Casting (1998) Part 9 pptx

F 232 Deformation with respect to drawing proportional for casting and mold; pattern conforms to drawing Deformed mold, mold creep, springback F 233 Casting deformed with respect to drawing; pattern and mold conform to drawing Casting distortion F 234 Casting deformed with respect to drawing after storage, annealing, machining Warped casting Inclusions or Structural Anomalies G 100: Inclusions G 110: Metallic inclusions G 111 (a) Metallic inclusions whose appearance, chemical analysis or structural examination show to be caused by an element foreign to the alloy Metallic inclusions G 112 (a) Metallic inclusions of the same chemical composition as the base metal; generally spherical and often coated with oxide Cold shot G 113 Spherical metallic inclusions inside blowholes or other cavities or in surface depressions (see A 311). Composition approximates that of the alloy cast but nearer to that of a eutectic Internal sweating, phosphide sweat G 120: Nonmetallic inclusions; slag, dross, flux G 121 (a) Nonmetallic inclusions whose appearance or analysis shows they arise from melting slags, products of metal treatment or fluxes Slag, dross or flux inclusions, ceroxides G 122 (a) Nonmetallic inclusions generally impregnated with gas and accompanied by blowholes (B 113) Slag blowhole defect G 130: Nonmetallic inclusions; mold or core materials G 131 (a) Sand inclusions, generally very close to the surface of the casting Sand inclusions G 132 (a) Inclusions of mold blacking or dressing, generally very close to the casting surface Blacking or refractory coating inclusions G 140: Nonmetallic inclusions; oxides and reaction products G 141 Clearly defined, irregular black spots on the fractured surface of ductile cast iron Black spots G 142 (a) Inclusions in the form of oxide skins, most often causing a localized seam Oxide inclusion or skins, seams G 143 (a) Folded films of graphitic luster in the wall of the casting Lustrous carbon films, or kish tracks G 144 Hard inclusions in permanent molded and die cast aluminum alloys Hard spots (a) Defects that under some circumstances could contribute, either directly or indirectly, to casting failures. Adapted from International Atlas of Casting Defects, American Foundrymen's Society, Des Plaines, IL Common Inspection Procedures Inspection of castings is most often limited to visual and dimensional inspections, weight testing, and hardness testing. However, for castings that are to be used in critical applications, such as in aerospace components, additional methods of nondestructive inspection are used to determine and to control casting quality. Visual inspection of each casting ensures that none of its features has been omitted or malformed by molding errors, short running, or mistakes in cleaning. Most surface defects and roughness can be observed at this stage. Initial sample castings from new pattern equipment should be carefully inspected for obvious defects. Liquid penetrant inspection can be used to detect surface defects. Such casting imperfections as shrinks, cracks, blows, or dross usually indicate the need for adjustment in the gating or foundry techniques. If the casting appears to be satisfactory upon visual inspection, internal quality can be checked by radiographic and ultrasonic inspection. The first visual inspection operation on the production casting is usually performed immediately after shakeout or knockout of the casting. This ensures that major visible imperfections are detected as quickly as possible. This information, promptly relayed to the foundry, permits early corrective action to be taken with a minimum of scrap loss. The size and complexity of some sand castings require that the gates and risers be removed to permit proper inspection of the casting. Many castings that contain numerous internal cores or have close dimensional tolerances require a rapid but fairly accurate check of critical wall dimensions. In some cases, an indicating-type caliper gage is suitable for this work, and special types are available for casting shapes that do not lend themselves to the standard types. Ultrasonic inspection is also used to determine wall thickness in such components as cored turbine blades made by investment casting (see the article "Investment Casting" in this Volume). Dimensional Inspection. Dimensional deviations on machined surfaces are relatively simple to evaluate and can be accurately specified. However, it is not so simple to determine the acceptability of dimensions that involve one or more unmachined surfaces. Dimensional inspection can be carried out with the aid of gages, jigs, and templates. Most initial machining operations on castings use a cast surface as a datum; the exceptions are those large castings that are laid out, before machining, to give the required datum. Therefore, it is important that the cast surface used as a datum be reasonably true and that it be in the correct position relative to other critical machined or unmachined surfaces on the same casting, within clearly defined limits. The cast surface used as a datum can be a mold surface, and variations can occur because of mold movement. The cast surface can be produced by a core; movement