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So complete! Common problems and improvement methods in CNC machining process

    I. Workpiece overcut

    1. Bounce the knife, the strength of the knife is not too long or too small, causing the knife to bounce.
    2. Improper operation by the operator.
    3. Uneven cutting allowance (eg: 0.5 on the side of the curved surface and 0.15 on the bottom)
    4. Improper cutting parameters (such as: tolerance too large, SF setting too fast, etc.)
    1. The principle of using a knife: it can be big or small, and it can be short or long.
    2. Add a corner cleaning program, and keep the margin as uniform as possible (the side and bottom margins should be the same).
    3. Reasonably adjust the cutting parameters, and round the corners with large allowance.
    4. Using the machine tool SF function, the operator can fine-tune the speed to achieve the best cutting effect of the machine tool.(Aluminummod Case)

    II. Midpoint problem

    1. Inaccurate when manually operated by the operator.
    2. There are burrs around the mold.
    3. The centring rod is magnetic.
    4. The four sides of the mold are not vertical.
    1. Manual operation should be carefully checked repeatedly, and the points should be at the same point and the same height as far as possible.
    2. Use a whetstone or a file to deburr around the mold, wipe it with a rag, and finally confirm it by hand.
    3. Demagnetize the centring rods before centring the mold. (use ceramic centring bars or others)
    4. Check whether the four sides of the mold are vertical with the calibration table. (if the verticality error is large, you need to review the plan with the fitter)

    III. Knife setting problem

    1. Inaccurate when manually operated by the operator.
    2. The tool is set incorrectly.
    3. The blade on the flying knife is wrong .(the flying knife itself has a certain error)
    4. There is an error between the R knife and the flat bottom knife and the flying knife.
    1. Manual operation should be carefully checked repeatedly, and the knife should be set at the same point as much as possible.
    2. Use an air gun to clean the tool or wipe it with a rag when clamping.
    3. One blade can be used when the blade on the flying knife needs to measure the shank and smooth bottom surface.
    4. A separate tool setting program can avoid the error between the R tool, the flat tool and the flying tool.(OEM CHASSIS METAL ENCLOSURE0

    IV. Collider - Programming

    1. The safety height is not enough or not set. (the tool or chuck hits the workpiece during rapid traverse G00)
    2. The tool on the program sheet and the actual program tool are wrongly written.
    3. The tool length (edge ​​length) and the actual machining depth on the program sheet are wrongly written.
    4. The depth Z-axis fetching and the actual Z-axis fetching on the program sheet are wrongly written.
    5. The coordinates are set incorrectly during programming.
    1. An accurate measurement of the height of the workpiece also ensures that the safety height is above the workpiece.
    2. The tool on the program list should be consistent with the actual program tool (try to use the automatic program list or use the picture to output the program list).
    3. Measure the actual depth of machining on the workpiece, and write the length of the tool and the length of the blade on the program sheet. (generally, the length of the tool holder is 2-3MM higher than the workpiece, and the length of the blade is 0.5-1.0MM)
    4. Take the actual number of Z axis on the workpiece and write it clearly on the program sheet. (This operation is generally written for manual operation and needs to be checked repeatedly).

    V. Collider - Operator

    1. Depth Z axis tool setting error.
    2. The number of touches and the wrong number of operands in the division .(for example: fetching a number from one side without a radius of infeed, etc.)
    3. Use the wrong tool (for example: D4 tool is processed with D10 tool)
    4. The program goes wrong. (eg: A7.NC goes to A9.NC)
    5. The handwheel is turned in the wrong direction during manual operation.
    6. Press the wrong direction during manual rapid traverse. (eg: -X press +X)
    1. The depth Z axis tool setting must pay attention to the position of the tool setting. (bottom, top, analysis, etc.)
    2. The number of hits in the score and the operands should be checked repeatedly after the completion of the operation.
    3. When clamping the tool, it should be checked repeatedly with the program sheet and the program, and then installed.
    4. The program should go one by one in order.
    5. When using manual operation, the operator should strengthen the operating proficiency of the machine tool.
    6. During manual rapid movement, the Z axis can be raised above the workpiece to move.

