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EPC research: creating a competitive U.S. market.

The expendable pattern casting (EPC) process is a relatively recent development in the metalcasting industry. Since the Full Mold process, on which the EPC method is based, was patented in 1958, this casting technique has gained steadily in acceptance by the foundry community.

Most of its acceptance and use today, however, is overseas where considerable resources have been committed to EPC research and production. Currently, Morikawa in Japan has the largest EPC foundry in the world, producing over 100,000 castings per month in 12 different components.

Extensive research has been and is being conducted to advance the state of the art of EPC in the United States so that we stay competitive with the rest of the world. One of these research projects is now underway, Phase I has just been completed and Phase II scheduled to begin July 1990. The participants in this project are the American Foundrymen's Society, Southern Research institute, the Universities of Alabama, Missouri and Wisconsin, the U.S. Department of Energy and 32 U.S. companies. (see Fig. 1)

The EPC process has several advantages over conventional casting techniques. The first is improved dimensional accuracy and tolerance capability in the castings. Second, the design freedom offered by the process allows engineers to incorporate many features that previously would have been machined, bolted or welded to produce the component.

Third, the surface finish of EPC castings enhances their functional efficiency, compared to conventional sand castings. Finally, effective designs for lower casting weights can improve component performance. These advantages, along with foundry productivity increases and reduced energy consumption, highlight some reasons for the market increases in EP castings.

The success of research funded jointly by industry and the Dept of Energy can be measured by the market projections for the casting technique. A 1986 market study conducted by a U.S. foundry supplier predicted a 3-5% growth in aluminum and gray iron EPC castings each year between 1987 and 1993.

The market predictions in late 1989, eight months into the AFS/DOE Phase I research, indicate a significant increase in EPC aluminum production, to over 150,000 tons in 1993. Similarly, the 1989 study projected a growth in EP iron castings to over 120,000 tons by 1993. By the year 2000, these tonnages are expected to double.

EPC aluminum components will have their greatest market penetration in automotive and transportation parts. EPC gray iron components will find their greatest growth in automotive and pipe fitting applications.

Despite the obvious benefits and positive long-term predictions for the EPC process, several hurdles must be overcome before widespread acceptance of EPC components will occur. The major hurdles identified include difficulty of quickly converting a blueprint to a casting, technical aspects of the process, resulting in defective parts and the lack of recognition of EP casting potential by many casting buyers and design engineers.

Technical Summary of Phase I

Phase I of the AFS/DOE casting project has resulted in a comprehensive literature review, analysis and technology status report. A concurrent analysis of EP casting defects submitted by participants in the project showed that five defects, related principally to poor sand compaction and pyrolysis products, were responsible for over 90% of the casting defects.

The Phase I results on pyrolysis events have shown conclusively that most of the previous theories on pattern removal are not accurate. This result aids the foam, glue and coating suppliers in assessing material performance needs. Compaction, flow, densification and permeability results from Phase I will assist the foundries in the system design and equipment operation for successful implementation of the process. Finally, the results of the defect identification and cause analysis provide a basis for process characterization and control.

The study also responds to the second hurdle of casting buyer awareness. Specifically, intra- and inter-process dimensional capability and tolerance comparisons between conventional foundry processes and EPC have supplied important information to individuals responsible for designing cast components. Overall, the study will raise the awareness of the technology's availability. Phase I Accomplishments

Task I - The first of two objectives was to review the available literature; 350 published papers and 80 patents were found. The technical aspects of implementing the process were identified by reviewing process parameters with participating companies. This information was summarized in the first quarterly report to the sponsors.

The second objective was to analyze a group of 100 castings, categorize the defects and develop control strategies. The major defects were the result of incomplete removal of pyrolysis products, sand fluidization produced by high pressure gas evolution during pouring and sand/burn-on penetration due to inadequate sand compaction. These control strategies will be investigated in phase II. Task 2 - Evaluated sand flow and compaction in EP castings. A subcontract with the Univ of Wisconsin was placed to analyze the literature relating soil mechanics to sand compaction. Task 3 - Evaluated the factors that influence the dimensional precision of EP castings and comparison with green sand and no bake processes. Two patterns were selected for dimensional measurements. A webbed cube casting was used to evaluate the influence of process variables on the dimensional precision and casting quality. These castings exhibited process defects in the area of broken bolt cores and sand penetration. These problems will be addressed in Phase II. A cone pattern was selected to evaluate inter-process variations comparing greensand, no bake, etc. Samples were poured in aluminum, iron and steel.

