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Kenplas Forum ==> Injection Mold ==> PART DESIGN - MOLD SHRINKAGE
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Mold shrinkage is the difference between the size of the molded article after it reaches equilibrium at room temperature and the size of the cavity in which it was molded. Mold design, part design, and operating conditions all affect mold shrinkage for any thermoplastic material. Any factor that tends to increase effective pressure within the mold cavity will reduce the shrinkage and make a larger part.
To reduce shrinkage:
1. Increase plastic melt temperature;
2. Increase injection pressure;
3. Reduce feed cushion;
4. Reduce mold temperature;
5. Increase gate size or gate land;
6. Increase nozzle size;
7. Install multiple gates;
8. Increase packing pressure;
9. Increase packing time;
10. Increase injection speed;
11. Increase mold closed time;
12. Increase cavity venting;
To increase shrinkage, use procedures opposite to those listed above.
For high shrinkage compounds, the rate of shrinkage may increase slightly with thickness but this will be affected by gate design, location and flow length. In cases where very close tolerances must be maintained, it is suggested that a prototype tool be made before the production tool is built.
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This forum published since July 03, 2002.
Renewed on June 22, 2005. |
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