A Review On Casting Defect Minimization Through Simulation
IJSRD - International Journal for Scientific Research & Development Vol. 3, Issue 11, 2016 ISSN (online): 2321-0613A Review on Casting Defect Minimization Through SimulationMahipalsinh G. Jadeja1 Manojkumar V. Sheladiya2 Mayursinh Gohil31M.E. Student 2Assistant Professor 3Production Manager1,2,3Atmiya Institute of Technology and Science, Rajkot, Gujarat, IndiaAbstract— The objective of this paper is to find defects incasting process. Causes for shrinkage defects are discussedand remedies for the shrinkage defect would help to improvethe quality of casting product. By proper casting technique,improving feeding design, proper location of ingates andrisers will reduce the shrinkage defect. Simulation insoftware SOFTCAST helps to detect shrinkage defect andusing discussed remedies help to reduce rejection rate.Key words: Casting, Casting Defect, Shrinkage, SimulationI. INTRODUCTIONCasting is a process which carries risk of failure occurrenceduring all the process of accomplishment of the finishedproduct. Hence necessary action should be taken whilemanufacturing of cast product so that defect free parts areobtained. Mostlycasting defects are concerned withprocess parameters. Hence one has to control the processparameter to achieve zero defect parts. For controllingprocess parameter one must have knowledge about effect ofprocess parameter on casting and their influence on defect.A well designed feeding system is very importantto ensure the better quality of castings. Design of feedingsystem also involves the decision about correct location ofrisers and number of risers to be used. For new castings orthe castings having very high rejection rates, modification offeeding system design is of prime importance. Thesemodifications are done manually which involves huge time,cost and other resources. Casting simulation can effectivelyovercome these difficulties and provide powerful tool forprediction of the process growth. Simulation of existingfeeding system provides the locations of the points wherechances of defects are high. This information can be used tomodify the feeding system design. Feeding systems aremodified and simulated unless satisfactory results areobtained.II. CASTING DEFECTSA. ShrinkageShrinkage defects occur when feed metal is not available tocompensate for shrinkage as the metal solidifies. Shrinkagedefects can be split into two different types: open shrinkagedefects and closed shrinkage defects. Open shrinkagedefects are open to the atmosphere, therefore as theshrinkage cavity forms air compensates. There are two typesof open air defects: pipes and caved surfaces. Pipes form atthe surface of the casting and burrow into the casting, whilecaved surfaces are shallow cavities that form across thesurface of the casting.Closed shrinkage defects, also known as shrinkageporosity, are defects that form within the casting.Isolated pools of liquid form inside solidifiedmetal, which are called hot spots. The shrinkage defectusually forms at the top of the hot spots. They require anucleation point, so impurities and dissolved gas can induceclosed shrinkage defects.1) Possible CausesThe density of a die casting alloy in the molten state is lessthan its density in the solid state. Therefore, when an alloychanges phase from the molten state to the solid state, italways shrinks in size. This shrinkage takes place when thecasting is solidifying inside a die casting die. At the centreof thick sections of a casting, this shrinkage can end up asmany small voids known as ‘shrinkage porosity’.If the shrinkage porosity is small in diameter and confinedto the very centre of thick sections it will usually cause noproblems.However, if it is larger in size, or joined together, it canseverely weaken a casting. It is also a particular problem forcastings which need to be gas tight or water tight.2) RemediesThe general technique for eliminating shrinkage porosity isto ensure that liquid metal under pressure continues to flowinto the voids as they form.III. BLOWHOLEBlowhole is a kind of cavities defect, which is also dividedinto pinhole and subsurface blowhole. Pinhole is very tinyhole. Subsurface blowhole only can be seen after machining.Gases entrapped by solidifying metal on the surface of thecasting, which results in a rounded or oval blowhole as acavity. Frequently associated with slag’s or oxides. Thedefects are nearly always located in the cope part of themould in poorly