Efficient Wear Simulation Methodology for Predicting Nonlinear Wear Behavior of Tools in Sheet Metal Forming.

In conventional wear simulation, the geometry must be updated for succeeding iterations to predict the accumulated wear. However, repeating this procedure up to the desired iteration is rather time consuming. Thus, a wear simulation process capable of reasonable quantitative wear prediction in reduced computational time is needed. This study aimed to develop an efficient wear simulation method to predict quantitative wear reasonably in reduced computational time without updating the geometry for succeeding iterations. The wear resistance of a stamping tool was quantitatively evaluated for different punch shapes (R3.0 and R5.5) and coating conditions (physical vapor deposition of CrN and AlTiCrN coatings) by using a progressive die set. To capture the nonlinear wear behavior with respect to strokes, a nonlinear equation from a modified form of Archard's wear model was proposed. By utilizing the scale factor representing the changes in wear properties with respect to wear depth as input, the simulation can predict the behavior of rapidly increasing wear depth with respect to strokes after failure initiation. Furthermore, the proposed simulation method is efficient in terms of computational time because it does not need to perform geometry updates.

Springback Reduction of Ultra-High-Strength Martensitic Steel Sheet by Electrically Single-Pulsed Current.

This paper investigates the reduction of springback by an electrically single-pulsed current for an ultra-high-strength martensitic steel sheet, MART1470 1.2t. In order to evaluate the springback reduction by the electric current, V-bending tests were performed with various parameter-sets (current density and pulse duration). The amount of springback reduction was then calculated from the measured bent-angle of tested specimens. Experimental results show the springback is reduced with the increase in the current density, the pulse duration, and the electric energy density. In order to clarify thermal and athermal portions in the effect of electric current on the springback reduction, two ratios of force and isothermal flow stress were calculated based on bending theory. From the comparison of the ratios, it is noted that the athermal portion mainly contributes to the force relaxation, so the springback amount decreases. The athermal portion significantly increases as the electric energy density increases. Microstructures and micro-Vickers hardness were observed to confirm the applicability of the single-pulsed current to forming processes in practice. The springback reduction can be achieved up to 37.5% without severe changes in material properties when the electric energy density increases up to 281.3 mJ/mm3. Achievable reduction is 85.4% for the electric energy density of 500 mJ/mm3, but properties remarkably change.

Numerical and Experimental Investigation on the Surface Defect Generation during the Hot Extrusion of Al6063 Alloy.

The surface quality control of extruded products is a critical concern in the home appliance manufacturing industry owing to the increasing need for products with a high surface quality, in addition to the essential mechanical properties of the final product. The underlying issue with achieving high-quality extrusion products is that surface defects, especially those resulting in surface gloss differences, called white line defects, are only observed after surface treatment. In this study, we aim to investigate the cause of white line defect generation on the surface of an extruded product. Accordingly, an experimental extrusion program is established using an L-shaped die that has a noticeable change in its bearing length along the inner corner of its cross-sectional profile. Laboratory-scale experiments were performed for the L-shaped extrusion of homogenized Al 6063 alloy at various ram speeds, in order to induce surface defects, considering the production yield rate required for mass production. Subsequently, the microstructural changes near the surface failure region were investigated using an arbitrary Lagrangian-Eulerian (ALE) technique-based thermomechanical finite element (FE) analysis. To scale-up the defect observation method from laboratory-scale to production-scale manufacturing and confirm the reproducibility of the surface defect, scaled-up L-shaped extrusions were performed in an actual industrial production line. Finally, the potential cause of white line defect generation is discussed by comparing the numerical and metallurgical analyses, including the scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) observations.

Intraocular pressure measured with Goldmann, noncontact, Schiøtz, and dynamic contour tonometry after DSEK.

PURPOSE: To compare intraocular pressure (IOP) measurements with various tonometers after Descemet stripping with endothelial keratoplasty (DSEK) and to measure the change in IOP during the follow-up period. METHODS: A total of 28 eyes of 28 patients having undergone DSEK for bullous keratopathy by a single surgeon from June 2008 to November 2011 were enrolled in this study. IOP values, which were measured with Goldmann applanation tonometry (GAT), noncontact tonometry (NCT), Schiøtz indentation tonometry (SIT), and dynamic contour tonometry, and central corneal thickness values were reviewed and analyzed up to 3 years after DSEK (range, 1 months-3 years). RESULTS: Different tonometers measured the IOP after DSEK differently. NCT showed the lowest IOP values, although GAT and NCT showed the smallest intertonometry difference. SIT showed extreme variation in IOP measurements. The dynamic contour tonometry values were higher than those of NCT or GAT. Central corneal thickness did not correlate with any of the IOP measurements. Only 2 episodes of IOP elevation greater than 30 mm Hg were detected. CONCLUSIONS: IOP measured with NCT or GAT may be lower than the real IOP after DSEK. SIT is not a reliable tonometry measurement after DSEK. Additional IOP measurements using different methods and consideration of other clinical signs may be the best method for ocular evaluation after DSEK.