Due to the shortened transmission chain, the CNC gear hobbing machine greatly reduces the transmission error and improves the machining accuracy. However, for high-precision gears, especially gears with a large number of teeth, a large diameter, a long tooth surface, a high precision requirement, and a long processing cycle, they require strict process guarantees in the hobbing process. Therefore, it is necessary to control the gear blank machining and fixtures. Tool, machine tool adjustment, and environment. Otherwise, even with a CNC hobbing machine, it is difficult to machine qualified high-precision gears. 1 Gear blanks The gear blanks, especially those with larger diameters, are easily deformed when they are mounted. This is difficult to make up for on gear hobbing machines, which may cause loss of gear meshing accuracy. As the gear surface machining often uses the gear hole and the end face as the reference surface, the precision of the gear blank mainly has a higher requirement on the dimensional accuracy and shape accuracy of the gear hole and the position accuracy of the hole and the end surface (see GB10095-88). For gears with 6-level accuracy, the size and shape accuracy of the positioning holes is IT6, and the roughness Ra is 1.6μm. The radial runout of the gear positioning holes and the round runout tolerance of the gears in the range of 125 to 400mm are not more than 0.014mm. Two kinds of processing methods are generally used to ensure: 1 Direct clamping and turning (the completion of the completion of the hole and the reference surface of the finishing car): 2 Axis turning (based on the previously processed hole, the completion of the face, cylindrical turning). Whichever method is used, the gear blank should meet the specified requirements and a high-precision hobbing positioning datum should be provided.
1.Screw holder 2.Special turning tool holder 3.Lathe tool 4.Fixture 5.Hobbing machine tableFig.1
1. Mandrel 2. Holder seat Figure 2
2 Tooth hobbing jigs for gear hobbing should have enough strength and can meet the accuracy of gear hobbing. After the jig positioning base surface is processed on other machine tools and then mounted on the hobbing machine work table, it is often not easy to ensure the parallelism. Therefore, a method of turning a positioning plane on a gear hobbing machine can be adopted. As shown in Fig. 1, the hob and the arbor are removed, and a special tool rest is fixed on the hob using the bolt holes in the hob. A radial cutting program is programmed to allow the hobbing machine table to drive the fixture to rotate, and the hob holder is fed into the turning tool to make a radial feed. Note that the rotation speed of the table should not exceed its rated speed, and the turning depth of the turning tool is only 0.2mm at a time. After the fixture is installed on the machine tool table, as shown in Figure 2, it is necessary to check the amount of run-out of A, B, and C. The distance between A and B depends on the length of the gear blank (Several gears are machined in tandem when machining several gear blanks. The total length of the blanks depends on the general requirements for maximum runout A at 0.006 mm and B and C at 0.003 mm. 3 Installation and adjustment of the hob system Installation and inspection of the hob bar should be installed in the hob hob of the hob steadily and tightened with a tie rod, then release the rod to eliminate the tensile stress, but not Make the cutter bar off again. Retighten the lever just enough to hold the cutter bar and fix it. This is due to the tension caused by pulling the arbor into the taper hole of the spindle, so that the tension bar is in tension. During the operation of the machine tool, due to the temperature rise of the machine tool, the spindle taper hole expands, and the arbor pulls the drawn bar to deeper into the taper hole. When the cooling is stopped, the taper of the main shaft shrinks, making it difficult to disassemble the arbor.
1. Dial gauge 2. Hob shaft 3. Spindle Fig. 3
1. Bushing 2. Adjustment washer 3. Hob 4. Roller bar 5. Micrometer 6. Coupling key Figure 4
Test shown in Figure 3, the two dial gauges were fixed on the machine tool holder, so that the dial indicator touches the cylinder surface of the arbor. Rotate the hob bar, check a and b, which allows the amount of bouncing to be determined by the machine's machining accuracy. For a gear hobbing machine with a machining accuracy of 6 degrees, the maximum allowable jump amount a is 0.005 mm, and b is 0.002 mm. Hob installation and adjustment The installation of the hob is based on the accuracy of the gear and selects a hob with considerable accuracy. Generally, gears with a grade of 6 or higher must use a hob of class AA accuracy. Adjust the position of the reel with respect to the center of the machine and use the adjusting washer to clamp it. The clamping of the hob should meet the driving requirements through the static friction between the hob, bushing and the end face of the adjusting washer. Even with a hob with an axial keyway, under normal circumstances, the key connection only serves as a backup drive. Hob adjustments for machining high-precision gears must be carefully calibrated on the hob. As shown in Fig. 4, fix the two dial gauges on the machine tool so that the contact points touch the correct circular surfaces on both ends of the reel. Rotate the hob to observe the beating condition of the dial gauge and then eliminate the radial runout of the hob by adjusting the hob, adjusting the spacer, or orientation of the sleeve. The general requirement for maximum runout a is 0.006mm and b is 0.003mm. 4 Effect of temperature on machining accuracy The temperatures discussed here are the machine temperature and the ambient temperature. For big gears with long machining cycles, temperature changes have a serious effect on the accuracy of gear machining. During processing, changes in temperature cause minor changes in the position of the various carriages of the hobbing machine relative to the workpiece. Practice has proved that the temperature has a greater influence on the accuracy of the gears, in particular the tooth-to-tooth accuracy, and will reduce the amount of contact spots on the meshed gears. The general CNC gear hobbing machine has the function of automatic adjustment of the internal temperature of the machine and has a numerical display. Therefore, in the processing must pay attention to observation, and focus on controlling the indoor temperature, it is best to keep the room temperature. The hobbing process introduced in this paper is aimed at high-precision gears. In practical applications, appropriate technological measures should be taken according to the specific conditions and different requirements of the workpiece to avoid unnecessary costs.
Wood Hammer Mill Machine
Wood Grinding Machine This hammer mill is widely used in crushing all kinds of crop stalk, cotton firewood, willow, straw, clover, peanuts shells, cotton seed, wood chip and etc. And spare parts of the hammer mill completely adopt quality material, outsourcing parts adopting domestic optimal product, the whole machine`s quality is reliable, long-lived
Wood Grinding Machine,Hammer Mill Grinder,Hammer Mill Crusher,Wood Grinder Machine
Jinan Shanghangda Machinery Co., Ltd. , https://www.shdmachines.com