BUMAX selected for demanding ultrasonic welding application


With 20,000 vibrations per second, BUMAX bolts must deal with extreme forces during the ultrasonic welding process.

Schunk Sonosystems is a global leader in developing and building machines for ultrasonic metal welding – such as their industry-leading flexure sonotrode. Their machines include a sonotrode or welding tip that transfers vibrational energy to the workpiece. Up to two high-strength bolts are required to fix the sonotrode, which is subject to extreme levels of vibration due to the very high frequency used in ultrasonic welding.

Increasing lifetime performance

To further improve the performance of its flexure sonotrode, Schunk Sonosystems switched from standard grade 12.9 steel bolts to BUMAX® DX 129 (Duplex stainless steel), which offers very high tensile strengths of min. 1,200 MPa and excellent fatigue resistance properties.

“The standard 12.9 steel bolts we previously used to attach the sonotrode were inconsistent in their performance and required regular replacement as they simply couldn’t cope with the extreme pulling and bending forces that ultrasonic vibration of around 20,000 vibrations/second placed on them,” explains Stefan Mueller, Head of R&D at Schunk Sonosystems. “In worst case, a screw breakage could limit the lifetime of the sonotrode.”

In the second half of 2022, Schunk Sonosystems tested different fasteners with the aim of finding screws that lasted throughout the lifetime of the sonotrode and did not break.

“Of all the screws we tested, only BUMAX met all our needs,” says Mueller. “Not only are BUMAX consistent in how they perform, they easily last the life of the sonotrode, do not create abrasion dust on the screw head and do not require rust protection.

Schunk Sonosystems now uses BUMAX® DX 129 for all its ultrasonic welding flexure sonotrodes. The machines are mainly used in the automobile industry.

Superior fatigue resistance

The high fatigue strength that BUMAX screws offer is crucial to their ability to withstand a high number of cycles without fracture. All BUMAX bolts are made with the highest quality European steel, and its advanced manufacturing processes result in the further enhancement of the material’s fatigue resistance properties.

Fatigue fracture often begins with a stress concentration such as inclusions, slags or surface defects. The high-quality raw materials BUMAX uses, together with the best metallurgical processes and good surface properties, guarantee excellent fatigue strength. BUMAX also uses rolled threads rather than cut threads, which further increases fatigue resistance.

“We are very satisfied with screws and the high level of support BUMAX provides us with,” concludes Mueller. “The use of BUMAX screws has been a gamechanger for our flex sonotrodes – to enable us to offer a product to customers that consistently meets our high standards for quality.”

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