How does near net shape manufacturing save time and money?
Manufactured metal objects are created through casting, forging, or machining, sometimes creating waste. Near net shape manufacturing aims to produce an item or part as close to its final shape as possible, reducing waste, saving time and money, and creating less environmental impact through decreased energy and resource demands.
What is near net shape manufacturing?
Near net shape manufacturing is the practice of planning your production process to make an object as close to its final shape as possible, reducing the time needed to produce a finished item.
What is casting?
Casting is usually the first step in near net shape manufacturing. Casting involves pouring hot metal into pre-shaped molds to form a close-to final shape product. Most foundries use sand casting to create metal castings. Sand casting uses sand molds to shape hot metal into objects. Sand casting was first used around 1300 C.E. during the Shang Dynasty, China’s earliest ruling dynasty.
Investment casting (sometimes called precision or lost wax casting) generates less waste than sand casting, producing objects closer to near net shape. Investment casting originated 6000 years ago and was historically used to create intricate sculptures and jewelry. Although it makes closer to near net shape products than sand casting, investment casting is a more complex, labor-intensive process, which can result in a higher overall production cost, depending on the project.
What is casting shrinkage?
The same principle you learned in high school physics – heat expands, cold contracts – also applies to metal manufacturing. Metal expands when heated and shrinks when cooled, a process known as thermal expansion.
The effects of thermal expansion during the casting process can result in product defects, such as shrinkage cavities, due to casting shrinkage. Foundries use risers, reservoirs of extra molten metal built into the casting mold, to reduce shrinkage and prevent cavities from forming inside a cooling casting. Insulated material, known as “hot toppings” help keep the riser hot while the metal in the cast solidifies. Risers must be removed from the final product, creating metal waste.
Metals react differently to thermal expansion depending on their elements and composition, but shrinkage can also be affected by cast design. These are typical shrinkage allowances during the casting process:
Grey cast iron
0.7 to 1.05
White cast iron
1.3 to 1.6
1.05 to 2.1
Choice of metal can therefore influence the near net shape of a cast metal object.
What is machining?
Machining is the process of carving, cutting, grinding, drilling, or boring a metal product into its final shape. Like sculpting stone or carving wood, machining shapes metal by removing excess material. Near net shape production usually begins with casting, as machining a metal shape from scratch would create too much waste to be practical. Machining is an important finishing step in producing metal products, ensuring the final product is smooth, finely shaped, and ready for its intended purpose. Near net production aims for as little machining as possible.
What is forging?
Forging shapes metal through compressive pressure, such as hammering, squeezing, or rolling. Forging methods can include both hot and cold forging. Perhaps the best example of forging is the classic image of an old-fashioned blacksmith using a hammer and tongs to pound a hot horseshoe out on an anvil. Today, most forging is done on an industrial scale using enormous pressing machines. Industrial forging requires machining to finish, but work is being done to develop forging machines that can shape and deliver a close-to-finished product, reducing or even eliminating the need for machining. Forging methods include drop, roll, press, open and closed die forging, and precision forging. Friction welding is another forging technique that uses motion and force-generated heat to produce forged metal joints.
What is 3D printing?
3D printing is a promising new near net technology. Industrial 3D printing is called additive manufacturing (or additive layer manufacturing). Additive manufacturing uses a computer to direct the layering of material to precisely produce a pre-designed object with very little waste. Materials are applied layer by layer to produce detailed component parts and products. Additive manufacturing is flexible enough to allow for customizable components and products, including customized parts for individual hearing aids and individualized shoes. Additive manufacturing is playing an increasing role in creating custom and component parts for the the transportation, aerospace and energy sectors.
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