Materials Science Forum Vols. 704-705

Abstract: The optical system used in aerospace works under a very difficult aerospace condition. The temperature difference between the sides which one is facing the sun and the other one is opposite the sun can reach about 200°C. These temperature grids can bring thermal deformation to the optical components and then influence the whole system’s image or detect results. To measure and analysis the deformation, we first use finite element method to establish a heat exchange model with definite temperature boundary condition to simulate the thermal distribution situation of an optical mirror, and then we establish a laboratory experimental environment and use the thermal imager to measure the temperature distribution on the surface of the mirror and use Zygo GPI XP-D/1000 interferometer to measure the thermal deformation, from the experimental results, we can see that the definite temperature boundary condition is good enough. And the definite flow boundary condition is not necessary under this non uniform heating situation. Key Words: thermal deformation, finite element model, non uniform heating

Abstract: Gears are very important and widely used driving components in mechanical instruments, and the demands of micro-gears are increasing more and more active as the MEMS technology develops in recent years. In this paper, a brass micro gear, which modulus m = 0.125 mm, pressure angle α = 20°, number of teeth z = 6, addendum circle diameter d = 1 mm, hot extruded from brass H62 billet with size Φ3×3 mm at 650°C was studied by experimental method. The microstructure of the micro gear was observed by scanning electron microscope and optical microscope, and the conclusions are as follows: the fiber flow lines within the micro-gear were formed by the extrusion, so that the anisotropic mechanical properties of the micro-gear was happened; The tissue distribution of micro-gear was that, the surface of the gear is almost entirely α-phase, while the internal part of the gear was the mixture of α-phase and β-phase, because the α-phase with lower hardness flowing outward to the surface of the gear during the extrusion process.

Abstract: Steering knuckle is the key part of vehicle steering system. The forming technology combined closed die pre-forging with open finish-forging has some advantages such as higher material utilization ratio and lower forming forces and so on. While simulating the closed die extrusion forming process of car steering knuckle, folding defect emerges on the contact area of Branch I and lower punch in the lateral extrusion process. The forming mechanism of the folding defect is studied by numerical simulations and experiments, which mainly consider the influence of lower punch shape and size, extrusion speed and friction conditions to folding length. The results show that the main factors that affect folding defects are the lower punch shape and size. Keywords: steering knuckle, folding defect, closed die forming, numerical simulation, experiment study

Abstract: In this study, the finite element method (FEM) was used to simulate the rotary forging process of a heavy and thick-walled container head, and the problems about load, strain distribution and optimization of rotary forging method were studied. First, five controlling factors of load were defined, which were single reduction amount (δ), reduction rate (ν), thickness of top die (ω), rotary angle (θ) and rotary way (γ) respectively, and their influence degree on load was studied later. Then the influence of γ on strain distribution was investigated. The results indicate δ, ν and ω have a strong influence on load, while θ and γ have a small influence on it; the strain distribution under crossed rotary way which is proposed in this paper is more homogeneous than stepwise rotary way. Based on the research results, a new multi-stage rotary forging method was proposed, by which load and strain distribution could be controlled effectively by means of an optimized combination of the five controlling factors in different forming stages. The simulation results are in good agreement with practical production. This study can provide valuable guidance in load control and process optimization for other similar heavy blind-hole forgings. Keywords: Heavy and thick-walled container head, FEM, Rotary forging method, Load control, Strain distribution

Abstract: In order to increase heating efficiency and decrease heating time, a new hot-forging method by means of direct resistance heating was investigated in this paper. Based on the approach, the hot upsetting experiments with cylindrical billet of 42CrMo4 were performed. Moreover, the influence of the multi-layer aluminium foils inserted between the billet and the die as a forming condition on heating and forming was researched. The results of the experiments show that prior to forming the billet could be heated quickly to forming temperature in about 10 seconds. During the upsetting process the billet cooling rate was effectively decreased and the forming time was extended in relation to the resistance heating. The insertion of multi-layer aluminium foils not only improved the efficiency of the heating, but also avoided the plastic deformation of the die and the occurrence of cracks on the billet’s surface. Keywords: Resistance heating, Hot forging, upsetting, Aluminium foils Introduction

