This Article takes an In-depth look at Casting Processes
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The art of casting has a rich history stretching back thousands of years, with evidence indicating its use as far back as 3000 BC or BCE. Archaeological discoveries suggest that early casting techniques involved using two-piece pottery molds bound together with rope, featuring an opening for pouring molten metal. It is believed that this method was used to create early weapons and hunting tools.
Ancient Egyptians employed casting methods to create plaster masks for mummies, reflecting their spiritual practices. This process also encompassed crafting jewelry and various artifacts. While the Egyptians advanced their casting techniques, similar practices were concurrently developed and utilized by cultures in the East.
By the time molding reached the Greeks and Romans, it had become an artform used to cast bronze statues using a hollow wax casting. Each part of a piece was cast separately. The core of the mold was made of clay and covered with wax followed by a layer of clay that was heated to melt the internal wax, which was heated a second time to burn out the remaining wax. Once the mold was stable and prepared, the molten metal was poured into the area where the wax had been removed, a method that is similar to modern day investment casting.
During the Renaissance, artisans were greatly inspired by the artistic achievements of the Greeks and Romans. They enhanced the casting process by developing more advanced molds crafted from wood, terracotta, or plaster. One of the most challenging aspects of this technique was ensuring the mold accurately captured the proportions of the desired form.
The practice of casting for making tools, bowls, and other practical items originated in China around 1000 BCE. The Chinese pioneered the mass production of farm implements and weaponry using iron. This technique did not reach European societies until centuries later, where it was adapted for producing cannons, cannonballs, and ammunition. With the rise of the industrial revolution in both America and Europe, casting evolved into a fundamental manufacturing process. As new metals were discovered and techniques refined, the quality and durability of cast products improved. Today, various casting methods are employed to produce a wide range of commercial and industrial goods.
With the advent of the industrial revolution in America and Europe, casting became a standard manufacturing process much like it is today. As new metals were discovered and techniques improved, the products produced were of higher quality and endurance. Today, a variety of metal casting methods are used to make everyday items for commercial and industrial use.
Metal casting evolved over millennia as techniques for heating and melting metals advanced. Gold was the first metal to be cast due to its pliability and relatively low melting point. Among the earliest surviving examples of metal casting is a copper frog dating back to 1500 BCE. China's contributions to the field included innovations like sand casting and the use of iron, also known as pig iron.
Key advancements during the first industrial revolution greatly influenced the progress of casting techniques. In 1809, A.G. Eckhart pioneered centrifugal casting, a method that ensures even distribution of molten metal through the rotation of the mold. Jarvis Adams introduced the first casting machine in 1837, designed specifically for producing printing press letters. Later, in 1856, Sir Henry Bessemer made a significant breakthrough by demonstrating that blowing oxygen into molten metal could eliminate excess carbon and impurities, thus simplifying the process of pouring molten metals.
Foundries have a long history, originating from times when casting was performed with rudimentary tools and manual labor. They have evolved alongside the casting process from small-scale operations to significant industrial entities. Foundries create castings by melting metal and pouring it into molds. Today’s foundries are highly advanced and automated, minimizing manual labor. They feature sophisticated equipment such as furnaces, ladles, forklifts, cranes, conveyors, and transfer containers, all designed to withstand extreme temperatures.
Foundries are categorized based on the metals they process, as the equipment is tailored to handle specific types of metal. For instance, steel foundries use electric arc furnaces, whereas copper foundries employ induction furnaces. The equipment in foundries varies widely, from compact tabletop units to massive machines weighing several tons, with production capacities ranging from ounces to tons. The environment in foundries is hazardous and challenging due to the extreme temperatures required for melting and forming metals.
In metal casting, each metal part has distinct requirements and standards, including strength, durability, appearance, and complexity. Meeting these specifications involves selecting the appropriate metal to ensure optimal performance. This selection process requires a thorough understanding of the properties and characteristics of various metals.
Aluminum alloys are highly favored for casting due to their excellent machinability and cost-effectiveness. The inherent properties of aluminum make it suitable for numerous applications. It can be cast using various methods, with the resulting parts being utilized in both industrial and commercial products.
Carbon steel is known for its excellent machinability and weldability while maintaining remarkable toughness. Castings made from carbon steel perform well under high-pressure conditions, where wear resistance and strength are crucial. The mechanical properties of carbon steel depend on its carbon content, with higher levels increasing hardness and strength. Low to medium carbon steels are typically cast using investment casting methods.
Copper, a highly malleable metal, has been used in casting for centuries. It is rarely cast in its pure form due to potential porosity issues. Instead, various copper alloys are utilized, such as those ranging from C80000 to C9999, which are selected for their strength, wear resistance, machinability, conductivity, and corrosion resistance. Copper alloys are categorized into three groups based on their solidification or freezing ranges. The most commonly cast copper alloys are brass, which combines copper and zinc, and bronze, which consists of copper and tin.
