Common CNC Machining Issues: Do You Know How to Solve Them?

Common CNC Machining Issues: Do You Know How to Solve Them?

 

1. Overcutting of the Workpiece:

Causes:

1. Tool deflection,The tool lacks sufficient strength or is too long or small, causing deflection.
2. Operator error.
3. Uneven cutting allowance (e.g., 0.5 mm left on the side of a curved surface, but only 0.15 mm left on the bottom).
4. Improper cutting parameters (e.g., large tolerance, excessively fast SF setting).

Improvements:

1. Tool selection principle: Use a larger, shorter tool when possible.
2. Add a corner cleaning program and keep the allowance as even as possible (ensure the side and bottom allowances are the same).
3. Adjust cutting parameters reasonably and round sharp corners in large allowance areas.
4. Utilize the machine’s SF function and allow the operator to fine-tune the speed for optimal cutting performance.

2. Coordinate System Alignment Issues:

Causes:

1. Inaccurate manual operation by the operator.
2. Burrs around the mold.
3. Magnetic centering rod.
4. Mold sides are not perpendicular.

Improvements:

1. Manual operation should be repeatedly checked, and centering should be done at the same point and height.
2. Use a whetstone or file to remove burrs around the mold, wipe clean with cloth, and confirm by hand.
3. Demagnetize the centering rod before use (ceramic centering rods or other alternatives can also be used).
4. Check if the mold sides are perpendicular with a dial indicator (significant deviations should be discussed with the mold technician).

3. Tool Offset Issues:

Causes:

1. Inaccurate manual operation by the operator.
2. Incorrect tool clamping.
3. Errors in the fly cutter blade (the fly cutter itself has some inherent errors).
4. Discrepancies between R-tool, flat-end tool, and fly cutter.

Improvements:

1. Manual operations should be thoroughly checked, and the same point should be used for tool setting.
2. Clean the tool holder with an air gun or wipe with a cloth before clamping.
3. Measure the tool holder when using a fly cutter; for flat surfaces, use only one blade.
4. Create a separate tool-setting program to avoid discrepancies between R-tools, flat tools, and fly cutters.

4. CNC Crash – Programming

Causes:

1. Insufficient or missing safe height (during rapid feed G00, the tool or chuck collides with the workpiece).
2. Mismatch between the tool specified in the program sheet and the actual tool in the program.
3. Incorrect tool length (cutting edge length) on the program sheet versus the actual machining depth.
4. Discrepancy between the Z-axis values in the program sheet and the actual Z-axis readings.
5. Incorrect coordinate settings during programming.

Improvements:

1. Accurately measure the workpiece height and ensure the safe height is above the workpiece.
2. Ensure the tool specified in the program sheet matches the actual tool (preferably use automated program sheets or include images).
3. Measure the actual machining depth on the workpiece and clearly note the tool length and cutting edge length on the program sheet (typically, the tool holder should be 2-3 mm higher than the workpiece, with a clearance of 0.5-1.0 mm for the cutting edge).
4. Use the actual Z-axis reading from the workpiece and note it clearly in the program sheet (this is usually done manually and should be checked repeatedly).
5. Ensure the correct coordinate settings are used during programming.

5. CNC Crash – Operator:

Causes:

1. Incorrect Z-axis tool setting depth.
2. Incorrect centering or data entry (e.g., failure to account for tool radius when measuring from one side).
3. Using the wrong tool (e.g., using a D10 tool instead of a D4 tool).
4. Running the wrong program (e.g., running A7.NC instead of A9.NC).
5. Incorrect manual control direction on the handwheel.
6. Wrong direction during manual rapid feed (e.g., pressing +X instead of -X).

Improvements:

1. Pay attention to the tool setting depth for different positions (bottom, top, analyzed surface, etc.).
2. Repeatedly check centering and data entry after completing these steps.
3. When clamping the tool, double-check it against the program sheet before installation.
4. Run programs one at a time in sequence.
5. Operators should improve their machine operation skills for manual control.
6. Raise the Z-axis above the workpiece before moving during manual rapid feed.

6. Curved Surface Precision:

Causes:

1. Inappropriate cutting parameters, resulting in rough surfaces.
2. Dull tool edges.
3. Tool clamping is too long, or the cutting edge is too far from the workpiece.
4. Poor chip removal, air blow, or coolant flow.
5. Programming feed path issues (try to use climb milling where possible).
6. Burrs on the workpiece.

Improvements:

1. Set reasonable cutting parameters, tolerances, allowances, and feed rates.
2. Operators should periodically check and replace tools as needed.
3. The tool’s extension length should be minimized as much as possible while meeting machining requirements, to avoid excessive tool overhang.
4. For flat tools, R-tools, and round-nose tools, set appropriate speeds and feed rates.
5. Burrs on the workpiece: This is directly related to the machine, tool, and feed path. Therefore, understanding the machine’s performance is crucial, and additional passes may be needed to remove burrs from the edges.