MELTING AND CASTING OF MATERIALS

NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY DEPARTMENT: Materials Engineering COURSE TITLE: MM-203: Melting and Casting of Materials FALL SEMESTER: 2012 TEACHER: Engr. Humair Ahmed / Engr. Faaz Butt. Text Book; 1) P L Jain, “PRINCIPLES OF FOUNDRY TECHNOLOGY” 2009; English: 5th ed. References; 1. C. W. Ammen, “METALCASTING”, 1999. 2. ASM HandBook - Vol 15 - Casting (2002s). 2. Peter, Beeley “FOUNDRY TECHNOLOGY”, Butterworth-Heinemann; 2nd ed., 2006 3. Chakrabarti, A K, “CASTING TECHNOLOGY AND CAST ALLOYS”, 2005. 5. Heine, R.W., et.al., PRINCIPLES OF METAL CASTING, 3rd. ed., Tata McGraw-Hill Publ., 1979. Evaluation; 1. Popup Quizzes (approx. 5): 5%. 2. Test: 10%. 3. Assignment: 10%. 4. Attendance: 5% 4. Final examination: 70% SYNOPSIS OF COURSE: � This course is one of the most important and interesting subject for Materials Engineering students. � It is advancement from the previously taught subject, the manufacturing processes for materials (MM-206). � The subject comprises a more emphasis on the manufacturing techniques by casting process. � It covers bigger spectrum for manufacture products by the casting techniques with require attributes specify for certain purpose such as intricacy, features detail, soundness and others. REMEMBER!!!! “The true art of memory is the art of attention” Samuel Johnson W H A T � A � R � S � G � R � A � C JO B T A L C A S A LI M A A LL IE D A L PI N E B A JW A BO L A N C H E N A E E H A B E X C E L H U SS E I H A JI K H H A SE EB IK R A MT Q U A L IT IE A sh ar p m in d R ef in ed k no w Su pe rb o be rs e G re at li st en in R ef le xi vi ty A tti tu de C om pu te r s ki TI T L E (s ): F O ST IR O N IN D U S A C H IN E T O O L D P R E C IS IO N E E S T E E L (P V T ) A A G R O IN D U S N C A ST IN G S L T A B E N G IN E E R I B S E N G IN E E R IN E N G IN E E R IN IN E N G IN EE R I H A L ID ID R E E S B W A Q A S E N G M E N G IN E E R IN E S IN A G O O d. w le dg e er va tio na l c ap g po w er lls . O U N D R Y E N ST R IE S C O M PA N Y (A M E N G IN EE R IN G LT D . T R IE S L T D . T D . IN G W O R K S & N G C O M PA N Y G (P V T ) L T D . IN G W O R K S (P S C A ST IN G & J G IN EE R IN G L T N G C O M PA N Y O D E N G IN E pa bi lit ie s N G IN EE R o r F M T C PD C ) G P R O D U C T S (P F O U N D R IE S ( Y (P V T ) L T D . PV T ) L T D . JE W EL L ER Y C T D . E E R ? FO U N D R Y P PA K FO U N PV T ) L T D . PV T ) L T D .� C EN T R E M IN I � � � � � PR O C ES S EN K IS TA N D R Y L IN JA G U A K A R A M A T C M E C A M A C H Q A D R Q A D C R A V I R A ST G SU PR A U M E R W ES TI M U M C O M C O M PU TE R M S O FF IC E � W O R D � PO W E � EX C E � PU B L I AU TO C AD . PH O TO SH O PR O E . N G IN EE R o r A N N K S A R P A K IS TA N A C H I S H IP Y A R C A ST (P V T ) L T A S FO U N D R Y H IN E C R A FT S ( R I F O U N D R Y (P C A ST (P V T ) L T D A U T O S (P V T ) L G A R E N G IN E E A A S T E E L S R B R O T H E R S & T E R N IN D U ST RM PU T E R S K R O PE R A TI O E D ER P O IN T EL I SH ER O P, C O RE LD TR A IN EE E N N (P V T ) L T D . R D & E N G IN E E T D . (P V T ) L T D . PV T ) L T D . D . L T D . E R IN G C O M PA & C O . ( U B C O H R IE S K IL L S ? O N S. D RA W e tc N G IN EE R a t E R IN G W O R K S A N Y (P V T ) L T D H O L D IN G S) t s om e Fo un dr S (K SE W ) L T D . D . PO SI TI VE � PO IN T� ry . M E L T IN G A N D C A ST IN G O F M A T E R IA L S M E L T IN G � To b e ch an ge d fr om a s ol id t o a liq ui d st at e es pe ci al ly by th e ap pl ic at io n of h ea t. � Th e st at e of b ei ng m el te d. � Th e pr oc es s o f b ec om in g m el te d C A ST IN G � C as tin g is a m an uf ac tu rin g pr oc es s w he re a s ol id i s m el te d, h ea te d to pr op er te m pe ra tu re an d is th en po ur ed in to a c av ity o r m ol d, w hi ch co nt ai ns it in th e pr op er sh ap e du rin g so lid ifi ca tio n. Th us , in a si ng le st ep , si m pl e or co m pl ex sh ap es c an b e m ad e fr om a ny m et al th at c an b e m el te d. M at er ia ls � Th e ta ng ib le s ub st an ce t ha t go es in to th e m ak eu p of a