Injection and Holding Time in Injection Moulding Process

The setting of injection and holding time is a very important part of the injection moulding process, which directly affects the quality, performance and productivity of the product. So, how to correctly set the injection and holding time of injection moulding process?

Injection time refers to the time from the beginning of the mould closure, until the molten plastic is completely injected into the mould. During this time, the plastic enters the mould through the nozzle under high pressure to form the shape of the product.

Holding time, on the other hand, is the time after the end of injection when a certain pressure continues to be maintained to allow the molten plastic to fully flow and cool in the mould. During this time, the plastic fills all the corners of the mould, removing internal stresses and increasing the density and strength of the product.

There are several factors to consider when setting the injection and holding pressure times:

1. Nature of the material: Different plastic materials have different flow and cure rates. For example, engineering plastics such as ABS and PC have better fluidity and can have relatively shorter injection and holding pressure times, while non-engineering plastics such as PE and PP have poorer fluidity and require longer injection and holding pressure times.

2. Shape and size of the product: products with complex shapes and large thicknesses require longer injection and holding times to ensure that all parts are fully filled and cured. For products with simple shape and small thickness, the injection and holding time can be shortened appropriately.

3. Mould design: The runner design, gate design and cooling system design of the mould will affect the setting of the injection and holding pressure time.

4. Parameters of the injection machine: the injection speed, pressure and temperature of the injection machine will also affect the setting of the injection and holding pressure time.

In the actual production process, the injection and holding pressure time can be adjusted in the following ways:

1. test method: by making a small number of specimens and observing their surface quality and internal structure, and then adjusting the injection and holding pressure time according to the test results.

2. computer simulation method: use injection moulding simulation software to simulate the injection and holding pressure process, and then adjust the injection and holding pressure time according to the simulation results.

3. Setting according to empirical values: For commonly used plastic materials and common product shapes, the injection and holding pressure time can be set according to empirical values.