:: resistance welding ... energy required P = current x current x resistance

this is a gone with the wind spreadsheet estimate of energies used to melt materials in resistance welding

materials in question are as follows



melt oC Kg/m3 Spec heat J/g.K fusion J/g 1 mm3 = g?
copper 1084 8940 0.380 205 0.008940
nickel 1453 8900 0.445 297 0.008900
iron 1510 7800 0.449 272 0.007800
Tin 505 7287 0.210 59 0.007287
brass 950 8730 0.380 200 0.008730
ALU 933 2698 0.900 396 0.002698
Steel 1400 7700 0.490 300 0.007700
graphite 3550 2300 0.710 8750 0.002300
tungsten 3422 19250 0.132 472 0.019250
tantalum 3017 16650 0.140 493 0.016650
Platinum 1768 21090 0.133 256 0.021090
Sn63Pb37 (145nΩ.m) 183 8400 0.145 ? ? ? 0.008400
Sn95Ag05 (137nΩ.m) 240 7400 0.145 ? ? ? 0.007400
Sn97Cu03 (118nΩ.m) 300 7320 0.145 ? ? ? 0.007320

relative energies involved (these are all theoretical calculations, not absolute real world)


Energy to fully melt 1mm3 (J) Energy to reach 95% of melting point per 1mm3 (J) Material resistivity
nΩ.m
TEST DISC vol
3.2mm diam x 0.5mm thick = 4.02mm3 - -resistance top to bottom (μΩ)
Energy to heat TEST DISC to 95% melting (J) heat generated by TEST DISC @ 3000A current (W)
5.515 3.498 17.2 0.53 12.38 4.8
8.398 5.467 69.9 2.17 19.35 19.5
7.410 5.024 97.1 3.02 17.78 27.2
1.203 0.734 109.0 3.39 2.60 30.5
4.898 2.994 63.0 1.96 10.60 17.6
3.334 2.152 28.2 0.88 7.62 7.9
7.592 5.018 170.0 5.29 17.76 47.6
25.922 5.507 9500.0 295.40 19.50 2658.6
17.781 8.261 50.0 1.55 29.24 14.0
15.241 6.681 130.0 4.04 23.65 36.4
10.358 4.711 1100.0 34.20 16.68 307.8
? ? ? 0.212 145.0 4.51 0.75 40.6
? ? ? 0.245 137.0 4.26 0.87 38.3
? ? ? 0.302 118.0 3.67 1.07 33.0
voltages /current required


voltage to create 3000A (top to bottom) voltage to heat TEST DISC to 95% melting in 1s current for 1s heating
0.00159 0.00256 4836
0.00650 0.00648 2986
0.00906 0.00733 2426
0.01017 0.00297 875
0.00587 0.00456 2325
0.00264 0.00259 2942
0.01587 0.00969 1833
0.88620 0.07590 257
0.00466 0.00673 4345
0.01213 0.00977 2421
0.10260 0.02388 698
0.01353 0.00184 408
0.01277 0.00193 451
0.01100 0.00198 540
in all of this, it seems graphite is a very interesting material. and it is used as an intermediate material in some commercial welding because the high resistances allow alot of heat to be created with a smaller current (hundreds instead of thousands of amperes)

so if we instead use gouging rods, in theory we could be saving alot of power? in theory? (actually somebody have tried it for fun https://hackaday.com/2011/11/06/diy-spot-welder-can-join-anything-together-even-copper)

what power levels are we looking into for graphite tips?

thermal conductivity W/m.K Energy limit as holder for gouge stick. Self heating to melt limit (0.185g) voltage needed to create TEST DISC 95% melt heat using 0.185g gouge probe Current needed to create TEST DISC 95% melt heat using 0.185g gouger 100A into 0.185g gouge heating time to 95% melt TEST DISC (s) 100A powered 0.74g gouger heating time to 95% melt TEST DISC (s) Mohs hardness
400 135 0.0780 44.8 2.6913 0.4421 3.0
91 181 0.0975 56.1 4.2065 0.6911 4.0
80 188 0.0935 53.7 3.8652 0.6350 4.0
67 63 0.0357 20.6 0.5652 0.0929 3.0
109 119 0.0722 41.5 2.3043 0.3786 3.5
235 116 0.0612 35.2 1.6565 0.2721 2.8
66 175 0.0934 53.7 3.8609 0.6343 5.5
140 443 0.0979 56.3 4.2391 0.6964 1.0
72 427 0.1199 68.9 6.3565 1.0443 7.5
170 376 0.1078 62.0 5.1413 0.8446 6.5
72 221 0.0905 52.1 3.6261 0.5957 3.5
50 23 0.0192 11.0 0.1630 0.0268 3.5
65 30 0.0206 11.9 0.1891 0.0311 3.5
65 37 0.0229 13.2 0.2326 0.0382 3.5
200 amperes? 400 amperes?

Energy limit as holder for gouge stick. Self heating to melt limit (0.74g) 200A into 0.74g gouge heating time to 95% melt TEST DISC (s) voltage to push 200A thru 0.74g gouge 400A into 0.74g gouge heating time to 95% melt TEST DISC (s) voltage to push 400A thru 0.74g gouge
541 0.1105 0.56011 0.0276 1.1202
725 0.1728 0.56043 0.0432 1.1209
754 0.1588 0.56060 0.0397 1.1212
252 0.0232 0.56068 0.0058 1.1214
474 0.0946 0.56039 0.0237 1.1208
466 0.0680 0.56018 0.0170 1.1204
699 0.1586 0.56106 0.0396 1.1221
1772 0.1741 0.61908 0.0435 1.2382
1708 0.2611 0.56031 0.0653 1.1206
1506 0.2112 0.56081 0.0528 1.1216
882 0.1489 0.56684 0.0372 1.1337
91 0.0067 0.56090 0.0017 1.1218
120 0.0078 0.56085 0.0019 1.1217
150 0.0096 0.56073 0.0024 1.1215
the idea is not new, it is already in industrial use, but maybe not pure graphite like a gouge stick.

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