Phase I results showed that the EPC aluminum castings were superior to sand castings because of cast-in holes, near zero taper, closer dimensional tolerances and surface finish when compared to sand castings. This task resulted in a very complete dimensional analysis of castings from a wide variety of processes and will be the subject of future publications.

Task 4 - Identified the critical process parameters and system properties controlling the dimensional precision and defect formation in EP castings. To support this effort a subcontract was placed at the Univ of Missouri/Rolla to test a mathematical fluid flow, pyrolysis and solidification model. A method for measuring casting permeability was devised and used to measure room and elevated temperature properties for coatings. Special tests and modeling efforts have clarified and continue to aid our understanding of the important mechanisms in the EPC process.

Proposed Phase II The Phase II proposal has been submitted to the DOE for their consideration of continued funding. Most of the original industry sponsors have become Phase II sponsors. AFS is currently seeking additional sponsors for future work. it is proposed that the research be continued in a 24-month Phase II program. The thrust of the first 12 months will be to develop control measures for the most common casting defects. This will involve extensive studies of sand migration and densification in both pilot and plant scale facilities. Methods for increasing sand modulus and controlling pyrolysis defects through vacuum treatment of molds during pouring will be investigated. Techniques for measuring in-situ mold quality will be developed so problems can be identified and corrected. Casting property data will be compiled and supplemented where necessary to provide designers with realistic property expectations of the EPC process for new product applications. The emphasis in the second year of Phase II will be to develop a strategy for part and tool design. Process techniques and parameters will be developed for coating, compaction and pouring to achieve the acceptable, defect free, castings.

A major effort of Phase II will be to construct a laboratory EPC facility incorporating instrumentation and vacuum capabilities not found in many commercial facilities. This facility, together with bench testing, will be used to develop and optimize EPC technology. Two focus areas involve how to eliminate pyrolysis products that cause internal and surface defects and how to minimize burn-on and penetration. Phase II has been broken down into seven technical tasks.

Task 1 - Will update the literature review and analyze all of the additional technical information obtained this past year from Phase 1. The literature also will be scanned for probes and other devices that might be used to measure mold properties such as density, modulus, permeability, flow and pressure.

Task 2- Will encompass both laboratory and plant tests to establish the best conditions (frequency, amplitude and direction) for sand migration into blind areas. The first major subtask will be to install a compaction table and set up sand migration experiments that are typical of industry practice. Instrumentation capable of measuring density, pressure, sand flow rate and currents also will be evaluated in the laboratory facility.

Task 3 - Will further evaluate sand migration and its effect on dimensional precision. The bench scale results already obtained will be further examined in a lab scale facility as well as a production environment. Once these results are obtained, the concepts will be tested on full-scale commercial equipment.

Task 4 - Will implement controls for defects as a result of laboratory and plant trials, The major defects of EP castings are sand burn-on and penetration, sand fluidization, pattern and glue residues and core shifts. Lab trials will be carried out to control these difficulties. It is expected that at least one seminar will be held on this subject and results will be compiled as a separate publication. The final subtask in this area will be to address glue pyrolysis as a source of carbon defects.

Task5- Encompasses several types of tests that will aid in understanding the EPC process. Computer modeling with laboratory verification of fluid f low into the mold cavity will be incorporated. There are six subtasks in this area that involve special test procedures. They include: determining the gas permeability, thermal conductivity and stiffness of foam coatings; thermal properties of representative metals; establishing the extent of vaporization and melting in the mold (this work will be conducted by the Univ of Alabama); and the testing and development of a mathematical model for the filling and solidification of EP castings (Univ of Missouri/Rolla).

Task 6-Will determine the feasibility of using probes to measure density, permeability, sand modulus and pressure during flask filling. Ultrasonic, X ray, vibrating speed and gas permeability methods will be examined.

Task 7- involves property measurements and comparisons for aluminum, gray and ductile iron to determine if there are significant variances in cooling rates. Tensile and fatigue test data will be developed.

Each sponsor's share of funding is 1.5% of the total dollar amount which will be spent on EPC research. AFS is presently soliciting additional sponsors to reduce the percentage per sponsor. Companies can receive over $1.2M of research for less than $20,000. For information on joining the AFS Research program contact Daniel L. Twarog, Director of Research-AFS at 800/537-4237.
COPYRIGHT 1990 American Foundry Society, Inc.
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Title Annotation:expendable pattern casting
Publication:Modern Casting
Date:Jun 1, 1990
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