Casting (metalworking) - Wikipedia. Molten metal before casting. Casting iron in a sand mold. In metalworking, casting means a process, in which liquid metal is poured into a mold, that contains a hollow cavity of the desired shape, and is then allowed to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods. Traditional techniques include lost- wax casting, plaster mold casting and sand casting.
The modern casting process is subdivided into two main categories: expendable and non- expendable casting. It is further broken down by the mold material, such as sand or metal, and pouring method, such as gravity, vacuum, or low pressure. This method of mold casting involves the use of temporary, non- reusable molds.
Sand casting. Sand casting allows for smaller batches than 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 one's 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.
Green (moist) sand has almost no part weight limit, whereas dry sand has a practical part mass limit of 2,3. Minimum part weight ranges from 0. The sand is bonded together using clays, chemical binders, or polymerized oils (such as motor oil).
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Sand can be recycled many times in most operations and requires little maintenance. Plaster mold casting.
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Casting Bullet Bullets Make Making Home Lead Mold. Compression Molding Process / SMC. Compression molding is the most common choice for high-volume composite parts and often associated with SMC and BMC materials. One of the most common methods of converting plastics from the raw material form to an article of use is the process of injection moulding. This process is most.
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Blow molding is a manufacturing process that is used to create hollow plastic parts by inflating a heated plastic tube until it fills a mold and. WELDING WITH OXYACETYLENE : 1. Introduction to Oxyacetylene Welding: 2. Gas Welding and Safety: 3. Steel Welding Procedure - Flat Steel Plates.
Generally, the form takes less than a week to prepare, after which a production rate of 1–1. The biggest disadvantage is that it can only be used with low melting point non- ferrous materials, such as aluminium, copper, magnesium, and zinc. The sand used is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern and hardened into a shell around the pattern.
Because of the resin and finer sand, it gives a much finer surface finish. The process is easily automated and more precise than sand casting. Common metals that are cast include cast iron, aluminium, magnesium, and copper alloys.
This process is ideal for complex items that are small to medium- sized. Investment casting.
From 5. 00. 0 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.
Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 3. 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 require little or no rework once cast. Waste molding of plaster. With the completion of a plaster, the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking.
With the low cost plaster at hand, the expensive work of bronze casting or stone carving may be deferred until a patron is found, and as such work is considered to be a technical, rather than artistic process, it may even be deferred beyond the lifetime of the artist. In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay mixture. When cured, it is then removed from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold.
The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this plaster may be further refined and may be painted and waxed to resemble a finished bronze casting. Evaporative- pattern casting. The two main processes are lost- foam casting and full- mold casting. Lost- foam casting. 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.
Full- mold casting. It uses an 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 mold casting. This technique includes at least four different methods: permanent, die, centrifugal, and continuous casting. This form of casting also results in improved repeatability in parts produced and delivers Near Net Shape results. Permanent mold casting.
The most common process uses gravity to fill the mold. However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds.
Permanent molds, while lasting more than one casting still have a limited life before wearing out. Die casting. Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium- based alloys, but ferrous metal die castings are possible.
The die casting method is especially suited for applications where many small to medium- sized parts are needed with good detail, a fine surface quality and dimensional consistency. Semi- solid metal casting. Rather than using liquid metal as the feed material, SSM casting uses a higher viscosity feed material that is partially solid and partially liquid. A modified die casting machine is used to inject the semi- solid slurry into re- usable hardened steel dies.
The high viscosity of the semi- solid metal, along with the use of controlled die filling conditions, ensures that the semi- solid metal fills the die in a non- turbulent manner so that harmful porosity can be essentially eliminated. Used commercially mainly for aluminium and magnesium alloys, SSM castings can be heat treated to the T4, T5 or T6 tempers. The combination of heat treatment, fast cooling rates (from using un- coated steel dies) and minimal porosity provides excellent combinations of strength and ductility.
Other advantages of SSM casting include the ability to produce complex shaped parts net shape, pressure tightness, tight dimensional tolerances and the ability to cast thin walls. Metal is poured into the center of the mold at its axis of rotation.
