What steel to use for locating pins?

[JJRCAN]

I am currently using 1144 steel heat treated to 50Rc for locating pins which are used on a fixture to build seats. When a seat is built a robot picks the seat from the fixture, there must be some binding happening between the locating pin and the part that sits on it. This causes the locating pins to break off at the undercut. The robot program has been modified to reduce binding but every few days a pin breaks at random. I am considering replacing these pins with ones made from a less brittle steel...any recommendations? Hopefully this will reduce the pins breaking.

 

[dhengr]

The pins locate the feet on the legs of the seat, in an assembly fixture, am I getting that right? Maybe you should eliminate the undercut on the pins, or shorten the pins so the bending moment isn’t so great as they cantilever up from their mounting surface. Why is the relatively exotic material used for the pins, except for wear? Use mild steel pins, and replace them once in a while, but still get rid of the undercut, a stress raiser at the max. stress point. Finally, maybe you should look at your assembly process to see what is causing the legs to move so drastically as to overstress the locating pins. Maybe put a little taper on the pins, except at the final positioning location, this the load is relieved before the bending or shear stress gets to high.

 

[chicopee]

Obviously, there are several types of pin locators, have you looked at the type that incorporate shoulders. Also, may be the head configuration needs to be changed perhaps to a round or bullet shape configuration.

 

[MikeHalloran]

Even two round pins can overconstrain a part with two round holes. Consider, if you haven't already, the diamond shaped pins commonly used in tooling, each of which substantially constrains a round hole in only one direction.



Mike Halloran
Pembroke Pines, FL, USA

 

[JJRCAN]

The fixtures were designed and built using the 1144 locating pins, I am unsure why they selected this material, probably because it is a stock item from jergens/mcmaster/carrlane. They are the lockscrew type with a tapper. I havent found any lockscrew type locating pins with a shoulder and no undercut. I will probably get them machined custom from mild steel. Thanks for the replies.

 

[JJRCAN]

Tried diamond locating pins and they still broke after a few days. As stated earlier I believe the undercut is the major flaw, it wont require much force to break a bittle steel such as this with an undercut.

 

[MikeHalloran]

You have to get a look at the surveillance camera footage, to figure out what they're doing differently when you're not around.



Mike Halloran
Pembroke Pines, FL, USA