Magnesium is extensively used as a base material in various alloys, with magnesium alloy AZ91D being the most prevalent. Its popularity stems from its lightweight nature, durability, excellent castability, and remarkable toughness. Magnesium is 75% lighter than steel while maintaining comparable strength. Its suitability for casting comes from its ability to form complex parts with thin walls and superior dimensional stability. Magnesium casting is performed using injection molding, where the mold is submerged in a pool of molten magnesium, and a piston injects the molten metal into the mold.
Nickel has been used in casting since ancient times. One notable alloy, known as Monel, consists of nickel and copper, along with trace amounts of iron, manganese, carbon, and silicon. While Monel offers greater strength than pure nickel, it can be challenging to machine after casting. Another significant nickel alloy is Inconel, an austenitic nickel-chromium alloy renowned for its resistance to oxidation and corrosion. Nickel alloys are typically cast using investment casting and are used in components designed for high-temperature or corrosive environments. When combined correctly, nickel and its alloys can achieve tensile strength comparable to carbon steel while also offering excellent ductility and wear resistance.
Like nickel, gold, and copper, iron has been cast for centuries, initially in the form of brittle pig iron. Iron is available in several varieties, including gray iron, white iron, malleable iron, ductile iron, and graphite iron, each with specific properties suited to various applications. Cast iron typically contains 2% to 4% carbon and 1% to 3% silicon. The high carbon content causes cast iron to solidify as a heterogeneous alloy with a distinctive microcrystalline structure.
Stainless steel refers to a group of metals containing chromium, renowned for their corrosion resistance and bright, silvery appearance. Common grades used in casting include the 300 series, 400 series, 14-4 PH, 15-5 PH, 17-4 PH, and 2205 series. The key distinction between these grades is their carbon content: low-carbon grades offer excellent corrosion resistance, while high-carbon grades provide heat resistance. These characteristics dictate the appropriate grade for specific casting applications, with investment casting being the most widely used method.
Zinc is a favored metal for casting because of its lower tooling costs. Its low melting point allows zinc casting dies to outlast aluminum dies by up to ten times and magnesium dies by five times. Zinc casting employs fast-cycling hot chamber die casting, where molten zinc is fed into the die through a gooseneck linked to a molten zinc reservoir. A plunger draws the zinc from the tank and injects it under pressure into the die, where the parts quickly solidify and are then ejected.
Despite technological advancements and modern production techniques, the fundamental process of casting has remained largely unchanged since its inception thousands of years ago. Today’s casting still relies on molds and molten metal, though the methods have evolved to become more precise and automated, resulting in higher quality products.
Significant advancements in casting have greatly improved efficiency and production capabilities. Unlike the methods of the Egyptians, Greeks, and Romans, today's engineers can design and produce parts with relative ease, thanks to automation and electronic technologies. Countless products are manufactured daily, ranging from items on store shelves to components used in cars, airplanes, and spacecraft.
Almost every device we use today is a product of the casting process. The most significant difference between modern casting and that of a century ago lies in the advanced planning, precision, design, and tolerances made possible by computerization and automation. Cores and molds are now crafted with exceptional detail and accuracy, down to the smallest component.
The casting process begins with designing the pattern, which serves as the model for the item to be cast. Patternmaking involves carefully shaping the mold cavity with precise dimensions. Once the item has solidified in the mold, considerations must be made for its removal without causing damage, accounting for shrinkage during solidification and potential distortions. The pattern also needs a system for feeding liquid metal into the mold. Any mistakes in pattern development can result in defects or failed castings.
Core making is used for casting processes that require internal cavities, such as sand casting, die casting, and injection molding. When a casting needs to be hollow, a core made of sand or metal shapes the interior of the form. These cores are strong yet collapsible, allowing for easy removal once casting is complete. Cores enable the creation of intricate designs, including holes or specialized chambers. For example, molding an automotive engine typically requires five cores to form the necessary chambers for an internal combustion engine.
Molding involves creating a cast from a pattern. In the casting process, the mold is secured within a frame known as a flask. Sand is packed tightly around the pattern within the flask, forming the mold. After the mold takes shape, the pattern is removed, leaving behind the cavity for casting. Once the mold design is complete, it may be fired, depending on the material, to harden it and prepare it for the introduction of molten metals.
The following step involves melting the metal and pouring it into the mold through an opening called a sprue. Once the molten metal solidifies, the mold is shaken or vibrated to release the sand from the casting, which is then collected for reuse.
