Aluminum conference draws hundreds from around the world.
The first AFS conference on permanent mold casting of aluminum drew nearly 250 registrants to the Novi (MI) Hilton Hotel, April 3-4. Convened by John Jorstad, Reynolds Metals Co, the conference truly was international, with speakers and attendees from Australia, Japan, North America and Europe.
Topics ranged from process basics and variations to new process concepts, new facilities, special process applications, process quality controls and the latest in tooling design techniques.
Commenting on the large number of attendees, Jorstad noted, "I think that we all are well aware of what's happening in the automobile industry, and the expectations of that industry over the next five or six years. We are expecting a rather large increase in the use of cast aluminum wheels, cylinder heads, engine blocks and other engine-related castings, internal transmission components and suspension parts. A large percentage of that is going to be accomplished in permanent mold. Prospects are right, too, in instruments, office machinery castings, aerospace and a variety of military-related hardware, as well as in consumer durables."
The conference began with presentations on the gravity pouring of aluminum. Allan Wirch and Simon Kwok, both from Accustar Canada's Etobicoke Casting Plant, discussed process parameters and production problems of aluminum gravity static pouring. The pros and cons of fluxes and filtration materials and techniques also were presented. Process parameters were introduced with a discussion of grain refinement, mold design and mold washes.
Also covered was the general operation of static gravity pour machines. Various quality considerations--cracks, shrinkage, gas porosity, dross and inclusions, cold shuts and misruns--were explained in some detail. Plant manager, Allan Wirch, concluded the joint presentation by introducing the audience to some interesting facets of the Etobicoke operation.
Gravity Tilt Pour
Glenn W. Stahl, Stahl Specialty Co, explained some of the advantages of another gravity pouring process--tilt pour. To achieve the desired progressive solidification specific to different parts, programmed tilt pouring is available. According to Stahl, by using a multiple cavity configuration--a "stacked" mold--"the hydraulic pressure of the metal `head' in the pour cup is controlled, filling the cavity without producing flash or core burn-in."
Stahl went on to explain why gravity tilt pouring lends itself to various automated processes, including "two up" pouring with one operator.
The final presentation devoted solely to gravity pour permanent molding was presented by Peter Petto III, Arrow Aluminum. Petto discussed a number of practical solutions to resolving gravity pour problems in terms of an overall framework he has developed after 11 years in the business.
Petto explained that the classic "ideal" gating system, while yielding a simpler mold, offers less sensitive process parameters: "Unwillingness to tweak your process and control it tightly means longer cycle times, poorer yield and higher trimming costs. This new `alternative ideal' requires that you commit development time and thought."
Petto recommends beginning with a minimal gating system, and proposed a number of solutions to remedy possible major and minor defects. This "bandage" approach, Petto believes, is essential to a well designed production process. Petto listed localized shrink and oxide inclusions as the two defects that receive the most attention and recommended various approaches to dealing with both. He also described approaches for dealing with two less serious common defects: core gas and nonfill (coldshot or misrun).
Various aspects of the squeeze casting process were discussed by two speakers: Jack Dorcic, IIT Research Institute, and Dr. Milton Toaz, J.P. Industries. Dorcic discussed the process both in terms of the production of metallic and ceramic-metal composite components.
Toaz noted that despite the interest in composites within the transportation industry, there have been few applications. But, the use of selectively reinforced composite castings, according to Toaz, provides for the level of consistent casting quality which has been demanded, but not provided, by totally reinforced castings.
Toaz explained that by controlling for only two variables, fiber content and fiber orientation, "it is possible to tailor material properties to match the material requirements of a specific application." He then explained some of the favorable test results of a ceramic-composite piston for a high-output diesel engine.
Low Pressure Molding
The advantages and applications of low-pressure diecasting were explained by Alan Plume, Roger Reamer and Dr. Heinrich Fuchs. According to Plume, A.W. Plume Co, "the low-pressure process will advance further than we know it today by increased development in die design, die techniques and thermal control." He emphasized that, "new technology has created new markets, such as casting low melting point alloys to be used as cores in carbon fiber [castings] which in the past was considered impossible because of the high density of the metal."
Reamer, Progressive Castings Group, Inc, presented a number of examples of permanent mold castings which had formerly been cast using gravity permanent mold. Increased casting yields coupled with reduced labor costs (pouring, finishing) were realized in the examples cited.
Fuchs described research done at Kolbenschmidt AG on various aluminum-silicon alloys in the production of automobile engine blocks and cylinder heads. Said Fuchs, "If modification is not required . . . melt treatment with phosphorus will improve the performance of aluminum-silicon alloys at elevated temperatures. Phosphorus additions of approximately 40-60 ppm lead to a `grainy' structure of the silicon in the eutectic."
Fuchs concluded by noting that with even more complex cylinder head designs likely in the future, core handling devices will be used more widely. Twin dies also may be used, he said, as well as increased computer process control.
