Rotational Molding Robot: ABB Arms in the Roto Shop

Kayak hulls, water tanks and playground slides share one odd thing: they are hollow plastic shells made in a mold that spins inside an oven. This is rotational molding, and it remains a hands-on trade. The cycle is slow and the molds are hot and heavy. This post explains how the process began, what a rotational molding robot can do in a modern roto shop, and where ABB arms such as the IRB 6700, IRB 1300 and PoWa cobots could take over the heavy and repetitive jobs around the machine.

A blue plastic water tank, one of the hollow products made by rotational molding. Photo: W. Carter / Wikimedia Commons (CC0)

How rotational molding began with spinning molds

The idea is older than plastic. In 1855 a British patent by R. Peters described a mechanism that turned a mold around two axes at right angles, used to make hollow vessels such as artillery shells. In 1910 G.S. Baker and G.W. Perks used a similar approach for hollow chocolate Easter eggs. Plastics came into the process in the early 1950s, with early uses including doll heads made from liquid PVC plastisol. The spinning mold stayed the same, and only the material inside it changed.

Rotation molding ovens and tooling in a small workshop. Photo: Jackyzhaoplastic / Wikimedia Commons (CC BY-SA 4.0)

Big parts arrived in the 1960s, when the Engel process from Europe made large hollow containers in low-density polyethylene. The basic routine has barely changed since. A worker loads a measured amount of plastic powder into the mold. The mold then rotates on two axes inside an oven until the powder melts and coats the walls evenly. Too much time in the oven degrades the plastic, and too little leaves bubbles in the wall. Nothing presses the plastic into shape, so the wall thickness depends on how the powder flows.

Plastic powder loaded into an open mold before heating. Photo: Rishi Saran / Wikimedia Commons (CC BY-SA 3.0)

Cooling comes next, and it is often the longest step, taking tens of minutes. The mold must cool in a controlled way or the part warps. Critics point out that a machine makes only one or two cycles an hour, against seconds for injection molding. Then comes the part people dread: opening a hot mold, pulling out a big shell and trimming it by hand. Carousel machines, with up to four arms and six stations, kept several molds busy at once, but the unloading still fell to workers.

A worker opens a rotational mold by hand after the cycle. Photo: Rishisaranroto / Wikimedia Commons (CC BY 4.0)

Rotational molding robots and trimming cells today

The industry is changing its heating and its controls first. Interplas Insights profiled Rototek on 17 September 2026. The company has two sites in Nottinghamshire, runs more than 22 machines and makes over 100,000 products a year, from water storage tanks to automotive and marine parts. It now runs a Persico SMART electrically heated machine and uses process monitoring for temperature and pressure. Its direction is electric heating, automation and data, with automation aimed at repeatability and at easing skills shortages. The article does not name any robots.

A carousel rotational molding machine with its arms, oven and cooling station. Photo: Stephan Courtois / Wikimedia Commons (CC BY-SA 3.0)

That leaves a clear job for robots at the end of the cycle. A finished tank or hull comes off the mold with flash and openings that need cutting, and some parts need holes, fittings or drilling. These jobs are heavy and repetitive, and the part is often large and awkward to hold, which is the kind of work industrial arms handle well. An ABB IRB 6700, which ABB has used for heavy grinding on steel parts in a Teqram EasyGrinder cell, shows the payload class involved. A robot can hold the shell and a spindle can trim it, or the arm can carry the cutter itself.

A large tank being unloaded from a rotational molding machine. Photo: Stephan Courtois / Wikimedia Commons (CC BY-SA 3.0)

ABB has not announced a rotational molding product, so this is a possibility and not a customer story. In practice, a trimming cell would use an IRB 6700 or similar large arm on OmniCore, with a fixture and a force-controlled cutter. ABB's IRB 1300 Foundry Plus 2 version is built to handle water and dust, which matters in a shop where plastic powder and washdown are part of daily life. Engineers would plan the cell and its reach first in RobotStudio. For a related plastics process, see ABB robots in injection molding.

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

What comes next for rotational molding automation

The next few years look like a mix of electric ovens, sensors and robots working together. Rototek's operations director named energy costs and the need to attract younger workers as the industry's main challenges. Robots can take on hot, heavy tasks, which may help with hiring, and data from process monitoring can tell a cell which part it is trimming and how thick the wall came out. The open question is cost, since roto shops often make small runs of many different parts.

An ABB IRB 1300 with Foundry Plus 2 protection, built to handle water and dust. Photo: ABB

Variety is the hard part for automation. A rock and roll machine for long, narrow parts, a carousel for tanks and a shuttle for small runs all present parts in different ways. A trimming robot needs to find each part, hold it and cut the right line without a new program every time. That calls for vision and simple teaching, and for good safety design. Hot molds and sharp cutters mean cells need guarding, and cobots can work next to people only when the tool and the part are safe.

A rock and roll rotational molding machine built for long, narrow parts. Photo: Stephan Courtois / Wikimedia Commons (CC BY-SA 3.0)

For homes, the impact is indirect. Most people never see the process, but they live with its products: a water butt in the garden, a storage bin or a kayak on the roof. Cheaper, steadier production could keep those prices down. Small shops may also look at hand-guided cobots like ABB's PoWa for light trimming and finishing, if the price drops far enough. Large automated cells, with several arms sharing one trimming line, are likelier to arrive first in bigger plants, and many roto shops will keep trimming by hand for years.

An engineer hand guiding an ABB PoWa cobot. Photo: ABB

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