Lost Foam Casting Essay Example

Lost Foam Casting Paper LOST FOAM CASTING ABSTRACT: The Report presents some theoretical and practical aspects regarding the casting of alloys in lost foam moulds. The stages of the procedure, the economic benefits and several ecological aspects are synthetically presented. KEY WORDS: casting, alloys, lost foam process, Expanded polystyrene Introduction The lost foam casting process offers several advantages over conventional sand casting processes, such as simplified production techniques and reduced environmental waste due to binder system emissions and sand disposal. The process is well-suited for castings with complex geometries, tight tolerances, and smooth as-cast surface finish requirements. When the castings are designed to fully exploit these advantages, cleaning and machining times are dramatically reduced if not completely eliminated. Therefore, the lost foam casting process is viewed as a value-added process rather than a substitute for sand casting. Lost foam castings are produced by pouring molten metal into a foam pattern contained in a flask filled with loose sand that is compacted through vibration. Generally speaking, a foam pattern is coated with a refractory slurry and dried before being placed in the flask and surrounded by large grain fineness sand. The foam pattern degrades immediately after molten metal is introduced, leaving a casting that duplicates all features of the foam pattern. We will write a custom essay sample on Lost Foam Casting specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Lost Foam Casting specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Lost Foam Casting specifically for you FOR ONLY $16.38 $13.9/page Hire Writer The degradation products are vented into the loose sand. In lost foam casting process, mold filling, thermal transport, and solidification are strongly influenced by the foam pattern degradation. There are three phenomena which are inherent in lost foam casting process: slow molten metal flow, reducing atmosphere, and degradation products. The first and second phenomena help reduce oxides or slag defects. The last one, however, may become casting defects if they remain in the cast parts. To improve lost foam casting design, it is ssential to understand the interactions between the foam pattern and molten metal as well as the displacement of degradation products. History The first patent for an evaporative-pattern casting process was filed in April 1956, by H. F. Shroyer. He patented the use of foam patterns embedded in traditional green sand for metal casting. In his patent, a pattern was machined from a block of expanded polystyrene (EPS), and supported by bonded sand during pouring . This process is now known as the full mold process. In 1964, M. C. Flemmings used unbonded sand for the process. The first North American foundry to use evaporative-pattern casting was the Robinson Foundry at Alexander City, Alabama. General motors first product using these processes was the 4. 3L, V-6 diesel cylinder head, which were made in 1981 at Massena, New York. A study found in 1997 that evaporative-pattern casting processes accounted for approximately 140,000 tons of aluminum casting in the United States. The same survey forecast that evaporative-pattern casting processes would account for 29% of the aluminum, and 14% of the ferrous casting markets in the near future. Definition Definition| A casting process whereby the pettern is made of polystyrene foam and is vaporized when the mold is fill with molten metal| Lost form consist of first making a foam pattern having the geometry of the desire finish metal| Expanded polystyrene casting use a mold or sand park around a polystyrene pattern that vapourizes when the molten metal is poured into the mold| Evaporating pattern casting (lost foam) : this process is also know as lost pattern casting under a trade name â€Å"full mold process†, it use a polystyrene pattern which evaporate upon contact with molten metal to form a cavity for the casting| Lost foam casting, where the mould cavity is filled with polystyrene foam (the ‘full mould’ process) , is a special case. | What is â€Å"Lost Foam†? The Lost Foam casting process originated in 1958 when H. F. Shroyer was granted a patent for a cavity-less casting method, using a polystyrene foam pattern embedded in traditional green sand. The polystyrene foam pattern left in the sand is decomposed by the poured molten metal. The metal replaces the foam pattern, exactly duplicating all of the features of the original pattern. Like other investment casting methods, this requires that a pattern be produced for every casting poured because it is evaporated (â€Å"lost†) in the process. Schematic of lost for casting Process The essential steps of the lost foam casting procedure are: 1) The execution of patterns, 2) Execution of moulds 