Papers by Author: Yong Tang Li

Abstract: The traditional production process of large seamless rings brought the serious waste of material and energy. 42 CrMo alloy steel was taken as material of the rings. The research of Casting-Rolling Continuously Forming process was Smelting Casting→ Ring blank→ Concurrent heating and heat holding →Hot rolling forming. The work reported here concentrates on resolving the energy consumption, consumables, low production efficiency of ring production, provided some reference for the rings production.

Abstract: In order to investigate the thermal forming behavior of as-cast 42CrMo steel, the isothermal compression tests were performed on a Gleeble-1500D thermal mechanical simulator in the deformation temperature ranging from 850 to 1150°C with an interval of 100°C, the strain rate ranging from 0.05 to 5s^-1 and the height reduction of 60%. On the basis of the flow stress data, dynamic materials model (DMM) and Prasad's instability criterion, the processing maps for as-cast 42CrMo steel were constructed at the strains of 0.4 and 0.6. The safe and unsafe areas and the corresponding deformation regimes were predicted during hot working, which are verified through the microstructure observation. The results indicate that the safe zones in the temperature range of 850~1150°C and strain rate of 0.05~0.35s^-1, which exhibit the dynamic recovery and recrystallization. However, the flow instability domains are in the domain of deformation temperatures 850~1150°C and strain rate higher than 0.35s^-1. Typical microstructure of instability is cracking, which should be avoided so as to obtain desired mechanical properties in hot processing. Finally, the forging parameters were predicted and optimized accurately by the processing maps, the temperature range of 1050~1150°C and strain rate of 0.05~0.1s^-1 were recommended as the optimum deformation conditions for hot processing of as-cast 42CrMo steel.

Abstract: The purpose of this study is to find the hot deformation behavior of as-cast 42CrMo steel. The thermal simulation experiments of as-cast 42CrMo steel were done on the Gleeble-1500 thermo-mechanical simulation machine. The hot deformation behavior of as-cast 42CrMo steel was analyzed. The true stress-strain curves in hot deformation at different deformation temperature (850°C,950°C,1050°C,1150°C), different strain rate (0.05S^-1, 0.5 S^-1, 1 S^-1,5 S^-1) were obtained. The influence rules of the deformation temperature and strain rate on the curves were analyzed. The analysis shows that the true stress increases with increase of deformation temperature and decrease of stain rate. The hot deformation behavior of as-cast 42CrMo steel was compared with forged 42CrMo steel. The results show that the flow stress of as-cast 42CrMo steel during hot deformation was higher than that of the forged 42CrMo steel. Compared to the forged 42CrMo steel, the dynamic recrystallization in as-cast 42CrMo steel during hot deformation is more difficult to occur. The above conclusions have significant theoretical and practical meanings for the design of hot deformation process of as-cast 42CrMo steel.

Abstract: The model proposed integrates process parameters including pressure and velocity and other important input parameters including the wafer hardness, pad roughness, abrasive size, and abrasive geometry into the formulation to predict the material removal rate. Based on the deformation of hyper-elastic asperities attached to a linear-elastic pad, contact mechanism between the asperities and the wafer is analyzed. Micro-contact mechanism between the particle and wafer is proposed on the basis of elastic-plastic deformation theory. Material removal rate of single abrasive particle is calculated by the abrasive wear theory. The fluid effect in the current model is attributed to the number of active abrasives. Wafer scale material removal rate is analyzed in detail, which is agreed with the experimental results. The Preston’s coefficient, which has been determined empirically, is now given as a function of various processing variables, pad roughness, wafer material properties and slurry status.

Abstract: A contact-mechanics-based finite model for Cu/ low-k chemical mechanical polishing is presented. 2D axisymmetric quasi-static model for chemical mechanical polishing which includes four-layer structure: Si, low-k, Copper and polishing pad is established. The mechanical response at the interface between the silicon, low-k, copper, and pad is simulated under the loading of the chemical mechanical polishing. The effect of slurry is simplified as the friction force reacted onto both the copper and the polishing pad in the finite element model. Down pressure, status of slurry and the elastic modulus of polishing pad are treated as the parameter in the simulation. Using the model, the effects of applied down pressure, pad properties, status of slurry on the non-uniformity of the wafer surface can be readily evaluated. Simulation results show that the distribution of the Von Mises stresses across a wafer’s surface correlates with experimental removal rate profiles.

