Introduction of tool safety measures

Mon Jul 04 11:52:04 CST 2022

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

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

The results show that the lighter the cutting tool mass is, the less the number of components and the contact surfaces are, and the higher the limit speed of tool fracture is. It is found that using titanium alloy as tool body material can reduce the mass of the component and increase the fracture limit and limit speed of the tool. But because of the sensitivity of titanium alloy to the incision, it is not suitable to manufacture the cutter body, so some high speed milling cutter has 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 groove, chip groove, keyway) will cause stress concentration, reduce the strength of the cutter body, so we should try to avoid through groove and groove bottom with sharp Angle. At the same time, the structure of the cutter body should be symmetrical to the rotating axis, so that the center of gravity through the axis of the milling cutter. The clamping and adjusting structure of the insert and tool holder should eliminate the clearance as far as possible, and the repetitive positioning is required. HSK shank has been widely used in high speed milling cutters to connect with the spindle of machine tools, which greatly improves the rigidity of the cutting tool system and the repeated positioning accuracy, and is conducive to the improvement of the cutting tool breaking limit speed. In addition, the diameter of machine clip type high speed milling cutter shows the development trend of smaller diameter and fewer teeth, which is also conducive to the improvement of tool strength and stiffness.

2. Improve the clamping method of cutting tools

The results of simulation and fracture test show that the clamping method of high speed milling cutter insert is not allowed to use the usual friction force, but to use a insert with a center hole, screw clamping method, or a specially designed tool structure to prevent the insert from flying. The clamping force direction of the insert seat and insert should be the same as that of the centrifugal force. At the same time, the pre-tightening force of the screw should be well controlled to prevent the screw from being damaged in advance due to overload. For small diameter handle milling cutter, hydraulic chuck or thermal expansion cold contraction chuck can be used to achieve high precision and high stiffness.

3. Improve tool dynamic balance

Improving the dynamic balance of cutter is very helpful to improve the safety of high speed milling cutter. This is because the cutting tool unbalance imposes an additional radial load on the spindle system proportional to the square of the rotational speed.

If 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 unbalance is:

F=emω2=U (n/9549) 2

Where: U is the tool system unbalance (g·mm), E is the tool system centroid eccentricity (mm), M is the tool system mass (kg), N is the tool system speed (R /min), ω is the tool system angular velocity (rad/s).

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