ph ys ic al ob je ct . � E ng in ee rin g M at er ia ls : M at er ia ls of e ng in ee rin g ap pl ic at io ns . � C la ss ifi ca tio n of m at er ia ls , ne xt sl id e Ev er yt hi ng is … M at er ia l !! M et al lic M at er ia ls • M et al lic : – Ir on – C op pe r – A lu m in um – M ag ne si um – N ic ke l – Ti ta ni um – Le ad – Ti n – Zi nc • A llo ys o f t he se m et al s: – St ee l ( Fe b as ed ) – B ra ss (C u + Z in c) – B ro nz e (C u + T in ) • T he y po ss es s t he m et al lic p ro pe rti es o f: – Lu st er – H ig h th er m al c on du ct iv ity – R el at iv el y du ct ile – So m e ha ve go od m ag ne tic pr op er tie s Th er e ar e tw o fa m ili es o f m et al lic m at er ia ls — F E R R O U S A N D N O N FE R R O U S. N on m et al lic M at er ia ls • N on m et al lic : – W oo d – B ric k – C on cr et e – G la ss – R ub be r – Pl as tic • T he ir pr op er tie s v ar y w id el y • G en er al ly th ey te nd to b e: – Le ss d uc til e – W ea ke r – Le ss d en se th an m et al s – H av e po or e le ct ric al a nd th er m al p ro pe rti es N on m et al lic M at er ia ls a re d ev el op in g • A dv an ce d ce ra m ic s • C om po si te m at er ia ls • E ng in ee re d pl as tic s M et al lic c as tin gs N on -m et al lic c as tin gs A dv an ta ge s o f t he M et al lic a nd N on m et al lic c as tin g pr oc es s C er ta in a dv an ta ge s ar e in he re nt in th e m et al c as tin g pr oc es s. Th es e of te n fo rm th e ba si s fo r c ho os in g ca st in g ov er ot he r s ha pi ng p ro ce ss es su ch a s m ac hi ni ng , f or gi ng , w el di ng , s ta m pi ng , r ol lin g, e xt ru di ng , e tc . S om e of th e re as on s fo r t he su cc es s o f t he c as tin g pr oc es s a re : � Th e m os t in tri ca te o f sh ap es , bo th e xt er na l an d in te rn al , m ay b e ca st . A s a re su lt, m an y ot he r op er at io ns , s uc h as m ac hi ni ng , f or gi ng , a nd w el di ng , c an b e m in im iz ed o r e lim in at ed . � C on st ru ct io n m ay b e sim pl ifi ed . O bj ec ts m ay b e ca st in a s in gl e pi ec e w hi ch w ou ld o th er w is e re qu ire as se m bl y of se ve ra l p ie ce s i f m ad e by o th er m et ho ds . � M et al c as tin g is a p ro ce ss h ig hl y ad ap ta bl e to th e re qu ire m en ts o f m as s pr od uc tio n. L ar ge n um be rs o f a gi ve n ca st in g m ay b e pr od uc ed v er y ra pi dl y. F or e xa m pl e, i n th e au to m ot iv e in du st ry h un dr ed s of th ou sa nd s o f c as t e ng in e bl oc ks a nd tr an sm is si on c as es a re p ro du ce d ea ch y ea r. � Ex tre m el y la rg e, he av y m et al o bj ec ts m ay b e ca st w he n th ey w ou ld b e di ff ic ul t or e co no m ic al ly im po ss ib le to p ro du ce o th er w is e. L ar ge p um p ho us in g, v al ve s, an d hy dr oe le ct ric p la nt p ar ts w ei gh in g up to 2 00 to ns il lu st ra te th is a dv an ta ge o f t he c as tin g pr oc es s. � So m e en gi ne er in g pr op er tie s a re o bt ai ne d m or e fa vo ra bl y in c as t m et al . � A d ec id ed e co no m ic a dv an ta ge m ay e xi st a s a re su lt of a ny o ne o r a c om bi na tio n of p oi nt s m en tio ne d ab ov e. Su rp ri se Q ui z: 1) D ef in e M el tin g an d C as tin g Pr ac tic e in te rm s o f i ts im po rta nc e. (M ax : 5 li ne s) 2) W rit e an y th re e sa fe ty is su es re la te d to th e M el tin g an d ca st in g of m at er ia ls . CASTING OF MATERIALS � The metal casting industry plays a key role in all the majorsectors of our economy. There are castings in locomotives, cars trucks, aircraft, office buildings, factories, schools, and homes. � Metal Casting is one of the oldest materials shaping methods known. � Casting means pouring molten metal into a mold with a cavity of the shape to be made, and allowing it to solidify. � When solidified, the desired metal object is taken out from the mold either by breaking the mold or taking the mold apart. The solidified object is called the casting. � By this process, intricate parts can be given strength and rigidity frequently not obtainable by any other manufacturing process. � The mold, into which the metal is poured, is made of some heat resisting material. Sand is most often used as it resists the high temperature of the molten metal. � Permanent molds of metal can also be used to cast products. Advantages The metal casting process is extensively used in manufacturing because of its many advantages. 