发动机缸体曲轴孔精加工专用夹具设计与研究_英文_肖铁忠.pdf

1、Dec 2014 机床与液压 Hydromechatronics Engineering Vol 42No 24 eceived: 2014 07 15 * Project supported by the Government in Chongqing Banan District and Chongqing University of Technology Special Program ( Item Number: 2012Q123) Tie- zhong XIAO，E- mail: 593712861 qq com DOI: 10 3969/j issn 10013881 2014 2

2、4 023 Design and study on special fixture for finishing cylinder crankshaft hole* Tie- zhong XIAO1，Xuan LI2，Juan HUANG1，Jing LUO3，Chun- ying YUAN4 1Sichuan Engineering Technical College，Deyang 618000，China 2Baotou Huihong Technology Engineering Co Ltd， Baotou 014030，China 3Key Laboratory of Manufact

3、ure Techniques for Automobile Parts Ministry of Education， Chongqing University of Technology，Chongqing 400054，China 4Guizhou Jonyang Kinetics Co ，Ltd，Guiyang 550006，China Abstract: Since the precision of finishing operations for crankshaft hole will directly affect the qual- ity and life of the eng

4、ine，an advanced and reasonable fixture system is very important for the machining accuracy According to the precision requirement of cylinder crankshaft hole in the real applications，the process parameters and the positioning reference were determined in this pa- per，and the main structure of fixtur

5、e system was designed and analyzed including the positioning mechanism，cutter relieving mechanism，clamping mechanism and boring mold Finally，the dy- namic characteristics of the boring bar were analyzed，and the effect of bearing stiffness on the dynamic characteristics of the boring bar was studied

6、as well By appropriately increasing the bearing preload，i e ，bearing stiffness，the stiffness of the boring bar system could be effective- ly increased Based on the practical process inspection，the correctness of the design has been tested and verified Key words:Crankshaft hole，Special fixture，Boring

7、 bar，Dynamic characteristics Since the processing requirements of engine are relatively high，while crankshaft hole machining is one of the three key processes for the engine，and its accuracy will directly determine the overall perform- ance of the engine 1 ，an advanced and reasonable fixture system

8、is very important for the machining precision and production efficiency 2- 3 According to the current status of processing engine crankshaft hole，the first approach is that rough，semi- finishing and finishing processes will be separated on a dedica- ted machine，and then three times different positio

9、- ning clamping are required Since the clamping er- rors will inevitably exist，the final positioning accura- cy will be influenced，then the requirements of preci- sion machining can not usually meet;another disad- vantage is that the finishing process is usually com- pleted at the precision machinin

10、g centers，which of- ten has high machining precision and low production efficiencyIn order to solve the above- mentioned problems，this paper will concentrate on the study of crankshaft hole semi- finishing and finishing in a process，i e ，a special fixture will be designed and the semi- finishing and

11、 finishing of crankshaft hole will be completed by a single setup Therefore，it will not only improve the machining accuracy and re- duce labor intensity，but also meet the requirements of mass production efficiency 1 Workpiece accuracy requirements and determined processes 1 1 Workpiece parameters an

12、d accuracy require- ments The main parameters of the workpiece and accu- racy requirements is as follows:Name:Q465 cylin- der;Dimensions:311 298 223;Bore diameter: 5 54 + 0 024 0 ;Workpiece material:HT250 ( crank hole cover) ，aluminum alloy ( crankshaft hole base body) ;Hardness:HB170 241 ( cast iro

13、n) ;work- piece weight: 30 kg As shown in Figure 1，the pro- cessing content and the accuracy requirements are presented Figure 1 Technical drawings 1 2 To determine the process Boring operation is generally used to make the crankshaft hole In this paper， since the rough boring process of workpiece h

14、as been completed，a special fixture is adopted by a single setup to accomplish the semi- fine boring and fine boring process of crankshaft hole 4 Semi- fine boring and fine boring processes use the CBN tools;cutting speed is 120 m/min，and boring spindle speed is 708 r/min;tool feed speed is 0 06 mm/

15、r;semi- fine boring unilateral margin is 0. 5，and fine boring single unilateral margin is 0 1; cycle time is 2 3 min/piece 5 1 3 To determine the Datum Cylinder bore rough boring and fine boring processes，which are ahead of boring crankshaft hole process，use bottom surface and craft pin hole for po-

