Drawing type 3

[Pekkeri]

Hi All

Say you have a part like the one on the attached pic. Basically it`s a single part that is manufactured by laser cutting, bending and welding (red corners on the pic). If one would create a drawing for the part, would that drawing be considered as a part drawing or a welding assembly drawing (it only has one part..)?
Or should there be different drawings for laser/bending and for welding?

Whats your opininon about this?

Please let me know!

BR

 

[drawoh]

Pekkeri,

When it comes back to you welded, it is one part, right? Don't think about your CAD model. Think about how you order parts and assemble them.

You need an assembly drawing and BOM when you are ordering, stocking and kitting the parts and then assembling them. When you order something from a vendor, you should be sending out one drawing with all the specifications the vendor requires. There may be a BOM on the drawing. There is no difference between a weldment, and a sheet metal part with PEM[ ]nuts.

--
JHG

 

[Pekkeri]

Thanks for the answer drawoh!

But my point was that it is one part also BEFORE welding! The box is made from single sheet metal piece by bending up the sides (flanges) and then welding the corners.
So my confusion is that whether the drawing of this part should be considered as a part drawing or an assembly drawing. Usually when we speak about welding drawings they are considered as a type of assembly drawings because we weld different parts into one bigger part (e.g. bicycle frame). In my example we weld together features of single part and it remains a single part.

BR

 

[3DDave]

Do whichever you feel better about.

 

[dgallup]

What difference does it make? The only difference in our drawings between parts and assemblies are the titles. Personally, I would call it a sheet metal part.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[drawoh]

(Mechanical)(OP)28 Apr 20 20:47
Thanks for the answer drawoh!

But my point was that it is one part also BEFORE welding! The box is made from single sheet metal piece by bending up the sides (flanges) and then welding the corners.

Who cares? Let's look at the logistics.

I have to build your assembly, so I look down through the BOM. I order each and every piece that has a part number and manufacturer such as McMaster Carr. For each and every piece that has your in-house part number, there should be a corresponding document, and I should be able to pull it out and examine it, and figure out how to acquire it.
[ul]
[li]The part may be an assembly. It will have a BOM. I can read through it and order the parts. [/li]
[li]It may be a specification control. Some manufacturers have weird unmanageable numbering systems. For example, MicroMo has an elaborate system for indentifying their gearmotors. You go to their website or catalogue and construct a long, complicated number that specifies the motor, voltage, gearhead, ratio, output shaft and who knows what else. They give you back an order number which is nice and simple, except that there is no way an engineer can read this and figure out what it refers to. The specification control tells engineering what the part is and it tells purchasing how to order it. In the case of a common part like a fan, the specification control may contain a list of acceptable parts.[/li]
[li]The part is to be fabricated by a subcontractor. The part may be a very simple, rectangular bracket with two holes in it. It may be an elaborate assembly with features welded, pressed in, riveted, or maybe even screwed together. The drawing may have multiple sheets, and it may have a BOM.[/li]
[/ul]

A lot of big manufacturers assign their own part number to everything on the BOM. The drawing either is an assembly, a fabrication drawing or a specification control.

I use SolidWorks. Unless my part is absolutely dead simple, I create an assembly model. I attach the fabrication drawing to the assembly model, and I attach the assembly model to the intended assembly. When I need thread inserts, dowel pins or welded-on features, I add them on and attach a BOM to the fabrication drawing.

--
JHG

 

[hatsegal]

Pekkeri,

Is your confusion of part vs. assembly because you are trying to account for the additional weld material?
If the sheet metal part were instead bent and coated (paint or other) with no welds, how would you approach that -- a part drawing or assembly drawing?


Cheers, hatsegal
"Think first"

 

[Pekkeri]

Hatsegal,

Not exactly because of the filler material addition, but rather because usually welding drawings are considered as assembly drawings.
But I think I get the direction you are heading with your question. I myself would rahter call it a part drawing.

But if you would call it a part drawing, then an another question will arise: should you show dimensions and requirements of all the operations (laser/bend/weld) on one drawing, or should you use different drawings for different steps? And here I mean a part drawing that`s gonna be listed in top-level assembly documentation (not a process drawing).

 

[hatsegal]

Pekkeri,
Typically, companies have internal standards to dictate these details.
What I've seen myself for sheet metal parts is a drawing showing the formed/bent part specifying the required final dims (with appropriate weld notes) and a flat-pattern view showing the developed flat before bending (no mention of what process to use). If all views don't fit on one sheet, then use multiple sheets. Of course, the developed flat pattern depends on how you calculate necessary bend deduction/allowance, but that's a separate topic.


Cheers, hatsegal
"Think first"

 

[3DDave]

An engineering drawing typically shows only the final configuration of the part or assembly. Some people think it should also have a flat pattern, but that allows for the chance that a flat part meets the drawing for itself, but does not form to match the formed part and results in angry finger pointing about who is at fault.

 

[Pekkeri]

3DDave,

"An engineering drawing typically shows only the final configuration of the part or assembly"..I`ve been used to think this way also.

And I have also noticed that some companies tend to put flat patterns to a sheetmetal part drawing. To some degree it makes sense in my mind because then you can add toleranced dimensions to check directly after laser cutting (and before bending). But yeah, then again you can also tolerance the final config.

But okay, say I create only final config drawing for the said part. Then I`ll have to use different standards for tolerancing laser-cut features, bended features and welded features. For example:

Unspecified general tolerances ISO 2768-mK;
Unspecified tolerances for welded features IS0 13920-BF;
...
(haven`t found specific ISO standard for tolerancing bends/bended features)

 

[3DDave]

So sorry for you having to use ISO standards. Don't leave any tolerances unspecified.

 

[looslib]

It is a single part. You will provide the supplier a drawing showing the single part with a note to weld the corners after bending. Nothing on your drawing should specify how the piece part is to be cut (Laser, shearing, nibbling) nor the bending process to use. You are only buying the finished part. How it is manufactured does not concern you as long as the finished, delivered product meets your drawing specifications.

If you put a flat pattern on your drawings, mark it For Reference Only, unless you know the bending process the manufacturer will use and what bend allowances the material needs for those processes. Where I used to work, we would sometimes sub-contract parts that we would also do in-house. We put a Internal Use Only on the flat pattern so the other company would not use it. We were buying the bent finished part and that is all we checked against the drawing when the parts arrived.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli