In an age that demands high productivity in manufacturing, there is no substitute for high quality molds in your injection molding process. Given the wide variety of mold steels available today, proper selection must take into account not only price and traditional practice but why they are used. In order to make the proper selection, one must understand the multiple demands that are placed upon mold steels, depending on the specific application. There are two major categories of demands which, together, highlight 12 desirable qualities.
- Wear Resistance - Important to consider for cavity components if the plastic material is abrasive, filled with glass or minerals.
- Toughness (Impact Strength) - Can be an important factor in repair or component replacement cost.
- Compressive Strength - Needed to withstand mold clamping forces to minimize damage to shut off areas.
- Heat Treated - Needed when molds operate at high temperatures.
- Corrosion Resistance - Very important in two major aspects - first when corrosive plastics or additives are used; and second, when molds operate in high-humidity areas or regions where the water is particularly corrosive.
- Thermal Conductivity - Can have an impact on the cycle time of high-production molds and although it's not often a major factor in selecting mold steels, it is a reason for choosing beryllium copper instead of steel in some cases.
Mold Makers Demands
- Hobbability - Permits production of numbers of intricate mold cavities. With the use of EDM (Electrostatic Discharge Machine), hobbability is becoming less important.
- Machinability - Of great economic importance for the mold maker.
- Polishability - Cavities that require a mirror-like finish must be made of special mold steels.
- Heat -Treating Dimensional Stability - A steel with good dimensional stability must be selected.
- Weldability - A mold steel should be considered because of part design and engineering changes or repair because of tool damage.
- Nitriding Ability - Nitriding gives a very hard surface layer to the steel and very good resistance to abrasion or corrosion. However, the nitriding layer (2 to 10 mils thick) is very brittle and easily cracks if subjected to impact blows, rapid temperature changes or uneven pressures.