The springback phenomenon that occurs during cold forming is the main problem that affects the dimensional accuracy of bent products. This article presents the results of the analysis of the springback phenomenon occurring during a three-point air bending of 0.5 mm, 0.8 mm, 1.0 mm and 2.0 mm thick AW-2024 aluminium alloy sheet, AW-1050A aluminium clad. For sheets with a thickness of 1.0 mm and 2.0 mm, the influence of heat treatment and natural ageing time of sheets on the value of the springback coefficient was also tested. The springback characteristics were determined by defining the dependence of the springback coefficient on the bending deflection of the band. The experimental results obtained indicate a linear dependence of the value of the springback coefficient on the relative deflection w/fg index (w – distance between supports, fg – deflection under load), both in the case of the influence of the sheet thickness and the ageing time of the sheets.
2
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Zastosowanie blach ze stali coraz bardziej wytrzymałych umożliwia obniżenie masy konstrukcji blaszanych, ale powoduje wzrost obciążenia narzędzi kształtujących. Z tego względu efektywne projektowanie i wytwarzanie narzędzi gnących wymaga znajomości sił działających na te narzędzia podczas gięcia.
The paper contains the results of experimental research on the AMS 5504 sheet spinning process. The research was carried out on a Leifeld SFC 800 V500 two-roller metal spinning machine with a vertical axis. Various shapes of rollers and different thicknesses of sheet metal were used.The relationships between the limiting spinning ratio, thin-wall ratio and the fillet radius of roller were determined, and the occurrence of negative phenomena during the spinning process, such as wrinkling or cracking, was taken into account. The conclusions contained in the work and the developed methodology allow for a practical assessment of the possibility of producing drawpiece with given parameters by spinning.
PL
W pracy przedstawiono wyniki badań eksperymentalnych procesu wyoblania blachy AMS 5504. Badania przeprowadzono na dwurolkowej wyoblarceLeifeld SFC 800 V500 o osi pionowej. Zastosowano różne kształty rolek i różną grubość blachy. Określono zależności pomiędzy granicznym współczynnikiem wyoblania, współczynnikiem cienkościenności i promieniem zaokrąglenia rolki, a także uwzględniono występowanie negatywnych zjawisk podczas procesu wyoblania, takich jak fałdowanie czy pękanie. Wnioski zawarte w pracy oraz opracowana metodologia pozwalają na praktyczną ocenę możliwości wytwarzania wytłoczki o zadanych parametrach metodą wyoblania.
Aluminum sheet drawpieces pressings with the ability to harden precipitation can be shaped from the sheet after annealing or heat treatment. In the second variant during the analysis and design of the technological proces, the change in the material properties of the shaped sheet due to natural aging should be additionaly taken into account. This article presents the results of research on the effect of the natural aging time after heat treatment of AW-2024 sheet material with a thickness of 1 mm on the course of the strain hardening curve. Strain hardening curves were determined on the basis of a uniaxial tensile test. The sheets were tested immediately after heat treatment and during natural aging, i.e. (20, 45, 90 and 120) minutes after heat treatment. The research showed a significant influence of natural aging in the tested range of times after heat treatment on the course of the deformation hardening curve of the sheet material. Based on experimentally determined in particular directions (0, 45 and 90 degrees to the rolling direction) the strain hardening curves, the values of material coefficients as a function of natural aging time were determined for four models of flow stress. Material coefficients in individual yield stress models were determined on the basis of approximation of strain hardening curves using the least squares method. On the basis of the analysis of approximation errors, the accuracy of the tested models of yield stress to describe the course of the hardening curve of the material of the tested sheet in the tested range of natural aging time was assessed.
PL
Wytłoczki z blach aluminiowych mających zdolność do utwardzania wydzieleniowego mogą być kształtowane z blachy po wyżarzaniu zmiękczającym lub po przesycaniu. W drugim przypadku podczas analizy i projektowania procesu technologicznego należy dodatkowo uwzględnić zmianę właściwości materiału kształtowanej blachy w wyniku starzenia naturalnego. W tym artykule przedstawiono wyniki badań wpływu czasu starzenia naturalnego po przesycaniu materiału blachy AW-2024 o grubości 1 mm na przebieg krzywej umocnienia odkształceniowego. Krzywe umocnienia zostały wyznaczone na podstawie próby jednoosiowego rozciągania. Badaniom poddano blachy bezpośrednio po przesycaniu oraz w trakcie starzenia naturalnego tj. (20, 45, 90 oraz 120) minut po przesycaniu. Badania wykazały, istotny wpływ starzenia naturalnego w badanym zakresie czasów po przesycaniu na przebieg krzywej umocnienia odkształceniowego materiału blachy. W oparciu o wyznaczone doświadczalnie na poszczególnych kierunkach (0, 45 oraz 90 stopni do kierunku walcowania) przebiegi krzywych umocnienia odkształceniowego wyznaczono wartości współczynników materiałowych w funkcji czasu starzenia naturalnego dla czterech modeli naprężenia uplastyczniającego. Współczynniki materiałowe w poszczególnych modelach naprężenia uplastyczniającego zostały wyznaczone na podstawie aproksymacji przebiegu krzywych umocnienia odkształceniowego metodą najmniejszych kwadratów. Na podstawie analizy błędów aproksymacji dokonano oceny dokładności badanych modeli naprężenia uplastyczniającego do opisu przebiegu krzywej umocnienia materiału badanej blachy w badanym zakresie czasu starzenia naturalnego.
