Analysis of 9 Causes of Tool Collision in CNC Machining Centers, Teaching You How to Prevent Collision

Compared to ordinary machine tools, CNC machining centers have high machining accuracy, good dimensional stability, low labor intensity for workers, and are convenient for modern management. However, due to improper operation or programming errors, it is easy for the tool or tool holder to collide with the workpiece or machine tool. In mild cases, it can damage the tool and the processed parts, in severe cases, 

it can damage the machine tool components, cause a loss of machining accuracy, and even cause personal accidents. Therefore, from the perspective of maintaining accuracy, it is strictly prohibited for cutting tools to collide with th machine tool or workpiece during the use of CNC machine tools. Below is a summary and analysis of the causes of knife collision.

Due to the CNC machining center being locked using software, it is not visually visible on the simulation interface whether the machine tool is locked when the automatic operation button is pressed during simulation processing. During simulation, the tool is often not aligned, and if the machine tool is not locked in operation, it is very easy to collide with the tool. 

So before simulating machining, you should go to the running interface to confirm whether the machine tool is locked. Forgot to turn off the idle running switch during processing. Due to the fact that during program simulation, the idle running switch is often turned on to save time. Idle operation refers to the operation of all motion axes of the machine tool at G00 speed. 

If the operation switch is not turned off during processing, the machine tool will ignore the given feed speed and operate at G00 speed, resulting in accidents such as cutting and collision with the machine tool. When verifying the program, the machine tool is locked and cannot move, while the tool relative to the workpiece processing is in simulation operation (absolute and relative coordinates are changing).

 At this time, the coordinates do not match the actual position, and the method of returning the reference point must be used to ensure that the mechanical zero point coordinates are consistent with the absolute and relative coordinates. If no problems are found after verifying the program and processing is carried out, it will cause tool collision. The direction of overtravel release is incorrect.

When the machine tool overtravels, the overtravel release button should be held down and moved in the opposite direction manually or manually to eliminate it. But if the direction of release is reversed, it will cause damage to the machine tool.

 Because when the overtravel release is pressed, the overtravel protection of the machine tool will not work, and the travel switch of the overtravel protection is already at the end of the travel. At this point, it is possible to cause the workbench to continue moving towards the overtravel direction, ultimately damaging the screw and causing damage to the machine tool. 

The cursor position during the specified line operation is incorrect. When specifying a row to run, it is often executed downwards from the position of the cursor. For a lathe, it is necessary to call the tool offset value of the tool used. 

If the tool is not called, the tool running the program section may not be the desired tool, which is highly likely to cause tool collision accidents due to different tools. Of course, on machining centers and CNC milling machines, it is necessary to first call the coordinate system such as G54 and the length compensation value of the tool. Because the length compensation value of each knife is different, if not called, it may also cause a knife collision.

CNC machining center CNC machine tools, as high-precision machine tools, collision prevention is very necessary. Operators are required to develop a habit of being careful, careful, and operate the machine tool in the correct way to reduce the occurrence of tool collision. 

With the development of technology, advanced technologies such as tool damage detection during machining, collision prevention detection of machine tools, and adaptive machining of machine tools have emerged, which can better protect CNC machine tools.

To sum up, there are 9 reasons:

(1) Programming error

The process arrangement is incorrect, the process acceptance relationship is not carefully considered, and the parameter settings are incorrect.

Example: 

A. The coordinate is set to zero at the bottom, but in reality, it is set to zero at the top;

B. The safety height is too low, resulting in the tool not being able to fully lift out of the workpiece;

C. The second opening has less rough margin than the previous knife;

D. After the program is written, the path of the program should be analyzed and checked;

(2) Program note error

Example: 

A. Write a unilateral collision number as a quadrilateral partition;

B. Incorrect labeling of the clamping distance of the vise or the protrusion distance of the workpiece;

C. Inadequate or incorrect remarks on the extension length of the tool result in tool collision;

D. The program list should be as detailed as possible;

E. When changing the program, the principle of replacing the old with the new should be adopted: the old program should be destroyed.

(3) Tool measurement error

Example:

 A. The input of tool setting data does not consider the tool holder;

B. The tool installation is too short;

C. Scientific methods should be used for tool measurement, and more accurate instruments should be used as much as possible;

D. The installation length should be 2-5mm longer than the actual depth.

(4) Program transfer error

Program number call error or program modification, but still using old program for processing;

The on-site processor must check the detailed data of the program before processing;

For example:

 the time and date when the program was written and simulated using the bear race.

(5) Tool selection error

(6) The blank exceeds the expected size and does not match the programmed blank

(7) The workpiece material itself has defects or high hardness

(8) Clamping factors, interference with cushion blocks, not considered in the program

(9) Machine tool malfunction, sudden power outage, lightning strike causing tool collision, etc