| 注塑制品变形、弯曲、扭曲现象的发生主要是由于塑料成型时流动方向的收缩率比垂直方向的大，使制件各向收缩率不同而翘曲，又由于注射充模时不可避免地在制件内部残留有较大的内应力而引起翘曲，这些都是高应力取向造成的变形的表现。所以从根本上说，模具设计决定了制件的翘曲倾向，要通过变更成型条件来抑制这种倾向是十分困难的，最终解决问题必须从模具设计和改良着手。这种现象的主要有以下几个方面造成：
1.模具方面：
(1)制件的厚度、质量要均匀。
(2)冷却系统的设计要使模具型腔各部分温度均匀，浇注系统要使料流对称避免因流动方向、收缩率不同而造成翘曲，适当加粗较难成型部份的分流道、主流道，尽量消除型腔内的密度差、压力差、温度差。
(3)制件厚薄的过渡区及转角要足够圆滑，要有良好的脱模性，如增加脱模余度，改善模面的抛光，顶出系统要保持平衡。
(4)排气要良好。
(5)增加制件壁厚或增加抗翘曲方向，由加强筋来增强制件抗翘曲能力。
(6)模具所用的材料强度不足。
2.塑料方面：
结晶型比非结晶型塑料出现的翘曲变形机会多，加之结晶型塑料可利用结晶度随冷却速度增大而降低，收缩率变小的结晶过程来矫正翘曲变形。
Plastic deformation, bending and twisting phenomenon is mainly due to the occurrence of plastic flow direction shrinkage is larger than the vertical, the shrinkage and warpage of different parts of anisotropy, and the injection molding is inevitable in the part of residual internal stress caused by large warpage, these are high stress orientation the distortion caused by the performance. So fundamentally speaking, mold design determines the warpage tendency of parts. It is very difficult to restrain this tendency by changing molding conditions. Finally, we must start with mold design and improvement. This phenomenon is mainly caused by the following aspects:
1. mold: the thickness and quality of
(1) parts should be uniform.
(2) the design of the cooling system to make the mold cavity uniform temperature of each part, gating system to make the material flow symmetric flow direction, avoid shrinkage caused by different warp, the shunt, the sprue is difficult to forming part of the appropriate bold, try to eliminate the cavity density difference, pressure difference, temperature difference. The transition area and corner of
(3) parts must be smooth enough to achieve good demoulding. For example, increasing the ejection allowance and improving the polishing of the die surface, the ejection system must maintain balance.
(4) exhaust should be good.
(5) increases the wall thickness of the parts or increases the direction of warping resistance, and strengthens the anti warping ability of the parts by reinforcing bars. The strength of the material used in the
(6) die is insufficient.
2. Plastics:
crystal has more opportunities for warpage than non crystalline plastics, and crystalline plastics can reduce the crystallization degree with decreasing cooling rate and reduce the crystallization process to correct warpage.
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