1 INTRODUCTION In our factory, 2000 pieces of B6 refrigerating vehicle tooth plates are required to be processed every month. Due to the lack of special tools, we can only use the planing process to process them. The tooth depth and tooth pitch of the tooth plates are controlled by the operator manually. The machining accuracy is difficult to guarantee, the scrap rate is high, and the machining efficiency is low (the average working time for planing a tooth plate is 45 minutes). For this reason, we propose a milling process instead of a planing process, and designed a special tooth profile forming cutter. 2 Milling tool design The tooth profile of the tool tooth profile is a straight tooth profile (see Figure 1). In the initial design, we designed the milling cutter as a straight-tooth forming cutter. The milling cutter can process one tooth plate at a time, the efficiency is improved, but the vibration during machining is large and the machining accuracy is not high. For this reason, we have improved the design of the helical tooth profile cutter. The helical cutter teeth of the milling cutter are distributed on the cylindrical outer surface of the cutter, which better solves the problem of milling vibration and improves the smoothness of the milling. The two tooth plates can be milled each time and a higher processing precision can be obtained. Figure 2 shows the geometry of the milling cutter's cutting edge (no secondary cutting edge).
figure 1
figure 2
In FIG. 2, the base surface Pr is a plane passing through the selected point on the cutting edge and including the axis; the cutting plane Ps is the cutting plane of the processing surface at the selected point; the main section P0 is a plane perpendicular to the axis end section; It is a plane perpendicular to the main cutting edge; the feed profile Pf is a plane perpendicular to the base surface. The rake angle g0 is machined into Q235 steel, and the impact is greater during milling. To ensure the cutting edge of the milling cutter has higher strength, the milling cutter should adopt a small rake angle; consider the tool material for high speed steel (W18Cr4, heat treatment hardness 62 ~ 65HRC), the rake angle should be slightly larger than the carbide tool, so select the tool front angle g0 = 10 °. The blade angle ls and the law forward angle gn The blade inclination angle ls is equal to the blade helix angle b. This cutter is a high-speed steel fine-toothed cutter, so ls=25° is selected. At this point the method forward angle gn = arctan (tang0cosls) ≈ 9 °. For easy manufacturing and measurement, gn should be marked in the drawings. The relief angle a0 and the lead angle Kr are measured in the main section P0. Select the posterior angle a0=12° and the leading angle Kr=90°. Aperture d, outside diameter do and number of teeth Z According to the size of the milling cutter rod in the machining workshop of our factory, the diameter of the inner hole of the milling cutter d=32mm is selected. The outer diameter of the cutter, do=80mm, and the number of teeth Z=9 can be found in the schedule of the cutter cutter.
image 3
Figure 4
Milling cutters The milling cutters are cutter cutters with an Archimedes helix. When the cutter is reground, it is only necessary to sharpen the rake face. The cutting amount of the milling cutter can be calculated by drawing or calculating. From the plotting method (see Fig. 3), the milling cutter cutting amount can be found as K=(pdo/Z)tanaf=(pdo/Z)tana0=(3.14×80/9)tan12°≈6mm. Groove design milling cutter slot size shown in Figure 4. Select the slot angle q=70°, the groove bottom fillet radius re=4mm, and the inter-tooth angle e=2p/Z=360/9=40°. Due to the narrow edge of the blade tool, μ can be ignored. By plotting the groove depth h=12mm can be measured. Dimensional Tolerance and Surface Roughness The diameter tolerance of the inner hole of the tooth plate forming cutter and the surface roughness of the tooth are marked according to the relevant tool standard requirements. In order to reduce the vibration, the non-parallel degree and the coaxiality of both ends of the cutter should be ≤ 0.025mm. To meet the requirements of manufacture and use, the cumulative error of the pitch of the three cutter teeth should be ≤ 0.02mm. Based on the above design parameters, a tooth profile forming cutter as shown in FIG. 5 can be designed. To reduce stress concentration, arc transitions are used at the sharp corners.
Figure 5
3 Conclusions The use of tooth profile forming cutters to machine the tooth plates can greatly increase production efficiency (only 1.8 minutes to mill a tooth plate), significantly improve machining accuracy and ensure product quality. The average service life of a toothed profile cutter is more than three years, reducing processing costs.
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