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Drilling wear and troubleshooting

​Troubleshooting

  • Indexable insert drill
  • Exchangeable-tip drill
  • Solid carbide drill
 

​Indexable insert drill

​Oversized holes

Rotating drill
  1. Increase coolant flow, clean filter and clear coolant holes in drill
  2. Try a tougher geometry on the peripheral side (keep center insert)
Non-rotating drill
  1. Check alignment on lathe
  2. Rotate drill 180 degrees
  3. Try a tougher geometry on the peripheral side (keep center insert)

​Undersized holes

Rotating drill
  1. Increase coolant flow, clean filter and clear coolant holes in drill
  2. Try a tougher geometry on the center side and a light cutting geometry on the peripheral side
Non-rotating drill
  1. Stationary: Check alignment on lathe
  2. Stationary: Rotate drill 180 degrees
  3. Try a tougher geometry at the center and a light cutting geometry at the periphery

​Pin in hole

Rotating drill
  1. Increase coolant flow, clean filter and clear coolant holes in drill
  2. Try a different geometry on the peripheral side and adjust feed rate within recommended cutting data
  3. Shorten drill overhang
Non-rotating drill
  1. Check alignment on lathe
  2. Increase coolant flow, clean filter and clear coolant holes in drill
  3. Shorten drill overhang
  4. Try a different geometry on the peripheral side and adjust feed rate within recommended cutting data

​Vibrations

  1. Shorten drill overhang, improve the workpiece stability
  2. Reduce cutting speed
  3. Try a different geometry on the peripheral side and adjust feed rate within recommended cutting data

​Insufficient machine torque

  1. Reduce feed
  2. Choose a light cutting geometry to lower the cutting force

​Insufficient machine power

  1. Reduce speed
  2. Reduce feed
  3. Choose a light cutting geometry to lower the cutting force

​Hole not symmetrical

Hole widens at bottom (due to chip jam on center insert)

  1. Increase coolant flow, clean filter and clear coolant holes in drill
  2. Try a different geometry on the peripheral side and adjust feed rate within recommended cutting data
  3. Shorten drill overhang

​​Poor tool life

  1. Check cutting data recommendation
  2. Increase coolant flow, clean filter and clear coolant holes in drill
  3. Shorten drill overhang, improve the workpiece stability and check tool holding
  4. Check tip/insert seat and screw for damage
  5. See typical wear for specific remedies
  6. Choose a more wear-resistant grade, if possible

​Broken insert screws

  1. Use torque wrench to fasten the screw together with Molykote

​Bad surface finish

  1. Important to have good chip control
  2. Reduce feed (if it is important to keep vf, increase speed as well)
  3. Increase coolant flow, clean filter and clear coolant holes in drill
  4. Shorten drill overhang, improve workpiece stability

​​Chip jamming in the drill flutes

​Caused by long chips
  1. Check geometry and cutting data recommendations
  2. Increase coolant flow, clean filter and clear coolant holes in drill
  3. Reduce feed within recommended cutting data
  4. Increase cutting speed within recommended cutting data

​​Deflection

  • Hole tolerance out of range
  • Bad surface finish – retraction mark
  • Wear on tool body
  • Insert breakage
 
CauseSolution
​Cutting forces too high 1. Choose geometry with smaller corner radius
2. Reduce feed
3. Reduce feed at entrance
​Insufficient stability 1. Increase stability
2. Choose a shorter tool body (4 × D -> 3 × D)

Chip forming problems

Long-chipping materials, e.g. stainless or low-carbon steel

​​Result​​​Possible cause​​Solution​
Bad/long chips – chip jamming​​Wrong geometry​Choose geometry -LM
​Bad surface finish​Cutting speed too low​Increase cutting speed
​Insert or tool breakdown​Feed too high​Decrease feed

Short-chipping materials, e.g. normal steel

ResultPossible causeSolution
Bad/long chips – chip jamming​​Non-rotating tool (lathe)​Choose geometry for low feed (GR -> GM)
​Bad surface finish​Wrong geometry​Increase feed
​Insert or tool breakdown 1. Cutting speed too low
2. Feed too low
​Increase cutting speed
 

Exchangeable-tip drill

​Out-of-hole tolerance

  1. Check tip wear
  2. Check run-out
  3. Decrease feed
  4. Check workpiece stability, tool holding and workpiece surface
  5. Pilot/spot drill for longer drills
  6. If non-rotating application, check alignment

Vibration

  1. Shorten drill overhang, improve workpiece stability, check tool holding
  2. Reduce cutting speed
  3. Adjust feed/rev

Insufficient machine power or torque

  1. Reduce speed
  2. Reduce feed
  3. Choose a light cutting geometry to lower the cutting force

Hole not cylindrical

Hole widens at entrance

  1. Check run-out
  2. Adjust feed
  3. Shorten drill overhang and check tool holding
  4. Make a pilot hole with a short drill for longer drills

