Yong Tang Li

Parameters and Experiments on the Precision Forming Process of Spline Cold Rolling

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.

Cracking Mechanism of Laser Cladding Rapid Manufacturing 316L Stainless Steel

Laser cladding rapid manufacturing technology is a kind of new developed advanced manufacturing technology integrating the advantages of rapid prototyping manufacturing and laser cladding surface modification. Due to the complex thermo-physical and metallurgical factors in the deposition process, the cladding layer is liable to crack, which seriously impedes the industrial application of this technology. Experiments of laser cladding rapid manufacturing 316L stainless steel were carried out. The cracking behavior and phenomena has been observed, cracking mechanism of 316L stainless steel was investigated by means of microstructure characterization and phase analysis with optical microscopy (OM), X-Ray diffraction (XRD), scan electronic microscopy (SEM) and phase diagram analysis. Factors influencing the cracking susceptibility has also been studied. Results show that the cracks of 316L stainless steel were hot solidification cracks caused by the high residual stress and separating of the liquid films among dendrites. Through the optimization of process parameters, adding protective atmosphere, etc. cracking sensitivity has been effectively reduced and crack free 316L stainless steel components have been obtained.

Study on the Life of High Speed Steel Taps with Cryogenic Treatment

The influences of various processes of cryogenic treatment, optimization of parameters and prolongation the life of the high speed steel taps have been studied in the paper. Taking W9Mo3Cr4V for an example, the influences of temperature raising and decreasing rate, cryogenic treatment temperature and holding time, times for treatment, temper process and sequence of cryogenic treatment are discussed. Two kinds of cryogenic treatment process that one is before temper and the other is after it are put forward. Process flow is designed according to the process suitability and economy, the reported research results and existent problem. The results show that the life is prolonged after cryogenic treatment and the life is longer if the cryogenic treatment is carried out before tempering. To different material, the quantity of prolonging is different. To 30CrMnTi, 1.43 times of life of the tap is prolonged if the cryogenic treatment is arranged before tempering and only 61% is prolonged after tempering. To 1Cr18Ni9Ti, 1.08 times is prolonged before tempering and only 46% is prolonged after tempering. To 5CrMnMo, 1.65 times is prolonged before tempering and only 89% is prolonged after tempering. Research indicates that after cryogenic treatment, the harder the material is, the better the cutting is.

Flow Stress Behavior of the Normalized and Tempered as-Cast 42CrMo Steel during Hot Deformation

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.

Process and Properties on the Precision Forming of Spline Cold Rolling

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 principle and the force of involute spline cold rolling precision forming process were analyzed. Forming experiments of involute spline cold rolling were carried out, and the microhardness map of the tooth outline was gained. The rule of the metal flow in the deforming area and the forming mechanics of the microstructure were analyzed. The influence of plastic deformation on the forming properties was also conducted. Experimental results showed that dramatic plastic deformation has taken place on the upper surface of the workpiece during the cold rolling process of spline, while the influence on the inner materials were very small. The grains were distributed as a flow line pattern along the tooth profile, and the grains in the plastic deformation zone presented a fine and long fibrous state. The hardness on the section of the tooth outline is regularly distributed. Compared with the spline components obtained from conventional cutting method, the hardness of the spline was greatly increased, therefore, comprehensive mechanical property such as wear resistance and impact resistance were largely improved. Precision measuring and hardness testing of the tooth outline section showed that the components obtained by the experiments were free of defects, and the application requirement can be satisfied.

The Research of New Rings Process of Casting-Rolling Continuously Forming

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.

Hot Processing Maps and Workability Characteristics of As-Cast 42CrMo Steel during Hot Compression

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 Prasads 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.

Numerical Simulation of the Temperature Field in Multi-Layer Powder-Feeding Laser Cladding Forming

The numerically simulation of temperature field was carried out by the ANSYS software in multi-layer powder-feeding laser cladding forming.3-D finite element model was found, which nonlinear characteristics of the material thermal properties and the boundary conditions of the convective transfer heat was considered; The process of powder falling into the substrate and cladding element growing was accomplished by “Element Birth and Death technology” in the process of numerical simulation. The result shown that the primarily solidified cladding layer to the following cladding layer has a preheating function in the process of multi-layer laser cladding forming, the initial temperature of following cladding layer is higher than primarily melted cladding layer; The thermal cycling curves of the molten pool nodes takes on periodic variation and basic similar in every layer cladding; The end effect problem is apt to happen in cladding layer, which the phenomenon of edge collapsing or partially burnt is formed; The temperature gradient distribution is divided into two parts, the temperature gradient level distribution along the laser scanning direction in the top and perpendicular distribution in the bottom, The temperature gradient appearances mutation and maximum value in the junction of the substrate and cladding layer, which the crack is apt to be caused in this region.

A Material Removal Modeling of Chemical Mechanical Polishing Based on Micro-Contact Mechanism

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.

Microstructure Simulation and Experimental Research of as-Cast 42CrMo Steel during Quenching Process

The CCT curve and TTT curve of as-cast 42CrMo steel were precisely simulated by using JmatPro software. The quenching process(which is as follow: quenching at 860°C by AQ251 quenching liquid and cooling to 200°C) was given by analysizing the CCT curve. The quenching microstructure, hot-stress field and hardness after quenching were simulated by using the Deform-HT module The results were obtained as follows:(1)The microstructure of the materials is martensite+bottom bainite at the surface and pearlite+ferrite at the centure.(2)The surface hardness and central hardness were separately 51.3 and 28.5 HRC. The metallographic observation and hardness experiment were done and the results of numerical simulation was finally verified.