Miller Axcess E 300, Owner'S Manual

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OM-244 814 Page 44
9-7. 30 Points Of Mechanics In MIG Welding
1. Check primary power connection at line disconnect switch or receptacle and/or cord plug.
2. Check primary power connection at welding power source.
3. Check secondary weld output connections at welding power source.
4. Inspect condition and routing of positive weld cable to wire drive motor.
5. Check connection of positive weld cable to wire drive motor.
6. Inspect condition and routing of negative weld cable to fixture.
7. Check connection of negative weld cable to fixture.
8. Inspect condition of any rotary grounds, grounding shoes or other auxiliary grounds.
9. Check gas hose connection to shielding gas supply regulator.
10. Check shielding gas flow rate.
11. Check gas hose routing.
12. Check gas hose connection at wire drive housing.
13. Inspect condition of dereeler. Check for wear at quick-connect coupling and replace if necessary.
14. Check placement of payoff pack or drum for smooth feed path.
15. Inspect condition and routing of input conduit.
16. Check installation of quick-connect coupling at rear of wire drive so that it does not contact drive rolls. Check for wear and replace if necessary.
17. Check drive rolls and replace if worn.
18. Check for drive roll tension setting.
19. Check intermediate guide for proper size to match wire size and replace if worn.
20. Check gun connection at wire drive and be sure O − rings seal at drive housing.
21. Check installation, routing and condition of welding gun.
22. Check for proper length of liner at both ends and be sure it is cut without burrs.
23. Check liner for proper size to match wire size.
24. Check liner for wear and clean out to prevent plugging.
25. Check contact tip for proper size to match wire size.
26. Check contact tip for wear and change at regular intervals.
27. Check contact tip for a tight fit and secure installation at gun.
28. Check condition of gas diffuser.
29. Check condition of nozzle.
30. Check O-ring for proper sealing at nozzle.
9-8. Arc Blow
Arc blow is the deflection of the welding arc from its normal path due to magnetic forces. This condition is usually encountered in direct current welding of
magnetic materials, such as iron and nickel. Arc blow can happen in alternating current welding under certain conditions, but these cases are rare and
the intensity of the arc blow is always less severe. Direct current flowing through the electrode and base metal will set up a magnetic field around the
electrode. This magnetic field tends to deflect the arc to the side at times, but usually the arc deflects either forward or backwards along the joint.
Back blow is encountered when welding toward the work cable connection on a workpiece near the end of a joint or into a corner. Forward blow is
encountered when welding away from the work cable connection on a workpiece at the start of a joint. In general, arc blow is the result of two basic
conditions:
1. The change of current flow direction as it enters the work and is conducted toward the work cable.
2. The asymmetric arrangement of magnetic material around the arc, a condition that normally exists when welding is performed near the end of
ferromagnetic materials.
Although arc blow cannot always be completely eliminated, it can be controlled or reduced to an acceptable level through knowledge of the two condi-
tions listed above.
Except in cases where arc blow is unusually severe, certain steps can be taken to eliminate or reduces its severity. Some or all of the following steps
may be necessary:
1. Place work cable connection as far as possible from joints to be welded.
2. If back blow is the problem, place the work cable connection at the start of the joint to be welded and weld toward a heavy tack weld.
3. If forward blow is the problem, place the work cable connection at the end of the joint to be welded.
4. Position electrode angle so that arc force counteracts arc blow.
5. Use the shortest possible arc that maintains good welding practices (this helps arc force to counteract arc blow).
6. Reduce welding current if possible.
7. Weld toward a heavy tack weld or runoff tab.
8. Use the back step sequence of welding.
9. Change to an AC welding operation which may require a change in electrode classification.
10. Wrap the work cable around the workpiece in the direction that sets up a magnetic field to counteract the magnetic field causing the arc blow.