of cores is a frequent cause of casting inaccuracy. Errors involving these surfaces can produce consequential errors or inadequate machining stock elsewhere on the casting. Where dimensional errors are detected in relation to general drawing tolerances, their true significance must be determined. A particular dimension may be of vital importance, but may have been included in blanket tolerances. This situation stresses the desirability of stating functional dimensions on drawings so that tolerances are not restricted unnecessarily. Weight Testing. Many intricately cored castings are extremely difficult to measure accurately, particularly the internal sections. It is important to ensure that these sections are correct in thickness for three main reasons: • There should be no additional weight that would make the finished product heavier than permissible • Sections must not be thinner than designed to prevent detracting from the strength of the casting • If hollow cavities have been reduced in area by increasing the metal thickness of the sections, any flow of liquid or gases is reduced A ready means of testing for these discrepancies is by accurately weighing each casting or by measuring the displacement caused by immersing the casting in a liquid-filled measuring jar or vessel. In certain cases in which extreme accuracy is demanded, a tolerance of only ±1% of a given weight may be allowed. Hardness testing is often used to verify the effectiveness of heat treatment applied to actual castings. Its general correlation with the tensile strength of many ferrous alloys enables a rough prediction of tensile strength to be made. The Brinell hardness test is most frequently used for casting alloys. A combination of large-diameter ball (5 or 10 mm) and heavy load (500 to 3000 kgf) is preferred for the most effective representation because a deep impression minimizes the influence of the immediate surface layer and of the relatively coarse microstructure. The Brinell hardness test is unsuitable for use at high hardness levels (above 600 HB), because distortion of the ball indenter can affect the shape of the indentation. Either the Rockwell or the Vickers (136° diamond pyramid) hardness test is used for alloys of extreme hardness or for high-quality and precision castings in which the large Brinell indentation cannot be tolerated. Because of the very small indentations produced in Rockwell and Vickers tests, which use loads of 150 kg or less, results must be based on the average of a number of determinations. Portable hardness testers or ultrasonic microhardness testers can be used on large castings that cannot be placed on the platform of a bench-type machine. More detailed information on hardness testing is available in Mechanical Testing, Volume 8 of ASM Handbook, formerly 9th Edition Metals Handbook. The hardness of ferrous castings can be related to the sonic velocity of the metal and determined from it if all other test conditions remain constant. This has been demonstrated on chilled rolls in determining the average hardness of the core. Liquid Penetrant Inspection Liquid penetrant inspection essentially involves a liquid wetting the surface of a workpiece, flowing over that surface to form a continuous and uniform coating, and migrating into cracks or cavities that are open to the surface. After a few minutes, the liquid coating is washed off the surface of the casting and a developer is placed on the surface. The developer is stained by the liquid penetrant as it is drawn out of the cracks and cavities. Liquid penetrants will highlight surface defects so that detection is more certain. Liquid penetrant inspection should not be confined to as-cast surfaces. For example, it is not unusual for castings of various alloys to exhibit cracks, frequently intergranular, on machined surfaces. A pattern of cracks of this type may be the result of intergranular cracking throughout the material because of an error in composition or heat treatment, or the cracks may be on the surface only as a result of machining or grinding. Surface cracking may result from insufficient machining allowance, which does not allow for complete removal of imperfections produced on the as-cast surface, or it may result from faulty machining techniques. If imperfections of this type are detected by visual inspection, liquid penetrant inspection will show the full extent of such imperfections, will give some indication of the depth and size of the defect below the surface by the amount of penetrant absorbed, and will indicate whether cracking is present throughout the section. Magnetic Particle Inspection Magnetic particle inspection is a highly effective and sensitive technique for revealing cracks and similar defects at or just beneath the surface of castings made of ferromagnetic metals. The capability of detecting discontinuities just beneath the surface is important because such cleaning methods as shot or abrasive blasting tend to close a surface break that might go undetected in visual or liquid penetrant inspection. When a magnetic field is generated in and around a casting made of a ferromagnetic metal and the lines of magnetic flux are intersected by a defect such