Metal Casting Processes PDF

2.0 Metal casting process 2.1 The basic principle of metal casting (fluidity, heating, pouring, solidification, defects) 2.2 Metal casting process (Sand Casting, Die Casting, Investment Casting)  https://www.youtube.com/watch?v =2CIcvB72dmk  Metal casting process  What...

2.0 Metal casting process 2.1 The basic principle of metal casting (fluidity, heating, pouring, solidification, defects) 2.2 Metal casting process (Sand Casting, Die Casting, Investment Casting)  https://www.youtube.com/watch?v =2CIcvB72dmk  Metal casting process  What is casting?  Advantages of Casting  Metal Casting Processes  gravity casting system  Casting Parameters  Porosity  Casting Defects  FUNDAMENTALS OF METAL CASTING ❑ Why metal casting is so important -casting in manufacturing process ❑ Solidification of molten metal -heating the metal, pouring, analysis, fluidity ❑ Solidification and Cooling -solidification of metals and time, shrinkage, directional solidifications  Why metal casting important?  Capability of metal casting ⚫ Can produce internal cavities or hollow section ⚫ Very large parts and complex part can be produced in one piece ⚫ Can utilize materials that are difficult or uneconomical to process ⚫ Can create both external and internal shapes ⚫ Some casting methods are suited to mass production ⚫ Some casting processes are net shape; others are near net shape  Disadvantages of Casting  Different disadvantages for different casting processes: ⚫ Limitations on mechanical properties ⚫ Poor dimensional accuracy and surface finish for some processes; e.g., sand casting ⚫ Safety hazards to workers due to hot molten metals ⚫ Environmental problems  Parts Made by Casting  Big parts ⚫ Engine blocks and heads for automotive vehicles, wood burning stoves, machine frames, railway wheels, pipes, church bells, big statues, pump housings  Small parts ⚫ Dental crowns, jewelry, small statues, frying pans  All varieties of metals can be cast - ferrous and non-ferrous.  Cooling Curve for a Pure Metal  A pure metal solidifies at a constant temperature equal to its freezing point (same as melting point) Figure 10.4 Cooling curve for a pure metal during casting.  Solidification of Alloys  Most alloys freeze over a temperature range rather than at a single temperature Figure 10.6 (a) Phase diagram for a copper-nickel alloy system and (b) associated cooling curve for a 50%Ni-50%Cu composition during casting.  Solidification of Alloys Figure 10.7 Characteristic grain structure in solidification  Solidification Time  Solidification takes time  Total solidification time TTS = time required for casting to solidify after pouring  TTS depends on size and shape of casting by relationship known as Chvorinov's Rule n V  TTS = C m    A where TST = total solidification time; V = volume of the casting; A = surface area of casting; n = exponent with typical value = 2; and Cm is mold constant.  Mold Constant in Chvorinov's Rule  Mold constant Cm depends on: ⚫ Mold material ⚫ Thermal properties of casting metal ⚫ Pouring temperature relative to melting point  Value of Cm for a given casting operation can be based on experimental data from previous operations carried out using same mold material, metal, and pouring temperature, even though the shape of the part may be quite different  What Chvorinov's Rule Tells Us  A casting with a higher volume-to-surface area ratio cools and solidifies more slowly than one with a lower ratio ⚫ To feed molten metal to main cavity, TST for riser must greater than TST for main casting  Since mold constants of riser and casting will be equal, design the riser to have a larger volume-to-area ratio so that the main casting solidifies first ⚫ This minimizes the effects of shrinkage  Casting  Process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity  The term casting also applies to the part made in the process  Steps in casting is simple: 1. Melt the metal 2. Pour it into a mold 3. Allow to freeze or solidify  Solidification Processes  Starting work material is either a liquid or is in a highly plastic condition, and a part is created through solidification of the material  Solidification processes can be classified according to engineering materials: ⚫ Metals ⚫ Ceramics, specifically glasses ⚫ Polymers and polymer matrix composites (PMCs)  Heating the Metal  Heating furnaces are used to heat the metal to molten temperature sufficient for casting  The heat required is the sum of: 1. Heat to raise temperature to melting point 2. Heat of fusion to convert from solid to liquid 3. Heat to raise molten metal to desired temperature for pouring  Pouring the Molten Metal  For this step to be successful, metal must flow into all regions of the mold, most importantly the main cavity, before solidifying  Factors that determine success ⚫ Pouring temperature ⚫ Pouring rate ⚫ Turbulence  Metals for Casting  