Investigation on the influences of clearance and notch-sensitivity on a new type of metal-bar non-chip fine-cropping system

Zhong, B.; Zhao, Shengdun; Zhao, Renfeng; Guo, Tong

doi:10.1016/j.ijmecsci.2013.09.019

Cited by 17 publications

(8 citation statements)

References 14 publications

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“…And the geometric parameters of the V-groove were all prepared in accordance with the previous works. 17 It is clear that the equivalent displacement load and the frequency of the strike hammers are, respectively, controlled by the pressure of the pneumatic system and the switching frequency of the valve. The switching frequency is 5 Hz.…”

Section: Experiments and Resultsmentioning

confidence: 99%

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New controllable and near net bar fine-cropping system

Zhong

Zhao

Bin³

et al. 2016

Proceedings of the Institution of Mechanical Engineers, Part B:

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In this article, a new controllable and near net low-stress bar fine-cropping system was proposed and developed by combined using the stress concentration effect of the prefabricated V-groove and the propagation crack. The bar finecropping experiments were successfully carried out using a new proposed cropping load control strategy. Although the level of the stress intensity factor range DK greatly influences the cropping time and the cross-section quality, the cropped-billets can be directly used for the precision forging industry without additional machining.

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Section: Experiments and Resultsmentioning

confidence: 99%

“…And the geometric parameters of the V-groove were all prepared in accordance with the previous works. 17…”

Section: Experiments and Resultsmentioning

confidence: 99%

New controllable and near net bar fine-cropping system

Zhong

Zhao

Bin³

et al. 2016

Proceedings of the Institution of Mechanical Engineers, Part B:

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“…In this process, fatigue cracks initiate from the notch tips and propagate steadily, which is controlled by loading curves with decreasing frequency [3]. The V-shape notches are processed by cutters with optimal depth as 4-5% of the bar diameter, opening angle of 60-90 • , and the minimum tip radius of 0.1-0.2 mm [4]. However, the stress concentration effect is limited by the cutter shape, and the hard material notching is still difficult.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Fracture Behavior and Mechanism in High-Speed Precise Shearing for Metal Bars with Prefabricated Fracture-Start Kerfs

et al. 2020

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A laser-assisted high-speed shearing (LAHSS) method has been proposed for metal bars, which prefabricates equally spaced fracture-start kerfs by Nd:Yag laser to make stress concentration, and applies a high-speed load to complete fracture separation. Comparative tests were conducted for Q235, 40Cr, and 304 steel bars, and the effects of fracture-start kerfs and axial clearance were investigated on the fracture section. Moreover, the fracture behavior was demonstrated by numerical simulation, and the micro-fracture mechanism was revealed by fractographic analysis. The numerical simulation results show that the material damage concentrates along with the kerf tips with peak equivalent plastic strain, and the corresponding stress triaxiality drops to almost zero at the kerf tip, which reveals that the material is subjected to pure shearing at kerf tip; the Max. loading force is reduced by 15.2%–29.6%, and the impact energy is decreased by 29.8%–46.9% for the three types of bar material. The experimental results showed that the fracture-start kerfs effectively inhibited the plastic deformation stage, and higher precision blanks were obtained in the LAHSS test: roundness error improved from 2.7%–10.9% to 1.1%–2.6%, Max. bending deflection decreased from 1.3–3.4 mm to 0.4–1.0 mm, and flatness error dropped from 0.9–3.3 mm to 0.3–0.7 mm. The fractographic analysis reveals that the crack initiation is related to alternative V-shape micro-notches at the laser-affected zone; the predominant fracture mechanism involves mode II microvoid coalescence at the main fracture plane; smaller and less elongated dimples were formed in 40Cr steels due to higher number density of grains and pinning effect of second-phase particles compared to Q235 and 304 steel bars.

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“…To improve the cropping efficiency and the section quality, much attention has been devoted to the factors which have a strong influence on the LCFC. Many authors 1,5–7 investigated the influence of the V-shaped notch. Zhao 1 found that the mean stress of the metal bar in the cropping process can be effectively reduced due to the stress concentration effect of the V-shaped notch.…”

Section: Introductionmentioning

confidence: 99%

The investigation of low-cycle fatigue crack propagation of 16 Mn eccentric bar based on the acoustic emission technique

Ren

Dong

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part B:

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Compared to the traditional cropping technology, low-cycle fatigue cropping can reduce load and improve cross-section quality. Geometric factors of V-shaped notch and processing parameters (such as load amplitude and load frequency) influence the cropping efficiency and section quality. By changing the factors, the sufficient efficiency of cropping and quality of cross-section get together. However, the influences of material defects, geometric parameters, loading frequency and other factors are different in each stage of the whole cropping process. If the effects of the parameters on the each stage of cropping process are clear, the higher productivity and the better cross-section quality will be obtained by applying suitable parameter on each stage of cropping process. To investigate the effects of eccentric ratio on each stage of low –cycle fatigue cropping process, a suitable monitoring method is needed. This study proposes acoustic emission (AE) technique to detect the low-cycle fatigue cropping process of 16 Mn eccentric bar (The bar prefabricated eccentric notches. The prefabricated notch improve the efficiency of cropping). The parameters of signals such as counts and kurtosis during the low–cycle fatigue process are obtained. According to the counts changes over time, the process of the 16 Mn metal bar cropping can be divided into three stages: the crack initiation stage, the crack propagation stage, and the fracture stage. Based on the cumulative counts, the eccentric ratio’s influence on the time of each cropping process stage is obtained. The time of the crack initiation stage and the final fracture stage doesn’t increase with the eccentric ratio. The time of the propagation stage influenced by the eccentric ratio greatly. Besides, the eccentric ratio’s influence on the cross-section quality is studied by using an advanced optical microscope system. The cross-section quality was influenced by the eccentric ratio significantly. The results of the paper indicate the acoustic emission (AE) monitoring technique is a useful method to detect the process of low-cycle fatigue cropping. Especially, it provide effective information to investigate the effects of the notch eccentric ratio during the low-cycle fatigue cropping process. The eccentric ratio’s effects on each stage of low-cycle fatigue cropping process offer guidance to improve low-stress fatigue cropping efficiency and cross-section quality.

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Investigation on the influences of clearance and notch-sensitivity on a new type of metal-bar non-chip fine-cropping system

Cited by 17 publications

References 14 publications

New controllable and near net bar fine-cropping system

New controllable and near net bar fine-cropping system

Investigation of Fracture Behavior and Mechanism in High-Speed Precise Shearing for Metal Bars with Prefabricated Fracture-Start Kerfs

The investigation of low-cycle fatigue crack propagation of 16 Mn eccentric bar based on the acoustic emission technique

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