Advanced Materials Research Vols. 291-294

Abstract: Al-Mg₂Si composite has such advantages as low density, high elastic modules, simple manufacture technology and low cost. However, its strength and ductility need to be enhanced. Thus, the alloying element P was added to control the microstructure of Al-Mg₂Si alloy and furthermore improve the mechanical properties of the composite. The experimental results show that the microstructure of the Al-Mg₂Si alloys subjected to electromagnetic stirring can be significantly refined and the mechanical properties of the alloy get improved due to the addition of phosphorus. It is found that the best modification effect can be achieved when the adding amount of phosphorus is in the range from 0.7% to 1.1% and the holding time is about 15 minutes, and the mechanical properties of the Al-Mg₂Si alloys get markedly enhanced.

Abstract: The slanted-guide-pillar core-pulling mechanism is the most commonly used side core-pulling mechanism in die-casting die. But when filling the die with pressure, aluminum leak frequently happens between lower motion-stopping surface of sliding block and side surface of moving die insert, since the clearance is bigger between side core and core hole. In many improved approaches, changing the lower motion-stopping surface of sliding block into upper motion-stopping surface of it or reducing the lower motion-stopping surface area is the simplest and reliable measure. The sliding block’s setback which occurs in die-casting process can be eliminated effectively and the workload of maintaining die can be reduced by this measure.

Abstract: Hollow parts with variable cross-section are widely used in the area of automotive and aerospace industries due to their excellent properties. Wrinkling is one of the most common forms of instability in the process of manufacturing the parts. The minimum curvature of the cross-section profile of bugled workpieces is proposed in this paper to as a wrinkling indicator to characterize the form and extent of the wrinkle. The wrinkle distribution of 1Cr13Mn9Ni1N stainless steel tube in hydroforming with radial crushing under linear and constant hydraulic pressures is analyzed and the influence of the bulging methods on the wrinkling is investigated via finite element simulation. The results indicate that wrinkling under constant hydraulic pressure is more obvious than that under linear one, wrinkling in hydroforming with radial crushing is more serious than that in free hydro-bugling, wrinkling on the cross-section away from the middle cross-section is more distinct and the wrinkling on the side edge is obvious than that on the bottom of the bugled workpiece.

Abstract: The die accuracy and die service life reduce due to die wear during precision forming processes of steel synchronizer gear ring. The most serious part of wear is the middle between two tooth shapes. The rules of the wear and initial die hardness and frictional coefficient are analyzed based on numerical simulation. It shows that the higher of the initial die hardness, the better antiwear and good lubrication is benefit to reduce wear and prolong the die service life. The effect of the temperature on die life is reflected through hardness. The relationship of die hardness and die temperature, forming time is deduced. The higher of the die temperature and the longer of the forging time, the more serious of die wear. To prolong the die life and improve the quality of forgings, the synthetic forming technology is adopted and the ejection way and control system of the Plate Friction Press are improved. Experiment verification shows that the die service life has been prolonged.

Abstract: One of the most sensitive features of sheet metal forming processes is the elastic recovery during unloading, called spring-back, which leads to some geometric changes in the product. This phenomenon will affect bend angle and bend curvature, and can be influenced by various factors. In this research, the effects of sheet thickness and die radiuses an sheet anisotropy on spring-back in L-die bending of CK67 steel sheet were studied by experiments and numerical simulations.

Abstract: The author introduces the method and steps of determining key parameters of spline cold-rolling die using back-stepping design method. To verify the feasibility of the back-stepping design method in theory, the author made forming simulation and experiment with cold-rolling tooth-entwisted spline designed, analyzing the relationship between die design parameters and spline forming precision and giving correction way. Finally, the related factors influencing the forming precision of spline are introduced and the practical significance in machine-building industry of the back-stepping design method is emphasized.

Abstract: It was hard to predict crack and wrinkle which are the main failure modes when drawing for the shallow tapered parts. In this paper crack and wrinkle can be avoided effectively by using the software DYNAFORM in combination with orthogonal design of experiment method. The influence of normal anisotropy coefficient, friction coefficient, drawbead resistance and blank holding force on deep drawing shallow tapered surface was analyzed by numerical simulation. The results show that the minimum-wall-thickness was the main criterion for the drawing process but not the only criterion. Crack and wrinkle can be moderately eliminated finally after optimization of the parameters and following trim process in the drawing for shallow tapered surface.

Abstract: Clothing combining knitted and woven fabrics gets more and more favor of people. In this study, three knitted fabrics and three woven fabrics which are common on market were selected and seamed. The tensile breaking strength, elongation at break and the fracture reason of the joint of knitted and woven fabrics were tested using the one-way vertically stretching method. The test results were analyzed and it was found there are many factors affecting the seam strength of knitted and woven fabrics. Experiment shows that the main factors include: stitch density, joint method and choice of the joining material. The study of this subject provides the basis for designing better joint wear and improving sewing quality and efficiency.

Abstract: Hot forging die bear periodic thermal load and mechanical load during service, and bad work environment makes the service life of dies generally short. Hot forging die damages mainly appear in temperature fluctuation zone, and gradient composite materials cladding process can be used to do surface treatment on homogeneous hot forging die. This process can greatly decrease the peak value of temperature and stress and prolong the service life of hot forging die. FE model of hot forging process under mechanical press was build based on Deform-2D, temperature and stress field of homogeneous hot forging die and FGM surface cladding hot forging die under mechanical press were compared. Then the characters of thermomechanical load based on FGM surface cladding hot forging die were described, which provided foundation for design and manufacture of FGM hot forging die.

Abstract: High casting speed would increase the occurrence probability of sticking, and make it harder for breakout signals catching. The coupled visco-elasto-plastic FEM models have been presented for thermal process analysis of steel shell and the mould copper plates. With the understanding to the mould thermal state and deformation for different casting speed, the principle for the layout of thermocouples is obtained. It is shown that, the set of the thermocouples to the meniscus for the plates should be decided by the highest design casting speed, and the location of the thermocouples from the cold side of the plates is deeper, the breakout signals would be caught easier.