The last stage of the process is cleaning the cast product. Any extra molding material is trimmed away, along with imperfections and rough edges. The product is then refined and shaped to its final form. Depending on the required finish, it may be burnished or polished.
Metals of all types can be shaped through the casting process, from hardened steel and stainless steel to copper and zinc. Among these, aluminum stands out as the most widely used due to its excellent strength-to-weight ratio, resistance to corrosion, and shiny finish. Various casting methods, including die casting, sand casting, and permanent mold casting, are commonly employed to form aluminum products.
The fundamental techniques from ancient times have evolved into a wide range of specialized casting methods, each tailored for specific purposes. These various processes can all produce high-quality parts, offering distinct manufacturing advantages. Understanding the pros and cons of each method is crucial in selecting the right approach to meet individual production needs. Some of the most popular casting processes include sand, die, investment, and plaster casting. While the basic principles may seem similar, the execution of each process and the quality of the resulting products differ significantly.
Die casting forms parts or designs by injecting molten metal into a die or mold using high pressure. An extinct method of printing called linotype used the die casting method to produce printing plates for large printing presses. Its development replaced or added to the gravure process that preceded it. With the development of the computer, linotype machines disappeared, replaced by efficient technical methods.
Die casting can be categorized into two types: cold chamber and hot chamber (also known as piston or gooseneck). These methods differ in how the molten metal is injected into the die. Understanding the distinctions between these processes is essential for selecting the appropriate production method based on the specific design requirements of a part.
Cold chamber die casting is used with metals that have a high melting point. Common materials used in this process are metal alloys such as aluminum, brass, and copper. The cold chamber process requires the use of a furnace and ladle for pouring molten metal. There are two methods of introducing the molten metal to the die in the cold chamber process – ladling or by a high pressure plunger. Cold chamber die casting requires much higher pressure than other die casting methods but takes a few minutes for the molten metal to solidify. Also, the dies can have multiple chambers making it possible to produce several parts at the same time.
In the piston or gooseneck process, the piston is removed, and the die is submerged in molten metal. Once fully immersed and the gooseneck is filled, the piston forces the molten metal out of the gooseneck and into the die. This process has a rapid cycle time of approximately 15 minutes, allowing for quick and efficient production of parts. However, it is limited to metals with low melting points and cannot be used with aluminum, as it tends to stick to the sides of the die.
The die casting process begins with the fabrication of two sections of a reusable steel mold. To facilitate the removal of the casting and manage temperature, a lubricant is applied. This lubricant aids in both temperature regulation and easy separation of the die. Once the two mold sections are securely clamped together, molten metal is injected into the mold. Die casting can produce highly complex and intricate parts as well as simple ones, but it is limited to non-ferrous metals.
Die casting molds fall into four basic categories: single cavity, multiple cavity, combination, and unit. Single cavity dies have just one chamber, whereas multiple cavity dies feature two or more chambers, which can be either identical or varied depending on the process. Combination dies are a subset of multiple cavity dies with different cavities. Unit dies, on the other hand, contain several cavities connected by a sprue, allowing multiple parts to be produced in a single casting.
Despite its restriction to non-ferrous metals, die casting offers the advantage of producing parts with precise dimensions and excellent shape tolerance. Its ability to maintain dimensional consistency and uniform design has made it a popular choice for many years. Additionally, die-cast parts typically require minimal machining after casting, similar to some other casting techniques.
The primary drawback of die casting is its high cost, primarily due to the creation and tooling of the die. Although die designs can be engineered using computer software, the process relies on molten steel, which limits experimentation and prototyping. However, since dies can be stored and reused, die casting is cost-effective for producing large quantities of parts, reducing the initial investment per unit. It is not ideal for single parts, prototypes, or small production runs.
Die cast parts have limitations in their mechanical properties and are generally not suited for use as structural components. They are typically designed for immediate use, such as engine blocks, rather than for applications requiring significant structural integrity.
In gravity die casting, molten metal is poured directly into the mold cavity using a ladle or similar container. The core principle is to rely on gravity to fill the mold cavity. The process aims to minimize turbulence during filling to reduce oxidation and foaming, which in turn helps to minimize porosity and inclusions, ensuring optimal characteristics in the final product.
Tilting the mold during gravity die casting results in denser, higher-quality castings with increased strength and stiffness. This makes the process particularly advantageous for producing components like brake and suspension systems. Gravity die casting is well-suited for high production runs and automated manufacturing.
Pressure die casting involves injecting molten metal into a closed die at high speed and pressure. The die consists of a stationary half and a moveable half, both mounted on the platen of the casting machine. Molten metal is delivered through a sprue connected to the stationary half and injected by a hydraulic piston that generates the required pressure. Toggles and hydraulics maintain the die's closure under pressure. Within a few seconds, the molten metal solidifies into a finished cast part.
