micro MIG welding of stainless - subcontractor wanted

[Richard Bointon]

I seek a subcontractor to weld a 430 Stainless steel strip (50mm x 7mm x 1mm thick) which has been printed with a thick film strain gauge to a 16mm round steel spring bar (material 56SiCr7).

The strip is parallel (50mm side) to the axis of the bar but will sit tangentially on the bar surface. The weld needs to be at the end of the strip and the heat effected zone needs to be less than 8mm from the ends. Initial trials will be aimed at 10 prototypes but production will be in the low thousands.

Has anybody any experience of such a technique or is anybody willing to have a go?

 

[Richard.]

If you wanna post me a couple with a drawing I'll be up for the challenge. I won't be interested in doing thousands though success or not but I'd be happy to do a couple up to you.

 

[Richard Bointon]

Here is a CAD image of the clip with welded on gauges

 

[Wendelspanswick]

The whole assembly could be immersed in water to just below the joint and welded, this would restrict the HAZ.

 

[Charlie390]

Would it not be easier to just use an epoxy?

 

[awemawson]

Is the clip really asymmetric, or is it just the rendering making it look squiffy? If it's asymmetric you probably need a jig to place the strain gauges to get repeatable results in use.

 

[Richard.]

Are you macro testing these first then to see the HAZ comes in under that. 8mm is a big HAZ I cannot see it becoming anywhere near that size.

 

[Dimitri De Spiegeleer]

railroad clips? or crane rail clips?
and I agree with the above, when welding a 1mm thick strip one side, the other side won't have an 8mm HAZ.
The spring steel will likely need preheating, depending on its fabrication finish.
A dissimilar filler metal may be needed to lower the preheating temp.
And I've had great results with micro-TIG, even for very short weldments, I'd try that first before any other process. Especially since you're joining two very different thicknesses.

 

[Richard Bointon]

Would it not be easier to just use an epoxy?

We have used epoxy and although it gave a reasonable result the long term adhesion was just not up to the job. We intend to invert the gauges so the sensitive side is protected and then epoxy powder coat the whole assembly, gauges and wire included.

 

[Richard Bointon]

Is the clip really asymmetric, or is it just the rendering making it look squiffy? If it's asymmetric you probably need a jig to place the strain gauges to get repeatable results in use.

The clip is symmetrical, its just the perspective in the rendered view. I still expect to use a jig in production to gain consistency.

 

[Richard Bointon]

Are you macro testing these first then to see the HAZ comes in under that. 8mm is a big HAZ I cannot see it becoming anywhere near that size.

We are using thermal crayons along the gauge and see how far the HAZ encroaches towards the gauge printing. I would like to reduce the size of the overall substrate but the HAZ will determine how long the gauge must be.

 

[mr migwire]

pandrol fast clip by the looks of it,

 

[Richard Bointon]

pandrol fast clip by the looks of it,

Yes it is a Fastclip, I work for part of the Pandrol group of companies specialising in track sensing.

 

[mechman]

pandrol fast clip by the looks of it,

I'm impressed.

 

[mr migwire]

work with them quite a lot, but also still work with steel keys and elastic spikes, the fast clips are now becoming the main stay on a lot of lines as they are upgraded.