We analyzed the last chapter in the form of plastic mould and causes of failure, we know, a reasonable choice of plastic mould steel to improve the quality of the mould is very important, then this chapter we introduce you to the principles of rational choice mould steel: 

With the plastics industry and everyday life in the widely applied, the mould industry, the demand for steel is growing. In the plastic moulding process, the quality of the mould on the product quality assurance is self-evident. Precision plastic mould has been present, large-scale and multi-cavity in the direction of development of the plastic mould steels have become increasingly demanding, mould steel, plastic type should be based on performance, product use, production volume, dimensional accuracy and surface quality requirements. 


 PlASTIC MOULD steel used should consider the following aspects 

Should be selected according to the mould working conditions and to meet the performance requirements of the mould steel. 
Should be used metallurgical quality, stable performance, reliable, convenient source, guaranteed steel. 
Should be selected process performance, using reliable, long working life of the steel. 
Should be a good choice of cutting, saving processing time of the steel. 
Should be selected Mirror performance, to ensure the accuracy of the steel. 
Should be selected With special performance requirements of the mould, should be used with the special properties of steel. 
Should be used for different production quantities of steel
     In the selection of mould materials, mould should be to ensure performance requirements, while as much as possible to improve its processing performance. For deformation, fracture failure of the common mould easily, the need to use high-strength, high toughness of the material (such as T10A); plastic mould cutting should be chosen, dense and polished performance of good material. In addition, the design of the punch and die, the appropriate selection of materials of different hardness or different to match the steel mould, the mould life can be increased by 5 to 6 times. 

Based on failure analysis of plastic mould, plastic mould in selected key performance requirements should be met: 

1 heat resistance 
With the emergence of high-speed moulding machines, plastic products faster. As the forming temperature of 200 - 3500C between, if plastic flow is not good, forming speed fast, some will die in a very short period of time moulding surface temperature over 4000C. Mould in order to ensure the accuracy and use small deformation, tool steel should be higher heat resistance. To reduce the temperature, tool steel should have good thermal conductivity and low thermal expansion coefficient. 

2 high intensity performance 
In the working temperature of sufficient strength; plastic injection moulding pressure, and pressure is generally closed mould injection pressure of 1.5 - 2 times, some as high as 4 times. Therefore, I hope to have a high strength tool steel. In order to improve hardness, heat treatment must be carried out. To take appropriate measures to reduce the heat deformation, heat treatment must be carried out for the mould, should be used in heat deformation of the material. 

3. Sufficient resistance to abrasion 
As the mould surface wear is the main form of failure, so the mould should have sufficient hardness, plastic mould surface to improve wear resistance and corrosion resistance, often to their appropriate surface heat treatment, surface treatment by mould, especially convex mould, die surface super-hardened surface to solve the problem of economic strain and effective there is a way. 

4. Good corrosion resistance 
Plus a flame retardant injection moulding PVC or other plastic additives, will break out with the rot 
Corrosive gases, the mould surface of a certain chemical corrosion, making this type of mould, 
Should be used with some corrosion resistance of steel. Add in the ABS resin and flame-resistant agents such as PVC, in the forming process may release corrosive gases and corrosive mould, sometimes in the air stream crossing at the rust and mould damage, and called for die steel with good corrosion resistance. 

5 excellent cutting performance technology 
With the plastic large, complex shapes and precision, requires cutting die steel with good work performance, to ensure that surface quality, requiring the mould material has good machinability, the pre-rigid material, is also required after quenching good workability, in order to avoid mould deformation affecting the accuracy, hoping to control the processing of residual stress to a minimum. Should take full account of the mould processing technology, try to use cutting, heat distortion, good wear resistance material. 

6. Good polishing properties and light patterns eclipse performance 
In order to obtain high-quality plastic products, mould cavity surface must be polished to reduce surface roughness, smooth surface cavity, forming a mirror polished surface requires the surface roughness of less than Ra0.4μm, to ensure that the suppression of plastic pieces look and ease of stripping. Tool steel should be high purity materials, organizational fine, uniform, dense, non-fiber direction, to ensure that the mould has a good electrical processing and mirror polishing, etching of patterns. 

7, according to the size of plastic parts and use precision 
For large high-precision injection mould, when large quantities of plastic parts production, the use of pre-hardened steel to prevent heat deformation, high-precision mould inserts with high accuracy, precision cavity size is generally 3-5 level. Fight inlaid seal cavity of joints required in order to avoid products squeeze into cracks. 

8. Batch selection 
We are in the selection of mould material should be based on different production batches, process the object selection and processing methods. Other factors in determining when you can use small quantities of quenching type structural steel or carbon steel, low-performance materials. Medium volume (30 to 1 million), you can choose P20, 5NiSCa, SM2 and so on. Mass production, should be used in long-life mould materials such as carbide, high toughness, high wear-resistant tool steel (eg, YG15, YG20), etc.: 

      Plastic mould parts are usually divided into two categories: one for the structural parts, including pouring system, guides, top of the template, the top of the organization, supporting documents, etc.; the other for the pieces of moulding include: cavity, core, mosaic pieces and so on. The moulded structure as complex and demanding piece of high dimensional accuracy, surface roughness is low, good seal joints where structural components can be mechanical parts of the requirements for strength and structural design, material from the mould to be taken into account the mechanical performance, wear resistance and processing a wide range of options to consider steel. 

      We know from actual production, relying solely on the base material to improve and enhance it is very limited, is not the economy, through the mould surface treatment especially for the mould convex and concave mould surface to solve the super-hardened surface strainThere are problems of economic and effective way. 

     The next chapter we introduce you to more economic and efficient plastic moulds with surface heat treatment!