Design and manufacture of large helix angle spline push blade

The FY50Q motorcycle engine adopts a spiral clutch mechanism to realize the start-up clutch, that is, a spiral spline groove is formed in the inner hole of the starter gear, a spiral spline tooth is formed on the start-up shaft, and when starting, the start-up shaft rotates to axially move the start gear in the spiral direction. Engage with the middle gear. Thus, the crankshaft is rotated; after starting, the starting shaft is reversed and reset under the action of the return spring, and the starting gear is moved axially under the action of the spline screw, and is rapidly disengaged from the intermediate gear.

Figure 1 starter gear parts

Figure 1 shows the starter gear part. Gear inner hole is involute right-handed spiral spline groove, spiral angle b=30°, modulus mn=1.75mm, number of teeth Z=10, small end diameter D is small=8.11+0.043mm, big end diameter D is large=20 +0.1+0.2mm, hole length L=113-0.1mm, hole tip chamfer 1.5×45°, tooth blank material is 20Cr. The spline hole has a large helix angle, a small diameter, and a large number of teeth, and broaching is preferred. Due to special spiral broach and specialized feeding mechanism for spiral composite motion during machining, it needs to be customized by a professional manufacturer, and the cycle is long and the cost is high; in addition, considering that the spline teeth only use the gradual opening of about 1 mm below the index circle when starting the clutch. Line tooth shape (can be regarded as a straight line approximately), spline tooth height is only about 1mm margin, and the width of the cogging is small, relatively large relative tolerance, so if the use of homemade spiral spline push knives for processing, can meet the processing requirements It can also shorten the design and manufacturing cycle of the tool and screw feed mechanism and reduce the processing cost. 1 The design of the push knife is based on the structure of the spiral spline of the starter gear, and the layered cutting method should be adopted for forming processing. Due to the short length of the pusher, a monolithic structure can be used. Tool material using W18Cr4V. The choice of tooth lift and pitch The choice of tooth lift af is extremely important and it is directly related to the size of the pushing force, the stability of the push and the wear condition of the push knife. If the amount of tooth lift is too small, the push blade will be long and easy to bend and break, affecting the processing stability and processing quality. According to the maximum tooth lift of the spline tooth (the number of teeth Z = 10, the diameter D = 16 ~ 28mm, afmax = 0.16mm), select af = 0.1mm. The principle of tooth pitch selection is: normal pitch pn=(1.2~1.5)(l/cosb) 1⁄2=4.65~5.8 mm; axial pitch p=pn/cosb=5.37~6.7mm. The chip flutes are designed to ensure the effective volume of the flutes, the strength of the cutting teeth and the smoothness of the broaching. The number of teeth at the same time that the push knife is used during the pushing process should be ≥3. The chip flutes should have enough chip space and a reasonable shape and rake angle, and the depth of the grooves should not be too deep to ensure that the push knife has sufficient strength, stiffness, and stability. This spline push knife adopts a circular groove structure. The number of chip pockets in the spiral spline lead is K = pD/pnsinb = 24.5, Kmax = 25. Calculation of pushing force A 3T jack is used to produce the pushing force in the pushing process. When designing a push knife, it is necessary to calculate the size of the push force and check the stability of the push knife when pressed. In order to prevent the pushing knife from being broken due to the inconsistent force during the pushing process, a conical pit with a Ø6 mm steel ball is placed on the end of the pushing tool shank. The geometry of the cutter tooth and the design of the pusher tooth profile can be determined by the design method of an ordinary (spiral) rectangular spline broach. The cutter tooth geometry is shown in Figure 2 (push push part drawing) and Figure 3 (push push knife 3D solid drawing), and the push knife size and tolerance are shown in the table below.

Figure 2 push knife parts

Figure 3 push knife three-dimensional solid map

Table Pusher size and tolerances Tooth number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 D
(mm) Size 18.1 18.3 18.5 18.7 18.9 19.1 19.3 19.5 19.7 19.9 19.95 20 Tolerance ±0.015 -0.015 2 Manufacturing of push knives The main manufacturing process of push knives is: blanks (blank material: W18Cr4V high speed steel) → rough, fine cars Push cutter outer circle, open chip hopper and push shank taper pit → roll the pusher helical tooth on the gear hobbing machine (Z=10, hob needs to correct the height of the cutter tooth) → heat treatment (hardness 63～66HRC), push knife Straight → grinding circle outside the Ministry of push the knife → in the broach grinding machine grinding the size of the teeth to the drawings. In order to improve the cutting conditions of the push knife, certain auxiliary and auxiliary relief angles can be milled on the side of the pusher teeth. The use of self-produced spiral push knives to process starter gear spline grooves can achieve the required machining accuracy of parts, shorten the production cycle, reduce processing costs, and obtain good rhyme economic benefits.

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