16、 sitioning Cylinder bore honing process，which is be- hind of boring crankshaft hole process，also use bot- tom surface and craft pin hole for positioning Follow- ing the above- mentioned benchmark principles，this process also uses the same methods to determine the bottom surface and locate the pin ho

17、le Following the datum principles，this boring process also use the bottom surface and craft pin hole for positioning As shown in Figure 2，it presents the process locating datum The bottom surface of the cylinder body is used as the first locating datum;craft pin hole near the rear end of the cylinde

18、r body is used as the sec- ond datum，and locating dowel pin is short cylindri- cal;craft pin hole near the front of the cylinder body is used as a third datum，and locating dowel pin is short argyle 6 7 Figure 2 Locating datum schematic diagram 2 Design of special fixture system Fixture system consis

19、ts of specific folder，boring mold and other components，as shown in Figure 3 1 specific folder; 2， 11 adjustable fine- tune support block; 3， 10 dowel pin; 4 Mechanism elevating cylinder; 5， 8 Clamping cylinder; 6， 9 Clamping block; 7 cylinder body Figure 3 Fixture schematic diagram 2 1 Design of pos

20、itioning mechanism Positioning method:two side pins;positioning principle:six positioning;locating pin programs: fixed the positioning pins The positioning mechanism is shown in Figure 3 Adjustable fine- tune support blocks 2， 11 and dowel pins of 3 and 10 consisted of two side pins positioning mech

21、anism Due to the manufacture accuracy，there is a gap 811Hydromechatronics Engineering between craft hole and dowel pin Therefore，the po- sitioning mechanism has a positioning error， as shown in Figure 4 Figure 4 Positioning error Schematic diagram After positioning，the maximum angle error of workpie

22、ce could be evaluated by Eq ( 1) = arctan 1 + 2 L ( 1) Where，1 is the largest gap between location center of cylindrical pin and location center of craft hole;2 is the largest gap between location center of the argyle pin and location center of craft hole;1 + 2 is the value of displacement error;L i

23、s the dis- tance between cylindrical pin and argyle pin All the values of 1，2 and L could be measured actually 2 2 Clamping mechanism This design used pneumatic clamping After the workpiece is accurately positioned，the appropriate clamping force will be selected to overcome the vibra- tion and overt

24、urn torque generated during cutting The clamping mechanism is shown in Figure 5 Once the workpiece is accurately positioned，the pneumatic cylinder 1， 7 will push the clamping rod 3， 9 and clamping plates 5， 11 to clamp the workpiece driven by guide bar 4， 10 1， 7 pneumatic cylinder; 2， 8 guide sleev

25、e; 3， 9 Clamping rod; 4，10 guide bar;5， 11 clamping plates;6，12 clam- ping soft board Figure 5 Clamping mechanism 2 3 Boring mold As shown in Figure 6，the boring mode structure is presented 1 boring bar; 2， 4， 5， 7 angular contact ball bearings; 3， 6 boring sleeve Figure 6 Boring mode structure Bori

26、ng mode structure is the external roll struc- ture，and there exists an axial relative movement and no relative rotation between the boring bar and boring sleeve Outside the boring sleeve，there equipped with angular contact ball bearings，and the boring sleeve will rotate with the boring bar When the

27、ma- chine is working，work federate of boring bar is low， and there only exist relative movement between the boring sleeve and the boring bar，and then boring bar will not be heated due to the rapid friction，so it will not appear “killed”phenomenon of boring bar sys- tem Angular contact ball bearings

28、are necessarily preloaded，support stiffness throughout the boring bar will be greatly improved There is relative movement between the boring bar and boring sleeve，i e ，a gap exits between them This gap will lead radial movement of boring bar in the boring process，then affect processing roundness and

29、 cylindrical If the gap is too big，pro- cessing precision may fail to meet the requirements; if the gap is too small，there may result in“killed” boring bar due to high- speed rotation boring sleeve in the process Therefore，the gap between the boring bar and boring sleeve needs to be chosen as a reas

30、on- able valueIn fine boring process，the minimum clearance value between the straight boring bar and the boring sleeve is recommended as from 1/5 to 1/6 of the corresponding processing site tolerances The maximum gap should be less than 1/3 of the corre- sponding processing site tolerances 8 3 Borin

