Casting Process

C ASTING P ATTERNMAKING C ASTING P ATTERNMAKING : In pattern making, a physical model of casting, i.e. a pattern is used to make the mold. The mold is made by packing some readily formed aggregated materials, like molding sand, around the pattern. After the pattern is withdrawn, its imprint leaves the mold cavity that is ultimately filled with metal to become the casting. n case, the castings is required to be hollow, such as in the case of pipe fittings, additional patterns, known as cores, are used to develop these cavities.

C OREMAKING & M OLDING C OREMAKING & M OLDING : In core making, cores are formed, (usually of sand) that are placed into a mold cavity to form the interior surface of the casting. Thus the annul space between the mold-cavity surface and the core is what finally becomes the casting. Molding is a process that consists of different operations essential to develop a mold for receiving molten metal

A LLOY M ELTING AND P OURING A LLOY M ELTING AND P OURING : Melting is a process of preparing the molten material for casting. It is generally done in a specifically designated part of foundry, and the molten metal is transported to the pouring area wherein the molds are filled

C ASTING C LEANING C ASTING C LEANING : The casting is separated from the mold and transported to the cleaning department. Burned-on sand and scale are removed. Excess metal is removed (Fins, wires, parting line fins, and gates). Subsequently the casting can be upgraded using welding or other such as procedures. Final testing and inspection to check for any defects Advantages: Improves the surface appearance and finish of casting Improves overall quality and functionality by removing impurities, such as sand, scale and excess metal Finally the sand from the mold is separated and processed through a reclamation system for further use.

I NDUSTRIAL P ROCESS D ESCRIPTION The metal casting process has been divided into the following five major operations: Obtaining the Casting GeometryObtaining the Casting Geometry : The process is referred as the study of the geometry of parts and plans, so as to improve the life and quality of casting. Advantages of Good Casting Geometry Reduces defects, post casting operations, and rejected castings Significantly reduce energy and environmental impacts Saves energy Improves overall quality and life of casting

A key part of designing a mold involves the use of cores. Cores are preformed masses of bonded sand or some other material that are used to make the internal passageways of a casting. Castings may require a single core, a complex assembly of cores or no cores at all. Like castings, cores are made in a mold, called a coldbox. Typically cores are made of sand and may be combined with other materials that bind the sand together. Metal cores are used in permanent mold and diecasting processes. The type of cores used in each metalcasting process will also be part of your decision making process.

TYPES OF MOLDING PROCESS 1 Expendable Mold 1.1 Permanent Pattern Sand Casting Plaster Molding 1.2 Expendable Pattern Lost Foam Lost Wax (investment casting) 1 Permanent Mold 1.1 Die Hot Chamber Cold Chamber 1.1.3Thixotropic Mold prepertation =) metal heating =) pouring =) cooling =) processing

E XPANDABLE MOLD PERMANENT PATTERN SAND CASTING

The set of channels through which a molten metal flows to the mold cavity is called gating system. Typical gating system consists of a pouring cup and a sprue receiving the poured melt, runner – a channel through which the melt is supplied to the gates through which the molten metal enters the mold cavity.

E XPANDABLE MOLD EXPANDABLE PATTERN INVESTMENT CASTING Use gravity to fill the mold. Mold is destroyed to remove casting Metal flow is slow Walls are much thicker than in die casting. Cycle time is longer than die casting because of inability of mold material to remove heat. The investment casting process uses expendable patterns made of investment casting wax: The wax patterns are commonly prepared by injection molding technology which involves injection of wax into a prefabricated die having the same geometry of the cavity as the desired cast part.injection molding

INVESTMENT CASTING

E XPANDABLE MOLD PERMANENT PATTERN SHELL MOLDING Shell moulding is a process for producing simple or complex near net shape castings, maintaining tight tolerances and a high degree of dimensional stability. Shell moulding is a method for making high quality castings. These qualities of precision can be obtained in a wider range of alloys and with greater flexibility in design than die-casting and at a lower cost than investment casting. INVESTMENT CASTING

Shell molding Advantages Better surface finish Better dimensional tolerances. Reduced Machining. Less foundry space required. Semi skilled operators can handle the process. The process can be mechanized. Disadvantages The raw materials are relatively expensive. The process generates noxious fumes which must be removed. The size and weight range of castings is limited.

E XPANDABLE MOLD PERMANENT PATTERN LOST FOAM CASTING INVESTMENT CASTING Lost foam casting Lost foam casting (LFC) is a type of investment casting process that uses foam patterns as a mold. The method takes advantage of the properties of foam to simply and inexpensively create castings that would be difficult to achieve using other casting techniques.investment casting

E XPANDABLE MOLD PERMANENT PATTERN LOST FOAM CASTING Lost foam casting Lost foam casting (LFC) is a type of investment casting process that uses foam patterns as a mold. The method takes advantage of the properties of foam to simply and inexpensively create castings that would be difficult to achieve using other casting techniques.investment casting

Lost foam casting

Lost foam, is similar to Investment or Lost wax, in that the medium, or pattern device, is Expendable, they melt or evaporate away, leaving the cast part. They both have advantages, for the type of function they were designed. One Process's advantage, could be the other Process's weak area. These points are brought up in the text portion of Education Section.