Most commercial castings are made of alloys rather than pure metals ⚫ Alloys are generally easier to cast, and properties of product are better  Casting alloys can be classified as: ⚫ Ferrous ⚫ Nonferrous  Ferrous Casting Alloys: Cast Iron  Most important of all casting alloys  Tonnage of cast iron castings is several times that of all other metals combined  Several types: (1) gray cast iron, (2) nodular iron, (3) white cast iron, (4) malleable iron, and (5) alloy cast irons  Typical pouring temperatures  1400C (2500F), depending on composition  Ferrous Casting Alloys: Steel  The mechanical properties of steel make it an attractive engineering material  The capability to create complex geometries makes casting an attractive shaping process  Difficulties when casting steel: ⚫ Pouring temperature of steel is higher than for most other casting metals  1650C (3000F) ⚫ At such temperatures, steel readily oxidizes, so molten metal must be isolated from air ⚫ Molten steel has relatively poor fluidity  Nonferrous Casting Alloys: Aluminum  Generally considered to be very castable  Pouring temperatures low due to low melting temperature of aluminum ⚫ Tm = 660C (1220F)  Properties: ⚫ Light weight ⚫ Range of strength properties by heat treatment ⚫ Easy to machine  Nonferrous Casting Alloys: Copper Alloys  Includes bronze, brass, and aluminum bronze  Properties: ⚫ Corrosion resistance ⚫ Attractive appearance ⚫ Good bearing qualities  Limitation: high cost of copper  Applications: pipe fittings, marine propeller blades, pump components, ornamental jewelry Nonferrous Casting Alloys: Zinc Alloys  Highly castable, commonly used in die casting  Low melting point – melting point of zinc Tm = 419C (786F)  Good fluidity for ease of casting  Properties: ⚫ Low creep strength, so castings cannot be subjected to prolonged high stresses  Solidification of Metals  Transformation of molten metal back into solid state  Solidification differs depending on whether the metal is ⚫ A pure element or ⚫ An alloy  Solidification of Pure Metals  Due to chilling action of mold wall, a thin skin of solid metal is formed at the interface immediately after pouring  Skin thickness increases to form a shell around the molten metal as solidification progresses  Rate of freezing depends on heat transfer into mold, as well as thermal properties of the metal  Solidification of Pure Metals Figure 10.5 Characteristic grain structure in a casting of a pure metal, showing randomly oriented grains of small size near the mold wall, and large columnar grains oriented toward the center of the casting.  Shrinkage in Solidification and Cooling Figure 10.8 Shrinkage of a cylindrical casting during solidification and cooling: (0) starting level of molten metal immediately after pouring; (1) reduction in level caused by liquid contraction during cooling (dimensional reductions are exaggerated for clarity).  Shrinkage in Solidification and Cooling Figure 10.8 (2) reduction in height and formation of shrinkage cavity caused by solidification shrinkage; (3) further reduction in height and diameter due to thermal contraction during cooling of solid metal (dimensional reductions are exaggerated for clarity). CLASS ACTIVITY (W2) Identify and discuss the process to produce a Spur Gear  Solidification Shrinkage  Occurs in nearly all metals because the solid phase has a higher density than the liquid phase  Thus, solidification causes a reduction in volume per unit weight of metal  Exception: cast iron with high C content ⚫ Graphitization during final stages of freezing causes expansion that counteracts volumetric decrease associated with phase change  Shrinkage Allowance  Patternmakers account for solidification shrinkage and thermal contraction by making mold cavity oversized  Amount by which mold is made larger relative to final casting size is called pattern shrinkage allowance  Casting dimensions are expressed linearly, so allowances are applied accordingly  Directional Solidification  To minimize damaging effects of shrinkage, it is desirable for regions of the casting most distant from the liquid metal supply to freeze first and for solidification to progress from these remote regions toward the riser(s) ⚫ Thus, molten metal is continually available from risers to prevent shrinkage voids ⚫ The term directional solidification describes this aspect of freezing and methods by which it is controlled  Achieving Directional Solidification  Desired directional solidification is achieved using Chvorinov's Rule to design the casting itself, its orientation in the mold, and the riser system that feeds it  Locate sections of the casting with lower V/A ratios away from riser, so freezing occurs first in these regions, and the liquid metal supply for the rest of the casting remains open  Chills - internal or external heat sinks that cause rapid freezing in certain regions of the casting  METAL CASTING PROCESSES 1. Sand Casting -patterns and cores, molds making, casting operation 2. Expendable Mold Casting Processes -shell, expended polystyrene, investment, plaster and ceramic 3. Permanent Mold Casting Processes - permanent mold, variation of permanent mold casting, die casting Figure 10.1 Classification of solidification processes.  