A Comprehensive Analysis of the Causes of Tool Collisions in CNC Machining Centers
Compared to ordinary machine tools, Cnc Machining Centers offer higher machining accuracy, better dimensional stability, lower labor intensity for workers, and are easier to manage in modern environments. However, due to improper operation or programming errors, the cutting tool or tool holder can easily collide with the workpiece or machine tool. This can result in minor damage to the cutting tool and the machined part, or more serious damage to machine tool components, leading to a loss of machining accuracy and even personal injury.
Therefore, from the perspective of maintaining accuracy, collisions between the cutting tool and the machine tool or workpiece are absolutely prohibited during the use of CNC machine tools. The causes of tool collisions are summarized and analyzed below. Because CNC machining centers use software for locking, during simulation machining, when the automatic run button is pressed, it is not directly visible on the simulation interface whether the machine tool is locked. Often, tool setting is not performed during simulation; if the machine tool is not locked during operation, tool collisions are highly likely. Therefore, before simulation machining, it is essential to check the running interface to confirm whether the machine tool is locked.
Forgetting to turn off the dry run switch during machining. During program simulation, the dry run switch is often left on to save time. Dry run refers to all machine tool axes running at G00 speed. If the dry run switch is not turned off during machining, the machine tool ignores the given feed rate and runs at G00 speed, causing tool breakage or machine collision accidents.
After the dry run simulation, there was no return to the reference point. During the calibration program, the machine tool is locked and stationary, while the tool is simulating machining relative to the workpiece (absolute and relative coordinates are changing). The coordinates do not match the actual position, so a return to the reference point method is necessary to ensure that the machine zero-point coordinates are consistent with the absolute and relative coordinates. If machining operations are performed without identifying the problem after the calibration program, tool collisions will occur. The direction of overtravel release is incorrect.
When the machine tool overtravels, the overtravel release button should be pressed and the tool moved in the opposite direction manually or by hand crank to clear the overtravel. However, if the release direction is reversed, it will damage the machine tool. This is because when the overtravel release button is pressed, the machine tool's overtravel protection will not function, and the overtravel protection limit switch will already be at the end of its travel range. This could cause the worktable to continue moving in the overtravel direction, eventually damaging the leadscrew and causing machine tool damage. Incorrect cursor position during specified line execution. When executing a specified line, execution usually starts from the cursor position and proceeds downwards.
For lathes, it's necessary to call the tool offset value of the tool being used. If the tool isn't called, the tool used in the program segment might not be the required tool, potentially causing a collision due to tool incompatibility. Of course, on machining centers and CNC milling machines, the coordinate system (such as G54) and the tool's length compensation value must be called first. Because each tool has a different length compensation value, failing to call it can also cause a collision.
As high-precision machine tools, CNC machining centers require robust collision protection. Operators must cultivate careful and meticulous habits, operating the machine tool correctly to minimize tool collisions. Technological advancements have led to the development of advanced technologies such as tool damage detection during machining, machine tool collision detection, and adaptive machining, which better protect CNC machine tools.
Programming error
The process arrangement was incorrect, the sequential relationship between processes was not considered thoroughly, and the parameter settings were incorrect.
- A. The coordinate system is set with the bottom as zero, but in practice, the top is set to 0.
- B. The safety height is too low, which prevents the tool from being fully lifted out of the workpiece;
- C. The allowance for the second roughing is less than that for the first cut;
- D. After the program is written, the program path should be analyzed and checked;
Error in program sheet remarks
- A. A single-sided collision number is written as a four-sided division;
- B. The vise clamping distance or workpiece protrusion distance is incorrectly marked;
- C. Tool collisions occur when the tool extension length is not clearly or incorrectly specified.
- D. The procedure sheet should be as detailed as possible;
- E. When a procedure sheet is changed, the principle of replacing the old with the new should be adopted: the old procedure sheet should be destroyed.
Tool measurement error
- A. The tool setting data input did not take the tool setting bar into account;
- B. The tool attachment point is too short;
- C. Tool measurement should use scientific methods and as precise instruments as possible;
- D. The tool length should be 2-5mm longer than the actual depth.
Program transmission error
- A. The program number is called incorrectly or the program has been modified, but the old program is still being used for processing.
- B. On-site processors must check the detailed data of the procedure before processing;
- C. For example, the time and date the program was written, and simulated using a bear.
Incorrect tool selection
The blank exceeds expectations
the blank is too large and doesn't match the blank set in the program.
The workpiece material itself has defects or excessive hardness.
Clamping factors, interference from the padding block
which was not considered in the program.