Sebastian Engler

Tool System for Ultrasonic-Assisted Forming and Material Characterisation with 15 kHz Oscillation Frequency

It is well-known that superimposed ultrasonic tool vibrations are capable of decreasing the forming force and the interfacial friction during the deformation of metal. The complex causes of this phenomenon were mainly investigated by focusing on oscillation frequencies above 20 kHz. Due to limitations of the load capacity and the power of the oscillating systems, mostly soft materials, such as aluminium and copper, were analysed. The present study is concerned with the development of a tool system for ultrasonic-assisted compression tests with a 15 kHz oscillation system. The advantages of this type of oscillating system are an increased power and robustness, which allow the testing of high strength materials. In preliminary ultrasonic-assisted compression tests with a S235JR steel a force reduction of up to 63 % was measured. The major challenges identified during the preliminary investigations are a transversal drift of the specimen, a periodic separation between the die and the specimen, a high sound emission and a high demand on the measuring and signal processing technology. Based on the technical challenges and the determined requirements a tool system is introduced.

Ultrasonic-Assisted Metal Staking with 15 kHz Oscillation Frequency

To comply with increasing product requirements, the use of function-optimized materialsis claimed. Joining technology thereby becomes increasingly important to use high strength materialonly in postulated sections. Staking is a joining by forming technology that is highly reliable andcost efficient. High process forces and sufficient formability of the material limit the suitability inclaimed miniaturization for use in industrial applications. A promising approach to break these processlimitations is the use of superposed high frequency oscillation, whereby joining forces could bedecreased. The present study indicates first trials of an ultrasonic (US) assisted staking process of highstrength martensitic steel. Based on high temporal instrumentation, such as laser vibrometer, contactdetection and high-resolution force measurement, the process sequence is characterized and studiedin detail. The researches confirm high potential in force reduction of mean values due to superimposedhigh frequency oscillation with a high dependency on amplitudes. In process, two differentforce-characteristics within three regimes can be identified. Since US assisted forming processes arewell known in literature with harmonic oscillating force signals during process, hammering and soirregular force peaks with changes in contact signal within process, are identified for first time anddemonstrate a highly promising field of application.

New approaches for highly productive laser welding of copper materials

Laser welding of highly conductive materials like copper is a difficult proposition, but offers a useful non-contact joining method, well geared for automation. Coppers high reflectivity at the 1 µm wavelengths has always been the barrier in the past to implement laser welding. Frequency doubled green lasers can remove this barrier and has a high potential to revolutionize the laser welding of copper materials in high volumes and for future applications. In this paper, we present new results for welding copper and copper alloys with a novel brilliant laser, emitting in the green wavelength region (up to 325 W@515 nm, 2 mm mrad). The results are compared with a state-of-the-art solid state laser, emitting in the infrared wavelength region (up to 1000 W@1030 nm, 2 mm mrad). Fundamental investigations on the absorption and energy coupling properties in the different phases of the process (heating up, heat conduction welding, deep penetration welding) were performed to learn more about process stability and process reproducibility of the welding process at copper alloys. Significant increase in process reproducibility can be demonstrated by using a green laser.