Deep Hole Drilling & Machining: Characteristics, Difficulties & Tips

2022.7.27

Deep hole machining is a kind of machining field dominated by cutting tools specially designed for existing applications. Deep hole machining is involved in many different industries. What is the difference between deep hole machining and other hole manufacturing methods? What difficulties are there in hole machining and how to improve the process?

Characteristics of Deep Hole Machining

Compared with general parts processing, deep hole machining has the following process characteristics:

1) Deep hole parts have high-quality requirements, with dimensional accuracy in the range of it6~it12 and surface roughness r in the range of 25~0.2um. Shape and position accuracy, work hardening layer, residual stress, and surface physical and mechanical properties are all required to be high.

2) The machining of the inner surface of deep hole parts is carried out in a semi-closed state, so the operator cannot directly observe the cutting condition of the tool. In addition, the chip holding space is small, the cutting heat is not easy to spread, and the chip removal, cooling, and lubrication are difficult.

3) The rigidity of the machining system is weak (especially the rigidity of the tool system), and the error reflection is relatively prominent. The processing stability is low, easy to produce vibration and deformation, and the processing accuracy and surface roughness of the hole is not easy to guarantee. Therefore, the guidance of cutting tools and the rigidity of the system are very important.

4) The cutting path is long, the chip discharge is difficult, the load of the cutting edge of the tool is uneven, the cutting temperature is high, and the tool is easy to wear, crack and collapse.

Difficulties in Deep Hole Drilling and Machining

1) The cutting condition cannot be observed directly, and the chip removal and bit wear can be judged only by listening to the sound, looking at the chips, observing the machine load, oil pressure, and other parameters.

2) Cutting heat is not easy to spread out.

3) It is difficult to remove chips. If chips are blocked, the drill bit will be damaged.

4) Due to the long length, poor rigidity, and easy vibration of the drill pipe, the hole axis is easy to deflect, affecting the machining accuracy and production efficiency.

Tips for Deep Hole Drilling and Machining

1) Key points of deep hole cutting and machining: the coaxiality of the central lines of the spindle and tool guide sleeve, toolbar support sleeve, workpiece support sleeve, etc. should meet the requirements; The cutting fluid system should be unblocked and normal; There should be no central hole on the machined end face of the workpiece, and drilling on the inclined plane should be avoided; The chip shape should be kept normal to avoid the formation of straight strip chips; Use a higher speed to process the through the hole. When the drill is about to drill through, reduce the speed or stop the machine to prevent damage to the drill.

2) Cutting fluid for deep hole machining: a large amount of cutting heat will be generated in the process of deep hole machining, which is not easy to diffuse, so it is necessary to supply sufficient cutting fluid to lubricate and cool the tool. Generally, 1:100 emulsion or extreme pressure emulsion is selected; When high machining accuracy and surface quality or machining toughness materials are required, extreme pressure emulsion or high concentration extreme pressure emulsion is selected. The kinematic viscosity of cutting oil is usually 10 ~ 20cm2/s (40 ℃), and the flow rate of cutting fluid is 15 ~ 18m / S; Select cutting oil with low viscosity when the machining diameter is small; For deep hole machining requiring high precision, the ratio of cutting oil can be 40% EP vulcanized oil +40% kerosene +20% chlorinated paraffin.

3) Tips for using deep hole drills:

– The end face of the workpiece is perpendicular to the axis of the workpiece to ensure the reliability of the end face seal.

– Before formal machining, a shallow hole is pre-drilled on the hole position of the workpiece, which can play a guiding and centering role during drilling.

– In order to ensure the service life of the tool, it is best to use automatic tool feeding.

– If the guide elements in the liquid feeder and movable center support are worn, they should be replaced in time to avoid affecting the drilling accuracy.