Mold Design Principle

Because different molding molds have been applied in many fields, and the manufacturing technology of professional molds has also changed and developed in these years, in this part, the general design rules of vacuum molding molds are summarized.
The design of vacuum plastic forming mold includes batch size, forming equipment, precision conditions, geometric shape design, dimensional stability and surface quality.
1. The batch size is used for experiments, and the mold output is small, which can be made of wood or resin. However, if the mold used in the experiment is to obtain data about shrinkage, dimensional stability and cycle time of the product, the single-cavity mold should be used for the experiment, and it can be used under production conditions. The mold is generally made of gypsum, copper, aluminum or aluminum-steel alloy, and aluminum-resin is rarely used.
2. In the design of geometric shape, the dimensional stability and surface quality should be considered comprehensively. For example, the design and dimensional stability of products require the use of female molds (female molds), but the products with high surface gloss requirements require the use of male molds (male molds). In this way, the ordering party of plastic parts will take these two points into consideration, so that the products can be produced under the best conditions. Experience has proved that designs that do not meet the actual processing conditions often fail.
3. Dimensional stability. During the forming process, the surface of the plastic part contacting the mold is better than the part leaving the mold. If the material thickness is required to be changed due to the material rigidity in the future, it may lead to the conversion of male mold to female mold. The dimensional tolerance of plastic parts shall not be less than 10% of shrinkage.
4. For the surface of plastic parts, the visible surface structure of plastic parts shall be formed at the contact with the mold in terms of the range that the molding materials can cover. If possible, the smooth surface of the plastic parts should not contact the mold surface. Just like the case of using female molds to make bathtubs and washbasins.
5. For decoration, if a mechanical horizontal saw is used to cut the clamping edge of the plastic part, there should be at least 6-8mm margin in the height direction. Other finishing work, such as grinding, laser cutting or jet cutting, must also have allowance. The gap between the cutting lines of the cutting edge is the smallest, and the distribution width of the punching die is also very small when trimming. These are all to be noted.
6. Shrinkage and deformation, plastic is easy to shrink (such as PE), and some plastic parts are easy to deform. No matter how to prevent, plastic parts will deform in the cooling stage. Under this condition, it is necessary to change the shape of the forming die to adapt to the geometric deviation of the plastic parts. For example, although the plastic wall remains straight, its datum center has deviated by 10mm; The mold base can be raised to adjust the shrinkage of this deformation.
7. Shrinkage, the following shrinkage factors must be taken into account when manufacturing the blister molding mold. ① Shrinkage of molded products. If the shrinkage of plastics cannot be clearly known, it must be obtained by sampling or testing with a mold of similar shape. Note: Only shrinkage can be obtained by this method, but deformation size cannot be obtained. ② Shrinkage caused by adverse effects of intermediate media, such as ceramics, silicone rubber, etc. ③ Shrinkage of the material used in the mold, such as the shrinkage when casting aluminum.