In deep hole processing, various processing difficulties are often encountered. Today, the editor has summarized ten common problems in deep hole processing and their solutions. Let's take a look together.

I. What is Deep Hole

In the machinery manufacturing industry, cylindrical holes with a depth exceeding five times the diameter of the hole are generally referred to as deep holes. Deep holes are generally classified into three types based on the ratio of hole depth to hole diameter (L/D) : general deep holes, medium deep holes, and special deep holes. (ps: The larger the ratio of L/D, the more difficult it is to process.)

1. When L/D is greater than 5, it is classified as a general deep hole and is often processed on a drilling machine or lathe using an extended twist drill.

2. L/D=20- 30, which is a medium-deep hole and is often processed on a lathe.

3. L/D=30- 100, which is a special deep hole, must be processed on a deep hole drilling machine or dedicated equipment using a deep hole drill. Deep hole drills are classified into two types based on chip removal methods: external chip removal and internal chip removal. External chip removal includes gun drills and solid alloy deep hole drills (which can be further divided into those with cooling holes and those without). Internal chip removal can be further classified into three types: BTA deep hole drilling, jet suction drilling, and DF system deep hole drilling.

Ii. Common Problems and Solutions in Deep Hole Machining

1. Aperture reduction

Cause: The design value of the outer diameter of the reamer is too small. The cutting speed is too low Excessive feed rate; The main deflection Angle of the reamer is too small. The selection of cutting fluid is inappropriate. When grinding, the worn part of the reamer was not ground off, and the elastic recovery reduced the hole diameter. When reaming steel parts, if the allowance is too large or the reamer is not sharp enough, elastic recovery is likely to occur, causing the hole diameter to shrink and the inner hole to be not round, resulting in an unqualified hole diameter.

Solution: Replace the outer diameter size of the reamer; Appropriately increase the cutting speed; Appropriately reduce the feed rate; Appropriately increase the principal deflection Angle; Select oil-based cutting fluids with good lubricating performance; Regularly exchange reamers and correctly grind the cutting parts of the reamers. When designing the size of a reamer, the above factors should be taken into account or the value should be determined based on the actual situation. Conduct experimental cutting, take an appropriate allowance, and sharpen the reamer.

2. The aperture increases

Cause: The design value of the outer diameter of the reamer is too large or there are burrs on the cutting edge of the reamer. Too high cutting speed; Improper feed rate or excessive machining allowance; The main deflection Angle of the reamer is too large, causing the reamer to bend. A built-up edge adheres to the cutting edge of the hinge. The deflection of the cutting edge of the hinge during grinding exceeds the tolerance. The selection of cutting fluid is inappropriate. When installing the reamer, the oil stains on the surface of the taper handle were not wiped clean or there were bumps and scratches on the taper surface. After the flat tail of the taper shank is offset and installed into the machine tool spindle, the cone of the taper shank interferes. The main shaft is bent or the main shaft bearing is too loose or damaged; The reamer does not float flexibly. The reamer shakes left and right when it is not on the same axis as the workpiece and when reaming by hand, the force applied by both hands is uneven.

Solution: Appropriately reduce the outer diameter of the reamer according to the specific situation; Reduce the cutting speed, appropriately adjust the feed rate or decrease the machining allowance. Appropriately reduce the main deflection Angle to straighten or scrap the bent and unusable reamers. Carefully polish it with an oilstone until it is qualified; Keep the swing within the allowable range; Select cutting fluid with better cooling performance; Before installing the reamer, the oil stains inside the reamer taper handle and the taper hole of the machine tool spindle must be wiped clean. Any bumps on the taper surface should be smoothed with an oilstone. Grind the flat tail of the reamer, adjust or replace the main shaft bearing; Readjust the floating chuck and adjust the coaxiality. Pay attention to the correct operation.

3. The inner hole reamed out is not round

Cause: The reamer is too long and lacks rigidity, resulting in vibration during reaming. The main deflection Angle of the reamer is too small. The cutting edge band of the hinge is narrow. The allowance of the reaming hole is off. There are notches and cross holes on the inner hole surface. There are sand holes and gas holes on the surface of the holes. The main shaft bearing is loose, there is no guide sleeve, or the clearance between the reamer and the guide sleeve is too large, or due to the thin-walled workpiece being clamped too tightly, the workpiece deforms after removal.

Solution measures: For reamers with insufficient rigidity, reamers with unequal tooth pitches can be used. The installation of reamers should adopt rigid connections and increase the main deflection Angle. Select qualified reamers and control the hole position tolerance of the pre-processing process. Unequal-pitch reamers are adopted, along with longer and more precise guide sleeves. Select qualified blanks; When reaming relatively precise holes with equal-pitch reamers, the clearance of the machine tool spindle should be adjusted. The fit clearance of the guide sleeve should be required to be higher or an appropriate clamping method should be adopted to reduce the clamping force.