as a crack, magnetic poles are induced on either side of the defect. The resulting local flux disturbance can be detected by its effect on the particles of a ferromagnetic material, which become attracted to the region of the defect as they are dusted on the casting. Maximum sensitivity of indication is obtained when a defect is oriented in a direction perpendicular to the applied magnetic field and when the strength of this field is just enough to saturate the casting being inspected. Equipment for magnetic particle inspection uses direct or alternating current to generate the necessary magnetic fields. The current can be applied in a variety of ways to control the direction and magnitude of the magnetic field. In one method of magnetization, a heavy current is passed directly through the casting placed between two solid contacts. The induced magnetic field then runs in the transverse or circumferential direction, producing conditions favorable to the detection of longitudinally oriented defects. A coil encircling the casting will induce a magnetic field that runs in the longitudinal direction, producing conditions favorable to the detection of circumferentially (or transversely) oriented defects. Alternatively, a longitudinal magnetic field can be conveniently generated by passing current through a flexible cable conductor, which can be coiled around any metal section. This method is particularly adaptable to castings of irregular shape. Circumferential magnetic fields can be induced in hollow cylindrical castings by using an axially disposed central conductor threaded through the casting. Small castings can be magnetic particle inspected directly on bench-type equipment that incorporates both coils and solid contacts. Critical regions of larger castings can be inspected by the use of yokes, coils, or contact probes carried on flexible cables connected to the source of current this setup enables most regions of castings to be inspected. Eddy Current Inspection Eddy current inspection consists of observing the interaction between electromagnetic fields and metals. In a basic system, currents are induced to flow in the testpiece by a coil of wire that carries an alternating current. As the part enters the coil, or as the coil in the form of a probe or yoke is placed on the testpiece, electromagnetic energy produced by the coils is partly absorbed and converted into heat by the effects of resistivity and hysteresis. Part of the remaining energy is reflected back to the test coil, its electrical characteristics having been changed in a manner determined by the properties of the testpiece. Consequently, the currents flowing through the probe coil are the source of information describing the characteristics of the testpiece. These currents can be analyzed and compared with currents flowing through a reference specimen. Eddy current methods of inspection are effective with both ferromagnetic and nonferromagnetic metals. Eddy current methods are not as sensitive to small, open defects as liquid penetrant or magnetic particle methods are. Because of the skin effect, eddy current inspection is generally restricted to depths less than 6 mm ( 1 4 in.). The results of inspecting ferromagnetic materials can be obscured by changes in the magnetic permeability of the testpiece. Changes in temperature must be avoided to prevent erroneous results if electrical conductivity or other properties, including metallurgical properties, are being determined. Applications of eddy current and electromagnetic methods of inspection to castings can be divided into the following three categories: • Detecting near- surface flaws such as cracks, voids, inclusions, blowholes, and pinholes (eddy current inspection) • Sorting according to a lloy, temper, electrical conductivity, hardness, and other metallurgical factors (primarily electromagnetic inspection) • Gaging according to size, shape, plating thickness, or insulation thickness (eddy current or electromagnetic inspection) Radiographic Inspection ** Radiographic inspection is a process of testing materials using penetrating radiation from an x-ray generator or a radioactive source and an imaging medium, such as x-ray film or an electronic device. In passing through the material, some of the radiation is attenuated, depending on the thickness and the radiographic density of the material, while the radiation that passes through the material forms an image. The radiographic image is generated by variations in the intensity of the emerging beam. Internal flaws, such as gas entrapment or nonmetallic inclusions, have a direct effect on the attenuation. These flaws create variations in material thickness, resulting in localized dark or light spots on the image. The term radiography usually implies a radiographic process that produces a permanent image on film (conventional radiography) or paper (paper radiography or xeroradiography), although in a broad sense it refers to all forms of radiographic inspection. When inspection involves viewing an image on a fluorescent screen or image intensifier, the radiographic process is termed filmless or real time inspection (Fig. 1). When electronic nonimaging instruments are used to measure