1. Molten material can flow into very small sections so that intricate shapes can be made by this process. As a result, many other operations, such as machining, forging, and welding, can be minimized or eliminated. 2. It is possible to cast practically any material that is ferrous or non-ferrous. 3. As the metal can be placed exactly where it is required, large saving in weight can be achieved. 4. The necessary tools required for casting molds are very simple and inexpensive. As a result, for production of a small lot, it is the ideal process. 5. There are certain parts made from metals and alloys that can only be processed this way. 6. Size and weight of the product is not a limitation for the casting process. Limitations 1. Dimensional accuracy and surface finish of the castings made by sand casting processes are a limitation to this technique. Many new casting processes have been developed which can take into consideration the aspects of dimensional accuracy and surface finish. Some of these processes are die casting process, investment casting process, vacuum-sealed molding process, and shell molding process. 2. The metal casting process is a labor intensive process METAL CASTINGS Metal castings form integral components of devices that perform useful functions for human beings: The cast component has a shape, size, chemical composition and metallurgical microstructure which is determined by engineering decisions arrived at by: A. Design Engineers (Mechanical Engineers) B. Pattern Makers (Skilled craftsman, CAD) C. Casting Engineers (Materials/Metallurgical Engineers) D. Manufacturing Engineers (Mechanical, Materials/Metallurgical Engineers) � It should be noted that the casting may only be a small part of the useful device (usually in more sophisticated devices like an automobile where there may be hundreds of components), or it may be the entire device (simple device like a frying pan). Metal Casting Process � The metal casting process is the simplest, most direct route to a near net shape product, and often the least expensive. � This process in its fundamental form requires a mold cavity of the desired shape and molten metal to pour into the mold cavity. � Human’s beings have been producing castings for thousands of years, most often pouring molten metal into molds made of sand. � This is schematically shown below, a figure defining the basic components of a mold cavity (cope, drag, parting line, riser, sprue, pouring basin, etc) � Engineering skills are used to help design a system which will allow the metal caster to produce a sound (pore free) casting, free from defects (sand inclusions, slag, cracks, etc.), with the correct dimensions and combination of mechanical properties to satisfy the designer’s requirements for the intended application. Producing a “good” casting requires a design effort to: 1. Create a gating system (pouring basin, sprue, runner) to bring molten metal into the mold cavity free from entrapped slag, sand or gases. 2. Provide a riser which feeds liquid metal into the casting cavity as the liquid is cooling and solidifying (all liquid metals will shrink as they cool and most liquid metals will shrink as they solidify). The riser may have to provide up to 5 - 7% by volume for the casting as it solidifies. 3. Control heat flow , out of the casting so that the last liquid to solidify is in the riser. 