Production flexibility through linear motion technologies

As the automotive industry enters a period of transition, vehicle production lines increasingly need to be smart, flexible and adaptable. In response to these requirements, Ewellix, formerly SKF Motion Technologies, has unveiled a number of innovative systems for the transport of vehicles on the line and for their efficient spot-welding.

Traditional assembly lines are fast, but inflexible. They are designed for the manufacture of cars in large numbers and at relatively high speeds, but they are extremely difficult to change. For example, making them go faster, or slower, than their rated speed can cause significant issues, while introducing a new car model can require months of retooling. When thedemand for a car increases, customers must sometimes wait a considerable time for the assembly operation to catch up, and when demand eases off, plants must often be left running well below capacity.

This is problematic given that the automotive industry is in something of a state of flux and is increasingly needs production to be flexible. Car models are refreshed approximately every two-to-three years, and a wide variety of models is required to reach a broader market and to maintain sales. In this scenario, car manufacturers must be able to react quickly to fluctuations in demand for each model, or shifts in the balance of demand for cars, sports utility vehicles (SUVs), trucks and electric vehicles (EVs). Each plant must therefore be able to produce more models, and switch between the manufacture of each car model and type on a single production line.

The use of one assembly line to build a variety of different body styles requires careful coordination that starts with the engineers who design the vehicles and extends to the construction of the tools used to assemble and weld them.

For these reasons, Ewellix has developed its highly flexible car transfer units (CTUs). These CTUs can be rapidly and efficiently reconfigured to transport different car-models on a single assembly line. In comparison with the use of conventional assembly equipment and tooling, the use of these CTUs reduces the amount of re-programming and commissioning needed to transition between the production of different models.

This translates into reduced capital investments. Indeed, compared with the design, assembly, installation and commissioning of a new fixture system for each new model produced on an assembly line, the Ewellix solution can reduce costs by around 84 percent. Further, Ewellix’s CTUs can be brought on-line in under two weeks, reducing time by 85 percent in comparison with conventional systems.

Each Ewellix CTU features a steel cover that provides protection from spatter, an inner mounted cableveyor, and integrated motors, controllers, cables, mechanical brakes and shock absorbers. Owing to the use of Ewellix’s precision ball screw system, the CTUs can be positioned accurately and repeatably. The precise alignment and secure fastening of attachments is achieved with threads and pin holes in the carriage and bottom plate. The CTUs come in various sizes and multi-axes options are available.

The different sizes and types of frames employed in flexible and modular assembly lines, coupled with many different types of materials used, also pose significant challenges when it comes to welding. For this reason, Ewellix has also developed a range of spot-welding actuators equipped with state-of-the-art inverted roller screw technology.

Ten years ago, a gun may have had to carry out ten million spot welds before being changed, but today that requirement has almost doubled. Similarly, actuator relubrication had to be carried out after two million spots, but now this has to wait until ten million spot welds have been produced. Both requirements can be met by minimising the weight and dimensions of the welding gun, which allows the use of smaller robots and improves their operating range around the chassis. This necessitates a move away from traditional pneumatic and electromechanical welding gun actuator technology.

That is why Ewellix, in partnership with some key OEMs, has developed its latest generation of spot-welding actuators. Being the inventors and leading manufacturer of roller screws, Ewellix has constantly improved the design of these core components to push their load carrying capacity and lifetime to the limits, achieving higher power density ratios.

By employing inverted roller screw technology, it is possible to use a specially designed hollow shaft motor to create an axially compact actuator. Compared with the former Ewellix CEMC series and other solutions on the market, this new series is smaller, meaning it can be integrated easily into existing welding gun designs.

Further, the new CEMC series is lightweight. Weighing just 12.5 kg, it is 10 percent lighter than its predecessor, improving robot dynamics during welding operations. By matching these values with a high load capacity of 25kN and linear speeds up to 600 mm per second, the new CEMC series offers the best power-to-weight ratio on the market.

In terms of field performances, the next generation CEMC delivers twice the lifespan of the former series (up to 20 million welding spots) and requires only one relubrication interval in between; up to 10 million spot welds can be carried out on a single gun without any relubrication. This minimises maintenance costs and related downtime, while keeping performance – in terms of force and positional repeatability – consistent during the entire life of the actuator.

Thanks to the modularity of their design, it is possible to equip the actuators with different position feedback devices and attachments. Indeed, customers can choose from among 336 different combinations as standard and can also specify attachment sizes, greases and so forth, leading to a high degree of flexibility in production.

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