Journal of Applied Metalworking

By using a virtual work approach and considering the effect of anisotropy and strain rate, a regression model was developed that accurately predicts the draw bead restraining force for rimmed steel, aluminum killed steel, 2036-T4 aluminum, and 5182-0 aluminum from experimental work by Nine2 using a draw bead tester. It has been shown that by differentiating a regression model it is possible to quantitatively assess the effect of variability of the independent variables on the variability of the dependent variable.

Lüders lines can appear on the surface during the stretch-forming of aluminum sheets for aircraft skins. These surface strain markings, due to discontinuous plastic deformation, detract from the appearance of the aluminum skins and may be a cause for their rejection. The test method described in this paper was developed to determine whether 2024-T3 sheet material would form Lüders lines during stretch-forming. An increase in the resolution of the load-deflection curve in the vicinity of the yield point during a tension test performed with pre-determined cross head and chart speeds forms the basis of this test method. This method has been successfully used to predict the forming behavior of many heats, as well as to modify stretch forming parameters for minimizing the problem in forming of transport aircraft skins of 2024-T3 alloy.

This paper describes how a model material technique has been applied in the analysis and development of a roll forming process for heading shanks, gun nails in particular. A commercial modelling wax “Filia” is extruded to the dimension of the model shank before the head is roll-formed by means of equipment designed for this process. The dependence of the roll diameter, of the velocity between the roll and the tool, and of the interface friction are shown for the model technique and compared with a theoretical estimate and with experimental results. A compound wax is used to study the proportion of virgin surface from the cropping in contact with the roll and the tool. A machine for production of gun nails was developed based on the model analysis. Experiments carried out with this machine confirm the results and the advantage of the model material technique.

The technique of generating curvatures in thin sheets by shot peening is well established for forming airplane wing skins to controlled contours. Success used to depend on the peening machine operator’s skills; therefore, a systematic experimental investigation was conducted into the effects of workpiece geometry and process variables on resulting curvatures. Most of the tests were conducted on 6 x 24 in. (152 x 610 mm) 2024-T3 and 7075-T6 aluminum alloy sheets of up to 0.5 in. (12.7 mm) thickness. Shot of 0.023 to 0.066 in. (0.6 to 1.7 mm) diam was used in a wheeltype machine at speeds up to 250 ft/s (80 m/s). The radius of curvature Rof a peened specimen can be expressed as R = A + B/Swhere Sis the shot density (weight per unit area) and Aand Bare parameters which are functions of other process variables. Specimens with a length-to-width ratio of L/W =1 have equal stiffness in the Land Wdirections but developed a predominant curvature the direction of which was affected by secondary variables such as the rolling direction in the sheet. However, transverse and longitudinal radii of curvature were almost identical in thicker specimens of L/W =1/4 and could be used to predict the transverse curvatures of long workpieces peened under production conditions, as confirmed by productionscale experiments.

Flexible manufacturing systems are, at present, the most advanced manufacturing systems and constitute an important step towards the automated factory. Their main area of application is in the small batch production and their use aims at integrating all the production activities, such as forming, machining, welding, painting, inspection, assembly, etc., into either an automated system or individual automated subsystems, which can be connected through the information and the material flow. They result in a high-level utilization of the work-stations a reduction of the throughput time of the orders and the work-in-process and implement faster any kind of changes on the products range. In this paper an overview of the development of the FMS is attempted. The main characteristics of the FMS used in the metal removal manufacturing processing are outlined.

Cracking of the workpiece in rolling, whether in the form of edge or surface cracking, alligatoring or nose splitting, or damage to the workpiece center, invariably results in increased scrap and production costs. This review of causes and effects concludes that inhomogeneous deformation and attendant large secondary tensile stresses are necessary criteria for the initiation of ductile fracture. Through thickness inhomogeneity results in surface or center fracture, whereas lateral inhomogeneity leads to edge cracking. Alligatoring, the least understood defect, is perhaps promoted by both types of inhomogeneity. A further necessary condition is a material of limited workability or the presence of inhomogeneous workability features. Means of avoiding or minimizing fracture are suggested, and workability in section, tube, and powder rolling is briefly discussed.