查看更多>>摘要：A fundamental study of the mechanisms of generation of the laser-induced periodic surface structure (LIPSS) includes electromagnetic deposition theories and matter reorganization theories. The proposed two-dimensional finite element model incorporates frequency-domain electric field analysis and the two-temperature model (TTM) to simulate the growth process of LIPPS in multi-pulse picosecond laser irradiation. The proposed simulation proceeds as follows: the electric field intensity (EFI) distribution is calculated by referring to the material surface morphology and determines heat distribution by the electromagnetic heating (EMH); the heat distribution is introduced into the TTM to calculate the electron and lattice temperatures; by comparing the lattice and the vaporization temperature, material ablation is determined to obtain a new surface topography and single-pulse simulation completes; and by introducing the new surface topography recursively, multi-pulse laser irradiation can be simulated. In the calculation of a picosecond laser with a wavelength of 1064 nm, pulse duration of 20 ps and different laser fluences for the irradiation of the Ti6Al4V alloy surface, this method could simulate the ripple-like distributed EFI, and a surface morphology similar to that of LIPSS grew after several pulses. The results were in agreement with the observed experimental results. The proposed assumption is a novel approach for the explanation of the LIPSS generation mechanism.
查看更多>>摘要：Mechanical clinching is a commonly used method for joining dissimilar materials in the automotive industry. The clinch-bonding process was developed based on the clinching process to ensure the fixation of the adhesively bonded parts up to the curing process, where the adhesive gains its maximum strength. However, the fluid flow of the adhesive during clinch-bonding interferes with the interlock formation, thereby causing quality issues. The lack of a systematic understanding of the dynamic behavior of adhesives during the process poses optimization obstacles. This study aims to clarify, using numerical simulation, the dynamic flow behavior of the adhesive and its influence on clinch-bonding joint formation. Simulation models of the clinching and clinch-bonding processes of high-strength steel JSC780 and aluminum alloy A5052-H34 under different process conditions were established and validated experimentally. The modeling clarified the critical role of blank holding force on the adhesive flow direction and local hydraulic pressure evolution that led to adhesive pockets. The Cockcroft-Latham damage criterion was introduced to evaluate the local damage to the steel, based on which the root cause of neck cracking generated under insufficient adhesive outflow condition was revealed. The knowledge obtained from the modeling was subsequently experimentally proven.
查看更多>>摘要：Superhard cutting tool materials such as polycrystalline cubic boron nitride (pcBN) are increasingly demanded in the aerospace and automotive industries. Although grinding is a common manufacturing technology for pcBN cutting tools, the lack of knowledge regarding thermal and mechanical loads during grinding of pcBN can cause workpiece damage and high grinding wheel wear. Therefore, this work presents a new approach of forcecompliant grinding (FCG) of different pcBN specifications considering the thermal and mechanical load as well as the productivity. During the FCG approach, the normal force between the grinding wheel and the pcBN workpiece was set to a predefined value before material removal starts. Based on an evaluation of the grinding force ratio, the temperature of contact and the material removal rate, a modification of Preston's theory of polishing was found to be applicable to predict the productivity. Accordingly, both an increasing grinding normal force and grinding force ratio lead to an increasing productivity during FCG of pcBN. However, the quantitative models developed in this work enable to predict the productivity as well as the mechanical and thermal load during FCG of pcBN. These models hence contribute to the extension of process knowledge for grinding pcBN and thus to prevent damage to the workpiece and high wear of the grinding wheel.
NSTL
Elsevier