welding bolts

[jpmpack]

I am designing an application where I would like to weld a shoulder bolt to a mild steel plate. I am using the bolt as a precision shaft for a rotation device. I am worried about the high strength properties of the bolt causing welding strength concerns.

 

[MASSEY]

jpmpack,

I hate to break it to ya, but you are not going to use a welded shoulder bolt for a "precision" anything.

If your trying to mount a belt driven pulley for your lawn mower deck - this may work. But don't expect any precision for an engineering project using welded shoulder bolts for a precision shafts.

Think of a different way to accomplish what you are trying to do...

What exactly are you trying to do??

 

[TVP]

jpmpack,

I'll be the first to jump on the bandwagon and concur wholeheartedly with MASSEY. Welding high strength bolts is a bad idea. Using a bolt as a "precision shaft" is even worse. Together they spell disaster. You should seriously reconsider this application.

There are many thoughtful and creative engineers on this forum, so why don't you provide some background on this problem, and maybe we can help steer you in a better direction.

 

[jpmpack]

Using the word precise was a mistake. The .002 inch tolerance on a shoulder bolt would work fine for this application. The application is for a seat rotation swivel on a power wheel chair. I was mainly concerned about the high strength steel bolt for welding.

 

[TVP]

Depending on what standard you reference, and what strength level is required, high strength steel bolts are manufactured from carbon or alloy steels, with carbon content varying from ~ 0.20 to 0.55. In the quenched and tempered form, these alloys provide high strength and good toughness.

Welding involves extreme heating and localized melting which produces the following:

1. Brittle weld, due to the presence of untempered martensite. The untempered martensite is produced because of the rapid cooling that takes place after welding in thick sections.

2. Overtempering of the heat affected zone (HAZ). Again, depending on the chemical composition and strength level, bolts are tempered at temperatures ~ 300-500 C, and this temperature is easily exceeded in the HAZ, which causes local softening.

3. Severe crack sensitivity, as tempered martensite is quite prone to hydrogen cracking and quench cracking.

So, if you feel that using a welded shoulder bolt is the only way to manufacture this component, you should be aware of these problems, and proceed accordingly.

 

[CoryPad]

If you use a welded fastener, use one that is designed for welding. Weld studs, using drawn-arc or projection welding, could be used for your application. They have lower carbon content, and lower strength, but they can be welded with acceptable strength. The following fastener suppliers may be helpful:

http://www.textronfasteningsystems.com

http://www.emhart.com