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Manufacturing Processes

Manufacturing Processes



Casting: Metal casting is definitely one of the oldest manufacturing processes. Castings have been found dating back 6000 years. Fundamentally, casting involves filling a mold with molten material. This material, upon solidification, takes the shape of the mold. There are two basic types of metal casting processes, expendable mold and permanent mold. Castings can be made into the same shape as the final product, being the only process required. Or sometimes, casting is the first manufacturing process in the production of a multi-process manufactured part. Metal casting can be used to make parts with complicated geometry, both internal and external. With casting, intricate parts can be made in a single piece. Metal casting can produce very small parts like jewelry, or enormous parts weighing several hundred tons, like components for very large machinery. Although careful influence of casting parameters and technique can help control material properties; a general disadvantage to metal casting is that the final product tends to contain more flaws and has a lower strength and ductility compared to that of other manufacturing processes, such as metal forming. 




Forming: The category of manufacturing by metal forming includes a large group of processes that use force to induce a shape change in a metal, by mechanical working and plastic deformation. The most desirable quality of a manufacturing material as a candidate for a metal forming process is high ductility and malleability and a lower yield strength of the material. When working with metals, an increase in temperature will result in a higher ductility and a lower yield strength. In manufacturing industry, metals are often formed at elevated temperatures. In addition to shape change, the metal forming process will usually change the mechanical properties of the part's material. Metal forming can close up vacancies within the metal, break up and distribute impurities and establish new, stronger grain boundaries. For these reasons, the metal forming process is known to produce parts with superior mechanical properties. With relation to temperature there are 3 types of forming. Cold working, (room temperature), warm working and hot working. Also, with relation to the surface area-to-volume of a material there are 2 main categories, bulk deformation and sheet forming




Powder Processing: Powder processing is a manufacturing technique that produces parts from the powder of certain materials. The powders are pressed into the desired shape, (called pressing), and heated sufficiently to cause the particles to bond together into a solid component, (called sintering). Powder processing is common for metal materials, however ceramics may also be subject to powder processing techniques. There are many advantages to powder processing. With powder processing you can obtain consistent dimensional control of the product, keeping relatively tight tolerances, (+/- .005"). It also can produce parts with good surface finish. Parts can therefore be made into their final shape, requiring no further manufacturing processes. With powder processing there is very little waste of material. Since powder processing can be automated, it minimizes the need for labor, requiring small amounts of skilled labor. Metals that are difficult to work with other processes can be shaped easily, (ie. tungsten). Also, certain alloy combinations and cermets that can not be formed any other way, can be produced with this technique. Lastly, parts can be produced with a controlled level of porosity, due to the nature of the process. Powder processes also have a number of disadvantages. The first is high cost. Powders are expensive compared to solid material, they are also difficult to store. Sintering furnaces and special presses are more complicated to construct than conventional machinery. Tooling is also very expensive. Since powders do not easily flow laterally in a die when pressed, there are geometric limitations to the parts that can be manufactured. Powder parts may have inferior mechanical properties, (unless they undergo a forging process). Finally, variations in material density throughout the part may be a problem, especially with more intricate geometries. Powder processing manufacturing is ideal for producing large quantities of moderately complex, small to medium size parts that do not require strong mechanical properties in the part's material. This is not true of some alternative powder processes, such as hot isostatic pressing, that can manufacture parts with superior mechanical properties. A process such as hot isostatic pressing, however, would not be efficient in the manufacture of large quantities of parts. 




Machining: In machining, a manufactured part is created to its desired geometric dimensions by the removal of excess material from a work piece, via a force exerted through a certain material removal tool. Qualities of a desirable manufacturing material for this purpose would be:

1) Lower Shear Strength (to make cutting easier) 
2) Shock Resistant (to withstand impact loading) 
3) Material must not have a tendency to stick to the cutting tool 
4) Material removed should separate from the work easily and completely 

A material's relative ability to be machined is called machinability. Ceramics have high shear strengths, making them difficult to cut. Also, they are not shock resistant, which causes them to fracture from the impact loading between the tool and work piece. Polymers, although having low yield strengths, melt from the heat generated in the process, causing them to stick to the tool. In addition, high ductility in polymers can make material removal difficult and machining is based on material removal. For these reasons, ceramics and polymers have poor machinability. Machining is generally applicable to metals. Machinability varies among metals, hardened metals present a particular problem, due to a very high shear strength. Often, metals are machined as close to their final shape as possible before being hardened. That way, the hardened material only has to undergo minimal finishing operations. This type of manufacturing process has many advantages. Machining can produce extreme dimensional accuracy, often more so than any other process alone, (tolerances of less than .001"). Also, it can produce sharp corners and flatness on a part that may not be able to be created through other processes. Machining accuracy allows it to produce surface finish and smoothness that can not be achieved any other way. By combining different machining operations, very complex parts can be manufactured. This type of manufacturing process does have disadvantages. This is a material removal process, thus wastes material. Although economical if the number of parts to be produced is small; labor, energy, equipment and scrap cost are relatively high for la
rge runs. Machining is very applicable for finishing operations on manufactured goods. 


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