All production tools should be made from high-quality steels manufactured to suitable BS, ASTM or DIN standards.
Several different metals are sometimes used, but the majority of mould tool metals used fall into three groups:
- Nickel–chromium alloy steels (H13 ASTMor BS EN30B)
- Mild steels or low-carbon steels (BS EN8) or those of higher carbon content.
- Beryllium-copper
Alloy Steels
Alloy steels are usually used for cavities and for any plates that come into direct contact with the moulding materials. Alloy steels may be used in their soft state or may be fully hardened depending on the application.
Generally all cavity components are fully hardened, as they have to withstand cyclical high loading, wear and thermal stresses. Cavity retaining plates and other shut off areas are normally made from the soft version. They do not need the higher strength and wear
resistance that the hardened steel gives but they do offer a higher degree of protection against damage than would mild steel.
In some cases a pre-toughened form of this steel is used for cavities, cores and punches, especially for larger components where through-hardening may not be desirable or possible. This type of steel is tempered back to give a steel whose hardness lies between the soft and fully hardened versions.
Mild Steel
This steel is normally used for all other tool plates. Mild steel should not be used for cavity inserts or contact with the moulding material. It should never be used where it may be subject to excessive sliding conditions, etc. Sometimes designers prefer to use a highercarbon-content steel on long-running jobs for greater resistance to wear and tear.
There is no reason why nickel–chromium steels should not be used throughout the tool – apart, that is, from cost. For large, expensive, long-running tools, however, this material may be preferable as the cost is small compared to the cost of the tool.
Beryllium-Copper
This material is an alloy of beryllium and copper. Beryllium is chosen for its strength and copper for its thermal properties. It will conduct heat away quickly and much more efficiently than steel.
Beryllium-copper is used when large quantities of heat have to be extracted from cavities or cores. Adequate provision for cooling must be provided to prevent excessive heat build-up.
Walsh's Plastic consulting. 