Manufacturing driven drawings

[JNO_BAT]

Hello All,

I have attached two drawings that I would like to hear some opinions on. Drawing 1 was created by someone in our engineering department here in the US and drawing 2 was created by a colleague in Germany. Our German engineering team is requesting that we follow the same methods. Personally while I have some critique for both drawings the second to me is incorrect (cluttered, too many sig. figs, not drawn with engineering intent in mind, etc). I understand that they are creating it for a manufacturer who does not use modern software so they manually program the CNC. In this specific case it could make sense to perhaps create a supplemental sheet but it should not drive the way all drawings are created. As a note we are a European company so drawings are metric and First angle projection.

 

[drawoh]

JNO_BAT,

That German drawing of yours looks over-constrained to me. This is much less of a sin in 3D[ ]CAD than it would have been on a drafting board. It looks like they want the toolpaths for CNC. Do you understand the process well enough that you can do this correctly? Is there any reason the Germans cannot send a DXF or a STP file to the vendor?

--
JHG

 

[greenimi]

They are simply two different drawings: One is a PRODUCT drawing (goals to achieve and not instructions on how to make the part) and the other is a PROCESS drawing (the PROCESS requirements are the instructions *for one particular supplier's chosen method* to achieve those goals that were stated on the PRODUCT drawing.)

The PRODUCT drawing is the legal requirement and obligation of the supplier. The PROCESS drawing is the chosen method for a given supplier, but another supplier could chose a different process to achieve the same PRODUCT requirements

Product drawing is controlled by Design.
Process drawing is controlled by Manufacturing.

 

[CWB1]

Agreed with greenimi, manufacturing teams typically have their own markup or even a separate print to go along with their process sheets and work instructions. The last thing you want to do is mix design with manufacturing, that guarantees unnecessary cost.

 

[mkcski]

I can sympathize with the above thread. We SUFFER constantly with the multi-discipline drawing dilemma at my company. We have everything from fabrication, welding, machining and even painting requirements on ONE drawing. The design engineer is supposed to be an expert in all of these areas. UNREALISTIC at best. The new engineers become quickly disillusioned.

My background is mfg. After many years I final convinced the design engineering manager that the GDT is based on part function and NOT on how the machine shop will process the part - especially the datum feature assignments - a major victory. I am now working to having each discipline sign-off on the drawing to confirm their info on the drawing is accurate.

Certified Sr. GD&T Professional

 

[Belanger]

mkcski -- that's kind of ironic that you as a manufacturing person had to convince the design engineering manager that GD&T should not be based on manufacturing! Usually the mfg people gripe about the datums and tolerances being based too much on function and not on their preferred thinking. (You're correct, of course, but it's still kind of funny.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[mkcski]

John-Paul

I just realized it's been almost a year since I met you at the Stacks Class - Geez.

Yeah. Really. I am a journeyman machinist in PA and have a mech engineering degree. So I see on both sides of the same fence.
To me the philosophy of GDT offers such clarity. I cannot help myself and frequently "yell" size, form, orientation, location and to hell with mfg. Let them figure out how to process the part - make it to the drawing. Obviously this is a head-in-the-sand approach - to not accommodate mfg. But to compromise the design to accommodate the precision/accuracy of the machine tools is also dangerous. The reality is somewhere in the middle. In the part has to work when mfg is done AND you need to make profit doing it!

Certified Sr. GD&T Professional

 

[dgallup]

Can't say I like drawing 1 very much but drawing 2 should be split into two different drawing or at least two different sheets of the same drawing. Because our manufacturing engineers are few and don't have the training and skills to use our design software (don't ask), I have started to add separate sheets to our product design drawings with the operation sequence steps and things like the ordinate dimensioning of all the inflection points for CNC programing. However, we very explicitly specify that the ordinate dimensioning is for CNC programing only and not to inspect to those dimensions. I have great experience with how we make the parts so it's not really a stretch for me to design for manufacturability. I don't see this as adding cost or being inefficient. It really makes it much more efficient to manage change as everything is in one model and if I change something in the product drawing than all the process sheets automatically update. The only thing that is difficult is when manufacturing wants to hold a functionally unimportant feature to a tighter tolerance because they are going to locate off it for subsequent operations. Then it's a bit extra work to juggle the tolerances.

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[JNO_BAT]

Thanks for the input all!
I feel as though some of you have put my thoughts into words more eloquently.
We work closely with our manufacturing department in house and try to consider the manufacturing aspect as well.
But his to me seemed over the top.
We supply drawing packages with multiple file formats to all our suppliers (dxf, step, etc) so typically this issue doesn't arise.
All shops seem to have their own preferences/processes so to try and meet them all at the design level seems silly.

I will add that we build custom equipment so many of the parts we make are only made once or twice. Also we send out the bulk of our parts to many different shops worldwide. If we made mass quantities of parts and worked with select shops I could see how more time spent working towards drawings catered to manufacturing would be valuable.

dgallup- Can ask what you don't like about the first drawing?

