Deep Hole Drill: Type, Characteristics, Applications And Selection

In the mechanical manufacturing industry, the cylindrical hole whose hole depth is more than 10 times of the hole diameter is generally called deep hole.

1. Deep hole concept

According to the ratio of hole depth to hole diameter (L/D), deep holes can generally be divided into general deep holes, medium deep holes and special deep holes.

(1) L/D=10 ~ 20, belonging to general deep hole.

It is often processed by lengthening fried dough twist drill on drilling machine or lathe.

(2) L/D=20 ~ 30, belonging to medium deep hole.

It is often processed on a lathe.

(3) L/D=30 ~ 100, belonging to special deep hole.

The deep hole drill must be used to process on the deep hole drilling machine or special equipment.

2. Difficulties in deep hole processing

(1) Cutting cannot be observed directly.

The chip removal and bit wear can be judged only by sound, chip, machine load, oil pressure and other parameters.

(2) Cutting heat is not easy to spread out.

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

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

3. Type, application scope and working principle of deep hole drill

Deep hole drills can be divided into external and internal chip removal according to chip removal methods.

The external chip removal includes gun drill and integral alloy deep hole drill (which can be divided into two types: with cooling hole and without cooling hole);

The internal chip removal is divided into three types: BTA Deep hole drill, spray suction drill and DF system deep hole drill.

The type and application scope of deep hole drill are shown in table 5-4, and its structure and working principle are shown in fig. 5-10.

Table 5-4 common types and application scope of deep hole drill

TypeScope of use
External chip removal deep hole drill (gun drill)It is used to process 2~ 20mm deep holes with length diameter ratio L/D>100, accuracy H8~H10, surface roughness Ra=12.5~3.2um, and the production efficiency is lower than that of internal chip removal deep hole drill
BTA internal chip removal deep hole drillIt is used to process deep holes of medium 6 ~ medium 60mm, length diameter ratio L/D>100, accuracy H7~H9, surface roughness Ra=3.2um, and the production efficiency is more than 3 times that of external chip removal
Jet suction drillIt is used in the processing of 16 ~ 60mm with low cutting fluid pressure. Other properties are the same as those of internal chip removal deep hole drill
DF system deep hole drillA drill pipe is supported by cutting fluid, which reduces vibration, has large chip removal space, has high machining efficiency and good precision, and can be used for high-precision deep hole machining; The production efficiency is 3~6 times higher than that of gun drill and 3 times higher than that of BTA internal chip removal drill.
External chip removal deep hole drill (gun drill)

a) External chip removal deep hole drill (gun drill)

b) BTA internal chip removal deep hole drill

Jet suction drill

c) Jet suction drill

DF internal chip removal system deep hole drill

d) DF internal chip removal system deep hole drill

Fig. 5-10 structure and working principle of deep hole drill

1 – drill bit 2 – drill pipe 3 – workpiece 4 – guide sleeve 5 – chip 6 – oil inlet 7 – outer pipe 8 – inner pipe 9 – nozzle 10 – guide device 11 – drill pipe seat 12 – sealing sleeve

4. Precautions for deep hole processing

(1) Key points of deep hole processing:

The coaxiality of the center lines of the spindle, tool guide sleeve, tool bar support sleeve and workpiece support sleeve shall meet the requirements;

The cutting fluid system shall be unblocked and normal;

There shall be no central hole on the machined end face of the workpiece, and drilling on the inclined plane shall be avoided;

The chip shape shall be kept normal to avoid the generation of straight strip chips;

The through hole shall be processed at a higher speed. When the drill bit is about to be drilled through, the speed shall be reduced or the machine shall be shut down to prevent damage to the drill bit.

(2) Deep hole machining cutting fluid:

Deep hole machining process will produce a lot of cutting heat, 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, 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 ~ 20cm (40 ℃) ²/ s.

The cutting fluid flow rate is 15 ~ 18m/s;

Cutting oil with low viscosity shall be selected when machining diameter is small;

For deep hole machining requiring high precision, the cutting oil ratio can be 40% EP vulcanized oil +40% kerosene +20% chlorinated paraffin.

The pressure and flow of cutting fluid are closely related to the hole diameter and machining method.

See table 5-5 for details.

