Journal of Applied Metalworking

Published by Springer Verlag
Print ISSN: 0162-9700
Selected components of U.S. Model 1855–63 and British Pattern 1853 rifled muskets were metallurgically examined for insights to the materials and thermomechanical processes available to mid-19th Century metalworkers engaged in the interchangeable (American) system of manufacture. Wrought iron, used soft or case hardened, was the principle material of construction. Only a few parts requiring greater strength were heat treated steel. These included a screw of case hardened puddled steel, a percussion ignition cone of selectively hardened eutectoid and a spring of through hardened eutectoid or higher carbon crucible steel, a tumbler of selectively hardened high (> 1 wt pct) carbon crucible steel, and a lock swivel of normalized “Damask” steel. Interchangeability of parts with other arms of a single design was achieved by hot working to near net shape, annealing, machining, heat treating, polishing, and assembling. Neither alloy nor Bessemer steels nor cold pressed parts were employed in Civil War arms production.
The 1981 North American Forging Technology Conference was held on December 1–2, 1981, in Atlanta, Georgia. It was sponsored by the Forging Committee of the ASM Mechanical Working and Forming Division in cooperation with The Forging Industry Association. The objective of the conference was to review and disseminate recent technological developments related to forging, with emphasis on improved utilization of raw material, tooling, machinery, and new processes. The 250 or so conference participants included overseas attendees from Japan, Australia, France, and West Germany. It was a well-attended and informative event, featuring 15 presentations (without publication). The highlights of each presentation are covered in this report, along with the detailed conference program listing and plans for next year’s conference.
The paper describes a 'test case' manufacturing process sequence for solar photovoltaic modules which will cost 50 cents/watt in 1986. The process, which starts with the purification of silicon grown into 75-mm-wide thin ribbons, is discussed, and the plant layout is depicted; each department is sized to produce 250 MW of modules/per year. The cost of this process sequence is compared to present technology at various companies showing considerable spread for each process; data are tabulated in a composite state-of-the-art cell processing cost summary for these processes.
The paper describes the heat exchanger method (HEM) for growing silicon crystals. The problem of ingot cracking was solved by using a graded structure silica crucible, and vacuum processing eliminated expensive high-purity argon. Solar cells fabricated from HEM silicon demonstrated conversion efficiencies up to 15% (AM1) at low cost, using square cross-section, single crystal silicon. A modified multiblade slurry machine was adapted for multiwire fixed abrasive slicing of silicon which uses a diamond attached to wires; this method provides a conversion ratio of 1.08 sq m of wafer per kg of silicon ingot, and produces wafers free of edge chipping with a surface damage of 3-5 microns.
Chip formation control is an important problem in unmanned machining operations. Short, discontinuous chips are often most desirable to avoid entanglement with tooling and to aid with mechanized removal systems. Chip formation conditions can change during machining, especially with single-point turning. Experiments were conducted on a machining center. Conditions of feedrate-induced segmented chips correlate well with the count rate of acoustic emission (AE). The sensitivity of AE signals to chip congestion or entangling due to continuous chip formation is illustrated.
The fundamental mechanisms responsible for the low rate of strain hardening during high temperature deformation and for a steady state of flow at high strains have been confirmed to be: I. Dynamic recovery, which limits the accumulation of dislocations through annihilation and which operates at all strains in all metals; and II. Dynamic recrystallization, which eliminates dislocations through the migration of grain boundaries and which only operates beyond a critical strain when the dislocation density becomes high enough to give rise to the nucleation and growth of new grains. These softening processes are retarded by the presence of solute atoms and second phase particles which reduce the mobility of both dislocations and high angle boundaries. These effects have some similarities to those observed under cold working and annealing but there is a strong dynamic element introduced by straining at the elevated temperature. As a result of the high strains imposed there is much more microstructural change than during creep loading. Industrial hot forming processes generally involve several stages of deformation separated by intervals during which static recovery or recrystallization take place. The interaction between dynamic and static softening processes under industrial conditions will be the subject of a sequel paper. This work will also consider the trends in hot ductility; the latter depends on the retardation of grain boundary cracking by dynamic recovery and recrystallization. Finally, since the effects of alloying in hot working have been treated only in a general way, the behavior of specific materials and their thermomechanical processing will be reviewed in the third and fourth papers of this-series.
