The economics of the use of numerically controlled machine tools and program development

Abstract

Brief History The introduction of numerically controlled machine tools into the manufacturing industries and design considerations for their technological progress. Classification Considered from three aspects: type of control, the machine tools with which they are combined and the procedure involved in machining. Programming The preparatory work which must be carried out before components can be machined in an N.C. machine tool. This includes planning and encoding the information into the input medium, using manual or computer assisted methods. N.C. Economics The number and type of N.C, machines in use in the U.K. are shown, plus an indication of their cost. This emphasises the fact that justification must be on economic grounds. Cost Analysis Comparison of N.C. and conventional methods. Examination of justification calculations shows the danger of using short cut methods. The method of discounting estimated future returns is used to show that accurate forecasting and alternative methods of investment must be considered before a decision can be made. Consideration of Batch Size A rational method of assessing batch size and component complexity is shown. Graphical results of several methods of manufacture are used to indicate the economic advantages and disadvantages of each process. Economic Considerations of Programming 'Analysed under two headings: planning and programming, the latter being considered under the headings of manual and computer assisted. The cost of preparing a control tape ready for prove out is examined and an analysis of special and general purpose systems has been carried out. Comparison of Methods The relative merits of in-house or computer bureau service have been analysed and a decision process outlined to assist in the correct system selection. Program Development Cost and levels of tape verification are considered, plus the essential facts of producing an accurate control tape. Methods of eliminating setting errors are considered. Program format is illustrated and an error checking program developed, using Fortran. Appendix A Fortran program description (T.E.S.P.) B Module table calibration chart. C Graph plotter output.