Help with revised titanium rivet die

[jeffescott]

I posted earlier with a first pass design of a ti pin.  MRWakefield provide some excellent input for my design.

So I am back with a new design.  I have created an assembly that shows the bttm die pin, right arm(attachment for the pin), the stock shape, and one of top dies.

My thought is to grind the point into the pin blank, then heat to red hot and insert into the die, and forge the upset.

Then insert the arm onto the pin, reheat and forge the rivet head with a second die....

All I really need is to  lock the pin onto the arm, at a precise point straight and true.

I have been using threads and a lock nut, but this  is heavy and cumbersome, for a ski binding

Any ideas, comments.

@MRWakefield

[MRWakefield · Accepted solution]

Thanks very much for the comments and the mention. Hopefully the simulations in the other thread provided some useful information?

I'm finding it hard to work out the mechanism and method of operation from your assembly model. Have you performed any trials to see how much force will be required to forge the various features? According to the simulations I posted you'll require 4-5 tonnes to upset the head and 6-7 tonnes to backward extrude the tubular feature. It would save a lot of work if a simple feasibility test was to be performed with some basic tooling to see whether it's close to being doable.

[jeffescott]

Whoa thats a lot.   I removed the tubular back.   I just need to make a tight rivet on the back.

Also on the front i have preformed the point.  I can grind that +/- .5 mm.

so i just need to clean that up and form some sort of upset on the front side.  What yield stress did you use, or perhaps what forming temperature is

that at.

The design load is only 600lbs pressing down on the pin.   If i can get a .5 mm to 1 mm up set it should rivet hold fine

[MRWakefield · Accepted solution]

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@jeffescott wrote:

Whoa thats a lot.   I removed the tubular back.   I just need to make a tight rivet on the back.

Also on the front i have preformed the point.  I can grind that +/- .5 mm.

so i just need to clean that up and form some sort of upset on the front side.  What yield stress did you use, or perhaps what forming temperature is

that at.

The design load is only 600lbs pressing down on the pin.   If i can get a .5 mm to 1 mm up set it should rivet hold fine

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As per my last post in your original thread here the simulation was done with a billet temp of 930°C. I don't know what the yield stress was, the material was picked from a library included with the FEA software. If you take a look at the simulation videos again you'll see the Z load vs time.

[TrippyLighting · Accepted solution]

You may want to rename the file into ...MrWakefield 😉

[jeffescott]

Very cool simulation.  I must have missed it before. Sorry.

K so here is my take.   The material used is some sort of high chrome metal.  Its harder than 300 series ss lets say 440.  Yield stress is similar to ti with a higher modulus.  So forging will be just as difficult.  The service is very light load,  500 N on 9mm2 and very low speed 90 degree arc at 240 rpm.   Yet the high chrome material wears out in 150 days of skiing,  i do 50 days a year.  Got a better material?

Also these pins are rivited in.  Ill make a thinner taper into the upset.  Let you know what happens. Hope to give it a go this week.

Thank you so much, you have been very helpful

[jeffescott]

This is what i am making notice to difficult extrusion in the rear, just have to upset a rivet.

[MichaelT_123]

Hi Mr JSScott6SWZG,

If I understand the intent of the design correctly,

I would:

• Create a simple jig for a lathe and bore the precise hole
• Optionally add an undercut for the pin's middle collar
• Turn (or grind if necessary) a pin, but without the back collar
• Machine pin/hole to press or thigh fit tolerances
• Gently heat the arm to 100 °C would do (or whatever units you are born for)
• Cool down the pin in liquid N₂
• Drop the pin into the hole
• With the assumption that there will be no pulling forces acting on a pin
• the press-fit, and in reality, the middle collar will resist pushing forces.

Regards
MichaelT

[MRWakefield · Accepted solution]

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@jeffescott wrote:

Very cool simulation.  I must have missed it before. Sorry.