This paper presents the results of experimental studies aimed at determining constitutive parameters for selected constitutive equations of flow stress as a function of the natural aging time of 2 mm thick AlCu4Mg1 (AW-2024) sheet. The knowledge of these constitutive parameters as a function of aging time is necessary to analyze and model the processes of forming sheet metal stampings after heat treatment during natural aging. The constitutive parameters in individual constitutive equations were determined on the basis of the approximation of the course of strain hardening curves. The courses of these curves for the tested natural aging times in the range of 0-120 minutes after heat treatment were made on the basis of uniaxial stretching tests of samples taken in the directions of 0, 45 and 90 degrees to the direction of sheet rolling. The values of constitutive parameters as a function of natural aging time were determined for four popular models of flow stress: Hollomon, Swift, Voce and El-Magd. Moreover, the relationship between the natural aging time and the value of the yield strength in the tested aging time range was determined, and the accuracy of the investigated constitutive equations for describing the course of the flow stress of the tested sheet material was assessed on the basis of the analysis of approximation errors.
In the paper the methods of laser hardening of external tool corners on the example of bending tools for press brakes were presented. The disadvantages and limitations of the most commonly used techniques for guiding a hardening laser light beam are presented, i.e.: (i) in one pass parallel to the tool corner plane symmetry, (ii) in two passes perpendicular to the surfaces adjacent to the corner, and (iii) in one pass perpendicular to the surface adjacent to the corner by using two diode lasers. The microstructure of the tool material after laser and induction hardening was compared. A significant influence of the heating method on the microstructure of the tool material after hardening was demonstrated. The original method of hardening the outer corners of bending tools using a hardening laser beam splitter was subject to a more detailed analysis. The analysis of material heating in simultaneously hardened corner area and adjacent surfaces was carried out using the Marc/Mentat software based on the finite element method. By analyzing the temperature distributions it was shown that if a beam splitter was used, obtaining a continuous and uniform hardened layer (i.e. with comparable hardness, depth, without tempered or non-tempered areas) in the area of the outer corner and adjacent surfaces was possible. In practice, achieving such a layer is conditioned by the correct selection of the size of the k parameter which determines the distance between the separated beams of laser light. Depending on the geometry of the hardened tool corner and the parameters of the hardening laser beam, this distance can be determined experimentally or on the basis of numerical simulation.
In the process of plastic bending of thin-walled profiles, there is a significant deformation of the cross-section, which has a very significant impact on the course and effects of the shaping process construction products. In this paper, the experimental, analytical as well as numerical analyses of the box profile bending process enabled to establish the relationships determining the dependence of the cross-sectional form and bending moment on the bending curvature. The following paper discusses pure bending moment and the cross-sectional deformation of 21.5×21.5×1.8 mm and 25×25×2.5 mm square tubes made of the 6060 aluminium alloy. Satisfactory agreement of the experimental results and numerical calculations was obtained for the values of horizontal and vertical wall deflection, as well as for the experimental, calculated and numerical bending moment characteristics.
In the paper a numerical comparative analysis of stresses in a steel die compressed by a ring during the extrusion process was presented. In the research, three design solutions of the die were used. The solutions vary depending on the quotient of the wall thickness of the die insert and the wall thickness of the compression ring while maintaining a constant tool diameter. The stresses occurring in the areas of the ring and the die were calculated depending on the design version of the tool and the pressure value. The analysis was carried out for the quotients of the die wall thickness to the ring wall thickness of 0.57, 1 and 1.75 and three press-in values of 0.004, 0.008 and 0.016 mm. The conducted research allowed determining the impact of the die design and assembly interference on the load bearing capacity. It was discovered that the use of a die insert with a smaller thickness com-pared to the thickness of the compression ring was the most advantageous from the point of view of the circumferential stresses.
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.