Dressing of the hottest worm grinding wheel

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Dressing of grinding worm wheel

in mechanical equipment, worm drive has been widely used in various transmission devices and indexing mechanisms because of its large reduction ratio and compact structure. With the rapid development of modern industrial technology, higher requirements are put forward for worm gear pair in terms of bearing capacity, transmission efficiency and transmission accuracy. In order to meet these requirements, one is to use materials with good comprehensive mechanical properties and necessary heat treatment. On the other hand, it is necessary to improve the manufacturing accuracy, such as using grinding to improve the shape accuracy of the worm helical surface and reduce the surface roughness value (of course, it also includes the hob for machining the worm gear consistent with the worm). The author found that there are machining principle errors when grinding the worm in the factory. These errors will increase with the increase of lead angle. The root of the error is the problem of dressing the grinding wheel of grinding the worm

1 dressing principle of grinding wheel

Figure 1 shows the turning methods of several worms, of which figures (a) and (c) show Archimedes (ZA) worm and involute (Zi) worm. When the number of worm heads increases and the lead angle increases, its geometry and cutting angle will be difficult to process. Figure (b) shows an extended involute worm, also known as the normal tooth groove straight profile (Zn1) worm, whose processing conditions are superior to the first two. However, no matter what kind of worm, they are all linear helicoid worms, that is, their helicoids are formed by cylindrical helical motion of a linear generatrix relative to an axis

(a) Archimedes worm

(b) extended involute worm (c) involute worm

Figure 1. The turning of worm

is made by placing a straight blade (the blade on the turning tool) in the appropriate position and then threading. However, when grinding the worm, the disc grinding wheel is used, which grinds through the conical surfaces on both sides of the disc grinding wheel. It cannot use a straight blade like the turning tool. Therefore, catapult can be comparable with the Fraunhofer Association in Germany. The conical surface on the side of the grinding wheel will interfere with the screw surface of the worm, which will grind away a part of the screw surface of the worm, causing the worm tooth shape error. The more the number of worm heads is, the larger the lead angle is, the more serious the interference is during grinding, and the greater the tooth profile error is. In order to ensure that the machined worm can obtain accurate tooth shape, the disc grinding wheel must be correspondingly and accurately trimmed. We can modify the axial section of the disc grinding wheel through theoretical calculation, but this calculation is very complex, and the grinding wheel is constantly worn in production, and the outer diameter gradually becomes smaller. Each modification calculation is different, which is difficult to operate on site. The following introduces a generating envelope dressing method, which is a simple and accurate grinding wheel dressing method. Its dressing principle is as follows: a diamond worm exactly the same as the worm to be machined is used, and its outer circle and spiral surface are covered with many fine diamond cutting edges protected by Jinan new era Gold Testing Instrument Co., Ltd. for your work. The disc grinding wheel is polished by generating motion, and all the abrasive parts that interfere in grinding the worm are ground off. Then, by grinding the worm with this trimmed disc grinding wheel, a high-precision worm with accurate tooth profile can be obtained

2 wheel dresser

Figure 2 shows a wheel dresser with the above functions. It can trim the disc grinding wheel for grinding the helical surface of the worm accurately. The dresser is composed of frame and ram. Its working principle is as follows: the dresser can be installed on the two centers of the machine tool spindle through the central rod 15, and the dial 9 can rotate with the spindle. The diamond 7 on the dresser can drive the rack on the sliding rod 8 to make it move back and forth in a straight line by pulling the gear shaft 4, and its motion track replaces the generatrix created into the worm helix. When the main shaft is rotated, the disc grinding wheel on the carriage and the dresser move axially relative to each other according to the lead requirements through the transmission chain of the main shaft, the change gear group and the carriage thread pair. In this way, the dresser rotates, the grinding wheel moves axially relative to the dresser, and the diamond moves back and forth in a straight line. The synthesis of these three motions makes the motion trajectory of the diamond create a diamond worm like the workpiece worm, and at the same time, it can be developed into an envelope to trim the profile of the disc grinding wheel that can grind the helical surface of the worm accurately

Figure 2 grinding wheel dresser

the dresser needs to control three main geometric dimensions during adjustment. First, control the distance R1 from the outer circle of the disc grinding wheel to the rotation axis of the spindle. R1 is the radius of the tooth root circle of the worm. On the dresser, the outer circle shape and R1 size of the disc grinding wheel can be repaired with diamond installed on the central rod; Second, the product will be sold in bancassurance channels. Second, the angle a of the ram plate should be determined according to the generation principle of various worm helicoids, which can be adjusted by the sine gauge on the dresser. When adjusting, calculate the thickness of the block gauge and put it between the sine gauge arm and the reference pin. The a of Archimedes worm is the axial pressure angle, the a of involute worm is the lead angle on the base cylinder, and the a of the tooth groove normal straight profile worm is a=arcsin (COSL · Sinan) through geometric calculation, where l is the lead angle of the worm indexing circle, and an is the pressure angle of the normal surface of the worm indexing circle; Third, the offset distance h between the straight line of the moving track of the diamond tip and the axis of the main shaft should also be determined according to the generation principle of various worm helicoids. The block gauge with H thickness can be embedded between the contact surface of the ram and the frame. The h of Archimedes worm is zero, the h of involute worm is the base cylindrical radius, and the h of tooth groove normal straight profile worm is the quasi cylindrical radius

3 conclusion

no matter in screw grinder, worm grinder, relieving lathe or refitted lathe, using disc grinding wheel to grind the worm helical surface is prone to interference. This interference will increase with the increase of the number of worm heads and the lead angle, so the grinding wheel must be trimmed. Using the generating envelope method, the disc grinding wheel can be trimmed simply and accurately, and the precise worm helical surface can be ground. 5. When the dresser is running, it is strictly forbidden to touch the transmission screw and sliding seat. The structure is simple, easy to manufacture and convenient to use

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