Problems in high speed turning slender shaft
"The Turner is afraid of the pole". This sentence reflects the difficulty of cutting a slender rod. Due to the characteristics and technical requirements of slender shaft, Dongguan CNC plant is prone to produce defects such as vibration, multi edge, slub, poor cylindricity and bending when turning at high speed. If we want to make it better, we must pay attention to the problems in the process.
(1) Machine tool adjustment. The connecting line between the two center lines of the lathe spindle and tailstock must be parallel to the lathe guide rail, and the tolerance should be less than 0.02mm.
(2) Workpiece installation. During the installation, try not to produce over positioning. When clamping one end with chuck, do not exceed 10 mm.
(3) Tool. use Κ R = 75 ° to 90 ° deviation, pay attention to the auxiliary posterior angle α′ 0 ≤ 4 ° to 6 ° should not be too large. When the cutter is installed, it should be slightly higher than the center.
(4) After the installation of the tool holder, it must be trimmed. The trimming method can be grinding, reaming, boring and other methods, so that the arc surface r of the tool holder claw in contact with the workpiece is greater than or equal to the radius of the workpiece, and must not be less than the radius of the workpiece, so as to prevent the generation of multiple edges. When adjusting with the tool holder claw, make the claw contact with the workpiece. Do not use force to prevent the occurrence of slub.
(5) Auxiliary support. When the length diameter ratio of workpiece is greater than 40, Dongguan CNC machining plant should add auxiliary support in the turning process to prevent the workpiece from vibration or bending due to centrifugal force. In the process of cutting, pay attention to the adjustment of the center, take the workpiece on the rigid top as appropriate, not tight, and adjust it at any time to prevent the workpiece from thermal expansion, deformation and bending.
2. Problems needing attention when turning slender rod with reverse cutter
There are many methods of turning slender rod, generally using the tool holder for forward or reverse cutting. However, compared with forward turning, reverse turning has many advantages, most of which are adopted.
There are two kinds of problems in turning in Dongguan NC machining plant. One is polygonal, which is mainly caused by the large back angle of the tool, which is inconsistent with the R of the tool holder claw and the diameter of the workpiece; The other is the slub problem. It is caused by the change of cutting depth from minimum to sudden increase when the tool is set and moved to the cutting surface after the tool holder is well followed at the shelf edge. As a result, the cutting force changes, and the workpiece turns outward, and the diameter suddenly increases. When the tool holder moves to the large diameter, the turning diameter decreases again. In this way, the processed workpiece is slub shaped.
In order to prevent the occurrence of slubby shape, when turning the b-section shelf, carefully follow the tool rest, and reverse the tool after tool setting. When the tool tip is close to point a, use the middle carriage handle to eat (0.04 ~ 0.08) mm deeper, but it should be flexibly controlled according to the cutting depth.
3 rolling straightening method
In the mechanical processing of Dongguan CNC plant, rolling is often used to improve the surface hardness, anti fatigue strength and wear resistance of the workpiece, reduce the surface roughness of the workpiece and prolong the service life of the workpiece. At the same time, in the rolling process, the metal plastic deformation under the action of external force can also be used to change the internal stress to straighten the shaft and rod parts with better rigidity.
In the process of rolling the workpiece, the workpiece is bent due to the uneven hardness of the surface layer under the action of external force. At the height of the bending center of rotation, the rolling force is large, and the plastic deformation is also large, which makes the bending degree of the workpiece more increased. Especially when using rigid rolling tools, this phenomenon is more prominent.
The method of rolling straightening is to check the radial runout of the workpiece after the first rolling, mark the concave part, adjust the concave part of the workpiece to the height of the rotary center of the machine tool with the four claw chuck, which is proportional to the bending of the workpiece, and then roll the workpiece for the second time, and then use the dial indicator and adjust the claw of the four claw chuck to correct the workpiece. Then check the bending condition with dial indicator. If it is still bent, adjust the workpiece with the above method and roll it for the third time until it reaches the required straightness of the workpiece. After the second time, the length of the knife should be based on the specific situation. It is not necessary to complete the whole journey, and the reverse knife should be used.
Dongguan NC machining plant adopts rolling straightening, which is generally completed in the process of rolling the workpiece. It not only does not damage the surface of the workpiece, but also makes the outer surface of the workpiece subject to relatively uniform rolling, which will not produce dead bending and is easy to operate.