Discussion in 'Manufacturing and Related Processes' started by S1D3K1CK, Apr 6, 2021.
What are your thoughts on preventing this.
Have you checked out some resources like Die Science: Splitting or Cracking?
What's the bend radius on the print?
The bend radius is R4.74 mm (TYP). Attached is the flat pattern of the design.
What material does the drawing call out?
What is the material in the picture?
How have you ensured there are no material substitutions?
Is the bend along the length or width of the sheet? (yes really) Sheet metal, especially cold rolled, has a grain so bend radii can be tighter if your bends run longitudinally than side-to-side (transverse).
What is the material thickness? Thicker and harder materials cannot tolerate as small a radius as thinner and softer materials.
The horizontal line marks suggest the brake's jaws forced the sheetmetal down into the lower "vee" which can contribute to the necking that Miner's resource referred to. I would try less pressure on the downstroke.
Protocase suggests you can also look at the proximity of the cutout, as well as consider dressing the edge prior to the bend operation.
I am not affiliated with Protocase.
My first thought, based on a lot of rejects from suppliers of sheet metal, is the bend radius needs to be appropriate for the thickness/type (malleability) of the material. After that, it might, as Jennifer suggests, be a material condition/spec issue which manifests itself in this position. Do all components exhibit such cracks? I'm also a little concerned about the surface damage/indentation. Is this a machine press brake or a manual one? Does the shop which produced it have the ability to feedback their understanding (I'm guessing this is not YOUR shop, maybe a supplier?)
This is our shop that is producing these parts. But we only produce the parts from our customer's designs, material requirements and the customer's requested, material supplier. I am not familiar with material tensile strengths needed for certain thicknesses/material types or even how to certify what we actually receive but I do know that our material certs match what the design drawing calls out. I am assuming because there is a radius (on the flat design) right where the form bend is, that's the culprit of the necking (possibly the heating from laser cutting the part is making it more fragile, especially because I can't get top management to realize the operator HAS to deburr all edges from the laser).
And no not every component is doing this, we were producing around 300 pcs and more than 70% had some kind of failure (some were noticeable like in the photo above, and some you had to know what to look for to notice but it was still a failure). Another assumption is the material supplier could have also provided the incorrect material and gave us the correct material certs to match what the drawing calls for, or just a bad design.
I will look into how the programmer "lays" the parts to be cut on the laser. I will also look into how they can modify their forming program to adjust the tonnage maybe?
Thanks for the link.
Bingo! Based on my previous post (the "lots of rejects" one) I had learned that unless the designer really knows what they are doing and liaises with the shop making the part, it's likely that this is a design issue. Can I ask if your planners/estimators who reviewed the part at quoting had any bad feelings about this feature?
I hate to throw him under the bus but, he tends to "overlook" ALOT of details on the drawings like this for example. In 2019, I completed a total of 56 PPAP's for our customer and I myself had to submit SRDC's (Supplier Request for Drawing Change) for around 48 of them. We are, as they say, a mom n pop shop, so details tend to get "overlooked".
Yup, I hear you (well, read, really). So, does this person utilize some kind of check-sheet with some guidance on acceptable feature sizing to minimize the risk of missing this type of thing again (not to mention the cost of your work in creating paperwork "after the fact")?
TBH - can I be brutal? - your estimator is likely costing your company a substantial amount of money or at a minimum, the $$ margins on the parts are lower than they should be. The fact that the parts are being damaged while held (clamped) to give that tight/small a bend could have been a reason for rejection, without the tear/crack. I wonder what a "5 Why" might reveal...
I am glad you mentioned this. I have done a 5 Why a few years ago on this exact situation and presented it to the owner but ended up "talking to a brick wall". We just changed ownership on April 1st, so I will bring this up again to the new owners, and maybe some more detailed analysis/training can be done during the quoting. There are checklists and procedures for quoting but he is the one writing those as well, unfortunately.
Now the issue at hand with this cracking/necking, I will be in contact with the engineer to either change the design and/or material. The involvement on this forum and helpfulness is amazing and I appreciate it from you all!
This is so true. For an example of just 1 part number, the part was quoted for laser, part marking, and paint (outside source). But the part was a formed and welded part (the process is: laser, part marking, form, weld, paint prep, and paint) so there were two of our most expensive operations left out of the quote. If I was a buyer, I'd jump all over that price as well.
Fabulous. This is great "fodder" for the Internal Audit program! When considering the "importance of the process" and if said process is "effectively implemented", process measurement/monitoring and also, to an extent, when demonstrating "risk-based thinking" of audits, this would be a fantastic opportunity to audit new business quotes time and again (not to an arbitrary calendar of 1/month or similar), until the issue is fixed. Boy, I'd be all over that like a rash!
We are due for an IATF re-certification audit in May. I would love for the IATF auditor to catch what is wrong with our system, not just what we discussed so far but also our auditing. Out audits consist of paying a consultant, which is in Washington state and we are in California, to do the audits over the phone, with ONE internal person providing requested documents. This sucks!!! Nothing gets fixed properly, certain people are left to "put out fires" while others stand back and watch it burn. Hopefully, with new ownership, it changes. Thanks!
Can the CFO be asked to make a justification for the value of such an expense? Do they know how to quantify it? It might be less expensive to have another internal person learn how to audit...
We used to do our own internal audits but the lead auditor became LAZY and decided to go to an external consultant for the sole reason of having someone to blame besides himself, in the case of a non-conformity.
Sounds like I'm complaining I know but just the struggles we have to deal with when we have no team effort and the Top Management controls everything but doesn't know everything.
I have presented some improvements to the new owners and they are willing to change things around, start continual improvement, statistical analysis, and not just "be compliant" to just get by.
A good start would be our quoting process!
Is this, perhaps, a downside of doing mega-audits of the whole QMS, based on similar methods as the CB audit is? If so, that WOULD be something which, having created a monster, anyone would become lazy when forced to feed it! Internal audits, experience shows (me) should be planned to take around 2-3 hours, because a) it's tough to do more and b) most processes can be effectively audited (sticking to scope etc) in that timeframe.
Your auditor would need to be experienced enough in sheetmetal to pick up on this and then follow back to design as Andy has pointed out. I used to audit for semiconductor, where the quality director really wished I knew enough about the processes to give these specific types of insights. What I instead had to offer was a systemic perspective. It's really hard to get both in one person.
I know we are all human. I understand that it can be hard to be responsible for so much but, that should be when you pass on some of the responsibility to personnel you can trust to get the job done and get it done right, not just place bandaids over issues. The Lead auditor was also a General Manager/QA Manager that came from the machine shop so that person knows (roughly) how the process work and how the metal reacts. My issue is, how can you say you have a core team when one person does 95% of the decision-making. I feel like in this case, being overwhelmed with so much something (in their eyes) as minor as this, was no problem.
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