37 Different Types of Metal Casting Methods
Metal casting is a manufacturing process in which molten metal is poured into a mold cavity that defines the desired shape, and then allowed to cool and solidify into that shape. The resulting object, called a casting, emerges with the geometry of the mold. This process is thousands of years old, dating back to the Bronze Age (around 5,000–7,000 years ago) when early civilizations cast copper, bronze (copper-tin alloy), and other metals into tools, weapons, and jewelry.
As industries continuously look for more precise and complex cast parts, metal-casting technologies are parallelly developing new methods and techniques. You can find numerous types of casting methods, such as sand or silica casting and die casting methods, each with some unique capabilities. The comparative analysis(process, benefits, and applications) of these techniques can help you decide which one is the best fit for your project.
Here are the common metal casting methods in manufacturing.
The investment casting process is relatively more complex than sand cast. It involves preparing a mold using wax patterns connected in a central wax sprue. Then, refractory material like ceramic surrounds this network. Next, heating the mold melts the wax patterns inside the refractory and leaves the cavity with a smooth finish, the reason why it is also known as lost wax castings. Then, liquid is poured into this cavity, and the mold is broken to remove the parts after solidification is complete.
Benefits:
Using a wax pattern allows the making of hollow sections, undercuts, and internal channels without inserting the core.
Fined grain structure and better surface finish.
Good dimensional accuracy (± 0.1mm)
Thin-walled parts with complex geometries
Applications: Military and aircraft components like engine parts, industrial plant components, automotive engine and exhaust systems, medical implants and instruments, etc.
Sand Casting
The sand mold casting method uses tightly packed fine silica-based materials or sand grains to make the mold. The mold involves two sections; cope and drag (upper and lower half). Meanwhile, the molten metal is poured into the cavity formed by these two sections. This mechanism also ensures precise alignment, easy handling, complex shapes, and efficient gating.
Benefits:
The mold-making and casting process is simple and highly cost-effective in terms of tooling cost.
Sand mold casting is compatible with almost every alloy, ferrous and non-ferrous both.
Versatility in shape and size. It can cast parts that are 200+ tons in weight.
Although the dimension accuracy is low, post-processing is straightforward and takes less time.
Applications: Pistons, bushings, electronic components, valves, bearings, engine crankcases, plant machinery, etc.
The pressure of the pouring or pressurized furnace attached to the casting machine typically consists of a pressure of 0.02 to 0.07 Mpa. The pouring furnace remains below the cast, forces the metal liquid above with the riser tube, and then transfers it into the cavity. The continuous pressure is necessary to fill the cavity. Once it is filled, the cooling channels cool the mold in a controlled manner until complete solidification is achieved.
Benefits:
The low pressure allows for precise control of filling and eliminates the turbulence, reducing defects like porosity and shrinkage.
High accuracy and detailed casting.
The low-pressure casting process is compatible with various non-ferrous materials like aluminum alloys.
The smooth filling also enables the casting of sharp corners and intricate geometries.
Applications: Cylinder hub and frame, wheel hubs, kitchenwares, custom hollow and complex profiles, fittings, electronic appliance components, etc.
This casting uses permanent molds ( called die) made from strong materials like hardened tool steel. It is typically used for materials like zinc, aluminum, copper, and tin. The die casting process includes melting the raw material in a furnace, which might or might not be attached to the casting machine. Then, the hydraulic plunger or injection mechanism transfers the liquid into the die. Meanwhile, the pressure can reach up to 25000 psi.
Benefits:
Tight tolerances and consistency across production cycles
Less requirement for post-processing operations
Cost-effective for high-volume production
Applications: It has a broad application spectrum; automotive parts, aircraft turbine blades and airframes, electrical housing, industrial items, machine tools, and household appliances are a few examples.
Pressure injection or plunger mechanism is unnecessary for the metal pouring during the gravity die-casting process. It involves transferring the material from the furnace or ladle into the mold using gravity. No other forces influence the flow until the filling is complete. Furthermore, it mainly accommodates non-ferrous alloys with low melting points, such as copper, zinc, aluminum, and magnesium.
