METHODING DESIGN IN SAND CASTING, HEURISTIC RULES OF METHODING DESIGN IN SAND CASTING: A REVIEW

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1 METHODING DESIGN IN SAND CASTING, HEURISTIC RULES OF METHODING DESIGN IN SAND CASTING: A REVIEW Adil Mohamed Elbasheer Ahmed 1 and Mohamed Ibrahim Shukri 2 1 Faculty of Engineering, Blue Nile University. 2 Faculty of Engineering & Technology, Nile Valley University Received May 2012 accepted after revision Feb 2013 م س ت خ ل ص ذصميم المصثاخ والمغذياخ من العناصز المهمح إلنراج مسثىكاخ خاليح من العيىب. هذه الىرقح ذخص ذجميع القىانين االسرنثاطيح لرصميم المصثاخ والمغذياخ في السثاكح الزمليح. القىانين اسرخلصد من خثزاخ المهنذسين والخثزاء وجمعد من المزجعياخ المعزوفح في هذا المجال. القىانين الرجزيثيح قسمد إلي قسمين: عناصز منظىمح الصة والمغذياخ. هذه القىانين نظمد ورصذخ تطزيقح لرسهيل اسرخذامها إلنراج مسثىكاخ عاليح الجىدج واقرصاديح. Abstract The design of gating and risering, or rigging systems as they are sometimes referred to, has been a very important task in producing good quality castings. This paper presents a compilation of common heuristic rules that are used for designing rigging systems in sand mould design. The heuristic rules are extracted from expertise of method engineers and compiled from well known published literature. The rules of thumb are divided into two sections: gating system components and riser configurations. These rules are organized and listed in a way to be easily used for producing sound and economical castings. Keywords: rigging system, sand casting, methoding design, heuristic rules. 1. Introduction The casting process basically involves pouring molten metal into a mould patterned after the part to be manufactured; allowing it to solidify and removing the casting from the mould [1]. Casting processes are widely used to produce metal parts in very economical way and to obtain complicated shapes with little or no machining [2]. The process of casting includes of two main areas: design of casted component and mould design. The mould design requires prior experience [3]. The successful casting of a pre-designed casting is vitally depending upon the skill and experience of the foundry engineer, who performs a task known as the methoding design [4]. Methoding of intricate casting is still considered as an art and not very well documented in technical literature; while few empirical equations are available [5].Heuristic rules of methoding design are becoming indispensable for producing sound casting. Sudan Engineering Society Journal, March 2013, Volume 59; No.1 33

2 HEURISTIC RULES OF METHODING DESIGN IN SAND CASTING: A REVIEW 2. Methoding design This deals with decision related to tooling including gating system, feeding system, orientation of the casting in the mould, and location of parting line. The designs carried out are based on past experience or using empirical equations that vary with material, geometry and process combination [6, 7,8]. Sound castings heavily depend on the rigging system used. Even after spending significant resource for casting development, one of the following situations may arise during regular production: Under. Over design: Borderline design: The three design conditions of feeders design are illustrated in Figure.1 3. Heuristic rules One type of shallow knowledge is heuristic knowledge. George Polya defines heuristic as "the study of the methods and rules of discovery and invention" [9]. Instead of, heuristic is the rule of thumb or empirical knowledge that gained from experience. Heuristics employed in two basic situations: A problem that may not have an exact solution, a problem that may have an exact solution, but not practical [10, 11]. Heuristic rules are applied in many fields such as engineering medicine, and other fields, by using many techniques such as expert systems and fuzzy systems[12-18]. 4. Rigging system design In sand casting process the manufacture of a part involves several steps, the first of which is the design of the part itself, and specification of the material to be used. This information is passed to methods engineer, who will choose the casting process, and then design gating and risering system, necessary to get the molten metal into all regions of the part to produce a sound casting. Ravi identified seven elements associated with rigging system design as reported in [19]. The terms gating system referred to all passage or channels through which the metal enters a mould cavity [20]. Figure.2 shows the elements of gating system: basin or cup. sprue or downsprue, runners, gates or in-gates, and extension or blind ends. There are three types of gating system, top gate bottom gate and side gates. Nearly 40% of casting defects are attributed to faulty design of gating and poor pouring practice [21-23] Riser (feeder) acts as a liquid reservoir provides liquid to the casting during solidification, serves as a heat reservoir, and creating a temperature gradient that induces directional solidification [24, 25]. Feeders appended to the casting at suitable locations are designed so that the shrinkage defects are contained within the feeders. Figure 1: (a) Over design, (b) borderline design (c) under design of feeder Figure 2: (a) Cup and sprue (b) Runner,in-gates and well shape 5. Heuristic rules of rigging system The following common rules of thumb that aid the design of rigging system components are compiled from expertise and well known published literature. 34 Sudan Engineering Society Journal, March 2013, Volume 59; No.1

