Over the course of more than 100 years, the manufacturing industry has seen a remarkable evolution in the manufacturing process or fabrication process, especially for metal and plastic materials. From the intricate turning, milling, and drilling techniques for metals to the specialized injection molding and extrusion methods for plastics, these processes have become the backbone of modern manufacturing, shaping the world around us in countless ways.
Metal Forming Techniques
Die casting is a machining method where melted metal is pushed into a mold using high pressure. It’s different from pressure casting. The molds are typically made of a stronger alloy, making this manufacturing process somewhat analogous to plastic injection molding.
Sand casting involves creating molds using sand. A model of the finished part, often made of wood, is placed in the sand, which is then packed around it. Once the model is removed, a cavity remains. To facilitate the casting of the metal, the mold must be designed in multiple parts, with channels for pouring the molten metal and vents for releasing gases. After casting, the mold is destroyed, necessitating a new mold for each casting.
Also known as lost-wax casting, this machining process includes steps like wax pressing, wax repair, tree assembly, slurry dipping, wax melting, metal pouring, and post-processing. A wax model of the part is created and then coated with slurry to form a ceramic mold. After the mold dries and is heated, the wax inside melts and goes away. Then, liquid metal is poured into the ceramic mold to make the final piece.
Forging and Types
Forging involves applying pressure to a metal blank to induce plastic deformation, resulting in a part with specific mechanical properties, shape, and size. Forging can eliminate defects like porosity found in metals from the smelting process. Forged parts generally have superior mechanical properties compared to cast parts. There are various types of forging, including hammer forging, crank press forging, flat forging, and friction press forging. Another method, roll forging, involves deforming material between rotating molds to produce the desired shape or blank.
Also known as rolling, this fabrication process involves shaping metal by passing it between rollers. If the metal is heated above its recrystallization temperature during this process, it’s termed “hot rolling”; otherwise, it’s “cold rolling”. Rolling is a prevalent metalworking method.
Pressure Casting and Variants
Pressure casting involves filling a die (or mold) with liquid or semi-liquid metal at high speeds under high pressure. There’s also low-pressure casting, where liquid metal fills the mold under low gas pressure. Initially used for aluminum alloy castings, its applications have expanded to include high-melting-point metals like copper, iron, and steel.
In this method, liquid metal is poured into a rapidly spinning mold. The centrifugal force ensures the metal fills the mold and forms the casting. Depending on the casting’s shape, size, and production volume, various molds like sand molds, shell molds, or metal molds with coatings can be used.
Metal Injection Molding (MIM)
Originating from the plastic injection molding industry, MIM is a novel powder metallurgy near-net-shaping technique. It involves adding metal or ceramic powder to plastic to produce products with higher strength and wear resistance. Over time, this idea evolved to maximize solid particle content and completely remove binders during subsequent sintering, leading to denser parts.
Turning and Milling
Turning is a fundamental cutting manufacturing process where a rotating workpiece is machined using a stationary tool. It’s primarily used for creating rotational parts like shafts, discs, and sleeves. Milling, on the other hand, involves fixing the workpiece and using a rotating cutter to shape it. CNC milling machines can handle complex shapes and features.
Planing is a cutting machining method where a planer tool moves in a horizontal relative straight line back and forth across the workpiece, primarily used for shaping external parts. The precision of planing ranges from IT9 to IT7, with a surface roughness of Ra between 6.3 to 1.6μm.
Grinding involves using abrasive materials and tools to remove excess material from a workpiece. It stands as one of the most widely applied cutting methods in manufacturing.
Selective Laser Melting (SLM)
In a tray filled with metal powder, a high-powered carbon dioxide laser, controlled by a computer, selectively sweeps across the metal powder’s surface. Where the laser touches, the top layer of metal powder fully melts and fuses together, while untouched areas remain powdery. This entire fabrication process takes place in a sealed chamber filled with inert gas.
Selective Laser Sintering (SLS)
The SLS method uses an infrared laser as an energy source and primarily employs powdered materials. During this step, the powder is heated up, but not enough to melt it. A leveling roller then spreads the powder evenly. Under computer control, the laser selectively sinters the powder based on layer-by-layer cross-sectional information. After one layer is completed, the next layer is sintered. Once all layers are sintered, excess powder is removed, resulting in a fully sintered part. Currently, mature processes use wax and plastic powders, while techniques using metal or ceramic powders are still under research.
Similar to the “whipped cream” style of molten deposition, this method sprays out metal powder. As the nozzle releases the metal powder material, it simultaneously provides a high-powered laser and inert gas protection. This method isn’t limited by the size of the metal powder container, allowing for the direct creation of larger components. It’s also well-suited for repairing parts that have localized damage.
Roll forming uses a series of continuous machine frames to shape stainless steel into complex forms. The sequence of rollers is designed so that each frame continuously deforms the metal until the desired final shape is achieved. For intricate part shapes, up to thirty-six frames might be used, but for simpler shapes, three or four frames suffice.
Die forging involves using specialized forging equipment and molds to shape a blank into a forged part. Parts produced through this method have precise dimensions minimal machining allowances, and can have complex structures with a high production rate.
Also known as the blanking process, this technique positions a pre-formed film on a punching mold, which then removes excess material, retaining the product’s 3D shape that matches the mold cavity.
