Hard metal

Hard metal tools are cleaned and coated. Residual magnetism plays a decisive role in both applications. One the one hand, the smallest particles adhere if there is increased magnetism and are coated along with the part inadvertently.

On the other hand, residual magnetism affects the PVD coating process on the components’ surfaces, in the form of coating thickness fluctuations or similar.

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To demagnetise hard metal completely, which normally consists of tungsten carbide with cobalt as a binding agent, very high field strengths of often more than 200 kA/m (250 mT / 2500 Gauss) are required. However, a reduction in residual magnetism is also possible with lower field strengths.
Demagnetising hard metal is a well-mapped process for us. The shape, size and alignment in the magnetic field are virtually immaterial due to the low material permeability. Special attention must be paid to ferromagnetic workpiece carriers that are equipped with hard metal tips, due to the high magnetic forces during the demagnetisation process and the high permeability of the shaft material.

Residual magnetism on hard metal cutting tools is undesirable for the end customer. Adhering particles or chips that can occur when milling, drilling, countersinking, shaping and forming affect the production process negatively.

Powder presses that process ferromagnetic powder into sintered parts for gear boxes, pumps, valves, seals, rings, housings, gear wheels, etc. are strongly affected by magnetism. Residual magnetism on the stamps and dies that are predominantly hard metal-tipped hardens the powder that is to be processed and therefore does not enable the dies to be filled as required.
Furthermore, the machine itself can transfer magnetism to the tools. This is discussed in the “Machine tools” section.

Hard metal parts can magnetise both in production and in operation, which reduces the tools’ service life due to chips adhering to the tools. The following application report discusses demagnetising hard metal.
On powder presses, increased wear of up to 20 % can be observed on magnetised tools, especially with particularly abrasive powder such as powder containing diamond.