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This article is about metal foundries. For other uses, see Foundry (disambiguation)

"Iron foundry" redirects here. For the music composition by Soviet composer Alexander Mosolov, see Iron Foundry

From Fra Burmeister og Wain's Iron Foundry, by Peder Severin Krøyer, 1885 A Foundryman, pictured by Daniel A. Wehrschmidt in 1899

A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.

Foundries are one of the largest contributors to the manufacturing recycling movement, melting and recasting millions of tons of scrap metal every year to create new durable goods. Moreover, many foundries use sand in their molding process. These foundries often use, recondition, and reuse sand, which is another form of recycling.[1]

Process

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In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it 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.[2]

Melting

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Melting metal in a crucible for casting A metal die casting robot in an industrial foundry

Melting is performed in a furnace. Virgin material, external scrap, internal scrap, and alloying elements are used to charge the furnace. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys. External scrap is material from other forming processes such as punching, forging, or machining. Internal scrap consists of gates, risers, defective castings, and other extraneous metal oddments produced within the facility.

The process includes melting the charge, refining the melt, adjusting the melt chemistry and tapping into a transport vessel. Refining is done to remove harmful gases and elements from the molten metal to avoid casting defects. Material is added during the melting process to bring the final chemistry within a specific range specified by industry and/or internal standards. Certain fluxes may be used to separate the metal from slag and/or dross and degassers are used to remove dissolved gas from metals that readily dissolve in gasses. During the tap, final chemistry adjustments are made.[3]

Furnace

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Several specialised furnaces are used to heat the metal. Furnaces are refractory-lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include electric arc furnaces (EAF), induction furnaces, cupolas, reverberatory, and crucible furnaces. Furnace choice is dependent on the alloy system quantities produced. For ferrous materials EAFs, cupolas, and induction furnaces are commonly used. Reverberatory and crucible furnaces are common for producing aluminium, bronze, and brass castings.

Furnace design is a complex process, and the design can be optimized based on multiple factors. Furnaces in foundries can be any size, ranging from small ones used to melt precious metals to furnaces weighing several tons, designed to melt hundreds of pounds of scrap at one time. They are designed according to the type of metals that are to be melted. Furnaces must also be designed based on the fuel being used to produce the desired temperature. For low temperature melting point alloys, such as zinc or tin, melting furnaces may reach around 500 °C (932 °F). Electricity, propane, or natural gas are usually used to achieve these temperatures. For high melting point alloys such as steel or nickel-based alloys, the furnace must be designed for temperatures over 1,600 °C (2,910 °F). The fuel used to reach these high temperatures can be electricity (as employed in electric arc furnaces) or coke. The majority of foundries specialize in a particular metal and have furnaces dedicated to these metals. For example, an iron foundry (for cast iron) may use a cupola, induction furnace, or EAF, while a steel foundry will use an EAF or induction furnace. Bronze or brass foundries use crucible furnaces or induction furnaces. Most aluminium foundries use either electric resistance or gas heated crucible furnaces or reverberatory furnaces.[2]

Degassing

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Degassing[4] is a process that may be required to reduce the amount of hydrogen present in a batch of molten metal. Gases can form in metal castings in one of two ways:

1. by physical entrapment during the casting process or
2. by chemical reaction in the cast material.

Hydrogen is a common contaminant for most cast metals. It forms as a result of material reactions or from water vapor or machine lubricants. If the hydrogen concentration in the melt is too high, the resulting casting will be porous; the hydrogen will exit the molten solution, leaving minuscule air pockets, as the metal cools and solidifies. Porosity often seriously deteriorates the mechanical properties of the metal.

An efficient way of removing hydrogen from the melt is to bubble a dry, insoluble gas through the melt by purging or agitation. When the bubbles go up in the melt, they catch the dissolved hydrogen and bring it to the surface. Chlorine, nitrogen, helium and argon are often used to degas non-ferrous metals. Carbon monoxide is typically used for iron and steel.

There are various types of equipment that can measure the presence of hydrogen. Alternatively, the presence of hydrogen can be measured by determining the density of a metal sample.

