Production flexibility through linear motion technologies

The automotive assembly line is a modern marvel of engineering. Over one hundred years ago, Henry Ford and his team at Highland Park plant in Michigan, USA, developed the first moving line. It simplified the assembly of the Ford Model T’s 3000 parts by breaking the process into 84 distinct steps, which were performed by groups of workers as the vehicle chassis was pulled by rope down the line. The process revolutionised automotive production and dropped the assembly time for a single vehicle from 12 hours to about 90 minutes.

By reducing the money, time and manpower needed to build cars as he refined the assembly line over the years, Ford was able to drop the price of the Model T from $850 to less than $300. For the first time in history, quality vehicles were affordable to the masses.

The design of assembly lines has evolved significantly since then, but while they are fast, they are also 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 the demand 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.

Flexible production

This is problematic given that the automotive industry is in something of a state of flux and 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 ability to produce multiple car models on the same assembly line in any sequence without set-ups was a radical new idea when it started with Toyota in the 1960s, but nowadays it is industry standard. Now, however, assembly lines need to be able to be moved around, rearranged and reconfigured at short notice.
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.

Easy integration

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 12.5kg, 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 300 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.
As factories become increasingly connected and internet-of-things (IoT)-enabled devices feature more prominently on the shop floor, it is critical that any new equipment is plug-and-play and can be monitored cost-effectively—enabling predictive maintenance to be carried out.

While conventional spot-welding guns require the usage of expensive piezoelectric sensors to monitor the welding forces they generate, Ewellix has integrated a set of strain-gauge sensors inside its actuators – so that they are protected from the production environment - that enable the reliable and precise measurement of forces. By including this technology as a standard option on the CEMC series, Ewellix plans to be the preferred partner for the development of the IoT-ready welding lines set to enhance the car manufacturing processes of tomorrow.