Mold structure design and service life
Speaking of die service life, it is related to mold design level, mold structure, mold material heat treatment, material selection, machining process, mold slip and other factors.According to the analysis and statistics of a large number of failure molds, among the various factors causing the failure of molds, the failure of molds caused by unreasonable mold structure accounts for about 25%. Obviously, the design of reasonable mold structure can effectively improve the quality and service life of molds.Then, following Shanghai pujonny to learn more about the mold structure design and service life.
What is the design of the mold?
The design of stoma: the design of vent hole of vacuum forming is the key of die design, the vent hole should be located at the back of sheet material stick the place of the die, be like when the die is formed at the bottom of the die and have the place of concave, when the die is formed at the bottom of the die, etc., specific circumstance depends on the shape and size of the molded part.For the complex profile of the plastic parts, the air vent should be concentrated, for the large flat plastic parts, air vent need uniform cloth.The hole spacing can be determined according to the size of the plastic part. For small plastic parts, the hole spacing can be selected from 20 to 30mm. For large plastic parts, the distance should be increased appropriately.
Usually molding plastic fluidity, molding temperature is high, then small air holes;The thickness of bad material plate is big, so the air hole is bigger.Billet plate thickness is small, by the air vent is smaller.In a word, the requirement for the size of the air vent is that the air can be drawn between the blank and the molding surface in a short time, and the air vent marks are not left on the plastic parts.Generally, the diameter of the air vent is 0.5-1mm. It is advisable that the diameter of the larger air vent should not exceed 50% of the thickness of the sheet. However, for plates less than 0.2mm, the excessively small air vent cannot be processed.
Cavity size: the cavity size of the vacuum mold should also take into account the shrinkage of plastics. The calculation method is the same as that of the injection mold cavity size.About 50% of the shrinkage of the vacuum forming part is produced after the part is unmoulded, 25% is produced after unmoulded and kept at room temperature for 1h, and the remaining 25% is produced within 8 ~ 24h later.The shrinkage of molded parts is 25% ~ 50% greater than that of molded parts.There are many factors that affect the size accuracy of the plastic parts. Besides reducing the size accuracy of the cavity, it is also related to the molding temperature, mold temperature and the type of plastic parts, so it is very difficult to determine the shrinkage in advance.If the production batch is relatively large and the size accuracy is required to be high, try to make the product with gypsum mold first, and measure its shrinkage rate. The above is the basis for designing mold cavity.
Surface roughness of dial cavity: generally, there is no ejection device in the mold of vacuum forming, and the mold is removed by compressed air after forming.If the surface roughness of the vacuum forming mold is too low, it is very unfavorable for the mold release after the vacuum forming. The plastic parts are easy to adhere to the surface of the mold forming and difficult to mold release.Therefore, the surface roughness of the vacuum forming die is higher.After its surface processing, as far as possible sandblasting.
Rear edge sealing device: in order to keep the air outside the cavity from entering the vacuum chamber during vacuum forming, a sealing device should be installed on the edge of the plastic sheet contacting with the mold.It is easy to seal the plastic sheet and mold contact surface on the flat parting surface, but difficult to seal on the curved or folded surface.
Heating and cooling device: heating of plastic sheet used in vacuum forming, usually with resistance wire or infrared.Resistance wire temperature can reach 350 ℃ ~ 450 ℃, for different plastic sheet needed for different molding temperature, usually done by adjusting the distance between the heater and plate.The distance usually used is 80 ~ 120mm.
The die life can reflect the level of metallurgical industry and mechanical manufacturing industry in a certain extent.