Root Cause help needed - Sheet metal breaking at press

Dear friends.,,

Can anyone help me in below?

A spring type sheet metal gets broken while pressing. The same was plated with PFZn5 and heat treatment processed.

What will be the root cause.

What will be the effect in failure of each process(plating,heat treatment)


Thanx.

Vivkrish, I split this post off from your previous thread and created its own thread because it's a separate issue from plastics. Hopefully it will get better attention on its own with a new thread title.

Good day Vivkrish,

When sheet metal fractures in the brake it is usually due to hardness/brittleness, or perhaps the gap of the jaws is too narrow. I am not familiar with the plating PFZn5 and wonder if the heat treatment was done before or after the plating?

I would look for temper following these treatments. Practical Machinist members describe this as a problem inherent with bending spring steel, though, and suggest annealing/hot bending. For more information, please read this article on Spring Steel Strip.

vivkrish said:

Dear friends.,,

Can anyone help me in below?

A spring type sheet metal gets broken while pressing. The same was plated with PFZn5 and heat treatment processed.

What will be the root cause.

What will be the effect in failure of each process(plating,heat treatment)


Thanx.

Click to expand...

Can you duplicate the issue constantly. If yes, I would look at the material. If no, it might still be the material but you should look at the press itself, the operator, the process, and the previous processes.

We had a corrective action regarding marks in the part. It turned out to be occurring 2 steps before the place where the mark 'should' be happening, and no one said anything (yes, hair was pulled out that day).

You're exceeding the tensile strength of the material. Now ask yourself why? It will depend on how/what you are forming.

Now with spring steel, I would suggest using an annealed spring steel for all but the simplest forms and then hardening after the fact if needed. Give yourself a chance.

As soon as I saw that the parts were plated, my initial thought was hydrogen embrittlement - not sure if your plating process CAN cause this or not (I'm not familiar with that plating process) however it is something that you should be easily able to determine. How does your plater clean your parts prior to processing? And is there a bake process after plating to relieve the trapped hydrogen?

all very good theories....which is correct? It might be obvious, but then why would the OP ask?

It might be as simple as determining what's wrong: is anything out of spec or obviously misprocessed?

We could ask what changed but this is often difficult to assess before we understand the causal mechanism as everything changes...and we rarely measure andrecord all of the input factors (material, process settings and conditions) to correlate to breaks. A better start is to ask what patterns exist? What is the rate? Is it all of the pieces or only some? Is there a time element to this breaking? Did it suddenly start, or has it 'always' been there at the current rate? Does it come and go, is what is the pattern: plot the data in time series it will tell you quite a bit.

We could ask what's different: is there any feature, dimension or property that is at one level for the parts that break and another level for the parts that don't break? Are there different material lots involved? Different operators? Different machines?

We could go fully functional: you are exceeding the strength of the material as Golfman says. But it it the material or the machine? Can you measure the strength of the material and the machine separately from each other?

If you have a recurrent non-conforming you need to utilize a problem solving tool such as DIVE - Define, Investigate, Verify, Ensure - or 8D. In both cases you need stats and a cross functional team to uncover the root cause and find a mistake-proof corrective action. In your particular case DOE could be useful in order to find the best solution.

Dear kirley,

Hardness is within the spec. And the gap between jaws is narrow only, because that's my drawing requirement.

Heat treatment is done after plating.

In this phenomenon what way is right to do analysis.

Thanks.

Just to ensure that the sequence is correct, are parts heat treated and plated BEFORE bending?
Have you done (or had done) a microstructure analysis of a failed part?
Have you validated the raw material (incorrect alloying elements can cause premature failure understress)
Have you validated the hardness and the coating?