Metal Casting Technologies : MCT-1STQRT-2017
24 www.metals.rala.com.au METAL Casting Technologies 1st Quarter 2017 25 TECHNICAL FEATURE may be portable such that the design data can be readily obtained on site, as in the example outlined earlier in MCT  relating to the emergency replacement of a corroded end cover for a cooling system in a ship stationed out at sea. For owners of vintage cars or museums seeking to restore historic equipment into working order 3D mould printing offers the only affordable production route e.g. producing a replacement engine for a 1912 motor car . An additional advantage of 3D Sand Printing is reduced storage. Only digital files are needed, no patterns or core- boxes. A foundry only needs to print a mould when the spare or replacement part is required by a customer. Furthermore, customers do not have to carry an excessive stock of spare parts, saving costs as well as space. Part supply can also be easier in that, if a machine is available, a mould can be printed anywhere in the world for local production further saving the time and costs of import and transport. Clearly 3D Sand Printing is best suited to one-offs or for short runs of relatively complex-shaped castings. A recent study , which was based on an assessed complexity factor of a casting design, has examined the cost-effectiveness of the technique. It was concluded that, at current equipment and operation costs, it is economically suitable for short runs (<45) of castings with low complexity and for runs of 1000 for highly complex designs. The method can also be used to produce complex cores for use with conventional moulds. Currently for commercial 3D sand systems furan is used as the binder but there is also interest in the possible use of phenolic or urethane resins and in the compatibility of the various binding systems during sand reclamation . There is also interest in comparing the behaviour of 3D printed moulds with conventionally produced moulds in terms of strength, binder burn-out behaviour and erosion during pouring, gas evolution, permeability, and casting quality [e.g. 11,12]. It has been found that a printed binder system generates less gas due to the lower binder content. It also offers moulds with improved mechanical properties and higher temperature shape retention than for conventional moulds . n CO-AUTHORS Nattinee Valun-araya Nattinee Valun-araya is currently Production Engineer at Speed 3D Mold Co. Ltd. She studied at Mahanakorn University of Technology in Thailand from 1993-1997 obtaining a B.Eng. degree in Mechanical Engineering. Following work as a Process Engineer at Chaophaya Foundry, Samutprakarn she moved to Canada to study Aircraft Maintenance Engineering at the British Columbia Institute of Technology and worked at Cascade Aerospace until 2011. She then returned to Thailand to help start up Speed 3D Mold. email@example.com Ongkarn Chantarasukkasem Ongkarn Chantarasukkasem is currently Additive Manufacturing Manager at Speed 3DMold Co. Ltd. He holds a Bachelor degree in Marine Engineering from the Merchant Marine Training Centre in Thailand and a Master of Engineering degree from Mahanakorn University of Technology, Thailand. Following experience in marine engineering at K Line (Thailand) Ltd, he moved to study Marine Engineering at the British Columbia Institute of Technology and to work as a marine engineer for the Upper Lake Group in Canada. In 2010 he became involved in setting up Speed 3D Mold. firstname.lastname@example.org REFERENCES 1. “Thoroughly Modern Metal”. D. Allen, Metal Casting Technologies (2013) Vol. 59 No.1 March pp.16-22 . 2. “Added Attraction”. D. Allen, Metal Casting Technologies (2015) Vol.61 No.1 March pp. 16-21. 3. “3D Printing – Material Wise to Grain Size”. E . Redahan, Materials World (2014) Vol.22 No.1 January pp.10-11. 4. “3D Printing offers a new solution to an old technique”. Metal Casting Technologies (2015) Vol. 61 No.1 March pp.22 -23. 5. “Technical Application Guide: FDM for Sand Casting”. Stratasys Publication 12pp. www.stratasys.com/solutions/additive- manufacturing/toolin/sandcasting 6. www.exone.com/resources/casestudies 7. “Thailand”. J.T.H . Pearce, Metal Casting Technologies (2014) Vol.60 No.3 September pp. 27-29. 8. www.3dealise.com 9. “Quantifying the Role of Part Design Complexity in Using 3D Sand Printing for Molds and Cores”. E .S . Almaghariz et Al. International J. of Metalcasting (2016) Vol.10 No.3 July pp.240-252. 10. “Advancement in Materials for Three-Dimensional Printing of Molds and Cores”. J. Thiel, S. Ravi & N. Bryant. Proceedings of the 72nd World Foundry Congress, 21-25 May 2016, Nagoya, Japan. Paper O-47 2pp. 11. “A Comparison of Binder Burnout and Mechanical Characteristics of Printed and Chemically Bonded Sand Molds”. D. Snelling et Al, Proceedings of International Solid Freeform Fabrication Symposium (2014) Austin , TX, USA pp.197-209. 