In cases where porosity still remains present after the degassing process, porosity sealing can be accomplished through a process called metal impregnating.

Mold making

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Diagrams of two pattern types

A diagram of draft on a pattern

In the casting process, a pattern is made in the shape of the desired part. Simple designs can be made in a single piece or solid pattern. More complex designs are made in two parts, called split patterns. A split pattern has a top or upper section, called a cope, and a bottom or lower section called a drag. Both solid and split patterns can have cores inserted to complete the final part shape. Cores are used to create hollow areas in the mold that would otherwise be impossible to achieve. Where the cope and drag separates is called the parting line.

When making a pattern it is best to taper the edges so that the pattern can be removed without breaking the mold. This is called draft. The opposite of draft is an undercut where there is part of the pattern under the mold material, making it impossible to remove the pattern without damaging the mold.

The pattern is made of wax, wood, plastic, or metal. The molds are constructed by several different processes dependent upon the type of foundry, metal to be poured, quantity of parts to be produced, size of the casting, and complexity of the casting. These mold processes include:

Pouring

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Bronze poured from a crucible into a mold, using the lost-wax casting process

In a foundry, molten metal is poured into molds. Pouring can be accomplished with gravity, or it may be assisted with a vacuum or pressurized gas. Many modern foundries use robots or automatic pouring machines to pour molten metal. Traditionally, molds were poured by hand using ladles.

Shakeout

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The solidified metal component is then removed from its mold. Where the mold is sand based, this can be done by shaking or tumbling. This frees the casting from the sand, which is still attached to the metal runners and gates — which are the channels through which the molten metal traveled to reach the component itself.

Degating

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Degating is the removal of the heads, runners, gates, and risers from the casting. Runners, gates, and risers may be removed using cutting torches, bandsaws, or ceramic cutoff blades. For some metal types, and with some gating system designs, the sprue, runners, and gates can be removed by breaking them away from the casting with a sledge hammer or specially designed knockout machinery. Risers must usually be removed using a cutting method (see above) but some newer methods of riser removal use knockoff machinery with special designs incorporated into the riser neck geometry that allow the riser to break off at the right place.

The gating system required to produce castings in a mold yields leftover metal — including heads, risers, and sprue (sometimes collectively called sprue) — that can exceed 50% of the metal required to pour a full mold. Since this metal must be remelted as salvage, the yield of a particular gating configuration becomes an important economic consideration when designing various gating schemes, to minimize the cost of excess sprue, and thus overall melting costs.

Heat treating

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A tank hull undergoing heat treatment

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case-hardening, precipitation strengthening, tempering, and quenching. Although the term "heat treatment" applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

Surface cleaning

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After degating and heat treating, sand or other molding media may remain adhered to the casting. To remove any mold remnants, the surface is cleaned using a blasting process. This means a granular media will be propelled against the surface of the casting to mechanically knock away the adhering sand. The media may be blown with compressed air, or may be hurled using a shot wheel. The cleaning media strikes the casting surface at high velocity to dislodge the mold remnants (for example, sand, slag) from the casting surface. Numerous materials may be used to clean cast surfaces, including steel, iron, other metal alloys, aluminium oxides, glass beads, walnut shells, baking powder, and many others. The blasting media is selected to develop the color and reflectance of the cast surface. Terms used to describe this process include cleaning, bead blasting, and sand blasting. Shot peening may be used to further work-harden and finish the surface.

Finishing

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Modern foundry (c.

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The final step in the process of casting usually involves grinding, sanding, or machining the component in order to achieve the desired dimensional accuracies, physical shape, and surface finish.

Removing the remaining gate material, called a gate stub, is usually done using a grinder or sander. These processes are used because their material removal rates are slow enough to control the amount of material being removed. These steps are done prior to any final machining.

After grinding, any surfaces that require tight dimensional control are machined. Many castings are machined in CNC milling centers. The reason for this is that these processes have better dimensional capability and repeatability than many casting processes. However, it is not uncommon today for castings to be used without machining.

