SIMULATION OF ORBITAL FORMING PROCESS
In this study the feasibility of 3D FEM simulation of the orbital forming process was investigated by evaluating the simulation time. Commercial FEA software DEFORM 3D v4.0 that has an efficient computation algorithm for simulating incremental forming process was used for the simulations and the savings in computation time was determined. In order to provide reliable flow stress for the simulation, a finite element based inverse analysis technique has been introduced. Results show that developed inverse analysis technique is efficient and accurate for use in 3D FEM simulation for process optimization.
Numerical and experimental investigations of the shaft-clinching assembly process of automobile wheel-hub-bearing units
A shaft-clinching process aimed at developing a lightweight, integrated and highly reliable assembly is a very effective technique for the assembly of hub-bearing units. In this study, a reliable elastic–plastic finite element model of the shaft-clinching assembly process was developed by using the Abaqus platform and was applied to simulate the shaft-clinching assembly process of automobile wheel-hub-bearing units. To ensure the precision of the developed finite element model, the motion equations of the rivet head during the shaft-clinching process were obtained on the basis of theoretical derivation, on-site testing and the structural parameters of the equipment. Further, a series of experiments was performed for identifying the mechanical properties of the investigated material and the realistic friction conditions existing at the rivet head–workpiece interface. Based on the obtained reliable preprocessing data, the developed finite element model was used to simulate the shaft-clinching assembly process. Subsequently, the finite element model was validated using experiments on the shaft clinching of a wheel-hub-bearing unit. Comparison between the simulation results and the experimental results in terms of the axial clinching force–time curve and the ultimate deformed shape of the hub shaft showed good agreement, thereby validating the developed model. Finally, the influences of the axial distance between the upper surface of the inner ring and the forming surface of the rivet head, the friction factor, the radius ratio of the internal gear to the external gear and the maximum inclination angle of the rivet head on the clinching process were studied. The results of this study are expected to aid optimization of the shaft-clinching assembly process.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.