The Process of Metal Working
Metalworking is the process of working with metals to create a diverse range of products, from the hulls of ships to engagement rings.
There are many reasons to practice metalworking. Metalworking can be used for experimentation, to create works of art, for enjoyment, as its own profession, or as part of a profession. The many specialized fields of modern metalworking can be grouped under the categories of joining, forming, or cutting.
Welding joins two pieces of metal through the use of heat, pressure, or some combination of the two. Though a third agent is often introduced to the process and melted between the two workpieces to aid in the weld, in order to be a true weld, the two pieces must blend and coalesce.
Brazing and Soldering are also standard metalworking joining processes. These differ from welding in that only a filler metal is melted between the two workpieces, while the workpieces themselves do not coalesce, and remain unchanged. Because it occurs at a much higher temperature and with different filler metals, brazed joints are much stronger than soldered.
Forming modifies metal without removing or adding anything to the original workpiece. This can be done with pressure and/or heat. Forming processes include casting, the melting and pouring of metal into a mold, as well as many processes performed with the metal at room temperature, such as bending, drawing, rolling, and stamping.
Cutting processes are any of those used in metalworking that results in a separation of the workpiece into two pieces. Machining uses cutting instruments such as a drill or saw, and produces swarf (chips of metal). Burning uses a torch, and does not produce swarf.
- Grinding is a metalworking process in which an abrasive, fast spinning disk is used to remove small amounts of the workpiece to smooth edges and create a smooth finish. Grinding can also be used as a cutting technique.
- Milling shapes metal by cutting away unneeded parts to reveal the final shape. Milling is able to produce complex three dimensional objects with a high degree of precision. Milling machines can be completely or partially automated by computer controls. Almost any metal can be milled, though different metals require different bits and bit speeds, depending on the hardness of the material. A liquid coolant is required to keep the material and bit from being deformed. This combines to make milling a costly process that must be factored into the final cost of the product being milled.
- Drilling and tapping produce holes in metal through the use of a drill and drill bit. This is the fastest way to machine material from a workpiece. Tapping uses a bit that cuts a female thread into the workpiece, creating a screw thread where a screw can be fastened.
- Filing is the use of a file to grind small bits of material away from the workpiece by hand. It is commonly used for deburring.
- Turning is the term used to refer to metalworking processes performed on a lathe. Other processes can be performed on a lathe, such as basic milling, but turning is always performed on a lathe. Lathes turn blocks or cylinders of metal at high speeds while different tools are applied to the workpiece, shaving away layers to produce the desired shape. Turning produces symmetrical objects such as table legs.
Different primary cutting processes exist which may or may not be used in conjunction with the above techniques. These include laser cutting, abrasive water jet cutting, plasma arc cutting, and oxyfuel cutting.
- Laser cutting uses either a gas or solid state laser to produce an extremely precise cutting area with very little heat affected zone. This method is expensive, and does not always work on material that is thick or highly reflective.
- Abrasive water jet cutting uses a pressurized stream of water with an added abrasive to cut metals with high precision and a low heat affected zone. While this method is less expensive than laser cutting, it has the disadvantage of being slow, thus reducing output.
- Plasma arc cutting uses a high speed gas simultaneously with an electrical arc between the nozzle and workpiece that combines to form plasma hot enough to cut the metal. The plasma is instantly blown away by the gas, reducing the size of the heat affected zone. Plasma cutting is quick, inexpensive, able to cut almost any metal, and capable of cutting very thick pieces and sheets. It leaves a large heat affected zone and forms dross at the bottom of the cut, making it less precise than laser or abrasive water jet cutting.
- Oxyfuel cutting uses a mixture of oxygen and gas which combined and burned in torch, just as in oxyfuel welding. Oxyfuel cutting is very low cost, but it is slow, produces a large heat affected zone requiring additional machining, and is less precise than some other methods.
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