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YIJIN Hardware Drilling Processing Common Problems and Solutions
In CNC machining, holes are the most common and most basic machining elements. There are many ways to machine a hole, we can drill, turn, boring, mill, discharge, and more.
Among them, drilling is the most common hole processing method, and the tool that realizes drilling is called drill bit.
Today, experts from Yijin Hardware will share some common problems in drilling processing. You are welcome to take a look at how Yijin Hardware can face and properly solve these problems.
Deep Hole Drilling
Deep hole drilling is the most difficult and most problematic process in drilling. Generally, the depth of the hole is more than 5 times the diameter of the drill bit, which is called “deep hole”, which must process in the deep hole drilling machine or special equipment to complete processing.
Otherwise, it is very likely that the hole diameter will be reduced or increased, the reaming hole is not round or the hole position accuracy is too poor, the inner hole surface is rough or the inner hole surface has obvious edges, the center line after reaming is not straight, and the service life of the reamer is low.
Reasons for shrinkage: too low cutting speed; too large feed; too small main declination angle of reamer; inappropriate selection of cutting fluid; when sharpening, the worn part of the reamer is not worn off, and the elastic recovery reduces the aperture; when reaming steel parts, If the allowance is too large or the reamer is not sharp, it is easy to produce elastic recovery, which reduces the aperture and the inner hole is not round, and the aperture is unqualified.
Reasons for Increase: Cutting speed is too high; Improper feed rate or excessive machining allowance; The main declination angle of the reamer is too large, and the reamer is bent; Chip edge adhered to the reamer cutting edge; When sharpening, the swing of the reaming cutting edge is out of tolerance; Inappropriate selection of cutting fluid; When installing the reamer, the oil on the surface of the taper shank is not wiped clean or the taper surface is bumped; After the flat tail of the taper shank is offset into the machine tool spindle, the taper shank taper interferes; The main shaft is bent or the main shaft bearing is too loose or damaged; Reamer floating is not flexible;When the axis is different from the workpiece and the force of both hands is uneven when reaming by hand, the reamer shakes from side to side.
Solutions: Appropriately reduce the outer diameter of the reamer according to the specific situation; Reduce the cutting speed to properly adjust the feed or reduce the machining allowance; Appropriately reduce the main declination angle to straighten or scrap the unusable reamer that is bent; Carefully trimmed with whetstone to pass; The control swing is within the allowable range; Choose cutting fluid with better cooling performance; Before installing the reamer, the reamer taper shank and the inside of the taper hole of the machine tool must be wiped clean, and the taper surface with bumps must be polished with whetstone; Grinding the reamer flat tail to adjust or replace the spindle bearing; Readjust the floating chuck and adjust the coaxiality.
Causes: The reamer is too long, the rigidity is insufficient, and vibration occurs during reaming; The main declination angle of the reamer is too small; The reaming cutting edge is narrow; Reaming allowance deviation; There are gaps and cross holes on the surface of the inner hole; Blisters and pores on the surface of the hole; The spindle bearing is loose, there is no guide sleeve, or the clearance between the reamer and the guide sleeve is too large, and the workpiece is deformed after being removed due to the thin-walled workpiece being clamped too tightly. Guide sleeve wear; The bottom end of the guide sleeve is too far from the workpiece; Short guide sleeve length, poor accuracy and loose spindle bearings.
Solutions: Replace the reamer with unequal pitch, use a longer and more precise guide sleeve and replace it regularly, repair the machine tool in time, and adjust the spindle bearing clearance. The reamer is installed with rigid connection to increase the main declination angle; Select qualified reamer to control hole position tolerance in pre-machining process;
When using an equal-pitch reamer to ream more precise holes, the spindle clearance of the machine tool should be adjusted, and the matching clearance of the guide sleeve should be higher or an appropriate clamping method should be used to reduce the clamping force.
Causes: The drilling deflection before reaming, especially when the hole diameter is small, cannot correct the original curvature due to the poor rigidity of the reamer; The main declination angle of the reamer is too large; Poor guidance makes the reamer easy to deviate from the direction during reaming; The reverse taper of the cutting part is too large; The reamer is displaced at the gap in the middle of the interrupted hole; When hand reaming, too much force in one direction forces the reamer to deviate to one end and destroys the verticality of the reaming hole; The reaming allowance is too large; The rear angle of the cutting part of the reamer is too large; The reaming cutting edge is too wide; There are air holes, sand holes on the surface and large spindle swing difference.
Solutions: reduce cutting speed; Select cutting fluid according to deep hole machining material; Appropriately reduce the main declination angle and correctly sharpen the reaming cutting edge; Appropriately reduce the reaming allowance; Improve the position accuracy and quality of the bottom hole before reaming or increase the reaming allowance; Select qualified reamer; grinding edge width; According to the specific situation, reduce the number of reamer teeth, increase the space of the chip groove or use a reamer with an inclination angle to make the chip removal smooth; Replace the reamer regularly, and remove the grinding area when sharpening; During sharpening, use and transportation of the reamer, protective measures should be taken to avoid bumps; For the damaged reamer, use extra-fine whetstone to repair the damaged reamer, or replace the reamer; Trim with whetstone to qualify, and use a reamer with a rake angle of 5°-10°.
Causes: The reaming allowance is too large; The hardness of the workpiece material is too high; The swing difference of the cutting edge is too large, and the cutting load is uneven; The main declination angle of the reamer is too small, which increases the cutting width; When reaming deep holes or blind holes, there are too many chips, which are not removed in time, and the teeth are cracked during sharpening.
Solutions: Modify the pre-machined hole size; Reduce the hardness of the material or switch to a negative Angle reamer or carbide reamer; The control swing is within the qualified range; Increase the main declination angle;Pay attention to remove chips in time or use a reamer with an edge angle; Pay attention to the sharpening quality.
Causes: The reaming allowance is too large; When reaming taper holes, the allocation of rough and fine reaming allowances and the selection of cutting amount are not appropriate; The chip space of the reamer teeth is small, and the chips are blocked.
Solutions: Modify the pre-machined hole size; Modify the allowance allocation and choose the cutting amount reasonably; Reduce the number of reamer teeth, increase the chip space or grind the gap between the cutter teeth by one tooth.
The cutting of the drill is carried out in a hole with a narrow space, and the chips must be discharged through the groove of the drill, so the shape of the chip has a great influence on the cutting performance of the drill. Common chip shapes include flake chips, tubular chips, needle chips, conical spiral chips, ribbon chips, fan chips, powder chips, etc.
Causes：The feed rate is too small, the chisel edge of the drill bit is worn or the angle is unreasonable; No professional chip breaker drills are used for deep hole drilling.
Solutions：The effect of chip breaking and chip removal can be improved by increasing the feed rate, intermittent feeding, grinding the chisel edge, and installing a chip breaker, respectively or in combination, to eliminate the problems caused by chips.
Holes can be drilled with a professional chip breaker drill. For example, adding a chip breaker blade to the groove of the bit will break the chip into more easily removed debris. Chips are expelled smoothly along the grooves without clogging in the grooves. As a result, the new chip breaker achieves a much smoother cutting effect than conventional drills.