Advanced Materials Research Vols. 690-693

Abstract: The continuous cooling transformation behaviors were researched on X70 pipeline steel through two pass deformation and non-deformed austenite using Gleeble-3500 thermal mechanical simulator, and static continuous cooling transformation curve and dynamic continuous cooling transformation curve were measured through thermal dilation method and metallographic method. The influence of cooling rate and deformation parameters on microstructure was analyzed. The results show that the hot deformation accelerates the acicular ferrite and polygonal ferrite phase transformation, increases the starting transformation temperature and the finishing transformation temperature significantly, and shifts the CCT curve moving upward to the left side corner. Acicular ferrite is obtained in practice using accelerated cooling rate after deformation Acicular ferrite can be obtained in wider range of cooling rates, and microstructure and island structure is finer through hot deformation.

Abstract: A low speed hydraulic control system applying to 3.15MN forging press isdesigned for isothermal forging processes. Based on the hydraulic theory andthe system structure, both the mathematical model and the simulation model ofthe hydraulic press are established with its features discussed. PID controlmethod is adopted and genetic algorithm is used to automatically tune theparameters of the controller to deal with nonlinearity and time-variant of thecontrolled plant. Co-simulation of the control system and hydraulic system isestablished to verify the feasibility of the design. It is proved by anisothermal forging of a turbine disc that the system has good performances andcan achieve an ultra speed control in the end.

Abstract: Stretch forming machine (SFM) is most effective plastic forming equipment for large-size, thin and flat-deformation parts, which can decrease the springback phenomenon in sheet metal forming. In order to enhance the performance of SFM, a flexible stretch forming machine (FSFM) was developed by the authors successfully, which is made up of jaw clamping mechanisms, stretching mechanisms, universal push-pull mechanisms, and a carriage. Our experimental results indicated that the rate of materials utilization and close-fitting dies can be increased to 80 %. In addition, FSFM can reduce the complex of control-system and decrease the expense of machine sharply. FSFM have been used for double-curved sheet metal manufacturing successfully, such as the cab of high-speed train. This work has a strong value in enhance the stretch forming technology for double-curved sheet metal parts.

Abstract: Lubrication plays important role in Quick Plastic Forming (QPF). Friction coefficient between AZ31B magnesium alloy and the die steel was examined by ring upsetting tests at 400°C with no lubrication, boron nitride (BN), graphite and molybdenum disulfide respectively. The effect of the four lubrication conditions on bulging height and wall thickness distribution of conical, rectangular and cylinder components in QPF within 300s was investigated. Macroscopic and microscopic morphology of the formed part surface in the four conditions was observed.

Abstract: In aluminum hot rolling process, strip thickness difference plays a more important role in deviation. An FE model was presented to simulate the rolling process in which strip thickness difference was taken as a horizontal asymmetry factor of disturbance. Parameters information of nodes is processed, with the characteristic quantity of deviation and the asymmetrical thickness difference rate calculated. The result of simulation illustrates the deviation result under the disturbance of thickness difference, and the relationship among deviation function, characteristic quantity of deviation and the asymmetrical thickness difference rate. Deviation tracks under these circumstances are figured out. The effect of thickness difference on deviation in aluminum tandem hot rolling is revealed.

Abstract: The surface roughness morphology of cold rolled sheet treated with three coarsen processes, including shot blasting texturing, electro-discharge texturing and laser texturing, was examined and analyzed before and after stamping. The influence of the micro-topography on the plastic deformation behavior during forming was then discussed. The results revealed that the sheet with uniform dispersion micro-pit, large concave valley and smooth convex hull exhibits a good forming performance.

Abstract: Using ProCast casting simulation software, the solidification process of the Aluminum Alloy steel casting was simulated according to its scene casting process, and the shrinkage porosity defect was forecasted. Based on the simulation, the casting technology was improved using the orthogonal test. An optimized plan was obtained, which provided a reference for the actual production of the casting.

Abstract: Full-scaled hot stamping dies were designed for a vehicle bumper, based on evaluation of cooling system by FE simulation and the temperature variation assessment by analytical model. The blank shape was gained using inverse algorithm and well-designed according to production practice. Experiments were conducted to verify the reliability of both the die and blank design, as well as tests for microstructure and mechanical properties of the hot-stamped part. Results show that, CAE analysis provides a robust support for hot stamping die and blank design; Position stability of hot blank is greatly improved during robotic transport process after shape designing; Metallographic analysis demonstrates the hot-stamped bumper obtained a fully martensitic microstructure, its tensile strength is about 1550 MPa, microhardness is 47.5 HRC, and the elongation is up to 6%.

Abstract: Al-22Si-5Fe-4Mn-3Cu-1Mg alloy billet was prepared by spray forming processing, and the morphology and microstructure development of the over-spray powder were investigated in this paper. The results show that the diameter of the most powder was about 38um. With the decreasing of the powder size, its shape became more round and surface more smooth. Heterogeneous nucleation was the main nucleation way and the microstructures were dendrite grains for the most of over-spray powder. The formation mechanisms of the different microstructures were investigated through comparison with the microstructure of the spray formed ingot.

Abstract: By referring to the mathematical model to design strip wound die based on fatigue theory which was already established by the authors, the design method is put forwards and the software is developed by using C language, in order to determine the design parameters such as winding prestress, winding layers and winding tension. Investigations into the influence of design parameters on die performance were conducted by employ orthogonal test method. According to the calculations, the order of design parameters can be concluded: firstly, allowable safety factor named [n]; secondly, friction coefficient named f; thirdly, thickness of strip named t. The most important factor is allowable safety factor named [n].