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Troubleshooting checklist

Check and correct Time required (mins)

A Nozzle contamination 1–2

B Laser power and pulsing conditions 1–5

C Cutting speed 1–2

D Cutting gas 1–2

E Nozzle stando 1–2

F Nozzle type, condition and alignment 1–10

G Material specication and condition 1–5H Lens type, condition and alignment 10–20

I Beam steering mirror condition and alignment 5–60 per mirror

 J Laser mode quality and polarization 20–40

A. Nozzle contamination• Dirt or spatter on the nozzle may defect the gas jet to one side – Wipe the nozzle or replace i damaged

Nozzle deects will only result in a less efcient cutting process and do not pose a saety risk

B. Laser power and pulsing conditions1. Compare laser power and pulse settings to those used successully on similar jobs

2. I power level is lower than usual:

 – The laser may need time to warm up (up to 30mins) – The helium supply is running low

 – The laser needs tuning

 – The laser needs servicing

E.g. internal mirrors need to be cleaned

Requires trained personnel

C. Cutting speed• Compare cutting speed to those used successully on similar jobs

 – Try increasing and decreasing the speed by 10% and 20%

D. Cutting gas1. Check the type o gas being used against similar successul jobs2. Check supply pressure and fow

 – Nozzle blockages will aect pressure and fow

 – It is best to have both a fow meter and a pressure gauge

 – Excessive oxygen pressure results in burning o corners and loss o ne details

3. Insucient gas purity or gas supply contamination

 – Contact your gas supplier – Oxygen cutting: cutting speed reduced

 – Nitrogen cutting: surace quality reduced

E. Nozzle material stando • Compare to earlier successul results

 – Normally the stando is 0.25-2mm – Changing non-identical nozzles may change stand-o 

Alter nozzle-lens distance to re-optimise process

Laser Cutting If you are not getting a good cut from your laser

you may be experiencing any of the following:

AcknowledgementsDr John Powell – LIA Guide to Laser Cutting(Pub: Laser Institute o America)

Correct conditionsGood cut

This shows a good cut in 8mm mild steel.

• Smooth, square cut edge with a light scale o oxide.

Common aultsDross

Eect Problem Action

Dross(oxygen &

nitrogen

cutting)

Insucient meltclearance

Reduce speedProcessing too ast

 – evidence o curved

drag lines

Low pressure – evidence o curved

drag lines

Increase gas

pressure

Low powerIncrease

power

Poor ocus Check lens

Nozzle too narrowIncreasenozzle

diameter

Side burning

Eect Problem Action

Side

burning

(oxygencutting)

Oxygen pressure

too high

Reduce gas

pressure

Processing tooslowly

Increase speed

Damaged nozzleCheck/replace

nozzle

Cutting unequal in x-y plane

Eect Problem Action

Cuttingunequal in

x-y plane

Polarisationproblems Check and

replaceDamaged phase

retarder

Beam o centre Align to nozzle

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Details given in this documen t are believed to be correct at the time of pr inting. Whilst proper care has been taken in the preparation, BOC Ltd excludes all and any liability permitted by law for injur y, damage or loss resulti ng from use. BOC is a trading name of BOC Limited, which is an operatingcompany within The BOC Group, the parent company of which is The BOC Group plc. The stripe symbol and the word BOC are a registered trademark of The BOC Group plc and used under licence by BOC Limited. © BOC Limited 2006. Reproduction without permission is strictly prohibited.

AUSTRALIA

131 262Fax: 132 427 • Email: contact@boc.comWebsite: www.boc.com.au

BOC Limited ABN 95 000 029 729

Riverside Corporate Park 

10 Julius Avenue North Ryde, NSW 2113

AUSTRALIA

NEW ZEALAND

0800 111 333Fax: 0800 229 923 • Email: customer-service-nz@boc.comWebsite: www.boc.co.nz

BOC Limited970–992 Great South Road

Penrose, Auckland

NEW ZEALAND

F. Nozzle type, condition and alignment

1. Is the nozzle o the right type (exit diameter) or the job?2. Is the nozzle worn or scratched?

3. Is the laser in the centre o the nozzle (i.e. centre o the gas jet)?

I not:

 – The machine will not cut equally well in all directions: – Sparks may exit top o the cut zone when cutting in

certain directions

 – Reduction o sparks leaving the bottom o the cut when

cutting in certain directions

G. Material specifcation and condition1. What is the material?

2. Is the condition o the material aecting the cutting?

 – Surace coating (rust, paint, mill scale, etc.)

 – Deep scratches

H. Lens type, condition and alignment1. Is the right ocal length lens being used? Is it tted correctly?2. Is the lens scratched or dirty? Both can give cutting problems

Even i it is clean it may have become over-heated

3. Is the laser beam correctly aligned onto the lens?

 – Beam steering mirrors may need re-alignment

I. Beam steering mirror condition and alignment1. Are the mirrors clean?

 – Take power readings ater each one. Power losses should be below 5% per mirror

2. Alignment should be square and central

 – Realignment o mirrors requires training

 J. Laser mode quality and polarisation1. The distribution o energy across the laser beam cross section is called its mode

 – Poor mode quality results in poor cutting quality

 – Laser mode identication and tuning require training

2. CO2 laser beam polarisation requires careul control or successul metal cutting

 – I circular proles are oval on the bottom but circular on top, the polarising mirror(s)

may need cleaning or replacing

Gas consumption v. nozzle size

Laser Cutting Material related ault

Example o how material quality can aect cut quality

– oxygen cutting o low grade mild steel.

Nitrogen purity related aults

• Oxidation o the cut is evident at 100 ppm purity.

• The edge becomes rough at 0.1% purity (1000 ppm).

Laser mode quality andpolarisation

Perspex “mode burn”. Laser evaporation gives good 3Dapproximation o beam prole, but it requires practice

or reproducability, and produces noxious umes.

Good mode (TEM00)

Bad mode

Nitrogen,1% oxygen

100 ppmoxygen

0.1% oxygen

 – cut edgeoxidised

25 ppmoxygen