12. “The Effects of 3D Printed Molds on Metal Castings”. D. Snelling et Al, Proceedings of International Solid Freeform Fabrication Symposium (2013) Austin , TX, USA, pp.827-845 TECHNICAL FEATURE Introduction etal castings are produced mostly in bonded sand based moulds due to its capability to produce wide range of weight and shape of castings and relatively low cost of production. Although castings having required quality are produced by sand casting process, it suffers from some drawbacks such as chances of sand fusion and sand inclusion defects in castings; pollution in the shop floor from fines in sand and emissions from binders; problem and cost associated with used sand reclamation and disposal. To overcome these problems associated with sand casting process, lost foam casting (LFC) was developed in 1950’s, also named as full mould process, that uses an expanded polystyrene (EPS) pattern, coated with a thin refractory layer and embedded in loose unbounded sand. During pouring, the liquid metal replaces the EPS pattern by burning. Lost foam casting has been used in foundries to produce complex shaped castings and it has been reported that production of aluminium and iron alloy castings by LFC process has increased by more than 1000% over the past two decades. The process is more suitable and economic for complex shaped castings and hence cylinder head and block are being produced in mass scale by this process. Still the number of foundries using LFC is negligible in comparison to the total number of foundries in any country probably due to difficulty in handling and storage of fragile EPS patterns and risk of mould collapse during or just after pouring. Sheet Metal Mould casting (SMMC) process, has been introduced in the recent past that uses sheet metal to form the mould cavity and loose unbounded sand as the mould material. In the first step, the surface of a casting to be produced is divided into two or more parts depending on the complexity of the casting in such a manner that each part of the surface can be produced of a sheet metal by sheet metal working. Each part is produced from sheet metal by cutting to required dimensions and subsequently by bending, drawing or combination of the two. The gating system and risers are also produced from the sheet metal. These parts are assembled to produce a sheet metal mould. The whole assembly is embedded in loose unbounded sand contained in a mould box and compacted. The subsequent steps are similar to conventional sand casting. Due to use of loose unbounded sand as the moulding material, risk of mould collapse prevails in this casting process too. LFC is being used in a limited number of foundries, whereas SMMC is a new concept and still to be used in foundries. Hence comparison of the characteristics of the two processes with respect to sand casting is apparently useful for adoption in metal casting industries. Basic steps of LFC and SMMC Lost Foam Casting (LFC) Sheet Metal Mould Casting (SMMC) 1. Patterns are produced from Expanded Polystyrene (EPS) either by machining EPS blocks manually or by moulding in a aluminium die filled with EPS beads and by passing steam into the die. 2. Pattern is assembled with gating system also made of EPS. 3. A thin refractory coating formulated specially for this process is applied over pattern assembly. 4. The coated pattern assembly is placed in a moulding box and filled with loose unbounded sand so that a few inches of sand are present at the bottom of pattern assembly. The loose sand in the mould box is vibrated to have better compaction of loose sand. 5. Liquid metal is poured into the mould. During pouring, liquid metal replaces the EPS pattern by burning. 6. Cooling and shake out. 1. The surface of the casting to be produced is divided into a minimum number of parts in such a way that each part can be produced from sheet metal by cutting, bending, drawing etc. 2. Gating system is also produced from sheet metal by sheet metal working. 3. Sheet metal shapes for the casting and gating system are assembled. 4. The sheet metal assembly is placed in a moulding box similar to LFC and filled with loose unbounded sand so that a few inches of sand are present at the bottom of pattern assembly. The loose sand in the mould box is vibrated to have better compaction of loose sand. 5. Liquid metal is poured into the mould. 6. Cooling and shake out. M Comparison of Lost Foam Casting (LFC) and Sheet Metal Mould Casting (SMMC) Processes P. C. Maity, Metal Casting and Materials Engineer E-Mail: email@example.com CURRENTLY FOR COMMERCIAL 3D SAND SYSTEMS FURAN IS USED AS THE BINDER BUT THERE IS ALSO INTEREST IN THE POSSIBLE USE OF PHENOLIC OR URETHANE RESINS AND IN THE COMPATIBILITY OF THE VARIOUS BINDING SYSTEMS DURING SAND RECLAMATION.