Lost Foam Casting free essay sample

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 or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page 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.