xiehe model

Turning slender shafts requires high geometrical accuracy and surface quality.

The workpiece is clamped between the spindle and the tailstock by conventional processing methods. There is no flexibility at either end. Under the influence of cutting force and thermal expansion, the workpiece produces internal stress and bending deformation, making it difficult to ensure straightness and dimensional accuracy. The reverse method is a method to overcome the above phenomenon. It is suitable for medium-speed rough machining and large-cut low-speed finishing. It has the characteristics of strong adaptability, low machine precision and high machining efficiency.

Process features:

(1) Change the process method to clamp the workpiece, change the surface contact to line contact, and reduce the conventional processing method of stress and deformation.

(2) The tip of the tail is changed to a flexible spring tip, which eliminates the forced bending of the workpiece due to thermal elongation.

(3) The three-jaw tool holder can better guarantee the centripetal parallel movement and prevent the chatter of the slender shaft during turning. (Note: Loosen the knife holder before processing, and then drive to eat the knife. Follow the knife holder quickly, do not retract the knife when touching the knife holder, adjust the strength of the blade bracket claw and the shaft surface, so as not to deform the top of the shaft, and the fit is too loose or too tight , The contact between the tool holder claw and the shaft surface is important, the shaft and the claw should be lubricated to prevent cutting, and can prevent the slender shaft from forming a bamboo shape.)

(4) Cut from the front end to the tailstock, the axial cutting force straightens the cutting part of the workpiece, and moves the part to be processed to the tailstock.

Tool Selection and Use

Due to the lack of rigidity of the extended shaft, the radial cutting force is required to be as small as possible. Therefore, the cutting edge of the tool is required to be sharp, the cutting is light, the chip removal is smooth, and the durability is high. The principle is to increase the rake angle and lead angle as much as possible without affecting the strength of the tool. Commonly used main deflection angle φ=75°～90°, rake angle γ=28°～30°. The carbide blade is yT15 and the handle is 45 high quality carbon steel. The main deflection angle φ=75°. The rake angle of the main cutting edge is γ=25°, the rake angle of the rib is 25°, and the chamfer is 0.4-0.8mm. Good chip breaking performance due to chamfer and R4mm chip breaker. At the same time, due to the increase of the tip angle, the tip strength and heat dissipation conditions are improved. The main relief angle of the turning tool is α=8°, the chamfering angle is 0.1-0.3mm, and the relief angle is -12°. This increases the contact area of the turning tool backing surface to support the workpiece and prevent internal structure of the workpiece material. Non-uniform sickling eliminates low frequency vibrations.

Fine turning tool.

The tool structure adopts elastic tool holder to reduce vibration and improve cutting conditions. The cemented carbide blade adopts YT15, and the tip of the knife should be 0.1mm lower than the center of the shaft. The blade is wider and the wiper blade is 8 to 10 mm.

The utility model can maintain a certain contact area between the turning tool and the shaft, and the cutting edge can be turned on the shaft to prevent the turning tool from being pinched when the turning force changes. The main deflection angle is small, forming thin and small deformation, which is beneficial to improve the surface finish of the machined surface, and the rake angle γ=30° makes the cutting light.

Choose a reasonable amount of cutting

In the reverse turning of the slender shaft, there are special requirements for the cutting amount. It requires the maximum feed rate F to increase the axial tensile stress of the workpiece and fundamentally prevent the vibration of the workpiece. However, the choice of cutting amount is limited by the geometric error of the machined surface. The selection sequence is usually: first take the maximum feed rate, then take the maximum tool amount ap, and finally take the maximum cutting speed v. Practice has proved that when the aspect ratio of the workpiece is 40 to 120, if v=40m/min, f is preferably 0.35 to 0.5mm/r; if v=45~100m/min, f should be 0.6~1.2mm/r should. In actual operation, the choice of cutting amount: during rough machining, the cutting speed is 50-60

m/min, feed rate 0.3-0.4 mm/r, depth of cut 1.5-2 mm; for finish turning, cutting speed 60-100m/min, feed rate 0.08-0.12mm/r, depth of cut 0.5- 1mm.