vented pockets and undercuts.1) Possible Causes Inadequate core venting Excessive release of gas from core Excessive moisture absorption by the cores Low gas permeability of the core sand2) Remedies Improve core venting, provide venting channels, andensure core prints are free of dressing Reduce amounts of gas. Use slow-reacting binder. Reduce quantity of binder. Use coarser sand ifnecessary. Apply dressing to cores, thus slowing down the rate ofheating and reducing gas pressure. Dry out cores and store dry, thus reducing absorption ofwater and reducing gas pressure.B. Sand BurningBurning-on defect is also called as sand burning, whichincludes chemical burn-on, and metal penetration.The defect occurs to a greater extent in the case of thickwalled castings and at high temperatures.The high temperature to which the sand is subjected causessintering of the bentonite and silicate components.In addition, the always present iron oxides combine with thelow-melting-point silicates to form iron silicates, therebyfurther reducing the sinter point of the sand. Sintering andmelting of the impurities in the molding sand enable theAll rights reserved by www.ijsrd.com380
A Review on Casting Defect Minimization Through Simulation(IJSRD/Vol. 3/Issue 11/2016/090)molten iron to penetrate even faster, these layers thenfrequently and firmly adhering to the casting surface.1) Possible Causes Lustrous carbon content too low Proportion of low-melting-point substances too high Uneven mould compaction Gating and pouring practice Uneven distribution of inflowing metal with resultantover-heating Temperature of liquid metal too high2) Remedies Increase proportion of lustrous carbon producer. This in-creases the amount of coke as well as theamount of lustrous carbon, which then results inpositive separation between mould and metal. Use purer silica sands or, if necessary, add new sand.Reduce dust content. If necessary, reduce the amount ofbentonite. Even out incoming metal flow Reduce pouring rateC. Sand InclusionSand inclusion and slag inclusion are also called as scab orblacking scab. They are inclusion defects. Looks like thereare slag’s inside of metal castings.1) Possible Causes Low core strength Excessive core mismatching Pouring rate too high, with heavy impact against mouldwall surface resulting in erosion Ladle too far above pouring basin Pouring time too long2) Remedies Increase the strength of the cores. Use greaterproportion of binder. Compact cores more evenly and effectively and, ifnecessary, inject gas more evenly Avoid core mismatching.D. Cold Lap Or Cold ShutCold lap or also called as cold shut. It is a crack with roundedges. Cold lap is because of low melting temperature orpoor gating system.When the metal is unable to fill the mould cavity completelyand thus leaving unfilled portion called mis-run. A coldshunt is called when two metal streams do not fuse togetherproperly.1) Possible Causes Lack of fluidity in molten metal Faulty design Faulty gating2) Remedies Adjust proper pouring temperature Modify design Modify gating systemE. MisrunMisrun defect is a kind of incomplete casting defect, whichcauses the casting uncompleted. The edge of defect is roundand smooth.When the metal is unable to fill the mould cavity completelyand thus leaving unfilled portion called misrun. A cold shuntis called when two metal streams do not fuse togetherproperly.1) Possible Causes Lack of fluidity in molten metal Faulty design Faulty gating2) Remedies Adjust proper pouring temperature Modify design Modify gating systemF. Gas PorosityThe gas can be from trapped air, hydrogen dissolved inaluminum alloys, moisture from water based die lubricantsor steam from cracked cooling lines.1) Possible Causes Metal pouring temperature too low. Insufficient metal fluidity e.g. carbon equivalent toolow. Pouring too slow. Slag on the metal surface. Interruption to pouring during filling of the mould. High gas pressure in the mould arising from moldingmaterial having high moisture and or volatile contentand/or low permeability. Lustrous carbon from the molding process. Metal section too thin. Inadequately pre-heated metallic moulds.2) Remedies Increase metal pouring temperature. Modify metal composition to improve fluidity. Pour metal as rapidly as possible without interruption.Improve mould filling by modification to running andgating system. Remove slag from metal surface. Reduce gas pressure in the mould by appropriateadjustment to molding material properties