High tech manufacturing has made inroads in many industries, and tiremaking is no exception. Though robotics has not displaced traditional tire building techniques on a large scale, it’s use is certainly growing.
Making a tire is a labor-intensive process for a variety of reasons. A tire consists of many individual components that all have to be assembled in a specific order.
The process begins with the formulating of rubber compounds. The raw ingredients, which include oils, carbon black and/or silica, pigments, antioxidants, accelerators and other additives, are mixed together in giant blenders called Banburys. This produces the gum-like material that will be milled and slit into strips that become the sidewalls, treads and other parts of the tire.
The body of the tire is created using rubber-coated fabric that comes in huge rolls. The fabrics used include polyester, rayon or nylon depending on the type of tire that’s being made. Most passenger car tires have polyester cord bodies.
Another component is the tire bead. Shaped like a hoop, the bead’s backbone is assembled from high tensile steel wire. The strands are aligned into a ribbon and coated with rubber for adhesion, then wound into loops.
Radial tires are built on a round drum or cylinder that is part of a tire building machine. The machine pre-shapes the tire into a form that is very close to the tire’s final dimensions.
When tires are built, they are assembled from the inside out. A skilled tire builder starts by creating the inner liner with a double layer of synthetic rubber. On top of this, he wraps two layers of ply fabric (the cords) followed by two strips called apexes to stiffen the area just above the bead. Next, a pair of chafer strips are added to help the bead resist chaffing when it is installed on a wheel. The steel belts that help resist punctures and provide support for the tread are added next, followed by the tread which goes on last.
Automatic rollers press all the parts firmly together, then the "green tire" is inspected before it goes into a curing press. The curing process heats the tire to over 300° F for 12 to 25 minutes to shape and mold the tread. This vulcanizes the rubber and produces a finished tire. Then a final inspection is made, which may include an x-ray to reveal internal flaws.
That was a pretty basic rundown, but you can see that making a tire involves a lot of steps and requires a high degree of precision and control at each step in the process.
The most difficult part of automating tire production has always been the assembly of the tire carcass. Automating the rest of the process (the blending of the raw ingredients, the handling of the components that go into the tire, the handling of the tire between stages, final curing and inspection) has been the easy part.
Ernie Rodia, vice president of global engineering and manufacturing technology at Goodyear, says his company’s IMPACT (Integrated Manufacturing Precision Assembly Cellular Technology) automates much of the material handling and preassembles some of the individual components.
Machines called "hot formers" are used at two Goodyear plants to combine tire carcass elements so only the belts and tread have to be added when the tire is finally assembled. This cuts the time and number of splices needed by half.
On a typical truck tire, the hot former combines 12 of the 23 separate elements into one; with passenger car tires it combines six of the 12 separate elements into one.
"We’re currently using IMPACT technology to produce about 30% of our truck tires and about 10% to 15% of our passenger car tires. The result is lower production costs, greater repeatability and higher overall quality," he said.
Smoke & Mirrors?
Kevin Gilhouly of Pirelli says there’s nothing magic or mysterious about Pirelli’s Modular Integrated Robotized System (MIRS) for producing tires. First developed at the company’s Milan, Italy, plant in July 2000, MIRS technology is now being used in Germany and the United Kingdom to build tires. Pirelli’s Rome, Ga., plant will also be using the new MIRS process to produce tires later this year.
So what exactly is MIRS? It’s a series of automated work stations that employs six robotic arms to build the tire. As the tire is being built on a drum, the components are added as long continuous strips – which eliminates the seams and joints that are necessary when a tire is hand-built.
The continuous winding process results in a much rounder, more reliable tire with less variation. Gilhouly says MIRS improves the tire 100% over traditional tire building methods. It also lowers costs about 25%. But it’s a slow process that does not yet lend itself to high volume tire production.
"What MIRS gives us is flexibility. Each module can produce up to 125,000 tires a year, which makes it ideal for low volume, high performance tires and specialty tires," he said. "We can do smaller runs and then quickly change to another size without the headaches you have to deal with when changing sizes in a traditional tire building process."
Gilhouly said Pirelli is using MIRS in its Germany plant to build run-flat tires for the new Mini Cooper.
"We believe the MIRS process will help us cope with the rapid proliferation in tire sizes we’re seeing today, and allow us to produce a wider variety of sizes in shorter runs economically," said Gilhouly.
Due to the competitive nature of the business, tire manufacturers are not anxious to share their production secrets with the world (especially their competitors). John McQuade of Bridgestone/Firestone said his company sees four main advantages to using robotics in tire manufacturing:
- Ergonomic improvement: robotics can eliminate a lot of the material handling that goes on inside a traditional tire plant.
- Improved process repeatability: by removing the human element, you get much better consistency and quality.
- Saves space:: allowing more efficient plant layouts and smaller facilities.
- Reduced costs: but to achieve this it requires a sizable investment in new technology up front.
"We believe robotics is the answer where it makes economic sense," McQuade said. "You can automate most passenger car and light truck tire production, but not larger tires.
"We’re using a lot of robotics at our Aiken, S.C., plant, which is our newest facility, to automate much of the tire handling. For example, we’re now using bar codes on tires to reduce the chance of shipping customers the wrong tires."
McQuade wouldn’t comment on the type of robotics being used in the tire building process except to say that BFS has developed its own proprietary processes – which it doesn’t want to reveal.
Super Top Secret
Michelin also has its own super-secret automated tire building process, called C3M, which very few people – including Michelin’s own employees – have ever seen.
Jim Dunbaugh, plant manager at Michelin’s Greenville, S.C., plant where two C3M units have been combined, says product quality, precision and ergonomic issues drove the development of the process.
"Our applications are primarily in situations where we have repetitive motions or movements in three or more axes," he said. "Currently, we use robotic systems by FANUC and ADEPT within our conventional tire building processes, primarily in applications of high ergonomic risk (repetitive motion) to our employees."
Michelin’s C3M system – Carcasse, Monofil, Moulage and Mechanique – has been installed on three continents since its introduction in 1997, Dunbaugh says, and have produced some 15 million tires.
"C3M is a very flexible process that we’ve demonstrated takes only 12 hours to set up and start building tires," Dunbaugh said. While it can make any passenger or light truck/SUV tire, Dunbaugh says C3M is best suited to short runs of "super-high performance and high performance SUV tires." Efficiency and quality are gained by simplifying the process. "The traditional manufacturing process consists of seven stages. With C3M, manufacturing is reduced to a single stage," he said.
C3M is not Michelin’s only "quality" answer, though. The process, Dunbaugh explains, forces upstream improvements in order to be effective. "Once the upstream product supply is improved, productivity increases."
It’s likely that as time goes on, the industry will see greater use of automation in tire plants and more hands-off tire building. For dealers, this should mean higher levels of quality and fewer warranty problems.
But it also means tiremakers could create entirely new designs that are currently too difficult or expensive to produce with manual assembly techniques. Time will tell.