Material selection for 2.5mm press-pin 2

[Poorpaulus]

Hi everyone,
I'm NOT an expert of any kind when it comes to this arena, which is showing the restults that I am getting.

I have a 2.5mm dia press tool pin that is pushing in a small, steel part with an interference fit in to aluminium. Unfortunately, the steel part needs to be pushed down approx 20mm, so the pins that we have tried so far have all bent, or failed quickly. We're working on redesigning the small part so that it doesn't have to be pushed down 20mm, but in the meantime, I need a solution to the bending pin problem. If it makes any difference, this is very low volume (circa 20/day).

Can anyone recommend a material and suitable heat treatment to stop my press tool from becoming a banana?

 

[3DDave]

Step 1 - see how warm you can make the aluminum part
Step 2 - find some dry ice to cool off the steel part (not the pin)
Step 3 - work fast
Step 4 - try progressively longer pins - a short one to start leaving only 5 mm unsupported at the start of each push, so that would be 4 pins.

You can try harder pins but buckling failure is mainly based on section properties (which I expect you have maximized), modulus of elasticity (which is nearly constant for all steels as to make no difference), and unsupported length.

Alignment is also critical. You know how staplers sometimes crunch the staple legs incorrectly? Almost always because side pressure on the top of the stapler has moved it relative to the anvil by a tiny amount if the paper isn't just too thick.

If you want to double the stiffness tungsten or tungsten carbide might work, but check

https://www.engineeringtoolbox.com/euler-column-formula-d_1813.html

. I think your case would be K=2.

You can see that supporting one end will help a lot over no support, but the length^2 is a big driver. Going from 20 to 5 means a 16X improvement.

 

[Poorpaulus]

That is super-helpful. Thank you vey much .

 

[3DDave]

Sorry - that would be n=2, k-0.7.

 

[EdStainless]

Very good alignment with no twist or play in it is important.
You have to be able to keep the force in line

Which is bending, the pin that you are putting in or your tool?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Tmoose]

What material are the pins made of now ?

As others asked , Is the tool pin bending or there pins being pressed into the aluminum part that are bending ?

 

[TugboatEng]

Two immediate suggestions are to use a harder pin.

Place a bushing over the pin to support it as it's pressed.

 

[Compositepro]

Make a simple tool to support the pin from buckling while pressing it into the hole. The tool (or bushing) would have a hole a few thousandths larger than the pin. Many engineering problems are just a matter of developing , or finding, the right tool to do something. A pin vise might work well. It can clamp onto the pin to push it in with only a short unsupported length.
Does the pin need to be an interference fit for its entire length?

 

[Poorpaulus]

At the moment, the material is EN32. Probably not the best choice, but that's what our job-shop had to hand. They also attempted a rudimentary heat-treatment. The pin is bending. It has a very small recess in the end to help alignment. Unfortunately, the equipment that is available means that modifying an off-the-shelf pin won’t work, so it’s a fully machined pin and holder.

There is very small clearance between the press pin and the hole, but it could be tighter – I’ll look at that again too.

Thanks for the advice – I’ll keep at it.

 

[3DDave]

It doesn't look like EN32 responds to heat treatment - the links Google coughs up list it as a low strength case carburizing hardening steel. This part is thin enough maybe the case depth could be a substantial section.

I keep seeing "EN32 is a case hardening steel with low tensile strength and is used in general engineering for the production of lightly stressed components."

It may be worth finding a far harder material and sending to an EDM shop to create the recess.

 

[TugboatEng]

<0.18% carbon typically means it does but respond to heat treatment.

Case hardening normally isn't going to improve the resistance to bending much but at only 2.5mm maybe it could be case hardened through.

 

[Qcprick63]

A class ZZ gage pin, can be purchased thru grainger. Choose the size you want. It's hardened tool steel about 50 mmm long. Next day delivery and they cost under $8.00!

 

[DAVIDSTECKER]

Have you tried using a lub or Anti-seize to reduce any galling?