【導(dǎo)讀】這些高性能的材料都比較難以加工，也。難以保證高的尺寸和形狀精度。磨削是應(yīng)用于精加工的最普遍和常見的方法之一，和其他機(jī)械加工方法如。車削、銑削相比，磨削時(shí)產(chǎn)生的熱量是非常高的。在散熱條件不佳的情況下，磨削產(chǎn)生的熱量會(huì)使工件溫。度迅速上升，這可能會(huì)導(dǎo)致工件被燒傷。由磨削過程產(chǎn)生的燒傷以被很好的證明而且可以按顏色對其進(jìn)行。分類，這些損傷在周期性載荷的作用下會(huì)降低產(chǎn)品壽命，甚至可能會(huì)導(dǎo)致災(zāi)難性的問題發(fā)生。用磨削產(chǎn)生的熱量來改進(jìn)表面強(qiáng)度和表面金相組織，并且要防止工件破壞。為此進(jìn)行了一個(gè)用氧化鋁砂輪。加工AISI6150和AISI5200的實(shí)驗(yàn)，并且結(jié)論被進(jìn)行了探討。如果工件表層溫度超過910℃，表面晶相將發(fā)生變化。Shaw和Vyas已經(jīng)對磨削產(chǎn)生的表面破壞進(jìn)行了深刻的理論闡述。零件表面損傷，不能達(dá)到質(zhì)量要求將給制造商帶來嚴(yán)重的浪費(fèi)。

　　

【正文】 at a large wheel depth of cut. However, heating and cooling of the surface would occur rapidly, and this may have the influence of producing phase changes in the surface. The theoretical model developed in this present work also gives the same temperature that developed at the contact area. The following graphs (shown in Figs. 3 4) show the coarse hardness of the ground material at various depths beneath the surface. 23 Figure 3. Hardening results depending on number of passes (AISI 6150). Figure 4. Hardening results depending on number of passes (AISI 52100). The higher hardness obtained during this grind hardening effect when paring ground specimen with turned specimen is shown in Figs. 5 6 (number of passes 10 in Fig. 3 and number of passes 14 in Fig. 4 ). The experiments were carried out with the application of a coolant, however the coolant does not have much impact in the grindhardening effect. Figure 5. Comparison of hardness of turned and ground specimen (AISI 6150). Figure 6. Comparison of hardness of turned and ground specimen (AISI 52100). With the higher depth of cut and increased number of passes (shown in Figs. 7 8), the area and the time for heat transfer is increased due to the increase (to certain depth of cut only) in traveling energy. A further increase in the total depth of the cut (increase in number of passes) decreases the hardness. This is because 24 the increase in the total depth of the cut after a certain period decreases the specific cutting energy. The grindhardened ponents were also inspected using an electromagic crack detector, and no flaws were found. Figure 7. Influence of number of passes (AISI 6150). Figure 8. Influence of number of passes (AISI 52100). 10 Control Of Surface Texture Surface texture is defined as the inherent or enhanced condition of a surface produced in a machining or other surfacegenerating operations. The nature of the surface layer may have a strong influence on the mechanical properties of the material. This association is more pronounced in some materials and under certain machining operations. Nam et al., (12) have stated that the surface finish is a major concern in manufacturing. Yet very little attention has been given to elucidate the relationship between the characteristics and the functional requirements of surfaces. A recurring problem in the specification of surface characteristics, and the design and manufacture of tribological surfaces has been the lack of a clear understanding of the friction and wear phenomena. Consequently, despite the engineering importance of lowfriction and lowwear surfaces and the resulting economic benefits, so far it has been impossible to design and manufacture sliding surfaces optimally. On structural applications, the nature of declivity troughs of the surface is the most important, while on bearing applications, the nature and number of crests on the surface is more significant. Therefore, the surface roughness of the ground specimen was also measured and the results were plotted (Figs. 9 10). 25 Figure 9. Surface roughness values of a ground specimen (AISI 6150). Figure 10. Surface roughness values of a ground specimen (AISI 52100). The results are at acceptable levels according to Japanese International Standard. (The acceptable range of finish Ra in grinding is to m). 11 Conclusion Experimental investigations have shown that the generated heat in cylindrical grinding could be effectively utilized as a new heat treatment process. With the existing knowledge in grind hardening and based on the test results, the following findings are presented: ? The grind hardened parts are characterized by fine grained martensitic layers, which were obtained by shorttime austenisation of surface layers with selfquenching. ? The application of coolant may avoid thermal damage and improve surface finish, but it has a negligible effect in quenching. ? Surface cracks are not found in the grind hardened ponent. It was also checked by using an electromagic crack detector. Machine parts that are used under normal loading conditions can be easily grind hardened. ? Possible industrial applications for surface hardening by the grinding lie in the production of running faces for rotary shaft seals, camshaft, lateral faces of the bearings, guide ways, and many other functional surfaces that are frequently ground (Fig. 11 ). ? It is also inferred that there is a considerable increase in hardness up to 10 passes (total depth of cut mm), and a depth of hardness peration is 1 mm for AISI 6150 (Figs. 3 7). The depth of hardness peration is mm for AISI 52100 (Figs. 4 8) at 14 passes (total depth of cut mm), after that the hardness decreases. This may be attributed to the increase in the carbon percentage and the number of passes in AISI 52100 than in AISI 6150. ? The theoretical temperature model is developed by using a grain contact model to find out the temperature at the interface between the cutting grain and the workpiece, which gives the best 26 agreement with the suggestions given by Doyle and Dean. (5) Actually, the temperature developed at the contact area is the main source for the phase transformation, ., austenite to fine martensite. It is promising to note that the adoption of this new surfacestrengthening method may have a great economical benefit due to its increased integration level, and it is also a technological alternative to the other surface hardening processes. This leads to shorter production sequences and reduced throughout time, as well as decreased cost. Figure 11. Industrial parts for grind hardening. reference 1 Des Ruisseaux ., Zerkle ., Thermal analysis of the grinding process, Trans. ASME J. Eng. Ind., 92 (1970) 428–432. 2 Shaw ., Vyas A., Heat affected zones in grinding of steels, Ann. CIRP, 4