Machining Parameters and Computer Control

Abstract

The interfacing of a computer to a machine tool gives very few advantages over the conventional Numerically Controlled machines with regard to actual machining time or the type of work that can be undertaken, but if the computer is used for its natural function of organisation then many overall production benefits can be gained by this amalgamation. As a step to the evaluation of computer control in a total Direct Numerically Controlled Manufacturing Cell, a vertical milling machine was connected on line in a behind the tape reader configuration to a mini computer. The research consisted of the design and manufacture of the hardware interface between the computer and the machine tool, and the subsequent development of programmes to establish machining parameters and the viability of the system. The interface was in two sections, the computer interface board, which takes the parallel information from the computer, buffers it and then transmits the data in a serial form, using different line drivers, to the machine interface board. The machine interface board receives the transmitted serial data a synchronously, converts the information into parallel form, and buffers it until required by the machine. The machine interface board also incorporates a code delete generator which outputs a signal on all lines when no data is available, and a voltage level circuit to give compatibility with the machine logic. The software programmes developed were of two basic types, those which generate the part programmes, which were written in Fortran programming language, and control programmes written in Assembler programming language, the latter arranges the previously generated part programmes into the correct format and code to suit the machine control logic requirements. The advantages of converting the machine from a non-contouring to contouring control system was then shown with practical tests and examples. Circular interpolation, "family" components, three dimensional contours and the production of Novikov gears all being examples of the on line control programmes developed. The wide range of facilities now available for manufacture with this on line communication indicates positively that many older Numerically Controlled machine tools can be retrofitted relatively easily into a Direct Numerically Controlled (DNC) system.