31、g bar system analysis 3 1 Boring bar modal analysis The geometrical model and mesh are shown in Figure 7 In order to solve this problem，the model has to be simplified and some assumptions will be made as follow:small structures such as chamfer and helical surfaces will be ignored，and clearance groov

32、e is treated as an entity;single row angular contact ball 911 Tie- zhong XIAO，et al:Design and study on special fixture for finishing cylinder crankshaft hole bearings are set as only bear radial load，and this ball bearings are simplified into springs;the density of boring sleeve and boring bar is s

33、et to be the same， and boring sleeve is treated as additional distribution quality of boring bar;spindle speed is low，the bear- ing stiffness is treated as a constant Boundary conditions are set as follows:zero dis- placement constraints are the only load in modal anal- ysis，and the results are show

34、n in Figure 8 Figure 7 Finite element mesh model of boring bar Figure 8 Modal analysis Former sixth- order natural frequencies and cor- responding mode shapes of boring bar are shown in Table 1，in which it shows that the minimum natural frequency of the boring bar is 370 5 Hz that is much greater th

35、an the excitation frequency 11 8 Hz during spindle operation Therefore，the resonance phenom- enon will not be generated Table 1 Boring bar natural frequencies and mode shapes OrderFrequency/HzMode shapes 1370526 1 translational motion and bending in the YZ plane 2443528 4warping in the YZ plane 3565

36、805 1bending in the XZ plane 4605591 0bending in the YZ plane 5645352 3distortion in the XZ plane ( right) 6668448 1distortion in the XZ plane ( left) 3 2 Calculate bearing stiffness In this paper，the experience of the formula that Lin Song summed up in 1982 is used to calculate the stiffness of ang

37、ular contact ball bearing K0= 0 39F1/3 r d0 463 8( 3) Where，K0is zero clearance angular contact bearing stiffness ( N/m) ;Fris the bearing radial load ( N) ;d is the bearing diameter ( mm) The selected bearing model is 7014AC/P4，d =70 mm;load Fr= 200 N By using Eq ( 3) ，the stiffness of angular cont

38、act ball bearing could be calculated， K0= 16 362 N/m，and for double support structure，the corresponding bearing stiffness is 32 724 N/m which is as much as twice of K0 3 3 Effect of bearing stiffness on the boring bar Bearing stiffness is not a fixed value，and it has a non- linear relationship with

39、suffered load and pre- load The arrangement of angular contact ball bearing is constant，and bearing stiffness values are taken as 0 327 24， 3 272 4， 32 724， 327 24， 3 272 4， 32 724 N/m，respectively The first natural frequency of boring bar variation is shown in Figure 9 Figure 9 Effect of bearing st

40、iffness on the boring bar stiffness As shown in Figure 9，the natural frequency of the boring bar system gets increased with the increase of bearing stiffness When bearing stiffness reaches a certain value，the natural frequency of the boring bar system will approach to a certain value It could be see

41、n that the bearing stiffness has an important influ- ence on the dynamic properties of boring bar system Therefore，it is very important to obtain the right bearing stiffness by adjusting the bearing preload in real applications 4 Conclusion In this paper，a special fixture system is suc- 021Hydromech

42、atronics Engineering cessfully developed，which will effectively improve the machining accuracy and production efficiency Through the actual operation and test，the accuracy of machining tools meets or exceeds the expected re- quirements，and the production efficiency is up to 2 3 min/pc Furthermore，du

43、e to the high automation degree of this fixture system， the labor intensity could be greatly reduced Currently，this technology has been applied in multiple production lines of a number of machinery manufacturing companies in Chongqing， and obtained some good feedbacks eferences 1 Li Wen- di，Wang He-

44、 zeng，Yang Hong- mei Develop- ment of NC Machine for Finish Milling Cylinder Bottom Drilling and eaming Pin Hole J Modular Machine Tool Automatic Manufacturing Technique， 2013( 6) : 124- 129 2 Wu Min，Zhuang Dong- hai Technical Processing Analy- sis and Special Fixture Design Based on Panel Parts J M

45、ACHINE TOOL HYDAULICS， 2013( 8) : 43- 46 3Liu Xu， Zhu Xue- chao，Li Hong- wei Machining Tech- niques ules and Drilling Fixture Design on Typical Shell Parts J Coal Mine Machinery， 2012( 8) : 125- 126 4 Luo Jing; Xiao Tiezhong; Gong Wenjun; Yuan Chunying Special boring machine design for processing of the crankshaf