In metal cutting, turning is a very important job. As the saying goes: "One-third of craftsmanship, seven-tenths of tool." A good lathe can sharpen turning tools with reasonable geometric angles according to different cutting conditions. This is crucial in cutting processing. It can reduce costs, Increase productivity. The following takes a 90° steel rough turning tool (YT15) as an example to introduce the general sequence, methods and precautions for manual sharpening.
grinding clearance angle
Use an aluminum oxide grinding wheel to first grind away the welding slag on the front and back of the turning tool, and grind the bottom surface of the turning tool flat, and then grind a 2° to 3° larger relief angle on the lower part of the main and auxiliary flank surfaces of the turning tool respectively. Back clearance angle, its function is to reduce the sharpening area of the flank surface, making it easy to sharpen and smooth. When grinding, the turning tool should move slowly left and right to make the grinding wheel wear evenly; when the grinding wheel reaches the carbide blade, it ends and moves upward to leave the grinding wheel in an arc shape.
Rough grinding of main and auxiliary rear corners
The function of the relief angle is to reduce the friction between the flank surface and the workpiece, reduce the wear of the flank surface, improve the quality of the machined surface and the durability of the tool, and adjust the sharpness, strength and heat dissipation volume of the blade and tool head in conjunction with the rake angle.
Use a green silicon carbide grinding wheel to rough grind the main and auxiliary rear corners of the turning tool. The main and secondary clearance angles obtained by rough grinding are generally 6° to 8°. The sharpening method is to place the ground clearance surface of the turning tool against the outer circle of the grinding wheel, and its position is close to the horizontal centerline of the grinding wheel, and then use The sharpening position gradually approaches the blade and moves left and right. When rough grinding the main relief angle, the main declination angle and the main relief angle should be sharpened at the same time. When the grinding wheel reaches the main cutting edge, it can be completed. When rough grinding the secondary relief angle, the secondary relief angle should also be ground to 6° to 8° at the same time, until it reaches the tip of the tool. At this time, the secondary cutting edge has been basically ground out.
grinding chip breaker
Chip breaking is a prominent problem in turning plastic metals. If the chips continue to wrap around the turning tool or workpiece in a ribbon shape, it will not only affect normal turning, but also roughen the machined surface, and even cause accidents. The purpose of grinding a chip breaker on the cutter face is to generate internal stress in the chip when it passes through the chip breaker, forcing it to deform and break. The chip breaker is sharpened with a green silicon carbide grinding wheel. The sharpening method is to sharpen the left or right corner of the grinding wheel. In order to ensure the quality of sharpening, it should be divided into two processes: rough grinding and fine grinding. When coarse grinding, you need to pay attention to the following points:
1. First, trim the grinding wheel. Trim the left or right corner of the grinding wheel into a smaller fillet. The starting position of grinding should be kept at a distance from the tool tip and the main cutting edge. Usually, the distance between the starting position and the tool tip can be It is equal to about half the length of the chip breaker; the distance from the main cutting edge is equal to about half the width of the chip breaker.
2. Ensure the rake angle value of the turning tool
The turning tool should be turned at an angle so that the angle between the bottom surface of the tool holder and the side angle of the grinding wheel is approximately equal to the rake angle value. Pay attention to the position of the chip breaker. For parallel chip breaker, it is required to be parallel to the main cutting edge. When sharpening, the main cutting edge should be parallel to the side of the grinding wheel. For external and internal inclined chip breaker, it is required to be parallel to the main cutting edge. At a certain angle, when sharpening, the main cutting edge should also form a corresponding angle with the side of the grinding wheel.
3. Do not use too much force when sharpening
The turning tool should move slowly up and down along the direction of the tool holder, and the tool tip should always be in front of the vertical line from the center of the grinding wheel to the main cutting edge, otherwise it is easy to collapse the front end of the chip breaker. The chip breaker should not be ground to the main cutting edge, nor should the main cutting edge be ground lower. When the chip breaker is rough ground to form, there must be a distance between it and the main cutting edge that is approximately the amount of tool feed. Keep the grinding The cutting edge thickness of the negative chamfer.
4. Repeatedly check the shape, position and rake angle of the ground chip breaker.
When the shape of the chip breaker is basically ground out and you are ready to finish rough grinding, the up and down movement of the turning tool should be slower, and it is better to withdraw the turning tool when the grinding wheel is at the rear end of the chip breaker.
After the rough grinding of the chip breaker is completed, fine grinding can be carried out. When fine grinding, in addition to the sharpening position of the turning tool should be as consistent as possible with the final position determined for rough grinding, special attention must be paid to the correct dressing of the grinding wheel, that is, the sharpening part of the grinding wheel should be trimmed to meet the requirements of the chip breaker. Shape, the turning tool should move up and down more slowly, and the force should be even and gentle. When the size and position of the chip breaker meet the requirements and the surface roughness is good, fine grinding can be completed.
