twisting and bending spring steel

[exxonvaldese]

We build a fan that has the back of the motor supported by 4, 6 gauge spring steel wire struts with mounting loops on the ends, bent and then heat treated to Rockwell C45-49.5
Drawing attached.

This arrangement was OK with a Roto-molded fan shell but we've moved to an Injection molded fan shell now and need something more accurate.

I was thinking we could use flat bar, punch holes, bend ends and twist center to enhance airflow but the manufacturer says they expect a +/-.25" variation in the parts.

So now I'm looking for any other ideas. How can I make a low cost strut with some spring to it that's accurate to +/-.05" between holes and .5 degree on bends?

Thanks, Jerry

 

[EdStainless]

Why did you heat treat the wire, did you need it weaker than it started?
I would use wire, bend the end loops, and then make a die to size them.
Only the two end pockets and the punches would need to be tool steel, the rest of the tool could be Al.
For wire use OTMB or music wire (I don't recall the ASTM spec numbers).
If you want to get fancy give them a 300-350F stress relief after forming and before sizing, but I doubt that you need it.

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P.E. Metallurgy, Plymouth Tube

 

[exxonvaldese]

EdSainless:

You ask: "Why did you heat treat the wire, did you need it weaker than it started?"
I don't know why and I don't know what exactly they do for treatment but I do know that the first samples we received snapped in half when the fan was drop tested. Not sure if they were heat treated at that point but the treatment they use now makes the wire more resilient, less brittle but still springy. Is that considered weaker?

When you say, "make a die to size them," are you meaning to make the loops slightly under sized and then run a punch through to remove a little material so the bolt has a rounder hole? That sounds like pretty good idea.

Thanks, Jerry

 

[EdStainless]

Specially a pair of punches a fixed distance from each other.
That would set the loop size and distance.

Look into using OTMB (oil tempered medium basic), it isn't as strong as Music wire and should be more forgiving.
You may need to look at a stress relief after forming the loops before sizing them.

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P.E. Metallurgy, Plymouth Tube