Journal of Applied Metalworking

For various reasons, ferrous warm rolling has been considered in the last 15 years to be a potentially valuable manufacturing process. However, no systematic approach has been undertaken to assess intrinsic manufacturability as indicated by such parameters as roll separating force and energy or power consumption. The purpose of this investigation is to characterize experimentally the effect of various process variables on the contact areacompensated roll separating force (separating pressure). AISISAE 1015 and 1059 steel billets were warm rolled at temperatures ranging between 300 °C and 700 °C with various thickness reductions per pass up to a short transverse strain of about — 1 at a strain rate of 10 s− 1. Two approaches were used to model in predictive fashion the influence of important warm rolling variables on the separating pressure. The first approach entailed the use of a least squares regression method to produce an empirical equation for the separating pressure. A second approach utilized a semiempirical warm working flow stress equation along with the theoretical slab method and a roll flattening concept. Good agreement was found between the experimental and the predicted roll pressures.

Spinning of tubes involves progressive localized deformation of a cylindrical ring between a rotating mandrel and a roller. The resultant product is a tube whose wall thickness is determined by the gap between the mandrel and roller. The process is also known as shear forming, flow turning, spin forging, rotary extrusion, roll extrusion, flow forming, hydrospinning, rotoforming, and floturning. Spinning of tubes is reviewed herein with the objective of providing an understanding of the basic mechanisms underlying the process,important variables and their influence on the process, some of the simpler tooling techniques that have evolved for specific parts, and the types of parts to which the process has been successfully applied in industry.

A new concept has been developed for the design of streamlined dies for the extrusion of “difficult-to-extrude” metal-matrix composite materials and P/M alloys. Based on this concept, CAD/CAM packages have been developed to facilitate the design and manufacture of these complex dies. The packages are interactive and user friendly and can help the user in arriving at an optimum design with relative ease within a short time. Use of 3- D graphics, hidden line removal, and shaded color aid the user in visualizing and understanding the complex die geometries. Two methods are presented for the manufacture of electrodes used for electro-discharge machining of dies. The first is by the use of a turnkey CAD/CAM system and the second is by the use of a special software known as CUTTER. Several electrodes (round to rounds, as well as round to shapes) have been machined using a three-axis vertical milling machine—the dies have been electrodischarge machined—and extrusion trials have been performed on several materials. The results have been very promising. It is concluded that streamlined dies have definite advantages over other dies when extruding difficult-to-extrude materials such as composites and P/M alloys.

The hot workability of two types of alloy steels at two different levels of cleanliness has been assessed using hot torsion tests. It is found that the hot ductility and the peak ductility temperatures improve with improved cleanliness. However, the high temperature deformation mechanism appears to be insensitive to the cleanliness of the steels studied in this investigation.

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.

New drawbead concepts have been developed which can increase the drawbead restraining force and also allow rapid adjustment of the force. Urethane inserts are added in the groove opposite the bead of a conventional drawbead to increase the deformation and friction. A flat-bottom drawbead design in conjunction with a urethane insert can increase the deformation component about one-third compared to a conventional drawbead. Studies have shown that these new methods can increase the drawbead restraining force of a conventional drawbead up to 20 pct. The flat-bottom drawbead can produce up to 40 pct more force than a comparable conventional drawbead.

The effect of aging on strain hardening and fracture in an aluminum copper alloy (2036) in sheet form was investigated. Two distinct types of strain hardening behaviour were identified. In the peak-aged and over-aged conditions, a high initial hardening rate was observed that was dependent upon the distribution of precipitates. The initial period was followed, after about 10 pct extension, by a low hardening rate similar to that of cold worked commercial purity aluminum. In the asquenched and in the naturally aged conditions, the initial rate was lower but strain hardening was maintained at a higher level at high strains. Observations of both forming limit data and fracture maps were interpreted on the basis both of measured strain hardening and of microstructure. Three different samples of the alloy in the naturally aged condition having known press shop performance were also studied. It was shown that the sample with poorest performance had a significant amount of grain boundary precipitaion. Re-heat treatment of these samples showed that reduction in the amount of grain boundary precipitation significantly improved the performance in small radius bend tests. It is suggested that variations in press shop performance may be related to changes in fracture behaviour and that the role of fracture events and their dependence on microstructure is an important one informing operations.