Applied Mechanics and Materials Vols. 395-396

Abstract: A kind of accelerating power supply device for electronic beam welder was introduced in this paper. The device adopts PWM modulation method, use IGBT as DC chopper. M, N two groups of H inverse bridge parallel with each other compose the inverter. Intermediate frequency AC produced by inverter was sent into intermediate frequency high voltage transformer, after the high voltage rectifying and filtering, the high voltage output running steadily. In order to improve the power supply devices output characteristics when power system fluctuates or load changes, feed-forward control strategy was introduced. Use the control method that feed-forward combining with feed-back. The experiments show that the adjusting speed of this power supply device is fast, the output voltage ripple is small, the technical indicators can meet high welding technology for electron beam welding machine.

Abstract: During the welding assembly process of automotive exhaust system, several welding defects will occur if the process parameters are incorrect, which affects the quality of products seriously. Six Sigma quality management is an advanced methodology for reducing the manufacturing costs, shortening the production cycle, and improving the product quality significantly. In this paper, the Six Sigma DMAIC method is applied to control the welding assembly process of automobile exhaust system. It is observed that the biting edge and stomata are the two main weld defects accounting about 85% of the total number of defects. In order to reduce the number of biting edge, causal diagram is used for analyzing the factors influencing the welding process. After the experiment, it is convinced that the process parameters of welding torch angle, welding speed and argon flow are the key factors affecting the biting edge significantly. Then, the optimum process parameters are determined by means of the DOE method, and the control chart is adopted to monitor the effect of process improvement. The results show that defects per million opportunities (DPMO) of biting edge could be controlled less than 1500 which is better than the target number of 5000. It is also proved that the Six Sigma DMAIC methodology is efficiently. Therefore, the stomata defects are reduced in the same way, the level of product quality is raised from 3.55σ to 4.52σ, and the competitiveness of the enterprise would be enhanced greatly.

Abstract: The normal static stiffness plays an important role in the whole connection of bolted joints. Both the design and the connection quality are depended on the normal static stiffness. But the nonlinear characteristics of its normal static stiffness is not well explained. An experimental test is developed herein to clarify the influence of the jointed surfaces. And the nonlinear effect of jointed surfaces of bolted members has been separated from the total stiffness. The nonlinear relation between the extensile force and the joints’ stiffness in the jointed surfaces under different preloads has been extracted through the experiment.

Abstract: Consumable double-electrode gas metal arc welding (consumable DE-GMAW) is a novel and high efficient welding method. According to the different polarity of two electrodes in consumable DE-GMAW, the metal transfer behaviors are analyzed by using the state force balance theory. For main torch with direct current electrode positive polarity, the arc root area is enlarged by bypass arc and increased electromagnetic force promotes main metal transfer. For bypass torch with direct current electrode negative polarity, the electromagnetic force does not work on the melting area. Only gravity force is major detaching force. The volume of bypass droplet is large and not easily detache to the weld pool.

Abstract: A novel and high efficient consumable double-electrode gas metal arc welding (consumable DE-GMAW) method has been introduced. Because of the coupled welding parameters, a multi-input multi-output (MIMO) control scheme was proposed and tested, which controlled the bypass arc by adjusting the bypass wire feed speed, and controlled the base metal current by adjusting the bypass current. Then, the welding experiment has been carried out. The results showed that the MIMO control scheme was effective. The base metal current was controlled at a nearly constant level and the welding process was stable. Also a good weld appearance was obtained.

Abstract: Explosive welding experiment of T2 red copper plate and DT4C electrical pure iron plate was carried out. Microcosmic analysis and plastic deformation test of the bonding interface were also studied. Results indicate that the welded zone presents periodical wavy metallurgical interface and Cu-Fe Solid solution is distributed on the wave interface. Moreover, large amplitude variation of the ratio of Cu to Fe in the Cu-Fe Solid solution is found. No separation happens after flattening test and bending test, which shows that Cu-Fe Solid solution does no harm to the bonding properties and the welding quality of T2/DT4C laminates can meet the needs of plastic working of complicated shape workpieces.

Abstract: Forming process of TC4 titanium alloy laser weld joint during superplastic deformation is simulated. The stress and strain curve, which is obtained in the simulation, is compared with that obtained by hot tensile experiments. The simulation results provides a basis for subsequent laser welding / superplastic forming technology, and proposes outlook to the analyze problems for laser welding / superplastic forming (LBW / SPF) technology.

Abstract: The experiments of laser cladding on the surface of 20 steel were made. High-chromium (Cr) cast iron powder was used as cladding material. The microstructure and hardness of laser cladding layers under different scanning speed were studied. The experiments showed that high-Cr cast iron cladding layer had better properties such as minute crystals, high density, no crack, no gas cavity and good metallurgical bonding with base metal. When the scanning speed was low, such as 10mm/min, the microstructure of cladding layer was cellular dendrite. There were much carbide with the shape of fish-bone distributing among cellular grains. Under higher scanning speed (from 100mm/min to 300mm/min), needle-shaped primary cementite would come into being. When laser scanning speed was 500mm/min, the carbide of cladding zone was very thin. With the increasing of laser scanning speed, the average hardness of cladding zone increased from 388HV0.2 to 580 HV0.2.

Abstract: The surface heat transfer coefficient is obtained by the calculation of water-flowing in the second cooling zone of continuous casting; the parameters of this formula are determined by the engineering experiment methods. This paper adopts a new method-numerical calculation method to obtain these parameters. Firstly, the paper uses the method of solving inverse heat conduction problems to calculate the surface heat flux and the surface heat transfer coefficient. Secondly, by using the least square method, the parameters in the formula between the surface heat transfer coefficient and water-flowing are identified. Finally, a plant steel data is used to do some simulation experiments. The results of this simulation prove this numerical method feasibility and effectiveness.

Abstract: The arising health problems of ride comfort of passenger cars point out that a lot of effort still has to be put into the design of passive suspension systems.The comfort problem originates from the vibrations transmitted to the driver and passengers caused by the unevenness of the road. This paper reports on an investigation to determine the spring and damper settings that will ensure optimal ride comfort of a passenger car at different speeds. D-optimal designs are developed via multibody dynamics software (ADAMS/Insight) with a model. Evaluation of the comfort improvement was done using an objective function according to the international organisation for standardisation (ISO)2631(1997). The optimised passive suspensions equipped in a passenger car were tested on a test rig in ADAMS/Car. The results show that the vibration levels can be reduced by 47%, generating a drastic comfort improvement.