Closed door machining error compensation of complex surfaces using the cutting compliance coefficient and on-machine measurement for a milling process

Abstract

Closed door machining is a strategy for producing a part within tolerance using on-machine measurement and automatic process adjustment as opposed to manual gauging interventions. This paper presents an integrated methodology for compensating errors detected using on-machine probing. In a multi-cut process, intermittent probing which is achieved through replacing the cutting tool with a touch probe, after each cut, can detect machining errors caused by deflection and the tool offset error. A cutting compliance coefficient model is used to estimate corrections to the tool path at the finishing cut based on a finite number of measured errors at discrete locations for previous cuts. The model also anticipates compliance changes and the effect of the compensated depth of cut. The complex surface to be machined is represented by a B-spline model. The compensated tool path is obtained from B-spline deformation techniques applied to the initial tool path according to the discrete corrections. Milling tests are carried out with and without compensation demonstrating a reduction of machining error from +140 to ±20 µm.

Keywords:

• milling
• accuracy
• on-machine measurement
• error
• compensation
• B-spline deformation