Abstract: The cold rolling technology of thread was rapidly developed due to its high efficiency, low cost and perfect property of its production. But theoretical researches on the precise forming were very few, especially for the hollow parts. In the rolling process, empirical (trial and error) methods have been a mainly part. This is unfavorable for the development of the new technology. In this paper, numerical simulation of the cold rolling process of hollow thread was studied. The DEFORM soft was used to perform the simulation work. The stress field, strain field and velocity field in the workpiece were obtained. The change curve of the rolling force and the relation curve of tangential force and torque were obtained. The failure process of hollow thread in the rolling process was also simulated. The failure reason of thin wall thread in the rolling process was analyzed according to the change of effective stress in the workpiece. The result is well agreement with theoretical ones. The further research will be done to promote the application of numerical simulation in the cold rolling of hollow thread parts.

Abstract: Laser cladding forming (LCF) is one of the new developed advanced manufacturing technologies. It integrates the advantages of rapid prototyping manufacturing and laser cladding surface modification, and three dimensional near-net-shape metal components can be directly manufactured without dies. Due to the dramatic heating and cooling characteristics of laser cladding forming process, the cladding layers is liable to crack, which greatly impedes the further and wider application of this technology. In this paper, numerical simulation on the three-dimensional transient temperature field and stress field of powder-delivery LCF has been carried out with parametric programming methods. The temperature field, temperature gradient and cooling rate of the laser cladding layer have been obtained. The influences of laser power and scanning speed on the temperature gradient and cooling rate of the cladding layers, especially the cooling rate of solid-liquid interface of the melt pool have been studied, which is tightly correlated with the cracking generation of the deposited layers. According to the simulation, process parameters were optimized to minimize the cracking possibility; LCF experiments have also been conducted to verify the simulation results.

Abstract: Design of hydraulic manifold blocks is a kind of complex solid special layout problem. Due to the complexity of the manifold blocks layout, intelligent optimization design system of the hydraulic manifold blocks is presented based on rule-based reasoning. The key of the manifold design is the hole’s connection, and the special layout of manifold is introduced. Based on the relative position and connection relationship of the holes, special mathematic model and rule-based reasoning are proposed for the holes layout and connection design. Rule-based reasoning which is used to guide algorithm search direction is proposed according to the holes special location. Goal actuation control strategy is adapted to search a group of optimization solution which is satisfied with the connection requirement. An example of hydraulic cartridge manifold block of high-speed bar cutting machine is given. It is testified that single line net algorithm satisfies the design requirement of real time checking, the shortest connection route and minimum number of craft hole.

Abstract: Cold rolling precision forming process of spline is one of the high-efficiency, precision and non-chip forming advanced manufacturing technologies. It has the characteristics such as high forming efficiency, energy-saving, low material consumption and better forming properties of components. The process and principle of involute spline cold rolling precision forming was analyzed. A measuring and testing system for the force and energy parameters in the forming process was set up, and the real-time variation curves of the torque moment of the spindle and the radial feeding force were obtained. Also, the influencing rules of process parameters on the maximum radial feeding force and spindle torque were investigated. Finally, Precision forming experiments of involute spline cold rolling were carried out with optimized parameters. Precision measuring and hardness testing of the tooth outline section shows that the components obtained by the experiments were free of defects. Compared with the spline components obtained from conventional cutting process, the hardness and wear ability was greatly improved, which is suitable for the requirement of application.

Abstract: Laser rapid forming is a kind of new developed technology combining laser surface modification and rapid prototyping technology. It provides a powerful tool for the manufacturing and repairing of metal components. Laser rapid forming repairing experiments of 45 and 2Cr12 steel have been carried out with 316L stainless steel powder. Microstructure and properties of the repaired components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electronic tensile experimental machine etc. Repaired components of different materials have been metallurgically bonded with the deposited layers, with fine microstructure, better mechanical properties and free of defects.