Multi-material injection molding and the best solutions for plastic products – Part 1

Today, various finishing injection molding processes provide more creative space for designers and engineers. They can arouse their inspiration to enhance the form and ergonomics of the product.

Often a material or color does not meet the production requirements of the product. Materials for these products range from plastic to metal.

Previously, this was done using additional secondary services or more complex assembly processes to create the finished product. However, today's multi-material injection molding process largely eliminates these additional requirements, making it easier, faster, and cheaper to make complex finished products.

What is multi-material injection molding?

   Multi-material injection molding or so-called Multi-Material Casting (MMM) is the process of casting two or more different materials into a part of plastic at a time. As in the case of traditional injection molding, the molding of various materials uses materials near or near their melting point so that semi-liquid (viscous) materials can fill the pores and niches in the pre-mold, hence the desired shape of the design instrument.

In general, the advantages of MMM over other production techniques include, but are not limited to, the creation of parts with different elastic modules with the location of a part (the plasticity of different polymers), forming a structural part with different materials in the region Similar to the previous advantage, but more focus on combining different polymers such as rubber and plastic), and also creating a single part with multiple independent polymer colors. Applications range from simple household items such as toothbrushes to the fabrication of items such as power tools.

In fact, we can see many different ways of casting multi-material but in summary in the main ideas, we can divide multi-material injection molding into:

  1. Multi-component injection molding
  2. Multiple Injection Molding (MSM)
  3. Excessive mold pressing

See also: Mold processing

Multiple Injection Molding (MSM)

Also known as c sequence injection molding, repeated injection molding refers to the creation of multiple layers related to the starting axis of the original mold. In other words, heated, warm materials are in turn inserted into the mold in a very specific sequence.

This creates a layering effect between materials while maintaining relatively high energy interactions at material boundaries. This is important because it implies that the links between layers are stronger in many cases than when the layers are applied to a previously cooled part, just as is the case with overcast. While there are other applications, this operation is preferred when it is desirable to have different molds (different shapes) between layers of material.

Repeated injection pressing applications

This technology or process is nothing new and is simply used to produce parts or products of two-color plastic. The two materials form a single plastic part by physical bonding (shooting, surface roll, thread) or chemistry (co-bonding, mixing).

In some places, it is called 2k injection molding. 2K injection molding (MSM) is by far the most flexible, complex and exciting process of the MMM process. It requires a specific two-color injection molding machine to complete the injection molding process. Plastic parts need to be molded twice, but the product is pushed out only once, usually with a set of molds.

Rubber Press Mold

3 types of mold structure

According to the movement different mold parts can be divided into:

  1. Multi-plate press mold
  2. Index Plate Multi-Shot Molding
  3. Core Toggle Multi-Shot Molding

Multi-plate press mold

Msm of rotary needle presses is the simplest and most common type of MSM. The figure below shows a simple diagram of a rotating AXIS MSM mold.

Multi-plate press mold

The feature of the mold is the rotating roller on the left side of the shape. The core plate contains two identical cores that are reflected on the center line of the roller and coincide with the rotating shaft. The cavity plate is connected to a fixed roller shaft containing two compartments of different geometric shapes. Basically, in each cycle, the rotating roller completes the conversion of spray casting parts. Eliminates the need for manual conversions.

Molding Process

To make our tissues better through the molding process many rotating plates we can observe the following image:

Molding Process

(1) First check if the mold has reached a stable state.That has the potential to create a complete plastic part.Make sure the mold can create a complete plastic part.

(2) After that, the plastic part A is pre-completed in compartment A, and part A is a semi-finished turntable that is rotated 180 degrees. Part plastic A enters compartment B. As pictured (a).

(3) Compartments A and B are molded simultaneously, but finished plastic parts A and ab finished plastic are created. As shown in Figure (b).

(4) The mold is opened and the AB plastic part is ejected.The turntable is rotated 180 degrees, rotated from (3) to (4).

Pros and Cons

Here only two materials are displayed, which may contain more materials.Three and four-compartment injection presses can also be used to create three materials and four materials.

The rotating shaft can rotate 90°, 120°or 180° depending on the amount of material used.

The disadvantage is the need for a special casting machine to provide the necessary rotational motion on the core side.This can significantly increase the cost of the mold.

Read more: The best multi-material injection molding solutions for plastic products – Part 2

Mold design and processing is a highly technical and meticulous job, the selection of manufacturing companies is also a noteworthy thing. VCC Molds we are proud to be one of the best Precision Molding companies with a team of experienced engineers and modern machinery equipment. Please contact us immediately via Hotline: 0934 683 166 for free advice and refer to the details of the quotes.

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