CNC -bearbejdningsproces almindelige problempunkter og forbedringsmetoder

2021/08/04



A. Workpiece overcut

Cause.
Play knife, tool strength is not long enough or too small, resulting in the tool play knife.
Improper operation of the operator.
Cutting allowance is not uniform. (e.g.: the side of the surface left 0.5, the bottom surface left 0.15)
Improper cutting parameters. (e.g., tolerance too large, SF set too fast, etc.)

Improvement.
Use knife principle: can be large, not small, can be short, not long.
Add corner cleaning procedures, and leave an even margin as much as possible. (Side and bottom margin left the same)
Reasonable adjustment of cutting parameters, the margin of large corners rounding.

Use the machine SF function, the operator fine-tune the speed so that the machine cutting to achieve the best results.


 Second, the division of the problem
Cause.
Operator manual operation is not accurate.
Burrs around the mold.
The centering bar is magnetic.
The four sides of the mold are not perpendicular.

Improvement.
Manual operation should be double checked repeatedly and the parting should be at the same height at the same point as far as possible.
Use oil stone or file to remove the burr around the mold and wipe it clean with a rag, and finally confirm by hand.
Demagnetize the centering bar before centering the mold. (Available ceramic centering rod or other)
Calibration table to check whether the four sides of the mold is vertical. (Perpendicularity error is large need to review the program with the clampers)

Third, the knife problem
Cause.
Operator manual operation is not accurate.
Tool clamping error.
Flying knife on the blade is wrong. (The flying knife itself has a certain error)
There is an error between R-knife and flat bottom knife and flying knife.


Improvement.
Manual operation should be repeatedly double-checked, and the pair of knives should be at the same point as far as possible.
Tool clamping with a wind gun to blow clean or rags to wipe clean.
Flying knife on the blade to measure the tool bar, light bottom surface when available a blade.
Separate out a pair of knife program, can avoid the error between the R knife flat knife flying knife.

Fourth, the collision machine - programming
Cause.
Safety height is not enough or not set. (Fast feed G00 when the knife or collet hit the workpiece)
The tool on the program list and the actual program tool is written wrong.
The tool length (edge length) on the program sheet and the actual depth of machining are wrongly written.
Wrong number of depth Z-axis on the program list and the actual Z-axis.
Incorrect setting of coordinates during programming.

Improvement.
Make an accurate measurement of the height of the workpiece also to ensure that the safety height is above the workpiece.
The tool on the program sheet and the actual program tool should be the same. (Try to use automatic program sheet or program sheet with pictures) Add WeChat: Yuki7557 send a macro program tutorial
Measure the actual depth of machining on the workpiece, and write down the length and edge length of the tool on the program sheet. (General tool clamping length 2-3MM higher than the workpiece, the blade length to avoid empty 0.5-1.0MM)
Take the actual Z-axis number on the workpiece and write it clearly on the program sheet. (This operation is generally a manual operation to write a good to double check)

V. Collision machine - operator
Cause.
Depth Z-axis tool alignment error-.
Score in touch with the number and manipulate the number of errors. (such as: single-sided take the number of no radius into the tool, etc.)
Using the wrong knife. (e.g.: D4 tool is used to process with D10 tool)
Wrong program. (Such as: A7.NC go A9.NC)
Wrong direction of handwheel during manual operation.
Press the wrong direction during manual rapid feed. (For example: -X press +X)

Improvement.
Depth Z-axis tool setting must pay attention to what position the tool is on. (bottom surface, top surface, analysis surface, etc.)
Dividing in the number of touches and manipulation number to be repeatedly checked after completion.
When clamping the tool should be repeatedly checked against the program list and the program before loading.
The procedure should be done one by one and in order.
When using manual operation, the operator himself should strengthen the proficiency of the machine tool operation.

When moving manually and quickly, the Z-axis can be raised to the top of the workpiece before moving.


 VI. Surface accuracy
Cause.
Cutting parameters are not reasonable, the surface of the workpiece surface roughness -.
The tool edge is not sharp.
The tool clamping is too long, and the tool edge is too long to avoid empty.
Chip evacuation, blowing, flushing oil is not good.
Programming the way of tool walking. (You can try to consider to take the smooth milling)
The workpiece has burrs.


Improvement.
Cutting parameters, tolerances, allowances, speed feed settings should be reasonable.
The operator is required to check the tool from time to time and replace it from time to time.
The operator is required to clamp the tool as short as possible, and the cutting edge should not be too long to avoid empty.
For flat knife, R knife, round nose knife undercutting, the speed feed setting should be reasonable.

The workpiece has burrs: the root of our machine tool, tool, the way to go directly related to the tool. 

So we need to understand the performance of the machine tool, the side of the burr to make up for it.


Seven, chipping edge
Causes and improvements.
Feeding too fast - slow down to a suitable feed rate
Feed too fast at the beginning of cutting - slow down the feed rate at the beginning of cutting
Loose clamping (tool) - Clamping
Loose clamping (workpiece) - Clamping
Insufficient stiffness (tool) - Use the shortest allowed tool, clamp the shank deeper, and try down milling
Cutting edge of the tool is too sharp -Change the fragile cutting edge angle, one edge
Insufficient rigidity of the machine and toolholder - Use a rigid machine and toolholder

Eight, wear and tear

Causes and improvements.
Machine speed is too fast -slow down, add enough coolant
Hardening materials - use advanced tools, tool materials, increase the surface treatment
Chip adhesion - change the feed rate, chip size or use cooling oil or air gun to clean up the chips
Improper feed rate (too low) -Increase feed rate, try down milling
Cutting angle is not suitable -Change to proper cutting angle
Tool's primary back angle is too small -Change to a larger back angle
 Nine, damage
Cause and improvement.
Feed too fast -slow down the feed rate
Cutting volume is too large - Use a smaller cutting volume per edge
The edge length and full length is too large -Shank clamp deeper, use a shorter cutter, try to smooth milling
Wear is too large - regrind at the beginning
 Ten, vibration pattern
Cause and improvement.
Feed and cutting speed is too fast - correct the feed and cutting speed
Insufficient rigidity (machine tool and toolholder) - Use better machine tool and toolholder or change the cutting conditions
The back angle is too large - change to a smaller back angle, processing edge band (use oil stone to sharpen the edge once)
Loose clamping - Clamp the workpiece
 ◆ Consider speed and feed
The interrelationship between the three factors of speed, feed and depth of cut is the most important factor in determining the cutting effect. Unsuitable feed and speed often lead to lower production, poor workpiece quality and large tool damage.
The use of low speed ranges for
high hardness materials
capricious materials
Difficult to cut materials
Heavy cutting
Minimum tool wear
Longest tool life

Use high speed range for
Soft materials
Better surface quality
Smaller tool outside diameter
Lighter cutting
Brittle workpieces
Manual operation
Maximum machining efficiency
Non-metallic materials

Use high feeds for
Heavy, rough cutting
Steel construction
Easy to machine materials
Roughing tools
Flat cutting
Low tensile strength materials
Rough milling tools

Use low feeds for
Light machining, fine cutting
Brittle structures
Difficult to machine materials
Fine tools
Deep vertical groove machining
High tensile strength materials
Finishing tools