Investigation of the morphology of internal defects in cross wedge rolling

ArticleinJournal of Materials Processing Technology 125:248-257 · September 2002with28 Reads
DOI: 10.1016/S0924-0136(02)00303-5
Since internal defects in the cross wedge rolling (CWR) process can weaken the integrity of the final product and may ultimately lead to catastrophic failure, it is necessary to investigate the mechanisms of their generation and growth. Using a specially designed CWR experimental apparatus, experiments were performed at more than 50 different operating conditions. The cross-sectional profiles of the workpiece specimens were examined and compared at each condition. Based on the experiments, the influence of three primary parameters in CWR process—the forming angle α, the stretching angle β, and the area reduction ΔA were determined. From the experimental results, the morphology of void generation and growth in CWR is ascertained and discussed. Through the definition of a non-dimensional deformation coefficient ε, a method for predicting the likelihood of void formation is also established and discussed with respect to optimizing CWR tooling design.
    • "Lower values of the stretching angle are associated with a greater length of the tool. For large stretching angles, the billet enlarges rapidly in the axial direction , which accelerates the growth of small internal voids created in the knifing and guiding zones and is considered a potential reason of uncontrolled slip between the rolled workpiece and the tool [7, 8]. To design the CWR tool, Hayama [15] recommended two criteria, namely the wedge angle (α) and stretching angle (β) that should satisfy the conditions described in the formulas (1), (2), and (3): Where according to the toughness of material, value of M varies between 0.35 and 0.40. "
    [Show abstract] [Hide abstract] ABSTRACT: Ni-base superalloys are a class of materials with high temperature excellent tensile, creep and corrosion properties that have widespread applications in manufacturing hot parts of gas turbines. Application of cross wedge rolling (CWR) process for manufacturing Ni-base superalloys is of least investigated areas. In this article, the effects of CWR tool parameters on formability of Nimonic® 80A and Nimonic® 115 wrought superalloys are presented. The normalized Cockcroft-Latham model is adopted through finite element analysis to predict the occurrence of internal burst. The analytical results are validated through comparing them with experimental data. Comprehensive results of the effects of various CWR tool parameters on formability of Nimonic® 80A and Nimonic® 115 are presented. The results show that in some cases for Nimonic® 115, regardless of the stretching angle value (β), the internal burst fails the process. The results also indicate that Nimonic® 80A displays a relatively good ductility in low wedge angles and low stretching angles without suffering internal bursts, leading to sound part.
    Full-text · Article · Jun 2014
    • "As is seen in the figure, the crack propagates to the mid cross-section at 0.52 s and elongates in a direction normal to the maximum stress triaxiality at 0.68 and 0.8 s. The above-explained phenomenon of crack formation also quite well agrees with the experimentally observed crack formation in the knifing and guiding zones in cruciform shapes propagating through the direction of the maximum principal stress in CWR [8]. Finally, it should be noted that the implemented failure model cannot capture the failures resulting from compression and shear. "
    [Show abstract] [Hide abstract] ABSTRACT: The cross wedge rolling (CWR) deformation and fracture of a Ti6Al4Al (ELI) alloy were investigated experimentally and numerically using a coupled thermo-mechanical finite element model analysis. The experimentally determined flow stress and damage model parameters were verified by tension split Hopkinson pressure bar testing of notched samples. The simulation and experimental CWR forces showed well agreements except near the end of the stretching zone. The model analysis showed that the temperature distribution in the work piece was non-uniform during the CWR. When the initial temperature of the work piece was relatively low, the work piece temperature increased, a heating effect of the plastic deformation, while relatively high initial work piece temperatures resulted in cooling the work piece, caused by the work piece contact with the tools. The cracks were shown numerically to initiate in the midsections of the work piece during the guiding action and elongated in a direction normal to the maximum tensile stress triaxiality, resulting in cruciform-shaped crack formation, which was well agreed with the previously observed crack shape.
    Full-text · Article · Apr 2012
  • [Show abstract] [Hide abstract] ABSTRACT: Efficient mechanisms for reliable transmission and flow control are required to provide enhanced throughput guarantee and network utilization on multimedia highways. An overview of high delay and multimedia transport protocol mechanisms with special focus on TCP and XTPX is given. Different retransmission strategies, dynamical rate control as well as window size adjustment and flow control techniques at connection establishment and error recovery are discussed and illustrated by simulation results and measurements for TCP and XTPX. For high delay networks and multimedia applications, we study and demonstrate the effect of go-back-N, selective retransmission, Slowstart, congestion avoidance of TCP as well as selectable retransmission techniques and rate based flow control of XTPX
    Conference Paper · Apr 1996 · International Journal of Advanced Manufacturing Technology
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