The round broach is a commonly used tool for efficient finishing of the bore. Round broach (hereinafter referred to as broach) is a blade-shaped complex cutter with high manufacturing precision, strict technical requirements and high price. It should be used reasonably. In production, there are often problems with the structure and use of the broach, which affects the surface quality of the pull hole and the service life of the broach. In severe cases, the broach is damaged.
1. Broken surface defects and their elimination
When broaching, the surface produces scales, longitudinal scratches, extruded bright spots, ring-shaped corrugations, and “sicklesâ€, which are common defects affecting the quality of broached surfaces. The main reason for the occurrence of scales is that the plastic deformation during the broaching process is serious; the main cause of the ripple is that the broaching force changes greatly, and the cutting process is not stable; the local scratches are due to the chipping of the cutting edge and the notch on the teeth. Or the chip condition is poor, the chip scratches the surface of the workpiece; the "sickle" is caused by the broach bending; the squeezing bright spot is caused by the strong squeezing friction between the flank face of the tooth and the machined surface, or Due to the high hardness of the workpiece material.
To eliminate razor surface defects and improve the quality of the hole, the following measures can be taken:
(1) Improve the quality of the cutting edge and keep the cutting edge sharp and the width of the cutting edge on the tooth.
(2) Improve the smoothness of broaching, increase the number of working teeth at the same time, preferably 4~5. If there are too few, stack several workpieces together; reduce the pitch of precision cutting teeth and calibration teeth or adopt no Equal pitch to increase the rigidity of the broaching system.
(3) Reasonably select the broaching speed, use a lower cutting speed (<2 m / m in) or use a carbide broach and a TiN coated broach to cut at a higher speed to suppress the formation of built-up edge. Improve the quality of broached surfaces.
(4) The heat treatment method is used to control the hardness of the workpiece material, because the scale is most likely to be produced when the hardness of the workpiece is less than 1 80 HBW, and the extrusion highlights and scratches are easily generated when the hardness is greater than 240H BW.
(5) Reasonable selection and full casting of cutting fluid. When slag-cutting steel parts, the concentration of 10% ~ 20% emulsion, extreme pressure emulsion or sulfurized oil is used. The kerosene is used to improve the surface quality of the broaching and the service life of the broach. The supply of cutting fluid should be sufficient. The cutting fluid should be supplied before the broach enters the workpiece hole and just after it is pulled out from the workpiece hole. The supply should not be less than 5 ~ 15L / m in.
2. Prevent broach breakage and tooth damage
When the broaching is too strong, the broach is not strong enough, which is the main reason for the broach damage. There are many factors that cause excessive force on the cutter teeth. For example, the broach has insufficient chip space or the chip sump is severely blocked. The tooth lift on the broach cutter teeth is too large or uneven, the broach is bent, and the cutting edge is at various points. The broaching allowance is uneven, the radial rotation of the cutter teeth is large, the pre-made hole size of the workpiece is not suitable or the surface of the pre-made hole is too rough, the hard material of the workpiece material is too hard or the hardness of the material is too high, and the workpiece clamping is skewed.
In order to smooth the broaching and extend the service life of the broach, the following measures can be taken:
(1) Strictly control the manufacturing precision and quality of the broach, such as tool geometry and tooth lift. If the rake angle of the broach is not suitable, the back angle is too small or the blade width is too wide, the cutting conditions are poor, and the teeth are worn quickly. In severe cases, the broach is caught in the workpiece hole, and the broach is broken. The rake angle of the broach can usually be 5 ° ~ 18 °, take a large value when pulling the plastic material, take a small value when pulling the brittle material. The back angle of the broach can be 3 ° ± 3 0 ' on the cutting teeth and 1 ° ± 30 ' on the calibration teeth. 5〜0.6毫米。 The width of the blade is usually ≤ 0.2 mm, the cutting tooth is 0. 3mm, the calibration tooth is 0. 5 ~ 0.6mm.
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