and ensuring Adequate venting of moulds and cores. Eliminate lustrous carbon where applicable. If possible, modify casting design to avoid thin sections. Ensure metal moulds are adequately pre-heated and useinsulating coatings.G. Mismatch DefectMismatch in mold defect is because of the shifting moldingflashes. It will cause the dislocation at the parting line.1) Possible Causes A mismatch is caused by the cope and drag parts of themould not remaining in their proper position. This is caused by loose box pins, inaccurate patterndowel pins or carelessness in placing the cope on thedrag.2) Remedies Check pattern mounting on match plate and Rectify, correct dowels. Use proper molding box and closing pins.H. Cracks Or TearsCracks can appear in die castings from a number of causes.Some cracks are very obvious and can easily be seen withAll rights reserved by www.ijsrd.com381
A Review on Casting Defect Minimization Through Simulation(IJSRD/Vol. 3/Issue 11/2016/090)the naked eye. Other cracks are very difficult to see withoutmagnification.1) Possible Causes Shrinkage of the casting within the die Undercuts or damage in die cavities Uneven, or excessive, ejection forces Thermal imbalance in the die Insufficient draft in sections of the die Excessive porosity in critical regions of the part Product design not matched to the process Inadequate die design2) Remedies Reduce dry strength; add saw dust, coal dust Reduce pouring temperature Avoid superheating of metal Use chills Provide feeders Avoid early knockout. Give sufficient cooling time. Correct composition Reduce sharp cornersI. Incomplete CastingPoured short, the upper portion of the casting is missing.The edges adjacent to the missing section are slightlyrounded; all other contours conform to the pattern. Thespree, risers and lateral vents are filled only to the sameheight above the parting line, as is the casting.1) Possible Causes Insufficient quantity of liquid metal in the ladle. Premature interruption of pouring due to workman’serror.2) Remedies Have sufficient metal in the ladle to fill the mold,Check the gating system. Instruct pouring crew andsupervise pouring practice.Fig. 1: Actual casting EP20Fig. 2: Monthlyrejection rate of EP 201) Modeling And SimulationSolid model of the casting which was simulated is shown inFig. 3. During uploading of the part, parameters such asmolding sand material and its mesh size are also specified.Fig. 4 shows simulation result of the castingIV. LITERATURE REVIEWA. Harshil Bhatta, Rakesh Barota, Kamlesh Bhatta,Hardik Beravalaa, Jay ShahIn this paper, authors have attempted to modify the existingfeeding system design of a component coded EP20 which isbeing cast by the Grey Cast Iron foundry FINE CAST PVT.LTD., V.U. Nagar. The component, as shown in Fig.1, iscasing of gear box and is made of Cast Iron having 240 kgweight. Foundry has problems such as shrinkage, cold shut,mismatch and crack for this casting, as shown in Fig.2. It isclearly seen that shrinkage is the most frequently occurringdefect out of all the three. In this paper, solution forshrinkage defect has been developed.Fig. 3: Solid Model of Casting EP20 Fig. 4: SimulationResult of the Casting EP 20.B. C. M. Choudhari, B. E. Narkhede, S. K. MahajanThe objectives of this study is to represents stepped platecasting design and its numerical simulation using AutoCAST-X software of square shaped (at top) plate havingthree perforationswith diminishing height (atbottom)followed by experimental validation.It has thick 208 x 208 mm square shape with athickness of 21mm and then the perforations of diminishingheight begins from left to right as 24mm (thickest section),19 mm (thicker section), and14 mm (thick section),respectively for the entire width of square shape.The simulation is based on Gradient VectorMethod (GVM), which computes temperature gradients(feed metal paths) inside the casting, and follows them inreverse manner to identify the location and extent ofshrinkage porosity. This is a new method that is found to bemuch faster than finite element or finite volume method, andusually more accurate too. The simulation costs are afraction of the costs of foundry trials, while providing betterand faster insight for casting optimization.All rights reserved by www.ijsrd.com382