3 Adil Mohamed Elbasheer Ahmed and Mohamed Ibrahim Shukri 5.1Gating system rules The rules of thumb of gating system elements are organized and listed as follows: 1. Part orientation rules: Orientation of the part refers to the cavity in the mould in the shape of the part that is going to be casted. The rules are[26, 27]: Orient the part so that the large part of the casting is relatively low. Place open space down. Orient the part so that the thin part of the casting is low [28]. 2. Parting line rules: Place the parting line at the cross-section of the largest area of the casting Place the parting line as low as possible relative to the casting [29]. The internal angle of the mould walls at the parting line is less than 5 0. It divides the part surface into separate regions, each produced by a different mould segment. 3. Cups rules: Pouring cups selection, whether external or cut in the moulding sand. Basin separates dross and slag from molten metal. Pouring of molten metal in the cup to be carried out at a point that is remote from the sprue hole Skimmer, filter or delay screen can be used in the cup to provide cleaner metal into the mould 4. Sprue rules: The sprue should be sized to limit the flow rate of molten metal. Rectangular cross-section sprue better than circular ones with same cross-section area. For non-ferrous, rectangular tapered is recommended. Generally, rectangular sprue is used to avoid vortex. Round sprue with small height and radius do not cause vortex. Choke area controls the sizing of gating component. Choke area can be calculated using the following formula [30]. Where: W C is weight of the casting, W R is weight of the riser, t is pouring time, ρ is density of metal, S L is sprue height, and C is constant Height of the sprue (S L ) is determined by the casting and the top riser height For top gate H S = 0, for parting line gate H S = half of casting height and for bottom gate H S is the height of the casting. H F is feeder height Sprue should be located as far from the gate as possible. The sprue should be located centrally on the runner with equal gates on each side. The sprue should be tapered by approximately 5% minimum to avoid aspiration and falling of metal. Unclean metal must be washed out in a well below the sprue. Well area for sprue box is 2-3 times the choke area. Sudan Engineering Society Journal, March 2013, Volume 59; No.1 35

4 HEURISTIC RULES OF METHODING DESIGN IN SAND CASTING: A REVIEW The well, is about 1.27 cm deeper than runners. 5. Runner rules: Standard sizes and shapes are used for runners. Rectangular cross-sections are preferred in sand mould. Runners run along the part for long part. Sharp edge must be fillet. Blind ends are 2.5 to 30.4 cm long. Runners are sized using gating ratio, for copper alloy range 1:2:2-1:4:4 and for aluminum 1:2:1-1:4:2 gating ratio is choke: runner: in-gate area [19]. The best thing is to keep part of the runner above and part of it below. 1.5.Gate rules: Woldman asserts that a good gate design is independent of the alloy cast [31]. Gate into thick regions. Rectangular gate are mostly used. Orient the gates in the direction of the natural flow path. Fillets between the gates and the casting are desirable. A slight flare between the castings is desirable. The number of gates is determined by casting base feature. The maximum gate thickness should be cm. The first gate located at a minimum 3.81 cm distance away from sprue for small castings and cm for large castings. Minimum gate length of 1.9 cm for small casting and cm for large casting [20] Feeder rules The first six rules are general rules, suggested by Cambell [32]. The feeder must solidify at the same time or later than the casting. The feeder must contain sufficient liquid to meet the volume -contraction requirements of the casting. The junction between the feeder and the casting should not create a hot spot. There must be path to allow feed to reach feeding point. There must be sufficient pressure differential requirement to cause the feed material to flow in the right direction. There must be sufficient pressure at all points in the casting to suppress the formation of cavities. Feeders are attached to heavy sections of castings and hot spot [33]. Use the direction of the thermal gradient to detect the hot spot [20] Use of side risers is common for thin wall casting. Side feeders are usually located on top of the gates. Top feeders are used for thick casting. Top feeders are located on bosses, away from the gates. If the top feeder or side feeder is open to atmospheric pressure the height to diameter ratio is 1:1 to 2:1. 36 Sudan Engineering Society Journal, March 2013, Volume 59; No.1

