Design Guide for Plastic Injection Molding Machine

A mold is a tool for making a model, and a tool for forming a product having a certain shape and size in a specific shape. Mold technology occupies a very high position in the manufacturing industry. As product designers, molds are closely related to our work content, because many of the product parts we design need to be realized through the mold, so mastering the knowledge of the mold is essential.

The mold (injection molding) includes many parts: casting system, guiding mechanism, demolding device, lateral split core pulling mechanism, temperature regulating and exhausting system, and a standard mold base.

Brief description of standard mold base structure

Different products require different molds to produce, while the mold structure has many identical structures. Therefore, in order to make molds more efficiently, people began to use some standard mold bases. The standard mold structure became the skeleton of the mold, we only need to change matching mold core then we can form different parts. For the whole mold, there are three parts: front template, back template and mold core. While a set of molds is quite complicated, here is just some basic parts of the mold.

Classification of standard mold frame

For plastic molds, according to the basic structure classification, it generally divided into two-plate mode mold (large nozzle) and three-plate mold (fine nozzle),and three-plate mold can be subdivided into a thin nozzle mold and a simplified type of nozzle mold. So corresponding there are large nozzle mold frame, fine nozzle mold frame and simplified nozzle mold frame.

Basis structure of mold frame (take the two-plate CI type for example)

As we can see the composition of the standard mold frame on the picture.

(1) The board part: front mold bottom plate, rear mold bottom plate, front template, rear template,  upper ejector plate, lower ejector plate, and two die feet.

The front and back mold bottom plates are respectively fixed with the fixed mold plate and the movable plate on the injection molding machine.

Front and rear templates: Two molds are to be embedded in two templates.

Top and bottom ejector plates: The ejector mechanism in the clamping system above the injection molding machine will withstand the two plates and push the plastic parts out.

Die foot: support a certain space for the ejection of the part.

(2) Fixing screw parts: front mold fixing screws, rear mold fixing screws, ejector plate locking screws, and die fixing screws.

(3) Auxiliary parts: guide column and guide sleeve, return needle.

Guide post and guide sleeve: the guide post is in the rear template, and the guide sleeve is in the front template.The front and rear mold coming together plays a leading role.

The return needle: also has a spring on the reset rod. When the ejector rod on the injection molding machine pushes out the ejector plate and pushes out the plastic part, the spring above the return needle resets the ejector plate.

(4) Auxiliary Spare parts: the ring hole is designed for handling easier during mold transporting.

After taking apart the rear mold: we can see the essence of the whole mold-- mold core. For a mold production, most time is spent on making the mold core. Firstly, milling a square at the front and back templates, and then place mold core inside and fix with rear mold by screws. The ejector pin is fixed on the ejector plate and passes through the rear template and the rear mold core. (As shown below)

After taking apart the rear template: as we can see there are guide post holes, return pin holes, thimble holes and screw holes on the rear plate, which are connected with the die plate and the back die bottom plate by large screws. (As shown below)