A Review on Casting Defect Minimization Through Simulation(IJSRD/Vol. 3/Issue 11/2016/090)Fig. 5: Shrinkage porosity (macro-red, micro-orange).The shrinkage porosity was computed from the temperaturegradients using metal-specific process characteristics, whichcan be adjusted to calibrate the results with respect to theobserved location of shrinkage porosity. Shrinkage porositycan be obtained in the solidification function under feedmodule by clicking on Shrinkage tab. It will be displayed asdots inside the casting: red for macro-porosity and orangefor micro-porosity (Fig. 5).C. Dr. B Ravi, Durgesh JoshiThis paper focuses on feedability analysis and optimisationdriven by solidification simulation (Fig. 6). It starts with theuser importing the CAD model of the as-cast part. Thefeeder design is carried out by identifying a suitable locationto connect the feeder, computing its dimensions, creating itssolid model and attaching to the part model. Thenfeedability analysis is carried out by solidificationsimulation followed by checking for the presence of hotspots inside the casting as well as connections between thefeed paths. If internal defects are predicted, then feederdesign is modified. If it is not possible to improve thequality by feeder design alone, then the part design ismodified. Finally, yield is computed and compared with theyield obtained by other layouts with acceptable quality, andthe one giving the highest yield is selected forimplementation. The steps are described in detail next.Fig. 6: Framework for feeder design and optimisationD. Mayur Sutaria, Vinesh H. Gada, Atul Sharma, B. RaviThe aim of this research paper is to compute feed-paths andhot-spots by combining level-set-method based sharpinterface and feed-path model. The model is based on thesolution of energy and level-set equations in solid andliquid, with Stefan condition on the interface. The energyand level-set equation are discretized using finite-volumeand finite-difference method, respectively. Feed-path iscomputed by tracking mass-less particles along the liquid–solid interface during solidification using combinedEulerian–Lagrangian framework. The proposed model isbenchmarked on six test cases, where temperature contoursand solidification time are compared with a finite-elementmethod based commercial software. The capability topredict the temporal evolution of interface and to identifymultiple hotspots is validated with an industrial aluminumalloy lug casting. The numerical as well as experimentalvalidations demonstrate the effectiveness of level-setmethod for feed-path calculation.Fig. 7: Liquid–solid interface (solid lines) and feed-paths(dotted lines) inside stepped casting.All rights reserved by www.ijsrd.com383
A Review on Casting Defect Minimization Through Simulation(IJSRD/Vol. 3/Issue 11/2016/090)Computation of the feed-path is proposed, using severalmass-less particles defined the interface. These particles areadvected along with the interface at each time step usinginterfacial velocity components computed by level-setmethod, which is essentially in the opposite direction of themaximum temperature gradients. Based on the shape of themold cavity and thermal condition on the boundary, themovement of mass-less particles will be different. Thus, thefeed-paths can be generated by tracking the position ofseveral mass-less particles on the interface. Accuratelocation of the hot-spot can be obtained as the point at whichthe mass-less particles converge. The feed-paths are alwaysnormal to the liquid-solid interface contours as shown in fig.7. The solid lines indicate liquid-solid interface contours anddotted lines indicate feed-paths.E. X. Sua,G.Wang, Y.T. Zhang, J.F.Li, Y.M.RongIn this paper, the simulation of whole manufacturingprocesses and manufacturing chains can be realized usingFinite Element Techniques. Casting can change thedimensions of the model obviously, the deformationconsidering casting was about 10times larger than that of theideal case. The stress generated by casting can quicken theaustenitizing during the heat up process. The stress has littleinfluence on organization transformation. The stressgenerated during casting is low, and during the heat upprocess much higher stress is brought in. Comparing figure8 (a) with figure 8 (b) in separately, the stress generatedduring casting cannot change the nature of the organizationtransformation. Furthermore, the distribution trends of thetwo cases have little difference. The stress generated bycasting cannot influence the organization transformationobviouslyThis technique uses thermal histories experimentallyregistered as base, and modifies the material properties