Re: Asking the experts - Material selection for tongs

I am designing a machine with a pair of tongs that will be used to
> stretch a grommet. It's very similar to the nose of long, thin needle
> nose pliers. The individual tongs are designed as follows:
> - 1.6" in length, protruding from a block of metal (the base will be
> connected to a gripper, and the base and tong are one piece, 2 of > which are required).
> - Each tong is a semi circle, so together they make a complete circle > when closed.
> - From the base of the tong (the top of the block) up, here is what it > looks like:
> -- .115 radius section protrudes up for .86"
> -- 3 deg. taper from .86" to about 1"
> -- .107 radius (the radius at the top of the taper) from 1" to > about 1.37"
> -- A conical nose with a 20 deg. taper at the end (from 1.37" to > 1.6")
> -- Each sharp edge broken (radiused)
> -- .0625 radius at base of tong
> I will be loading this thing about 30 times per minute with the
> following cycle:
> - Apply ~25 lbs (each tong) distributed along the tong, with 25% of
> the total force applied in the first half of the tong and 75% applied
> in the second have of the tong, which would be the tip end (this is
> the act of opening the tongs to stretch the grommet. The force
> deflects the tongs towards each other.
> - Hold for .5 seconds while inserting a .110" object between the > tongs.
> - Grip the .110" object with ~20 lbs of total force (10 lbs per tong).
> This will most likely cause the bottom of the tongs to touch, or
> almost touch, while the tips of the tongs are separated by the .110"
> distance, therefore they are declected away from each other.
> Now, to make the picture a little clearer, the .110" object is a lead
> wire that I am pulling through the grommet (that's the reason for > stretching it).
> On to the reason for polling the experts:
> As you can see, this is a tough application. I need to balance
> stiffness and resistance to breaking and fatigue. In essence, I am
> bending this thing back and forth like one might do to break a
> paperclip!
> I cannot make the tongs beefier because of geometric issues with the
> grommet. So the dimensions are fixed. The only variable is the
> material. If it is too flexible, the tip of the tongs will not open
> enough or perhaps not apply the 20 lbs of force when closing before
> reaching the maximum deflection (when the bottom of the tongs touch).
> If it is too stiff and brittle, it will break. What material do you
> guys recommend? I need this to cycle at least 1,000,000 times before > failing.
> Thanks in advance for any help. I have some ideas, and have gotten
> some from colleagues. We are thinking perhaps 1095 or 4140 steel,
> hardened to about 42 RC. I have tried with Crucible CPM 10V material,
> but it was too brittle (really a terrible material selection, I didn't
> realize the forces were so high). It failed after about 20,000 cycles. >
> My guess is that there is some material out there that will perform
> really well in this application, but do not know what that material > is!
> TIA.
> - Luther
for your highly stressed application
may I suggest that you discuss the applicability
of Ultra High Strength Steel, with the technical
support of manufacturers like the following:
formatting link

Best regards,
formatting link

Reply to
Elia Levi
Loading thread data ...

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.