3) casting the alloy. Execution of Patterns: A pattern is made from  polystyrene foam (Expanded Polysterene), which can be done many different. What is Expanded Polystyrene? Expanded Polystyrene in its broadest sense is a rigid cellular plastic which is found in a multitude of shapes and applications. Raw Material Manufacturing: Expanded polystyrene (EPS) is the most commonly used foam pattern, it can be produced by bead pre-expansion into polystyrene (PS) beads that are ready for moulding. PS precursors are formed from ethyl benzene through an aluminum catalyst with benzene and ethylene obtained from crude oil and natural gas [Shivkumar, 1994]. Ethyl benzene is then converted to styrene at high temperature with nitrogen gas and iron catalysts. It forms polystyrene when exposed to a peroxide catalyst and polymerized in a water solution [Goria et al. , 1986]. These unexpanded beads have a density of 600 g/l (38 pounds per cubic feet (pcf)) and they are expanded 20~50 times with heat at 100 oC until the desired density is reached [Kanicki, 1985]. Polystyrene (PS) MOLECULAR FORMULA: The C=C double bond in each monomer is transformed into a C-C single bond in the polymer. | Properties: ease of forming, clarity, low heat transfer, good thermal insulation. Density: 1. 03-1. 06 g/ccStatistic: In 1999 PS usage as a plastic bottle resin was essentially nil. | Description: Polystyrene can be made into rigid or foamed products. It has a relatively low melting point. Packaging applications: Plates, cups, cutlery, meat trays, egg cartons, carry-out containers, aspirin bottles, compact disc jackets Recycled products: Thermal insulation, light switch plates, egg cartons, vents, rulers, foam packing, carry-out containers Raw Material Manufacturing: Expanded Polystyrene (foam)  is obtained from expandable polystyrene (beads), which is a rigid cellular plastic which contains an expansion agent. Expandable polystyrene is therefore obtained from oil as can be seen from the diagram. The EPS Manufacturing Process is inextricably linked with the process described in the last section, which brought us from the oil well to expandable polystyrene, now we will see what happens in the transformation process that leads us to Expanded Polystyrene foam parts. We have seen that the raw material is obtained through a chemical process. The next process involves the use of physics and the conversion process is carried out in three stages. 1st stage   PRE-EXPANSION: The raw material (beads)  is heated in special machines called pre-expanders with steam at temperatures of approximately 215-f. The density of the material falls from 40lbs/cu ft to values of usually between 1 ~ 2lbs/cu ft. During the process of pre-expansion the raw materials hard beads turns into cellular (foam) plastic beads with small closed cells that hold air in their interior. 2nd stage   INTERMEDIATE MATURING AND STABILIZATION: On cooling, the recently expanded particles form a vacuum in their interior and this must be compensated for by air diffusion. This is how the beads achieve greater mechanical elasticity and improve expansion capacity, something very useful in the following transformation stage. This process is carried out during the materials intermediate maturing in aerated silos or mesh bags. The beads are dried at the same time. 3rd stage   EXPANSION AND FINAL MOLDING: During this stage the stabilized pre-expanded beads are transported to molds where they are again subjected to steam so that the beads bind together. In this way large blocks are obtained block molding   (that are later sectioned to the required shape like boards, panels, cylinders etc. ) or products in their final finished shape shape molding. Execution of moulds and casting alloy The basic steps to the process include: A foam pattern and gating system are made using a foam molding press * The foam pattern and the gating system are glued together to form a cluster of patterns * The cluster is coated with a permeable refractory coating and dried unde r controlled conditions * The dried, coated cluster is invested in a foundry flask with loose, unbonded sand that is vibrated to provide tight compaction * The molten metal is poured on to the top of the gating system which directs the metal throughout the cluster and replaces the foam gating and patterns * The remaining operations such as, shakeout, cut-off, grinding, heat treat, etc. are straightforward and similar to other casting processes. The series and major steps in lost foam casting (LFC) What metals can be poured in the Lost Foam process? Generally, all ferrous and non-ferrous materials can be successfully cast using the Lost Foam process. Because the foam pattern and gating system must be decomposed to produce a casting, metal pouring temperatures above 1000 °F are usually required. Lower temperature metals can be poured, but