Two Categories of Casting Processes 1. Expendable mold processes - mold is sacrificed to remove part ⚫ Advantage: more complex shapes possible ⚫ Disadvantage: production rates often limited by time to make mold rather than casting itself 2. Permanent mold processes - mold is made of metal and can be used to make many castings ⚫ Advantage: higher production rates ⚫ Disadvantage: geometries limited by need to open mold  Open Molds and Closed Molds Figure 10.2 Two forms of mold: (a) open mold, simply a container in the shape of the desired part; and (b) closed mold, in which the mold geometry is more complex and requires a gating system (passageway) leading into the cavity.  Foundry Sands  Silica (SiO2) or silica mixed with other minerals  Good refractory properties - capacity to endure high temperatures  Small grain size yields better surface finish on the cast part  Large grain size is more permeable, allowing gases to escape during pouring  Irregular grain shapes strengthen molds due to interlocking, compared to round grains ⚫ Disadvantage: interlocking tends to reduce permeability Binders Used with Foundry Sands  Sand is held together by a mixture of water and bonding clay ⚫ Typical mix: 90% sand, 3% water, and 7% clay  Other bonding agents also used in sand molds: ⚫ Organic resins (e g , phenolic resins) ⚫ Inorganic binders (e g , sodium silicate and phosphate)  Additives are sometimes combined with the mixture to increase strength and/or permeability PROPERTIES OF MOULDING SAND -1  PERMEABILITY- give way gases to escape, water and steam vapor  COHESIVENESS-Ability of sand particles to stick together  ADHESIVENESS – Sand particles must be capable of sticking to other bodies particularly to molding box. Capable of adhering to another body  PLASTICITY – acquiring pre-determined shape under pressure and to retain it when the pressure is removed.  Collapsibility- Free contraction of mold PROPERTIES OF MOUDLING SAND - 2  REFRACTORINESS- ability to withstand high heat without breaking down or fusing.  CHEMICAL RESISTIVITY- sand should not chemically react or combine with molten metal so that it can be used again and again.  BINDING PROPERTY- Binder allows sand to flow take up pattern shape  FLOWABILIY- This is similar to plasticity. It is the ability of sand to take up the desired shape. Ability to behave like a fluid. Flowability increases as clay and water content increased.  Porosity- Allow gas to escape  Advantages and Disadvantages  More intricate geometries are possible with expendable mold processes  Part shapes in permanent mold processes are limited by the need to open the mold  Permanent mold processes are more economic in high production operations  Sand Casting Mold Figure 10.2 (b) Sand casting mold.  Forming the Mold Cavity  Mold cavity is formed by packing sand around a pattern, which has the shape of the part  When the pattern is removed, the remaining cavity of the packed sand has desired shape of cast part  The pattern is usually oversized to allow for shrinkage of metal during solidification and cooling  Sand for the mold is moist and contains a binder to maintain its shape  Use of a Core in the Mold Cavity  The mold cavity provides the external surfaces of the cast part  In addition, a casting may have internal surfaces, determined by a core, placed inside the mold cavity to define the interior geometry of part  In sand casting, cores are generally made of sand  Gating System  Channel through which molten metal flows into cavity from outside of mold  Consists of a downsprue, through which metal enters a runner leading to the main cavity  At the top of downsprue, a pouring cup is often used to minimize splash and turbulence as the metal flows into downsprue  Riser  Reservoir in the mold which is a source of liquid metal to compensate for shrinkage of the part during solidification  The riser must be designed to freeze after the main casting in order to satisfy its function  Steps in Sand Casting 1. Pour the molten metal into sand mold 2. Allow time for metal to solidify 3. Break up the mold to remove casting 4. Clean and inspect casting ⚫ Separate gating and riser system 5. Heat treatment of casting is sometimes required to improve metallurgical properties  Making the Sand Mold  The cavity in the sand mold is formed by packing sand around a pattern, then separating the mold into two halves and removing the pattern  The mold must also contain gating and riser system  If casting is to have internal surfaces, a core must be included in mold  A new sand mold must be made for each part produced  Sand Casting Production Sequence Figure 11.2 Steps in the production sequence in sand casting. The steps include not only the casting operation but also pattern-making and mold-making.  