Principles Of Mold Design

Because different forming molds have been applied in many fields, and the manufacturing technology of professional molds has also undergone certain changes and developments in recent years, in this section, the general design rules for vacuum suction molding molds are summarized.
The design of vacuum plastic forming molds includes batch size, forming equipment, accuracy conditions, geometric shape design, dimensional stability, and surface quality.
1. Batch size experiments are used, and when the mold production is small, wood or resin can be used for manufacturing. However, if the experimental mold is used to obtain data on shrinkage, dimensional stability, and cycle time of the product, a single cavity mold should be used for the experiment, and it should be ensured that it can be used under production conditions. Molds are generally made of gypsum, copper, aluminum, or aluminum steel alloys, with little use of aluminum resin.
2. When designing geometric shapes, it is often necessary to comprehensively consider dimensional stability and surface quality. For example, product design and dimensional stability require the use of female molds (concave molds), but products with high surface gloss requirements require the use of male molds (convex molds). In this way, the ordering party of plastic parts will comprehensively consider these two points to ensure that the product can be produced under the best conditions. Experience has shown that designs that do not meet actual processing conditions often fail.
3. Dimensional stability, during the molding process, the surface of the plastic part in contact with the mold has better dimensional stability than the part that leaves the mold. If the material thickness needs to be changed in the future due to the need for material stiffness, it may result in the conversion of male molds to female molds. The dimensional tolerance of plastic parts shall not be less than 10% of the shrinkage rate.
4. The surface structure of the plastic part that can be enveloped by the forming material should be formed at the contact with the mold. If possible, the smooth surface of the plastic part should not come into contact with the surface of the mold. Just like using a female mold to make bathtubs and laundry basins.
5. Decoration: If a mechanical horizontal saw is used to cut off 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 blade die cutting is the smallest, and the distribution width during the trimming of the punching die is also very small, which should be noted.
6. Shrinkage and deformation, plastic is prone to shrinkage (such as PE), and some plastic parts are prone to deformation. Regardless of prevention, plastic parts will deform during the cooling stage. Under such conditions, it is necessary to change the shape of the forming mold to adapt to the geometric deviation of the plastic part. For example, although the plastic part wall remains straight, its reference 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 considered when manufacturing vacuum forming molds Shrinkage of formed products. If the shrinkage rate of plastic cannot be clearly known, it must be obtained by sampling or testing with molds of similar shapes. Note: Only the shrinkage rate can be obtained through this method, and the deformation size cannot be obtained Shrinkage caused by adverse effects of intermediate media, such as ceramics, silicone rubber, etc The shrinkage of the material used in the mold, such as when casting aluminum.