the intensity of radiation, the process is termed radiation gaging. Tomography, a radiation inspection method adapted from the medical computerized axial tomography scanner, provides a cross-sectional view of a testpiece. All of the above terms are primarily used in connection with inspection that involves penetrating electromagnetic radiation in the form of x-rays or γ-rays. Neutron radiography refers to radiographic inspection using neutrons rather than electromagnetic radiation. Fig. 1 Schematic of real time x-ray inspection system. Source: TFI Corporation. The sensitivity, or the ability to detect flaws, of radiographic inspection depends on close control of the inspection technique, including the geometric relationships among the point of x-ray emission, the casting, and the x-ray imaging plane. The smallest detectable variation in metal thickness lies between 0.5 and 2.0% of the total section thickness. Narrow flaws, such as cracks, must lie in a plane approximately parallel to the emergent x-ray beam to be imaged; this requires multiple exposures for x-ray film techniques and a remote control parts manipulator for a real time system. Real time systems have eliminated the need for multiple exposures of the same casting by dynamically inspecting parts on a manipulator, with the capability of changing the x-ray energy for changes in total material thickness. These capabilities have significantly improved productivity and have reduced costs, thus enabling higher percentages of castings to be inspected and providing instant feedback after repair procedures. Advances. Several advances have been made to assist the industrial radiographer. These include the computerization of the radiographic standard shooting sketch, which graphically shows areas to be x-rayed and the viewing direction or angle at which the shot is to be taken, and the development of microprocessor-controlled x-ray systems capable of storing different x-ray exposure parameters for rapid retrieval and automatic warm-up of the system prior to use. The advent of digital image processing systems and microfocus x-ray sources (near point source), producing energies capable of penetrating thick material sections, have made real time inspection capable of producing images equal to, and in some cases superior to, x-ray film images by employing geometric relations previously unattainable with macrofocus x-ray systems. The near point source of the microfocus x-ray system virtually eliminates the edge unsharpness associated with larger focus devices. Digital image processing can be used to enhance imagery by multiple video frame integration and averaging techniques that improve the signal-to-noise ratio of the image. This enables the radiographer to digitally adjust the contrast of the image and to perform various edge enhancements to increase the conspicuity of many linear indications. Interpretation of the radiographic image requires a skilled specialist who can establish the correct method of exposing the castings with regard to x-ray energies, geometric relationships, and casting orientation and can take all of these factors into account to achieve an acceptable, interpretable image. Interpretation of the image must be performed to establish standards in the form of written or photographic instructions. The inspector must also be capable of determining if the localized indication is a spurious indication, a film artifact, a video aberration, or a surface irregularity. Note cited in this section ** This section was prepared by Frederick A. Morrow, TFI Corporation. Ultrasonic Inspection Ultrasonic inspection is a nondestructive method in which beams of high-frequency acoustic energy are introduced into the material under evaluation to detect surface and subsurface flaws and to measure the thickness of the material or the distance to a flaw. An ultrasonic beam will travel through a material until it strikes an interface or defect. Interfaces and defects interrupt the beam and reflect a portion of the incident acoustic energy. The amount of energy reflected is a function of the nature and orientation of the interface or flaw as well as the acoustic impedance of such a reflector. Energy reflected from various interfaces or defects can be used to define the presence and locations of defects, the thickness of the material, or the depth of a defect beneath a surface. The advantages of ultrasonic tests are as follows: • High sensitivity, which permits the detection of minute cracks • Great penetrating power, which allows the examination of extremely thick sections • Accuracy in measurement of flaw position and estimation of defect size Ultrasonic tests have the following limitations: • Size-contour complexity and unfavorable discontinuity ori entation can pose problems in interpretation of the echo pattern • Undesirable internal structure for example, grain size, structure, porosity, inclusion content, or fine dispersed precipitates can similarly hinder interpretation • Reference standards are required Ultrasonic inspection is more commonly used for wrought and welded products than for castings. It should be noted, however, that slag, porosity, cold shuts, tears, shrinkage cracks, and inclusions