The little knowledge in the mold design

1. Mold Material.
When the lot size of the experiment or production is small and the mold output is not high, wood or resin can be selected as the manufacturing material of the mold for cost, efficiency and experimental convenience. However, if the experimental mold is used to obtain data on shrinkage, dimensional stability and cycle time of the product, it should use a single cavity mold for experiment and makes it work under production conditions. The mold is generally made of gypsum, copper, aluminum or aluminum-steel alloy, but not generally made of aluminum-resin.

2. Geometry Design.
When designing, dimensional stability and surface quality are often considered comprehensively. For example, product design and dimensional stability require the use of a female mold (matrix), but products with higher surface gloss require the use of a male mold (punch). In this way, the plastic parts buyer will take these two points into consideration so that the parts can be produced under the best conditions. Experience has shown that designs without meeting actual processing conditions often fail.

3. Dimension.
During the molding process, the surface dimensions of the plastic parts in contact with the mold are more stable than some parts after demoulded. If the material thickness needs to be changed due to material stiffness, it may lead to the conversion of the male mold to a female mold. The dimensional tolerance of the plastic part cannot be less than 10% of the shrinkage rate.

4. Plastic Part Surface.
In terms of the range that the molding material can cover, the visible surface structure of the plastic part should be molded at the contact with the mold. If possible, the plastic part surface should not touch the mold surface.

5. Trim.
If a mechanical horizontal saw is used to cut off the clamping edge of the plastic part, there should be at least 6-8 mm of margin in the height direction. Other finishing work must also leave a margin, such as grinding, laser cutting or jetting. It is noted that the cutting lines gap of the knife die is the smallest, and the distribution width of the piercing die during trimming is also very small.

6. Shrinkage and Deformation.
Some plastics are easy to shrink such as PE and some plastic parts are easy to deform. No matter how to prevent them, the plastic parts will deform during the cooling stage. In this case, it needs to change the forming mold shape to meet the geometric deviation of the plastic part. For example, although the plastic part wall keeps flat, its reference center has deviated by 10 mm, so the mold base can be raised to adjust the shrinkage of this deformation.

7. Shrinkage Rate
The following shrinkage factors must be considered when manufacturing vacuum forming molds.
①Shrinkage of molded parts. If the shrinkage rate of the plastic is not known, it must be obtained by sampling or testing with a mold of similar shape. It should be noted that this method can only obtain the shrinkage rate, not the deformation size.
②Shrinkage is caused by the adverse effects of the intermediate medium, such as ceramics, silicone rubber, etc.
③Shrinkage of mold material, such as shrinkage during casting aluminum.