1 Introduction In the hobbing process, increasing the number of hobs can double the speed of the table, greatly improving the processing efficiency, so the multi-head hob as a highly efficient tool has been widely used in the processing of medium and small module gears. However, when machining a large module gear with a multi-head hob, as the number of hobs increases, the number of teeth per tooth surface of the enveloping workpiece decreases proportionally, and the cutting load of each tooth of the hob increases. In order to improve the rigidity of the hob and reduce the flank of the cut tooth surface, the outer diameter and the hole diameter of the hob must be increased accordingly, and the number of teeth of the hob (the number of chip flutes) must also be increased. Due to the large allowances and deeper cutting depth of large-module gears (especially for large-displacement gears), it is prone to uneven cutting, increased tool wear and burns, and reduced tool durability. Tool, tooling rigidity is higher. Due to the above reasons, the application of multiple hobs in the processing of large modulus, large displacement gears is difficult. In order to improve the processing efficiency of large-modulus and large-displacement gears (especially rough hobbing efficiency), we designed a large-diameter double-headed hob. After process testing and mass production, we obtained good processing results and economic benefits. 2 The design of the double-headed hob is processed gear parameters: modulus m=12mm, pressure angle a=20°, displacement coefficient X=1. 3, tooth number Z1=38; tooth blank is forging; performed on Y30100 hobbing machine Processing. Through analysis and calculation of the machining capability of hobbing machines and double-headed hobs, the design parameters of the non-standard double hob are determined as follows: outside diameter De=200mm, aperture d=50mm, number of chip flutes Z=10, and rounding thread angle Lf = 8 ° 22', straight groove, 0 ° front angle, with a circular head antenna, tooth thickness DS = 1.6mm, right hand. The design points are explained below. The allowable speed of Y30100 hobbing machine indexing worm is [nworm] ≤500r/min. Worm speed n Worm and spindle speed (Rotary speed) n The relation between the number of knives, the number of hob heads k and the number of workpiece teeth Z1 is n Worm = 99n K-head / 2Z1 Substituting design parameters into the above formula can be obtained: n Worm = 83. 3r/min<[n Worm]. When the Y30100 hobbing machine works on steel workpieces, the allowable maximum outer diameter of the hob is [De]max = 220mm, and the allowable cutting speed for rough hobbing [v knife] = 20 ~ 25m/min. Cutting speed calculation formula is v knife = pn knife De/1000 In order to avoid the cutting tool speed is too high to reduce tool life, the lower limit value of allowable cutting speed is used in design. Substituting the selected outer diameter of the reel De=200mm into the formula can be obtained: v knife=20.1m/min, slightly higher than [v knife]=20m/min. According to the design requirements, there should be no common denominator between the number of hobs and the number of teeth of the gear being cut, so as to avoid inconsistency in the tooth thickness of the gear being cut. However, if three or more hobs are used, the helix angle of the tool is large, which is not conducive to machining, and the hob is mainly used for rough rolling. The machining accuracy is not too high, and the machining efficiency should be mainly considered. Therefore, the design still has Use double hob. When designing multiple hobs, increase the outer diameter of the hob and increase the number of chip flutes. When the number of hob teeth Z knife=11 is selected, the thickness of the blade is reduced by 5.7 mm when Z cutter=10 is selected, the tool life is reduced more; and the interference phenomenon occurs when the grinding wheel is grinded by drawing verification. Considering the factors of roughing, it is reasonable to use Z knife=10. Using a positive rake angle can improve the accuracy of hob tooth design and improve cutting conditions, especially for large modulus hobs with large thread angles. According to the straight groove positive rake hob design method, the axial tooth angle calculation formula is ctgaqz=ctgancoslf(1-Z knife Ke/2prf2cosgf) The left and right front blade face tooth angle calculation formula is tanaq=(tanancosgf± Sinlfsingf) / coslf Type: an - hob normal tooth angle lf - hob rounding thread angle Z knife - hob chip pocket K - hob radial amount, K = pDetanae/Z knife e - Eccentric position of the front surface of the hob, e = Resinge rf - The rounding radius of the hob gf - The rake angle of the hob, gf = arcsin (e/rf) ae - Hob top Blade Re Re - hob top edge radius ge - hob top edge rake angle calculated, straight slot positive angle hob axial tooth angle than straight slot 0 ° front angle hob increased 48 ' . Because the straight-arc corner radius of the 0° straight-edge hob has reached the lower limit of the required workpiece root