Multi Component Plastic Injection Molding

Multi-component injection molding or multi material injection molding is referred to as a process in which two or more dissimilar viscous materials are inserted in a part made of plasticto form a layer of material that has a specific property or function i.e. making of multi colors in the core material, for obtaining core materials like PP and TPE. This insertion of different material to obtain high quality plastic assemblies or parts, create a unique structure where both the material forms a sandwich like structure.

The apparatus consists of turret which can be moved to a desired location. The runner is used to or pour down the material to different cavities or the gate present for each cavity. The mold has degree of freedom for moving to each point by rotating, moving or covering longitudinal distance in order to provide material to the cavity properly. The gating process vary for different molds but in order to have a good injection process and proper gating system valve gating is preferred for multi component molding types. The molds are usually different for multi component molding i.e. first mold receives the material for forming the first layer while the other mold has cavities to place another layer of the material on the already molder layer. The molding is divided into stages, multi stages are present for forming layer after layer of different materials in each mold.

Two or more component injection molding can be done in several ways as it is the mixture of two dissimilar materials, and it depends how those materials are mixed or molded together. These methods are as follows:

Mixed Material Molding:

This is the simplest method for performing multicomponent plastic injection molding, in which two or materials are just together fed to the machine and they are heated, and mixing occurs. In this simple process, either different color mixture is done as in dyes and resins or also to obtain a material with different properties to have a fine plastic

Co-injection Molding:

In this method, two or materials are injected in such a way that one forms the layer on the other as one is inserted just after the other forming a very hardened plastic. This technique or method is implied where a core of different layer as compared to outer layer is required

Bi-Injection Molding:

Bi-Injection molding is a technique used where there is not contact between the material usually appears to be, as both or more material if used are inserted in different cavities through different positions in order to refrain from mixing. The finished product shows layered materials. However, in order to physically join the materials, it should be inserted with a quick insertion process through the gates that before hardening they approach each other.

Multi-Shot Molding:

This Process consist of providing multi shots of the material to the mold, so layers of the materials are formed as both materials are provided shot by shot one after the other so, there is not much hardening in the finished product and stacks of the different materials are visible in the finished plastic product.

Over Molding:

Over molding takes time to complete the finished product as it is done in number of steps. Materials are not inserted together instead one component is made and then it is finished and cooled down and then next material is injected or inserted over the first material then it is hardened, and cools and then next component is made over the already made components. This process is usually implemented where, totally different materials are used, and they are not expected to mix with each other as some grip made up of rubber is made for holding over any other component that is already made through molding.

Different techniques for multi-component plastic injection molding:

Multi component injection molding can be performed on different types of injection molding machines which are either on table or are rotary, few of them are listed below:

Rotary plate technology: In this technique, a machine which is rotating and that consists of two parting lines is used for making larger components and has smaller size of mold, also less force is required for the machine used for injection.

Turntable Mold technology: this type of technology is very easy and effective as mold doesn’t need to rotate as it is mounted on a plate which can be rotated using turntable, so the movement of the outer turntable provide degree of freedom for the mold cavity to easily receive material. The advantages of this technique is that, the ejector side temperature is controllable or can be changed as desired.

Index Plate Mold Technique: in the method, the mold is subjected to rotation and different sections are needed in order to keep the material or the component to be made in proper place. The advantages of this method include that there is an easy access for making the second component. The component which is molded can be easily reverted and material can be increase or over-spaying can be done easily.

Sliding Table Molds: In this technique of multi-component injection molding process, the mold can be made to slide with the help of the table which is mounted on the machine used for injection. The advantage of this mold is that a bit smaller mold as compared to other techniques can be used as because of sliding table.

Advantages of Multi Component Plastic Injection Molding:

Vast benefits are offered by this method of injection molding which are as follows,

• Desired material core is easily made.
• Complex shapes can be easily made.
• Finished product of desired physical properties can be obtained
• Material that is not available, can be made with the help of mix molding
• It is highly efficient and economically better method
• Different or multi-color variation is obtained in the finished product.
• Less cycle time is required in this molding
• Contrary to other methods, assemblies having many parts are easy to make.
• Higher and fine quality plastic or product is obtained.

Application or the Best use:

Multi component injection molding offers a wide range of application. Few of them are discussed below:

• Sensors (different type of sensors can be made easily i.e. light, rain, distance etc.)
• Tooth brushes (plastic tooth brushes are made readily by two component injection methods)
• Different Electrical components are made only using multi component injection method
• Springs (Different elements with different outer layer and core material).
• Different stationary items can also be made.