part size is limited. In addition, very low carbon ferrous castings will require special processing. What size range of parts can be produced by the Lost Foam process? Lost Foam castings can be produced in most all metals from a fraction of a pound up to thousands of pounds. Slightly more advanced techniques are used for very large castings. What type of tooling is required and at what cost? Typically, tooling is composed of a split-cavity machined aluminum die that is the negative mold from which the foam pattern is produced. The tooling is highly specialized and must be constructed by experienced tooling manufacturers familiar with the requirements of the foam molders and foundries. Most tooling for Lost Foam patterns will compare favorably with permanent and die cast tooling. Prototype and simple tools may be in the $3000-5000 range while high-end tooling for complex or very large parts can be in the several hundred thousand dollar range. As a result of the materials used and the process stresses, Lost Foam tools can be expected to have 3 to 4 times the cycle life of permanent mold or die casting tools. What lead times can be expected when ordering a Lost Foam casting? As with all processes, lead times vary greatly depending on part complexity. Generally, 8 to 16 weeks is typical for completed tooling and first castings produced. After casting approval, 6 to 12 weeks is typical for production run startup. Rapid prototyping methods can produce castings in as little as 2 to 3 weeks. What size range of parts can be produced by the Lost Foam process? Lost Foam castings can be produced in most all metals from a fraction of a pound up to thousands of pounds. Slightly more advanced echniques are used for very large castings. What is the cost of using the Lost Foam process? Lost Foam castings are generally more expensive than forged parts, or parts made by other casting processes. The value inherent in the Lost Foam process v ersus other processes is seen in tighter tolerances, weight reduction and as-cast features which all results in less machining and cleanup time. Many castings that require milling, turning, drilling and grinding can be made in the Lost Foam process with only . 020† . 030† of machine stock. It is imperative that the features to be cast are discussed by all parties to determine the net finished product cost. What quantities need to be made to make the Lost Foam process practical? The answer, simply, is not as many as you would think. Tooling amortization is a key factor in this determination. Potential overall savings for your application will aid in your decision. Generally, 500-1000 pieces per year is the minimum production run to be economical. Prototyping runs, however, may be as few as 3-5 pieces for Fabricated Foam patterns or 20-100 pieces for Quick-Cut CNC machined aluminum tooling. Application Lost foam casting  is used mostly for automotive applications. Cast iron, aluminum alloys, steels, nickel and in some cases stainless steel and copper alloys are cast in this process. The flexibility of LFC is useful in making complicated casting assemblies for automotive and other metal cast like cylinder heads, weldments, pump housing, Manifolds for automobile, machine bases, automobile-body-dies, brake component. etc. This simple and inexpensive method is used in hobby foundry work. Examples of product produce from lost foam casting http://www. glmmarine. com/ManifoldArticle. html Superior Marine Manifolds Agricultural Equipment Part / Farm Machinery Part Product Description Detail Feature: Product Name: Agricultural equipment part / Farm machinery part   Materials: Grey iron, Ductile Iron, High Chrome iron, resistent ironcarbon steels, alloy steels, stainless steels, High Manganese steel   Items: FOB NingBo or Shanghai Place of Origin: Ningbo, China Software for specification drawings: PDF, Auto CAD, Solid work, JPG, ProE   Main production equipments: Wax injection, CNC-machine, machine-center, Heat treatment Furnace lost foam casting for yacht gas piping Specifications 1). lost foam casting 2). reliable product quality 3). on time delivery 4). excellent after-sale service 5). 3D design It is designed for the yacht or the ships gas exhaust piping. Materials: pig iron 250 Surface treatment: galvanizing, and spray-paint Weight: 19. 