The purpose of a relap is to enable the tool to be used as new again, by creating a new sharp cutting edge. Other definitions found for the term relapping are such as re-sharpen, re-grind, repair, re-polish, re-cut...
While a tool is used the cutting edge will wear due to several dynamics. At a certain point, the cutting edge is becoming too blunt or worn out for doing its cutting job. This is when you decide to take out the diamond and sent it for relap.
Example of a relap
Shown is a synthetic radius diamond, used on a 2-axis cutting lathe. It has cut approx. 16,000 RGP lenses. Visible is a severe cutting edge and form wear nicely spread over the entire radius, which is mostly typical 2-axis use.
a radius tool before relap (at 75x nomarski)
By grinding off diamond material from the table side, the wear will be disappeared on both table and clearance once enough is taken off. This means that a clean table and clearance shape have become the cutting edge. The wear-gallery is giving examples of wear on the clearance.
the same radius tool after relap (at 75x nomarski)
As a new cutting edge is formed, some tool parameters might have changed. For those applications where the exact properties need to be known, the radius size and the waviness will be measured. This new data, including the amount of diamond taken off and the wear detected, will be noted on the Tool Record. Also, just like with new tools, a current Measurement Certificate can be made of the relapped tool, displaying the waviness characteristics more in detail.
When the tool is properly used, a relap can be done several times using the same tool. The amount of relaps per tool depends however on the application, the machine used, the material cut, the cutting strategy, the environmental conditions, the geometry of the tool, and even sometimes the operator involved.
On average, a tool used for roughing purposes can be relapped 20-50 times. A tool used for finishing purposes can be relapped 30-80 times. In combination with our Tool Management system, the usage can be extended up to over 100 times.