Plastic shrinkage and mold size

Plastic mold design, make sure you can die structure of the mold after the detailed design of parts, which determine the templates and componentsSize, cavity and core sizes and so on. Then the shrinkage of the material involved in major design parameters. Consequently, only the specific graspForming plastic shrinkage to determine the size of various parts of the cavity. Even if the selected mold structure is correct, but the parameters used properly, is notMay be qualified to produce quality plastic parts.PRM IndustryAbstract...Articles section Plastic shrinkage and its influencing factorsThermoplastics is characterized by the expansion in heating, cooling contraction, of course, will reduce the volume after compression. In the injection moldingShaped process, the first molten plastic injected into the mold cavity, filling the cooling after the melt solidified, removed from the mold when the plastic partsThe contraction, this contraction is called forming contraction. Remove the plastic from the mold to the stability of this period of time, there will still be tiny sizeChange, a change is to continue to shrink, this contraction is called after the contraction. Another change is the plastic due to moisture absorption and some swelling occursInflation. For example, the water content of 3% nylon 610, the size increase is 2%; glass fiber reinforced nylon 66 40% moisture contentSize increases when the amount of 0.3%. But which play a major role in the forming contraction. At present the identification of plastic shrinkage (contraction shape+ After contraction) of the method, generally recommended in the German national standard DIN16901 requirements. That is 23 ℃ ± 0.1 ℃, when the moldCavity size and shape after 24 hours at a temperature of 23 ℃, relative humidity of 50 ± 5% measured under the conditions of the corresponding plastic rulerInch difference calculated.Shrinkage S by the following formula: S = {(D-M) / D} × 100% (1)Including: S-shrinkage; D-die size; M-size plastic parts.If the plastic parts according to the known size and material shrinkage rate of the mold cavity, compared with D = M / (1-S) in order to simplify the design of the moldThe calculation, the size of the mold using the following formula requirements:D = M + MS (2)If you need to implement a more accurate calculation, the application of the following formula: D = M + MS + MS2 (3)However, in determining the shrinkage, due to the actual shrinkage is also affected by many factors, only an approximation, and thus using equation (2)Calculated cavity size is also largely meet the requirements. In the manufacture of the mold, the cavity is processed according to the following error, according to the deviation of core processing,Can be used when necessary to facilitate the appropriate dressing.

PRM Industry
Peter Huang