Pressure die casting primarily utilizes metals such as aluminum, zinc, and magnesium. This method is capable of producing large quantities of lightweight alloy products with remarkable speed and efficiency. After casting, the products typically require minimal or no additional finishing processes.
Miniature die casting is employed to create small, detailed, and intricate components using specialized dies and die casting machines. While the process mirrors that of standard die casting, it features faster cycle times, contributing to a longer lifespan for the die casting tools. In addition to reduced tool costs, miniature die casting offers exceptional precision, achieving tolerances of +/- 0.001 inches and wall thicknesses of 0.020 inches in parts weighing up to 0.75 lbs (0.34 kg).
Parts manufactured through miniature die casting include control units, computer hardware, telecommunication components, and various electronic devices. Similar to pressure die casting, miniature die cast parts typically require minimal to no post-casting finishing.
Aluminum is the most commonly used non-ferrous metal in casting. It produces highly durable, lightweight parts while preserving its inherent properties and characteristics. Aluminum die cast parts offer various surface finishing options and can withstand higher operating temperatures compared to other non-ferrous metals. Like high-pressure and miniature casting, aluminum casting benefits from rapid cycle times, enabling high-volume production.
Aluminum die casting excels at producing highly complex shapes with intricate features, achieving exceptional tolerances and superior part finishes that often eliminate the need for additional surface finishing. This process typically uses aluminum alloys, with A380, 383, B390, A413, A360, and CC401 being the most common. The choice of alloy depends on the intended application of the cast part, as each alloy offers specific properties and characteristics suited to different uses.
Sand casting uses sand molds to form and shape castings. It is a common production method for the manufacture of metal parts of varying sizes and weights and can produce complex detailed parts using any type of metal alloy. Though sand casting is a cost effective and economical method, it is capable of efficiently producing high quality parts. All of the materials used in the process are reusable and recyclable, which adds to its low cost.
The sand casting method is one of the few processes to be used with metals that have a high melting point such as certain types of steel, nickel, and titanium. The flexibility and heat resistance of sand casting as well as its low cost has made it the most widely used casting process.
Castings are created by pouring molten metal into a mold cavity. The sands used in casting have special bonding materials that enhance their resistance to heat and ability to retain shape. Traditionally, green sand, a mixture of sand, coal, bentonite clay, and water, has been the primary choice for creating castings. However, silica (SiO2) has recently become more widely used due to its superior properties.
There are several characteristics of sand molding, aside from low cost, that have made it a popular process. Sand molds retain their shape under mechanical stress but are permeable enough to release gases and steam. When sand is applied to the pattern, it can fill small recesses to create a precise mold of minute details. Though molding of large heavy parts is a difficult process, sand casting easily adapts and adjusts to produce parts of any size and can cast ferrous and non-ferrous metals.
Despite its popularity, sand casting has some drawbacks and limitations, including less precise dimensional accuracy and difficulty in producing parts with high tolerances. Additionally, parts produced through sand casting often have a rough or coarse finish.
Despite these disadvantages, sand casting remains one of the most popular and cost-effective methods for part production.
Gray iron casting involves pouring molten iron into a mold cavity and allowing it to solidify. As one of the oldest casting methods, gray iron casting has been used for centuries to produce a variety of items, including weapons, cookware, tools, and utensils. The type of gray iron cast depends on the alloys added to the iron. Key differentiators between types of gray iron include the amount of carbon they contain, which affects their melting temperature, weldability, and machinability.
Gray iron casting, also known as grey iron casting, utilizes smelted gray iron, an alloy composed of iron and carbon with traces of phosphorus, sulfur, silicon, and manganese. The materials used in gray iron casting exhibit a graphitic microstructure, which is an indicator of the strength and impact resistance of the iron castings.
A common practice in the production of gray iron castings involves heat treatments to enhance the casting's mechanical properties. These treatments improve thermal conductivity, strength, durability, and machinability while also affecting the overall cost. Finished gray iron castings are then subjected to various finishing processes to achieve the required tolerances.
Gray iron castings are used in a variety of applications, including valves, engine blocks, brake drums, pump housings, and cookware. The methods for producing gray iron castings include lost foam, mold casting, and sand casting.
Investment casting uses a wax pattern coated with a ceramic material, which hardens to the shape of the casting. Once the ceramic sets, the wax is melted away and molten metal is poured into the emptied cavity. When the metal solidifies, the casting is broken to release the metal part. Also known as lost wax processing, it is a method that has existed for over 5000 years and dates back to the time of the ancient Egyptians and Chinese.
