Design of breakaway connection tabs on sheet metal parts.

[KirbyWan]

Howdy all,

I asked this question in Machines and Machining Engineering forum and didn't get much repsonse, so I thought I would put it out here to see if the people who work with CAD might have more information.

I have a series of parts that I would like to have laser cut out of sheet aluminum, but still be connected to the parent sheet for PAA processing. Here are the details:

Sheet 1, .010 aluminum with 34 parts fit on a 4' X 12' sheet. I want the parts laser cut, but still connected to the parent sheet so that they can be run through our FPL etch/phosphoric acid anodize line then bond primed and the bond primer cured in an oven. Then the individual parts seperated to be used in a bonded panel assembly.

Sheet 2, .025 aluminum chem milled down to .012/.014 in areas with 8 parts on a 4' X 10' sheet. Same processing as above.

What are best practices for desinging connections. I need them thin enough to break out easily, but thick enough that the parts will not fall out during processing and handling. The anodize also will need to run current through the tabs of course. I tried to do a search on this, but I'm not sure what the correct terms for these tabs are.

Thanks for your help.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[MadMango]

This isn't a CAD question either... in the past I have made tab widths holding parts equal to the material thickness and have had good results for post processing after cutting. The number of tabs depends solely on the size and shape of your parts.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[SnowCrash]

I agree with MadMango plus the number of tabs should also take into account the current requirements.

--
Hardie "Crashj" Johnson
SW 2010 SP 2.1
HP Pavillion Elite HPE

 

[drawoh]

KirbyWan,

By the sound of it, it will be difficult to attach your parts to an assembly. This is the fundamental functionality of SolidWorks, so it sounds to me like bad practise.

What data does your fabricator need to do laser cutting? Could you combine your separate parts in an assembly model and generate a drawing? Your fabricator probably can work from the resulting DXF file.

JHG

 

[KirbyWan]

I usually send my fabricator a .DXF. I position all the parts on a sheet so he just has one file to work with. I just need to tweek it to add the tabs. It's a bit more work for me, but it makes it more cost effective down the road.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[drawoh]

KirbyWan,

Who is the expert on laser cutting, you, or your supplier?

Tell him what you want. Let him figure out how to make it. Dropping your DXF file into AutoCAD and patterning it ought to be easy.

JHG

 

[Updraft]

Kirby,

When we switched to an autonesting software at a previous company we found that software to have all the options we needed. We had to learn how to use it properly, but once we did it was a dream, not only in material utilization (we saved over $20K/month!), but in JIT and reduced inventory. But to your need, the autonesting software just needed to know if we were punching or laser cutting and if we were using common-line cutting. There were general parameters we had control of for the breakout tabs, which is really the issue you are describing.

Unless you are creating your own nesting and therefore a composite cut DXF file for the entire sheets (unfortunately that is what it sounds like you are doing - wow!) I suggest you or your fabricator look into the various autonesting software packages. Even if you do not purchase it you may be able to glean the particular information you need to make your nests with the right breakout tabs. It is an interesting problem, but not really a CAD problem. If you were to learn some rules/guidelines perhaps you can get some help writing a macro to run around the perimeter of your traces and put the breakouts in. Good luck.

- - -Updraft

 

[karmoh]

Even the most basic laser cutting software has an ability to add tags. These can be corners or along edges. Supply the dxf/dwg and the laser cnc programmer should do the rest.
Their CNC software should profile the perimeter edges and any cutouts. Cutout excess material should fall away from the laser via a chute. You can specify on your DXF where you require tagging. The Programmer will then simply add the tags to parameters you specify.

Some points to take in to account

• The material you specify is thin for normal fabrication shops, is the laser a specialist shop?

• Most tags are no larger than 0.010 - this is your material thickness, with your specifications these tags will be particularly difficult to remove cleanly. Mostly likely damage the parts with shaking or clipping.

• The flexibility of the size sheets once lasered will also be difficult to handle, unless tagged sufficiently which will take you full circle the point above and damage the parts.

I hope that makes sense!

 

[KirbyWan]

Thanks for everyone's help. I'll give the fabricator a call and ask them what their capabilites are. I hadn't thought to ask them about this, I just thought it was my job to give them the line for their laser to follow.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[MikeHalloran]

Then you have been working too hard.

Most cutters prefer to get a file showing the part you want, not the cutter path to make it.

... but they do get files both ways, so it's best to specify on your PO and somewhere in the drawing file exactly what you want.



Mike Halloran
Pembroke Pines, FL, USA

 

[Russell67]

We ran into this issue at a previous company. Because we supplied the material we also supplied the patterns. We made alot of parts that we also were post processed in sheet format and we found the more info we gave them the less we spent and the better the final product. I agree that to do this in solidworks is not the way. Use autodcad create the plines, tooling holes the whole nine yards. It takes more time on your end but you get less of a headache.

 

[KirbyWan]

That took me a minute to parse correctly, because when you wrote 'use autocad' I read 'beat myself over the head with a brick'. I might not mind AutoCAD if I knew how to use it of if it was designed so that you could figure it out in a few minutes. I mean I'm an Engineer not a Luddite after all, but AutoCAD just get's on my nerves. Alright I mean SolidWorks DWG editor, but I think it's a functional copy. For now we are just going to cut the parts out and rack them individually for processing, we just thought this is the way to go to cut back on cost in the future.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[MikeHalloran]

I don't much care for SW's DWG editor either.
I also don't much care for the way it insinuates itself into regular AutoCAD and nags you with stupid questions.
I don't care for recent versions of AutoCAD, either; that big A and ribbon toolbar just annoy the hell out of me.


I forgot to write earlier that you want your tabs to comprise rectangles meeting at their corners, or triangles intersecting edges; you don't want to generate thin linear slivers that fall off and foul the machinery and stab the workers.



Mike Halloran
Pembroke Pines, FL, USA