5 Adil Mohamed Elbasheer Ahmed and Mohamed Ibrahim Shukri Feeders considered as a liquid and heat reservoir. Feeders are sized by the volume fed. In case of multiple risering, each riser is considered to be feeding a part of the casting. If it is necessary to use multiple feeders, they should be located at cm apart. If two nearby thick sections are fed, thin section in between may contain porosities. The problem may be avoided by risering one thick section and chilling the other. The maximum feeding distance depends upon whether the alloy is of the short freezing range or long freezing-range. The cross section of the feeder is slightly larger than the section it feeds. casting, SF is the shape factor, V R and V C is the weight of riser, and casting respectively. 6. Conclusion A collection of gating system and feeders design common heuristic rules are presented in a way that is to be easily used. From the rules of gating system design, it can be observed that the geometric features of the casting such as casting boundaries, parting line, orientation of casting and flow path are essentially for the design of gating system. Also, from the feeders rules of thumb it can be observed that, beside the geometric feature of casting, solidification rate, directional solidification and location of gating system are important factors of feeders design The design of feeder based on Chvorinov rules to ensure adequate feeding and have been widely investigated [34,35,36], which states that the total freezing time (T f ) in the casting of the volume (V) given by: ( ) Where B is a constant for given metal and mould condition, A is the surface area. Type of feeders and location of dimension as shown in Figure 3. For the design of feeder, N.R.L method may be used for thin section casting as shown in Figure 3 Figure 3 Riser volume to casting volume, plotted equation originally from [37] based on data from [38] Where: L is the length of the casting, W is the width of the casting, T is the thickness of the Sudan Engineering Society Journal, March 2013, Volume 59; No.1 37

6 HEURISTIC RULES OF METHODING DESIGN IN SAND CASTING: A REVIEW References 1. Kalpakjian, S., Manufacturing and Technology, Addison-Wesley Publishing Company,(book) Guleyupoglu, S, Casting Process Design Guidelines [On line]: /transaction/ df.,pp , sighted on July B. Ravi, Design for Casting, Presented at SOURECON`99, Hyderabad, Organized by the Institute of Indian Foundry, Brain, Knight, Cowell and Preddy, an Object-Oriented Support Tool for the Design of Casting Procedures. Technical paper [On-line]. 5. B. Ravi, Casting Design Knowledge Management, 51 st Indian Foundry Congress, R. G. Chougule, B. Ravi, Collaborative design for manufacture-model casting applications, 8 th IEEE International conference on intelligent engineering system, ClujNapoca Romania, September S Ou, K. D Carlson, R. A. Hardin, Development of new feeding distance rules using casting simulation: Part II, the new rules, metallurgical and materials transactions B, Vol. 33B, pp , R.C. Greese, Benchmarking and Lead Time Reduction, AMC Benchmarking Project Report, West Virginia University, Oct George F Luger, Artificial Intelligence: Structures and Strategies for Complex Problem Solving, 5 th Ed., Addison Wesley, Giarratano and Riley, Expert System: Principles and Programming, 4 th Ed., Course Technology Publisher, Efraim Turban, Decision Support and Expert Systems: Management Support Systems, 2 nd Ed., Macmillan publishing Company, Mirit Shamir, Lior Shamir Mary H. Durfee The application of fuzzy logic to the precautionary principle, Springer Science Media B.V., Published online April T. Liao Fuzzy reasoning based automatic inspection of radiographic welds, Journal of Intelligent Manufacturing, Vol.15 pp.69-85, Adil M. Elbasheer Ahmed A featurebased and fuzzy expert system for designing rigging systems of castings, PhD Thesis, Bouhiuhe, lahreche and Moussaoui, Quality monitoring using principle component analysis and fuzzy logic application in continuous casting process, American Journal of Applied Science Vol.4(9) pp , S. H., P. Webb, A hybrid fuzzy knowledgebased expert system and genetic algorithm for efficient selection and assignment of material handling equipment, expert sysrem with applications,vol.36, pp , O. Maeda, Y Cao, Y. Altintas, Expert spindle design system, International 38 Sudan Engineering Society Journal, March 2013, Volume 59; No.1

