1、 1 Annals of CIRP Vol.47/2/1998:p651-665 Grinding Process Achievements and their Consequence on Machine Tools Challenges and Opportunities H.K. Toenshoff , B. Karpuschewski Abstract The dynamic states of temperature field and temperature history of points in various model placements are investigated
2、 by simulation. It has been demonstrated that the simulation results are in accordance with measurement results due to the reliable simulation method and the accurate heat model. Therefore the simulation may be studied instead of experiment. Usually, crank have to be grinded using several positionin
3、g and clamping operations because of the differences in axes orientations of the main journal and the connecting rod journal. In the operation, there are many problems such as relatively excessive errors of positioning and clamping, low productivity, large investment of equipment and workshops, long
4、 period in the adjustment of the machine tool and fixtures and poor surface finish of the ground part etc. Keywords Crank Coordinated grinding Grinding temperature Grind-hardening is a new technology which utilizes grinding heat to induce martensitic phase transformation and strengthen workpiece sur
5、face in grinding process by raising surface temperature above Ac3 instantaneously and cooling quickly. The application of this new technology can reduce production cycle, improve working efficiency, and decrease manufacturing cost by integrating the two operations of grinding and surface heat treatm
6、ent into one, which has the great social and economical benefits. Grind-hardening experiments for external grinding mode are carried out. The results indicate that the hardened workpiece surface consists of three parts of hardened layer, transition layer, and body. The metallurgical structures of th
7、e parts are martensite, mixture of martensite and ferrite, and mixture of ferrite and pearlite respectively. Under the experiment condition, the top value of hardness and hardened depth is HV824.1 and 1.1mm respectively, which achieves the effect of high-frequency hardening. The orthogonal experimen
8、ts with different cut depths, workpiece speeds and wheel characteristic are performed, contribution and pattern of the factors influence to hardening effect are analyzed. The results show that hardened layer thickness rises with increasing cut depth, and rises and falls with increasing workpiece spe
9、ed. White alundum wheel increased more hardened layer thickness than pink alundum, while small grain granularity products more hardened layer thickness than big one. The order of factors is cut depth, workpiece speed, and wheel characteristic according to the contribution. The results also indicate
10、that surface hardness 2 is only affected by cut depth, and the hardness value rises with increasing cut depth. Under the present experiment condition, the adoption of 0.4mm cut depth, 0.5m/s workpiece speed and wheel WA46L8V may achieve good comprehensive grind-hardening results of both hardened lay
11、er thickness and surface hardness.40Cr steel and 45 steel are adopted simultaneously in the experiments to research hardening effects with different materials. The results show good hardened effectiveness of both materials as well as the similar pattern of metallurgical structure and hardness distri
12、bution. It has been found that 40Cr steel has more hardened layer thickness while 45 steel has higher surface hardness. The difference derives from the material property. The observation of the metallurgical structure and test of hardness distribution for the overlap hardened zone demonstrate the re
13、hardening is occurred and the metallurgical structure or hardness distribution changes little. Due to the inertance of conductivity, the residual heat in the zone tempered the material at its end part. A little tempered sorbite appears while the hardness value drops accordingly. However, because the
14、 tempered area is small in size (1.0mm) and even the bottom value (HV479.6) can satisfy the hardness requirement, it has little influence to the total hardened effectiveness. Fine grinding stage is taken for the surface roughness and quality after the hardened layer is obtained in the coarse grindin
15、g stage, and the fine grinded sample is analyzed. The result indicates the same metallurgical structures and surface hardness to the sample of coarse stage. Therefore, with rational choiced grinding parameters and condition, requirement of surface hardness and machining precision may be met simultan
16、eously. Grinding force and temperature are measured in the experiments by adopting elastic core clampers and infrared thermometer, which provides data for theory study. Moreover, the variation regularity and influence factors are analyzed. The results indicate that grinding force is proportional to
17、workpiece speed and cut depth in external grind-hardening process, and the ratio of normal force to tangential force is more than that of common grinding. Grinding temperature is influenced by cut depth, wheel characteristics and workpiece speed in the contribution order, and has the same change reg
18、ularity of hardened layer thickness. Calculation equations of grinding force for external grind-hardening are derived through the study of grain cutting mechanism and the utilization of grain energy cost and distribution. Plough stage and large cut depth of grain are considered for accurate results.
19、 It has been shown that the calculation results have consistency with measurement results. Process of material remove is considered to consist of various stages. The compound heat and heat distribution ratio are modeled for the whole process. Moreover, the influence pattern of grinding condition to
20、distribution of heat is evaluated. The results demonstrate that grain granularity and wheel velocity are the major factors. Both increasing grain granularity number and decreasing wheel velocity may reduce the heat conducted into workpiece surface. A computational finite element method software, ANS
21、YS, is introduced to simulate the process of external grind-hardening. The dynamic states of temperature field and temperature history of points in various model placements are investigated by simulation. It has been demonstrated that the simulation results are in accordance with measurement results
22、 due to the reliable simulation method and the accurate heat model. Therefore the simulation may be studied 3 instead of experiment. Usually, crank have to be grinded using several positioning and clamping operations because of the differences in axes orientations of the main journal and the connect
23、ing rod journal. In the operation, there are many problems such as relatively excessive errors of positioning and clamping, low productivity, large investment of equipment and workshops, long period in the adjustment of the machine tool and fixtures and poor surface finish of the ground part etc. Fr
24、om analyzing the mentioned shortcomings, a new grinding principle named coordinated grinding is studied, which allows both connecting rod journal and main journal of the crank to be grinded in only one positioning and clamping operation. Theory of coordinate grinding and some key techniques in the r
25、ealization and application of this new method are focused on in this paper. This article analyzes the motion specialties of crank connecting rod journal coordinated grinding, finds the necessity of variant velocity motion of crank. In order to get high grinding precision and fine surface quality, th
26、e motion model must bases on constant linear velocity for the crank connecting rod journal grinding. The constant linear velocity is used to guarantee the surface quality of crank connecting rod and the constant removal rate guarantees the precision. This paper predigests the motion model of constan
27、t linear velocity crank connecting rod journal grinding and makes the model to be easy to calculate. Then it analyzes the error due to predigested model comparing with original model. Grinding force is the key reason which influences precision about crank grinding. According to specialties of crank
28、coordinated grinding, this article contrasted analyzes two kind of calculate formula； chooses one of them which is more suitable to calculate grinding force of crank coordinated grinding. Then it builds the dynamics model of wheel slide relate to grinding force and calculates the acceleration of whe
29、el slide. This article discusses the main reasons which influence the precision and surface quality of crank connecting rod journal coordinated grinding and the relative solutions to improve the precision and surface quality of crank connecting rod journal coordinated grinding. Then it analyzes the
30、rule of influence about the precision and surface quality of crank connecting rod journal due to main error sources, according to theory of error compensation； it builds the relative error compensation model. According to required capacity of wheel slide motion system, which can satisfy high speed coordinated grinding. This article analyzes two kinds of wheel slide drive mode. Due to specialties of each drive mode and required capacity of wheel slide motion system, it chooses linear motor as the drive mode of wheel slide motion system.
