Causes of overcutting of workpiece
Reasons
● The knife bounces. The knife is not strong enough or is too long or too small, causing the knife to bounce.
●Improper operation by the operator.
●Uneven cutting allowance (e.g. 0.5 on the side of the curved surface and 0.15 on the bottom surface)
● Improper cutting parameters (e.g. too large tolerance, too fast SF setting, etc.)
improvement methods
● Principles of using a knife: It can be big, not small; it can be short, not long.
●Add a corner cleaning program and keep the margins as even as possible (keep the margins on the sides and bottom consistent).
● Reasonably adjust cutting parameters and round the corners where there is a large margin.
●Using the machine tool SF function, the operator fine-tunes the speed to achieve the best cutting effect.
The problem of dividing
Reasons
●Inaccurate manual operation by the operator.
●There are burrs around the mold.
●The centering rod is magnetic.
●The four sides of the mold are not vertical.
Improvement methods
●Manual operations should be checked carefully and repeatedly, and the center should be at the same point and height as much as possible.
● Use an oil stone or file to remove burrs around the mold, then wipe it clean with a rag, and finally check it by hand.
● Demagnetize the centering rod before centering the mold (ceramic centering rod or other can be used).
●Calibrate to check whether the four sides of the mold are vertical (if the verticality error is large, you need to review the plan with the fitter).
Tool setting problems
Reasons
●Inaccurate manual operation by the operator.
●The tool is clamped incorrectly.
●The blade on the flying knife is wrong (the flying knife itself has a certain error).
●There is an error between the R knife, flat knife and flying knife.
Improvement methods
●Manual operation should be checked carefully and repeatedly, and the tool should be aligned at the same point as much as possible.
●When clamping the tool, blow it clean with an air gun or wipe it clean with a rag.
●When the blade on the flying cutter needs to measure the tool rod and the smooth bottom surface, one blade can be used.
● Create a separate tool setting program to avoid the error between R tool, flat tool and flying tool.
Collider – Programming
Reasons
●The safety height is not enough or is not set (the tool or chuck hits the workpiece during rapid feed G00).
●The tool on the program sheet and the actual program tool are written incorrectly.
●The tool length (edge length) on the program sheet and the actual machining depth are incorrectly written
●The depth Z-axis reading and the actual Z-axis reading on the program sheet are written incorrectly.
●The coordinate setting is wrong during programming.
Improvement methods
●Accurately measuring the height of the workpiece also ensures that the safe height is above the workpiece.
●The tool on the program sheet should be consistent with the actual program tool (try to use automatic program sheet or picture program sheet).
●Measure the actual processing depth on the workpiece, and write down the length of the tool and the blade length clearly on the program sheet (generally the tool clamp length is 2-3MM higher than the workpiece, and the blade length is 0.5-1.0MM).
● Take the actual Z-axis data on the workpiece and write it clearly on the program sheet. (This operation is usually a manual operation and needs to be checked repeatedly).
Collider-Operator
Reasons
●Depth Z-axis tool setting error.
● Errors in the number of collisions and operations during the division (such as: single-sided data acquisition without a cutting radius, etc.).
●Using the wrong tool (e.g. using a D10 tool to process a D4 tool).
●The program is wrong (for example: A7.NC goes to A9.NC).
●The hand wheel was turned in the wrong direction during manual operation.
● Press the wrong direction during manual rapid feed (e.g., -X presses +X).
Improvement methods
●When setting the tool in the depth Z axis, you must pay attention to the position of the tool. (bottom surface, top surface, analysis surface, etc.)
● Check repeatedly after completing the points and operations.
●When clamping the tool, check it against the program sheet and the program repeatedly before installing it.
●The procedures must be followed one by one in order.
●When using manual operation, the operator himself must improve his proficiency in machine operation.
●When moving quickly manually, you can first raise the Z axis to the top of the workpiece before moving.
Surface accuracy
Reasons
●The cutting parameters are unreasonable and the surface of the workpiece is rough.
●The cutting edge of the tool is not sharp.
●The tool clamping is too long, the blade clearance is too long, and the chip removal, air blowing and oil flushing are not good.
●Program the cutting method (try to consider forward milling).
●The workpiece has burrs.
Improvement methods
●The cutting parameters, tolerances, allowances, speed and feed settings should be reasonable.
●The cutting tools require the operator to check and replace them from time to time.
●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 air gap.
●For the downward cutting of flat knife, R knife and round nose knife, the speed feed setting should be reasonable.
●The workpiece has burrs: It is directly related to our machine tools, cutting tools, and cutting methods, so we need to understand the performance of the machine tools and make up for the burred edges.
Chipping edge
Causes and solutions
●Feeding too fast – slow down to a suitable feed speed.
● Feed too fast at the beginning of cutting – slow down the feed at the beginning of cutting
● Loose clamping (tool) – clamp.
● Loose clamping (workpiece) – clamp.
● Insufficient rigidity (tool) – try down milling with the shortest clamping depth allowed for the tool shank.
●The cutting edge of the tool is too sharp – change the fragile cutting edge angle, primary edge.
●The machine tool and tool holder are not rigid enough – use a machine tool and tool holder with good rigidity.
Wear
Causes and solutions
● Machine speed is too fast – slow down and add enough coolant.
● Hardened material – use advanced cutting tools and tool materials, and increase surface treatment methods.
● Chip adhesion – change the feed speed, chip size or use cooling oil or air gun to clean the chips.
● Inappropriate feed speed (too low) – increase the feed speed and try down milling.
● Inappropriate cutting angle – change to an appropriate cutting angle.
●The primary clearance angle of the tool is too small – change it to a larger clearance angle.
Destroy
Causes and Improvement Methods
● Feed too fast – slow down the feed speed.
● Cutting amount is too large – use a smaller cutting amount per blade.
● Blade length and total length are too large – clamp the shank deeper, use a shorter tool, and try down milling.
● Too much wear – grind again in the early stage.
Vibration
Causes and Improvement Methods
● Feed and cutting speed are too fast – correct feed and cutting speed
● Insufficient rigidity (machine tool and tool holder) – use better machine tool and tool holder or change cutting conditions
● Too large back angle – change to a smaller back angle, process the edge band (grind the edge once with an oilstone)
● Loose clamping – clamp the workpiece
● Consider speed and feed rate
Interrelationship
The relationship between the three factors of speed, feed rate and cutting depth is the most important factor in determining the cutting effect. Inappropriate feed rate and speed often lead to reduced production, poor workpiece quality and severe tool damage.
●Use the low speed range for:
High hardness materials, large dimensional materials, difficult-to-cut materials, heavy cutting, minimum tool wear, and maximum tool life.
●Use the high speed range for:
Soft materials, good surface quality, small tool diameter, light cutting, brittle workpieces, manual operation.
Maximum machining efficiency, non-metallic materials.
●Use high feed rates for:
Heavy, rough cutting, rigid structure, easy-to-process materials, rough machining tools, plane cutting, low tensile strength materials, coarse tooth milling cutters.
●Use low feed rates for:
Light machining, fine cutting, brittle structure, difficult-to-machine materials, small tools, deep groove processing, high tensile strength materials, and finishing tools.