The Pattern  A full-sized model of the part, slightly enlarged to account for shrinkage and machining allowances in the casting  Pattern materials: ⚫ Wood - common material because it is easy to work, but it warps ⚫ Metal - more expensive to make, but lasts much longer ⚫ Plastic - compromise between wood and metal  Types of Patterns Figure 11.3 Types of patterns used in sand casting: (a) solid pattern (b) split pattern (c) match-plate pattern (d) cope and drag pattern  Core  Full-scale model of interior surfaces of part  It is inserted into the mold cavity prior to pouring  The molten metal flows and solidifies between the mold cavity and the core to form the casting's external and internal surfaces  May require supports to hold it in position in the mold cavity during pouring, called chaplets  Core in Mold Figure 11.4 (a) Core held in place in the mold cavity by chaplets, (b) possible chaplet design, (c) casting with internal cavity.  Desirable Mold Properties  Strength - to maintain shape and resist erosion  Permeability - to allow hot air and gases to pass through voids in sand  Thermal stability - to resist cracking on contact with molten metal  Collapsibility - ability to give way and allow casting to shrink without cracking the casting  Reusability - can sand from broken mold be reused to make other molds.  Types of Sand Mold  Green-sand molds - mixture of sand, clay, and water; ⚫ “Green" means mold contains moisture at time of pouring  Dry-sand mold - organic binders rather than clay ⚫ And mold is baked to improve strength  Skin-dried mold - drying mold cavity surface of a green-sand mold to a depth of 10 to 25 mm, using torches or heating lamps  Expendable Mold Processes  Shell Molding  Expanded Polystyrene Process  Investment Casting  Plaster Mold and Ceramic Mold Casting  Shell Molding Casting process in which the mold is a thin shell of sand held together by thermosetting resin binder Figure 11.5 Steps in shell-molding: (1) a match-plate or cope-and-drag metal pattern is heated and placed over a box containing sand mixed with thermosetting resin.  Shell Molding Figure 11.5 Steps in shell-molding: (2) box is inverted so that sand and resin fall onto the hot pattern, causing a layer of the mixture to partially cure on the surface to form a hard shell; (3) box is repositioned so that loose uncured particles drop away;  Shell Molding Figure 11.5 Steps in shell-molding: (4) sand shell is heated in oven for several minutes to complete curing; (5) shell mold is stripped from the pattern;  Shell Molding Figure 11.5 Steps in shell-molding: (6) two halves of the shell mold are assembled, supported by sand or metal shot in a box, and pouring is accomplished; (7) the finished casting with sprue removed.  Advantages and Disadvantages  Advantages of shell molding: ⚫ Smoother cavity surface permits easier flow of molten metal and better surface finish ⚫ Good dimensional accuracy - machining often not required ⚫ Mold collapsibility minimizes cracks in casting ⚫ Can be mechanized for mass production ⚫ Special cores may be eliminated ⚫ Thin sections can be cast. ⚫ Permeability of the shell is high and no gas inclusions ⚫ Mechanisms is readily is possible, it is simple process Disadvantages  Patterns are very expensive  Size is limited. Up to 200 kg may be used.  Highly complicated shape cannot be produced.  More sophisticated equipment is needed for handling.  Expanded Polystyrene Process  Uses a mold of sand packed around a polystyrene foam pattern which vaporizes when molten metal is poured into mold  Other names: lost-foam process, lost pattern process, evaporative-foam process, and full-mold process  Polystyrene foam pattern includes sprue, risers, gating system, and internal cores (if needed)  Mold does not have to be opened into cope and drag sections  Expanded Polystyrene Process Figure 11.7 Expanded polystyrene casting process: (1) pattern of polystyrene is coated with refractory compound;  Expanded Polystyrene Process Figure 11.7 Expanded polystyrene casting process: (2) foam pattern is placed in mold box, and sand is compacted around the pattern;  Expanded Polystyrene Process Figure 11.7 Expanded polystyrene casting process: (3) molten metal is poured into the portion of the pattern that forms the pouring cup and sprue. As the metal enters the mold, the polystyrene foam is vaporized ahead of the advancing liquid, thus the resulting mold cavity is filled.  Advantages and Disadvantages  Advantages of expanded polystyrene process: ⚫ Pattern need not be removed from the mold ⚫ Simplifies and speeds mold-making, because two mold halves are not required as in a conventional green-sand mold  Disadvantages: ⚫ A new pattern is needed for every casting ⚫ Economic justification of the process is highly dependent on cost of producing patterns  Expanded Polystyrene Process  Applications: ⚫ Mass production of castings for automobile engines ⚫ Automated and integrated manufacturing systems are used to 1. Mold the polystyrene foam patterns and then 2. Feed them to the downstream casting operation Investment Casting (Lost Wax Process)  A pattern made of wax is coated with a refractory material to make mold, after which wax is melted away prior to pouring molten metal  "Investment" comes from a less familiar definition of "invest" - "to cover completely," which refers to coating of refractory material around wax pattern  It is a precision casting process - capable of producing castings of high accuracy and intricate detail  Investment Casting Figure 11.8 Steps in investment casting: (1) wax patterns are produced, (2) several patterns are attached to a sprue to form a pattern tree  Investment Casting Figure 11.8 Steps in investment casting: (3) the pattern tree is coated with a thin layer of refractory material, (4) the full mold is formed by covering the coated tree with sufficient refractory material to make it rigid  Investment Casting Figure 11.8 Steps in investment casting: (5) the mold is held in an inverted position and heated to melt the wax and permit it to drip out of the cavity, (6) the mold is preheated to a high temperature, the molten metal is poured, and it solidifies  Investment Casting Figure 11.8 Steps in investment casting: (7) the mold is broken away from the finished casting and the parts are separated from the sprue Advantages  Complex shapes which are difficult to produce by any other method are possible  Very fine details and thin sections can be produced  Very close tolerance and better finish can be produced  Very little or no machining required  Since no parting line, dimensions across it would not affect Disadvantages  Size is limited to weight of the casting  More expensive process because manual labor is required  Plaster Mold Casting*  Similar to sand casting except mold is made of plaster of Paris (gypsum - CaSO4-2H2O)  In mold-making, plaster and water mixture is poured over plastic or metal pattern and allowed to set ⚫ Wood patterns not generally used due to extended contact with water  Plaster mixture readily flows around pattern, capturing its fine details and good surface finish  Advantages and Disadvantages  Advantages of plaster mold casting: ⚫ Good accuracy and surface finish ⚫ Capability to make thin cross-sections  Disadvantages: ⚫ Mold must be baked to remove moisture, which can cause problems in casting ⚫ Mold strength is lost if over-baked ⚫ Plaster molds cannot stand high temperatures, so limited to lower melting point alloys  Ceramic Mold Casting*  Similar to plaster mold casting except that mold is made of refractory ceramic material that can withstand higher temperatures than plaster  Can be used to cast steels, cast irons, and other high-temperature alloys  Applications similar to those of plaster mold casting except for the metals cast  Advantages (good accuracy and finish) also similar Permanent Mold Casting Processes  Economic disadvantage of expendable mold casting: a new mold is required for every casting  In permanent mold casting, the mold is reused many times  The processes include: ⚫ Basic permanent mold casting ⚫ Die casting ⚫ Centrifugal casting  The Basic Permanent Mold Process  Uses a metal mold constructed of two sections designed for easy, precise opening and closing  Molds used for casting lower melting point alloys are commonly made of steel or cast iron  Molds used for casting steel must be made of refractory material, due to the very high pouring temperatures  Permanent Mold Casting Figure 11.10 Steps in permanent mold casting: (1) mold is preheated and coated  Permanent Mold Casting Figure 11.10 Steps in permanent mold casting: (2) cores (if used) are inserted and mold is closed, (3) molten metal is poured into the mold, where it solidifies.  Advantages and Limitations  Advantages of permanent mold casting: ⚫ Good dimensional control and surface finish ⚫ More rapid solidification caused by the cold metal mold results in a finer grain structure, so castings are stronger ⚫ Economical for large production ⚫ Inserts can be readily cast in place  Limitations: ⚫ Generally limited to metals of lower melting point ⚫ Simpler part geometries compared to sand casting because of need to open the mold ⚫ High cost of mold  Applications of Permanent Mold Casting  Due to high mold cost, process is best suited to high volume production and can be automated accordingly  Typical parts: automotive pistons, pump bodies, and certain castings for aircraft and missiles  Metals commonly cast: aluminum, magnesium, copper-base alloys, and cast iron  