    VI. Surface Accuracy

    1. The cutting parameters are unreasonable and the surface of the workpiece is rough.
    2. The cutting edge of the tool is not sharp.
    3. The tool clamping is too long, and the blade avoidance is too long.
    4. Chip removal, air blowing, and oil flushing are not good.
    5. Program the tool pass method .(you can consider down milling as much as possible)
    6. The workpiece has burrs.
    1. The cutting parameters, tolerances, allowances, and speed feed settings should be reasonable.
    2. The tool requires the operator to check and change from time to time.
    3. When clamping the tool, the operator is required to clamp it as short as possible, and the blade should not be too long to avoid the air.
    4. For the lower cutting of flat knife, R knife and round nose knife, the speed and feed setting should be reasonable.
    5. The workpiece has burrs: it is directly related to our machine tool, cutting tool and cutting method. Therefore, we need to understand the performance of the machine tool and make up for the edge with burrs.

    VII. Chipping

    Reason and improvement:
    1. Feeding too fast.
    –Slow down to a suitable feed rate
    2. The feed is too fast at the beginning of cutting.
    –Slow down the feed rate at the start of cutting
    3. Clamp loose .(tool)
    4. Clamp loose. (workpiece)
    5. Insufficient rigidity .(tool)
    –Use the shortest knife allowed, the shank is a little deeper, and try down milling in addition
    6. The cutting edge of the tool is too sharp.
    –Change the fragile cutting edge angle, one edge
    7. Insufficient rigidity of machine tool and tool holder.
    –Use a rigid machine tool and tool holder

    VIII. Wear

    Reason and improvement:
    1. The machine speed is too fast.
    –Slow down, add enough coolant
    2. Hardened material.
    –Using advanced cutting tools and tool materials to increase surface treatment
    3. Chip adhesion.
    –Change the feed speed, chip size or clean the chips with cooling oil or air gun
    4. Improper feed rate. (too low)
    –Increase the feed rate and try down milling
    5. Inappropriate cutting angle.
    –Change to appropriate cutting angle
    6. The primary clearance angle of the tool is too small.
    –Changed to larger back angle


    Reason and improvement:
    1. Feeding too fast.
    — slow down the feed rate
    2. Too much cutting.
    –Use a smaller cutting amount per edge
    3. The blade length and overall length are too large.
    –The shank clamp is deeper, use a short knife, try down milling
    4. Too much wear.
    –Regrind at the initial stage

    X. Vibration pattern

    Reason and improvement:
    1. The feed and cutting speed are too fast.
    — Corrected feed and cutting speed
    2. Insufficient rigidity .(machine tool and tool holder)
    –Use a better machine tool and tool holder or change the cutting conditions
    3. The rear corner is too large.
    –Change to a smaller relief angle, and process the margin (grinding the edge with a whetstone)
    4. Clamping loose.
    –Clamp the workpiece

    ◆ Consider speed and feed

    The relationship between the three factors of speed, feed and depth of cut is the most important factor in determining the cutting effect. Inappropriate feed and speed often lead to reduced production, poor workpiece quality, and large tool damage.

    Use the low speed range for:
    High hardness material
    Willful material
    hard-to-cut materials
    heavy cutting
    Minimal tool wear
    longest tool life

    Use the high speed range for
    soft material
    better surface quality
    Smaller tool outer diameter
    light cutting
    Brittle workpiece
    Manual operation
    Maximum processing efficiency
    non-metallic material
    Use high feed rates for
    Heavy and rough cutting
    steel structure
    easy-to-process material
    roughing tool
    plane cutting
    low tensile strength material
    Coarse tooth milling cutter
    Use low feeds for
    light machining, fine cutting
    brittle structure
    difficult-to-machine materials
    small knife
    Deep groove machining
    High tensile strength material
    finishing tool

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