Abstract: The main failure forms of whetstones forming die is serious wear on the work face, and the boronizing technology can be used to improve the hardness and wear resistance on the work face of the whetstones forming die. In this paper, the orthogonal test was used to obtain the optimum parameters of temperature, time and the amount of addition of rare earth in the boronizing process of die. The line scan spectrum shows that there are some of elements such as B, C, Al, Cr, Si and Fe etc in boronizing layer, and their content are changed during boronizing. The microhardness of boronization layer was measured, and the result showed that maximum value of microhardness of boronizing layer appears in subsurface, not in surface, and lowers along depth of boronizing layer. By comparing different wear curve of abrasive samples with different treated, we can see that the highest wear resistance of surface is in the sample with the optimization of boronization treatment +970°C quenching and 200°C tempering; followed by quenching and tempering treatment; the lowest wear resistance of the surface is the sample without the boronizing treatment, and the rest sample are between these two samples. After optimization of boronization treatment +quenching and tempering, the lifetime of the whetstones forming die with boronizing is 3.5 times than the old one. Keywords: Boronizing; Whetstone; Forming Die

Abstract: The dynamic mechanical behaviors of as-cast sour service drill pipe steel under development during hot deformation were studied in this paper by using Gleeble-3500 thermal mechanical simulator. The compressions were carried out at the temperature of 900°C, 1000°C, 1100°C, 1200°C and strain rates of 10s^-1, 1s^-1 and 0.1s^-1. The compress degree was about 70%, and then the maximum true strain for each specimen was 1.2. The experimental results show that the peak stress was related to the compression temperatures and the strain rates. Through respectively analyzing and studying the true stress-true strain curves, the hot deformation constitutive equation and the deformation activation energy were obtained by regression analysis. The evolution of microstructures at various strain rates and temperatures was discussed. Experimental results can provide scientific basis for analyzing the hot deformation processes and controlling quality. Keywords: sour service drill pipe, hot compression, true stress-true strain, constitutive equation, microstructure

Abstract: ] Theoretical calculation formula of punch force during tube extrusion has been proposed by means of slab method. On the basis of theoretical and experimental study, it is found that theoretical results of extrusion force given by the calculating formula approached to that of the experiment, and the relative errors are less than 20％. It is also found that the extrusion force is closely related to deformation temperature, lubricant and the ratio of extrusion. The calculating formula of extrusion force is given by considering the factors which are the conical angle of die, and the friction coefficient between the deformation zone and the extrusion container, and the friction coefficient between the undeformed zone and the mandrel. Key Words: Tube, Extrusion, Force, Physical model

Abstract: The purpose of this study is to find out the tribological characteristics of the various lubricants in cold forging of helical gear, which is used in mobile auto-transmission. Five kinds of lubricant were used in this study, i.e. L1, L2, L3, L4 and L5. The pin-on-disk type of friction wear test system has been adopted here. The normal load of 20, 40, 60, 80 and 100N has been applied to the test specimen. The sliding velocities were 0.06, 0.10, 0.14, 0.18, 0.22, 0.26, 0.30 and 0.34m/s. Experimental results show that the friction coefficients of oils having higher kinematic viscosity such as L1, L2, L4 and L5 tend to increase gradually as the sliding velocity increases. The increasing rate of the friction coefficient is relatively high in lower sliding velocity range. However in case of L3 which has low kinematic viscosity the friction coefficient tends to decrease as the sliding velocity increases. The friction coefficients of Bondelube and Bondelite were 3 times higher than those of L1 and L5. The Stribeck curve indicates that L1, L2, L4 and L5 were in hydrodynamic lubrication condition and L3 was in boundary lubrication condition. SEM micrographs revealed that there were some scratch, adhesive wear, adhesion wear and scuffing on the worn surface.

Abstract: Based on the analysis of primal process and structure of gray iron brake pad failing early, hydrodynamic software Flow-3D was used to simulate the defect distribution and temperature fields of different improved technology schemes. According to simulation results, the merits and faults of all schemes were investigated and the feasible casting system was determined. The results showed that uniform temperature distribution could be achieved and potential defects mainly distributed in gate riser or nonworking surface when adopting the casting system with single ingate, which gave brake pad better service performance.