PVD quality considerations
◆ Cutting
tools and molds should avoid burnout and burrs during grinding.
◆ The
key surface of the workpiece cannot be treated with phosphoric acid film and
galvanizing, and the surface should avoid adhesion such as residual glue, wax,
PVC, etc. If the workpiece must be coated with anti-rust oil, non-silicon-based
oil should be selected.
◆ The
temperature of the PVD process, generally about 400 to 500 °C, affects the
adhesion between the coating and the substrate. In order to avoid the decrease
in the hardness of the substrate, dimensional changes or heating deformation
after PVD, materials with heat resistance above 500 °C must be selected, such
as high speed steel, hot-work die steel.
◆ Heat
treatment should avoid the salt bath method as possible, and attention must be
paid to whether there are residues on the surface of the workpiece or in the
gap, which will cause poor adhesion of the coating.
◆ After
electrical discharge machining, a white layer and a heat-affected deterioration
layer are easy to form on the surface. This layer is in a brittle state and has
poor adhesion to the substrate. If PVD sputtering is carried out, cracks are
more likely to occur on the hard coating, which must be treated by grinding and
polishing until the white layer is completely removed.
◆ If there are rust spots and black skin on the surface of the workpiece,
impurities will be precipitated during the coating process and the coating will
be poorly adhered. If the workpiece is welded or repaired, it must not contain
impurities such as flux and must be able to withstand vacuum and high
temperature(600°C).
◆ For
complex-shaped molds such as deep-hole slits, the substance to be deposited is
not easy to enter during PVD processing. The
effective depth of the hole treatment is equivalent to the hole diameter;
beyond this range, the thickness, adhesion, and crystal structure of the
coating will drop sharply and deteriorate.
◆ The
surface roughness of the mold processed by PVD will have a certain degree of
influence. Generally speaking, the smaller the substrate roughness, the lower
the friction coefficient, the better the adhesion of the coating, and the
smaller the pressure on the surface. As the load of working conditions
increases, the roughness requirements become stricter. Therefore, such molds
should be properly polished.