can be detected, particularly in castings that are not complex in shape. Wall thickness examination of cored castings is also conducted by ultrasonic inspection. Leak Testing Castings that are intended to withstand pressures can be leak tested in the foundry. Various methods are used, according to the type of metal being tested. One method consists of pumping air at a specified pressure into the inside of the casting and then submerging the casting in water at a given temperature. Any leaks through the casting become apparent by the release of bubbles of air through the faulty portions. An alternative method is to fill the cavities of a casting with paraffin at a specified pressure. Paraffin, which will penetrate the smallest of crevices, will rapidly find any defect, such as porosity, and will show quickly as an oily or moist patch at the position of the fault. Liquid penetrants can be poured into areas of apparent porosity and time allowed for the liquid to seep through the casting wall. Pressure testing of rough (unmachined) castings at the foundry may not reveal any leaks, but it must be recognized that subsequent machining operations on the casting may cut into porous areas and cause the casting to leak after machining. Minor seepage leaks can be sealed by impregnation of the casting with liquid or filled sodium silicate, a synthetic resin, or other suitable substance. As-cast parts can be impregnated at the foundry to seal leaks if there is to be little machining or if experience has shown that machining does not affect the pressure tightness. However, it is usually preferable to impregnate after final machining of the casting. Inspection of Ferrous Castings Ferrous castings can be inspected by most of the nondestructive inspection methods. Magnetic particle inspection can be applied to ferrous metals with excellent sensitivity, although a crack in a ferrous casting can often be seen by visual inspection. Magnetic particle inspection provides good crack delineation, but the method should not be used to detect other defects. Irrelevant magnetic particle indications occasionally occur on ferrous castings, especially with a strong magnetic field. For example, a properly fused-in steel chaplet can be indicated as a defect because of the difference in magnetic response between low-carbon steel and cast iron. Even the graphite in cast iron, which is nonmagnetic, can cause an irrelevant indication. Standard x-ray and radioactive-source techniques can be used to make radiographs of ferrous castings, but the typical complexity of shape and varying section thicknesses of the castings may require complex procedures. Radiography is sometimes used to inspect critical production castings that will be subjected to high service stresses, but it is more often used to evaluate design or casting procedures. Ultrasonic inspection for both thickness and defects is practical with most ferrous castings except for the high-carbon gray iron castings, which have a high damping capacity and absorb much of the input energy. The measurement of resonant frequency is a good method for inspecting some ductile iron castings for soundness and graphite shape. Electromagnetic testing can be used to distinguish metallurgical differences between castings. The criteria for separating acceptable from unacceptable castings must be established empirically for each casting lot. Gray Iron Castings Gray iron castings are susceptible to most of the imperfections generally associated with castings, with additional problems resulting from the relatively high pouring temperatures. These additional problems result in a higher incidence of gas entrapment, inclusions, poor metal structure, interrupted metal walls, and mold wall deficiencies. Gas entrapment is a direct result of gas being trapped in the casting wall during solidification. This gas may be in the metal prior to pouring, may be generated from aspiration during pouring, or may be generated from core and mold materials. Internal defects of this type are best detected by radiography, but ultrasonic and eddy current methods of inspection are useful when the defect is large enough to be detected by these methods. Inclusions are casting defects in which solid foreign materials are trapped in the casting wall. The inclusion material can be slag generated in the melting process, or it can be fragments of refractory, mold sand, core aggregate, or other materials used in the casting process. Inclusions appear most often on the casting surface and are usually detected by visual inspection; however, in many cases, the internal walls of castings contain inclusions that cannot be visually detected. The internal inclusions can be detected by eddy current, radiographic, or ultrasonic inspection; radiography is usually the most reliable method. Poor Metal Structure. Many casting defects resulting from metal structure are related to shrinkage, which is either a cavity or a spongy area lined with dendrites or is a depression in the casting surface. This type of defect arises from varying rates of contraction while the metal is changing from a liquid to a solid. Other casting defects resulting from varying rates of contraction during solidification