Shrinkage rate and mold layout of PP thermoforming sheets

As we all know, PP materials are relatively difficult to form products in the application of blister thermoforming. Due to the high crystallinity of pp material, the shrinkage rate is relatively large, usually around 1.0-2.0, but the specific shrinkage rate is related to its size, thickness, and molding time. The shrinkage rate of PP materials mainly depends on the molding time of the material. The longer the molding time, the lower the shrinkage rate will be.

PP materials are generally divided into two types in thermoforming: blister molding and cup molding. Blister materials are divided into high transparency, white mother/natural color/gold and silver, etc. Different components have different thermoforming shrinkage ratios. Therefore, the difficulty of thermoforming is also different.
Shrinkage is a relative value, and the specific data will be affected by molding conditions, mold part structure (water flow/water soaking) and other factors. In actual applications, different materials and molding processes must be selected according to specific conditions to minimize the impact of shrinkage on the size and shape of parts. Picture example:

1.012 is said to be 12 thousandths, that is, using this shrinkage rate of material, 1000 mm will shrink by 12 mm, and 100 mm will shrink by 1.2 mm.
Generally, the length and width of lunch boxes are 280/200. If the material shrinks between 1.012-1.018, it will shrink by about 3-5 mm.

How to calculate the relationship between different shrinkage rates and the layout of the blister mold?
In fact, there is no direct relationship between shrinkage and typesetting. Whether the product shrinks by 1.012 or 1.018, it does not affect the typesetting spacing. Typesetting is only related to the depth and height of the product.

Generally, a single product is shrunk before typesetting. The depth of the product depends on the depth of the die typesetting. The deeper the depth, the greater the spacing between the boards.
The height of the product depends on the typesetting of the punch. The aspect ratio between the height of the product and the distance between the mold should be at least 1:0.8.

If the punch is 40 mm high, based on the aspect ratio of 1 to 0.8, the die spacing is 40x0.8 = minimum spacing of 32 mm