Employees at S&F Foods dreaded lifting heavy cardboard boxes from a conveyor belt and placing them onto pallets for shipment all day. So Mike Calleja, the plant manager for the company, which makes frozen food for school cafeterias, hired a robot.

Buying a robot could cost as much as $500,000, and Mr. Calleja wasn’t even confident that one would work. Instead, he rented a robot from Formic, a Woodridge, Ill., firm that takes care of installation, training, programming and repairs. It costs about $23 an hour, roughly the same as a human.

“We have very low turnover because we try to make jobs easier,” Mr. Calleja said of the company, which is outside Detroit. “We are a small facility, but we produce about 65,000 pounds of food a day.” Stacking it was “a backbreaking job,” he said.

In an era when manufacturers consistently list attracting and retaining workers as a top challenge, companies are automating some of the worst jobs in their plants as a worker retention strategy.

The robot rental model has the potential to transform the American industrial base by making automation accessible to small and medium-size businesses that have traditionally been slow to adopt new technology.

Of the roughly 244,000 manufacturers in the United States, about 93 percent have fewer than 100 workers and 75 percent have fewer than 20, according to the Manufacturing Extension Partnership. Those small and medium-size companies often lack the capital or in-house knowledge to integrate new equipment into their assembly lines.

“That’s where the opportunity is,” said Saman Farid, chief executive of Formic, which rents robots to about 150 different factories across the country.

Formic’s customers run the gamut from makers of dog food to manufacturers of automotive parts. Many are small, family-owned businesses that have to turn down orders because of a lack of staffing. Automating the most arduous and repetitive jobs allows them to redirect employees to more productive tasks, keeping them satisfied and boosting sales.

Some factories report having turnover rates of 100 percent for certain jobs, Mr. Farid said, leaving managers to constantly hire, train and drug-test new employees. “When they adopt robots to do some of the most dull, dirty, dangerous, repetitive, backbreaking tasks, people stay, right? Because you’re not lifting heavy boxes 12 hours a day,” he said.

Robot rental companies specialize in certain commonplace tasks — stacking boxes, sorting parts, welding or feeding material into machines — often the same jobs that cause bending, lifting and twisting injuries in humans.

Formic was one of at least three robot rental companies started in 2020 when the Covid-19 pandemic created acute labor shortages. AAA20 Group, a Las Vegas company, leases robots called palletizers that stack boxes onto pallets and wrap them in plastic for about $4,950 a month.

RobCo, a German robot-leasing firm, was also founded that year. In January, RobCo acquired the assets of Rapid Robotics, a U.S. firm that was shutting down, to get a foothold in the U.S. market. RobCo will open an office in San Francisco next month. It is also equipping a manufacturing facility in Austin, Texas, to make robots to rent, according to Lorenzo Pautasso, general manager of RobCo’s U.S. office.

He said the company’s clients in the United States are often motivated by a desire to decrease employee exposure to harmful toxins, or other tasks that threaten health.

“It’s not about driving down the cost of labor,” Mr. Pautasso said. “It’s about ensuring the consistency of labor, that the people that are there today will be there tomorrow.”

Matt Kunach, operations manager and co-owner of MattPak, a contract manufacturer of detergent pods for laundry machines and dishwashers in Franklin Park, Ill., said that renting three palletizers from Formic saves a little money, but that the main reason for the switch was to cut down the risk of injury to employees.

All the workers who had been stacking boxes on pallets have been reassigned to different jobs in the plant, he said, which has opened up capacity to expand into new product lines. Some have been promoted to machine operators and line leaders, positions that carry more prestige and higher pay, he said.

Rentals make up a tiny but growing slice of the overall market, according to the International Federation of Robotics, a nonprofit group that publishes an annual survey of robot manufacturers around the world. About 113,000 transportation and logistics robots were sold globally in 2023, up 35 percent from the previous year. About 5,000 were available for rent, a 20 percent increase.

The robot rental model has also become trendy in Silicon Valley, where some investors find it attractive because of the recurrent revenue and the focus on building long-term, habit-forming relationships rather than on one-time sales, according to a report issued by Silicon Valley Bank last year. Companies that use the model “raise more capital and at better valuations” than those that don’t, it noted.

Sankaet Pathak, founder of the defunct fintech company Synapse Financial Technologies, has raised more than $11 million for his new venture, Foundation, a company that aims to build and rent a fleet of humanoid robots.

He said Foundation has robots deployed in a car factory in Georgia, where they sort parts on a conveyor belt. The stiff-fingered humanoids are still a work in progress, but they have come so far that he is charging $33,000 per shift for them. They currently work one shift, and he hopes they will eventually work around the clock. Right now, he said, factory workers see his humanoid robots as a novelty rather than a threat.

“It would be more contentious if robots start taking jobs that people actually like doing,” Mr. Pathak said.

He said reviving the American industrial base requires the widespread adoption of robots that look like people, since most factory assembly lines have been built for humans.

But Mr. Farid, who spent years in factories in China, said the whole point of a robot is that it can do things that human beings cannot, and should not be limited to the human form. For instance, the robot arm in the S&F factory has a vacuum suction instead of a hand that picks up boxes from the top and places them on a pallet far more efficiently than a human could.

Yet there are headwinds. Purchasing robots outright has become more affordable since the most recent policy and budget bill passed this summer. It includes a provision that allows businesses to deduct the full cost of new equipment the year it is placed in service, according to Kevin Harris, a partner at EisnerAmper, a firm that advises companies on accounting and tax law.

But some companies still can’t afford robots, or prefer to keep the cost as an operating expense, according to Andra Keay, managing director of Silicon Valley Robotics, an industry association that supports the commercialization of robotics technology. Others simply aren’t ready to commit to a big purchase at a time when technology is evolving so rapidly or they want to test solutions before they invest.

“It is a great idea as an introduction,” Ms. Keay said. “Robots are needed to deal with labor shortages and that includes making jobs more enjoyable and pleasant.”

Alain Delaquérière contributed research.