“Concept feasibility” has been shown for laser-assisted machining (LAM) using a 15 kW continuous-wave laser— the concept being that a laser beam will selectively heat the workpiece in a machining operation, and will thereby enable higher rates of metal removal to be achieved without a corresponding loss in tool life. The concept feasibility study involved two aerospace materials: Inconel 718 and Ti-6Al-4V. Ceramic tools were used for Inconel 718 and carbides for the titanium alloy. For both materials, the metal removal rate was significantly increased without aggravating either cutting force or tool wear, the gain in removal rate being 33 pct for Inconel 718 and 100 pct for Ti-6Al-4V using current tool materials and beam coupling techniques. The commercial feasibility of LAM requires (a) incorporation of the process into a “laser integrated manufacturing system,” or (b) dropping the power requirement to approximately 5 kW through improved beam coupling techniques, both of which serve to reduce the effective capital investment and operating costs for LAM. Application of LAM is foreseen for difficult-to-machine materials in parts for which the machining time is a major portion of the total floor-to-floor time and thus warrants minimizing.
The limiting dome height (LDH) test has been proposed as a simulative test to evaluate the stretch formability of sheet metals which shows good correlation with field forming performance. The present study investigates how deviations from the LDH test procedure and test geometry given in the literature affects the dome test results for aluminum body sheet alloys. The results should be helpful in explaining between-lab variability and helpful to laboratories which cannot perform the LDH test according to specification, because of equipment limitations, in interpreting their data. Two dome test procedures, both of which are currently being used in R& D departments in the automotive and basic metals industries, were evaluated using four aluminum body sheet alloys. It was found that the procedures gave different numerical results and that the relative formability ratings varied with the procedure used. The effects of sample thickness and lubrication on dome test results were also studied. A purely geometrical effect of thickness was found, with increasing thickness resulting in higher dome heights at failure. Well-lubricated samples resulted in different formability ratings for the four ABS alloys than do solvent-cleaned samples, accenting the need for dome tests to be performed dry since the ratings from the lubricated tests do not agree with production experience. It is concluded that before a “best” procedure for performing dome tests can be selected, a correlation study similar to that of Ayres, Brazier, and Sajewski must be performed using both procedures. Cooperative efforts are under way to select and standardize a procedure for dome testing for both the automotive and basic metals industries.
The paper describes the designs, hardware, and installations of NASA photovoltaic power systems in the village of Schuchuli in Arizona and Tangaye in Upper Volta, Africa. The projects were designed to demonstrate that current photovoltaic system technology can provide electrical power for domestic services for small, remote communities. The Schuchuli system has a 3.5 kW peak solar array which provides power for water pumping, a refrigerator for each family, lights, and community washing and sewing machines. The 1.8 kW Tangaye system provides power for pumping, flour milling, and lights in the milling building. Both are stand-alone systems operated by local personnel, and they are monitored by NASA to measure design adequacy and refine future designs.
This article reviews foreign studies on methods of using electronic computers to improve productivity and lower the costs of manufacturing discrete parts by forming processes. Some improvements will result from applying electronic controls, similar to those used quite widely for metalcutting machines, to metalforming equipment. That change will reduce the charges for direct labor on product costs. It appears, however, that the use of computers will have more important and drastic effects by changing the production system for making parts in small and medium-size lots. Computer assistance in design, production planning, scheduling, record keeping, and material handling is capable of reducing the labor input of white-collar and overhead personnel. Substantial benefits are anticipated. For instance, some investigators claim that 60 pct of the manual effort in the design stage can be eliminated by using computers. Productivity based on total labor effort should, eventually, improve by more than a third. The cost benefits will be less because generating useful software programs, for computers, is expensive.
