Plastic Injection Mould Making
Injection moulding is a high production moulding procedure where a liquid thermoplastic or thermoset material is injected under high pressure into a mould for solidification. The moulds can be extremely complicated and expensive.
A substantial part of the total tooling cost is connected to the manufacturing of the mould. It is therefore of great importance that the mould making process should be as straight-forward as possible.
An experienced mouldmaker places high demands on the steel supplier when it comes to steel quality and properties as well as availability. The mould maker is looking for a mould steel free from defects, easy to machine and polish, stable in heat treatment and suitable in many cases for EDM and/or photo-etching.
All material supplied by voestalpine has been subjected to various external and internal inspection procedures, including ultrasonic testing. This en sures that high and even quality standards are met.
Steel Grade Selection
The steel types most commonly used are pre-hardened mould steel, through-hardened mould steel and thermoset plastics. The requirements of the mould material
depends on factors such as the number of shots, plastic material used, size of the mould and desired surface finish. Following basic mould material properties must be considered. strength and hardness, toughness, wear resistance, cleanliness, corrosion resistance, thermal conductivity
| Injection Moulding Process / Type of Steel | Steel Grades | Hardness HRC (HB) |
| Thermoplastics | ||
| Pre-hardened mould steel | Alumec 89* | (~160) |
| Impax Supreme | 33 (~310) | |
| Ramax HH | 37 (~340) | |
| Mirrax 40 | 40 (~380) | |
| Nimax ESR | 40 (~380) | |
| Nimax | 40 (~380) | |
| Through-hardened mould steel | Corrax | 36–50 |
| Mirrax ESR | 45–50 | |
| Orvar Supreme | 45–52 | |
| Stavax ESR | 45–52 | |
| Polmax | 45–52 | |
| Vidar 1 ESR | 45–52 | |
| Unimax | 50–58 | |
| Tyrax ESR | 55–58 | |
| Elmax | 56–60 | |
| Vanadis 4 Extra | 58–64 | |
| Thermoset plastics | ||
| Unimax | 52–58 | |
| Tyrax ESR | 55–58 | |
| Elmax | 56–60 | |
| Vanadis 4 Extra | 58–64 |
| Type of Steel | BÖHLER grade | |
| Corrosion Resistant Steels | BÖHLER M303 ISOPLAST | |
| BÖHLER M310 ISOPLAST | ||
| BÖHLER M314 | ||
| BÖHLER M315 | ||
| BÖHLER M333 ISOPLAST | ||
| BÖHLER M340 ISOPLAST | ||
| BÖHLER M380 ISOPLAST | ||
| Powder Metallurgical Steel | BÖHLER M368 MICROCLEAN | |
| BÖHLER M390 MICROCLEAN | ||
| BÖHLER M398 MICROCLEAN | ||
| Pre-hardened and Precipitation Hardened Steel | ||
| BÖHLER M238 | ||
| BÖHLER M238 HIGHHARD | ||
The mould maker is primarily interested in the machinability of the steel, its polishability, heat treatment and surface treatment properties
HOW IMPORTANT IS GOOD POLISHING?
Polishing sometimes accounts for up to 30% of the total mould cost. This is no suprise, since it is a very time consuming and expensive process.
The result obtained depends to a large extent on the polishing techniques and a few other factors, such as the cleanliness of the steel, i.e. the type, distribution, quantity and size of non-metallic inclusions, the homogeneity of the steel, the hardness of the steel and, for hardened steel, how the heat treatment has
been carried out.
Non-metallic inclusions are reduced to a minimum if the steel is vacuum-degassed and Electro Slag Remelted (ESR process) during production. The ESR treatment results in improved homogeneity and mini-mal amount of inclusions compared to conventional steel production processes.
WHY HEAT TREATMENT ?
The purpose of heat treatment of a finished tool is to obtain suitable mechanical properties such as hardness, toughness and strength. However, there are some problems associated with heat treatment. Problems like distortion and dimensional changes has to be solved
WHY TEXTURING/PHOTO ETCHING?
Plastic mouldings with a textured surface have become increasingly popular. Texturing by photo etching is frequently used as a finish on moulding tools instead of polishing.
The photo-etching process gives the product
an attractive, easily held surface, relatively
insensitive to minor scratches and damage