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Controlling a spring clips dimensions 4

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Charon99

Industrial
Nov 10, 2006
22
Hi, I hope someone can help me. I’m having problems with our manufacturing partners not being able to control the final dimensions of a spring clip.
The clip is as shown in the image below. The problem is they can’t maintain the 60.54 dimension with in a tolerance of +0/-5mm. After forming the dimension can vary but this isn’t the big problem (but it is an issue); because after heat treatment it can vary again by up to an additional 8 mm in any direction. How can they resolve this?
They have tried widening the clip to get a better cross-sectional area to length ratio (increasing the 6mm dimension). This seems to have little effect.
The material of manufacture is:- GB/T 1222 65Mn Spring steel.
The forming press is a 16T press.
Heat treatment :- Quenching temperature 830°c, tempering temperature 450°c, heat treatment duration 1.5hrs.

Any ideas why the final product 60.54 dimension is so inconsistent?

Capture_arnjhu.jpg
 
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Hi
Which way is the clip varying is it going plus the 60.54 or negative?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
 
So these are being cold formed after HT and then stress relieved? This is how springs are normally fabricated.

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P.E. Metallurgy, consulting work welcomed
 
You are asking for tolerances beyond process capabilities. Learn the process capabilities and design accordingly.

Otherwise... There's the ol' sort-and-scrap.
 
Thanks for your help,

These are being cold formed and then ht (as above) to make them "springy".
Surely they must form them before ht otherwise they would not take form???
They can vary in either direction but normally the gap is opening but without any consistency.

The supplier tells me they can't achieve the tolerance because the material is too thin or the 6mm width is too small.
 
@charon99
The design is not helping, a very thin material with a large radii, it's an uphill battle.

couple of suggestions:
since this is a very inexpensive part it is a matter of cost vs cost of the process.
is this material being formed in the annealed condition can material be purchased in the annealed condition?
the forming induces stress thus during heat treat the part will move. in addition during the transformation of the material causes movement.
a pre-heat temperature which should be specified in the heat treat specified will lessen the movement but not eliminate.

Important information: make stainless steel heat fixture. with the same configuration as the clip, except for easy loading slide the clips
on to the fixture to restrain them. simple and fast. run the parts thru all the cycles , harden and temper, then remove them.
this is and will be a trial and error, it's is what it is. until the right size on the fixture is obtained.

look into the speed of the quenching oil, insist on a slow acting quench oil, most the distortion happens here.

a thin un-restrained part like this will be difficult to maintain geometry. because it is so thin.
 
@mfgenggear

I'm confused. I thought you had to 1, Form the shape, 2, Anneal it to release stresses, 3, "harden" heat treat the part to make it springy.

If 65Mn spring steel is already hardened, how do they form it without it springing back to its original shape?

Why is the factory telling me they purchase 65Mn spring steel, cut and form it and then HT it?

What material should you start with?

p.s. With the samples I have seen the material is ductile before it is heat treated but the specification for 65MN includes hardening ht. Why are the un-heat treated samples ductile if they are 65Mn?

 
@charon
It is standard practice to form metals in the annealed condition.
Please advise the condition of the material as purchased, hardness ?
Please investigate if it can be purchased in the annealed condition.
Material will work harden after forming, so I do agree with the post anneal and harden.

Now my expertise is not spring steel.
But basics is basics. Looking at the % elongation is only 5%

 
Charon99,

Your parts are sheet metal. My understanding is that sheet metal is bent to a tolerance of [±]0.4mm. Your 32mm[ ]radius may be the problem. If you lose the big curve, you can do two 90[°][ ]bends. This may be easier to do accurately.

Are you talking to your vendor about this?

--
JHG
 
@mfgenggear

Thanks for your help. I’m trying to get details on the material they are using. They told me 65Nm. But I think that can’t be right.
 
@drawoh

This has to sit over a curved face, like a ring clip on a hose. The rad could be made with multiple flat faces (I guess 10). But I imagine that wouldn’t help (lots of bends with a tolerance on each bend to deal with).
 
Charon99,

Can you configure the thing so that there is one sharp bend that controls that final dimension?

--
JHG
 
I couldn’t imagine how I could loose 8mm out of tolerance in a final bend. The part is just too small. Your idea with a screws wouldn’t work because there’s no free space bellow the 3.15 flanges. I have done some tests and I think I can accept a tol as high as +0/-15mm on the 60.54dim. and it still work. I’m getting a large qty of samples measured to evaluate what the scrap rate would be with such a wide tolerance.
But saying all that I’m still confused as to the raw material that should be used. Is 65Mn a hard spring steel? If so surely this shouldn’t be used?

What grade of steel should we start with? Don’t we need a ductile grade that can be hardened after forming. I’m interrogating the factory now but would love to be able to say you should be using x material and performing y hardening. Any additional advice on this?
 
If the tolerance is +/-15mm it makes no sense to specify the dimension to two decimal points.
 

quote "Your idea with a screws wouldn’t work because there’s no free space bellow the 3.15 flanges."

the clips slide on from the end of the fixture not from above. quick and fast, under the flange has a relief for clearance. , the only restrain is on the R32. to keep it restrained.
 
spring steel can be soft while forming, then formed, because of the carbon content then can be heat treat to the spring steel hardness,
it's really simple. analogy: tool steel can be purchased annealed condition so it can be machined, then after machining it will be harden to full hardness required.
go and talk to your supplier under stand the heat treat process. they can help you.
 
No, spring wire is full hard when it is coiled or formed. The only thing done afterwards is a low temp stress relief (350-400F).
I have never seen springs formed while soft.
If you insist on post-form HT then you need to press quench these to hold the shape.

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P.E. Metallurgy, consulting work welcomed
 
Ed
with that bend will it crack?
I did mention I am not spring steel expert, most forming I have done it's been in the annealed condition to prevent cracking.
spring steel only has 5% elongation please advise maybe I will learn also.
 
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