This paper reviews the status of CAD/CAM applications in forging and the significant variables of the forging process, which must be considered in developing and applying computer technology in forging. In addition, the principles of CAD/CAM for design and manufacture of finisher and blocker dies are reviewed. Examples are given to illustrate the computer simulation of metal flow to design blocker shapes for forging applications. Finally, the paper discusses the present status of CAD/CAM in forging, the immediate economic and practical applications of this technology, and the expected future research and development.
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. This paper describes a CAD system, implemented on a VAX 11/780 minicomputer, for the design of forging dies. This system uses a front end preprocessor to input the desired machined part geometry. Appropriate cross-sections of the machined parts are then chosen to design preform and finisher dies for most axisymmetric and nonaxisymmetric forging cross-sections. This concludes conversion of machined part geometry to the forged part geometry. Estimation of the number of preforming stages, design of flash geometry, and estimation of load and energy requirements of the process is based on widely used empirical, rule-of-thumb guidelines. The results of the system are compared with those available in the current literature.
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.
The following conclusions summarize the above results.1. In drilling the SCr420 series as heat treated, the maximum tool life occurs around Hvl70 to 190 in the ferrite plus pearlite structure and is considerably reduced with the coexistence of spherical cementite. 2. In drilling the SCr420 series after cold forging, tool life is shortened slightly, while the torque is suppressed. Free machining additives, S and Te, improve tool life even for heavily forged materials. 3. In the gear hobbing SCM420 series, the softer and more spheroidized steel exhibits the longer tool life. The Ca addition with S and Te increases the life of the TiN coated hob tool.
Machining of aluminum alloys was the subject of a technical session at the Materials and Processing Show and Congress held in Chicago on November 13, 1979. This article presents some of the highlights on machining of aluminum alloys discussed at this session. The papers presented were: “Influence of Aluminum Casting Alloy Characteristics on Machinability” John L. Jorstad, Reynolds Metals Company “A Practical Approach to Aluminum Machining” Daniel R. Stashko, Valeron Corporation “Successful Broaching of Aluminum Automotive Engine Components” Myron J. Schmenk, Cincinnati Milacron “Drilling of 380 and 390 Aluminum” Thomas J. Skingle, Acme-Cleveland Corporation “The Skiving of Extruded Aluminum Tubing for Automotive Condenser Tubes” Robert B. Jagers, Chrysler Corporation “Ultra High-Speed Machining of Aluminum” Robert I. King, Lockheed Missile & Space Co.
Aluminum sheet alloys with potential application as lightweight automotive body panels have been assessed for formability using a new stretchbend test. Results obtained are in the form of RtH curves for mainly stretching and tRH curves for mainly bending conditions. The curves show 5182 0 and 6009- T4 to be slightly more formable than 2036-T4 or 6010- T4. The four alloys, however, are slightly less formable than either HSLA-F50 or DP- 90T, but are much less formable than AK steel. The RtH and tRH curves are useful formability guidelines for ranking, downgaging, substitution, and selection of sheet metal.
An ancient silver bowl with a unique incurved rim (U.C.8955) reputed to stem from dynastic Egypt, earlier thought to have been manufactured by spinning, was examined and was replicated by the authors in copper by spinning and by hammering. Based on 1) the results of the replicated bowls, 2) the actual variation and surface finish of the antique bowl, and 3) an examination of the historical facts of metal working in dynastic Egypt, the authors suggest that the bowl was manufactured by hammering. This appears to support the contention of many investigators that spinning was not practiced in ancient Egypt and that it is a much more modern invention.