Poor tool life

Check cutting data recommendation

  1. Increase coolant flow, clean filter and clear coolant holes in drill
  2. Shorten drill overhang, improve workpiece stability and check tool holding
  3. Check tip/insert seat and screw for damage
  4. See typical wear for specific remedies
  5. Choose a more wear-resistant grade, if possible

Bad surface finish

  1. Important to have good chip control
  2. Reduce feed (if it is important to keep vf, also increase speed)
  3. Increase coolant flow, clean filter and clear coolant holes in drill
  4. Shorten drill overhang, improve the workpiece stability

Chip jamming in the drill flutes

  1. Adjust cutting data for improved chip control
  2. Increase coolant flow, clean filter, clear coolant holes in drill, check coolant concentration
  3. Problems with chip jamming can cause extreme drill body wear
  4. Remove any workpiece material stuck on the drill body to avoid chip jamming

Entrance chip

"Needles" on the periphery
  1. Risk of excessive wear if needles can be seen on the start-chip periphery
  2. Probable cause – imbalance due to:
    • Run-out
    • Inclined entrance
    • Feed too high
    • Unstable/weak conditions
    • Corner breakage/wear

Chip control – optimization

  1. A scratch mark on the chips, as seen above, is a sign of chip jamming, which influences hole quality negatively. To improve hole quality, the recommendation is to reduce feed and, if possible, increase speed
 

Solid carbide drill

Entrance chip – solid carbide/exchangeable-tip drills

"Needles" on the periphery
  1. Risk of excessive wear if needles can be seen on the start-chip periphery
  2. Probable cause – imbalance due to:
    • Run-out
    • Inclined entrance
    • Feed too high
    • Unstable/weak conditions
    • Corner breakage/wear

Chip control – optimization

  1. A scratch mark on the chips, as seen above, is a sign of chip jamming, which influences hole quality negatively. To improve hole quality, the recommendation is to reduce feed and, if possible, increase speed
 

Drilling wear types

  • Indexable insert drills
  • Exchangeable-tip drill
  • Solid carbide drill
 

Indexable insert drills

Flank wear

Flank wear is the preferable wear type when balanced. Flank wear can result in

  • Poor surface finish
  • Hole tolerance out of range
  • Power increase
​Cause ​Action
​1. Cutting speed too high (vc)​1. Decrease cutting speed (vc)
​2. Insufficient wear resistance in grade​2. Select a more wear-resistant grade

Crater wear

Central insert
Peripheral insert
 

Crater wear can result in

  • Weak cutting edge that can cause edge breakage and generate bad chips
  • Poor surface finish
  • Power increase
Cause​Action
​Central insert: abrasive chips (workpiece material)​Central insert: reduce feed
​Peripheral insert: diffusion wear caused by high temperature (worse for PVD)​Peripheral insert:
1. Decrease cutting speed
2. Select a more wear-resistant grade (often MT-CVD)
​Select a more positive geometry for better chip formation

Plastic deformation

Depression
Impression
 

Edge depression or impression can cause poor chip control, poor surface finish and the hole to be out of tolerance.

CauseAction
​Cutting temperature too high, combined with high pressure (feed and/or workpiece hardness)​Decrease feed (fn)
Select grade with better resistance against PD (hot hardness)
Decrease cutting speed (vc)
​A final result of excessive flank and/or crater wear​Select grade with better resistance against PD (hot hardness)
Decrease cutting speed (vc)

Chipping in cutting zone

Chipping in cutting zone can result in

  • Exaggerated flank wear
  • Poor surface finish
Cause​Action
​Unstable conditions​Improve stability (tool overhang, fixating)
​Irregular surface​Reduce feed at entrance. Choose tougher geometry
​Insufficient toughness of grade​Select a tougher grade
​Insert geometry too weak​Select a stronger geometry
​Insufficient cutting fluid​Increase cutting fluid
​Sand inclusions (cast iron)​Choose a stronger geometry, reduce feed

Breakage

Breakage can result in

  • Tool breakdown
  • Destroyed workpiece
CauseAction
​Insufficient stability​Improve stability (shorten tool overhang, better workpiece fixturing, etc.)
​Intermittent cutting​Reduce feed, choose tougher geometry (-GR or -GT)
​Insufficient cutting fluid​Increase cutting fluid
Feed too high or cutting speed too high/low​Adjust cutting data
​Grade too brittle (P-insert)​Choose a tougher grade
​Insert worn out​Determine safe tool life on peripheral insert

Built-up edge (BUE)

Built-up edge can result in

  • Poor surface finish and edge frittering when BUE is ripped away by chips
  • Chipping of cutting edge
Cause​Action
​Unfavorable temperature (cutting speed)​Increase/decrease cutting speed (high/low temperature)
Select a coated grade
Cutting geometry too negative​Select a more positive geometry
​Sticky material​Increase oil mixture and volume/pressure in cutting fluid
Oil mixture in cutting fluid too low​Increase oil mixture and volume/pressure in cutting fluid
 

