From Forging to Stamping: The Spectrum of Metal Forming
Die casting is a metal casting process that uses mold cavities to apply high pressure to molten metal. Unlike pressure casting, die casting is not an abbreviation for it. The molds are typically made from a stronger alloy, and the process resembles injection molding.
Sand casting involves creating a mold using sand. This process starts by placing a finished part model, or a wooden model known as a pattern, into the sand. Once the pattern is positioned, the sand is packed around it to form a mold. After the pattern is carefully removed, the sand retains the shape of the mold.
To extract the model before pouring in the metal, the mold is typically divided into two or more parts. During the mold-making process, it is essential to incorporate openings and vents for pouring the metal, which collectively create a pouring system. Once the mold is filled with liquid metal, it is allowed to sit for a specific duration until the metal solidifies. After the metal has hardened and the part is removed, the mold is destroyed. Consequently, a new mold needs to be created for each casting.
Investment casting, also known as lost wax casting, involves several processes: pressing wax, trimming wax, forming trees, dipping in slurry, melting wax, pouring molten metal, and post-processing. The process starts by creating a wax mold of the part to be cast. A layer of mud is then applied to the wax mold, forming what is known as the mud mold. After the mud mold dries, it is baked to create a ceramic mold. Once the baking process is complete, the wax is completely melted away, resulting in only the ceramic mold remaining. Typically, a pouring port is left in the mud mold so that molten metal can be poured in. After the metal cools, the final parts are produced.
Die forging is a method that uses a die to shape a blank using specialized die forging equipment, resulting in a forged part. Depending on the equipment used, die forging can be categorized into several types, including hammer die forging, crank press die forging, flat forging machine die forging, and friction press die forging.
On the other hand, roll forging is a plastic forming process in which a material is deformed under the action of a pair of counter-rotating dies. This process produces the desired forging or forging blank. Roll forging is a special type of forming rolling, specifically longitudinal rolling.
Forging is a manufacturing process that uses specialized machinery to apply pressure to metal billets, causing them to undergo plastic deformation. This results in forgings with specific mechanical properties, shapes, and sizes. It is one of the two main types of metal processing, alongside stamping.
One of the key advantages of forging is its ability to eliminate defects found in cast metal produced during the smelting process, while also optimizing the metal’s microstructure. Furthermore, because forging maintains the integrity of the metal flow lines, forgings typically exhibit superior mechanical properties compared to castings made from the same material.
Forgings are primarily used for critical components in machinery that experience high loads and harsh working conditions. In contrast, simpler shapes can often be produced using rolled plates, profiles, or welded parts.
Rolling, also known as calendering, is the process of passing a metal ingot through two rollers to shape it. When the temperature of the metal exceeds its recrystallization temperature during this process, it is referred to as “hot rolling.” Conversely, if the temperature remains below that threshold, it is called “cold rolling.” Calendering is the most commonly used method in metal processing.
The essence of pressure casting is to fill the die-casting mold cavity with liquid or semi-liquid metal at a high speed under high pressure, and then form and solidify it under pressure to obtain a casting.
Low-pressure casting is a method that utilizes low-pressure gas to fill a mold with liquid metal, allowing it to solidify into a casting. This technique was initially developed primarily for producing aluminum alloy castings. Over time, its applications have expanded to include the production of copper, iron, and steel castings, especially those with high melting points.
Centrifugal casting is a method for injecting liquid metal into a high-speed rotating mold. Through the action of centrifugal force, the liquid metal fills the mold and solidifies to form a casting. The molds used in centrifugal casting can vary; they may be non-metallic (such as sand molds, shell molds, or investment shell molds), metallic molds, or molds that have a coating layer or a resin sand layer inside the metal mold. The choice of mold depends on the shape, size, and production volume of the casting being produced.
Lost foam casting is an innovative casting method that utilizes wax or foam models, which are similar in size and shape to the final casting. The process involves creating a cluster of these models, applying refractory paint to them, and allowing it to dry. The models are then buried in dry quartz sand for vibration molding. Once prepared, liquid metal is poured under negative pressure, causing the foam or wax models to vaporize. The molten metal fills the space left by the models, solidifying and cooling to form the final casting.