5 KG Color: black Process: lost foam casting Dimensions:360mm*167mm*102mm Certificate: ISO9001:2000 Advantages * Foam is to carve glue and manipulate Can be used for precision castings of ferrous and non-ferrous metals of any size. * Fewer steps are involved in lost foam casting compared to sand casting. * Core making is eliminated. * Binders or other additives and related mixing processes are eliminated. * High dimensional accuracy can be achieved and thin sections can be cast (i. e. 3 mm). * There is lower capital investment. * The flasks used are less expensive and easier to use because they are in one piece. * The need for skilled labor is reduced. * Multiple castings can be combined in one mould to increase pouring efficiency. * Lower operating costs can be achieved for appropriate castings. Complex castings, particularly internal sections, which require high dimensional accuracy and have thin sections, can be produced very cost effectively in comparison with to conventional sand moulding processes. * Fettling and machining is minimized due to high dimensional accuracy and the absence of parting lines or core fins. * The shakeout process is simplified and does not require the heavy machinery required for bonded sand systems. * High levels of sand reuse are possible. As little as 1-2% of the sand is lost as a result of spills. Periodically a portion of sand may need to be removed or reclaimed to avoid the build-up of styrene. * Complex components can be formed where other casting processes would require multiple components to be assembled. Excellent dimensional tolerances for precision casting. * Lower production cost than traditional Green Sand casting. * Castings can be made from 1 pound up to thousands of pounds with no size limitations. * Lost Foam is an environmental ly friendly process. * The sand is un-bonded and can be recovered and re-used at a low cost. * There is lower capital investment. Disadvantages * pattern costs can be high for low volume application * patterns are easily damaged or distorted due to their low strength. If a die is used to create the patterns there is a large initial cost * The pattern coating process is time-consuming, and pattern handling requires great care. Good process control is required as a scrapped casting means replacement not only of the mold but the pattern as well. What type of tooling is required and at what cost? Typically, tooling is composed of a split-cavity machined aluminum die that is the negative mold from which the foam pattern is produced. The tooling is highly specialized and must be constructed by experienced tooling manufacturers familiar with the requirements of the foam molders and foundries. Most tooling for Lost Foam patterns will compare favorably with permanent and die cast tooling. Pr ototype and simple tools may be in the $3000-5000 range while high-end tooling for complex or very large parts can be in the several hundred thousand dollar range. As a result of the materials used and the process stresses, Lost Foam tools can be expected to have 3 to 4 times the cycle life of permanent mold or die casting tools. What â€Å"as-cast† tolerances can be expected? Typically, a linear tolerance of +/-. 005 inches/inch is standard for the Lost Foam process. This tolerance will vary depending on part size, complexity and geometry. Subsequent straightening or coining procedures will often enable even tighter tolerances to be held on critical dimensions. A targeted effort between the foam pattern producer, the casting producer and the casting user will often result in a Lost Foam casting that substantially reduces or completely eliminates previous machining requirements. Diameter Tolerance 0-1 in. [ or -]0. 007 in. 1-3 in. [ or -]0. 15 in. 3-6 in. [ or -]0. 025 in. In the case of diameters split by glue lines, 0. 005-0. 010 in. should be added dependent on foam size. Linear Tolerance 0-2 in. [ or -]0. 005-0. 10 in. 2-5 in. [ or - ]0. 010-0. 20 in. 0-5 in. with glue lines [ or -]0. 025-0. 035 in. Flatness Tolerance Area 3 x 3 in. [ or -]0. 007 in. Area 10 x 10 in. [ or -]0. 015-0. 020 in. More than 10 in. [ or -]0. 030-0. 050 in. Flatness can be affected by the foam, foam geometry, molding cycle control and foam removal. True Position Tolerance 0-2 in. 0. 025 in. 2-4 in. 0. 030 in. 4-10 in. 0. 030-0. 60 in. 10 in. 0. 080 in. Limitations 1. For low volume applications, the pattern costs are relatively high, therefore in order to increase the substantial economic benefits and decrease the pattern costs, only bulk quantities should be produced. 2. Due to their low strength, the patterns are very easily damaged and/or distorted. 3. There is a very high initial cost if a die is used to create the patterns. 