K so here is my take.   The material used is some sort of high chrome metal.  Its harder than 300 series ss lets say 440.  Yield stress is similar to ti with a higher modulus.  So forging will be just as difficult.  The service is very light load,  500 N on 9mm2 and very low speed 90 degree arc at 240 rpm.   Yet the high chrome material wears out in 150 days of skiing,  i do 50 days a year.  Got a better material?

Also these pins are rivited in.  Ill make a thinner taper into the upset.  Let you know what happens. Hope to give it a go this week.

Thank you so much, you have been very helpful

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Ok, here are my thoughts:

I think attempting to forge (hot or cold) anything which isn't very soft such as low alloy aluminium, copper or brass is going to be difficult without a proper forging press (and obviously these materials aren't a consideration for this application!). You might be able to hot forge an alloy steel and through harden just the wear points, leaving the back end relatively soft to enable it to be swaged over.

A small induction heater might be better than a flame as the heat can be more accurately applied to the relevant areas (bearing in mind that induction heaters only work on certain materials). Heating by induction will also be very much quicker than heating by flame. You'll find many simple plans on the internet for small induction heaters if you don't want to buy a ready-made one).

Additional case-hardening and/or nitriding could be applied to the high wear areas as well but that's unlikely to be something you can do yourself so it would need to be subbed out. Similarly with TiN/TiCN/DLC coatings (although these are very thin and might wear through quite quickly even though they're very hard (and probably very expensive)). Hard chrome can be applied very thickly and is very hard wearing. Hard chroming kits are available but might not be something you want to do at home. After hard chroming you might need to grind it to finished form.

I don't know what material this part is contacting but another consideration is the tendency for galling. Stainless steel parts that slide or rotate against each other have a tendency for galling which increases the wear rate (similarly with aluminium against aluminium).

So, in summary:

If it were me (and this is just my personal opinion!) I wouldn't pursue hot forging. I would get these turned by a local machine shop or hobbyist then either induction harden the pointy bit or get that area hard chromed.

Hope you find this helpful.

[jeffescott]

Yeah i was hoping for a riveted joint.  Oh for a lathe.   

[MRWakefield]

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@jeffescott wrote:

Yeah i was hoping for a riveted joint.  Oh for a lathe.   

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I don't think any of the options I mentioned will prevent you being able to rivet it into place.

Oh for a lathe indeed!!. I had a Willson slant-bed  lathe in the mid to late '80's when I lived with my parents. It had an 18" swing so I could turn some pretty big stuff with it. It was this that enabled me to get my first job in engineering. Unfortunately I had to sell it in 1989 and I haven't had the space for another one since ☹️

I've found a photo of what looks like the same model as the one I had on the interwebs:

If I think of any other options I'll let you know, and don't forget to keep us updated with your progress or if you need any more help.

[jeffescott]

Hah it kinda worked.   Heat die and punch to 500c.  Looking to hold 400c.  For a couple of whacks.

Set up wasn’t ideal si first whack was off center so that is why it is a little bent. 
pin took the form well. Unfortunately.  Taper bit was a little small so tip of die is out.

rivet sucked up nice.

put on the piece ass backwards bad set up.

Think one or two more and ill get the feel right

Also will go with a longer blank to keep ii lined up better.

i cant thank you enough.

[MRWakefield]

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@jeffescott wrote:

Hah it kinda worked.   Heat die and punch to 500c.  Looking to hold 400c.  For a couple of whacks.

Set up wasn’t ideal si first whack was off center so that is why it is a little bent. 
pin took the form well. Unfortunately.  Taper bit was a little small so tip of die is out.

rivet sucked up nice.

put on the piece ass backwards bad set up.

Think one or two more and ill get the feel right

Also will go with a longer blank to keep ii lined up better.

i cant thank you enough.

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Great! Ah yes, if you're giving it a sharp blow rather than a relatively slow application of force then I guess you should have a better chance of it forming.

Don't forget to keep us updated!