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Wide tyres, narrow cabinets

Wide tyres, narrow cabinets

For over 50 years, Wormser Hofmann Maschinen- und Anlagenbau GmbH has been one of the leading manufacturers of semi-automatic and fully automatic tyre assembly lines. The final assembly lines of almost all automobile manufacturers must have the right wheels available for the right car just in time – a process that has become more and more complex in recent years due to the growing variety of tyre and wheel rim dimensions. Maintaining a cycle of 8 seconds in the face of these challenges requires not only a great deal of know-how but also powerful drive and control technology from Siemens

By Sascha Heck, Johanna Gebhardt

The trend towards greater variety and different sizes of rims and wheels has continued unabated for years, not only for high-end SUV models from premium manufacturers. The wheel dimensions fitted on the conveyor belts of the automotive industry now range from small 14-inch spare wheels to enormous 24-inch wheels. This represents a big challenge for manufacturers of tyre assembly lines like Wormser Hofmann Maschinen- und Anlagenbau GmbH, whose plants assemble all wheels and spare wheels needed on the assembly line, as ordered by the customer, in unsorted mixing mode. Michael Zintel, head of electrical design at Hofmann Maschinen- und Anlagenbau GmbH says, “To ensure that a fully assembled wheel can leave our plants every eight seconds, all changeover processes must be performed within this cycle frequency – no matter which wheel follows which other wheel.” As not only tools and clamping fixtures are moved in these changeover processes, but also very large masses (24-inch light-alloy rims weigh up to 30 kg each), the Wormser specialists decided to convert to Siemens drive technology back in 2014.

Control cabinets 33% smaller

The manager responsible for automation at Hofmann explains: “The reasons for choosing Siemens were obvious at the time: with the new drive systems, our customers benefit from Siemens’ worldwide availability, we save space in the control cabinet, complete installation more quickly and can make better use of braking energy.” For example, S120 Booksize Motor Modules are available as single or double motor modules and can be easily mounted side by side and connected with Drive-CLiQ. Thanks to their three-fold overload capability, the Motor Modules also frequently enable a smaller module to be chosen because the peak loads usually only occur very briefly during tyre assembly, which is a discontinuous process. “At a rough guess, the control cabinet of our tyre assembly machine is now around 33% smaller for the same power output than it used to be.” With its central infeed, the Sinamics S120 drive system also enables braking energy to be used directly in the DC link of the machine, energy that was previously just wasted as heat in braking resistors. In practice, this means that up to 22% of the drive energy is saved.

For efficient engineering, more than 30 Sinamics S120 modules are stored in Siemens’ own configuration tool Sizer, from which the correct module is chosen based on all available technical data, such as friction values, gear ratios and performance requirements. The Wormser specialists also ensure that not too many different types are used, so that the end customers only need to keep a manageable number of spare modules in stock.

Transition to TIA Portal

Hofmann GmbH is also making sure the control technology they deploy is sustainable. Since more and more measurement data is captured relating to the whole tyre assembly process – from mounting, matching and inflating the tyres to optimizing tyre fit, and semi-automatic and fully automatic balancing of the wheels – Hofmann GmbH has gradually been switching all their machines to the TIA Portal since 2018. The pilot for this is the tyre inflation dome which inflates each tyre to the required pressure within one second using four different tyre sealing rings and a single inflation dome with an air pressure of 4.2 bar. The air enters the tyre not through the valve but via the edge of the tyre. To ensure this process also works completely smoothly in unsorted mixing mode, a Simatic S7-1516 PLC controls the entyre inflation process and checks via RFID whether each tyre matches the tyre sealing ring.

Hofmann greatly appreciates the efficiency of the solution. As Michael Zintel, head of electrical design, says, “As part of automating the tyre inflation dome, we had to redesign numerous communication links. Initially, this meant extra work for us, but overall we are already seeing very clearly the benefits of the TIA Portal in our second project, tyre fit optimization: We can re-use many more software modules than before and save translation costs due to the graphical user interface.” Not only that, the new Sirius Act pushbuttons have been used for the first time on the inflation dome, which was connected directly to the PLC via a ribbon cable and via Profinet. “This saves a lot of installation time because we can do the wiring much faster and avoid wiring problems from the outset with the new type of cable.”

Increased performance requirements

The move to the TIA Portal also provides a way of assigning the constantly growing quantity of data to the relevant wheel during the process. For example, some automakers now demand not only acquisition of tyre, DOT and TAG numbers of the radio valves and the inflation pressure, but also of all forces that have been exerted on the tyres during assembly and all measurements relating to the tyre fit and smooth running. Thanks to the TIA Portal, we can assign this data to each wheel and store it more easily than was previously possible. And because we expect the quantity of required data to continue to increase in the future, we are in a good position to handle this with the TIA Portal.

This is not the only area in which the company sees itself as being very well prepared for the future. As electromobility expands, the Wormser experts are expecting more and more rigid tyres to be used because they will have to withstand higher and higher torques. This trend will require greater performance from the assembly machines, which, according to Zintel, “can be integrated in new plants without any problem thanks to Siemens drive technology, and can easily be installed in existing control cabinets during retrofits.”

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