Challenges of Manual Assembly

During the pilot phase, manual assembly of a new Siemens medium-voltage switch took over an hour and demanded significant physical exertion while requiring meticulous attention. However, with ergonomically optimized processes and workstations, the assembly time has been halved to approximately 25 minutes. This optimization not only reduces the strain on employees but also eliminates potential safety hazards.

Siemens AG's Energy Management Division developed a new medium-voltage switch for industrial, power station, and changeover station applications. Initially assembled at a makeshift manual workstation in 2012, the success of the product led to increased demand and necessitated production expansion at the Berlin facility. To optimize the assembly workstation, the Medium Voltage & Systems department sought assistance from Bohnert Systemtechnik.

Petra Stielow, a designer at the engineering office in Rödermark near Frankfurt, recalls their involvement in the process, “The work was carried out manually at a normal table, and the subassembly weighing around sixty kilograms had to be rotated and turned by hand. There was a constant danger of fingers being squeezed or jammed. Tools and small parts were not at hand.”

The Impressive Ergonomic Assembly Workstation

The ergonomic assembly workstation, devised by Stielow and her colleague Dirk Siemko, technical manager at Bohnert, was introduced at Siemens in Berlin in the spring of 2013. Initially, it reduced the throughput time by half an hour, bringing it down to approximately 35 minutes. The concept revolves around a rotatable assembly surface, which can be mechanically locked in position via a plain bearing. Additionally, with the help of two rotating modules, the surface can be tilted towards or away from the worker, facilitating easy and secure assembly of medium-voltage switches from all angles.

Indexing ensures precise engagement at the correct angle, while hydraulic unlocking via a foot pedal ensures that the operator's hands remain free throughout the process. Furthermore, the workstation's height can be adjusted to match the employee's height and the assembly height of the subassembly, thanks to two electric lifting columns of the "Shopfloor" type. These columns are controlled manually using a control switch, with a synchronous control unit managing the components.

Reliable and flexible modules for handling technology

Since 2012, Bohnert system technology has partnered with ROEMHELD, the specialist in assembly and handling technology based in Laubach near Gießen in Hesse. Stielow emphasizes the reasons behind this partnership, "For us as a development service provider, it is also important that the advice and the support in our planning is extremely competent, prompt and helpful. Also, the modulog range is a modular system that can be used very flexibly; the individual components can be easily combined with each other.”

ROEMHELD's modulog program encompasses a wide array of modules for horizontal and vertical rotation, tilting, lifting, positioning, and movement. Standard components are engineered to accommodate various loads ranging from 100 kg to 1,000 kg, or 220 lbs to 2200 lbs. They can be manually operated directly on the module or via levers or pushbuttons, either by hand or foot. One of ROEMHELD's recent innovations is a rotating module with a media feed-through, allowing fixtures clamped with zero-point clamping systems to be operated hydraulically, electrically, or pneumatically without complex piping.

The Shopfloor lifting column utilized by Bohnert offers a stroke range of 200 to 600 mm, available in three variants capable of handling loads up to 600 kg, or 1325 lbs. It can be operated using a hand switch, foot lever, or foot switch. The horizontal rotating modules employed are designed to bear a load of 200 kg each, or 440 lbs. One of them features indexing of the rotating position in 60-degree increments, while the other functions as a counter-bearing without position markings.

Follow-up Order for Enhanced Production Line

Siemens expressed great satisfaction with the initial assembly workstation, prompting them to place an order for a second version for a production facility in China during the same year. Shortly after, they requested a production line for the medium-voltage switch comprising three workstations.

“For this line, we divided the assembly work into three steps and designed the corresponding manual workstations,” remembers Petra Stielow. First, the basic components of the support plate, pole plate and the poles are assembled, the pole plate is fixed by hand on the side of a stop. “This prevents it from slipping and at the same time the subassembly is optimally positioned at the center of gravity,” emphasizes the designer.

Gravity roller belts facilitate the movement of various parts, components, and assembled subassemblies between the adjacent workstations. At the second assembly station, a pre-assembled shaft is mounted, followed by the installation of the cable harness at the third station. In the end, the throughput time was further reduced by an additional ten minutes.

In Addition to Time Savings

Stielow highlights various advantages, “Thanks to the adjustable working height and the reduction of the force required from 500 N to 50 N, employees tire more slowly and can concentrate longer. The improved and safe handling and the simple and logical operation also increase the assembly quality. At the same time, the risk of accidents has decreased, so that long-term workplace-related absences and absenteeism are reduced.”

The company is also effectively supported in meeting professional association requirements for hazard analysis aimed at reducing psychological stress in the workplace, a mandate implemented since 2015.

When designing the production line, Siemko and Stielow ensured Siemens could utilize the workstations flexibly: If assembling small quantities, all work can be completed at the second assembly workstation, with the remaining stations activated via the control panel.

Moreover, the system could be adapted for assembling other switch types after appropriate modifications. Bohnert Systemtechnik's production line impressed the customer, prompting consideration of implementing another line at a location in China.