A number of market developments are converging right now to bring squeeze-type resistance spot welding to the attention of collision repairers. The availability of inverter-based equipment has overcome some of the power-supply issues of earlier spot welders, OEMs are specifying the use of spot welding for some repairs and welds can be performed more quickly than with MIG equipment.
So, does every collision repair shop need a resistance spot welder? "Absolutely," responds Terry Acton, product manager at Car-O-Liner. "Especially the independent repairers, because they may be repairing many different brands, some of which require resistance welding. But there's an even better reason to invest in one: it does a better job, and it's faster than MIG welding."
Jason Bartanen of I-CAR notes that Asian and European car manufacturers have recommended spot welding for many years. Among the Big Three automakers, some recommend spot welding alone, others recommend it in conjunction with adhesives.
One reason that spot welding is becoming more prevalent as a repair method is that it does not create as large of a heat-effect zone as MIG welding, explains Bartanen. This is relevant for some of the newer high strength steels.
Inverter technology solves earlier problems
The widespread availability of inverter-style resistance welders has also aided the adoption of spot welding for collision repair, says Acton. "Where resistance welding wasn't practical before, inverter technology now makes it possible." He says the inverter-based units "weld smoother, weld better, and demand less electrical load from the facility."
With the older, transformer-based welders, the distance of the unit from the facility's power supply could be a factor in the performance of the welder. Inverter units have a capacitor on-board, so that an electrical charge is built-up before welding begins. As well, inverter-type welders complete the weld more quickly, so power supply problems are rare, explains Acton.
If purchasing a resistance welder, Acton advise repairers to choose one equipped with a PLC, so that it can be reprogrammed when necessary to meet changing industry or manufacturer demands. He also suggests that purchasers ensure they will have strong local support for the brand they choose, because of the need for technical support and consumables, such as tips.
Automated current control marks cutting edge units
AMH Canada Ltd. has developed a new "high frequency" inverter spot welding machine in cooperation with the European PSA Group (Peugeot/ Citroen France). The CompuSpot model 800HF was designed to meet the technological requirements for resistance spot welding advanced high strength steels such as HR45, HR60, HR80, DP800, and boron steel in specific auto body and framework applications.
New features on the 800HF allow the welding current (amps) to be specified via the control panel and offer automated real time control of current to achieve constant output current. The unit also measures clamping force at the tips.
The liquid cooled 800HF features a maximum 14,000 amp output at the electrode tips, welding pressure up to 1000 lb force (550 daN), and power on demand for consistent performance throughout any job.
Car-o-Liner's CR500 resistance spot welder is powerful, robust and compact welder, equipped with cutting-edge inverter technology.
Automated current control compensates for heat loss and variations of the main supply voltage. Energy control automatically compensates for heat losses by keeping a fixed energy level according to the thickness and quality of the sheets to be welded. This results in less load on the main supply system while still achieving high-quality welding performance.
The CR500 offers 11 operating modes, with up to 25 programs each. A built-in memory function also preserves personal configurations as user profiles to be recalled as necessary.
The unit has four welding cables to provide quick access to two-sided, single-sided and other types of welding without switching tools. This promotes efficient and rapid welding work.
Pro Spot International also has a new line of inverter spot welders which incorporates the latest in current monitoring technology. The i4 welders can measure, monitor and adjust the weld current; they do so on the secondary loop at the tip. The powerful AD converter (analog to digital) allows the i4 to deliver the exact weld current set by the operator, regardless of outside circumstances such as low voltage supply, large weld nuggets, or dirty tips.
The i4 has an OEM-programmable feature which allows the operator to store and retrieve detailed repair illustrations and customized weld programs.
It is equipped with the PS-500 two-sided, double-acting spot gun which provides high squeeze pressure (> 600 lb.). The electrodes spread wide for hard-to-reach areas, and are self-aligning so no adjustment is needed after changing arms.
Simple and versatile
Saitek's SK-Series spot welders use preset programs to eliminate guesswork and incorporate a "Plug and Weld" system which requires minimal instruction. The units use air cooling and can weld through wet or dry glue.
The SK welders have high squeeze force and use inverter technology. Both the SK-1 and SK-2 can operate on single-phase or three-phase power supply.
Beyond the horizon
Acton estimates that only about 15 to 20% of shops currently have resistance welding technology. "The market is young."
Looking ahead at joining technologies, Bartanen notes that rivets and rivet bonding techniques will migrate from aluminum to steel structures. "We're going to start seeing rivets and rivet bonding used for steel. There are already GM vehicles that have a laminated steel cowl and use rivet bonding, such as the Cadillac CTS."