A few foundries provide other services before shipping cast products to their customers. It is common to paint castings to prevent corrosion and improve visual appeal. Some foundries assemble castings into complete machines or sub-assemblies. Other foundries weld multiple castings or wrought metals together to form a finished product.[3]

More and more, finishing processes are being performed by robotic machines, which eliminate the need for a human to physically grind or break parting lines, gating material, or feeders. Machines can reduce risk of injury to workers and lower costs for consumables — while also increasing productivity. They also limit the potential for human error and increase repeatability in the quality of grinding.[5]

Casting process simulation

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A high-performance software for the simulation of casting processes provides opportunities for an interactive or automated evaluation of results (here, for example, of mold filling and solidification, porosity and flow characteristics).

Casting processes simulation uses numerical methods to calculate cast component quality considering mold filling, solidification and cooling, and provides a quantitative prediction of casting mechanical properties, thermal stresses and distortion. Simulation accurately describes a cast component's quality up-front before production starts. The casting rigging can be designed with respect to the required component properties. This has benefits beyond a reduction in pre-production sampling, as the precise layout of the complete casting system also leads to energy, material, and tooling savings.

The software supports the user in component design, the determination of melting practice and casting methoding through to pattern and mold making, heat treatment, and finishing. This saves costs along the entire casting manufacturing route.

Casting process simulation was initially developed at universities starting from the early '70s, mainly in Europe and in the U.S., and is regarded as the most important innovation in casting technology over the last 50 years. Since the late '80s, commercial programs (such as PoligonSoft, AutoCAST and Magma) are available which make it possible for foundries to gain new insight into what is happening inside the mold or die during the casting process. [6]

See also

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References

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This article will examine the fundamental principles of lost-foam casting, as well as its numerous uses in the manufacture of items from cast iron and other metals and their alloys.

What Is Lost-Foam Casting?

Lost-foam casting, also known as evaporative casting or the expanded polystyrene process, is a sophisticated technique for crafting intricate metal components. This procedure makes use of an expanded polystyrene (EPS) foam mold. The foam pattern may be cut from a foam block, carved, or produced using a process akin to injection molding. The foam mold is then given a ceramic refractory covering to isolate it from the sand surrounding it in the mold frame. Sand holds the EPS mold in place as molten metal is poured into it. As the foam evaporates, the required metal shape is left behind.

What Is the Origin of Lost-Foam Casting?

Lost-foam casting has its origins in a patent that H.F. Shroyer filed in April 1956. He proposed the idea of embedding foam patterns within green sand to cast metal. This creative method required cutting a pattern from expanded polystyrene (EPS) and supporting it with bonded sand throughout the casting process. Shroyer's creative strategy, which was formally patented in 1958, served as the basis for lost-foam casting, often known as the whole-mold technique.

What Is the Importance of Lost-Foam Casting in Manufacturing?

Lost-foam casting is important in the industrial industry because it uses less energy than sand casting and has a smaller carbon impact. Additionally, it reduces waste production and metal consumption. This helps to create a cleaner and more productive industrial environment.

How Does Lost-Foam Casting Work?

Lost-foam casting first involves creating a pattern of the desired shape from expanded polystyrene (EPS) foam. The foam pattern is then placed within a mold box and packed on all sides with sand, leaving a passage through which to pour molten metal onto the foam. The polystyrene vaporizes due to the heat from the molten metal, which shapes the casting inside the mold. Intricate and sophisticated metal items can be produced with amazing precision by ejecting the casting from the mold chamber after it has been formed.

What Makes Lost-Foam Casting Stand Out Among Other Types of Casting?

Lost-foam casting has definite advantages over conventional casting techniques like sand casting or investment casting. Complex shapes and elaborate designs are possible that could be difficult with other approaches. Lost-foam casting can also reduce material waste and streamline manufacturing procedures, making it more effective and economical. To learn more, see our guide on the Types of Casting.

What Is the Process of Lost-Foam Casting?