This casting technique is notable for its nearly zero excess material and precise molding capabilities. Additionally, it does not require mold removal, parting surfaces, or sand cores, leading to castings that are free from flash, burrs, or draft angles. This also helps minimize dimensional errors that can occur due to core combinations.
Squeeze casting, also known as liquid die forging, is a method used to inject molten metal or semi-solid alloy directly into an open mold. The process begins by closing the mold to ensure the metal fills the mold’s shape. High pressure is then applied, causing the solidified outer layer of the metal (the shell) to undergo plastic deformation, while the still-liquid metal experiences isostatic pressure. This high-pressure solidification leads to the formation of a part or a blank.
There are two types of squeeze casting: direct and indirect. In direct squeeze casting, the molten metal is injected into an open mold, followed by mold closure and the application of pressure. In contrast, indirect squeeze casting involves injecting the molten metal or semi-solid alloy into a closed mold cavity through a punch. Here, high pressure is also used to induce crystallization and solidification, ultimately resulting in the production of a part or a blank.
Continuous casting is a method that involves a through-mold, continuously pouring liquid metal into one end and pulling out the molded material from the other end.
Drawing is a metal processing technique that involves applying external force to the front end of a metal piece, which is then pulled through a die hole that is smaller than the cross-sectional area of the metal blank. This CNC manufacturing process shapes the metal into a product of specific dimensions. Since drawing is typically performed at room temperature, it is often referred to as cold drawing.
Stamping is a manufacturing process that utilizes a press and a die to apply external force to materials such as plates, strips, tubes, and profiles. This force causes the materials to undergo plastic deformation or separation, resulting in a workpiece—or stamping part—that has the desired shape and size.
Metal injection molding is an advanced powder metallurgy near-net shaping technology evolved from the plastic injection molding industry. While plastic injection molding can produce various complex-shaped products at a low cost, plastic products tend to have lower strength. To enhance their performance, metal or ceramic powders can be added to the plastic, resulting in products with greater strength and improved wear resistance. In recent years, this concept has progressed to maximize the solid particle content while completely removing the binder. The molded blank is then densified during the subsequent sintering process. This innovative powder metallurgy molding method is known as metal injection molding.
Turning refers to the lathe processing method used in mechanical manufacturing. This technique primarily involves a turning tool that shapes a rotating workpiece. Lathes are mainly employed to process components like shafts, discs, sleeves, and other workpieces with rotating surfaces. They are the most commonly used machine tools in both manufacturing and repair industries.
Turning is a cutting process that operates by rotating the workpiece in relation to the tool. The cutting energy is mainly supplied by the workpiece, not the tool itself.
As the most fundamental and widely used cutting method, turning plays a crucial role in production. It is particularly suited for processing rotating surfaces; nearly all workpieces with such surfaces can be shaped using turning techniques. This includes internal and external cylindrical surfaces, internal and external conical surfaces, flat end faces, grooves, threads, and various rotating formed surfaces. The primary cutting tools utilized in this process are turning tools.
Milling involves securing a workpiece and using a high-speed rotating cutter to shape it into the desired form and features. Traditional milling is primarily used for creating simple shapes and features, such as contours and grooves. In contrast, CNC milling machines are capable of processing complex shapes and features. Milling and boring machining centers offer three-axis or multi-axis capabilities, making them suitable for a variety of applications, including machining molds, inspection fixtures, jigs, thin-walled complex curved surfaces, artificial prosthetics, and blades. When selecting CNC milling working as a processing method, it is important to fully leverage the advantages and key functionalities of CNC milling machines.
Planing is a machining method that uses a planer to create a linear reciprocating motion horizontally across the workpiece. This technique is primarily used for shaping parts. The precision of planing ranges from IT9 to IT7, and the surface roughness can vary from Ra 6.3 to 1.6 micrometers.
Grinding Grinding refers to the process of using abrasives and tools to remove excess material from a workpiece. Grinding is one of the most widely used cutting methods.
Selective laser melting is a process that uses a high-power carbon dioxide laser, which is controlled by a computer, to selectively scan the surface of metal powder in a tank. When the laser reaches specific areas, it completely melts the metal powder, causing those areas to fuse together. The parts that are not illuminated by the laser remain as powder. This entire process must take place in a sealed chamber filled with inert gas to ensure safety and optimal results.
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