Page 68 - MetalForming October 2011

Resistance Welding
single phase-transformer it replaced, yet produces more secondary amps at a lower primary draw.
The purchase of a centralized, self- contained water chiller to cool the machine—and several others in the plant—also contributed to the success of the project. MFDC transformers and controls are more susceptible to failure due to low water-flow rates and exces- sive KVA demand.
Economies of Scale Support Quick ROI
Although significantly more expen- sive than comparable single-phase AC resistance-welding components, prices of transformers and controls used in MFDC welding machines have dropped somewhat, due to economies of scale. RoMan Manufacturing’s Don DeCorte, vice president of sales and marketing, reports that MFDC power
supplies represent more than 60 per- cent of its welding sales, confirming that the multiple advantages of MFDC systems are offsetting higher costs. In addition, DeCorte reports that some local utility companies offer financial incentives if customers install the electrically efficient MFDC units.
Metrican Stamping personnel care- fully documented the before-and-after variables of the conversion, and the results are impressive.
With the previous AC welding sys- tem, electrodes were only good for about 40,000 welds; the new MFDC system enables the machine to run 200,000 welds prior to an electrode change (although just to be conserva- tive, operators change electrodes after 150,000 welds).
The facility was able to replace the Elkonite-faced upper electrodes with less-costly Class 3 copper, and life of the copper lower-electrode bases and locating pins increased from two months to nine months. Annual expen- ditures for consumables dropped by more than $10,700 due to the lower initial cost of the electrodes and increased life.
MFDC technology, which delivers more energy to the welds, allowed the machine’s cycle time to be reduced from 9.5 sec. to 7.5 sec., increasing pro- duction rate by 101 parts/hr. Weld qual- ity has greatly improved as well, with welds of the 7⁄16-in.-dia. ring projec- tion rarely failing the 5800-lb. destruc- tive test. The machine’s primary current draw has dropped to an average of only 300 A/weld.
Following the retrofit, Metrican Stamping’s welding machine has pro- duced more than 2.4 million parts, and more productivity-improving moves are on the way. To further increase pro- duction of the seat component, Metri- can plans to add another rotary-dial index welding machine, equipped to weld both nuts simultaneously without a gun shift.
This time, the machine will include modern MFDC resistance-welding technology from day one. MF
66 MetalForming/October 2011
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