The first step in the investment casting process is to produce a wax pattern, which can be made from plastic but is most often made from wax. The mold can be cast or machined with its dimensions carefully calculated and engineered to avoid shrinkage. Since the process requires precise measurements, several trials may be necessary to reach the proper proportions, which makes investment casting molds expensive.
Investment casting is used to produce precision parts from several alloys or metals, including aluminum, stainless steel, carbon steel, brass, and bronze. The parts produced are found in several industries including fluid power, oil and gas, food and dairy, military, firearms, aerospace, and aviation as well as agriculture.
Investment casting parts offer excellent dimensional tolerances and high accuracy, often requiring minimal finishing or machining. This process can produce complex shapes with intricate designs. Similar to sand casting, investment casting generates minimal waste, as the ceramic material used can be recycled. Additionally, it is versatile and capable of producing parts from a variety of alloys.
Though investment casting is an expensive process compared to sand casting, the quality of the parts it produces makes its use appealing. Parts have an excellent finish and require very little machining or finishing, which can compensate for the added initial cost.
Investment casting can be performed using two methods: gravity fed and vacuum. In the gravity fed process, molten metal flows into the mold solely through the force of gravity, without the aid of pressure or other mechanisms. Vacuum casting, on the other hand, is a precision technique used for components such as aircraft parts. It involves drawing molten metal into the mold under negative pressure, ensuring greater accuracy and quality.
Vacuum casting differs from traditional investment casting in that it uses a vacuum to draw the molten metal into the mold. The process starts with a two-part mold placed in a vacuum chamber, where negative pressure pulls the molten metal into the mold. Unlike investment casting, which allows the workpiece to cool in the sand mold, vacuum casting solidifies the casting in an oven.
As the name implies, permanent mold casting uses reusable molds much like die and centrifugal casting and has a variety of applications for jobs that require mass production or duplication. Though it is more expensive than the other forms of casting, it is ideal for the production of parts for major industrial operations.
In permanent mold casting, molds are typically made of metals with high melting points, such as steel, graphite, bronze, or cast iron. The mold consists of two tightly fitting sections with an opening at the top for the molten metal to enter. Once the molten metal cools and solidifies, the two sections of the mold are separated to release the finished part.
The permanent mold casting process starts with heating the mold to remove any moisture and to prevent damage from thermal expansion when the molten metal is introduced. Preheating the mold also helps maintain the temperature of the molten metal, preventing it from cooling too quickly during the casting process.
There are different methods for introducing the molten metal into the mold include gravity, pressure assisted, vacuum assisted, and slush casting. With the gravity method, the molten metal is simply poured into the mold. It is the least expensive method. When a mold requires fine details, low pressure is used to force the molten metal into the mold. With the vacuum method, air is removed from the mold creating a vacuum that sucks the molten metal into the mold. The use of low pressure and vacuum is for parts with small spaces and fine details. In the slush method, the molten metal is poured into the mold and allowed to harden against the outer surface of the mold. Once the surface material is solidified, the remaining molten metal in the center is poured off leaving a hollow casting. The slush method is used to make hollow chocolate Easter bunnies.
In the lost foam casting process, the mold is made from polystyrene foam, which can be shaped from a block of foam or created through injection molding. This method is a variant of investment casting, where foam replaces wax to form the mold. Introduced in 1958 by H. F. Shroyer, who patented the use of polystyrene in green sand for forming foam patterns, lost foam casting offers an innovative approach to creating complex castings.
The tooling for lost foam casting involves using a split cavity aluminum die to produce the foam pattern. These lost foam patterns are quite similar to permanent die casting molds and demand a comparable level of expertise and experience in their tooling. Aluminum dies used in lost foam casting are exceptionally durable, offering a long life cycle.
The pattern-making process for lost foam casting involves creating a foam pattern complete with a gating system, typically produced using a foam press. This process also includes the addition of risers and gates. Precision in pattern making is crucial for the quality and value of the final casting, requiring meticulous attention to detail. Patterns can be formed using a closed die or shaped from a solid piece of polystyrene.
A single or multiple parts can be produced from a lost foam pattern. The gating system and pattern are collectively known as a cluster, which must be coated with a permeable ceramic refractory. This coating process can be achieved through dipping, brushing, spraying, or flow coating. The primary purpose of the coating is to create a barrier between the foam surface and the surrounding sand. Additionally, the coating manages permeability and allows gases from the vaporizing foam to escape into the sand.
The cluster is allowed to dry and harden before being placed in a foundry flask filled with loose, unbounded sand. To create a tight, compact seal around the pattern, the flask, sand, and pattern are vibrated, impressing the shape and pattern into the sand. A special type of sand known as green sand is used in the lost foam process. This mixture consists of sand, clay, sludge, anthracite, and water. It is called green sand not because of its color, but because it remains unset and pliable.
