CNC Knowledge: Too complete! Common problems and improvement methods in CNC machining process

1. Overcutting the part

reason:

• Knife kickback, the tool is not sturdy enough and is too long or too small, causing the knife to bounce back.

• Bad operation on the part of the operator.

• The cutting margin is uneven. (For example: leave 0.5 on the side of the curved surface and 0.15 on the bottom)

• Incorrect cutting parameters. (For example: tolerance is too large, SF adjustment is too fast, etc.)

improve:

• The principle of using a knife: it can be big but not small, it can be short but not long.

• Add the process of cleaning the corners and try to keep the rest as uniform as possible. (Leave the same margin on the sides and bottom)

• Adjust the cutting parameters reasonably and round the corners with large margins.

• Using the machine’s SF function, the operator adjusts the speed to achieve optimal cutting results.

2. The question of grading

reason:

• Inaccuracy when operated manually by the operator.

• There are burrs around the mold.

• The central rod is magnetic.

• The four sides of the mold are not vertical.

improve:

• Manual operations should be carefully checked repeatedly, and the points should be at the same point and height as much as possible.

• Use a sharpening stone or file to remove the burrs around the mold, wipe it with a cloth and finally confirm with your hands.

• Before centering the mold, first demagnetize the centering rod. (Ceramic centering rod or other available)

• Calibrate the meter to check if all four sides of the mold are vertical. (If the verticality error is significant, please review the plan with the installer)

3. Tool setting problem

reason:

• Inaccuracy when operated manually by the operator.

• The tool is loose.

• The blade of the flying knife is fake. (The flying knife itself has some errors)

• There is an error between the R knife, the flat knife and the flying knife.

improve:

• Manual operations should be carefully checked several times, and the knife should be adjusted to the same point as much as possible.

• When the tool is tight, clean it with an air gun or wipe it with a cloth.

• When the blade of the flying knife needs to be measured on the toolbar and the bottom surface is smooth, a blade can be used.

• A separate tool setting program can avoid the error between R knife, flat knife and flying knife.

4. Collision programming

reason:

• The safety height is not sufficient or not adjusted. (The knife or chuck hits the workpiece during rapid stroke G00)

• The program list tool and the actual program tool are poorly written.

• The tool length (blade length) and actual machining depth on the program sheet are incorrect.

• Depth Z-axis recovery and actual Z-axis recovery are written incorrectly on the program sheet.

• The coordinates are incorrectly defined during programming.

improve:

• Accurately measuring the height of the room also ensures that the safe height is above the room.

• The tool on the program list must be consistent with the tool in the actual program. (Try to use automatic program list or use images to generate program list)

• To measure the actual processing depth on the workpiece, add WeChat: Yuki7557 to receive a copy of the macro program tutorial, and clearly note the length and tool blade length on the program sheet. (Generally, the length of the tool pliers is 2-3mm longer than the workpiece, and the length of the blade is 0.5-1.0mm)

• The actual Z axis number on the part must be clearly written on the program sheet. (This operation is usually written manually and must be checked several times)

5. Collision operator

reason:

• Z axis tool depth adjustment error.

• The number of points is reached and the operation is incorrect. (For example: unilateral recovery without feed radius, etc.)

• Bad knife. (For example: D4 knife is processed with D10 knife)

• The program went wrong. (For example: A7.NC changed to A9.NC)

• The steering wheel is turned in the wrong direction during manual operation.

• Tap in the wrong direction during manual fast traverse. (For example: -X press +X)

improve:

• When performing deep tool adjustment on the Z axis, you need to pay attention to where the tool is set. (Bottom surface, upper surface, analysis surface, etc.)

• The number of strokes and operations should be checked repeatedly after completion.

• When tightening the tool, check it several times with the program sheet and program before installing it.

• The procedure must be followed one by one in order.

• When using manual operation, the operator himself must improve his skills in operating the machine tool.

• During rapid manual movement, the Z axis may be raised above the part before moving.

6. Surface precision

reason:

• The cutting parameters are unreasonable and the workpiece surface is rough.

• The edge of the knife is not sharp.

• Tool clamping time is too long and blade clearance is too long.

• Chip removal, air blowing and oil flushing are not good.

• Path of the programming tool. (You may consider milling as much as possible)

• The part has burrs.

improve:

• Cutting parameters, tolerances, allowances, speed and feed settings should be reasonable.

• The tool requires the operator to check and replace it from time to time.

• When tightening the tool, the operator should keep the clamp as short as possible and the blade should not be too long to avoid air.

• For downward cutting with flat knives, R knives and round nose knives, the speed and feed settings should be reasonable.

• The part has burrs: they are directly linked to our machine tools, tools and tool feeding methods. Therefore, we need to understand the performance of the machine tool and compensate for the edges with burrs.

7. Broken blade

Reasons and improvements:

Feeding too quickly

—Slow down to an appropriate feed rate

Feed too fast at start of cut

—Slow the feed rate at the start of the cut

Loose tightening (tool)

—Tightening

Loose tightening (piece)

—Tightening

Insufficient rigidity (tool)

—Use the shortest knife allowed, grip the handle deeper, and try milling.

The edge of the tool is too sharp

—Change the angle of the fragile cutting edge, the main edge

The machine tool and tool holder are not rigid enough

—Use machine tools and rigid tool holders

8. Wear and tear

Reasons and improvements:

Machine speed is too fast

—Slow down and add enough coolant

hardened material

—Use advanced cutting tools and tool materials to increase surface treatment methods

Chip adhesion

—Change the feed speed, chip size or use cooling oil or air gun to clean the chips

Incorrect feed speed (too low)

—Increase feed rate and try to reduce milling

Incorrect cutting angle

—Change for proper cutting angle

The main clearance angle of the tool is too small

— Switch to a greater backrest angle

9. Destruction

Reasons and improvements:

Feeding too quickly

—Slow down the feed rate

Too much cutting

—Use a smaller amount of cut per edge

Blade length and overall length are too long

– Tighten the handle deeper, use a shorter knife and try countersinking.

Too much wear

—Regrinded in early stages

10. Vibration marks

Reasons and improvements:

Feed and cutting speed are too fast

—Correct feed and cutting speed

Insufficient rigidity (machine tool and tool holder)

—Use better machine tools and tool holders or change cutting conditions

The back corner is too big

—Switch to a smaller draft angle and process the edge (use a whetstone to sharpen the edge once)

The tightening is loose

— Tighten the part

◆ Consider feed speed and quantity

The relationship between the three factors of speed, feed and cutting depth is the most important factor in determining the cutting effect. Improper feed and speed often result in reduced production, poor part quality, and serious tool damage.

Use the low speed range to:

High hardness material

A capricious material

Materials that are difficult to cut

Heavy cut

Minimal tool wear

longest tool life

Use the high speed range to

Soft material

better surface quality

Smaller tool outer diameter

light cut

Fragile parts

manual operation

Maximum processing efficiency

non-metallic materials

Use high feed rates to

Heavy, coarse cut

steel structure

Easy to process materials

roughing tools

Plane cut

low tensile strength material

Large tooth cutter

Use a low power supply to

Light machining, fine cutting

fragile structure

Difficult to process materials

Small knives

Machining deep vertical grooves

High tensile strength material

Finishing tools