4. The coating process is very time consuming as the pattern handling requires great care. Design considerations: Ensure that there is adequate material: Insufficient material usually leads to incomplete castings in the manufacturing of parts. It is important to calculate the volume of all areas f the casting while also accounting for shrinkage. Consider the Superheat: Superheat is the temperature difference between the metal at pouring and freezing. An increase in the superheat can increase the fluidity of the material for the casting, which can assist with its flow into the mold. Insulate Risers: The riser should be the last to solidify because it is the reservoir of molten material for the casting. Therefore insulating the top will greatly reduce cooling in the risers from the steep temperature gradient between the liquid metal of the casting, and the room temperature air. Consider V/A Ratios: V/A ratio represents the volume to surface area ratio. In casting, sections with low volume to surface area will solidify faster than sections with higher volume to surface area. It is therefore important to consider the V/A ratios in order to avoid premature solidification of the casting and the formation of vacancies. Heat Masses: Sections of the casting with low V/A ratios should be located further away from the risers as this will ensure a smooth solidification of the casting. It is important to avoid large heat masses in locations distant to risers. Sections of the Casting: A heavy section should not be fed through a lighter one. In the manufacturing process, the flow of material is very important. Prevent Planes of Weakness: After the solidifications of castings, columnar grain structures pointing toward the center develop in the material. This causes the sharp corners in the casting to develop a plane of weakness. This is prevented by rounding the edges of sharp corners. Reduce Tubulence: Turbulence is bad because it traps gases in the casting material and causes mold erosion. It can be reduced by the design of a gating system that promotes a more laminar flow of the liquid metal. FUTURE EPF can safely be incinerated and will yield only carbon dioxide and water if the procedure is handled correctly, but the trend has been to recycle it wherever possible. EPF can be recycled into  concrete,  egg cartons, office products, foam insulation, and garbage cans. Unfortunately, only one percent of the 11 billion kilograms of EPF thrown away each year is being recycled. The National Polystyrene Recycling Company, which consists of seven major corporations, including Amoco, Dow, and Mobil, plans to increase this to 25 percent by 1995 by focusing on big users of EPF—fast food outlets and college dining establishments. Since the Montreal Protocol of 1988, new research has focused on ways to reduce CFC use, and on developing alternative blowing agents that will not harm the ozone layer. Recent developments include a process that uses pressurized carbon dioxide to produce smaller, more uniform cells. These in turn provide a foam that is stronger and smoother than earlier foams. All this will bring us an un-imaginable shape that can be use for EPF pattern which will aid quality, best and control of casting. STRATEGY EMPLOYED TO THE IMPROVEMENT OF LOST FOAM CASTING CAPABILITY 1. The major strategy employed is the partnership of governments, universities and industries in research and development of metal casting in general and cost of research is shared. Examples are U. S. Department of Energy and metal casting industry industries of the future (IOF), University of Alabama-Birmingham and over 30 universities and industry partners. This strategy has significantly improved the use of LFC in the past years. Emphasis is based on universities research with strong industry participation. The direct results of LFC researches are quickly applied by these positioned partner industries and results from the various applications are evaluated and analyzed. 2. Another strategy used is introducing hundreds of students to metal casting industries were they are well trained and becomes more innovative bringing latest technical knowledge and processes. this has tremendously improve state-of-the-heart technology in improving LFC in the past years. 3. Material(s) selection requires a specific type of manufacturing process(s) and different type(s) of casting techniques. The casting materials specific heat as well as that of the mold material will be influential in controlling the thermal gradients in the system. e. g. melts  fluidity and flow. A material high heat of fusion will take longer to solidify and may improve flow characteristics within the casting. 4. Gases being expelled by the material during solidification can be eliminated by a proper venting system in the mold. This can be planned out during the manufacturing design phase of the casting process. WAYS TO IMPROVE LOST FOAM CASTING 1. Development of computational fluid dynamics tool for modeling the blowing and steaming of expandable polystyrene (EPS) pattern for lost foam casting(mathematical tool). it allows analytical approach to systematically design EPS pattern molds that produces higher quality pattern with reduced lead-time and expense. http://www. arena-flow. com 2. Reduction of porosity and fold defects has improve production efficiency, mechanical properties and marketability of lost foam casting. 