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This study investigates flange fracture formation in unconventional incremental radial extrusion. This manufacturing technique involves using rings with a gradually increasing inside diameter for constraining the free flow of material in the radial direction. As a result, the shaped flange has a constant thickness and a significantly larger diameter than that formed using the standard extrusion process conducted without the use of rings. EN AW 6060 aluminum alloy tube sections were used as the billet material, and the extrusion process was conducted under cold forming conditions at ambient temperature. For the determination of material fracture initiation, a new method was proposed involving the analysis of strain, strain rate and values of the normalized Cockcroft-Latham fracture criterion integral. The main advantage of the new method is that it allows for the prediction of fracture initiation via only FEM results analysis, i.e., it is not necessary to carry out additional experiments aimed at calibrating or determining limit parameters of a given material. It was shown that the occurrence of differences in the distribution of the above-mentioned parameters coincided with flange fracture initiation.
RESUMEN
This paper presents a new method for forming hollow flanged products. The method involves extrusion with the use of a sleeve moving in the opposite direction to that of the punch. A tube with a constant hole diameter and two different outside diameters, made of aluminum alloy EN AW 6060 was used as a material. Numerical calculations were performed using Deform 2D/3D. Experiments were conducted on the PYE 160SS hydraulic press equipped with a specially designed device in which the punch is driven by the press slide while the moveable sleeve is driven by two hydraulic servomotors. Both numerical simulations and experiments were conducted under cold forming conditions. The aim of this study was to determine the effect of selected parameters (flange diameter, height of the cavity in the moveable sleeve, and the chamfer angle between the regions with different outside diameters on the workpiece and in the moveable sleeve cavity) on the stability of the extrusion process. Results were then used to undertake detailed comparative analyses of underfill, flange heights, and flange flank inclination angles. Findings of the analyses served as a basis for drawing conclusions regarding the effect of the analyzed parameters on the investigated extrusion process.
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The originality of this paper lies in the presentation of a new, innovative method for manufacturing medical screws with a cylindrical head of 316 LVM. This method is unique on a global scale, and its assumptions have been granted patent protection. The paper presents selected results of theoretical and experimental research on the developed process of forming of medical screws based on new technology. In the first part of the study a review of the types of screws used in the medical industry is made and the previous methods of their manufacture are described. The second part of the paper presents the assumptions and analysis of the elaborated process of metal forming of medical screws with a cylindrical head and ring thread made of 316 LVM austenitic steel. The theoretical analysis of the new process of forming a screw selected for testing was performed on the basis of numerical simulations. The experimental verification of the proposed theoretical solutions was carried out on the basis of laboratory tests, industrial research and qualitative research. The positive results obtained from computer simulations and experiments confirmed the effectiveness of the developed technology and the validity of its use in future in industrial practice.
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Magnesium alloys are highly strain rate sensitive and exhibit good workability in a narrow forging temperature range. Consequently, parts made of these materials are usually forged with low-speed hydraulic presses, using specially designed tool heating systems in order to ensure near-isothermal conditions. This study investigates whether popular magnesium alloys such as Mg-Al-Zn can be forged in forging machines equipped with high-speed forming tools. Experimental upset forging tests on AZ31B, AZ61A and AZ80A specimens were conducted, using a screw press with a ram speed of 0.5 m/s and a die forging hammer with a ram speed at stroke of about 5 m/s. Test specimens were preheated to 350 °C, 410 °C and 450 °C. After the upset forging process, they were air- or water-cooled and then examined for their workability, hardness and grain size. To validate the results, a forging process for a producing handle was designed and modelled by the finite element method. Distributions of strain, temperature and fracture criterion were analysed, and energy and force parameters of the forging process were calculated. After that, experimental tests were performed on AZ31B and AZ61A specimens in order to determine mechanical properties of forged parts and examine their micro- and macrostructure. Results have demonstrated that AZ80A is not suitable for forging with either the screw press or the die forging hammer, that AZ61A can be press- and hammer-forged but to a limited extent, and that AZ31B can be subjected to forging in both forging machines analysed in the study.
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The paper presented a new method for forming flanges on hollow parts by incremental radial extrusion. In the classic process of radial extrusion, additional rings were used to limit the free flow of material in the radial direction. The flange was formed progressively, using rings of increasing diameters. The proposed method was verified by numerical analysis and experimental tests. The numerical calculations were performed by the finite element method using the Deform-3D software package. Tubes made of aluminum alloy EN AW 6060 were used as billets. Laboratory tests were carried out using the Instron 1000 HDX testing machine. The objective of the study was to determine the validity of the proposed flange extrusion method. Results demonstrated that the new method made it possible to produce flanges with a relatively large diameter and uniform thickness, confirming the effectiveness of the proposed forming technique.
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The study presents the effect of annealing process parameters on the microstructure, hardness, and strain-hardening coefficients, that is, the strength coefficient c and the strain-hardening exponent n, of 42CrMo4 steel. Seven selected annealing time-temperature schemes are examined for superior steel formability in cold metal forming conditions. The c and n coefficients are first determined in experimental upsetting of annealed samples and then used in FEM (finite element method) simulations of the upsetting process. The results demonstrate that the strain-hardening coefficients (c and n) depend on the employed annealing scheme. Compared with the as-received sample, the annealing process reduces the true stress and effectively decrease the hardness of 42CrMo4 steel; improves microstructural spheroidization; and, consequently, facilitates deformability of this material. The annealing schemes, relying on heating the material to 750 °C and its subsequent slow cooling, lead to the highest decrease in hardness ranging from 162 to 168 HV. The results obtained with the SEM-EDS (scanning electron microscopy-energy dispersive spectrometer), LOM (light optical microscopy), and XRD (X-ray diffraction) methods lead to the conclusion that the employed heat treatment schemes cause the initial ferritic-pearlitic microstructure to develop granular and semi-lamellar precipitation of cementite enriched with Mo and Cr in the ferrite matrix. In addition, the annealing process affects the growth of α-Fe grains. The highest cold hardening rate, and thus formability, is obtained for the annealing scheme producing the lowest hardness. The results of FEM simulations are positively validated by experimental results. The obtained results are crucial for further numerical simulations and experimental research connected with developing new cold metal forming methods for producing parts made of 42CrMo4 steel.
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Authors present the review of current literature on the subject of nephrological complications in tuberous sclerosis complex (TSC) on the basis of two ease reports of children with familial TSC. In 18-years-old girl the features of polycystic kidney disease with end-stage renal failure, epilepsy, mental retardation, calcifications of structures in central nervous system and skin abnormalities coexist. In 10.5-years-old boy morphological changes in both kidneys revealed hyperechoic renal cortex (renal function - creatinine clearance within normal ranges), other features are similar as compared to sister. In the girl during the one month of observation asymptomatic acute bleeding to a cyst and under the renal capsule occurred. It was necessary to perform bilateral nephrectomy because of these life threatening events.