4. Control the rate of heat flow so as to control the nature of the solidified product. Modern industrial castings are produced by a wide variety of processes, processes which are broadly defined in terms of: I. The type of mold material (sand, permanent, etc.); II. The manner in which the molten metal is introduced into the cavity (gravity, pressure, vacuum); III. The state of the metal (percent which is liquid); IV. The state of the mold cavity itself (air, vacuum, solid, gas). EXPENDABLE MOLD CASTING Expendable mold casting is a process that refers to temporary, non-reusable molds that have to be broken to remove the materials cast. Expendable casting uses a variety of materials for the mold - plaster, concrete, resins, and wax. 1) Sand casting Sand casting is one of the most popular and simplest types of casting that has been used for centuries. Sand casting allows for smaller batches to be made compared to permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at a low cost, but there are other benefits to sand casting, such as very small size operations. From castings that fit in the palm of your hand to train beds (one casting can create the entire bed for one rail car), it can all be done with sand casting. Sand casting also allows most metals to be cast depending on the type of sand used for the molds. The sand is bonded together using clays, chemical binders, or polymerized oils (such as motor oil). Sand can be recycled many times in most operations and requires little maintenance. 2) Shell molding Shell molding is similar to sand casting, but the molding cavity is formed by a hardened "shell" of sand instead of flask filled with sand. The sand is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern and harden into a shell around the pattern. Because of the resin it gives a much finer surface finish. The process is easily automated and more precise than sand casting. This process is ideal for complex items that are small to medium sized. 3) Investment casting Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity. Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused. The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Compared to other casting processes such as die casting or sand casting, it can be an expensive process, however the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so requiring little or no rework once cast. 4) Evaporative-pattern casting This is a class of casting processes that use pattern materials that evaporate during the pour, which means there is no need to remove the pattern material from the mold before casting. The two main processes are lost-foam casting and full-mold casting. i. Lost-foam casting Lost-foam casting is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This process takes advantage of the low boiling point of foam to simplify the investment casting process by removing the need to melt the wax out of the mold. ii. Full-mold casting Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses a expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact. NON-EXPENDABLE CASTING TECHNIQUES Non-expendable casting involves the use of permanent or long-lasting molds which do not need to be broken in order to remove the cast material once it has set or cooled. 1) Permanent mold casting � Permanent mold casting uses metal as a mold and requires a set-up time of weeks. Typically, cast iron or Meehanite (a dense cast iron) is used as the mold material and the cores are made from metal or sand. � Cavity surfaces are coated with a thin layer of heat resistant material such as clay or sodium silicate. � The molds are pre-heated up to 200C before the metal is poured into the cavity. � When cooling the mold, care has to be taken to ensure proper thermal balance, by using external water cooling or appropriate radiation techniques � The process is highly automated, as the only necessary input is the coating applied regularly. � Typically, permanent mold casting is used in forming iron, aluminum, magnesium, and copper based alloys. � Typical parts include gears, splines, wheels, gear housings, pipefittings, fuel injection housings, and automotive engine pistons. 2) Die Casting � Die-casting is similar to permanent mold casting except that the metal is injected into the mold under high pressures. This results in a more uniform part, generally good surface finish and good dimensional accuracy. � For many parts, post-machining can be totally eliminated, or very light machining may be required to bring dimensions to size. � Die casting mold