Here is a step-by-step explanation of the procedure:

1. Use Foam Molds for Foam Pattern and Gating System Production

In lost-foam casting, foam patterns mimic the precise geometry of the finished metal object. The gating system has passages that direct molten metal into the mold and may be integrated into the foam pattern or attached (glued on) later. These passages enable precise designs and streamlined metal flow, resulting in castings that are accurate and effective.

2. Bond Patterns and Runners To Create a Mold Bundle Module

Tightly bind the foam patterns and gating mechanisms to form the mold bundle module prior to  casting. This assembly makes the casting process easier by ensuring precise component alignment, reducing mistakes, and facilitating reliable, consistent manufacture of complex metal parts.

3. Apply Dip Paint and Allow the Paint To Dry

An application of refractory dip paint follows the assembly of the mold bundle module. When this paint dries, it creates a protective ceramic coating that improves the mold's surface toughness, heat resistance, and capacity to handle the temperature and pressure of the molten metal.

4. Place the Module in a Sandbox and Fill It With Dry Sand

Coat the mold bundle module, set it within a molding flask, and cover it in dry sand. This phase ensures accurate replication of the desired metal part by supporting the module's shape, keeping it in place during casting, and facilitating uniform sand compaction.

5. Vibrate Molding To Fill the Cavity and Compact the Sand

Sand may now flow into every nook and cranny of the mold bundle module thanks to vibrations imparted to the molding flask. Through careful sand compaction and the elimination of air spaces, this procedure enables the creation of a high-quality casting with exact measurements and fine details.

6. Pour Molten Metal To Vaporize the Foam and Create Desired Castings

Carefully pour the molten metal into the mold, replacing the vaporized foam patterns. The metal solidifies to create the desired casting as it fills the spaces the foam left behind. As a result, the finished product closely resembles the planned form while minimizing flaws and blemishes. This technique supports complicated and complex shapes.

7. Clean the Castings After They Have Cooled

After the castings have cooled and set, clean the casting to get rid of any remaining sand, ceramic shells, and other impurities. To produce high-quality and aesthetically pleasing metal parts, this phase means that the final castings fulfill quality requirements, have smooth surfaces, and are ready for subsequent finishing procedures or assembly.

The lost-foam casting process significantly lowers labor requirements and waste production. It is also possible to recycle used dry sand, which is in line with objectives for lowering emissions and using less energy.

What Is the Type of Sand Used in Lost-Foam Casting?

The use of dry sand is common in lost-foam casting. Some practitioners choose "green sand," fine, soft sand that has been blended with bentonite clay. Due to the combination's improved pliability, it can keep its shape even when somewhat damp. Even though "green sand" isn't usually green, its clay content makes it a good material to use when casting complicated foam shapes.

What Are the Metals Used in Lost-Foam Casting?

Metals used in lost-foam casting are discussed below:

1. Stainless Steel

Stainless steel is a versatile alloy composed mainly of iron and chromium. It is notable for its great corrosion resistance and amazing strength. This metal is preferred for uses that call for both durability and aesthetic appeal. Molten stainless steel is carefully poured into the foam design during the lost-foam casting procedure. The molten metal replaces the foam as it evaporates, forming the required complex shape. Stainless steel might be more expensive to make and more difficult to work with, but it has high strength and corrosion resistance. To learn more, see our guide on Stainless Steels.

2. Aluminum Alloys

Aluminum alloys are characterized by their blend of aluminum with other elements. They offer a remarkable combination of lightweight properties and effective thermal conductivity. In the area of lost-foam casting, these alloys find their application where parts necessitate a particular blend of strength and weight. Their lightweight nature and thermal conductivity stand as advantages, while their suitability for certain strength-demanding applications might be limited. To learn more, see our Aluminum Alloy article.

3. Steels

Steels, encompassing various steel types tailored to specific applications, present a versatile array of properties in lost-foam casting. These options span a spectrum of strength, hardness, and wear resistance, catering to diverse industrial needs. While offering a spectrum of advantageous attributes, it's worth noting that certain nuances might arise, such as the need for precise alloy selection based on application requirements. For more information, see our guide on Steels.

