Macro Defects in Steel - Polishing Defects

Polishing Defects

According to DIN 8589, polishing is not a manufacturing technique in its own right and is only used in combination with other manufacturing processes such as polish grinding, honing and lapping.
In the tool and mold making industry, the different ”polishing levels“ such as brush fi nish, gloss or high-gloss are considered the subjective opinion of the polisher. The divergence in quality standards often leads to disputes or even legal proceedings between steel manufacturers, polishing specialists and the plastics processing companies.

Cracks
Very deep scratches, sharp edges, generally due to strong loads on the material.
Tip: Can not be avoided during the polishing process as it is more a problem of the material itself. The workpiece should therefore be checked for hidden cracks/material defects beforehand.

Peak
Uneven elevations. This is due to either the workpiece material being removed unevenly during the polishing process or to polishing particles being forced into the workpiece surface during the polishing process.
Tip: Homogeneous pressure distribution. Use an abrasive with a higher viscosity.

Comet tails
Inclusions that leave a trail behind them and giving the impression of a comet.
Tip: During metallographic sample preparation, avoid polishing with parallel feed if comets appear. During manual polishing, use higher rotational speed to prevent comet tails from emerging.

Corrosion
Reaction of the workpiece to materials in the environment. Corrosion is often the result of insuffi cient drying after the cleaning process.
Tip: Thoroughly clean and dry samples immediately after machining. Store samples in dry conditions.

Burn marks
Branding on the workpiece surface. If too much heat builds up during the polishing process, this will often damage the surface structure (micro-cracks).
Tip: Use sufficient coolant/lubricant during the process.

Discoloration
Areas that look different to the rest of the surface (generally matt). There is usually no topographical difference.
Tip: Use a neutral abrasive to avoid damage to the surface. Work at low pressures when polishing soft materials in order to prevent polishing grains accumulating in the workpiece surface.