Injection Tooling Molding PP PVC PVDF HDPE

Basic Info

Runner	Hot Runner
Design Software	AutoCAD
Certification	ISO
Standard	PUNCH
Customized	Customized
Transport Package	Pallets
Origin	China

Product Description

Injection mold is a tool for producing plastic products; It is also a tool to endow plastic products with complete structure and precise dimensions. Because the main production method is to inject high temperature molten plastic into the mold through high pressure and mechanical drive, it is also called plastic injection mold.

The screw barrel temperature is set according to the properties of different plastic materials. The barrel temperature is generally 10 ºC - 30 ºC higher than the plastic melting point. It must be noted that the melting point and allowable residence time in the barrel of materials provided by different manufacturers will also vary due to different synthetic methods or types of additives.

Injection Tooling Molding PP PVC PVDF HDPE

The mold temperature is generally cooled by circulating water when it is set, but when producing products with high precision size or surface quality requirements, the mold temperature machine that can be accurately controlled should be used according to the process requirements.

Injection holding time and cooling time

The injection time, pressure holding time and cooling time must be set according to the product thickness, mold temperature, material properties, etc. The injection time is generally set to be slightly longer than the time for the screw to complete the injection stroke movement. Too long injection time will not only produce negative effects such as mechanical wear and increased energy consumption, but also prolong the molding cycle. The pressure holding time is set according to the thickness of the product. The pressure holding time is not required for thin-walled products during molding;

When setting the pressure holding time, as long as there is no obvious depression on the surface of the product, it can also be determined by the weighing method. The best pressure holding time can be determined by gradually extending the pressure holding time until the product quality no longer changes. The cooling time also needs to be determined according to the product thickness, mold temperature and material properties. Generally, the cooling time of amorphous polymer is longer than that of crystalline polymer.

Injection Tooling Molding PP PVC PVDF HDPE

Injection pressure and speed

The setting of injection pressure should follow the principle of low rather than high, as long as it can provide enough power to reach the required injection speed, so that the melt can smoothly fill the mold cavity, too high pressure will easily cause internal stress in the product; However, when molding products with high dimensional accuracy, in order to prevent excessive shrinkage of products, high pressure injection can be used to reduce the shrinkage of products after demoulding.

The injection speed will affect the appearance quality of the product, and its setting should be based on the geometric structure of the mold, exhaust condition, etc. Generally, on the premise of ensuring a good appearance, try to improve the injection speed to reduce the filling time.

In injection molding, when the melt flows in the mold, the mold wall will form a curing layer, thus reducing the thickness of the flowable channel. Generally, according to the mold structure and injection speed, the mold wall will have a curing layer of about 0.2mm. Therefore, a faster injection speed is usually used in the molding.

Injection stroke, multi-level injection parameters

In molding, the injection stroke must be determined first. In theory, the injection stroke can be calculated as follows:

Injection Tooling Molding PP PVC PVDF HDPE

S1=4(CVp+Va)/ ρ Ds2

Due to the different geometric shapes of the runner system and various parts of the mold, in order to meet the product quality requirements, different parts have different requirements for the flow state of the mold-filling melt (mainly refers to the pressure and speed when flowing). In an injection process, when the screw pushes the melt into the mold, it is required to achieve different pressure and speed at different positions, which is called multi-stage injection molding.

Generally, it is more scientific to set at least three or more injection sections for plastic parts during molding, that is, the first section is at the main runner, the second section is from the runner to the gate, the third section is about 90% of the cavity filled with the product, and the remaining section is the fourth section. The weight calculation method can be used to determine the switching position of each section;

In actual production, the multi-stage injection process parameters should be scientifically analyzed and reasonably set according to product quality requirements, runner structure, mold exhaust conditions, etc. Usually, the adjustment and observation method can be used to set the pressure/speed of the switching position point needed for injection to 0, observe the melt direction and the product defect condition, and gradually adjust until a reasonable position point is found. However, in the process of debugging and observation, attention must be paid to the demoulding condition of under-injected products to avoid mold sticking due to under-injection at some concave parts of the mold.

Other process parameters

In injection molding, in addition to the setting of several main parameters, such as molding temperature, pressure, speed, time, and multi-level injection switching position, there are many other process parameters, such as back pressure, screw speed, screw rewind, anti-flow and other action parameter settings, which cannot be ignored.

Example of process parameter setting

Take the production of nylon cable ties as an example, the product quality requirements are as follows:

The product meets the specified tension standard; The surface shall be free of silver wire, bubbles, shrinkage marks and other undesirable phenomena; After forming, the product has good tightness and no looseness. The material used is PA66, the mold structure is hot runner type, and the gate type is point gate.