molding include:
● Size Of Their Production Run
Two-shot molding is more suitable for high-volume production runs, unlike overmolding. However, production teams must carefully evaluate the manufacturing process before deciding on the right choice.
● Compatibility of Material
It occurs between compatible materials. Therefore, there is no need for any form of the post-bonding process after cooling. The post-bonding process is evident in some overmolding processes when you have incompatible materials. For example, you might have post-bonding issues when you are working with two plastic materials.
Why Use Two-Shot Molding? Advantages And Disadvantages
We already said that two-shot plastic injection molding is excellent for large volume production due to its efficiency and cost-effective nature. However, those are not the only advantages and even disadvantages of the process. Below are the advantages and disadvantages of usage.
Advantages of Two Shot Molding
Below are the advantages of using two-shot molding:
● It is More Flexible
Two-shot molding is more flexible than other injection molding processes design-wise. For example, it allows the creation of complex geometry. It is also possible to create products that are aesthetically pleasing using how easy it is to accommodate multiple colors.
● Leads to Lesser Manufacturing Time
Two-shot molding takes place in a single machine. Also, it also does not require any post-processing due to the fact that there is normally no compatibility issue on cooling. Consequently, these two conditions lead to a lesser manufacturing time, better lead time, production efficiency, and cost-effectiveness.
● Strengthen Product Quality and Aesthetics
Two-shot injection molding produces products of very high quality due to the strong bond between the materials used. There is also an improvement in aesthetics as it is possible to incorporate different colors and polymers into the design. Therefore, the end product is durable, reliable, and has a long life.
● Accuracy and Precision
When compared to other injection molding processes, e.g., overmolding, two-shot molding is more accurate and processed. For example, there is a great reduction in the number of misalignments when it is used. Consequently, manufacturers can create complex mold designs from multiple materials.
Two-shot molding is applicable over a wide range of industries which includes automotive interior parts, medical equipment, tools, and toys. This occurs as a result of its ability to combine multiple materials of multiple colors to make a product of unique design.
Disadvantages of Two Shot Molding
Below are the disadvantages of using two-shot molding:
● Cost of Mold
Even though two-shot molding is cost-effective, the two-shot molding machine costs more than the standard injection molding machine. However, it is possible to offset the cost of the machine by using it in large production runs.
● Too Many Defects Based on Lack of Experience
Doggedness is an important attribute of any engineering team that wants to use a two-shot molding process. When there is a lack of experience, there is a chance of encountering several defects such as
- Flash, curling, fraying, and peeling in the shut-off areas: These occur when there is a poor seal between the first shot and the second shot mold. It can also occur when the substrate material is too thin in the shut-off area.
- Unwanted material protruding from the gate area on the first-shot substrate
- A weak bond: This occurs due to weak material selection. Therefore, careful consideration of the type of materials to use must be taken for the first shot and second shot material.
Two-shot molding might seem a little challenging. However, the method is not hard to master. Like any other injection molding technique, understanding the necessary factors that can improve the seamless process can be your redeeming quality. That is why this article introduced the two-shot molding, its advantages and disadvantages, and other things you need.