Due to centrifugal force the liquid metal is thrown out towards the periphery. Centrifugal casting is both gravity- and pressure- independent since it creates its own force feed using a temporary sand mold held in a spinning chamber at up to 9.
N. Lead time varies with the application. Semi- and true- centrifugal processing permit 3.
Industrially, the centrifugal casting of railway wheels was an early application of the method developed by the German industrial company Krupp and this capability enabled the rapid growth of the enterprise. Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting.
Continuous casting. Molten metal is poured into an open- ended, water- cooled mold, which allows a 'skin' of solid metal to form over the still- liquid centre, gradually solidifying the metal from the outside in. After solidification, the strand, as it is sometimes called, is continuously withdrawn from the mold. Predetermined lengths of the strand can be cut off by either mechanical shears or traveling oxyacetylene torches and transferred to further forming processes, or to a stockpile.
Cast sizes can range from strip (a few millimeters thick by about five meters wide) to billets (9. Sometimes, the strand may undergo an initial hot rolling process before being cut. Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increased quality of the final product. Metals such as steel, copper, aluminum and lead are continuously cast, with steel being the metal with the greatest tonnages cast using this method.
Terminology. The other end of the sprue attaches to the runners. Runners: The horizontal portion of the gating system that connects the sprues to the gates.
Gates: The controlled entrances from the runners into the mold cavities. Vents: Additional channels that provide an escape for gases generated during the pour.
Parting line or parting surface: The interface between the cope and drag halves of the mold, flask, or pattern. Draft: The taper on the casting or pattern that allow it to be withdrawn from the mold. Core box: The mold or die used to produce the cores.
Some specialized processes, such as die casting, use additional terminology. Casting is a solidification process, which means the solidification phenomenon controls most of the properties of the casting. Moreover, most of the casting defects occur during solidification, such as gas porosity and solidification shrinkage. In the nucleation stage solid particles form within the liquid.
Sand casting - Wikipedia. Cope & drag (top and bottom halves of a sand mold), with cores in place on the drag. Two sets of castings (bronze and aluminium) from the above sand mold. Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. Sand castings are produced in specialized factories called foundries. Over 7. 0% of all metal castings are produced via sand casting process.
In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop the strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or mold boxes known as a flask. The mold cavities and gate system are created by compacting the sand around models, or patterns, or carved directly into the sand. Basic process. Sand can be ground, swept or strickled into shape. The metal to be cast will contract during solidification, and this may be non- uniform due to uneven cooling.
Therefore, the pattern must be slightly larger than the finished product, a difference known as contraction allowance. Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others.
Patterns also have core prints that create registers within the molds into which are placed sand cores. Such cores, sometimes reinforced by wires, are used to create under- cut profiles and cavities which cannot be molded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks. Paths for the entrance of metal into the mold cavity constitute the runner system and include the sprue, various feeders which maintain a good metal 'feed', and in- gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via risers. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object—flat on one side—the lower portion of the box, closed at the bottom, will be filled with a molding sand. The sand is packed in through a vibratory process called ramming, and in this case, periodically screeded level.
The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added.
Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed.
Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a . If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about.
In some cases, the sand may be oiled instead of moistened, which makes casting possible without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine- hardened resins. To control the solidification structure of the metal, it is possible to place metal plates, chills, in the mold. The associated rapid local cooling will form a finer- grained structure and may form a somewhat harder metal at these locations. In ferrous castings, the effect is similar to quenching metals in forge work. The inner diameter of an engine cylinder is made hard by a chilling core. In other metals, chills may be used to promote directional solidification of the casting.
In controlling the way a casting freezes, it is possible to prevent internal voids or porosity inside castings. To produce cavities within the casting—such as for liquid cooling in engine blocks and cylinder heads—negative forms are used to produce cores.
Usually sand- molded, cores are inserted into the casting box after removal of the pattern. Whenever possible, designs are made that avoid the use of cores, due to the additional set- up time and thus greater cost. With a completed mold at the appropriate moisture content, the box containing the sand mold is then positioned for filling with molten metal—typically iron, steel, bronze, brass, aluminium, magnesium alloys, or various pot metal alloys, which often include lead, tin, and zinc. After being filled with liquid metal the box is set aside until the metal is sufficiently cool to be strong.
