The Equipment Selection for the Plastic Injection Molding Process

The plastic injection molding is a complex process. The entire process cycle is often one to several minutes, and the most critical filling process is generally only tens of seconds. In this very short process cycle, plastics experience a very complex thermal and rheological history. So, how to choose a plastic injection molding machine?

According to some technical requirements of the plastic products to be produced (such as the types and grades of raw materials used in the products, the weight and dimensions of the products, etc.), find the performance parameters of the injection molding machine in the injection instructions. The key data to be compared in the specifications and models is the proportional relationship between the weight (or volume) and the external dimensions of the product and the parameter values.

That is, the ratio between the weight of the plastic injection molding products and the theoretical injection volume (or volume) of the injection molding machine, the sum of the length (height) of the product and the thickness of the molding mold (the thickness of the mold on the moving template), and the moving template of the injection molding machine. Dimensional requirements between travel distances.

Ⅰ. Select theoretical injection volume of the plastic injection molding equipment according to product weight

The weight of the product refers to the amount of melt required for plastic injection molding products. The calculation method sequence is as follows:

1. Calculate the total weight of the melt used in the product

Qs=K×(weight of product + weight of materials used in gate system); in the formula, K is the coefficient, which is 1.1 to 1.3.

2. Calculate the amount of melt that should be injected when the plastic injection molding machine is injection molding the product

The theoretical injection volume of the injection molding machine for injection molding this product should be slightly larger than the Qs value.

Ⅱ. Select the plastic injection molding machine according to the clamping force for plastic injection molding of the product

The clamping force of the injection molding machine (also called the clamping force) refers to the maximum clamping force for combining two (or more) molds into a product cavity in the clamping device.

When the molten material enters the mold cavity with a certain injection force and flow rate, the clamping force acts to prevent the plastic injection molding mold from being expanded by the injection force of the molten material.

In the specification and model standard of the injection molding machine (GB/T12783-1991), the numerator value is the theoretical injection volume (g or cm³) of the injection molding machine, and the denominator value is the clamping force (t).

The calculation of the clamping force for the plastic injection molding products is more complicated. It is related to the injection pressure of the melt, the viscosity of the melt, the plasticizing conditions of the raw materials, the shape of the product, the structure of the mold and the product, and the cooling setting temperature in the mold and other factors. Therefore, it is difficult to calculate a more accurate clamping force.

The method of roughly calculating the clamping force for the plastic injection molding of products is as follows: clamping force = constant for calculation of clamping force × vertical projected area of the product on the template.