Effect of compression process parameters on residual stress of injection⁃ compression⁃molded polycarbonate transparencies

doi:10.19491/j.issn.1001-9278.2021.12.002

Abstract

Abstract:

Transparencies were injection-compression-molded under different compression conditions using polycarbonate （PC） as a raw material. Through combining the mold cavity pressure test during the molding process， the effect of the core compression process parameters on the residual stress of the PC transparencies such as compression start position， compression distance， melt temperature and mold temperature were investigated using two methods， qualitative （stress polarization method） and quantitative （hole drilling strain gage method）. The results indicated that the cavity pressure increased as the compression start position was delayed or the compression distance increased. This resulted in a decrease in both flow residual stress and thermal residual stress and a decrease in the residual stress of the product. When the compression start position was delayed from 10 % to 70 %， or the compression distance increased from 0.5 mm to 2.0 mm， the Von Mises equivalent residual stress at the test point of the transparent parts obtained an average decrease by 82.0 % and 64.7 %， respectively. With an increase in melt temperature or mold temperature， there is no significant change in cavity pressure. However， a decrease in thermal residual stress resulted in a decrease in the residual stress of the PC transparencies. When the melt temperature rose from 290 ℃ to 320 ℃， or the mold temperature rose from 80 ℃to 120 ℃， the Von Mises equivalent residual stress at the test point of the transparencies decreased by an average of 56.2 % and 77.0 %， respectively.

Key words: injection-compression molding, polycarbonate, residual stress

CLC Number:

TQ 320.66

CHEN Yuhong, ZHAN Maosheng. Effect of compression process parameters on residual stress of injection⁃ compression⁃molded polycarbonate transparencies[J]. China Plastics, 2021, 35(12): 9-15.

Figures/Tables 14

压缩距离/mm	压缩启动位置/%	模具温度/℃	熔体温度/℃
0.5	10	80	290
1.0	30	100	300
1.5	50	110	310
2.0	70	120	320

Tab.1. Compression parameters of injcetion?compression molded PC transparencies

Fig.1. Cavity pressure measurement position of polycarbonate transparencies

Fig.2. Cavity pressure during molding process of polycarbonate at various compression start positions

Fig.3. Photographs of transparencies molded at different compression start positions under orthogonal plane polarized light

压缩启动位置占总注射量的百分比/%	σ_{von ，A}	σ_{von ，B}	σ_{von ，C}
10	12.3	13.8	10.1
30	11.4	12.9	8.5
50	6.3	3.3	6.2
70	2.4	2.3	1.8

Tab.2. Von Mises equivalent residual stress of PC transparencies molded at different compression start positions

Fig.4. Cavity pressure during molding process of polycarbonate at various compression distances

Fig.5. Photographs of transparencies molded at different compression distances under orthogonal plane polarized light

压缩距离/mm	σ_{von ，A}/MPa	σ_{von ，B}/MPa	σ_{von ，C}/MPa
0.5	6.1	6.5	5.8
1.0	5.0	5.5	3.7
1.5	4.5	3.2	2.3
2.0	2.4	2.3	1.8

Tab.3. Von Mises equivalent residual stress of PC transparencies molded at different compression distances

Fig.6. Cavity pressure during molding process of polycarbonate at various melt temperatures

Fig.7. Photographs of transparencies molded at different melt temperature under orthogonal plane polarized light

熔体温度/℃	σ_{von ，A}/MPa	σ_{von ，B}/MPa	σ_{von ，C}/MPa
290	5.5	5.7	3.8
300	4.8	4.5	4.6
310	2.9	2.8	2.2
320	2.4	2.3	1.8

Tab.4. Von Mises equivalent residual stress of PC transparencies molded at different melt temperature

Fig.8. Cavity pressure during molding process of polycarbonate at various mold temperatures

Fig.9. Photographs of transparency molded at different mold temperaures under orthogonal plane polarized light

模具温度/℃	σ_{von ，A}/MPa	σ_{von ，B}/MPa	σ_{von ，C}/MPa
80	10.9	9.7	7.8
90	7.7	8.5	7.4
110	4.7	7.0	5.9
120	2.4	2.3	1.8

Tab.5. Von Mises equivalent residual stress of PC transparencies molded at different mold temperature

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