Entity

Time filter

Source Type

Erlangen, Germany

Weigl M.,Bavarian Laser Center GmbH | Schmidt M.,University of Erlangen Nueremberg
Physics Procedia | Year: 2010

The present article deals with the laser-welding of copper and stainless steel connections for applications in power electronics. Here, the particular demand for such dissimilar connections is caused by the increasing implementation of electronics in areas with contact to corrosive fluids, which copper cannot resist. In this context the influence of a lateral displacement of the laser beam and the feed rate on the metallurgical properties of the dissimilar materials' connection is highlighted. The effects of these parameters are discussed on the base of metallographic specimen, micro-hardness measurements and element analysis. © 2010 Published by Elsevier B.V. Source


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Optics Express | Year: 2013

The spatial distribution of the laser energy absorbed by nonlinear absorption process in bulk glass w(z) is determined and thermal cycles due to the successive ultrashort laser pulse (USLP) is simulated using w(z) based on the transient thermal conduction model. The thermal stress produced in internal melting of bulk glass by USLP is qualitatively analyzed based on a simple thermal stress model, and crack-free conditions are studied in glass having large coefficient of thermal expansion. In heating process, cracks are prevented when the laser pulse impinges into glass with temperatures higher than the softening temperature of glass. In cooling process, shrinkage stress is suppressed to prevent cracks, because the embedded molten pool produced by nonlinear absorption process behaves like an elastic body under the compressive stress field unlike the case of CW-laser welding where the molten pool having a free surface produced by linear absorption process is plastically deformed under the compressive stress field. © 2013 Optical Society of America. Source


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physics Procedia | Year: 2011

Thermal conduction model is presented, by which nonlinear absorptivity of ultrashort laser pulses in internal modification of bulk glass is simulated. The simulated nonlinear absorptivity agrees with experimental values with maximum uncertainty of ±3% in a wide range of laser parameters at 10ps pulse duration in borosilicate glass. The nonlinear absorptivity increases with increasing energy and repetition rate of the laser pulse, reaching as high as 90%. The increase in the average absorbed laser power is accompanied by the extension of the laser-absorption region toward the laser source, suggesting the seed electrons for avalanche ionization are provided mainly by thermal excitation at locations apart from the focus. © 2011 Published by Elsevier Ltd. Source


Weigl M.,Bavarian Laser Center GmbH | Albert F.,Bavarian Laser Center GmbH | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physics Procedia | Year: 2011

Laser micro welding of direct copper-aluminum connections typically leads to the formation of intermetallic phases and an embrittlement of the metal joints. By means of adapted filler materials it is possible to reduce the brittle phases and thereby enhance the ductility of these dissimilar connections. As the element silicon features quite a well compatibility with copper and aluminum, filler materials based on Al-Si and Cu-Si alloys are used in the current research studies. In contrast to direct Cu-Al welds, the aluminum filler alloy AlSi12 effectuates a more uniform element mixture and a significantly enhanced ductility. © 2011 Published by Elsevier Ltd. Source


Miyamoto I.,Osaka University | Cvecek K.,Bavarian Laser Center GmbH | Okamoto Y.,Okayama University | Schmidt M.,Bavarian Laser Center GmbH | Schmidt M.,Friedrich - Alexander - University, Erlangen - Nuremberg
Applied Physics A: Materials Science and Processing | Year: 2014

Internal modification process of glass by ultrashort laser pulse (USLP) and its applications to microwelding of glass are presented. A simulation model is developed, which can determine intensity distribution of absorbed laser energy, nonlinear absorptivity and temperature distribution at different pulse repetition rates and pulse energies in internal modification of bulk glass with fs- and ps-laser pulses from experimental modified structure. The formation process of the dual-structured internal modification is clarified, which consists of a teardrop-shaped inner structure and an elliptical outer structure, corresponding to the laser-absorbing region and heat-affected molten region, respectively. Nonlinear absorptivity at high pulse repetition rates increases due to the increase in the thermally excited free electron density for avalanche ionization. USLP enables crack-free welding of glass because the shrinkage stress is suppressed by producing embedded molten pool by nonlinear absorption process, in contrast to conventional continuous wave laser welding where cracks cannot be avoided due to shrinkage stress produced in cooling process. Microwelding techniques of glass by USLP have been developed to join glass/glass and Si/glass using optically contacted sample pairs. The strength of the weld joint as high as that of base material is obtained without pre- and post-heating in glass/glass welding. In Si/glass welding, excellent joint performances competitive with anodic bonding in terms of joint strength and process throughput have been attained. © 2013 Springer-Verlag Berlin Heidelberg. Source

Discover hidden collaborations