During sheet metal forming on a doubleaction toggle press, drawbeads on the die binder supply a restraining force which controls the flow of sheet metal into the die. To study the restraining force and the related binder holddown force, an apparatus was built which simulates a drawbead. The apparatus can separate the restraining force into its bending deformation and friction components. From experimental measurements of the appropriate forces a coefficient of friction for drawbeads may be obtained. A comparison of experimental and calculated friction forces shows that Coulomb’s Law (a constant coefficient of friction) satisfactorily represents the friction force in low and medium load ranges. However, Coulomb’s Law breaks down at higher loads. The load at which breakdown occurs depends on interactions among many variables including sheet metal material, lubricant, and surface roughness.
The present level of technology is briefly reviewed in four areas of powder metallurgy: hot forging/forming (P/F), cold forging of sintered preforms, injection molding and sintering of metal powder/plastic mixtures, and high temperature sintering. Some historical background on the factors that have slowed the market acceptance of P/F are reviewed as a guide to understanding future growth. Several examples of current commercially produced parts are cited for each technical area.
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.
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.
Formability tests simulating stretch-bend conditions have been developed for simple angular and hemispherical contours. The tests were designed to determine the influence of material and geometrical variables on sheet metal formability. Data obtained from the tests have produced families of curves relating the punch radius (R) and sheet thickness (t) to the height of the configuration at failure (H). The (RtH) curves define formability envelopes which contain all possible combinations of (R), (t) and (H). Results obtained for AK steel, HSLA-F50, dual phase 80 and 2036-T4 aluminum show that the (RtH) curves can be used as guidelines for designing and stamping sheet metal parts. They can be especially helpful in determinations concerning the ranking, downgaging, selection and substitution of sheet metal.
(1) An empirical equation has been developed that predicts springback for a variety of die geometries on the basis of yield strength, thickness, and bend radius; and for some die conditions for bend angle, hold-down, plan view curvature, and punch-to-die clearance. Since an internally consistent rationalization of the predictive equation has also been developed, the predictive equation would appear to have some general validity. However, the extent of this validity cannot be established until it has been more thoroughly evaluated. (2) By using variation analysis of the predictive equation for springback, important insights have been established about the interrelationships between variation in springback; variation in yield strength; variation in thickness divided by the nominal thickness, (R/t); and nominal yield strength. This analysis indicates the importance of interactions between the causative variables on variations in springback.
The objective of this investigation was to gain an understanding of the phenomenon of edge crack formation during the bending of plate cut to size by shearing. The stages of sheared edge creation as well as the effect which blade gap and dullness have on the sheared edge properties were studied using the microhardness scanning technique. The material used throughout this experimental work was AISI 1020 hot-rolled steel 6.4 mm (0.25 in.) thick. Bending of actual sheared edges was performed to evaluate the effect of shearing process control and subsequent sheared edge treatments prior to bending on the magnitude of edge cracking. Significant results of this study show that shearing blade gap and dullness affect the magnitude of edge cracking. The presence of a burr on the sheared edge did not significantly affect the magnitude of edge cracking. Annealing of the sheared edge eliminated edge cracking completely.
Steel plate subjected to transverse force bending will develop cracks in the outer edges of the curved portion of the bent part, if bending strains are sufficiently high, and the plate has been cut to size by shearing. A pilot study was undertaken to determine the feasibility of a model for predicting the approximate lengths of such cracks. It was stipulated that the model be sufficiently compact to be programmed on a hand-held programmable calculator. A semi-empirical model was developed based on the hypothesis that edge cracks propagate away from the edge and into the plate until the effective strain based on the sums of the true shearing and bending strain components equals the effective plane strain fracture strain. The model was applied to three different steels. Variables were blade gap and blade sharpness in shearing, and rolling direction in bending. Bending conditions were kept constant with the plates bent in plane strain and with the punch radius equal to the plate thickness. The tests showed that the model predicts the range of edge crack lengths for the chosen shearing and bending conditions with reasonable accuracy.
