The promise of wiper inserts developed for turning is this: By smoothing out the scallops that are generated when a part is turned, a wiper insert can improve surface finish. Compared to turning with a standard insert, turning with a wiper insert can either improve the finish by a factor of two, or else it can hold the finish constant while cutting at approximately twice the feed rate. In short, either quality or productivity can increase.
But the problem with wiper inserts developed for turning is this: The insert's profile is both unusual and complex. Instead of following a single radius, the profile blends multiple radii. As a result, NC offsets that assume a conventional geometry are likely to generate an inaccurate tool path.
Sandvik Coromant and Pathtrace have been working to solve this problem. Sandvik Coromant is the Fair Lawn, New Jersey, supplier of various wiper inserts for turning. Pathtrace, of Southfield, Michigan, is the CAD/CAM developer responsible for EdgeCAM. Thanks to the collaboration between the companies, the latest version of the Pathtrace software has Sandvik wiper geometries built in. The user can select a wiper insert catalog number, and the software will generate tool paths that automatically take account of that insert's particular geometric profile.
The effect of a wiper insert's unusual geometry is essentially to give the insert a flatter nose. With the flatter shape, the insert removes more material with the back of the profile. It "wipes" the material. The scallops between turns are smaller because of this effect, and the surface finish is improved.
Compensating for this insert geometry during a straight pass along one is easy. The difficulty lies in an interpolated pass that generates a curved or angular feature. To ensure that the tool edge meets the part at precisely the right location along this interpolated path, the software calculates custom offsets that are derived from the wiper insert's form.
Another consideration is to maintain a smooth finish during the interpolated cutting. The "wiping" effect only works along the straight, single-axis path, because the back of the insert doesn't have the same effect when the insert cuts in a different direction. The software has to keep this limitation of the insert from affecting the part. Therefore, to keep the part's surface finish constant, the software automatically slows the wiper insert's feed rate as multi-axis interpolation begins.