include carbide formation, hardness variations, and microporosity. Internal shrinkage defects are best detected by radiography, although eddy current or ultrasonic inspection can be used. Soft or hard gray iron castings are usually detected by Brinell hardness testing; electromagnetic methods have proved useful on some castings. Interrupted Metal Walls. Included in this category are such flaws as hot tears, cold shuts, and casting cracks. Cracking of castings is often a major problem in gray iron foundries as a result of the combination of casting designs and high production rates. Visual inspection, or an aided visual method such as liquid penetrant or magnetic particle inspection, is used to detect cracks and cracklike flaws in castings. Mold wall deficiencies are common problems in gray iron castings. They result in surface flaws such as scabs, rattails, cuts, washes, buckles, drops, and excessive metal penetration into space between sand grains. These flaws are generally detected by visual inspection. Malleable Iron Castings Blowholes and spikes are defects that are often found in malleable iron castings. Spikes are a form of surface shrinkage not normally visible to the naked eye but appear as a multitude of short discontinuous surface cracks when subjected to fluorescent magnetic particle inspection. Unlike true fractures, spikes do not propagate, but they are not acceptable where cyclic loading could result in fatigue failure. Spikes are usually seen as short indications about 1.6 mm ( 1 16 in.) long or less and never more than 75 μm (0.003 in.) deep. These defects do not have a preferred orientation but a random pattern that may or may not follow the direction of solidification. Shrinkage or open structure in the gated area is a defect often found in malleable iron castings that may be overlooked by visual inspection, although it is readily detected by either liquid penetrant or magnetic particle inspection. Ductile Iron Castings Ductile iron is cast iron in which the graphite is present in tiny balls or spherulites instead of flakes (as in gray iron) or compacted aggregates (as in malleable iron). The spheroidal graphite structure is produced by the addition of one or more elements to the molten metal. Casting defects associated with foundry practice that is, shrinkage, voids from entrapped gas, nonmetallic inclusions, and failure to fill the mold shape are essentially the same for ductile iron as for gray iron. Carbonnodule segregation occurs when the carbon equivalent (CE) of ductile iron [CE = % total carbon + 0.3 (%Si + %P)] is incorrect for the section thickness of the casting. Subsurface inclusions arise from the formation of nonmetallic compounds (mainly sulfides) following inoculation of the molten iron. Slag inclusions form in ductile iron in appreciable amounts upon inoculation with magnesium because some of the magnesium ignites in the molten metal. Desulfurization also promotes slag formation. Inspection of Aluminum Alloy Castings Effective quality control is needed at every step in the production of an aluminum alloy casting, from selection of the casting method, casting design, and alloy to mold production, foundry technique, machining, finishing, and inspection. Visual methods, such as visual inspection, pressure testing, liquid penetrant inspection, ultrasonic inspection, radiographic inspection, and metallographic examination, can be used to inspect for casting quality. The inspection procedure used should be geared toward the specified level of quality. Stages of Inspection. Inspections can be divided into three stages: preliminary, intermediate, and final. After tests are conducted on the melt for hydrogen content, for adequacy of silicon modification, and for degree of grain refinement, preliminary inspection may consist of the inspection and testing of test bars cast with the molten alloy at the same time the production castings are poured. These test bars are used to check the quality of the alloy and effectiveness of the heat treatment. Preliminary inspection also includes chemical or spectrographic analysis of the casting, thus ensuring that the melting and pouring operations have resulted in an alloy of the desired composition. Intermediate inspection, or hot inspection, is performed on the casting as it is taken from the mold. This step is essential so that castings that are obviously defective can be discarded at this stage of production. Castings that are judged unacceptable at this stage can then be considered for salvage by impregnation, welding, or other methods, depending on the type of flaw present and the end use of the casting. More complex castings usually undergo visual and dimensional inspection after the removal of gates and risers. Final inspection establishes the quality of the finished casting, using any of the methods previously mentioned. Visual inspection also includes the final measurement and comparison of specified and actual dimensions. Dimensions of castings from a large production run can be checked using gages, jigs, fixtures, or coordinate-measuring systems (described later). Liquid penetrant inspection is extensively used as a visual aid for detecting surface flaws in aluminum alloy castings. Liquid penetrant inspection is applicable to castings made from all the aluminum casting alloys as well as to castings produced by all methods. One of its most useful applications, however, is for inspecting small castings produced in permanent molds from alloys such as 296.0, which are characteristically susceptible to hot cracking. For example, in cast connecting rods, hot shortness may result in fine cracks in the shank sections. Such cracks are virtually undetectable by unaided visual inspection, but are readily detectable by liquid penetrant inspection. All of the well-known liquid penetrant systems (that is, water-washable, postemulsifiable, and solvent-removable) are applicable to inspection of aluminum alloy castings. In some cases, especially for certain high-integrity castings, more than one system can be used. Selection of the system is primarily based on the size and shape of the castings, surface roughness, production quantities, sensitivity level desired, and available inspection facilities. Pressure testing is used for castings that must be leaktight. Cored-out passages and internal cavities are first sealed off with special fixtures having air inlets. These inlets are used to build up the air pressure on the inside of the casting. The entire casting is then immersed in a tank of water, or it is covered by a soap solution. Bubbles will mark any point of air leakage. Radiographic inspection is a very effective means of detecting such conditions as cold shuts, internal shrinkage, porosity, core shifts, and inclusions in aluminum alloy castings. Radiography can also be used to measure the thickness of specific sections. Aluminum alloy castings are ideally suited to examination by radiography because of their relatively low density; a given thickness of aluminum alloy can be penetrated with about one-third the power required for penetrating the same thickness of steel. Aluminum alloy castings are most often radiographed by an x-ray machine, using film to record the results. Real time radiography is also widely used, particularly for examining large numbers of relatively small castings, and is best suited to detecting shrinkage, porosity, and core shift. Gamma-ray radiography is also satisfactory for detecting specific conditions in aluminum castings. Although the -ray method is used to a lesser extent than the x-ray method, it is about equally as effective for detecting flaws or measuring specific conditions. Aluminum alloy castings are most often radiographed to detect about the same types of flaws that may exist in other types of castings, that is, conditions such as porosity or shrinkage, which register as low-density spots or areas and appear blacker on the film or fluoroscopic screen than the areas of sound metal. Aluminum ingots may contain hidden internal cracks of varying dimensions. Depending on size and location, these cracks may cause an ingot to split during mechanical working and thermal treatment, or they may show up as a discontinuity in the final wrought product. Once the size and location of such cracks are determined, an ingot can be scrapped, or sections free from cracks can be sawed out and processed further. Because the major dimensions of the cracks are along the casting direction, they present good reflecting surfaces for sound waves traveling perpendicular to the casting direction. Thus, ultrasonic methods using a wave frequency that gives adequate penetration into the ingot provide excellent sensitivity for 100% inspection of that part of the ingot that contains critical cracks. Because of ingot thickness (up to 406 mm, or 16 in.) and the small metal separation across the crack, radiographic methods are impractical for inspection. Ultrasonic Inspection. Aluminum alloy castings are sometimes inspected by ultrasonic methods to evaluate internal soundness or wall thickness. The principal uses of ultrasonic inspection for aluminum alloy castings include detection of porosity in castings and internal cracks in ingots. Inspection of Copper and Copper Alloy Castings Inspection of copper and copper alloy castings is generally limited to visual and liquid penetrant inspection of the surface, along with radiographic inspection for internal discontinuities. In specific cases, electrical conductivity tests and ultrasonic inspection can be applied, although the usual relatively large cast grain size could prevent a successful ultrasonic inspection. Visual inspection is simple yet informative. A visual inspection would include significant dimensional measurements as well as general appearance. Surface discontinuities often indicate that internal discontinuities are also present. For small castings produced in reasonable volume, a destructive metallographic inspection on randomly selected samples is practical and economical. This is especially true on a new casting for which foundry practice has not been optimized and a satisfactory repeat-ability level has not been achieved. For castings of some of the harder and stronger alloys, a hardness test is a good means of estimating the level of mechanical properties. Hardness tests are of less value for the softer tin bronze alloys because hardness tests do not reflect casting soundness and integrity. Because copper alloys are nonmagnetic, magnetic particle inspection cannot be used to detect surface cracks. Instead, liquid penetrant inspection is recommended. Ordinarily, liquid penetrant inspection requires some prior cleaning of the casting to highlight the full detail. For the detection of internal defects, radiographic inspection is recommended. Radiographic methods and standards are well established for some copper alloy castings (for example, ASTM specifications E 272 and E 310). [...]