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Li H.,Hefei University of Technology | Chen W.,Hefei University of Technology | Zhou R.,Hefei University of Technology | Shi W.,Jiangsu Sunway Precision Forging Co. | Wu Y.,Hefei University of Technology
Zhongguo Jixie Gongcheng/China Mechanical Engineering | Year: 2014

Based on the geometric features of back gear with double boss, a new two-step warm forging process before finishing was put forward to reduce the number of cold forging process. Empty corners in the bottom of profile of all teeth were found when using the above process. In order to solve the problem, a rigid plastic FE model was built to simulate the warm forging process. The velocity, stress and strain field were investigated, and the metal flow rules were discussed with the experimental results. Then a qualified gear was achieved through expanding the radial wave shape by means of an indentation established in die. The measured results show that the new process can satisfy a high level precision of forging. The work presented herein may be used as basic data for the design of the precision forging processes. ©, 2014, China Mechanical Engineering Magazine Office. All right reserved.

Hu C.,Shanghai JiaoTong University | Zhao Z.,Shanghai JiaoTong University | Zhang Y.,Shanghai JiaoTong University | Xu X.,Jiangsu Sunway Precision Forging Co.
Applied Mechanics and Materials | Year: 2011

40Cr steel is categorized as quenched-tempered steels and is widely used in gears, bolts, couplings, spindles, etc. To study the plastic deformation behaviour of the steel after quenching and tempering, compression and double-pass compression tests have been carried out. The quenched samples are tempered at the temperature of 540°C, 580°C, 600°C and 630°C, and the microstructures, compression load, hardness after compression and load of double-pass compression are investigated. The compression peak load is higher when the tempering temperature is lower. The hardness average and its increase amplitude decrease with the tempering temperature. An interesting phenomenon of the double-pass compression load can be well explained by the microstructures. © (2011) Trans Tech Publications.

Hu C.L.,Shanghai JiaoTong University | Zhao Z.,Shanghai JiaoTong University | Gong A.J.,Jiangsu Sunway Precision Forging Co. | Shi W.B.,Jiangsu Sunway Precision Forging Co.
Journal of Materials Engineering and Performance | Year: 2014

The effect of warm deformation parameters and cooling rates on transformation of the microstructure of 40Cr steel was investigated using both single- and double-pass compression tests. The compression tests were performed at temperatures ranging from 800 to 700 °C followed by controlled cooling at rates from 0.1 to 5 °C/s. All of the final transformation microstructures were observed by optical microscopy, and they were mainly composed of ferritic and pearlitic microstructures. For further quantitative analysis, a program based on image processing technology was developed to automatically calculate the volume fractions of ferrite and pearlite. After qualitative and quantitative analysis of the final microstructures, the results showed the following. The ferrite volume fraction significantly increased with increasing strain for the same deformation temperature. The strain rate had almost no effect on the ferrite fraction at the lower cooling rates. The ferrite fraction markedly increased with increasing strain rate when the cooling rate was greater than 1 °C/s. The ferrite fractions after single- and double-pass compression were 27-49 and 24-43% for a total strain of 0.7. The cooling rate after deformation had a remarkable effect on the microstructure morphology, and the ferrite volume fraction significantly decreased with increasing cooling rate. © 2014, ASM International.

Hu C.,Shanghai JiaoTong University | Zhao Z.,Shanghai JiaoTong University | Gong A.,Jiangsu Sunway Precision Forging Co. | Shi W.,Jiangsu Sunway Precision Forging Co.
Materials and Manufacturing Processes | Year: 2015

Deformation behavior was investigated in detail from cold extrusion and upsetting tests on medium carbon steel. A new "cold forging after quenching and tempering" (CFAQT) process was proposed. Compared with conventional processes, including annealing before cold forging, plus quenching and tempering after forging, the CFAQT process could shorten the process chain and avoid subsequent heat treatment distortion with clear energy-saving and cost-reduction benefits. The CFAQT process was applied successfully in the mass production of a lock set for industrial automobile wheels and in laboratory spline extrusions. Copyright © Taylor & Francis Group, LLC.

Zhang Y.,Shanghai JiaoTong University | Hu C.L.,Shanghai JiaoTong University | Zhao Z.,Shanghai JiaoTong University | Li A.P.,Tongji University | And 2 more authors.
Materials and Design | Year: 2013

The low cycle fatigue (LCF) behaviour of a Cr-Mo-V matrix-type high-speed steel (matrix-type HSS), which was used as cold forging tool material, was investigated. Fatigue tests were conducted under strain-controlled cyclic loading conditions with different axial strain amplitude levels at room temperature. The tests indicated that hysteresis loops formed when the total strain amplitude was 1.5%, 1.0% and 0.75%. At total strain amplitudes that were less than 0.7%, there was no cyclic plastic deformation or hysteresis loop observed. The material fatigue behaviour was analysed specifically at the above three strain levels to investigate the cyclic plastic deformation of the material because the low cycle fatigue behaviour was of principal interest in this study. At all selected total strain amplitudes, the cyclic stress responses showed cyclic softening, and reached a "quasi-stabilised" softening state before the material finally ruptured from fatigue. The cyclic strain-stress relationship and the strain-life relationship were obtained through the test results, and related material parameters were calculated. Fractographic and metallographic analyses were also conducted in this study. The metallographic structure of the steel before and after heat treatment was examined. Two types of carbide phases were found in the steel. The fatigue damage process through the crack initiation and propagation was explained by observing the features of the fractures. © 2012 Elsevier Ltd.

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