Tham khảo tài liệu 'threading technologies part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Threading Technologies 201 removal rate may increase by up to 300 at each successive infeed. Therefore in order to minimise these induced stresses on the cutting edge and keep them as uniform as possible the DOC must be reduced with each pass along the workpiece. Thread Finishing and Close Tolerancing In order to obtain a good surface finish texture or a close tolerance on the finished thread flanks the CNC machine tool can be programmed to make either one or two additional finishing passes. These additional passes are termed spring-cuts 18 and improve both accuracy and precision in the final thread form. Spring-cuts cannot be utilised on workpiece materials that have a tendency to work-harden for example when thread turning stainless steels and so on as they cause high tool wear. With work-hardening materials cuts of mm should be avoided as these materials elastically-deform instead of being cut. The severity of the problem of work-hardening is even greater when thread turning austenitic steels and their equivalents and here it is recommended that an infeed pass should always be mm. These comments are confined to steels and their alloys and even here an appropriate number of infeeds by trial-and-error may be necessary. When a threading insert breaks it is normally the result of induced high stresses so the remedy is usually to increase the number of infeed threading passes. This solution is also true for machining threads in most cast iron grades the exception here being for austempered ductile irons ADF . It seems somewhat obvious that the greater the number of passes the threading operation is divided into the smaller the DOC and the stresses on the threading insert s tip. Moreover if this philosophy is pursued too far and very many infeed passes are programmed the tool will simply not be able to cut at all - owing to insufficient DOC and this in turn will result in simply elastic deformation of the workpiece material. Such a timid approach to thread .
