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> Spot Welding Question
jonnie45
post Jan 9 2017, 08:24 AM
Joined: 9-Jan 17



Hello

I have a one man artisan business.

I have stick welded for ages but I am now looking at spot welding for a particular purpose and
I want to see if it will/may work before I spend money on (used) equipment.

All metal is low carbon mild steel, high draw type CR04 1mm thick my supplier says is the same stuff that car enthusiasts use for panel repairs.

I want to spot weld a small 1 cm diameter cup face down onto a flat sheet.

If you scale it up then it would be similar to putting a whiskey glass upside down on a table (so that the glass rim was fully in contact with the table ) and then placing electrodes one on top of the glass and one underneath the table and to weld the glass to the table. I will drill a tiny vent hole just in case air pressure were a problem. I will be sanding down the "rim" so that the cup and table fit flush before the weld.

The weld does not need to pass strict tests, if it cannot be pulled off by hand it is fit for purpose.

I was hoping I could get away with a hand held spot welder in the 500 pound range? Is that a fair expectation?

I will be doing the same thing repeatedly so its not a "one-off" - I can't use glues or adhesives or brazing.

Thanks for any advice given

Jon



arceyethenoo
post Jan 9 2017, 03:54 PM
Joined: 14-Dec 07



Hello Jon
Here's my thinking FWIW.
Spot welding is about current density and pressure. The rim of your cup has an area of about 36 sq mm which is approx. a 6x6 mm spot.
I have only used a hand held m/c on which this would be quite large.
The other contact point at the 'bottom' of the cup will also heat up and since it is point contact under pressure, deform. You will then loose the necessary pressure for the weld.
There is a process called projection welding were the contact on a large surface is reduced by forming dimples which form small contact points for the spots.
You might try peening ( choose your own preferred spelling) the edge of the rim in about 4 places to gain a similar effect.
Trial and error really.
ps. you don't say how big the sheet is so just check your intended welder has the gub you need.
Best of luck.
Richard
jonnie45
post Jan 10 2017, 10:49 AM
Joined: 9-Jan 17



Hi Richard

Thanks that sounds like a good suggestion.

I was concerned that the whole cup might heat up - if the contact area is reduced then presumably the benefits are reduced overall required amperage but also creating more localised resistance at the contact area and so hopefully also more localised heating.
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