A method has been developed for predicting the drawcavity shape of a draw blank during the blankholder closed, predraw punch impact stage in the sheet metal draw stamping process. By selecting and progressively feeding particular increments of a proposed set of blank holder surface displacements as input boundary conditions, the nonlinear shell computer program developed by Ford Research is utilized to accurately predict the deformed shape of a blank during this stage. The method and computer program have been successfully applied to several symmetrical body panels on an experimental basis. Further work is required to both expand the scope and provide a practical system for the production engineering of sheet metal stampings. However, this method represents a step forward to computerized predictive binder design.
This paper describes a mathematical model of the stretch flanging of sheet metal blanks which are initially curved in the shape of a “V.” By assuming that all intermediate flange surfaces are developable and the effect of tool friction is negligible, the deformation in the flange is equivalent to that of an in-plane stretching operation. Strain distributions in the latter are shown to be conveniently calculated by elastic-plastic finite element analyses. To assess the applicability of the model, an existing flanging apparatus was used to produce specimens for a variety of flange configurations with AKDQ steel, HSLA-60 steel, and 2036-T4 aluminum. Comparison of the calculated and measured strain distributions along the free edges of these specimens show that the present model is reasonably accurate to be useful in feasibility studies of the design of sheet metal parts.
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.
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 type of lubrication regime which occurs in a metal forming operation has a strong influence on the frictional conditions as well as on other important factors such as product surf ace finish and tooling wear rate. The characteristics of the different types of regimes which can occur are reviewed, together with what is known about their incidence in drawing, extrusion, rolling, and upsetting operations. In the light of this information it is evident that the commonly used methods of characterizing friction can often lead to erroneous results. Suggestions for improved methods of characterizing friction are made.
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 forging engineer must often estimate the load necessary in a press forging operation. Thus, the appropriate press capacity can be selected and, in some cases, it can be decided whether or not in-house capability exists for quoting on a given forging. This paper describes a simple load calculation method and its application to forging a steel connecting rod. The results, obtained with a hand calculator, are evaluated by comparing them with the results of computer-aided analysis and with experimental forging data. This comparison indicated that hand calculator results are sufficiently accurate for estimating forging loads and stresses. It is expected that the technique, described in this paper, will be a useful tool for the engineers in forge shop practice.
Eighteen container steels of three tempers were evaluated for their redrawability. The die combinations employed ranged from 27 pct to 42 pct for the drawing reduction and from 22 pct to 48 pct for the redrawing reduction. The results indicated that higher tensile strength and/or lower work hardening exponents improved the redrawability. Consequently, the DR (double reduced) steels had the best redrawability, CA-T4 steels were next and BA-T1 steels had the least. Thickness, surface finish, metallic coating and average strain ratio (r) showed either little or no effect on the redrawability. The LRDR (limiting redrawing ratio) generally decreased with the increasing of drawing ratio. However, the TDR (total drawing ratio) usually increased with the drawing ratio. For each steel the tallest container could be made from the die combination with the highest drawing reduction. As for the redrawn cans, the can wall showed thickening at the upper part and thinning at the lower part of the container. The change in thickness tended to increase with the TDR and to be relatively independent of r-value. As for the earing, it was observed to increase with the TDR and, to a lesser extent with the plastic strain ratio anisotropy, Δr. The normalized earing (ratio of earing to can height) was generally less than 5 pct of the can height for most of the die combinations. Finally, the normalized can height (ratio of can height to can diameter) was found to vary linearly with the TDR employed.
It has been shown that when machining low carbon free cutting steels, two important factors need to be considered in explaining the behavior of the materials: (a) the relative plasticity of the inclusions and/or phases present and the variation of these with temperature, and (b) the ductility of the continuous phase,i.e., ferrite. The relative plasticity concept leads directly to the concept of triaxial stress systems around deforming second phases, and these, in turn, to the microcracking of the material. The amount of deformation necessary to cause microcracking will control the chip/built-up edge contact length, while the amount of microcracking will affect the built-up edge height. Large amounts of microcracking are attained by having a material containing both softer and harder inclusions, and these lead to short chip/B.U.E. contact lengths. Increasing the ferrite strength results in a smaller B.U.E. as the ferrite/pearlite relative plasticity moves closer to unity, and the MnS then is the major crack initiator. Thus, increasing the machining temperature by increasing the cutting speed tends to cause the MnS and pearlite relative plasticities to approach unity, although above 800 °C, MnS may have an effect as its relative plasticity is then much less than unity, but the increased ductility of the matrix at these higher temperatures is likely to influence this effect. The important engineering parameters associated with the machining of these steels,i.e., surface finish, tool forces, and tool temperatures (an indicator of wear rates), are explained by these concepts.
