Automatic generation of NC-code for hole cutting with in-process metrology

A novel method for milling flat-bottomed circular holes with more accurate diameters has been added to the data preparation software for the vertical workstation of an automated manufacturing research facility. Additional design functions, a new process planning function, and a new numerical control (NC) code-generating function have been added to the software to implement the method. The cutting algorithm uses a touch probe to measure the diameter of the semifinished hole during the cutting process. The radius used to finish cut the hole is then changed from its nominal value by an amount equal to the difference between the nominal and measured values of the radius of the semifinished hole. The new hole milling process corrects errors caused either by tool deflection or by using a tool whose actual radius differs from its nominal radius. With this process, errors in the diameter of a hole cut with an end mill have been reduced from roughly five mils (plus tool diameter error) to about one mil (regardless of tool diameter error), as compared with a process that does not measure during cutting.<
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