arc radius, and the straight-edge radius of the straight-edge hob is smaller, it does not meet the processing requirements. , And will reduce the tooth top strength, is not conducive to rough rolling processing; In addition, straight groove positive angle hob is left and right front blade surface angle difference of 2 ° 7 ', inconvenience to the detection. Therefore, the 0° rake angle is still used in the design. When the screw thread angle lf> 5°, the chip flutes should be in the form of spiral grooves perpendicular to the direction of the thread of the reel (ie, chip flutes with helix angle bf=lf). Straight groove 0° front angle hob axial tooth angle calculation formula is ctgaz=ctgancoslf Spiral groove hob left and right axial tooth angle calculation formula is ctgalz=ctgaz±KZ knife/T type: T——Roll Knife chip kerf lead, T=pdf/tanlf df—The diameter of the hob is calculated by calculation. The straight tooth angle of the hob and the axial tooth profile of the helical groove hob The average angle is 18'. When processing with a straight groove with a 0° front angle, the effect of one-side tooth thickness calculated by cutting depth is 27 × tan18' = 0.14mm. Due to the existence of tooth thickness, it does not affect semi-finishing The tooth profile accuracy, coupled with the spiral groove hobs purchased will increase the cost, sharpening, inconvenient to detect, so the design still uses a straight slot chip pockets. In order to achieve semi-finishing, only the effective tooth-shaped part of the tooth side is machined, and the root portion is not machined, so as to improve the durability and processing efficiency of the semi-precision hob, and the design has used the allowance of the tooth side and directly processed to the tooth depth. Circular arc rooting. 3 Application of double-head hob Our company has been using a single-head hob with outer diameter De=180mm for rough hobbing. The processing parameters are: spindle speed n knife = 32r/min, and the feed amount f = 0.79mm/r , Cut deep ap = 27mm, down milling, the speed of the workbench and workpiece is n work = n knife / Z work = 0.84r/min. After using a double-headed hob for rough hobbing, the same machining parameters are used. The speed of the table and the workpiece is n = n kniper/Z = 1.68 r/min, and the machining efficiency is higher than that of the single hob Times. Throughout the machining process, the spindle tool holder has no vibration, the crawling phenomenon is not obvious, the worktable and the workpiece run smoothly, and the noise, smoke, and workpiece surface temperature caused by the hobbing process are normal. After processing, it was found that there was no groove mark on the tooth surface of the workpiece and the hob was worn properly. Through the trial processing (4 pieces), small amount of processing (20 pieces) and small batch processing (60 pieces), the rough-rolling effect was better, the single-piece processing efficiency was almost doubled, and the semi-precision rolling was also very good. The accuracy of the shape is good, the machining efficiency is improved by about 20%, and the durability of the semi-fine hob is significantly improved. The overall production efficiency is more than doubled and the economic benefits are considerable. In the hobbing process, the following matters should be noted: The tightness of the main motor belt should be regularly adjusted (or replaced) to avoid rapid and slow rotation of the table due to looseness of the belt and slippage of the motor shaft, which may affect processing. The degree of clamping between the knife holder bar and the guide rails should be adjusted regularly. The gap between the clip bar and the guide rail will cause the hob to vibrate. If the clip bar and the guide rail are clamped too tightly, it will cause the knife holder to crawl. Lubricate the vertical rails before processing and during processing to avoid crawling. The floating of the worktable should be regularly tested and adjusted. Because the underside of the worktable and the base of the bed are worn over for a long time, a large gap is generated. Under the action of the lubricating oil, the workbench floats on the base of the bed, so that the workbench and the workpiece may vibrate during the processing. Chattering (most noticeable when the hob is ejected) can affect the smoothness of the cut, aggravate the wear of the hob, and reduce the durability of the hob. The gap between the worm gear and the worm gear pair should be regularly detected and adjusted. The worm and worm gear pair clearance is too large to produce cutting unevenness. At the same time, it should always check whether the worm and the worm wheel are lubricated properly, so as to avoid the occurrence of worm gears and damage the machine tool. Since the lubrication oil in the headstock of the headstock is closed and does not circulate, regular special lubricants for the spindle should be replaced (3 to 6 months) to avoid affecting the spindle drive quality.
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