Causes of easy breakage of milling cutters
1. The main reasons for the fracture of high-precision milling cutters are improper cutting conditions, and the reasons for the high-precision milling cutter itself: uneven bottom of the blade, uneven shim, chipping of the cutting edge, cracks of the blade during manufacture, etc.
2. Reasons for the cutting process of high-precision milling cutters: When processing high-chromium, high-nickel, high-vanadium and other alloy cast iron materials, the working layer contains a large amount of high-hardness carbides, and the cutting process has a scratch effect on the blade, and the edge appears the gap. The constant impact of long-term cutting eventually makes the high-precision milling cutter insert unbearable, resulting in the breakage of the high-precision milling cutter insert.
3. When selecting the cutting depth, try to control that the cutting depth is not at half of the cutting edge. This point is a dangerous point where high-precision milling cutter inserts are prone to breakage. So how can the machine tool reduce the frequency of milling cutter breakage at this time?
Measures to improve the breakage of milling cutters
1. Improve the clamping method of the tool
Simulation calculation and fracture test research show that the clamping method of high-speed milling cutter inserts does not allow the use of normal friction clamping. Inserts with central holes, screw clamping methods, or special designed tool structures to prevent inserts from being thrown are used. fly.
The direction of the clamping force of the tool holder and the blade should be consistent with the direction of the centrifugal force. At the same time, the pre-tightening force of the screw should be controlled to prevent the screw from being damaged in advance due to overload. For small-diameter shank milling cutters, hydraulic chucks or thermal expansion and contraction chucks can be used to achieve high precision and high rigidity clamping.
2. Improve the dynamic balance of the tool
Improving the dynamic balance of the tool is of great help to improve the safety of the high-speed milling cutter. Because the unbalance of the tool will generate an additional radial load on the spindle system, the magnitude of which is proportional to the square of the rotational speed.
Suppose the mass of the rotating body is m, and the eccentricity between the center of mass and the center of the rotating body is e, then the inertial centrifugal force F caused by the unbalance is:
F=emω2=U(n/9549)2 In the formula: U is the unbalance of the tool system (g mm), e is the eccentricity of the center of mass of the tool system (mm), m is the mass of the tool system (kg), and n is the tool system Rotation speed (r/min), ω is the angular velocity of the tool system (rad/s).
It can be seen from the above formula that improving the dynamic balance of the tool can significantly reduce the centrifugal force and improve the safety of the high-speed tool. Milling cutters used for high-speed cutting must pass the dynamic balance test, and should meet the requirements of the G4.0 balance quality level or above specified by ISO1940-1.
3. Reduce the quality of the tool, reduce the number of tool components, and simplify the tool structure
The lighter the tool mass, the less the number of components and the contact surface of the components, and the higher the limit speed of tool breakage. The use of titanium alloy as the material of the cutter body reduces the mass of the components, and can improve the fracture limit and limit speed of the cutter. However, due to the sensitivity of titanium alloy to the incision, it is not suitable for manufacturing the cutter body, so some high-speed milling cutters have used high-strength aluminum alloy to manufacture the cutter body.
In addition, in the structure of the tool body, attention should be paid to avoid and reduce stress concentration. The grooves on the tool body (including tool seat grooves, chip grooves, and key grooves) will cause stress concentration and reduce the strength of the tool body. Therefore, it should be avoided as far as possible. The groove and groove bottom have sharp corners. At the same time, the structure of the cutter body should be symmetrical to the rotary axis, so that the center of gravity passes through the axis of the milling cutter. The clamping and adjustment structure of the insert and the tool holder should eliminate the clearance as much as possible, and require good repeatability of positioning.
