Measures to improve the safety of high speed milling cutter

According to the safety standard of high speed milling cutter and the analysis of finite element calculation model, in order to meet the safety requirements, the following measures can be taken:

1. reduce the quality of the tool, reduce the number of tool components, simplify the tool structure

The relationship between the breaking limit of different tools with the same diameter and the weight of the tool body, the number of tool members and the number of member contact surface is obtained by the test. It is found that the lighter the tool quality is, the fewer the number of tool members and the number of member contact surface is, and the higher the breaking limit speed is. It is found that using titanium alloy as the tool material can reduce the mass of the component and improve the breaking limit and limit speed of the tool. However, due to the sensitivity of titanium alloy to the incision, it is not suitable to manufacture the cutter body, so some high speed milling cutter have used high strength aluminum alloy to manufacture the cutter body.

In the structure of the cutter body, attention should be paid to avoid and reduce stress concentration. The grooves on the cutter body (including the cutter seat grooves, chip grooves and key grooves) will cause stress concentration and reduce the strength of the cutter body. Therefore, the groove and groove bottom with sharp angles should be avoided as far as possible. At the same time, the structure of the cutter body should be symmetrical to the axis of rotation, so that the center of gravity through the axis of the milling cutter. The clamping and adjusting structure of the blade and knife holder should eliminate clearance as far as possible, and require good repetitive positioning. At present, HSK tool holder has been widely used in high-speed milling cutter to connect with the spindle of machine tool, which greatly improves the stiffness and repeated positioning accuracy of the tool system, and is conducive to the improvement of the breaking limit speed of the tool. In addition, the diameter of the clamp type high speed milling cutter shows that the diameter is smaller and the number of cutter teeth is reduced, which is also conducive to the improvement of tool strength and stiffness.

 

2. Improve the clamping mode of the tool

The simulation calculation and fracture test show that the clamping method of high speed milling cutter insert is not allowed to adopt the usual friction force clamping method, and should use the blade with center hole, screw clamping method, or use the specially designed tool structure to prevent the blade from flying. The clamping force direction of knife holder and blade should be consistent with the centrifugal force direction, and the pre-tightening force of screw should be controlled to prevent the screw from being damaged in advance due to overload. For small diameter milling cutters with shank, hydraulic collet or thermal expansion and cold contraction collet can be used to achieve high precision and high stiffness of clamping.

3.Improve the dynamic balance of the tool

It is very helpful to improve the safety of high speed milling cutter to improve the dynamic balance of cutter. Because tool unbalance creates an additional radial load on the spindle system, the magnitude of which is proportional to the square of the rotational speed. Let the mass of the rotating body be m, and the eccentricity between the center of mass and the center of the rotating body be E, then the centrifugal force of inertia caused by unbalance F is:

F=emω2=U (n/9549) 2

Where: U is the unbalance of the tool system (g·mm), e is the eccentricity of the tool system centroid (mm), m is the mass of the tool system (kg), n is the speed of the tool system (r/min), and ω is the angular velocity of the tool system (rad/s).

It can be seen from the above equation that improving the dynamic balance of the tool can significantly reduce the centrifugal force and improve the safety of the high-speed tool. Therefore, according to the draft requirements of the standard, the milling cutter used for high speed cutting must pass the dynamic balance test, and should meet the requirements of THE G4.0 balance quality level of ISO1940-1.