New Milling Method Of Spiral Bevel Gear Based On Generating Principle Of Tooth Surface With Spherical Involute

Spiral bevel gears have advantages of large coincidence degree, steady transmission andhigh strength. And they are widely used in fields of aerospace, ships, national defenseequipment and kinds of machines, such as machine tools, automotive vehicle, engineeringmachine and mining machine. And the tooth profile of spherical involute is ideal profile ofspiral bevel gear. However, the surface of spiral bevel gear with spherical involute is spatialspiral surface, and it’s mathematical model is relatively complicated, thus making theprocessing technology of spiral bevel gear more complicated, and the cost of machine tooland cutting tool more expensive. In the cutting process of spiral bevel gear, the machiningmethod is the method of engineering approximation, and the tooth profile of bevel gear isapproximated by the profile of equivalent cylindrical gear which is unwrapped on the backcone. In order to pursue that the cutting tool can be designed and manufactured more simply,the machined surface of cutting edge is designed as conical helicoid which is formed by thestraight line. And it is used to cut the surface of spiral bevel gear by the method of envelopeexpansion. Strictly speaking, the tooth profile generated by this method is not the sphericalinvolute. And many excellent properties are lost, such as interchangeability, constanttransmission ratio. Many disadvantages appear, such as large transmission noise, adversecontact area, strength reduction and so on. In order to gain better performance of toothcontact, parameters of machine tool and cutting tool must be adjusted iteratively. These makethat we must cost much time to adjust the tooth contact. In addition, the key cuttingtechnology of spiral bevel gears has been blocked by the foreign countries. Thus thetechnology progress of spiral bevel gears in my country has been restricted seriously.Base on the generating principle of tooth surface with spherical involute, two new millingmethods of spiral bevel gears are proposed in the paper which breaks through the existingcutting system of Gleason. The first method is that the surface generating line is used ascutting edge, and the tooth surface can be machined out through three axes linkage. Theother is that based on the research of first method, the arc generating-line is approximated bysome dispersed points, and the tooth surface can be machined through two axes linkage. Themain research contents of this paper are as follows:1. The generating principle of tooth surface was analyzed. The tooth surface of spiralbevel gear with spherical involute is formed by the arc generating-line’s pure rolling on thebase cone. The concave tooth surface is generated by generating line from the big end to theother end. And the generation of convex surface is opposite exactly. The relationshipbetween the movements in the cutting process was calculated and analyzed by usingknowledge of three-dimensional modeling and analytic geometry.2. Based on the the generating principle of tooth surface with spherical involute, a newcutting method was proposed. The generating line of tooth surface is used as cutting edge,and the cutting movement is the inverse movement of surface generation. The tooth surfacecan be machined out through three axes linkage by using this method. The cutting motions ofsurfaces with different revolving direction were calculated and analyzed by using knowledge of space geometry. And the motion model of surface cutting was built.3. The new cutting tool was designed according to the requirements of tool based on thenew method in this paper. When the tool rotates at high speed in the cutting process, it willform a half-spherical cutting edge. The intersection of this half-spherical cutting edge and (Q)face is the generating line of tooth surface. The geometric shape and key parameters weredesigned and caculated by using knowledge of structure design and space geometry. And thethree dimensional models of tools were built up by using CATIA software.4. The three axes linkage mechanism was designed, and the cutting simulation was carriedout by using VERICUT software. According to the analysis of cutting motion, three linkagemotions in the cutting process are as follow: spin motion of gear blank (ω1), rotary motionthat gear blank rotates around the endpoint of cutting edge (ω2), linear movement that gearblank moves along the boundary line between cutting zone and adjustment region (V). Themechanisms for above motions were designed. And the three dimensional models of thesemechanisms and their assembly product were built up by using CATIA software. In order toverify the feasibility of the three axes linkage mechanism and new cutting method, models ofmachine tool, gear blank and cutting tool were built by using VERICUT software. And NCprogram was compiled by using software of MATLAB and EXCEL. At last, the cuttingsimulation of spiral bevel gear was carried out.5. Based on the research of the three axes linkage method, a more simple cutting methodwas proposed, by which spiral bevel gear can be machined with two axes linkage. The arcgenerating-line of tooth surface is approximated by some dispersed points, and tooth surfacewas machined with the mode of envelope expansion. Firstly, two linkage motions in thecutting process were calculated and analyzed. Then mechanisms of machine tool and cuttingtool were designed. At last, the three-dimensional model of cutting tool was built up by usingCATIA software. And how the designed mechanism completes motions in the cuttingprocess was analyzed.6. In order to verify the feasibility of the two axes linkage mechanism and the cuttingmethod, cutting simulation analysis of two axes linkage method was carried out by usingVERICUT software. Firstly, models of machine tool, cutting tool and gear blank were builtby using VERICUT software. And then, NC program was compiled by using software ofMATLAB and EXCEL. At last, in the simulation environment of VERICUT, sin840d controlsystem was called, the compiled NC program was added, and the two axes linkage cuttingsimulation of spiral bevel gear was carried out.7. The principle prototype of two axes linkage NC cutting machine was successfullydeveloped, and the cutting experiment and the measurement of profile deviation were carriedout. According to the analysis of cutting motions and the designed machine structure, aprinciple prototype of cutting machine was developed by refitting and adding key functionelements on the XK716NC milling machine. Taking a concrete spiral bevel gear forexample, the gear blank was designed, and the cutting tool was purchased. Then the cuttingexperiment was carried out by using the designed machine tool. At last, the measurement ofprofile deviation was carried out by using3906T gear measuring center. The measurementresults show that the surface normal deviation is between-0.0227mm and0.0097mm. These verify the feasibility of two axes linkage milling method which is proposed in this paper.