Machine tools work with much greater power than a craftsman can exert with his hands. They therefore fashion metal parts faster and at a lower cost. But far more important is the fact that they exert rigid control over the workpiece and are cutting or shaping it all the time. They can go on making the desired number of pieces, each identical to the last, so that the machine-made parts are interchangeable. Each conforms exactly to an original drawing showing precise shapes, dimensions, and tolerances.
The tolerances indicate by how much a dimension can be slightly larger or smaller than the desired value, and are measured in micrometers or thousandths of an inch. A craftsman would be hard-pressed to maintain such accuracy and output would be very low.
Machining metal involves cutting it with a machine tool such as a milling machine (miller), planer, router, or lathe.
Millers hold the work still while rotating cutters pass over it. Planers draw large items past a fixed cutter, whereas a router resembles a drill that mills the surface instead of boring holes.
Grinders use another method of machining, but instead of having cutting tools of very hard metal (or sometimes even diamond) they use wheels with surfaces made up of millions of hard fragments, each of which takes a small cut.
Turret lathes rotate the workpiece while tools are arranged in various positions to cut it.
Since 1950 many completely new ways of working with metal have been brought from the research laboratory to the production plant. The aircraft industry pioneered chemical milling, in which sheets of any size are etched away in baths of acid or other corrosive chemicals. Portions of sheet can be protected by a surface mask that prevents them from being attacked. The rest can be eaten away in a controlled way, with no scratches or machining marks on the surface.
This is important because even the smallest scratch or imperfection can induce metal fatigue.
Electrochemical machining (ECM) is a variation in which the liquid bath is not corrosive but an electrolyte (carrier of electric current). The workpiece is connected in an electric circuit and then eaten away by a shaped electrode, rather like electroplating in reverse.
Another electrical method is spark erosion, in which even the hardest parts are gradually shaped by millions of sparks. Yet another, and totally different, electrical method is electromagnetic forming, when massive currents are suddenly switched through magnetic coils that slam the workpiece against shaped dies.
In contrast there are other new methods of extreme delicacy used for shaping on a microscopic scale.
Ultrasonic machining is a form of grinding, useful for extremely hard material or non-metals that must be finely shaped. Electron-beam machining uses a concentrated beam of electrons to melt away parts not wanted.
Laser machining does the same with an intense beam of light. Such methods can be used to shape electronic circuits that would easily fit on a pin’s head.
Incoming search terms:
No related posts.
About Firebrand