PERMANENT MOLD DIE CASTING Liquid metal injected into reusable steel mold, or die, very quickly with high pressures. Die casting is a process in which the molten metal is injected into the mold cavity at an increased pressure The mold used in the die casting process is called a die.

In a cold chamber process, the molten metal is ladled into the cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This is particularly useful for metals such as Aluminum, and Copper (and its alloys) that alloy easily with Iron at the higher temperatures. PERMANENT MOLD DIE CASTING COLD CHAMBER

In a hot chamber process the pressure chamber is connected to the die cavity is immersed permanently in the molten metal. The inlet port of the pressurizing cylinder is uncovered as the plunger moves to the open (unpressurized) position. This allows a new charge of molten metal to fill the cavity and thus can fill the cavity faster than the cold chamber process. The hot chamber process is used for metals of low melting point and high fluidity such as tin, zinc, and lead that tend not to alloy easily with steel at their melt temperatures. PERMANENT MOLD DIE CASTING HOT CHAMBER

Manifacturing techniques

T ERMS OF CASTıNG Riser: A column of metal placed in the mold to feed the casting as it shrinks and solidifies. Also known as a "feed head." Runner: The channel through which the molten metal is carried from the sprue to the gate. Cores: A separated part of the mold, made of sand and generally baked, which is used to create openings and various shaped cavities in the casting. Gate: A channel through which the molten metal enters the casting cavity. Sand: A sand which binds strongly without losing its permeability to air or gases.

T ERMS OF CASTıNG Binders: Materials used to hold molding sand together. Parting Line: Joint where mold separates to permit removal of the pattern. The axe which shows how and where to open the mold Centrifugal Casting: Process of filling molds by pouring metal into a mold which is spinning or revolving about an axis. Cast iron pipe can be created using this method. Chaplet: A metal support used to hold a core in place in a mold. Not used when a core print will serve. Draft: Slight taper given to a pattern to allow drawing from the sand. Pouring: Filling the mold with molten metal. Shrinkage: The decrease in volume when molten metal solidifies.

S ELECTING THE R IGHT M ETAL C ASTING P ROCESS For any Metal Casting Process, selection of right alloy, size, shape, thickness, tolerance, texture, and weight, is very vital. Special requirements such as, magnetism, corrosion, stress distribution also influence the choice of the Metal Casting Process. Views of the Tooling Designer; Foundry / Machine House needs, customer's exact product requirements, and secondary operations like painting, must be taken care of before selecting the appropriate Metal Casting Process. Tool cost. Economics of machining versus process costs. Adequate protection / packaging, shipping constraints, regulations of the final components, weights and shelf life of protective coatings also play their part in the Metal Casting process.

AdvantagesDisadvantages Recommended Application Least Expensive in small quantities (less than 100) Ferrous and non - ferrous metals may be cast Possible to cast very large parts. • Least expensive tooling Dimensional accuracy inferior to other processes, requires larger tolerances Castings usually exceed calculated weight Surface finish of ferrous castings usually exceeds 125 RMS Use when strength/weight ratio permits Tolerances, surface finish and low machining cost does not warrant a more expensive process S AND C ASTING

P ERMANENT AND S EMI - PERMANENT M OLD C ASTING AdvantagesDisadvantages Recommended Application Less expensive than Investment or Die Castings Dimensional Tolerances closer than Sand Castings Castings are dense and pressure tight Only non-ferrous metals may be cast by this process Less competitive with Sand Cast process when three or more sand cores are required Higher tooling cost than Sand Cast Use when process recommended for parts subjected to hydrostatic pressure Ideal for parts having low profile, no cores and quantities in excess of 300

P LASTER C AST AdvantagesDisadvantages Recommended Application Smooth "As Cast" finish (25 RMS) Closer dimensional tolerance than Sand Cast • Intricate shapes and fine details including thinner "As Cast" walls are possible • Large parts cost less to cast than by Investment process More costly than Sand or Permanent Mold- Casting Limited number of sources Requires minimum of 1 deg. draft Use when parts require smooth "As Cast" surface finish and closer tolerances than possible with Sand or Permanent Mold Processes

I NVESTMENT C AST AdvantagesDisadvantages Recommended Application Close dimensional tolerance Complex shape, fine detail, intricate core sections and thin walls are possible Ferrous and non- ferrous metals may be cast As-Cast" finish ( RMS) Costs are higher than Sand, Permanent Mold or Plaster process Castings Use when Complexity precludes use of Sand or Permanent Mold Castings The process cost is justified through savings in machining or brazing Weight savings justifies increased cost

D IE C ASTING AdvantagesDisadvantages Recommended Application Good dimensional tolerances are possible Excellent part-part dimensional consistency Parts require a minimal post machining Economical only in very large quantities due to high tool cost Not recommended for hydrostatic pressure applications For Castings where penetrant (die) or radiographic inspection are not required. Difficult to guarantee minimum mechanical properties Use when quantity of parts justifies the high tooling cost Parts are not structural and are subjected to hydrostatic pressure