Castings produced using the UBE high-pressure process were shown by Shu Suzuki, UBE Industries, Ltd. The UBE process is designed to control the mold fill rate, with a claimed reduction in porosity problems. Castings shown and discussed were an automotive wheel and brake caliper in 356 T6, a shift fork in A390 (high silicon), a master brake cylinder in 2014 (very low silicon), and a manifold in ADC-12, a conventional diecasting alloy.
Suzuki explained that the UBE process is a bottom filled vertical shot system. The metal is tilt poured into the sleeve. Castings are melted and tested under vacuum for retained air or gas.
Metal is forced into the mold cavity using a precisely controlled plunger, which results in metal velocity at the gate of 100 to 300 mm/sec, according to Suzuki. He noted that, " . . . with proper gating, residual oxides can be trapped in the biscuit...."
Suzuki gave an evaluation of the cost effectiveness of the vertical system in terms of residual gas content--porosity. He then presented a second comparison on the basis of fracture toughness. Macro- and micro-specimens used to evaluate the internal structure of a number of different castings produced using the system were shown.
One example showed sections of a shift fork produced in A390 which had previously been cast using the Pore Free process. Comparison of macro- and micro-sections produced using both processes were shown and discussed.
Two speakers, David Schmidt, AFS, and George Metevelis, Foseco, Inc, addressed the subject of computer-designed molds. Metevelis introduced a new software program which is "capable of generating solid models directly into the form of finite difference elements, carries out thermal analyses and goes on to predict where solidification-related defects are likely to occur." The program creates a colored, graphic representation of the casting during all stages of processing. Upon solidification, either 2-D slices of the casting or 3-D views may be chosen.
The solidification simulation described by Metevelis operates, "by assuming that an element becomes solid when its thermal value falls to a predetermined level according to the type of metal being studied. The occurrence of shrinkage is illustrated by removing elements from the solid model where it has calculated the shrinkage would occur in the actual casting," he said.
Metevelis concluded by presenting a solidification simulation of a hypothetical casting. He noted that, "Although the program used to do these solidification simulations has been empirically demonstrated to accurately predict solidification defects in ferrous materials in sand molds, a comprehensive study . . . is being planned and design of experiments is taking place."
Three well known speakers on the subject of process control made presentations: Robert Mrdjenovich, Ford Motor Co/Casting Div; Larry Smiley, Reliable Castings Corp; and Wayne Tolliver, CMI Permanent Mold, Inc.
Mrdjenovich noted that the Essex Aluminum Casting Plant, Windsor, Ontario, was the second foundry in the world to receive Ford's Q1 award. Essex has been able to achieve what Mrdjenovich termed "giant leaps" in quality through the use of both full factorial and Taguchi Design of Experiments techniques.
Statistical Process Control (SPC) is used in the melt department to control density and silicon particle size. In finishing, ". . . SPC charts are maintained for each rough machining unit, covering everything from cast locators to turned dome dimensions," he said.
Smiley began by addressing the illusions which we have held about our processes and organizations--illusions that have prevented us from understanding and controlling process variability. According to Smiley there are two key concepts involved in defining a transformational manufacturing process: "a process is actually defined by activity, not by physical plant or equipment; second . . . repetition [means] actions that occur in a repeatable, controlled fashion," he said.
Smiley then went on to explain random or "common cause" as distinguished from "special cause" variation. he emphasized that, ". . . the responsibility for change lies squarely on the shoulders of company management and the engineering support people. This is the great lesson of statistical thinking as applied to industrial processes.
Montupet and Teksid
Conferees were given an AV tour of two new permanent mold facilities. Jacques Pascal presented an interesting look inside Montupet's new foundry outside of Montreal. Prof. Sergio Gallo, the featured dinner speaker, described Teksid S.P.A.'s approach to permanent molding which it has brought to its new facility in Dickson, TN.
Teksid uses permanent mold gravity casting because, according to Gallo, it permits greater control of the mold temperatures and permits greater flexibility in placing risers. Gallo mentioned that a robot is used to automatically check more than 100 data points on sampled castings from each mold, each shift. The robot is connected to a computer, which generates a printout of the exact value for each point, together with any deviation from the standard, facilitating rapid response to required process adjustments.
Gallo closed with a promising forecast for increased use of permanent mold aluminum castings in automobile applications, and explained some of the processes he believes will be used more extensively in high-volume production of large V6 and V8 cylinder blocks.
PHOTO : Peter J. Petto III, Arrow Aluminum, presented some solutions for resolving gravity pour casting problems.
PHOTO : Robert Mrdjenovich, Ford Motor Co/Casting Division presented case studies involving various casting process controls at Ford's Essex Aluminum Plant.
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|Title Annotation:||American Foundrymen's Society conference|
|Author:||Burditt, Michael F.|
|Date:||Jun 1, 1989|
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