andboundary conditions used in simulation until reaching agood correlation between numerical simulated coolingcurves and they registered experimentally. The adjustmenthas been also focused on the shrinkage defects.The simulation model is a FEM model developed incommercial software specifically focused on metal castingsimulation. The case of study is an investment castingprocess, vacuum poured, of a nickel base super alloydesignated Hastelloy X. Usual in the manufacture ofcomponents for aeronautical turbines.G. F. J. Bradley, M. SamondsThis paper concerns the numerical simulation ofsolidification of near eutectic ductile iron alloys, which issomewhat more difficult than simulation of freezing rangealloys from a number of standpoints, particularly in the caseof graphitic cast irons, which may solidify according to thestable austenite-graphite system or the metastable austenitecarbide system. Commercial near eutectic ductile irons areoften of slightly hypereutectic composition.For such irons the start of solidificationtemperature is difficult to determine from thermal analysisdata, since the evolution of latent heat associated withgraphite precipitation in the primary solidification range isgenerally insufficient to produce a distinct arrest in thecooling curve. Similarly, the end of solidificationtemperature is difficult to precisely determine because ofsegregation effects. While most solidification takes placeover a narrow temperature range associated with the eutecticplateau, ductile iron may in fact freeze over quite a widerange of temperature.V. CONCLUSIONDefects like shrinkage, blow holes, sand burning, sandinclusion, cold shut, mis-run were identified during castingprocess. Among all, shrinkage defect was major cause forrejection rate. It is suggested that simulation to be carriedout in FEM based software SOFTCAST where shrinkagedefect is identified and during simulation an optimumfeeding design is to be found out and at that feeding designthere is no shrinkage defect found. And the experiment canbe carried out to validate the simulation.REFERENCESFig. 8: Distribution of Lower Bainite (volume fraction) (a)ideal case; (b) the case considering the results of casting.F. E. Anglada, A. Meléndez, L.Maestro, I. DomiguezThis paper presents the adjustment process of a simulationmodel to improve the correlation between simulation resultsand parts industrially manufactured. It includes the dataregistration at foundry plant, the preliminary set-up of themodel and the later adjustment process to reach a correlationlevel according to the industrial necessities. The adjustmenthas been performed by means of inverse modelling.[1] Harshil Bhatta, Rakesh Barota, Kamlesh Bhatta, HardikBeravalaa, Jay Shah “Design Optimization of FeedingSystem and Solidification Simulation for Cast Iron” 2ndInternational Conference on Innovations in Automationand Mechatronics Engineering, ICIAME 2014 Elseviervolume 14 (2014) 357 – 364[2] C. M. Choudhari, B. E. Narkhede, S. K. Mahajan“Methoding and Simulation of LM 6 Sand Casting forDefect Minimization with its Experimental Validation”12th Global Congress On Manufacturing AndManagement, GCMM 2014 Elsevier volume 97 (2014)1145 – 1154[3] Dr. B Ravi, Durgesh Joshi “Feedability Analysis andOptimisation Driven by Casting Simulation” Technicalpaper submitted to the Indian Foundry Journal IndianFoundry Journal April 2007All rights reserved by www.ijsrd.com384
A Review on Casting Defect Minimization Through Simulation(IJSRD/Vol. 3/Issue 11/2016/090)[4] Mayur Sutaria, Vinesh H. Gada, Atul Sharma, B. Ravi“Computation of feed-paths for casting solidificationusing level-set-method” Journal of Materials ProcessingTechnology Elsevier volume 212 (2012) 1236–1249[5] X.Sua,G.Wang,Y.T.Zhang,J.F.Li,Y.M.Rong“Modeling on stress evolution of step part for castingheat treatment processes” International Federation forHeat Treatment and Surface Engineering 20th CongressBeijing Elsevier volume 50 (2013) 360 – 367[6] E. Anglada, A. Meléndez, L.Maestro, I. Domiguez“Adjustment of Numerical Simulation Model to theInvestment Casting Process” The ManufacturingEngineering Society International Conference, MESIC2013 Elsevier volume 63 (2013) 75 – 83[7] F. J. Bradley, M. Samonds “A comparison of sourceterm and enthalpy approaches to the numericalsimulation of the solidification of ductile irons”Applied mathematics modeling, volume 16, (1992).All rights reserved by www.ijsrd.com385
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