 

[mkcski]

Another consideration:

I work for an engineer-to-order firm who manufactures what is designed at the same facility. So it is very convenient for the shop and engineering to discuss drawing interpretation (and other) issues. The physical proximity is a crutch because engineering knows if somethings is "missing" from the drawing the shop will just ask. Engineering gets lazy - the shop gets pissed.

Recently, one of our major components is being outsourced. This will test the "completeness" of the product definition on the drawing. Hopefully the supplier will call and ask questions. But we might get parts that are unacceptable because they did not "find" the "missing" information on the drawing. This is a case to make sure part definition complete in every way.

Also, if mfg info is on the drawing, the supplier might request the drawing be revised to reflect how they mfg using different processes, so their work scope is not in violation of drawing requirements. But who cares how it is made if the result is the same. Leave mfg off of product definition drawings.

Certified Sr. GD&T Professional

 

[dgallup]

First off I see no default tolerances (you don't specify the tolerance class of ISO 2768) yet nearly all dimensions do not have tolerances specified. There are no geometric tolerances like an over all profile, neither are there very many features of size except the thickness & holes that I could put a caliper on to check. There are no datums, the part is drawn at a weird orientation to a non-existent vertical axis (the 16.1 degree dimension to free space). There is a 0.1 degree dimension that it is impossible to tell what it controls. I could go on ...

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[djhurayt]

I'm not dg, but I see odd things about the first drawing also, like:
[ol ]
[li]Why not rotate the part clockwise either 6.9 even better 16.1° so that things like your first hole/c'bore near the bottom is not taken from some imaginary plane in space[/li]
[li]The 23° dimension is odd, if the above rotation is considered, the angular dimension would be 6.9 off the end. Now you have some symmetry to the part and just like your "2X" on the hole/c'bore call out, you could do 2X on 6.9° and drop both the 16.1 & 23° dimension[/li]
[li]I'm not really sure what 0.1° dimension is about[/li]
[/ol]

That is just my take on it.

 

[3DDave]

One project I was on was trying to justify not shipping the drawings that were contractually required. Mid-level management had taken the money for drawing creation and change incorporation and 'given' it to corporate and in turn they got bonuses. They were very motivated to convince people to work for $0 in exchange for the new cars they bought. My boss proposed that since the product was made to manufacturing instruction sets, that the engineering drawings could be entirely discarded, killing two birds. One, the drawings weren't needed, and two, neither were all the expensive engineers. Which was odd for a guy in charge of the engineering group, but not that odd considering he was engineer by degree only.

Another project did one better. They called out a finish must-use process at a particular company**. The company was not only out of business, there was a for-sale property sign clearly visible on Google maps Street View with small trees growing from cracks in the sidewalk. Management didn't want to let the FDA know they were accepting products from another company and justified it on the basis the other company had bought a batch of chemistry, though they apparently didn't know what was in it. Why change the drawing and let the regulatory agency know that a product substitution is being made on a regulated product?

**As in, parts shall be processed by XYZ using their proprietary materials in their proprietary process, as opposed to using material xyz in accordance with supplier instructions.

 

[mkcski]

3DDave:

Geez. That's all I can say (as I shake my head in disbelief). Thanks for the testimonial. Listen to others and learn.

Certified Sr. GD&T Professional

 

[ctopher]

The default tolerances are cutoff at the bottom of the sheet.
It seems to me Drawing 1 may be missing some minor info, Drawing 2 is an overkill.
I have worked with D2 type drawings before. Inspection has a fit with them.
Most people like visual clues. I would take D1 and rotate it and make on of the ends vertical or horizontal, start there for the angles and locations.
Make it simple.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[Tunalover]

Guys:
I have always been on a mission to convince people who want to pollute the drawings with process information that, to do so, you are telling the manufacturer (in-house or otherwise) HOW to make the part. That is a recipe for suppressing the manufacturer's ingenuity and process knowledge in doing it the way HE wants to do it. To add all that process poop on the drawing bootstraps the manufacturer to do it only the way the drawing says to do it. Result = highers costs + lower quality.

I often pull out ASME Y14.100-2013 and read off this definition of "drawing" from there:

"drawing: an engineering document or data set that discloses, directly or by reference, by means of graphic or textual
presentations, or by combinations of both, the physical or functional requirements of an item."

IMO to put more on the drawing than is required to meet the part function is a violation of that standard. End-item-focused drawings are usually short and sweet. Also, why put the process information under formal configuration control if a separate process document can be used (under informal control?) for and by Manufacturing? The drawing ends up being a living breathing beast under constant revision!



Tunalover
Electro-Mechanical Product Development
UMD 1984
UCF 1993

 

[ctopher]

I agree, process information should not be on drawings.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion