Chin Joo Tan

Increase of Wall Thickness around Corner of Multi-Stage Drawn Cup with Flange Using Conical Punches

The wall thickness around an inner corner in 3-stages formed cups with a flange was increased by means of conical punches in the 1st and 2nd stages. Since the strength of the formed cups is greatly improved by the increase in wall thickness, the weight of the formed products is reduced by an optimum distribution obtained from the increase in wall thickness. The increase in thickness around the inner corner is obtained by compressing the side wall and conical bottom of the cup in the 3rd stage. As the punch angle increases, the increase in thickness at the inner corner becomes large. The amount of compression is expressed by a drawn volume after the 2nd stage. A maximum 9% increase in wall thickness around the inner corner was successfully obtained for the punch angle of 25º.

A developed friction test for sheet metal stretch forming processes

Punch friction test is considered to be the best simulator of sheet metal stretching over the punch corner. In this study, an improved punch friction test eliminating the error due to the strain-rate effect was developed. This method enables the direct force measurement and the online evaluation of the friction coefficient. Also, an improved boundary friction model was introduced to predict the friction coefficients and the real contact areas around the punch nose portion. The predicted values were then compared with the experimental one obtained from the newly developed test for verification. A good agreement was obtained between the theoretical and the experimental results. Finite element simulation of the punch friction test under dry friction condition for annealed aluminium was performed using the experimental friction coefficients. Since the simulated force-displacement results are in good agreement with the experimental one, the accuracy of the test is high and reliable.

Numerical Simulation of a Corner Crack Growth in Metals under Multiaxial Fatigue Loading

In practical engineering applications, many components especially rotating members are frequently subjected to fluctuating multiaxial loading. In this case, fatigue failure is recognized as a major cause of failure of engineering components in service. Hence it is important to characterize fatigue behaviour of the material.

Design and Analysis of an Optical Coupler for Concentrated Solar Light Using Optical Fibers in Residential Buildings

Concentrated sunlight that is transmitted by fiber optics has been used for generating electricity, heat, and daylight. On the other hand, multijunction photovoltaic cells provide high efficiency for generating electricity from highly concentrated sunlight. This study deals with designing and simulating a high-efficiency coupler, employing a mathematical model to connect sunlight with fiber optics for multiple applications. The coupler concentrates and distributes irradiated light from a primary concentrator. In this study, a parabolic dish was used as the primary concentrator, a coupler that contains nine components called a compound truncated pyramid and a cone (CTPC), all of which were mounted on a plate. The material of both the CTPC and the plate was BK7 optical glass. Fiber optics cables and multijunction photovoltaic cells were connected to the cylindrical part of the CTPC. The fibers would transmit the light to the building to provide heat and daylight, whereas multijunction photovoltaic cells generate electricity. Theoretical and simulation results showed high performance of the designed coupler. The efficiency of the coupler was as high as , whereas the rim angle of the dish increased to an optimum angle. Distributed sunlight in the coupler increased the flexibility and simplicity of the design, resulting in a system that provided concentrated electricity, heat, and lighting for residential buildings.

Estimating surface hardening profile of blank for obtaining high drawing ratio in deep drawing process using FE analysis

We constructed an FE axisymmetric model to simulate the effect of partially hardened blanks on increasing the limiting drawing ratio (LDR) of cylindrical cups. We partitioned an arc-shaped hard layer into the cross section of a DP590 blank. We assumed the mechanical property of the layer is equivalent to either DP980 or DP780. We verified the accuracy of the model by comparing the calculated LDR for DP590 with the one reported in the literature. The LDR for the partially hardened blank increased from 2.11 to 2.50 with a 1 mm depth of DP980 ring-shaped hard layer on the top surface of the blank. The position of the layer changed with drawing ratios. We proposed equations for estimating the inner and outer diameters of the layer, and tested its accuracy in the simulation. Although the outer diameters fitted in well with the estimated line, the inner diameters are slightly less than the estimated ones.

Formation of a square tube having a middle circular section for axial crushing

Abstract A new forming method for the tapered square tube is demanded. In this study, a four-stage forming process for a square tube having a circular section in the middle from a seamless round pipe is developed. The transitions between the square and the circular sections form the tapered walls for the reduction in initial peak load. The height of the circular section is minimised to increase the number of folds per unit length of the tube. In the first and the second stages, about half length the pipe is expanded into a circular section before compressing it into a square section. The square section is formed by pushing the expanded circular section through a square die with a square punch. This process is repeated at the opposite site of the pipe in the third and fourth stages to form the square tube. Both finite element simulation and experiment are performed to evaluate this process. A square tube having a circular middle section is successfully obtained from both the simulation and experiment. The corner radii of the square section reduce when the diameters of the circular dies in the first and third stages are increased. However, the wall thickness distribution of the square section becomes small and uneven. The height of the circular middle is reduced to around 10 mm by increasing the punch strokes in the first and third stages. A quasi-static axial compression test is performed on the square tube. The compressive load has an initial peak value of 250 kN. The crush force efficiency of the square tube, i.e. the ratio of its average load to the initial peak load is about 54%, much higher than the one for the plain straight tube which is usually around 30%.

End Formation of a Round Tube into a Square Section with Reduced Forming Loads

Low formation loads are desirable in metal stamping industries as it reduces the press capacity of the machine and the tooling cost. In the previous study, the author had successfully developed a 2-stage end formation process of a round tube into a square section having small corner radii. However, the formation load in this process increased linearly with the punch stroke in the 1st stage due to the continuous expansion of the tube end by the conical die. Hence, buckling and cracks occurred at the circular section and the bottom end of the square section respectively when the punch stroke was excessive. In this study, the author proposes a circular die having a conical bottom replacing the conical die for the expansion of the tube end. Although the formation load increases when the tube end is expanded at the conical bottom, the amount of increase becomes small when the tube end reaches the circular section of the die due to its constant diameter. At the circular section, the tube end curls and wraps over the die when the punch stroke is increased. In the 2nd stage, the squaring process is performed with a conical bottom square punch and a taper square die for the two different expanded tubes i.e. the one formed with the conical die and the one formed with the conical bottom circular die. Both Finite Element Method (FEM) simulation and experiment were performed to evaluate these two processes. The distribution of plastic strains, forming loads and product appearances are investigated. With the circular die, the maximum forming loads are successfully reduced by 20% and 33% in the 1st and the 2nd stages respectively in the experiment when compared to the ones formed with the conical die. No buckling and cracks are observed for the tube formed with the circular die.