Die Casting  A permanent mold casting process in which molten metal is injected into mold cavity under high pressure  Pressure is maintained during solidification, then mold is opened and part is removed  Molds in this casting operation are called dies; hence the name die casting  Use of high pressure to force metal into die cavity is what distinguishes this from other permanent mold processes  Die Casting Machines  Designed to hold and accurately close two mold halves and keep them closed while liquid metal is forced into cavity  Two main types: 1. Hot-chamber machine 2. Cold-chamber machine  Hot-Chamber Die Casting  Metal is melted in a container, and a piston injects liquid metal under high pressure into the die  High production rates - 500 parts per hour not uncommon  Applications limited to low melting-point metals that do not chemically attack plunger and other mechanical components  Casting metals: zinc, tin, lead, and magnesium  Hot-Chamber Die Casting Figure 11.13 Cycle in hot-chamber casting: (1) with die closed and plunger withdrawn, molten metal flows into the chamber  Hot-Chamber Die Casting Figure 11.13 Cycle in hot-chamber casting: (2) plunger forces metal in chamber to flow into die, maintaining pressure during cooling and solidification. Cold-Chamber Die Casting Machine  Molten metal is poured into unheated chamber from external melting container, and a piston injects metal under high pressure into die cavity  High production but not usually as fast as hot-chamber machines because of pouring step  Casting metals: aluminum, brass, and magnesium alloys  Advantages of hot-chamber process favor its use on low melting-point alloys (zinc, tin, lead) Cold-Chamber Die Casting Figure 11.14 Cycle in cold-chamber casting: (1) with die closed and ram withdrawn, molten metal is poured into the chamber  Cold-Chamber Die Casting Figure 11.14 Cycle in cold-chamber casting: (2) ram forces metal to flow into die, maintaining pressure during cooling and solidification.  Molds for Die Casting  Usually made of tool steel, mold steel, or maraging steel  Tungsten and molybdenum (good refractory qualities) used to die cast steel and cast iron  Ejector pins required to remove part from die when it opens  Lubricants must be sprayed into cavities to prevent sticking  Advantages and Limitations  Advantages of die casting: ⚫ Economical for large production quantities ⚫ Good accuracy and surface finish ⚫ Thin sections are possible due to injection of metal ⚫ Small thickness can be easily filled ⚫ Rapid cooling provides small grain size and good strength to casting ⚫ Longer die life -30,000 pieces ⚫ Better mechanical properties  Disadvantages: ⚫ Generally limited to metals with low metal points ⚫ Part geometry must allow removal from die  Casting Quality  There are numerous opportunities for things to go wrong in a casting operation, resulting in quality defects in the product  The defects can be classified as follows: ⚫ General defects common to all casting processes ⚫ Defects related to sand casting process  General Defects: Misrun A casting that has solidified before completely filling mold cavity Figure 11.22 Some common defects in castings: (a) misrun  General Defects: Cold Shut Two portions of metal flow together but there is a lack of fusion due to premature freezing Figure 11.22 Some common defects in castings: (b) cold shut  General Defects: Cold Shot Metal splatters during pouring and solid globules form and become entrapped in casting Figure 11.22 Some common defects in castings: (c) cold shot  General Defects: Shrinkage Cavity Depression in surface or internal void caused by solidification shrinkage that restricts amount of molten metal available in last region to freeze Figure 11.22 Some common defects in castings: (d) shrinkage cavity  Sand Casting Defects: Sand Blow Balloon-shaped gas cavity caused by release of mold gases during pouring Figure 11.23 Common defects in sand castings: (a) sand blow  Sand Casting Defects: Pin Holes Formation of many small gas cavities at or slightly below surface of casting Figure 11.23 Common defects in sand castings: (b) pin holes  Sand Casting Defects: Penetration When fluidity of liquid metal is high, it may penetrate into sand mold or core, causing casting surface to consist of a mixture of sand grains and metal Figure 11.23 Common defects in sand castings: (e) penetration example  Sand Casting Defects: Mold Shift A step in cast product at parting line caused by sidewise relative displacement of cope and drag Figure 11.23 Common defects in sand castings: (f) mold shift example  Foundry Inspection Methods  Visual inspection to detect obvious defects such as misruns, cold shuts, and severe surface flaws  Dimensional measurements to insure that tolerances have been met  Metallurgical, chemical, physical, and other tests concerned with quality of cast metal [email protected]