Grinding negative chamfer
In order to increase the strength of the main cutting edge and improve its stress and heat dissipation conditions, a negative chamfer is usually ground on the main cutting edge of the turning tool. The inclination angle of the negative chamfer is generally -5°~-10°, and its width b is 0.5~0.8 times the tool feed, that is, b=(0.5~0.8)f. The negative chamfer sharpening method is to use a green silicon carbide grinding wheel. The turning tool needs to be rotated through two angles, so that the bottom surface of the tool holder forms an angle equal to the edge inclination angle with the side of the grinding wheel in the vertical direction, and makes an angle equal to the edge inclination angle with the side of the grinding wheel in the horizontal direction. Form an included angle equal to the negative chamfer inclination angle value. Use gentle force when sharpening, and the turning tool should move slowly left and right in the direction of the main cutting edge. When the ground negative chamfer connects with the chip breaker, sharpening can be completed. Otherwise, it will affect the shape and size of the chip breaker or affect the next sharpening process. In order to ensure the quality of the cutting edge, it is best to use the direct grinding method.
Precision grinding of main and auxiliary rear corners
Choose cup-shaped green silicon carbide grinding wheel or diamond grinding wheel. Before fine grinding, the grinding wheel must be dressed to keep the grinding wheel rotating smoothly. When fine grinding the relief angle, first adjust the angle baffle to tilt it at an angle equal to the relief angle value, and then place the turning tool on it so that the main cutting edge gently leans against the end face of the grinding wheel for sharpening. In order to heat the blade evenly and avoid cracks, the turning tool should also move left and right along the direction of the main cutting edge.
When the main cutting edges are all ground out and there are no zigzag gaps, it is necessary to check whether the width of the negative chamfer meets the requirements. If it does not meet the requirements, you need to continue sharpening. If the sharpening area is too large at this time, you can grind away some of the back clearance angle until the negative chamfer meets the requirements. When fine grinding the secondary relief angle, except that the tilting angle of the angle baffle is equal to the secondary relief angle value and the position of the turning tool should be such that the vertical line between the main cutting edge and the end face of the grinding wheel forms an angle equal to the secondary relief angle value, the rest are consistent with the secondary relief angle value. The same is true when sharpening the relief angle. The sharpening can be completed when all the secondary cutting edges are ground out.
Grind transition edge
The transition edge can be divided into two types: linear and arc. The deflection angle of the linear transition edge is approximately equal to half of the main deflection angle, and its length is equal to 0.5 mm to 2 mm. The sharpening method is to tilt the angle baffle by an angle equal to the rear angle. value angle, then place the turning tool on it and sharpen it according to the shape of the transition edge. When it is necessary to sharpen a linear transition edge, the main cutting edge of the turning tool and the end face of the grinding wheel should be at an angle roughly equal to half of the main deflection angle, and then use a very small force to slowly push the tip of the tool toward the grinding wheel. When the length of the ground transition edge meets the requirements (generally equal to about 1/3 to 1/4 of the cutting depth), the sharpening can be completed. When it is necessary to sharpen an arc-shaped transition edge, the tool tip should be in slight contact with the end face of the grinding wheel. The tool holder should basically take the tip as the center of the circle. The angle between the main and secondary cutting edges and the end face of the grinding wheel should be approximately equal to 15 Within the range of °, rotate slowly and evenly. At this time, the force should be light and the advancement should be slow. When the sharpened tool tip fillet meets the requirements of the tool tip arc radius, the sharpening can be completed.
In order to improve the strength of the linear transition edge, it is generally necessary to use a whetstone to grind a negative chamfer on it after sharpening; and use a whetstone to sharpen the intersection angle between the transition edge and the main cutting edge and the secondary cutting edge into a small rounded angle. Generally, It is R0.1~0.3mm. When the turning tool requires a wiper edge, whetstone grinding should be done after the wiper edge is ground. For arc-shaped transition edge turning tools, if a wiper edge is required, the wiper edge should be ground first and then the arc-shaped transition edge.
Polishing edge
The angle of the wiper blade is equal to zero degrees, and its length should be slightly larger than the tool feed, that is, l=(1.2~1.5)f. The sharpening method is to tilt the angle guide plate to an angle equal to the secondary clearance angle (if there are special requirements for the wiper clearance angle, the angle guide plate should be tilted to an angle equal to it), put the turning tool on it, and The main cutting edge is perpendicular to the end face of the grinding wheel. Along the direction perpendicular to the end face of the grinding wheel, use very slight force to slowly push the tool bar for sharpening. When the width of the ground wiper edge meets the requirements, sharpening can be completed. If the wiper edge is required to be ground wider, the tool holder can be appropriately moved in the left and right directions during sharpening. However, special attention should be paid to the fact that the wiper edge must be ground straight and not in an arc shape.
Sharpening Precautions
The newly installed grinding wheel must be strictly inspected to ensure that there are no cracks before sharpening can begin. The linear speed of the grinding wheel is generally 25 to 35 meters/second. If it is too high, it will burst and hurt people and cause accidents. If it is too low, it will affect the sharpening quality.
The grinding wheel must be firmly clamped and run smoothly, especially the precision grinding wheel. The selection of grinding wheel must be based on the material of the turning tool, otherwise the sharpening effect will not be achieved. The angle guide must be straight and rotated at the correct angle.
The pressure should not be too high when sharpening, and the turning tool should not be cooled in water to prevent the blade from breaking due to sudden contraction; when sharpening high-speed steel turning tools, it is necessary to cool it with water at any time to avoid annealing of the blade. The rotation direction of the grinding wheel must be from the cutting edge to the direction of the cutter body, otherwise the cutting edge will cause a zigzag gap.
When sharpening, try to avoid facing the grinding wheel. It is better to stand on the side of the grinding wheel.