3. The combination of LFC with 3DP (three dimensional printing) to eliminate machining of mold contours and manual process of drilling and finishing steam holes, i. e. repeatedly printing thin layers of bonding materials on a thin layer of powder to build up a tool(mould) shape from computer-aided design(CAD) 4. Complex and detailed passages and other features are cast directly e. g. oil galleries, crank case ventilation channels, oil drain back passage, coolant passage etc are cast directly into cylinder blocks 5. The use of Flow Particle Image Analyzer to analyzed the wet slurry (prior to its application on the foam pattern) by measuring ceramic particle size and shape. 6. Single and multiple air gauge developed for rapid determination of pattern dimension 7. Compaction gauges were developed to measure sand density in cavities during pattern compaction 8. Distortion gauge to determine when and under what conditions pattern distortion occurs during compaction 9. Developed procedures to measure liquid absorption characteristics of liquid pattern pyrolisis 10. Developed instruments to measure gas permeability 11. X-ray radiography was developed to measure time of fill and also to inspect casting qualities and defects in LFC. Material selection is another way to improve the capability for example: * Certain materials react, (particularly in a molten state), a certain way with other materials they may encounter during the casting process. This should always be a consideration. For example liquid aluminum will react readily with iron. Iron ladles and surfaces contacting the molten aluminum can be covered with a spray-on ceramic coating to prevent this. * When selecting a specific type of manufacturing process, remember that certain materials are more applicable to different types of casting techniques than others. * The casting materials specific heat will as well as that of the mold material will be influential in controlling the thermal gradients in the system. Different materials will factor heavily on the melts  fluidity * A material high heat of fusion will take longer to solidify and may improve flow characteristics within the casting * When manufacturing a casting an alloy that freezes over a tempe rature range problems may occur due to the solid phase interfering with the liquid phase -both of which will be present within the temperature range. To help reduce this problem an alloy with a shorter solidification temperature range may be selected to manufacture the casting with. Or select a mold material with a high thermal conductivity, which could reduce the time spent in this range by increasing the cooling rate. Conclusion using the method of casting by lost foam patterns, we can obtain pieces for industry and ornamental elements / applied art, with complex layouts and different sizes, without the danger of offsetting * using the method of casting by lost foam patterns we can obtain pieces with weights between a few kilograms and tenths of tones, with wall’s width between 1 mm and 50 mm, made of different alloys: ferrous (cast iron and steel) and non ferrous (basic alloys of Al, Cu, Mg); * using the method of casting by lost foam patterns we can obtain pieces with a l ow consumption of materials and energy; * The method of casting by lost foam patterns can be used also for: structural changes and superficial alloying of the pieces; obtaining composite materials with powders insertion and the guidance of hardening by using some active powders, internal coolers or exterior coatings. The gases resulted from the thermal destruction of the polystyrene are toxic for the human being and can generate negative effects on the environment, aspect which imposes the obligation of maintaining under control both the evacuation in the working environment as well as the evacuation in the atmosphere. REFERENCES Design for manufacturability handbook   By James G. Bralla , McGraw-Hill Professional, 1999 Technology ; Engineering Energy research at DOE, was it worth it? : energy efficiency and fossil energy research 1978 to 2000, National Academies Press, 2001 Business ; Economics Fundamentals of Modern Manufacturing: Materials, Processes, and Systems  By Mikell P. Groover, John Wiley and Sons, 2010 Technology ; Engineering A textbook of manufacturing technology: (manufacturing processes)   By R. K. Rajput, Firewall Media, 2008 Technology ; Engineering John Campbell, Butterworth-Heinemann, 2003   Technology ; Engineering   http://www. technalysis. com/lost_foam_casting. aspx http://civil-engg-world. blogspot. com/2011/02/polystyrene-ps. html http://www. achfoam. com/Lost-Foam-Casting-Process. aspx http://www. madehow. com/Volume-1/Expanded-Polystyrene-Foam-EPF. html http://www. alibaba. com/product-gs/411205184/lost_foam_casting_for_yacht_gas. html? newId=411205184;pn=1;pt=10;t=12;cids= http://nb-pft. en. made-in-china. com/product/HMZxTjlJqEDn/China-Agricultural-Equipment-Part-Farm-Machinery-Part. html http://www. nyserda. org/programs/industry/CaseStudies/lost%20foam. pdf