Spot Welding Robot: Unimate to ABB IRB 6700

How the spot welding robot replaced hand welding guns, from Unimates at GM Lordstown in 1969 to EV body shops, and what ABB IRB 6700 and IRB 7600 arms do.

INDUSTRIAL ROBOTICS

Chat With Robot

10/8/20265 min read

A spot welding robot squeezes two sheets of steel between copper electrodes and passes a heavy current through them for a fraction of a second, leaving a small fused nugget. A car body needs thousands of these spots, so spot welding was the first big job that industrial robots took over in car plants. This post looks at how the work was done by hand, how Unimate robots arrived at GM's Lordstown plant in 1969 and how body shops filled up with hundreds of robots. It ends with where ABB arms such as the IRB 6700 and IRB 7600 fit on modern EV body lines.

A white six axis robot arm holding a large C shaped spot welding gun on a blue steel stand

A spot welding robot with its welding gun on a training stand at a polytechnic university, 2019. Photo: Mukszwei / Wikimedia Commons (CC BY-SA 4.0)

How car bodies were spot welded by hand

Resistance welding goes back to Elihu Thomson, who filed a patent on the idea in 1886 after years of experiments with low voltage, high current electricity. The principle has not changed since: clamp the metal, send current through the joint and let the resistance heat melt a spot. Early spot welders were fixed machines with long copper arms, a bit like a giant stapler. A worker carried each part to the machine and placed it between the tips, one spot at a time. That was fine for small parts. A whole car body is too big to move around a welding machine, though.

A blue spot welding machine with two long copper arms sticking out from its top

A Miller fixed spot welder with long copper tongs, the kind of machine a worker fed parts into by hand. Photo: Triddle / Wikimedia Commons (CC0)

Car plants got around this with portable welding guns hung from overhead balancers and fed by thick cables from transformers. Workers on the line pulled the guns onto the body and fired them, spot after spot, through every shift. Fixed machines stayed in use for smaller parts; at Ford's Willow Run bomber plant in Michigan in 1942, teams of women spot welded engine nacelle parts on them. The guns were heavy and the work was hot and repetitive. Weld quality depended on how squarely each worker held the tips against the metal.

Black and white photo of three women in goggles holding a metal part in a spot welding machine

Women spot weld parts for an engine nacelle at Ford's Willow Run bomber plant, Michigan, July 1942. Photo: Ann Rosener, Library of Congress via Wikimedia Commons (public domain)

George Devol's Unimate, the first industrial robot, started work at a General Motors plant in New Jersey in 1961, handling hot die castings. Spot welding came next. In 1969 GM rebuilt its Lordstown plant in Ohio with Unimate robots that welded car bodies on the moving line. Each robot remembered the exact point in space for every weld, and the plant could build 110 cars an hour, more than double the rate of other car plants at the time. In Sweden, ASEA launched the all-electric IRB 6 in 1974. Much later, in 1990, ABB bought Cincinnati Milacron's robot business, which grew its spot welding work for American carmakers, and in 1991 it introduced the IRB 6000, a modular arm designed for spot welding.

A row of blue and yellow small cars with open hoods moving along a factory assembly line

Chevrolet Vegas on the assembly line at GM's Lordstown plant in Ohio, 1972. Photo: Chevrolet via Wikimedia Commons (public domain)

Spot welding robots in body shops now

In a modern body-in-white shop, rows of robots weld the underbody, side frames and roof at separate stations while conveyors or automated guided vehicles move bodies between them. On 8 September 2026 Kia showed reporters its new EVO Plant in Hwaseong, South Korea, which builds the PV5 electric van. Kia said body welding there is 100% automated, and it uses laser welding on areas a normal gun cannot reach. The body shop handles more than 180 specifications of the van on one line.

Many orange robot arms working around a bare metal car body in a bright factory hall

A large fleet of robots in the BMW Leipzig body shop. Photo: BMW Werk Leipzig / Wikimedia Commons (CC BY-SA 2.0 de)

Most welding guns on robots are now servo guns. An electric motor closes the electrodes in place of an air cylinder, so the robot controls the force and the closing speed for each spot. ABB's IRB 6700, which covers payloads from 150 to 300 kg, is a common arm for this work, and the larger IRB 7600 carries heavy guns and big parts. Both run on ABB controllers, now OmniCore. Engineers usually lay out and test the weld paths offline in RobotStudio before a line is built.

Several white ABB robot arms around car body frames on a fixture line

ABB robots working on car bodies in a body shop. Photo: ABB

Electric vehicles bring new parts to weld. Battery trays, aluminium parts and mixed materials need tighter control of heat and force, and many plants combine spot welding with riveting, adhesive bonding and laser welding. ABB's September 2026 Automotive Manufacturing Outlook Survey asked 473 industry decision makers about EV production. Half of them (51%) said EVs are now easier to build than a year ago, against 8% who said harder, and 41% reported lower EV manufacturing costs. ABB puts part of that down to investment in automation.

Rows of white ABB robots standing beside body fixtures in a large car factory

ABB robots in the body shop at BAIC's electric car plant in Qingdao, China. Photo: ABB

What comes next for robotic spot welding

Carmakers want lines that can switch between models and powertrains without a long rebuild, much as Kia's line already runs many versions of one van. Getting there means robots that ride on AGVs and cameras that locate parts. It also means weld programs generated straight from the car's design data. ABB says its robots are heading toward more autonomous behaviour, where the robot plans and adjusts its own motions. How far that will go inside a spot welding cell is still open.

A robot with a welding gun making sparks on a steel table as a man holds a control pendant

A spot welding robot cell throwing sparks while an operator watches with a teach pendant, 2008. Photo: Robotworx / Wikimedia Commons (CC BY-SA 3.0)

Weld checking is changing too. Weld controllers now record current, voltage and force for every spot, so a bad weld can be flagged before the body leaves the station. Aluminium is harder to spot weld than steel because it carries heat and current away so well, and the electrode tips wear faster, so most cells include automatic tip dressing and tip changing. All of this depends on good offline programming, which is what RobotStudio's I/O and simulation modules teach.

Two people at a desk with a screen beside a white controller cabinet and a robot cell

Engineers with an ABB OmniCore controller and robot cell. Photo: ABB

For people at home, spot welding robots show up mostly in the price and crash safety of the car in the driveway. In factories the open problems are cost, finding people who can program and maintain hundreds of robots, and keeping workers safe around heavy guns and moving bodies. Smaller manufacturers also use single spot welding cells for products such as cabinets and seat frames. For robot welding in smaller shops, see our post on cobot welding from job shops to garages.

A long low factory seen across a wide field from a road lined with power poles

The Lordstown Assembly plant in Ohio in June 2024, now run by Foxconn. Photo: Mr. Matté / Wikimedia Commons (CC BY-SA 4.0)

Innovation

AI solutions for effortless ABB robot control.

Automation

Robotics

ceojohntran@chatwithrobot.net

+84905311611

qtran1215@gmail.com

Instagram