Influence of injection product thickness on shrinkage change

Time：2023-07-04 08:45:26 / Popularity： / Source：

Molding of injection products is a very complex dynamic processing process with multi-factor coupling action. Each factor in molding process has an important impact on molding quality of product, and molding shrinkage is one of key factors affecting quality of product.
There are many factors that affect shrinkage of injection molded products, such as molding materials (including molecular chain structure, crystallinity, mechanical properties, rheological properties of polymers, etc.), product structure (including product thickness, insert structure, etc.), process conditions (including injection molding, etc.) Speed, dwell pressure, dwell time, cooling time, etc.) and mold design (including gate location and number, cooling loop distribution, etc.) all affect its shrinkage behavior.
This paper adopts method of CAE to study influence of variation of product thickness on transverse shrinkage (along flow direction) and longitudinal shrinkage (vertical flow direction) of injection molding.

Simulate experimental conditions

(1) Structure and size of experimental products

Sructure of product used in simulation experiment is shown in Figure 1. Product is a square product of 36mm * 36mm. In order to study effect of thickness on injection molding shrinkage rate, within thickness range of 0.8 to 4.0mm, a product is obtained for every 0.5mm increase in thickness, measure transverse shrinkage Sh (average value of shrinkage at Sh1, Sh2, Sh3, etc.) and longitudinal shrinkage Sz (average value of shrinkage at Sz1, Sz2, Sz3, etc.).

(2) Process conditions and methods of simulation experiments

In experiment, two kinds of materials were used for research on products with different thicknesses, crystalline material PP and amorphous material ABS were simulated. Each material is simulated by "filling + warpage" according to commonly used process conditions, and process conditions are shown in Table 1.
Process conditions of same material are used for products of different thicknesses, and gate location is shown in Figure 1. “Filling + warpage" analysis was carried out on products of each thickness, then shrinkage rates of 6 positions such as Sh1, Sh2, Sh3, Sz1, Sz2, Sz3 as shown in Figure 1 were measured, average value of 3 positions such as Sh1, Sh2, and Sh3 is taken as transverse shrinkage rate Sh of product, shrinkage rate of three positions, such as Sz1, Sz2, and Sz3, is is longitudinal shrinkage Sz of product.

Simulation results and data processing

Using product shown in Figure 1 and process conditions in Table 1, "Flow+Warp" function of MoldFlow software is used to simulate shrinkage of product, as shown in Figure 2. Figure 2 shows warpage of product with PP plastic and a thickness of 1.4mm.

In simulation results, result query function of MoldFlow is used to measure shrinkage rates of six positions shown in Figure 1, shrinkage rates of six positions, such as Sh1, Sh2, Sh3, Sz1, Sz2, and Sz3, are obtained, which were recorded in Table 2 and Table 3.

According to above simulation results of parts with different thicknesses, use MATAB software to perform spline curve fitting to fit result data of product shrinkage, we can get shrinkage rate change curve of different thickness products as shown in Figure 3 (crystalline material PP) and Figure 4 (non-crystalline material ABS).

Concluding remarks

It can be seen from curves in Figure 3 and Figure 4 that whether it is a crystalline plastic or an amorphous plastic product, when thickness of the product is different, shrinkage rate of product is very different. Longitudinal shrinkage and transverse shrinkage are both increasing.
However, this increasing trend is non-linear, but gradually slows down with increase of thickness, and longitudinal shrinkage rate is slightly smaller than transverse shrinkage rate.

Gud Mould Industry Co., Ltd