塑料模具的工作条件与冷冲模不同,一般须在150°C-200°C下进行工作
塑料模具的工作条件与冷冲模不同,一般须在150°C-200°C下进行工作,除了受到一定压力作用外,还要承受温度影响。现根据塑料成型模具使用条件、加工方法的不同将塑料模具用钢的基本性能要求大致归纳如下:
The working condition of plastic die is different from that of cold
punching die. Generally, it must work under 150 C - 200 C. Besides being
subjected to certain pressure, it must also bear the influence of
temperature. The basic performance requirements of steel for plastic
moulds are summarized as follows according to the different working
conditions and processing methods of plastic moulds.
1、足够的表面硬度和耐磨性
1. Adequate surface hardness and wear resistance
塑料模的硬度通常在50-60HRC以下,经过热处理的模具应有足够的表面硬度,以保证模具有足够的刚度。模具在工作中由于塑料的填充和流动要承受较大的压应力和摩擦力,要求模具保持形状的精度和尺寸精度的稳定性,保证模具有足够的使用寿命。模具的耐磨性取决于钢材的化学成分和热处理硬度,因此提高模具的硬度有利于提高其耐磨性。
The hardness of plastic moulds is usually below 50-60 HRC. The heat
treated moulds should have sufficient surface hardness to ensure that
the moulds have sufficient stiffness. Because the filling and flowing of
plastics must bear large compressive stress and frictional force in the
work of the die, it is required to keep the shape accuracy and
dimensional accuracy of the die stable, and ensure that the die has
sufficient service life. The wear resistance of the die depends on the
chemical composition of the steel and the hardness of heat treatment, so
improving the hardness of the die is beneficial to improving its wear
resistance.
2、优良的切削加工性
2. Excellent machinability
大多数塑料成型模具,除EMD加工外还需进行一定的切削加工和钳工修配。为延长切削刀具的使用寿命,提高切削性能,减少表面粗糙度,塑料模具用钢的硬度必须适当。
In most plastic moulds, besides EMD processing, certain cutting and
fitter repairs are needed. In order to prolong the service life of
cutting tools, improve cutting performance and reduce surface roughness,
the hardness of steel for plastic die must be appropriate.
3、良好的抛光性能
3. Good polishing performance
高品质的塑料制品,要求型腔表面的粗糙度值小。例如,注塑模型腔表面粗糙度值要求小于Ra0.1~0.25的水平,光学面则要求Ra<0.01nm,型腔须进行抛光,减小表面粗糙度值。为此选用的钢材要求材料杂质少、组织微细均一、无纤维方向性、抛光时不应出现麻点或桔皮状缺陷。
For high quality plastic products, the surface roughness of the cavity
is required to be small. For example, the surface roughness of injection
mold cavity is required to be less than Ra 0.1-0.25 level, while the
optical surface is required to be Ra < 0.01 nm. The cavity must be
polished to reduce the surface roughness. For this reason, the selected
steel requires less impurities, uniform microstructure, no fiber
orientation, and no pitting or orange peel defects in polishing.
4、良好的热稳定性
4. Good thermal stability
塑料注射模的零件形状往往比较复杂,淬火后难以加工,因此应尽量选用具有良好的热稳定性的,当模具成型加工经热处理后因线膨胀系数小,热处理变形小,温度差异引起的尺寸变化率小,金相组织和模具尺寸稳定,可减少或不再进行加工,即可保证模具尺寸精度和表面粗糙度要求。
Plastic injection mold parts are often complex in shape and difficult to
process after quenching. Therefore, good thermal stability should be
selected as far as possible. When the mold is processed by heat
treatment, the linear expansion coefficient is small, the heat treatment
deformation is small, the size change rate caused by temperature
difference is small, the metallographic structure and the size of the
mold are stable and can be reduced. The dimensional accuracy and surface
roughness of the die can be guaranteed without further processing.