Laser drilling of square hole in countersinks

[CdotS]

I am trying to make square holes after drilling countersinks in a carbon steel plate.
Plate thickness = 5/8 inch
Counter sink hole depth = 0.310 inch
Depth of laser drilling = 0.315 inch
Hole size = 0.562 inch with corner radius of 0.125 inch

The laser cutting company I have contacted says that they can make the square holes in the countersinks from the back of the plate where it is flat and not from the side where the countersinks were made. My question to the forum members are as follows:
1. Can we drill from the side where the counersinks are made?
2. If we make holes from the bak side, will the alignment of square hole to the countersink be a problem?
3. What kind of laser system be more suitable for this purpose?
4. What is the maximum thickness of carbon steel we can drill and what at power rating?

Thanks in advance.

 

[axiomatrix]

I've tried to laser cut shaped holes like you are surgesting
and have failed miserably. Its basically due to the counter sink or counter bore geometry disrupting the process gas and diverting it of axis from the beam interaction which at best gives a crap cut, the other reason is the size of nozzle is usually too large to get in real close to the material inside the counter sink. The only way I've managed it is by doing exactly what was advised. ie cut from the reverse side. As long as your jig is accuractly made and positioned, hole and countersink alignment should be fine.

Alternativley the hole profiles could be cut before the counter sink. But I guess thats not an option!!!

 

[CdotS]

Thanks for your comments. I thought I may never get a reply for my posting.

Just a few days ago, we have managed to cut square holes from the backside by vendor, similar to what you have described above.

I am just wondering whether any new laser machine has autofocus capabilities so that we will be able to cut from the countersink side.

 

[Broach]

Please excuse this comment if I make a rookie observation here. I do not know how large the plates are which are being laser cut. Is the part small enough to be put on a lathe as a second operation. Perhaps a rotary broach tool would be able to cut the square? Of course, this depends on how accurate you need the square cut also. just another idea for you.

 

[CdotS]

Plate dimensions vary widely:
Thickness = 0.5 to 3 inch
Width = 8 to 16 inch
Length = 2 to 12 ft

It is not posisble to put on a lathe, as you will appreciate.
We are still exploring the possibility of using a laser system.

 

[Broach]

Yep, tooo big.

 

[JayMaechtlen]

Beam focus isn't really the issue-
The problem is like AXIOMATRIX said:
The nozzle tends to be bulky, and may not get the tip down close enough to the cut zone. Sloping surfaces at the cut line tends to do bad things to gas flow and poor cut results.
Proper fixturing (reference the part from the same edges when performing successive processes) should let you cut from the flat side of the plate and get decent results.

Since you are performing the countersink and hole cutting operations on different machines, it shouldn't be a big deal to locate the parts "flat side up" for the laser process.

How thick you can cut depends on the laser cutting system- power, etc, etc. The thickness number of interest is the material actually being cut, not the raw blank thickness.

Jay Maechtlen

 

[SERVOCAM]

Could you do an Excimer and ablate away the material or DPSS Yag and slowly ablate away material w/ a galvo scanner? Pretty thick material for this?

 

[CdotS]

JayMaechtlen:
Thanks for your advice. We have already tried from the flat side up and it worked. If we go that route, we need to flip the plate and make sure the origin is located so that there is no offset when the square holes are cut on the back of the countersink.

Servocam:
I am not very familiar with laser cutting technologies. Could you describe the systems you mentioned in a bit more detail? Many thanks.

 

[SERVOCAM]

I'm not a laser expert (so read at your own risk), but work with many companies the use lasers or build laser machines. Instead of blasting a hole right throught he product with a high-power CO2 laser, when your processing with an Excimer or thick metal, you are delivering a high peak power and a very quick pulse rate. Each pulse, you slowly vaporize the material. Many micro machining applications use these types of lasers. You won't have a nozzle that you need to get down into the part so that won't interfere. Excimer uses a mask for the beam. If using a DPSS and galvo you have a large focal point, so you could be like 3 inches away from the material with the scanner or fixed beam (may need to be closer). Then you just program the galvo your path. Now since it is only taking away a small material at a time, it takes many passes. I have only seen people processing up to like 0.080 inch thick materials, so not sure how well it would work for your process. These process are also very precise of what they are doing.

Contact some of the laser mfg's like Lambda Physik.