The effect of maganese sulfide inclusion size on the machinability of low-carbon, leaded, resulfurized, free-machining steel was investigated by plunge machining using high-speed steel cut-off tools. The cutting and thrust forces were measured as a function of cutting speed. It was observed that the force-cutting speed curves are shifted toward higher cutting speed and tool life to catastrophic failure increases with increasing sulfide size. Observation of Build-up edge (BUE) indicates that a minimum in the cuttingforce curve is generally associated with B UE and that the cutting speeds where BUE is observed are also shifted toward higher speed with increasing inclusion size. It was also found that increasing sulfide size reduces BUE size. Based on these observations, the mechanisms by which manganese sulfide inclusions influence BUE formation are discussed. The possibility of manganese sulfide inclusions indirectly influencing the BUE formation condition through their influence on temperature distribution is suggested.
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.
Long turning tests on nitrogenized and non-nitrogenized 1214 and plunge forming tests on a range of AISI 12L14 steels with varying nitrogen contents have been carried out. Both tests have revealed an adverse effect of nitrogen on high-speed steel tool life in machining, and this is attributed to static strain aging of the cold-drawn feed stock prior to testing. No compensating beneficial effect of nitrogen on surface roughness was observed in the plunge forming tests, so it is concluded that, overall, nitrogen has a detrimental effect on machinability. Regression analysis revealed that, after nitrogen, manganese sulfide size and shape had the next most significant effect on machinability of the commercially produced 12L14, all other compositional factors being essentially constant.
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.
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.”
Squeeze casting is a pressurized solidification process whose conception in Russia dates back over a hundred years. It has been cited frequently since 1950 as a major production process in Soviet foundries. The process has recently been commercialized in Japan for automotive wheels; and considerable progress appears to have been made in the United States towards squeezecast diesel engine pistons. This paper reviews recent progress in developing and applying squeeze casting in these countries. Process parameters and details for ferrous and nonferrous applications are also covered, along with the highlights of a recently concluded experimental program for squeeze casting mortar shells from ductile iron.
CBN is to be seen as a further development in cutting tools. CBN is the second hardest known substance and because of its physical properties, many advantages appear when using CBN tooling as an alternative to tungsten carbide or to grinding operations. In the present investigation, CBN cutting edges were used in turning tests of the materials 50CrMo4, 16MnCr5, 90MnV8, and X210CrW12; all of them provided a hardness of at least 55 HRC. Even though the cost of CBN cutting edges is relatively high in relation to tungsten carbide, the results of the tests performed show that an economical usage of the new cutting material is possible for turning operations. The wear behavior of CBN cutting edges is characterized by crater and flank wear, as well as small cracks on the cutting edge, depending upon the cutting conditions. The surface quality of the machined workpieces is fairly good and remained good even though relatively long cutting times were reached.
A process-model was developed based on the slab-method to calculate stress distributions and strains. The heat transfer problem was analyzed using FEM-methods and simplified by using non-dimensional analysis. The process-model could then be expanded with heat transfer calculations between billet and die. Using the model optimal forging condition for hot-die and isothermal forging were calculated. The upsetting of a stainless steel and one nickelbase alloy was analyzed over a wide range of die temperatures (20° to 1200 °C) and ram speeds (0 to 1000 mm /s). The geometries of the billets were also changed. Three different die materials were analyzed, a tool steel, a superalloy and a molybdenum alloy. For each billet and die temperature the analysis resulted in calculation of optimum ram speed, optimum die material choice and total force necessary for this upsetting. Using these data it was possible to choose the most suitable forging method as well as to calculate die temperature and ram speed for one specific billet material. Experimental data on die load as well as die failure due to plastic deformation was used to verify the calculated die load and to set up a criteria for die failure. The experimental die load and die failure data included both upsetting dies as well as shaped dies.
