| As a special measuring tool, non API or special thread gauge is used to integrateinspecting the machining quality of special thread joint in oil well pipe. The structure designof special thread gauge is complexity and it also has intricate machining processes, at he sametime, it has high requirement for superior abrasion-resistance, good dimension stability andhigh machining precision. But for a long period the forming grinding technology of specialthread gauge had been monopolized by foreign companies, they had much patent protection inthis area. Because lack of advanced manufacturing techniques, these products which made bydomestic organizations have become synonymous with short service life and poorperformance. Domestic products only have tiny market share, let alone compete with foreignlike products. According to this situation, optimizations of special thread gauge materialdesign and grinding processes which were studied in this dissertation had been driven by therequirement of good service performance. The superabrasive grinding wheel had highgrinding ability and efficiency in special thread gauge machining, all of the grinding defectshad been solved. The major researches works in this dissertation included:（1）Starting with the heat treatment of workpiece material9Mn2V, the relationshipbetween heat treatment processes and grinding performance had been built. Serious meshysegregation of carbide, excessive amounts of retained austenite, coarse and inhomogeneousdistribution of material structure were significant causes of grinding burn and grinding crack.In order to improve the abrasion-resistance and mechanical properties of workpiece material,cryogenic and tempering treatment were added, they were of great help. Disappear of meshy segregation of carbide, network carbide was within second grade, retained austenite contentwas within4%, martensite became much more fine and homogeneous, all of these advantagescould be obtained by adopting cryogenic and tempering treatment in twice. And then,workpiece material9Mn2V provided superior grinding performance.（2）Based on the distribution mode of surface grinding temperature, a new method fortemperature theoretical calculation of forming grinding was set up. The junction of two planesin forming grinding is the place where grinding burn was most likely to happen. The flangehad much less material to conduct heat, this was the first reason. Next, the heat intensity at thejunction was amount of heat intensity of two adjacent planes, this made the junction had thehighest temperature. Ratio of heat that conducted into workpiece during forming grinding wasinvestigated. A new method which used for measuring temperature distribution in forminggrinding was developed, theoretical calculation model had been verified by the experiment.（3）Under different grinding wheel speeds and grinding depths in single grit grinding,strain rate hardening and thermal softening of workpiece material exert an influence on eachother, but the thermal softening induced by high grinding temperature played a leading role.The critical grinding depth of No.100size grain is0.007mm according to morphology changeof grinding chips. Above this depth, the grinding stage changed from plowing to cutting. Theresult of numerical simulation provided strong guidance for selection of abrasive andoptimization of grinding parameters. A detailed design of grinding wheel matrix structure andcontour had been completed, a brief description of the manufacturing process of grindingwheel hub and electroplating process had also been introduced. Test results indicated thesingle layer electroplated CBN grinding wheel had favorable ability for holding chips.（4）Grinding and dressing parameters were significant causes of grinding defects. Inorder to avoid grinding burn, larger worktable feed rate and cooling in both directions shouldbe used in rough and finish grinding of special thread gauge. In rough grinding, it should givepriority to sharpening of grinding wheel in dressing. But in finish grinding, it should give the first place to reshaping of grinding wheel. For the problem of uneven abrasive wear, it couldbe solved by modifying the dressing parameters of roller. There were many reasons forunilateral and large area of wear happened on superabrasive grinding wheel, it includednon-uniform deformation of workpiece blank and large radial run-out in high speed becauseof assembly clearance. Good quality was obtained by using conventional abrasive grindingwheel and improved superabrasive grinding, along with optimized grinding processes.Grinding defects had been conquered in the end.On the basis of fundamental theory, experiment and application research, the fulltechnique of processing quality control in forming grinding of special thread gauge used in oilwell pipe had been developed. The technique had been applied in the production linesuccessfully, the manufacturing technology had also been nationalized. The application ofsuperabrasive grinding wheel and optimized grinding parameters, the time required to processa piece decreased from18hours to9hours, machining efficiency had risen by50%.Performance of the special thread gauge products had been improved significantly, service liferose to16000～17000number of times. The replacement of foreign products had beenrealized. |
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