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WhatsGoingOn (Industrial) (OP)
4 Mar 08 8:48
The prevailing wisdom in our shop is that the minimum hole diameter is equal to the plate thickness. Is this correct? We need to put 13/32" holes into 1/2" plate on a Bystronic 1500W laser.
btrueblood (Mechanical)
4 Mar 08 10:42
I have seen very high aspect ration (L/D > 20) holes laser drilled in various materials.  I believe they were made in multiple steps/passes.
Helpful Member!  1plus1 (Industrial)
4 Mar 08 18:31
No, that is not true. Good quality holes smaller than the thickness of the metal can be accomplished by specific cutting conditions. Although I am not familiar with a Bystronic laser, try decreasing the feed rate, power, duty, and frequency. A .406 diameter hole in .500 plate should not require too much adjustment. Smaller holes will require a greater adjustment that results in small bursts, or pulses, that eat away the material slowly without generating too much heat that could deform or melt the affected area. This requires experimenting on a scrap piece of plate. The smaller the hole the more tricky it becomes. However you will reach a limit when piercing the hole interferes with the cut. A water assist option on your laser helps a lot by keeping the heat affected area cool. We have burned .312 and .343 holes in .500 plate successfully, although it is slow. Contacting the manufacturer for some advice or at least a good starting point to work from.
WhatsGoingOn (Industrial) (OP)
5 Mar 08 10:23
I tested a couple of pieces, slowing down the feedrate by ~10% gave us decent holes.  These should be fine (clearance holes for bolts), but don't look as good as usualy where diameter > thickness.  I will try to do some more tweaking, though it is usually hard to convince the powers that be to let us do that.
1plus1 (Industrial)
8 Mar 08 9:39
I understand your dilema. Fortunately for me, I work for a job shop where experimentation is welcome. An operator should be allowed to be somewhat of a process engineer. I have spoken to several operators at maintenence and operation training programs and it is amazing to find out that a lot of companies who have lasers do not use it to its full potential. Sometimes you cannot just lay a sheet of metal on the table and press the start button. You have to play around with the cutting conditions to find the best speed and quality combination. Sometimes one part can have several cutting conditions. One for holes, one for contour,etc. The more an operator is allowed to experiment, the better that person will understand the laser.

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