Analysis of basic knowledge in the mold design process
Author: SZTC
2024-10-09
1. Batch size experiment. When the mold output is small, it can be made of wood or resin. 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 experiment, and it can be guaranteed to 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. Geometric shape 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 (concave mold), but products with higher surface gloss require the use of a male mold (convex mold). In this way, the plastic parts orderer will take these two points into consideration so 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 leaving the mold. If the material thickness is required to be changed in the future due to the need for 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. As far as the molding material can cover, the surface structure of the visible surface of the plastic part should be molded at the contact with the mold. If possible, the smooth surface of the plastic part should not contact the mold surface. Just like the case of using a negative mold to make a bathtub and a laundry tub.
5. Modification. If a mechanical horizontal saw is used to cut off the clamping edge of the plastic part, there should be at least 6 to 8 mm of margin in the height direction. Other finishing work, such as grinding, laser cutting or jetting, must also leave a margin. The gap between the cutting lines of the knife die is the smallest, and the distribution width of the punching die during trimming is also very small. These are all things to pay attention to.
6. Shrinkage and deformation. Plastics are easy to shrink (such as PE). Some plastic parts are easy to deform. No matter how to prevent it, the plastic parts will deform during the cooling stage. Under this condition, the shape of the molding mold must be changed to adapt to the geometric deviation of the plastic part. For example: although the wall of the plastic part remains straight, its reference center has deviated by 10 mm; 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. ① Shrinkage of molded products. If the shrinkage rate of the plastic is not clearly known, it must be obtained by sampling or testing with a mold of similar shape. Note: This method can only obtain the shrinkage rate, not the deformation size. ② Shrinkage caused by the adverse effects of the intermediate medium, such as ceramics, silicone rubber, etc. ③ Shrinkage of the material used in the mold, such as shrinkage during casting aluminum.
2. Geometric shape 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 (concave mold), but products with higher surface gloss require the use of a male mold (convex mold). In this way, the plastic parts orderer will take these two points into consideration so 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 leaving the mold. If the material thickness is required to be changed in the future due to the need for 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. As far as the molding material can cover, the surface structure of the visible surface of the plastic part should be molded at the contact with the mold. If possible, the smooth surface of the plastic part should not contact the mold surface. Just like the case of using a negative mold to make a bathtub and a laundry tub.
5. Modification. If a mechanical horizontal saw is used to cut off the clamping edge of the plastic part, there should be at least 6 to 8 mm of margin in the height direction. Other finishing work, such as grinding, laser cutting or jetting, must also leave a margin. The gap between the cutting lines of the knife die is the smallest, and the distribution width of the punching die during trimming is also very small. These are all things to pay attention to.
6. Shrinkage and deformation. Plastics are easy to shrink (such as PE). Some plastic parts are easy to deform. No matter how to prevent it, the plastic parts will deform during the cooling stage. Under this condition, the shape of the molding mold must be changed to adapt to the geometric deviation of the plastic part. For example: although the wall of the plastic part remains straight, its reference center has deviated by 10 mm; 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. ① Shrinkage of molded products. If the shrinkage rate of the plastic is not clearly known, it must be obtained by sampling or testing with a mold of similar shape. Note: This method can only obtain the shrinkage rate, not the deformation size. ② Shrinkage caused by the adverse effects of the intermediate medium, such as ceramics, silicone rubber, etc. ③ Shrinkage of the material used in the mold, such as shrinkage during casting aluminum.
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