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Development of double arc hard tooth surface gear scraping hob and carbide scraping hob (CITIC Heavy Machinery Company Tool Factory, Luoyang, Henan 471039) Zhang Bangdong Shen Ming Fu Luda Xingshao, for the manufacture of carburized and hardened double round hard tooth surface The gear made a useful exploration.
The double circular arc gear has many advantages such as high contact strength and good lubricating performance; however, since the tooth shape has a plurality of arc connections, it is difficult to perform the grinding process, thereby limiting the production of the double arc hard tooth gear, thereby limiting The bearing capacity and service life of the double arc gear are further improved. After the carburizing and quenching heat treatment of the involute hardened gear, in addition to the conventional grinding process, in recent years, the scraping process with a negative rake angle carbide hob has been developed. Because it is a linear envelope forming, the grinding wheel dressing and the negative rake angle scraping of the carbide hob are easier, so it develops very quickly. The double arc negative negative angle carbide hob tooth shape is connected by multiple arcs, so it is difficult to manufacture. No one has tried it for a long time; it was not until 1996 that the Ministry of Machinery Industry Technology Development Fund Committee made a research.
Our factory and Zhengzhou Machinery Research Institute jointly researched, designed and manufactured the m6 double arc hard tooth surface gear scraping hob and carbide scraping hob, and obtained some preliminary experience.
The manufacturing of the negative rake angle scraping hob cutter tooth front of the scraping hob should not be involved in the cutting, so it is best not to leave a margin in the gear root arc. To this end, we determine the 6-tooth circular arc gear before the scraping knife retaining amount of tooth shape and retention form as shown, because the gear tooth tip is generally chamfered, the gear tooth root is not left part of the amount is slightly larger than The non-working part of the standard tooth profile.
It is best to keep the single-side retention before the gear scraping between 0.15~0.25mm in the normal tooth profile of the hob. If the value exceeds this value, the number of scraping needs to be added.
For the convenience of manufacturing, inspection and sharpening, the scraping hob is designed as a straight groove 0 front angle. Therefore, the normal tooth shape needs to be converted into an axial coordinate, and is divided into a tooth top arc, a convex arc, a transition arc, and a concave arc. Five samples were made for shovel and initial inspection, such as final inspection on the projector according to the enlarged view.
Manufacture of double arc negative rake angle scraping hob 2.1 Test of scraping hob negative rake angle According to the experience of involute scraping hob blade material, we chose the material of Zigong Cemented Carbide Factory (code 726 Because the blade of this material has good wear resistance and high strength, hardness and toughness.
Because the non-working part of the tooth root is small when the double circular arc gear meshes, the hob tooth top of the double arc carbide hob is inevitably involved in cutting. In the face of this reality, we have carried out some simple tests. .
Carbon quenching 58HRc; tooth outer diameter shirt 40mm. Test tool: welding turning tool, blade material 726 cutting edge rounded corner R2, rear corner 6 changing negative rake angle and cutting amount, intermittent cutting, test conditions are listed in Table 1. Table 1 shows different negative rake angles. Cutting amount test condition Tool cutting amount test result Front angle cutting development length / m tool condition / mm 舛 front blade surface is larger than rear blade surface chipping 0.5 normal wear 0.1 front blade surface is larger than rear blade surface chipping 0. Normal wear 0.1-15 Normal wear 0.15 knife tip off 0.8 normal wear 0.1 after the blade surface is larger than the front blade surface chipping 0.5 shape is the qualified tooth shape each arc shovel grinding order We estimate the scraping hob tooth tip cutting thickness does not exceed 0. 2 so choose the depth of cut t=0.2, the thickness of the single-side cutting is between 0.1~0.25mm, so the cutting distance is 0.24mm. From the table, the front angle 15 of the tool is optimal, so the negative rake angle of the scraping hob is 15°. .
2.2 Blade welding Considering that there are not many blades during the trial production, it is uneconomical to order the blade with the shape of the coordinate point of the front blade surface. Therefore, the appropriate size of the involute scraping blade is selected, and the wire is cut into the same. Need to shape the residual blade (select m7, a 30 front angle involute scraping hob blade, special model is T87073). After the welding surface is ground flat, the CNC wire is cut into a double-arc toothed blade with a 0.2 mm circumference of the front blade surface, as shown. The bottom projection is 5X 5mm for welding positioning.
The welding temperature is gradually increased from low to high to 900C (the blade has a temperature diffusion time). The temperature rises too fast, and the blade will be cracked due to the large temperature difference between the blades and the increase of the amount. Immediately after the welding, 250~260C tempering, the time is 3~5h, it is best to cool with the furnace to eliminate the welding stress. Based on our years of experience in welding involute carbide scraping hobs, this soldering and soldering method provides reliable soldering strength.
2.3 Precision grinding of the front surface of the hob To ensure the accuracy of the hob, the type of grinding machine imported from Germany AGW482 is used. The deviation value is e19.41, the deviation is controlled at 0.01mm; the adjacent error of the chip pocket does not exceed 0. . 02mm, the cumulative error of the chip pocket is within 0.031mm; the surface roughness is Ra). 4. 2.4 Tooth shovel grinding Because the tooth shape is shaped and shaped, in order to trim the grinding wheel shape to the full qualified hob tooth shape, we have selected synthetic diamond RVD, particle size 150, concentration 100%, resin. Bonding agent B and forming special diamond grinding wheel. In order to facilitate the trimming, four kinds of grinding wheels, such as a circular arc, a convex arc, a concave arc and a transition arc, are respectively processed, and the corresponding arc shapes of the hob tooth shape are respectively processed.
The shovel order of each arc segment of the tooth shape is as follows, and each label has a corresponding template, and the template controls the grinding surface based on the ground surface and is associated with each other. Finally, check the enlarged picture of the computer drawing on the projector. When the sample, tooth height, tooth thickness measurement, projection inspection, all three meet the requirements, the main items, required tolerances and actual test values ​​of the manufacturing accuracy of the tooth 2.5 manufacturing precision m6 double arc carbide scraping hob are listed in Table 2. The table requires a precision value of AA, and the hob photo is as follows.
Table 2m6 double arc carbide scraping hob manufacturing precision serial number inspection item numerical value / chemical requirements measured aperture deviation of the shaft of the radial runout of the end of the shaft end of the beating teeth radial and offset value deviation of the chip pocket The maximum cumulative error of the circumferential section of the adjacent peripheral section is the parallelism of the front of the cutter and the axis of the bore. The tooth profile of the cutting edge is offset by the tooth thickness deviation of the cutting edge of the 25th 10 adjacent cutting edge. Helical error of the inner cutting edge of the cutting blade 3 rotation of the inner cutting edge of the spiral cutting error of the cutting edge of the cutting edge of the 12 rolling test m6 double arc carbide hob rolling test at Zhengzhou Machinery Research Institute, test piece gear The material is 20CiNi2Mo, the heat treatment hardness after punching and quenching is 56HRc, the single-side scraping amount is 0.15 scraping result, the cutter tooth has no desoldering chipping; the cutting length of one sharpening is more than 80m, the maximum wear amount behind the tooth does not exceed 0.02mm; the tooth surface of the workpiece is rough The degree is close to Ra. 8Mm.