Once the sand is tightly packed and the impression of the pattern is securely encased, molten metal is poured into the top of the gating system. As the molten metal fills the mold, it causes the polystyrene foam pattern to vaporize. The quantity of molten metal is carefully calculated and measured before pouring. Air vents on the sides of the flask allow the vapor from the foam to escape, ensuring a clean casting.
The solidification of the casting varies depending on the type of metal used. Cooling starts immediately after pouring and may take several minutes. As the temperature decreases, the molten metal begins to form crystals near the walls of the sand mold, continuing until the entire casting is solidified.
Once the casting has sufficiently hardened, it is removed from the sand mold. The sand is typically shaken off or extracted from the flask. After removing the sand, the gating system is dismantled, leaving behind the finished parts.
The fully shaped and formed part is now ready for various post-treatments aimed at perfecting and enhancing the cast piece. These treatments include removing gates, risers, and runners, as well as sandblasting or grinding the metal workpiece to achieve the desired smoothness, tolerance, and shape. Additionally, a range of machining processes may be employed to further refine the final component.
Centrifugal casting, also known as the deLavaud process, uses a spinning mold to produce lengths of pipe through the use of G force created by rapidly rotating the mold. The concept was invented by French engineer Dimitri Sensaud deLavaud as a more efficient method of producing iron pipe.
The centrifugal process consists of a spinning steel mold enclosed in a jacket of water or water spray. Molten metal is injected into the casting by a ladle through a trough, which rides on a movable carriage or platform. As the molten metal enters the casting, it stretches to the full length of the mold. The molten metal is first ladled into a bell from which it enters the casting and continues to enter the mold until the full length is full to the spigot end. The centrifugal movement forces the iron to the wall of the mold where it solidifies to a seamless pipe. Joints are created by a resin coated core of sand of the correct dimensions for the mold, which prevents molten metal from escaping.
To increase the adhesion of the mold, it is peened to improve surface friction and enhances the life of the mold. Also, peening helps sprays stick to the walls of the mold to make removal of the casting more efficient. During the casting process, the die can be spinning vertically or horizontally depending on the configuration of the part to be produced where ring and cylinder parts are shaped vertically, and tube shapes are made horizontally.
The centrifugal force in the process expels less dense materials such as impurities and "floats." Solidification occurs under the pressure of the spinning force, resulting in a defect-free part with no cavities or gas pockets.
In addition to pipes, centrifugal casting is used to produce flywheels, cylinder liners, and axi-symmetric parts. The high quality achieved with cylinder liners and sleeve valves through centrifugal casting is unmatched by other casting methods.
Pressure casting, a form of centrifugal casting, is used for asymmetrical parts that cannot be spun around their own axis. The method is quick and cost effective for the production of high volume parts with a tight tolerance. A molten metal alloy is injected into a steel mold under high pressure and solidifies almost immediately to be extracted. This method can be used for large gear rings and other such items.
Plaster casting is a process used to manufacture non-ferrous alloy parts with a smooth, even finish. This method is ideal for producing precise, detailed parts with high dimensional accuracy. Typically, the pattern for the casting is designed using CAD or similar software, with allowances made for shrinkage.
The mold-making process starts with a plaster mixture composed of gypsum or calcium sulfate, combined with talc, asbestos, sand, sodium silicate, and water. This forms a slurry that is sprayed onto the pattern, which has been treated with an anti-adhesive to prevent the plaster from sticking. The molds form within minutes, are removed from the pattern, and allowed to dry. Once dry, the cores and mold are assembled, and molten metal is poured into them. As with investment casting, the mold is broken away once the metal has cooled and hardened to release the finished part.
There are limitations with plaster casting since the process is complicated and takes time, which increases its cost. Its greatest success is with materials that have a low melting point such as aluminum, copper, magnesium, or zinc. Since it takes little time to produce a mold, it is an excellent method for taking a CAD rendering and making a prototype.
Final products produced using plaster casting feature smooth, even surfaces with exceptional detail. Unlike other casting methods, this process accurately replicates intricate and complex features, even in parts with thin walls. Additionally, plaster casting can handle large parts made from non-ferrous metals with low melting points, similar to sand casting.
Vacuum casting, also known as urethane or polyurethane casting, differs from permanent mold casting and die casting by using silicone molds to produce plastic and rubber components. The process begins with creating a silicone mold using 3D modeling techniques, followed by the traditional injection molding process. The pattern is equipped with cores, inserts, and gates before being placed in the casting box. Risers are then added to allow air to escape from the mold.