7 Adil Mohamed Elbasheer Ahmed and Mohamed Ibrahim Shukri Journal of machine tools & manufacture Vol. 45, pp , A. Iqbal, N. U. Dar., N. he, M. M. I. Hammouda, Self developing fuzzy expert system: a novel learning approach, fitting for manufacturing domain, J IntellManuff Vol. 21, pp , Ravi, Digital Methoding Child's Play? Yes and No., Technical Paper for Presentation at Steel and Alloy Steel Castings (SAS- 2001), Mumbai, April 14-15, A. M. Mikailov, Metal Casting, (book) B. Ravi, Srinivasan, Computer Aided Gating and Metal Rising Simulation, Technical Paper Proceedings of the 40 th Annual convention of IIT,Madrass,14-16 Feb J. Gerin Sylvia, Cast Metal Technology, (book), B. Ravi and M.N. Srinivasan, Casting solidification analysis by modulus vector method, Int. Journal of cast metals Research, Vol. 9,pp. 1-7, Steel Founders', Society of America, Feeding &Risering Guidelines for Steel Castings, Steel Founders' Society of America, Steel Founders' Society of America, Risering Guidelines for Steel Castings, Steel Founders' Society of America, S. Guleyupoglu and J. L. hill, Parting direction and parting plane selection criteria for sand casting. AFS transactions, 103: , L.l. Chen, S.Y. CHOU and T.C Woo Parting directions for mould and die design, Computer-Aided Design,Vol.25 PP , Elbasheer, an Expert System for Designing Gates & Risers for Small and Medium Size Castings, M.Sc. Thesis, Atbra-Sudan, R. M., The missing algorithms to fully computerize gating, risering and tooling manufacture, Part 1. AFS Transaction, Vol. 97, pp , Shukri and Elbasheer, An expert system for designing gates and risers for small and medium size castings, Sudan Engineering Society Journal, Vol. 52,May American Foundry's Society, Recommended Practice for Sand Casting Aluminum and Magnesium Alloys, Des Plaines, II,2 nd edition, Cambell, John, Castings. Oxford: Butterworth-Heinemann, Gerin Sylvia, J. Cast Metals Technology, American Foundry Society And Research Institute (book), J. Cambell, Casting Reprinted series, Butterworth Heinemann, Oxford, UK N. Sirilertworakul, PD. Webster and T.A. Dean,Computer prediction of location of heat centers in castings, Material Science and Technology, Vol.9, pp , J. Berry, V. Kondic and G Martin, Solidification times of simple shaped castings in mould design, Modern Castings, Vol. 36,pp, W.D. Spiegelberg, Computation of Solidification Gradient in Cast Steel Sections, Ph.D. Thesis, Department of Sudan Engineering Society Journal, March 2013, Volume 59; No.1 39

8 HEURISTIC RULES OF METHODING DESIGN IN SAND CASTING: A REVIEW Metallurgy and Materials Science, Case Western Reserve University, H.F. Bishop,E.T. Myskowski and W. S. Pellini, A simplified Method for Determining Riser Dimensions, AFS Transactions, Vol. 63, pp , Sudan Engineering Society Journal, March 2013, Volume 59; No.1