4. Cast Irons

Cast irons, notably encompassing variations like gray iron and ductile iron, play a crucial role in lost-foam casting with their pronounced attributes. Their remarkable compressive strength and resistance to wear make them prime candidates for heavy-duty applications. However, while they excel in specific scenarios, the casting process requires precise controls and considerations to ensure optimal outcomes.

5. Nickel Alloys

In lost-foam casting, nickel alloys take center stage due to their distinctive attributes. These alloys boast remarkable resistance to both high temperatures and corrosion, making them ideal contenders for use in extreme environments and specialized applications. However, their exceptional properties often come with considerations related to cost and specific alloy selection to match the intended application requirements. For more information, see our guide on Nickel Properties.

Can Copper Alloys Be Used as Casting Material for Lost-Foam Casting?

Yes, the lost foam casting process can be employed with copper alloys. However, casting copper alloys successfully requires careful consideration due to the unique challenges they pose. Molten copper alloys have the potential to produce sulfurous gases and are prone to absorbing oxygen, which can result in casting defects. Special precautions are necessary to address these issues. The incorporation of specific openings or risers within the mold becomes imperative. These serve a dual purpose: facilitating the controlled pouring of the molten metal and allowing the escape of impurities and gases that may compromise the casting quality.

What Are the Applications of Lost-Foam Casting?

The primary uses of lost-foam casting are in the creation of parts with internal channels, thin walls, and delicate designs. The method excels in producing components like cylinder heads, engine blocks, and cooling system housings. Its capacity to perfectly reproduce intricate forms and details helps to produce high-quality and precisely engineered parts.

What Industries Use Lost-Foam Casting Products?

A wide range of industries, including: the automotive, marine, military, and agricultural fields, find use for lost-foam casting. It is a useful approach in creating components for these various sectors.

What Is the Quality of Lost-Foam Casting Products?

Lost-foam casting produces high-quality components with intricate details due to its ability to replicate complex shapes accurately. The durability of these products depends on factors such as: the chosen material, design considerations, and proper casting techniques. When executed with precision, lost-foam casting can yield durable and reliable products.

Are Lost-Foam Casting Products Heat Resistant?

Yes, products made with lost-foam casting can be heat resistant. The method is used to make heat-resistant components, especially those with elaborate designs and small sizes. It is often employed to make components that have strong heat-resistance qualities, which helps to make them suitable for a variety of applications.

What Are the Advantages of Lost-Foam Casting?

Listed below are the advantages of lost-foam casting:

1. Excels in producing castings with high dimensional accuracy. 
2. Inherently avoids flash, the unwanted material accumulation on castings. The absence of a draft requirement ensures clean castings with impeccable dimensional accuracy.
3. It's simpler than many other casting methods, involving fewer steps. 

What Are the Disadvantages of Lost-Foam Casting?

Listed below are some disadvantages of lost-foam casting:

1. When closed-die molding is employed for pattern creation, the cost of the die can become a significant factor.
2. While patterns are lightweight and easy to handle, they are susceptible to damage and distortion. This requires careful handling throughout the process.
3. The presence of burnt polystyrene foam can lead to a higher degree of porosity in the castings. This can potentially affect their structural integrity and quality.

Is Lost-Foam Casting Expensive?

Yes, lost-foam casting is more expensive than other techniques. But, it has the advantage of having tighter tolerances, being lighter, and having features that are as-cast, which cut down on machining and cleanup time. It is possible to cast a large number of components that need milling, turning, drilling, and grinding with a small amount of machine stock. 

Is Lost-Foam Casting the Same as Investment Casting?

No, lost-foam casting and investment casting are not the same thing. While lost-foam and investment casting are similar, the latter uses wax patterns while the former uses expanding polystyrene foam. The selection of pattern material distinguishes the two methods even though they are fundamentally similar.

What Is the Difference Between Lost-Foam Casting and Sand Casting?

Lost-foam casting and sand casting are distinct techniques employed in metal casting. Lost-foam casting excels in detailed, high-surface finish parts, while sand casting's versatility lies in larger components. While both yield metal parts, they differ significantly in their processes, complexity, costs, and the part types they cater to. Table 1 below lists their differences in more detail:

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