... AFS, Vol 59, 198 5 23 V.G Parodi, Robots in the Automated Production of Aluminium-Alloy Pressure Diecasting, Foundry Trade J Int., Dec 197 8 24 N.W Rhea, Robots Improve a Die Casting Shop, Tool Prod., Vol 43, March 197 8 25 Die Casting With Robot, in Die Casting and Metal Molding, Cutlands Press, p 16-20 26 Robots at Work: Unimation Designs Automated Investment Casting System, Robotics Today, Fall 198 1 27... Foundry Mgmt Technol., April 198 5 5 C.F James and J.G Sylvia, The Robot's Role in Foundry Mechanization, Mod Cast., May 198 2 6 H.J Heine, New Ideas for the Cleaning Room Part I, Foundry Mgmt Technol., Aug 198 3 7 J.C Miske, Improving Cleaning Room Productivity, Foundry Mgmt Technol., Oct 198 4 8 E Ford, Automating Britain's Foundries, Mod Cast., June 198 2 9 D Williamson, Automating Castings: What GM Gets for... What GM Gets for $214 Million, Mfg Eng., Aug 198 5 10 Foundry Management and Technology Data Book, 198 8 11 Costs and Methods for Fettling Castings, IVF Result 766 39, Svenska Gjuteriforeningen, 197 6 12 R.G Godding, Fettling in the Light of Recent Developments, Br Foundryman, Vol 76, Dec 198 3 13 R.A Wragg, Practical Experiences of Using a Robot to Fettle Casting, Seminar Proceedings, BCIRA 14 B.J Sims... Conference, Steel Castings Research and Trade Association, 198 4 15 Experiments With Robots in Foundries, Mekanresultat 760 09, Svenska Gjuteriforeningen, Nov 197 6 16 W Sturz and D Boley, Development in Using Industrial Robots for Deburring and Fettling of Castings, Fraunhofer Institute 17 R.G Godding, Fettling in the Light of Recent Developments, Br Foundryman, Vol 76, Dec 198 3 18 W.T Hickman, Cleaning Casting. .. die casting (Ref 24, 28, 29, 30) Robots are used to spray both water and die lubricants on the die during each cycle References cited in this section 1 R Asfahl, Robots and Manufacturing Automation, John Wiley & Sons, 198 5 2 W.R Tanner, Industrial Robots, Society of Manufacturing Engineers, 197 9 3 C.W Meyers and J.T Berry, The Impact of Robotics on the Foundry Industry, Paper 30, Trans AFS, 197 9, p... Programming for Robotic Mold Venting, Paper 106, Trans AFS, 198 4 28 R.C Rodgers, Robots 9 Show and Conference Highlights Vision Systems, Foundry Mgmt Technol., Sept 198 5 29 W.A Wiesmueller, Robots in the Real World of Die Cast Foundries, Robotics Eng., March 198 6 30 J Canner, Automated Die Casting A Concept Comes Full Circle, Die Cast Eng., March/April 198 6 Cell Applications Many traditional manufacturing... is over 400 castings per day Fig 1 Schematic of a first-generation robotic system designed to perform fettling operations at a rate of one completely machined casting every 3 min Depending on casting size, the robot can either hold the casting and move it to the grinding machine or it can hold the grinding tools and apply them to the casting The advantages of using a robot to manipulate a casting include... Sept 198 4 19 M.D Schneider and R.R Petersen, Production Applications of Manipulators and Robots for Riser Cutting, Paper 161, Trans AFS, 198 6 20 M.D Schneider, Automatic Riser Removal at Rockwell International, in Proceedings of the 39th Annual Technical and Operating Conference, 12 Nov 198 4, Steel Founders' Society of America 21 G.E Munson, Foundries, Robots and Productivity, Unimation Inc., 197 8 22... computer technology to the dimensional inspection of castings Importance of Dimensional Inspection One of the most critical determinants of casting quality in the eyes of the casting buyer is dimensional accuracy (see the article "Dimensional Tolerances and Allowances" in this Volume) Parts that are within dimensional tolerances, given the absence of other casting defects, can be machined, assembled, and... cycle to change tools The robot can put the casting down on a fixture and regrip it to allow access to other surfaces of the casting For example, the robot can turn the casting around or completely over Upon completion of cleaning, the robot can place the casting in a fixture, drop it in a bin, or place it on any predetermined position on a pallet When the casting weight is high or when a variety of . unacceptable castings must be established empirically for each casting lot. Gray Iron Castings Gray iron castings are susceptible to most of the imperfections generally associated with castings,. after final machining of the casting. Inspection of Ferrous Castings Ferrous castings can be inspected by most of the nondestructive inspection methods. Magnetic particle inspection can be applied. through the casting. Small castings can be magnetic particle inspected directly on bench-type equipment that incorporates both coils and solid contacts. Critical regions of larger castings can