Benefits:
Deine structure, better mechanical properties, and surface finish.
The absence of pressure flow provides minimal porosity in the final parts.
It has more straightforward tooling than other permanent molds due to no need for an injection mechanism.
Applications: Gravity die casting offers diverse applications across many industries, including automotive components, industrial machinery parts, aerospace engine and housing elements, decorative items, parts for household appliances, and more.
Centrifugal Casting
The centrifugal or rotatory cast method uses a cylindrical mold that rotates around its axis, and liquid metal is poured into this rotating mold. The centrifugal force pushes the poured metal against the mold walls, forming a uniform layer. Then, solidification gives the shape of the mold with a specific thickness.
Benefits:
Free from porosity due to continuous feeding of metal liquid
As centrifugal casting parts solidify inwardly, there is minimal risk of gas pockets and shrinkage cavities.
The absence of a risner reduces the material consumption during the pouring stage.
A dense and homogenous structure of grains.
Applications: This casting manufacturing is predominantly used to manufacture symmetrical items, such as hollow cylinders, shaft sleeves, pipes and tubes, pressure vessels, disk shapes, etc.
Vacuum Die Casting
As the name suggests, the vacuum casting process molds the molten states of metal or plastics into the vacuum. Generally, a pump or similar mechanism removes all the air inside the mold during the process.
Silicone molds, like polyurethane, are used for rubber and plastic molding. However, other types of mold and dies are also applicable to vacuum-cast different materials. Additionally, this casting manufacturing mimics some characteristics of the injection molding technique. This vacuum casting strategy is also adaptable to standard die casting to minimize the risk of air trapping.
Benefits:
High precision and accuracy, especially for projects where molds are 3D printed.
Fine cast with intricate details
It eliminates the pore formation risk inside the cast metal.
Good capability of casting the parts with thinner walls
Applications: Functional plastic prototypes, medical implants and prosthetics, consumer goods, automotive body panels and other components, food processing components, etc.
Squeezing Die Casting
This method creates the parts by pressing the liquid and semi-solid material inside the die. First, the liquid metal fills the heated open die, then the upper parts close it and give pressure through the attached hydraulic plate or other suitable mechanisms. The parts solidify under pressure and provide better mechanical property characteristics. Furthermore, it is also known as liquid-metal forging.
Two types of squeezing die casting exist: direct and indirect. In the direct process, the molten metal fills the die, and the upper half closes the die. On the other hand, indirect types first inject the molten metal into the cavity, followed by applying high pressure via a punch or plunger.
Benefits:
Excellent surface texture and minimal porosity.
Quick production cycles.
The squeeze casting produces accurate (near-net-shape) parts.
Quick heat transfer during pressing results in fine microstructures.
Applications: High-strength automotive components like chassis and engine brackets, aerospace parts, industrial gears and hydraulic components, medical device parts, etc.
Lost Foam Casting
The reason behind the name “lost foam” is that a polystyrene foam pattern of the desired part is responsible for producing the final shape. The pattern is placed inside the refractory materials, which melt away after pouring the liquid material and provide the shape after solidification. Then, breaking the mold reveals the part.
Benefits:
Intricate geometries with excellent surface quality and minimal post-machining requirements.
Lost foam casting is compatible with various materials, including iron, stainless steel, aluminum, and copper.
It simplifies manufacturing, reducing time, labor, and material waste.
Applications: Rapid prototypes for testing, automotive cylinder heads and weldments, pipe fittings, valves, pump enclosures, etc.
Continual Casting
The continual casting includes continuous pouring, solidification, and part removal in a production line. The setup and process involve a ladle or furnace, and material flows to the mold cavity, passing a control system. Subsequently, a cooling mechanism ( water channels) in the mold reduces the temperature quickly. So, while leaving the mold parts significantly cooler, further water spray brings them to room temperature.
Benefits:
It is a straightforward process as continual casting does not require a runner, sprue, and riser.
100 % rating yield, no material wastage.
The automation of continual cast boosts efficiency and productivity.
Applications: Parts with consistent profiles, such as beams, columns, rods, strips, tubes, etc.
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