The sand is then removed, revealing a rough casting that, in the case of iron or steel, may still be glowing red. In the case of metals that are significantly heavier than the casting sand, such as iron or lead, the casting flask is often covered with a heavy plate to prevent a problem known as floating the mold. Floating the mold occurs when the pressure of the metal pushes the sand above the mold cavity out of shape, causing the casting to fail. Right: - Pattern (used with the core) and the resulting casting below (the wires are from the remains of the core)After casting, the cores are broken up by rods or shot and removed from the casting. The metal from the sprue and risers is cut from the rough casting.
Various heat treatments may be applied to relieve stresses from the initial cooling and to add hardness—in the case of steel or iron, by quenching in water or oil. The casting may be further strengthened by surface compression treatment—like shot peening—that adds resistance to tensile cracking and smooths the rough surface. And when high precision is required, various machining operations (such as milling or boring) are made to finish critical areas of the casting. Examples of this would include the boring of cylinders and milling of the deck on a cast engine block. Design requirements. A slight taper, known as draft, must be used on surfaces perpendicular to the parting line, in order to be able to remove the pattern from the mold.
This requirement also applies to cores, as they must be removed from the core box in which they are formed. The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mold in order to avoid an incomplete casting.
Should a piece of core or mold become dislodged it may be embedded in the final casting, forming a sand pit, which may render the casting unusable. Gas pockets can cause internal voids. These may be immediately visible or may only be revealed after extensive machining has been performed.
For critical applications, or where the cost of wasted effort is a factor, non- destructive testing methods may be applied before further work is performed. Processes. Green sand is not green in color, but . Unlike the name suggests, . Coal, typically referred to in foundries as sea- coal, which is present at a ratio of less than 5%, partially combusts in the presence of the molten metal, leading to offgassing of organic vapors. Green sand casting for non- ferrous metals does not use coal additives, since the CO created does not prevent oxidation.
Green sand for aluminum typically uses olivine sand (a mixture of the minerals forsterite and fayalite, which is made by crushing dunite rock). The choice of sand has a lot to do with the temperature at which the metal is poured. At the temperatures that copper and iron are poured, the clay gets inactivated by the heat, in that the montmorillonite is converted to illite, which is a non- expanding clay.
Most foundries do not have the very expensive equipment to remove the burned out clay and substitute new clay, so instead, those that pour iron typically work with silica sand that is inexpensive compared to the other sands. As the clay is burned out, newly mixed sand is added and some of the old sand is discarded or recycled into other uses. Silica is the least desirable of the sands, since metamorphic grains of silica sand have a tendency to explode to form sub- micron sized particles when thermally shocked during pouring of the molds.
These particles enter the air of the work area and can lead to silicosis in the workers. Iron foundries spend a considerable effort on aggressive dust collection to capture this fine silica. The sand also has the dimensional instability associated with the conversion of quartz from alpha quartz to beta quartz at 6. Often, combustible additives such as wood flour are added to create spaces for the grains to expand without deforming the mold. Olivine, chromite, etc. Since they are not metamorphic minerals, they do not have the polycrystals found in silica, and subsequently do not form hazardous sub- micron sized particles. The latter may also be referred to as no bake mold casting.
When these are used, they are collectively called . Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand); the latter is generally preferred due to its more consistent composition. With both methods, the sand mixture is packed around a pattern, forming a mold cavity. If necessary, a temporary plug is placed in the sand and touching the pattern in order to later form a channel into which the casting fluid can be poured. Air- set molds are often formed with the help of a casting flask having a top and bottom part, termed the cope and drag. The sand mixture is tamped down as it is added around the pattern, and the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold.
Then the pattern is removed along with the channel plug, leaving the mold cavity. The casting liquid (typically molten metal) is then poured into the mold cavity. After the metal has solidified and cooled, the casting is separated from the sand mold. There is typically no mold release agent, and the mold is generally destroyed in the removal process.
Sand castings made from coarse green sand impart a rough texture to the surface, and this makes them easy to identify. Castings made from fine green sand can shine as cast but are limited by the depth to width ratio of pockets in the pattern.