Die Cutting Process – Knife Mold
In this method, a film panel or circuit is positioned on a base plate, and a knife mold is fixed on a machine template. The machine’s downward force controls the knife edge to cut the material. Unlike the punching mold, this method results in smoother cuts. By adjusting the cutting pressure and depth, effects like embossing and partial cuts can be achieved. Additionally, the mold is cost-effective, and the operation is more convenient, safe, and fast.
Plastic Processing Techniques
Injection molding is a prominent method for producing industrial products. Typically, rubber and plastic are used in this fabrication process. Injection molding can be further divided into injection mold pressing and die-casting. Injection molding machines, often referred to as injectors or molding machines, are the primary equipment used to mold thermoplastic or thermosetting materials into various shapes using plastic molds. The molding process is achieved through the combination of the machine and the mold.
Extrusion is a manufacturing process where material undergoes plasticization by the combined action of an extruder barrel and screw. As it’s heated and pushed forward by the screw, it continuously forms products or semi-finished products of various cross-sections through the machine head.
Also known as hollow blow molding, this rapidly developing plastic processing method involves taking a tubular plastic blank obtained through extrusion or injection molding, heating it (or reheating it to a softened state), placing it in an open mold, and then inflating it with compressed air. This causes the plastic blank to expand and adhere to the mold walls. After cooling and mold release, various hollow products are obtained.
A plastic processing technique where flat plastic sheets are heated until soft and then shaped using vacuum suction onto a mold surface. Once cooled, the formed shape is retained, and this technique finds applications across various industries.
Also known as press molding or compression forming, this involves placing powder, granular, or fibrous plastic into a mold cavity under forming temperature. The mold is then closed and pressed, causing the material to shape and solidify. This method is suitable for thermosetting plastics, thermoplastics, and rubber materials.
This method involves passing molten thermoplastic through a gap between two or more parallel, counter-rotating rollers. The melt is squeezed, stretched, and formed into continuous sheet products, which are then naturally cooled. Calendering is commonly used for producing plastic films or sheets.
Foaming involves introducing appropriate foaming agents into foaming materials like PVC, PE, and PS, creating a microporous structure in the plastic. Almost all thermosetting and thermoplastic materials can be made into foam plastics, making foaming a significant area in plastic processing.
This manufacturing process involves winding resin-soaked continuous fibers (or tapes or pre-impregnated yarns) onto a core mold in a specific pattern. After curing and mold release, the product is obtained.
Laminating refers to the manufacturing process of bonding multiple layers of the same or different materials into a whole under heat and pressure. It’s commonly used in plastic processing and also in rubber processing.
Casting in plastic processing is a method where liquid monomers or prepolymers are poured into a mold under atmospheric pressure. They then undergo polymerization and solidify into products that match the mold’s internal shape. With the evolution of molding technology, the traditional casting concept has changed, and polymer solutions, dispersions (like PVC paste), and melts can also be used for casting.
This technique leverages the variable state of thermoplastic high polymer materials. In their viscous flow state, they can be shaped into a desired form and then solidified at room temperature.
Compression Resin Transfer Molding
Primarily used for thermosetting plastic products, this method involves melting the material, pressing it with a mold, and then curing it through heating. After mold release, the product is obtained.
Resin Transfer Molding (RTM)
RTM is a technique where resin is injected into a closed mold to impregnate reinforcing materials and then solidify. This technology eliminates the need for pre-impregnated materials and autoclaves, effectively reducing equipment and molding costs. In recent years, its rapid development has found applications in the aviation, automotive, and naval industries. Variants such as RFI, VARTM, SCRIMP, and SPRINT have emerged to cater to diverse application requirements.
Extrusion is a pressure processing method where a punch or male mold applies pressure to a billet placed in a female mold, causing it to flow plastically and take on the shape of the mold’s cavity or profile. During extrusion, the billet experiences triaxial compressive stress, allowing even materials with low plasticity to be formed.
Thermoforming is a unique method of transforming thermoplastic sheets into various products. The sheet is held in a frame and warmed up until it’s soft. Then, with some pressure, it’s shaped to match the mold. After cooling and setting, the product is trimmed and finished.
Also known as manual lamination or contact molding, this technique involves manually applying a release agent to a mold, layering reinforcing materials, and brushing resin until the desired thickness of the plastic product is achieved. The product is then cured and demolded.
Laser Rapid Prototyping (LRP)
LRP integrates advanced technologies like CAD, CAM, CNC, lasers, precision servo drives, and new materials. Compared to traditional manufacturing methods, LRP offers high prototype replicability and interchangeability, manufacturing processes independent of prototype geometry, shorter processing cycles, and reduced costs. It achieves a design-manufacturing integration.
Fused Deposition Modeling (FDM)
FDM extrudes filamentous materials like thermoplastics, waxes, or metals from a heated nozzle. Following the predetermined trajectory of each part layer, molten material is deposited at a fixed rate.
Computer Numerical Control (CNC) machines are automated machine tools equipped with a program control system. This system logically processes program instructions encoded with control codes or other symbols, decodes them, and then drives the machine to move and machine parts.
3D printing, which is a kind of rapid prototyping, builds objects one layer at a time from digital designs using materials like metal powders or plastics. It’s typically achieved using digital material printers and is widely used in mold manufacturing, industrial design, and more. There are various 3D printing technologies differing in the way materials are layered and the parts are constructed. Common materials include nylon glass fiber, polylactic acid, ABS resin, durable nylon, gypsum, aluminum, titanium alloy, stainless steel, silver plating, gold plating, and rubber-like materials.