This work has established that a linear relationship exists between the change in Δr, the planar anisotropy, and the amount of true reduction strain imparted in the second cold reduction used to produce DR-9 product for drawn-and-redrawn cans. It also showed that a relationship exists between Δr and the degree of earing in the drawing of a cylindrical cup. The changes in Δr were also found to be consistent with the changes in crystallographic texture.
In this paper a shipline field model was used to analyze the initiation and development of bulge formation in drawing of a rigid perfectlyplastic material with light reduction under plane strain condition. An equation is presented for predicting the equilibrium bulge height as a function of the angle between bulge surface and central axis, a parameter determined numerically for a given boundary condition. The experimental data on an annealed aluminum showed good agreement with the theoretically predicted values. In addition to strip drawing, this analysis should be applicable to other similar forming processes including extrusion and ironing.
The emergence of instabilities in clad sheet metals subjected to rolling is studied theoretically. These instabilities are modelled as bifurcations from a state of homogeneous strain into periodic non-uniform deformations. With this model, a sharp distinction may be drawn between the instabilities observed in rolling, which are not diffuse, and the diffuse necking observed in uniaxial tension. It is demonstrated that while a maximum load criterion is valid for diffuse necking in uniaxial tension, it is inappropriate for rolling. Various aspects of the predictions made here compare favorably with experiments by Semiatin and Piehler1,2,3
Experimentally measured forming pressures, obtained from plane strain punching of 99.95% continuous cast copper ingots, are correlated with observed deformation fields. The deformation fields are revealed with optical metallography of recrystallized zones within the large as-cast columnar grain structure of the cast copper. The results are interpreted based on predictions of slip line field theory.
Successful competition in the seamless tubular products market demands improvements in surface and dimensional quality in products from seamless pipe mills. It is reported that pass design, piercer setup and operating parameters have critical effects on both dimensional and surface quality. Defects which form during the piercing process are the result of these mechanical parameters (which control the localized stress states) in combination with metallurgical factors (which determine the material’s resistance to fracture by aggravating stresses). Understanding the detrimental effects of inclusions led to the development of cleaner materials, but economically feasible operations in this direction have been exhausted. Because of this, attention is directed to improvement of deformation limits by control of mechanical processing factors, such as piercer setup and point/pass design. Control of these parameters leads to an optimum pass design that produces conditions favorable not only for enhanced deformation before fracture, but also for energy and power requirements.
The application of computer-aided design and manufacturing (CAD/CAM) techniques to forgings is gaining popularity as the resulting productivity improvements are becoming more and more apparent. The use of computerized techniques for the analysis and design for forging dies has considerably augmented the experience and skill of the die designer.
Flexible manufacturing systems (FMS) have been used efficiently in metal removal applications. Recently it became evident, however, that a true economic advantage of FMS will become available only when an integration between forming, cutting, and other operations will be materialized. In this paper developments encountered in FMS used in metal forming operations are reviewed. Several functional problems of FMS in forming are identified and discussed.
The edge formability of a spectrum of high-strength cold-rolled steels has been evaluated using the hole expansion test. The effects of edge condition, micro structure, and tensile properties on hole expansion performance were determined. Modification of stringer inclusions through rare-earth treatments caused the hole expansion response of these steels to be much less sensitive to edge condition, as-blanked vs de-burred. Independently of edge condition, rare-earth treatment also produced a significant increase in hole expansion performance compared to the same steel untreated. Circle grid analysis showed that deformation modes generated in a hole expansion test are drawing near the hole edge, stretching farther from the edge, and plane strain separating these two modes. Recovery annealed steels with low transverse ductility were observed to fail away from the edge in the plane strain region during hole expansion. The hole expansion performance of the entire range of steels tested was found to vary linearly with the product of the steels’ transverse total elongation and rm values. A phenomenological expression that determines hole expansion performance was derived using linear analysis. It predicts that for steels with total elongations of about 30 pct, each increase in rm of about 0.1 will increase its hole expansion performance by greater than 10 pct.
An algorithm has been developed for determining the tensile test properties of sheet metal. The data are analyzed in real time using a modified cubic spline to smooth and differentiate a moving window of data. From the resulting information, the test results can be determined for upper and lower yield stress or proof stress, yield elongation, uniform elongation, tensile stress, total elongation, and plastic strain ratio. The accuracy of the algorithm, which has been in use for eight years, is shown to be equivalent to that obtained by a skilled operator using conventional methods.
Use of NC machine tools is now common even in high production, and this is presently increasing requirements toward higher productivity. Interesting cutting tool geometries have been developed and used in production during the past ten years. Use of computer technology is now a necessity for efficient utilization of productivity potentials offered by hardware machines and tools.
