Processing characteristics of deep hole drilling
- The tool holder is limited by the aperture, small diameter, and considerable length, resulting in insufficient rigidity, low strength, vibration, ripple, and taper during cutting, which affect the straightness and surface roughness of the deep hole.
- When drilling and reaming, it is difficult for the cooling lubricant to enter the cutting area without special equipment, which reduces the tool’s durability and makes chip removal difficult.
- In the process of deep hole processing, you cannot directly observe the tool’s cutting condition. You can only judge by working experience by listening to the sound during cutting, watching chips, hand vibration, and workpiece temperature, and viewing instruments (oil pressure gauge and electric meter) Whether the cutting process is normal.
- Chip removal is difficult, and reliable means are needed to break the chips and control the chips’ length and shape to facilitate smooth removal and prevent chip jams.
- To process smoothly, if the deep hole wants to achieve the required processing quality, the chip removal device inside (outside) the tool, the tool guide, support apparatus, and the high-pressure cooling and lubricating device should be added.
Generally, the hole depth is more than five times the hole’s diameter is called a deep hole. Its difficulty lies in chip removal and cooling. A twist drill can be used to drill a hole with a smaller depth. To remove the chips smoothly, the iron filings must become thin strips and straight out. And bring out smaller fragments while the coolant is easy to enter.
The grinding method of the drill bit can be relatively simple grinding method:
- Increase the angle of the drill edge to 130-140 degrees to increase the chip thickness and change the direction of chip discharge (the law of chip discharge is perpendicular to the cutting edge)
- Grinding the chisel edge to reduce the axial cutting tool, and at the same time, the cutting edge produces a bevel angle at the core to facilitate chip separation.
- Chamfer a 1 mm 45 degrees angle at the cutting edge’s outer corner to reduce wear and improve the finish.
- The drilling speed is slightly lower, and the feed amount should be more considerable so that the thickened chips are discharged in strips.
- The coolant’s nozzle should face the hole inward so that the coolant can enter the cutting area.
Common problems and solutions did
Rough hole surface
- Chip bonding: reduce cutting speed; avoid chipping; switch to cutting fluid with too high pressure, improve filtration; increase the pressure and flow of cutting fluid.
- Poor coaxial: adjust the coaxiality of the machine tool spindle and the drill sleeve; use a suitable drill sleeve diameter.
- The cutting speed is too low, the feed is too large or uneven: use the appropriate cutting amount.
- The tool geometry is not suitable: change the geometric angle of the cutting edge and the shape of the guide block
The orifice is flared
Poor coaxial: adjust the coaxiality of the machine tool spindle, drill sleeve, and support sleeve; use a suitable drill sleeve diameter, and replace the over-wearing drill sleeve in time.
- The chip breaking is not right, and the chips can not be discharged: change the size of the chip breaker to avoid too long and too shallow; find the chipping in time and replace it; increase the pressure and flow of the cutting fluid; use a workpiece with uniform material structure.
- Feed rate is too large, too small, or uneven: Use appropriate cutting amount.
- Excessive wear of the drill: replace the exercise regularly to avoid excessive wear.
- Inappropriate cutting fluid: select suitable cutting fluid and improve filtration.
Low bit of life
- The cutting speed is too high or too low, and the feed rate is too large: use a suitable cutting amount.
- The drill is not suitable: change the tool material; change the position and shape of the guide block.
- Unsuitable cutting fluid: switch to cutting fluid with too high pressure; increase the pressure and flow of the cutting fluid; improve the filtration of the cutting fluid.