Bathtub Manufacturing: ABB Robots From Iron to Enamel

Bathtub manufacturing looks simple until you try to picture it. A tub is a large, deep shape that has to be formed, finished with a hard glossy surface, and moved around a factory without a scratch. Cast iron, enamelled steel and acrylic each solve that in a different way, and each leaves jobs that are heavy, hot or dusty. This post follows the bathtub from foundry to press line, and looks at where ABB robots already work in a Swiss bath plant and where they could help with shower trays and finishing.

A roll top bath on claw feet in a black and white tiled bathroom. Photo: Gürkan Sengün / Wikimedia Commons (CC BY-SA 3.0)

From cast iron tubs to enamelled steel

Early English tubs were made of cast iron, or of tin and copper with paint that tended to peel. The cast iron clawfoot tub lined with porcelain became the luxury version, and it stayed popular from the 1880s to the 1930s. It was a casting job. Molten iron went into a mould, the casting was cleaned up, and a glassy coating made it smooth and easy to wash. The weight that makes these tubs feel solid also made them hard to move, and that is still true of an antique one.

A cast iron clawfoot bathtub, the type popular from the 1880s to the 1930s. Photo: Yannick Trottier / Wikimedia Commons (CC BY-SA 3.0)

The coating came from an older craft. Vitreous enamel was first applied commercially to sheet iron and steel in Austria and Germany around 1850. In 1883 John Michael Kohler enamelled a cast iron horse trough in Wisconsin and sold it as the company's first bathtub. Enamel powder was sprinkled onto the hot iron at about 1,700 degrees Fahrenheit. The know-how had come from Andrew Vollrath, who learned the process in Germany and returned to Sheboygan in 1874. By 1900 Kohler earned 98 percent of its revenue from enamelled iron goods such as tubs and sinks.

The Kohler Company foundry in Kohler, Wisconsin, seen from the east in 2016. Photo: Asher Heimermann / Wikimedia Commons (CC BY 3.0)

Enamelling stayed manual for decades. A Matson Collection photograph from 1939 is titled "Enameling of a bath tub" and shows the hot, manual work at the Vulkan metalworks near Haifa. Steel changed the shape of the job. Kaldewei says it commissioned two hydraulic bathtub press lines in 1957, and ABB says Wilhelm Schmidlin installed a 630-ton deep draw press in 1961, which ABB credits with making his firm the first to produce deep-draw tubs 45 centimetres deep. A pressed steel tub is also much lighter to carry than a cast iron one.

Enamelling a bath tub at the Vulkan metalworks near Haifa, 1939. Photo: Matson Collection, Library of Congress via Wikimedia Commons (public domain)

Steel enamel baths and the robots that handle them

Steel enamel is still a living product. On 11 September 2026 THP News reported that Kaldewei had added a colour called Dusty Pink to its Meisterstück Classic Duo Oval freestanding bath, first shown at Milan Design Week in the Palazzo Crespi. Kaldewei describes steel enamel as a composite of steel and glass. German rivals such as Bette, based in Delbrück, work with the same material. The news is about colour, not robots, but every new shade also has to be applied and fired cleanly on the line.

The Bette headquarters in Delbrück, Germany, home of a steel enamel bath maker. Photo: Bette GmbH & Co. KG / Wikimedia Commons (CC BY-SA 4.0)

The best documented robot story is Swiss. ABB's case study says Wilhelm Schmidlin AG, the only Swiss maker of enamelled steel baths and shower trays, uses six ABB robots. They load steel blanks into the press, take out the formed tubs, and handle welding and enamelling, taking people off heavy and hazardous work. The 1961 press is still running, now loaded by a robot, and a newer press with a 3D laser is being added at the Oberarth plant. ABB says almost every second steel tub installed in Switzerland comes from Schmidlin. The page gives no date and no robot model.

A Schuler press in the Mercedes-Benz press shop in Bremen, 2023, the kind of machine that forms steel panels. Photo: Uhu2600 / Wikimedia Commons (CC BY-SA 4.0)

Applying a glassy coating is where paint robots come in. ABB's IRB 5500 is built for the air inside a paint booth, where fumes can ignite, so it can work where solvent paint is sprayed. Bath enamel is a different material from automotive paint, so the same arm would need its own process development, and we found no source saying ABB paint robots are used on bath enamel. Schmidlin's case study says only that its ABB robots handle enamelling, so the model is unknown.

An ABB IRB 5500 paint robot, a design built to work in explosive paint-booth air. Photo: ABB

Finishing is the dirty end of the line. A 2023 paper in the Journal of Energy Technology by Petrčić, Kralj, Mihalić and Šimunić describes robotic sanding of freestanding bathtubs, using an industrial manipulator that detects contact force automatically. The authors report more than 30 percent savings on consumables such as sandpaper and almost 50 percent higher productivity, and say two robotic cells gave four times the labour saving of manual sanding. An ABB IRB 6700 grinding steel parts at Ancofer in Teqram's EasyGrinder cell shows the same kind of arm at work.

An ABB IRB 6700 grinding a steel part in Teqram's EasyGrinder cell at Ancofer. Photo: ABB

Acrylic, shower trays and what comes next

Acrylic and fibreglass take a different route. In 1979 James and Richard Wheeler adapted spa acrylic to make bathtubs, working with Spartech Plastics on a durable co-extruded sheet. Lasco says its Nevada plant uses five robot cells to spray gelcoat, a barrier coat and three laminate layers on tubs and showers, which cuts overspray. In 2019 AZoRobotics reported a Motoman robot milling and finishing fibreglass tubs at Carefree Bathing. Shower trays are the quieter product, but they need the same forming, finishing and handling as a tub.

A shower tray set into a bathroom floor beside a bathtub. Photo: 汩汩银泉 / Wikimedia Commons (CC BY-SA 4.0)

The next steps are mostly about people and risk. Schmidlin's robots took over the heaviest lifts, but a tub plant still needs staff who can set up enamel lines, tune a polishing path and keep a press from 1961 safe next to a robot. Programs are normally built and tested first in RobotStudio before they run on the real arm. Cost matters for small plants, and a flexible cell has to earn its place across many tub shapes. See also ABB robots in grinding and deburring and paint robots from car bodies to walls.

ABB paint robots working on a car body inside a paint booth. Photo: ABB

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