In the vacuum casting process, silicone is poured over the master pattern under pressure to ensure it thoroughly covers and captures every detail. The silicone mold is then cured at 40°C (104°F) for 8 to 16 hours, depending on its size. Once curing is complete, the casting box and risers are removed, leaving behind a precise silicone mold ready for casting.
After curing, the mold is cut along a wavy pattern to reveal the negative cavity of the part. This wavy pattern helps ensure proper alignment of the mold halves during production. The resin for the part is then prepared and mixed with precise proportions, potentially including colors, and placed in a pouring bowl. To eliminate air pockets and ensure a smooth flow, the resin mixture is poured into the mold under a vacuum, which helps create a bubble-free casting and reduces resistance to the resin's flow.
After the resin is cast, the mold is placed in a heated chamber for curing. Once the curing process is complete, the part is removed from the mold. The finished part undergoes additional finishing steps, including clipping off the gates and risers and addressing any imperfections or rough surfaces to achieve the final desired quality.
Vacuum casting is ideal for producing small batches of high-quality parts, making it suitable for prototyping and low-volume production. It offers a wide range of resins to meet various application needs, including clear, rubbery, flame retardant, and colored options. Resin types can be easily switched without changing the tooling, allowing for flexibility in testing different materials to find the best fit for specific applications.
Squeeze casting merges the processes of casting and forging, where molten metal solidifies under pressure within a closed die positioned between the plates of a hydraulic press. In the direct squeeze casting method, molten metal is poured into one half of a preheated die, and the upper half is then closed over it, forcing the metal to fill the die. During solidification, pressures ranging from 70 MPa to 140 MPa or more are applied using a hydraulic press. The indirect squeeze casting method involves injecting liquid metal into an indirect squeeze casting machine through a shot sleeve and then into the die chamber through a gate.
As the molten metal begins to solidify, the upper half of the die is pressed with increasing force into the lower half until the casting is fully set. This pressurization ensures that the molten metal is evenly distributed, preventing defects such as separation or breakage in the metal part. Once solidification is complete, the hydraulic press ram retracts, and the casting is ejected. The pressure applied by the hydraulic press during squeeze casting is significantly lower than that used in forging, resulting in improved uniformity of the metal structure and enhanced mechanical properties.
Continuous casting involves pouring molten metal into a mold that solidifies it quickly, resulting in a fine, uniform grain structure and excellent physical properties. In this process, molten metal is continuously fed from an induction furnace into the mold through a series of openings at the top. The mold is surrounded by a water-cooled jacket, which accelerates the solidification of the metal. Additionally, the molten metal above the mold acts as a riser, maintaining the fill level in the die and preventing shrinkage.
After the molten metal solidifies, it is ejected from the bottom of the mold using a mechanical device. The flow of metal is precisely controlled until it reaches the desired length, at which point it is cut off by a saw. The combination of low casting temperatures, a chilled mold, and directional solidification results in castings with a homogeneous, fine-grain structure and high density.
Continuous casting can be performed using two main methods: horizontal and vertical. In the horizontal method, the equipment operates on a single horizontal level, utilizing gravity to produce hollow tubes. Both methods can create various shapes, including rectangular, hexagonal, square, and gear teeth. Continuous casting is particularly well-suited for producing long tubular forms and small inside diameters, which are challenging for other casting techniques. The primary advantage of continuous casting is its capability to produce extended, consistent tubular shapes efficiently.
Shell molding is akin to sand casting but differs in that it uses a hardened sand shell to form the mold cavity based on the pattern of the part. In this process, finer sand mixed with resin is heat-treated to create a shell around the metal pattern. The sand-resin mixture is poured into a heated mold, reaching temperatures between 204°C and 371°C (400°F to 700°F), which activates the resin. As the sand mixture contacts the pattern, it forms a solid shell on the inner surface, establishing the mold.
The mold in shell molding is typically a metal form that shapes the shell mold around the desired part. Unlike the patterns, which are reusable, the formed molds are disposable, similar to sand casting molds. Shell molding can accommodate both ferrous and non-ferrous metals, including cast iron, alloy steel, stainless steel, aluminum alloys, and copper alloys. Common parts produced using shell casting include gear housings, cylinder heads, connecting rods, and level arms. The patterns used in shell casting are often made from different metals, with steel and iron being the most common choices. However, aluminum may also be used for low-volume production or graphite casting.
Waupaca Foundry specializes in producing ductile iron and gray iron castings through advanced technological methods. Serving top markets in automotive, agricultural, construction, and industrial sectors, the company is committed to minimizing its environmental footprint and enhancing efficiency. Notably, Waupaca has boosted its energy efficiency by over 13% through its compressed air optimization project.