Exchangeable-tip drill

Typical wear in different materials for -PM geometry

Unalloyed steel / CMC01.1
  • Margin/periphery wear starts as notch and develops along margin width and into flute
  • Continuously growing wear on main edge
Low-alloy steel / CMC02.2
  • Continuously growing wear on main edge/margin close to corner

Flank wear


Flank wear on main edge

Flank wear on circular land
 

Normal and preferable wear type when balanced

CauseAction
​Cutting speed too high​Decrease cutting speed
​Percentage of oil in cutting fluid flow too low​Increase percentage of oil in cutting fluid
(check with oil distributor to be sure not to exceed recommended percentages of oil)
​Insufficient cutting fluid flow​Increase cutting fluid flow
​Total indicator run-out too large (if wear on margin)​Check radial run-out (if wear on margin)

Plastic deformation

CauseAction
Cutting speed and/or feed too high​Decrease cutting speed and/or feed
Insufficient cutting fluid flow​Increase cutting fluid flow

Chipping


Chipping on periphery

Chipping on main edge
 

Chipping is a very common wear type when drilling into a pre-drilled hole. If the point angle is smaller on the pre-drilled hole, stability will be poor and the corners can be damaged. This can also happen if tolerances on point angles do not match. This can be avoided with custom-made drills or with flat bottom holes made by milling.

CauseAction
Unstable conditions​Check set-up
​Total indicator run-out too large​Check radial run-out
​Feed too high​Decrease feed
Insufficient cutting fluid flow (thermal cracking)​Check cutting fluid supply

Built-up edge

CauseAction
Unsuitable cutting speed​1. Increase cutting speed when BUE in center
2. Decrease cutting speed when BUE in periphery
Percentage of oil in the cutting fluid too low​Increase percentage of oil in cutting fluid (check with oil distributor to be sure not to exceed recommended percentages of oil)

If you cannot fully avoid the BUE zone, calculate a speed that locates the BUE in the strongest part of the drill (= 50% of diameter).

The use of external cutting fluid can influence chip evacuation negatively.


Increase cutting speed to move BUE
towards BUE center of the drill

Decrease cutting speed to move
to periphery or eliminate BUE​
 
 

Solid carbide drill

Flank wear


Flank wear on main edge

Flank wear on circular land
 

Preferable wear type when balanced

CauseAction
​Total indicator run-out too large​Check radial run-out
Cutting speed too high​Decrease cutting speed​
Feed too low​​Increase feed
​Grade too soft​Use a harder grade
Insufficient cutting fluid​Increase cutting fluid pressure​

Flank wear on chisel edge

CauseAction
Total indicator run-out too large​​Check radial run-out
​Cutting speed too low​Increase cutting speed
​Feed too highDecrease feed​
 

Flank wear on chisel edge will also influence hole quality due to bad centering.

Chipping


Chipping on periphery

Chipping on main edge​
 

Chipping is a very common wear type when drilling into a pre-drilled hole. If the point angle is smaller on the pre-drilled hole, stability will be poor and the corners can be damaged. This can also happen if tolerances on point angles do not match. This can be avoided with custom-made drills or with flat bottom holes made by milling.

Cause​Action
​Unstable conditions​Check set-up
​Total indicator run-out too large​Check radial run-out
​Insufficient cutting fluid (thermal cracking)​Check cutting fluid supply
​Maximum allowed wear exceeded​Adjust cutting data

Drill breakage

Cause​Action
​Total indicator run-out too large​Check radial run-out
​Unstable conditions​Check set-up
Insufficient spindle power​Check cutting data
​Chip jamming​Check cutting fluid supply
Feed too high​Decrease feed
​Excessive wear​Check wear more frequently

Built-up edge

Cause Action​
​Cutting speed and edge temperature too low 1. Increase cutting speed when BUE in center
2. Decrease cutting speed when BUE in periphery​
​Negative land too large​Sharper cutting edge
​No coatingCoating on the edge​
 

If you cannot fully avoid the BUE zone, calculate a speed that locates the BUE in the strongest part of the drill (= 50% of diameter).

The use of external cutting fluid can influence chip evacuation negatively.


Increase cutting speed to move
BUE towards center of the drill​

Decrease cutting speed to move
BUE to periphery or eliminate BUE
 

Typical wear

Regardless of material

  • Always flank wear
  • Chipping is seldom seen
    • Process security
Unalloyed steel / CMC01.1
  • Margin/periphery wear
    • Wear starts as notch
    • Grows towards corner
Low-alloy steel / CMC02.2
  • Corner wear
High-alloy steel / CMC03.11
  • Significant flank wear
  • Small damages on corner

Corner design

Caution!
  • Do not misjudge the reinforcement as wear

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