.025" Thk. S/S for small spring latch 2

[BR2006]

Good Morning---

I'm in need of some advice about material selection for a small sheet metal latch I'm defining for fabrication. This is a smal latch with 3 bends, one bend past 90°. I need to define a S/S material that allows this item to be formed, w/o cracking and still remain as a spring type device once attached to it's mating part. Is there a material that lends itself to this short of buying basic 300 series SS, forming and tempering it to suit.
P.S.- I've had someone suggest material 301 1/4 hard SS but I'm afraid it won't form without cracking.Any help would be greatly appreciated.

 

[israelkk]

301 1/4 hard is not "springy" enough and can not harden after forming. For a spring 301 Full hard or 301 extra hard are used. It is difficult to give an answer if the stresses and deflections of your spring will see are not known.

You may use material such as 17-7PH condition C and after forming to heat treat (aged) to CH900.

http://israelkk.googlepages.com/home

 

[EdStainless]

How tight is the bend radius? I really think that you need to look at a PH grade (17-4, 17-7, Custom 455). Buy it annealed, form the part, and then age.

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[BR2006]

Thanks to the both of you for your speedy response. It appears that my best course is to go with 17-7PH, laser cut-it to size/add features, form (.008 inside Bend radii) and heat treat accordingly. My only and last concern is how to determine the actual hardness required to become "springy" and still maintain tolerance. Another thing I wondering is if the material with suffer and neg. affects of laser cutting(?).

 

[BR2006]

Wow, I just spoke to my potential spring guy who will make this in production and he freaked out at the concept of going with 17-7. He believes 301 spring tempered 1/4 to 1/2 hard will work fine. He mentioned if it doesn't, he'll but annealed 301 and trat as required when done to accomplish the "springy-ness". I thought you couldn't heat treat 3xx series stainless....

 

[israelkk]

Your potential spring guy is wrong!! 301 can not be heat treated. It receives its strength through cold working to 1/4 hard, 1/2 hard, 3/4 hard, full hard and extra hard. The amount of cold reduction dictates the hardness type. After you anneal it there is no way to re harden it. I suggest you find another spring guy.

Did you do any stress calculations for the latch spring?

http://israelkk.googlepages.com/home

 

[BR2006]

Maybe either he or I is not communicating correctly. Hard to say. He was pretty short about the subject when we last spoke. Q: how do you achieve a particular/desired hardness when cold working (i.e.- measurable between 1/4, 1/2, etc.)
As for the calculations, I have none as yet but really appreciate your help on this.

 

[israelkk]

The hardness condition is done in the material manufacturing process when the strip or sheet is rolled from the billet. It can not be done on the manufactured product.

http://israelkk.googlepages.com/home

 

[EdStainless]

Your tight bend radius in hard rolled stainless will be a problem. The spec (ASTM A666) only requires that material be bent at a radius of twice the strip thickness.

You have two issues to balance, forming and service. You need softer material to form, but stonger material in service. You will not get there with a 3xx series, unless it turns out that using rather soft strip (1/8 or 1/4 hard) will be good enough in service.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm