The welding of aluminium and its alloys

Surface condition and preparation

The surface condition of the aluminium sheets is one of the most impor­tant deciding factors in achieving consistent quality of resistance spot and

9.3 Modern robotic resistance spot welding cell. The robot welds on one jig while the operator unloads/loads the second jig. Courtesy of British Federal.

seam welds. Variations in the thickness of the oxide film will affect the resis­tance between both the electrodes and the plates and at the plate interface. The resistance may be measured by clamping a single plate between two electrodes and applying a set current of some 10-15 A, measuring the voltage and calculating the resistance by the use of Ohm’s Law. Material as delivered may have a resistance of between 300 and several million microhms, cleaned and prepared plate should have a resistance of 10-100 microhms. For the highest and most consistent quality this range should be tightened to some 10-30 microhms.

To achieve this low level of resistance the cleaning and storage recom­mendations in Section 4.7 should be followed. Mechanical abraded surfaces generally provide longer electrode lives than chemically cleaned surfaces, with mill finished sheets giving the shortest lives. Special lubricating oils such as polybutene have been used to extend electrode life by reducing the

Table 9.1 Typical welding parameters for 50Hz equipment single phase AC units. Valid for 1XXX, 3XXX, 5XXX and 6XXX alloys

Sheet

thickness

(mm)

Electrode

diameter

(mm)

Dome

radius

(top)

(mm)

Dome

radius

(bottom)

(mm)

Electrode

force

(kN)

Welding

current

(kA)

Welding

time

(cycles)

0.4

16

1.0

Flat

1.4

15

4

0.5

16

1.0

Flat

1.5

18

4

0.65

16

2.0

Flat

1.75

21

5

0.8

16

2.0

Flat

2.2

26

6

1.0

16

3.0

Flat

2.7

30

7

1.25

16

3.0

Flat

3.0

33

7

1.6

16

3.0

Flat

3.35

35

8

1.8

16

4.0

4.0

3.6

35

8

2.0

22

4.0

4.0

3.8

41

8

2.3

22

6.0

6.0

4.25

46

10

2.5

22

6.0

6.0

4.7

56

12

3.2

22

6.0

6.0

5.8

76

12

friction between electrode tip and the sheet but care needs to be taken to ensure that there is not excessive oil present.

The welding of aluminium and its alloys

Alloy designations: wrought products

Table A.4 BS EN BS EN Old BS/DTD Temperature (°C) numerical chemical number designation designation Liquidus Solidus IVIdUng range Al 99.99 1 660 660 0 AW-1080A Al 99.8 1A AW-1070A …

Principal alloy designations: cast products

Table A.3 BS EN numerical designation BS EN chemical designation Old BS number ANSI designation Temperature (°C) Liquidus Solidus Melting range Al 99.5 LM0 640 658 18 AC-46100 Al Si10Cu2Fe …

Physical, mechanical and chemical properties at 20°C

Table A.2 Property Aluminium Iron Nickel Copper Titanium Crystal structure FCC BCC FCC FCC HCP Density (gm/cm3) 2.7 7.85 8.9 8.93 4.5 Melting point (°C) 660 1536 1455 1083 1670 …

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