Galvanized steels have been increasingly used to improve the corrosion resistance of automobiles, particularly of corrosion critical components. In addition to the studies of the effect of coating on weldability and paintability, a further understanding of the effect of galvanized coating on the formabilities of steel is needed. Two forming tests, i.e., limiting dome height and hole expansion, were used to determine the plane strain and edge formabilities of four widely-used, hot-dipped galvanized high strength steels both in the as-coated and the as-stripped conditions. These two modes of fracture are believed to be the most frequently encountered problems in stamping operations. The results indicate that the hot-dipped galvanized coating increases the plane strain formability while it decreases the edge formability of high strength steels. Thus, galvanized steel and uncoated steel are interchangeable in plane strain-controlled applications. However, when regular uncoated steel is replaced with galvanized steel in edge/flange stretching-controlled applications, care must be exercised in determining blank size and tooling design.
Many opportunities for machining cost savings are believed to exist for those who understand the metallurgy of cast iron and are willing to develop a business approach to ensure good machinability. User requirements for castings are increasing simultaneously with casting cost reduction pressures. Many productivity improvements and cost reduction opportunities begin with higher value castings. Users would seem to benefit significantly by being open to paying extra for castings that reduce machining and other manufacturing costs even more. This paper illustrates how metallurgical technology has been applied to solve problems and reduce total net costs through use of castings metallurgically designed for improved machinability. It is the intent of this paper to present a few specific metallurgical facts and examples that illustrate the benefits of moving out of the “ruts of established technology” and ahead of the “conventional wisdom.”
A method to determine surface strains in industrially stamped sheet panels has been studied. The method incorporates a quadrilateral grid imposed to the blank and automatic image analysis. The quadrilateral grid makes it possible to analyze complex strain histories with rotations of the deformation system. The grid size can easily be increased from a minimum value upward during the analysis of a panel, for example, from one area to the next. In areas of the panel where cracking occurs, a small size grid is required because of the sharp strain gradients close to the crack. In relatively flat areas of the panel with low levels of strain attention is usually focused on strain variations over larger distances than in failure regions, and larger grids are used. Such long range strain variations are of interest in analyzing buckling, springback, or shape fixation. An inner auto body component was stamped in a high strength rephosphorized sheet steel and analyzed in some detail. Complex strain histories were identified with rotations of the deformation system. The distribution of strains in different areas of the stamping was determined. The analysis gives both the magnitude of the strains and the direction of the largest strain. Such information can be used by a die engineer in tooling development and in selecting blank holder pressure. Cracking occurred at one location of the stamping. The corresponding strain path was complex. The failure could be predicted with the present strain analysis and the forming limit diagram.
A review of recent progress in metal forming tribology, both in bulk and sheet-forming processes, with regard to advances in fundamental concepts, test methods, developments in various areas of metal forming processes, lubricants and lubrication, improvements and new applications.
A number of simulative tests have been developed over the years to assess sheet metal formability. Two of the tests, namely, the Forming Limit Diagram (FLD) and the Limiting Dome Height (LDH), are being used as standard tests for the evaluation of stretch-type forming operations. The tests do not include the effect of bending on formability and hence are limited in their application. Recently, the Hemispherical Stretch-Bend Test (HSBT) was introduced to assess the combined effect of material and design variables on stretchbend type forming. This paper presents a strain data base for the HSBT and gives the influence of punch curvature and sheet thickness on the limit strains and the strain distributions after forming. Curvature and thickness alter the strain distribution so much that one punch cannot be representative of all stretch-bend forming operations.
Previous experimental work has focused on determination of forming limits in terms of local strains. The present study extends this approach. Fracture loci and strain paths were determined experimentally from cold upset tests on cylindrical specimens. Several combinations of cylinder length, diameter, lubrication conditions, and die surfaces were used to determine the influence of these parameters on fracture. Strain paths have been shown to be process and geometry dependent but material independent. On the other hand, fracture loci depend upon material properties but not on process parameters. The point of intersection of the process strain path with the material fracture locus represents fracture. Using a series of curve-fitting techniques, expressions were developed for determining this point in terms of process and material parameters.
A system for major classification of sheet metal forming process variables is established. Subsequently five major sheet forming process variables — blank size, blank location, binder force, material thickness and lubrication — were selected for investigation. The effects of these variables on panel quality were quantified by determining panel strain state and buckle severity.
The machinability of stran-dcast free-machining steels newly developed jointly by Nippon Steel Corporation and Inland Steel Company is compared to that of ingot-cast steels. The effect on machinability of such metallurgical factors as the size and shape of manganese sulfide inclusions, lead particles, and oxides, that are likely to change as the shift is made from the ingot-casting process to the strandcasting process is discussed. The results of this study show that strand-cast products contain somewhat smaller manganese sulfides, but that, unlike ingot-cast products, they are free from the segregation of machinability-improving inclusions and hard oxides. Therefore, strand-cast steels are as machinable as the average ingotcast steels, are less variable in machinability and are more consistent in quality. It has also been found that machinability is improved as the amount of manganese sulfides, lead particles, and the size of manganese sulfides increase and as the amount of oxides decreases. However, it has been observed that the effect of manganese sulfide shape varies with the machining condition. This report also discusses the effect on improved machinability of the manganese sulfide deposit on the tool.