4. The positional accuracy of the reamed hole exceeds the tolerance

Cause: Wear of the guide sleeve; The bottom end of the guide sleeve is too far from the workpiece. The guide sleeve is short in length, has poor precision and the main shaft bearing is loose.

Solution: Replace the guide sleeve regularly; Extend the guide sleeve to improve the fit accuracy of the gap between the guide sleeve and the reamer. Timely repair the machine tool and adjust the clearance of the main shaft bearing.

5. The surface roughness value of the inner hole is high

Cause: Excessively high cutting speed; The selection of cutting fluid is inappropriate. The main deflection Angle of the reamer is too large, and the cutting edge of the reamer is not on the same circumference. The allowance of the reaming hole is too large. The allowance for reaming is uneven or too small, and the local surface is not reamed. The swing of the cutting part of the reamer is out of tolerance, the cutting edge is not sharp, and the surface is rough. The cutting edge band of the hinge is too wide. The chip removal was not smooth during reaming. Excessive wear of the reamer; Reamers are scratched, with burrs or chipping left on the cutting edge. There is a built-up edge on the cutting edge. Due to material conditions, it is not suitable for zero-degree rake Angle or negative rake Angle reamers.

Solution: Reduce the cutting speed; Select the cutting fluid based on the deep hole processing material. Appropriately reduce the main deflection Angle and correctly grind the cutting edge of the hinge. Appropriately reduce the reaming allowance; Improve the positional accuracy and quality of the bottom hole before reaming or increase the reaming allowance; Select qualified reamers; Sharpen the width of the cutting edge band; According to specific circumstances, reduce the number of teeth on the reamer, increase the space of the chip groove or use a reamer with a cutting edge Angle to ensure smooth chip removal. Replace the reamer regularly and grind off the grinding area when sharpening. During the grinding, use and transportation of reamers, protective measures should be taken to avoid scratches. For the reamers that have been damaged, a very fine oilstone should be used to repair the damaged reamers or replace them. Trim it to the qualified level with an oilstone and use a reamer with a rake Angle of 5° to 10°.

6. The inner surface of the hole has obvious edges

Cause: Excessive allowance of the reaming hole; The relief Angle of the cutting part of the reamer is too large. The cutting edge band of the hinge is too wide. There are pores, sand holes on the surface of the workpiece and excessive spindle swing.

Solution: Reduce the allowance of the reaming hole; Reduce the relief Angle of the cutting part; Sharpen the width of the cutting edge band; Select qualified blanks; Adjust the spindle of the machine tool.

7. The centerline of the hole after reaming is not straight

Cause of occurrence: The drilling before reaming is skewed, especially when the hole diameter is small. Due to the poor rigidity of the reamer, the original curvature cannot be corrected. The main deflection Angle of the reamer is too large. Poor guidance makes the reamer prone to deviate from its direction during reaming. The inverted cone of the cutting part is too large. The reamer is displaced at the middle gap of the discontinuous hole. When reaming by hand, excessive force was applied in one direction, causing the reamer to deviate to one end and disrupting the verticality of the reaming.

Solution: Add reaming or boring processes to correct the holes. Reduce the principal deflection Angle; Adjust the appropriate reamer; Replace the reamer with a guiding part or an extended cutting part; Pay attention to the correct operation.

8. The service life of the reamer is low

Cause: The material of the reamer is not suitable; The reamer was burned during grinding. The cutting fluid was not properly selected. The cutting fluid failed to flow smoothly, and the surface roughness values at the cutting point and after grinding the hinge cutting edge were too high.

Solution measures: Select the reamer material based on the processing material. Hard alloy reamers or coated reamers can be used. Strictly control the grinding and cutting parameters to avoid burning. Frequently select the correct cutting fluid based on the processing material. Regularly remove the chips from the chip trough and use cutting fluid with sufficient pressure to finely grind or polish them to meet the requirements.

9. The teeth of the reamer are chipped

Cause: Excessive allowance of the reaming hole; The hardness of the workpiece material is too high; The swing of the cutting edge is too large and the cutting load is uneven. The main deflection Angle of the reamer is too small, which increases the cutting width. When reaming deep holes or blind holes, there are too many chips that have not been removed in time, and the cutting teeth have been cracked during grinding.

Solution: Modify the aperture size of the pre-processed hole; Reduce the hardness of the material or use negative rake Angle reamers or carbide reamers instead; Keep the swing within the qualified range. Increase the principal deflection Angle; Pay attention to timely removal of chips or use a cutting edge inclined reamer. Pay attention to the grinding quality.

10. The handle of the hinge is broken

Cause: Excessive allowance of the reaming hole; When reaming conical holes, the distribution of rough and finish reaming allowances and the selection of cutting parameters are inappropriate. The chip space of the reamer teeth is small, causing chip blockage.

Solution: Modify the aperture size of the pre-processed hole; Modify the allowance allocation and rationally select the cutting parameters; Reduce the number of teeth on the reamer, increase the chip space or grind off one tooth from the tooth gap.