Shibaura is a leading provider of high-pressure die casting (HPDC) machines, offering a range of equipment for aluminum and magnesium casting, including high pressure, cold chamber, and semi-solid machines with capacities ranging from 1,350 kN to 35,000 kN. Their comprehensive line of die casting machines features models in small, medium, and large sizes, as well as the E-series, which integrates the speed of an electric servo motor with three-platen toggle clamping.
BMC specializes in the manufacture of aluminum and zinc die casting machines and trim presses. In addition to production, the company offers rebuilding and remanufacturing services for die casting, injection molding, blow molding, and trim press machines. BMC provides a comprehensive range of hot and cold chamber machines known for their exceptional reliability and low maintenance. The company's double pump system ensures continuous high flow and pressure for its die actuating operations.
RDO specializes in manufacturing vacuum induction casting machines and induction heaters for casting prototypes. Their CS casting system is designed for both high-volume small parts and low-volume large parts. The SuperCast Pro system, used by foundries, metal recyclers, and large casting manufacturers, serves as an advanced investment casting solution that offers similar capabilities to traditional rotocasting systems. RDO’s CS1, CS2, and CS3 models are versatile, accommodating a wide range of metals and alloys.
Gesswein manufactures induction-heated, pressure-over-vacuum casting machines designed for producing dense castings. Their product lineup includes the Galloni G1, Galloni G3, Galloni Heavy Duty, and Galloni Pressovac Dual Touch. Gesswein’s high-production casting machines efficiently cast platinum, gold, silver, and steel, achieving cycle times of 3 to 4 minutes for gold and platinum. Castings from Gesswein’s vacuum casting machines feature exceptionally smooth surfaces and a dense molecular structure.
An understanding of the various casting methods is critical to making the decision of how to produce a conceptualization. Each of the different types has their advantages. The major considerations are the cost of production and the number of parts to be produced. Casting manufacturers specialize in one of the varieties of approaches. There are a few producers who will offer a variety of production methods. Carefully reviewing the qualifications of each producer as listed in the IQS Directory can assist in selecting the proper company for the job.
Aluminum casting is a method for producing high tolerance and high quality parts by inserting molten aluminum into a precisely designed and precision engineered die, mold, or form. It is an efficient process for the production of complex, intricate, detailed parts that exactly match the specifications of the original design...
Die casting is a high pressure metal casting process that forces molten metal into a mold. It produces dimensionally accurate precision metal parts that have a flawless smooth finish...
Investment casting is a metal working process that uses a ceramic shell built over a wax pattern to produce parts with extraordinarily uniform and smooth surfaces. The wax pattern is produced from an aluminum die.The final products of investment casting are without parting lines, mold half marks, or other deformities...
An iron casting is a hard product obtained from combining iron with carbon. This can be readily cast in a mold, and it contains a higher proportion of carbon compared to steel. The proportion typically ranges from 2 to 4.3...
Lost wax casting is a casting process that uses a wax pattern to create a ceramic mold for creating a part or product design. It has been known over the years as lost wax or precision casting due to its accuracy in recreating parts with precise tolerances...
Permanent molding casting is a casting process that uses strong durable reusable molds to produce parts and components using molten metals. The molds for permanent mold casting are made from steel or...
Sand casting is a manufacturing process in which liquid metal is poured into a sand mold, which contains a hollow cavity of the desired shape and then allowed to solidify. Casting is a manufacturing process in which...
Aluminum forging is a method for processing aluminum alloys using pressure and heat to form high strength, durable products. The process of aluminum forging involves pressing, pounding, and...
Cold forging is a metal shaping & manufacturing process in which bar stock is inserted into a die and squeezed into a second closed die. The process, completed is at room temperature or below the...
Copper and brass forging is the deformation of copper and brass for the purpose of manufacturing complex and intricate shapes. The temperature at which copper and brass are forged is precision controlled and...
Forging is a metal working process that manipulates, shapes, deforms, and compresses metal to achieve a desired form, configuration, or appearance outlined by a metal processing design or diagram...
In this article, there are key terms that are typically used with open and closed die forging and it is necessary to understand their meaning. Forging is a process in manufacturing that involves pressing, hammering, or...
Rolled ring forging is a metal working process that involves punching a hole in a thick, solid, round metal piece to create a donut shape and then squeezing and pressuring the donut shape into a thin ring...
Forging steel is a manufacturing process used to shape steel by using localized compressive forces, which include hammering, pressing, and rolling. It is a widely used method for producing high quality steel products...
Zinc die casting is a casting process where molten zinc is injected into a die cavity made of steel that has the shape, size, and dimensions of the part or component being produced. The finished cast zinc product has...
The ancient art of forging falls into two distinct categories – hot and cold where hot forging has been around for centuries while cold did not begin until the industrial revolution of the 19th Century. Though they are quite different ...