Table 5-5 pressure and flow of cutting fluid for internal and external chip removal deep hole drill

External chip removal deep hole drill

Internal chip removal deep hole drill

Hole diameter /mm

Pressure /MPa

Flow / (L/min)

Hole diameter /mm

Pressure /MPa

Flow / (L/min)

4~10

2.5~6

8~20

8~15

5~6.5

20~50

10~15

2~5

20~30

15~25

4~5.5

50~70

15~20

1.5~4.5

30~40

25~35

3~4.5

70~100

20~25

1.5~4

40~50

35~45

2.5~3.5

100~125

25~30

1.5~3

50~60

45~80

2~3

125~200

Table 5-6 shows the faults and troubleshooting measures in deep hole machining.

Table 5-6 faults and troubleshooting measures in deep hole machining

Fault

Reason

Elimination measures

break

During spud in

Machine tool cause

Check the feeding mechanism (whether the feeding is too fast) and check whether the workpiece is clamped or loose; Prevent deflection and check whether the sleeve is installed correctly

Bit cause

Whether there is any problem in regrinding

Reason for end face of sleeve

Check whether there is oil leakage and whether there is cutting fluid stuck at the end face

During drilling

Machine tool cause

Check whether the feed speed is uniform and stable

Large tool damage

Refer to the tool life section

When drilling through

Feed rate

The axial thrust decreases during tool withdrawal, and the feed speed is too fast, so the feed speed is reduced

During tool withdrawal

Shape of workpiece to be machined

Check whether the hole of the quick drilling part is crooked

Small aperture increases the extruding torque

Reduce cutting speed

Tool life

Short tool life

Unreasonable drilling conditions

Check whether the drilling speed is too high and set the feed speed appropriately

Machine tool cause

Check whether the main shaft deflection is too large and whether the main shaft and the guide sleeve are concentric; Whether the clearance between the guide sleeve and the drill handle is too large to prevent deflection, and whether the sleeve is installed correctly

Tool reason

Whether the selection of drill point angle and guide block is correct; Whether the drill bit length is too long than the required length; Whether the regrinding meets the requirements (whether the grain size of the grinding wheel is too coarse and the broken edge is not grinded off)

Cause of cutting fluid

Whether the selection of cutting fluid is correct (additives, viscosity, etc.); Check whether the filtering of cutting fluid is good. If the injection temperature is too high, increase the volume of oil tank

Processed material

Whether the material performance is uniform

Machining accuracy

Rough surface

Incorrect cutting conditions

Decrease feed speed

Machine tool problems

Check the spindle runout, uniformity of feed speed, accuracy of guide sleeve and whether the workpiece is clamped

Tool problems

Whether the bit clamping is loose

Cutting fluid problems

Whether the selection of cutting fluid is correct, select appropriate cutting fluid and fully filter the cutting fluid

Out of tolerance of roundness, cylindricity and hole expansion

Incorrect cutting conditions

Select the appropriate feed rate

Machine tool problems

Improve the precision of the guide sleeve and the concentricity between the guide sleeve and the spindle

Tool problems

Select appropriate drill point shape and angle

Cutting fluid problems

Select appropriate cutting fluid

bend

Machine tool problems

Improve the precision of the guide sleeve and the concentricity between the guide and the spindle; Stably clamp the workpiece

Tool problems

Select the appropriate drill point shape, angle and guide block

Material problem of workpiece to be processed

Check whether there are chips and sand holes on the surface; Check whether the surface has slope, and process the surface smoothly.

Deal with cutting

Chip clogging

Low cutting fluid pressure

Correct selection of cutting fluid pressure

Low cutting fluid flow

Correctly select cutting fluid flow; Check whether the viscosity of cutting fluid is too high and reduce the viscosity

Chip shape is not ideal

When the chip is very hard, reduce the feed speed; Correct selection of drill point shape and angle

Machine tool problems

Increase chip space

Filiform chip

Increase the feed speed; Check whether the wear at the corner of the drill point cutting edge is too large; Check the corner of the drill point cutting edge and whether the cutting edge breaks; Whether the grinding wheel granularity is too coarse during regrinding; When drilling the center hole, filiform chips are generated, which increases the cutting fluid pressure and reduces the feed rate

Serrated chip

Check whether the cutting edge at or near the drill point is broken

(3) Precautions for using deep hole drill

1) The end face of the workpiece is perpendicular to the axis of the workpiece to ensure reliable end face sealing.

2) Before formal machining, a shallow hole shall be pre drilled on the hole position of the workpiece, which can play the role of guiding and centering during drilling.

3) In order to ensure the service life of the tool, it is better to use automatic tool feeding.

4) 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.

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