Molding Technology for DURACON® POM - Product Design

With regard to the standard dimensional tolerance of parts molded with DURACON® POM, the standard specified by SPI of the United States can be used as a reference, as shown in Fig. 7-1. Namely, in case of precision molding, the tolerances are as follows:

For size of approximately 20-40 mm: ±0.20%~0.25%
For size of approximately 80-100 mm: Approximately ±0.15%

As a rule, dimensional fluctuations for a multi-cavity mold are greater than those for a single cavity mold. Therefore, it is necessary to take measures, such as the improvement of flow balance of resin and uniform distribution of mold surface temperature.

Fig. 7-1 Dimensional tolerance of polyacetal

(b) Dimensional fluctuation

Table 7-1 Molding dimensions and fluctuation

Molding day		Average χ (mm)	Standard deviation ±3σ_n-1	Fluctuation factor (%) ^(*1)
Molding day		Average χ (mm)	Standard deviation ±3σ_n-1	Fluctuation within a single day	Fluctuation within a period of 3 consecutive days	Total
Initial value		49.025	0.006	0.012	-	0.047 (49.045±0.023) ^(*2)
After 1 month	1st day	49.047	0.005	0.010	0.020
	2nd day	49.047	0.005	0.010
	3rd day	49.053	0.003	0.006
After 2 month		49.055	0.005	0.010	-
After 3 month		49.055	0.009	0.018	-
After 4 month	1st day	49.049	0.007	0.014	0.024
	2nd day	49.057	0.006	0.012
	3rd day	49.055	0.006	0.014
After 5 month		49.046	0.004	0.008	-
After 6 month		49.046	0.004	0.008	-
After 7 month		49.042	0.006	0.012	-
After 8 month	1st day	49.039	0.006	0.012	0.020
	2nd day	49.045	0.005	0.010
	3rd day	49.045	0.006	0.012
After 9 month		49.045	0.006	0.012	-
After 10 month	1st day	49.046	0.006	0.012	0.020
	2nd day	49.040	0.004	0.008
	3rd day	49.039	0.006	0.012
After 11 month		49.033	0.004	0.008	-

(*1) ±3σ_n-1 ⁄ ( χ ×100) (%)

(*2) χ ±3σ_n-1 (mm)

Points Accuracy Deformation Dimension Control Strength of Molded Products

Molding Characteristics

Product Design

Mold Design

Countermeasures for Defects