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
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.
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.
The results of three different upsetting tests on four commercial steels are presented. The specimen geometry is shown to have a marked effect on the free surface ductility. The so-called collar test obviates the need of a grid of lines on the free surface of the specimen from which the axial, εz, and hoop, εgq, strains are usually determined. The collar test results in reduced fracture strains vis à vis those achieved when compressing a circular cylinder. Consequently fracture can be induced earlier when compressing more ductile materials. It is demonstrated that the fracture strains from the three different upsetting tests do not lie on a straight line fracture locus, as proposed by Kuhn. A knowledge of the εgq-εz strain path can lead to an evaluation of the stress history on the equatorial free surface of an upset specimen. In turn the stress history permits the assessment of various ductile fracture criteria. Two models were examined in the present work, neither of which suited all the experimental data. A maximum shear stress fracture criterion appeared to be more appropriate for the present set of experiments. The deleterious effect of MnS inclusions on the fracture strains is exhibited by comparing the behavior of AISI 1045 and 1146 steels.
A computerized system, called CPDSSM, was developed/or design and optimization of the forming operations used in manufacturing artillery shells. The system is capable of simulating the cabbaging, piercing, drawing, and nosing processes, and it can also design streamlined dies for drawing and nosing preforms. This system is augmented by interactive computer graphics and can also be applied in manufacturing cupshaped products other than shells. For a given set of input data, which includes the billet, die, punch geometries, and the processing conditions such as temperatures, ram speed, and interface conditions, CPDSSM predicts the deformation geometry and the loaddisplacement relationship in a step-by-step fashion. The system is validated by comparing the predictions with the experimental measurements. In all cases, the agreements are good. In addition, the use of the computerized system as a design aid for shell manufacturing is demonstrated by a specific shell, which is in production. This example illustrates the capability and the potential benefits of this computerized system.
On the basis of experimentally determined lateral spread data a program for computer aided roll pass design was developed. The experimental data are expressed in terms of area ratios vs width-to-thickness ratio for different material properties. A maximum allowable deformation is put in by the designer and the program iterates until the calculation and experimentally determined value of the lateral spread coincide. Flash and neutral line are interactively selected. Center of gravity, initial cross sectional area (rectangular), and roll pass schedule are calculated. The results for a roll pass schedule are compared successfully with experiments. The program has been applied for different profile types (airfoil shapes, flat, and complex profiles) and compared with manually designed airfoil shapes.
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 results to date on a study of all-metal thick film electrodes are reported. The requirements for an all-metal thick film electrode to semiconductors include a screenable, solid oxide scavenger, a low melting point metal powder furnishing a liquid phase sintering medium as a replacement for the glass frit, a vehicle with the proper rheological properties, and appropriate dopants to provide an ohmic, low-resistance metal-semiconductor interface. The silver system was chosen as the test vehicle for this concept. Three solid state oxide scavengers were identified. The most effective of these, silver fluoride, dissociates at firing temperatures into metallic silver and nascent fluorine gas. The gas etches the silicon dioxide which goes off as gaseous silicon tetrafluoride. The finely divided silver metal ″wets″ the silicon surface forming a tenaciously adhering layer. Differential thermal analysis and thermal gravimetric analysis show the reaction temperatures of silver fluoride and the acrylic binder.
Top-cited authors
John J. Jonas
  • McGill University
David A Plankenhorn
  • Indiana University-Purdue University Indianapolis
Ron Adamczyk
  • Lock Joint Tube LLC
J. Danckert
  • Aalborg University
Natarajan Chandrasekaran