:: 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.