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Two Shot Injection Molding Design Guide - WIT MOLD

Author: Jessica

Jun. 11, 2022

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If you're not familiar with secondary injection molding, you may think it's more complex, expensive or time-consuming than other plastic molding processes. In isolation, these may be true, but twice-shotting also creates considerable functionality and savings. Maybe you've been turned off by a manufacturer's quality or delivery issues. We're here to tell you that you deserve better.


What is secondary molding?

Two-shot molding, also known as two-color, multi-color or two-color molding, is a subcategory of injection molding that allows engineers to create multi-material or multi-color parts without adding additional assembly steps.


The secondary injection molding process is best understood in terms of the different layers or colors of material produced by the injection molding machine. The first material is injected into the mold to form the substrate around which the other materials or materials will be molded. The substrate is cured and cooled before being transferred to another chamber of the mold by hand, a robotic arm or rotary plane.


From there, the mold opens and the side with the substrate is rotated 180° to meet another mold chamber and injection nozzle. Once the substrate is in place, the second material is injected and bonded to the substrate to form a solid hold. Once the second layer has cooled, the final portion is ejected.


Engineers should be aware that secondary injection molding can be sped up or slowed down depending on how the substrate is transferred to another chamber of the mold. Hand and robotic arm transfers take longer than rotating planes, but rotating template molding is more expensive and is usually only a valid option for high-volume runs.


In addition, it is critical that the mold is made of materials that bond together easily and that the mold is properly aligned to prevent part distortion.


Secondary Molding Process

Bi-injection, also known as bi-injection, bi-injection, multi-injection and overmolding, is a plastic molding process in which two different plastic resins are molded together in one processing cycle.


The secondary molding process has two stages. The first is similar to traditional injection molding: the resin is injected into the mold and cooled to form a solid part. In the second stage, the freshly molded part is transferred to a second mold by a rotating template or robot arm and receives a second resin injection - in, through or around some portion of the first molded part, depending on the design. The two plastic resins then form molecular bonds and the multi-resin molded part cools and is ejected.


This process is not difficult to understand, but it is difficult to master. It requires a high level of technical expertise and attention to detail, and even the smallest mistakes can cost a lot of money, especially in high-volume production scenarios.


That's why finding a highly capable supplier is critical. Look for a great supplier quality scorecard, clear processes to reduce spills, flow lines and short shots, and contingency plans to expand capacity as your business and secondary molding needs grow.


Once you find a supplier, involve them early in the design phase of the part. They can identify potential problem areas and design value for your product.


How does 2K injection molding work?

2K injection molding, sometimes referred to as two-color injection molding, two-color injection molding, or 2-injection molding, is an innovative manufacturing process for producing complex molded parts of two different materials into a multi-cavity mold.


2K injection molding is performed on a machine that is programmed to perform two shots in one cycle. In the first cycle, a nozzle injects plastic into the mold. 2K plastic injection molding then automatically rotates and another plastic is injected into the mold from a second nozzle.


Secondary Injection Molding Applications

Secondary injection molding is the ideal plastic molding process for complex, multi-color, multi-material plastic products, especially in high-volume production scenarios. Serving a variety of industries, including lawn and garden, agriculture and consumer, with extensive experience in the automotive sector.


Secondary molded components are used in virtually every industry, from consumer products to construction, but are most commonly used in applications that require


Removable segments or assemblies

Rigid substrates with soft grips

Vibration or sound deadening

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Surface description or marking

Multi-color or multi-material assemblies


Benefits of Secondary Molding

Compared to other plastic molding methods, secondary molding is ultimately a more cost-effective way to produce assemblies with multiple components. The reasons for this are as follows.


Part consolidation| Secondary molding reduces the number of components in a finished assembly, eliminating an average of $40,000 in development, engineering and validation costs associated with each additional part number.


Improved efficiency│ Secondary molding allows multiple components to be molded using a single tool, reducing the labor required to run the part and eliminating the need to weld or join components after the molding process.


Improved quality│ Secondary molding is performed in a single tool, resulting in lower tolerances, higher accuracy and repeatability, and lower scrap rates than other molding processes.


Complex molding│ Secondary injection molding allows for the creation of complex mold designs that incorporate multiple materials to perform functions not possible with other molding processes.


2K Injection Molding Parameters

Plastic Material


Mold Material

718H, P20, NAK80, S316H, SKD61, etc. 20~60 HRC

Mold Base

HASCO, DME, LKM, JLS standard

Mold Runner

Cold runner, hot runner

Mold Cold Runner

Point way, side way, follow way, direct gate way, etc.

Mold Hot Treatment

Nitridation, tempering, etc.

Mold Surface

texture, EDM, high gloss polishing

Mold Cooling System

water cooling or Beryllium bronze cooling, etc.

Lead time

25-60 days


WIT Mold, is a professional mold manufacturer in China, with 10+ years rich experience in mold making, specializing in making different types of injection molds widely used in automobiles, household electrical appliances, telephone housing molds etc.What are you waiting for? Our technical sales team is on standby to provide you with the information you need to help you make a wise second decision.

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