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Willy
09-10-2010, 01:09 AM
I've got a small job coming up where I will be required to mill several slots into and through about 16-20 spot welds.

The material consists of two layers of .080-.090 mild steel spot welded together with what appears to be spot welds of approximately 1/4"-5/16" diameter.

The slots will be 5/16" wide.
I have at my disposal both HSS and cobalt 5/16" end mills, unfortunately my solid carbide inventory is either too small or too big, although I realize I could take two passes with a 1/4" solid carbide end mill in order to obtain a 5/16" slot.

Not having cut through a lot of spot welds I am a little skeptical of the HSS end mill's ability to handle the HAZ of the spot welds. For economics sake I was hoping to use the HSS mills but I don't really want to just waste one to find out.
Any thoughts from those who have done a bit of this before would be greatly appreciated.

ADGO_Racing
09-10-2010, 01:31 AM
If the base material is a low carbon steel (under 00.30%) it probably didn't get hard. Spot welds are routinely drilled out with HSS drills and a hand drill. I doubt you will have any problems using HSS endmills.

Willy
09-10-2010, 02:02 AM
Thanks!
After having turned and milled flame cut mild steel I'm just a bit gun shy of toasting a new Niagara end mill.
I'll give it a go in the morning.

Black_Moons
09-10-2010, 03:09 AM
Heh, Flame cut steel isent really steel anymore, and really has to be ground off before machining as you found out. basicly its steel that has ignited and burned into iron oxide, a wonderful abrasive ;)

loose nut
09-10-2010, 10:23 AM
It can also absorb some of the carbon from the cutting flame and get harder.

atty
09-10-2010, 11:41 AM
Heh, Flame cut steel isent really steel anymore, and really has to be ground off before machining as you found out. basicly its steel that has ignited and burned into iron oxide, a wonderful abrasive ;)

I also found out the hard way that you're absolutely right. Can this result be minimized somewhat by reheating with OA and allowed to cool slowly? I realize it won't help the abrasive part, but would that anneal it enough to get through the machining?

aboard_epsilon
09-10-2010, 11:48 AM
if you want to remove them

zipcut spot weld remover

http://www.comparestoreprices.co.uk/car-tools/sykes-pickavant-zipcut-spot-weld-remover-spare.asp

all the best.markj

Willy
09-10-2010, 12:00 PM
Although I haven't really noticed flame cut material to be abrasive it does get extremely hard. I have been aware of this characteristic for well over forty years so it's nothing new to me. I usually just grind off the affected area before machining but depending on the work piece it is not always piratical to do so. Not everything is on an outside surface where it is easy to grind it off.

Willy
09-10-2010, 12:05 PM
if you want to remove them

zipcut spot weld remover

http://www.comparestoreprices.co.uk/car-tools/sykes-pickavant-zipcut-spot-weld-remover-spare.asp

all the best.markj

Thanks Mark, looks like I'll just use an end mill though.
Probably stick with a good cobalt one just to be on the safe side.

Weston Bye
09-10-2010, 12:43 PM
A spot weld should not alter the chemistry of the steel as a flame cut would. The presence of carbon in the cutting gas may migrate into the steel, raising the carbon content. If the surrounding steel is sufficiently cold, the area of the cut with the added carbon, will harden as heat is rapidly quenched away into the surrounding cold steel.

Similar quenching may occur around the spot weld, but no carbon has been added to the weld. Since *most* spot welding is done with mild or low carbon steel, you shouldn't encounter hard spots at the welds.