Machining and Aerospace Machining
Machining is a name for processes of manufacturing categorized by removing material in order to make a component. Milling and turning are two different types of machining which can be manually controlled or CNC, computer numerical controlled. Machining can be used in order to manufacture a component completely from a raw material or a blank that has been casted. Machining can be used to rough cut components or with a casting blank can be used as a finishing process for components. These processes lend themselves to versatility and have the capabilities to achieve the higher accuracy and surface quality in a more economic way than other manufacturing processes.
Machining originated with machine tools, machines that can reproduce other machines; the first of which was the bow lathe and bow drill that were hand-made and human powered around 1200 BC. Eventually during the development of the steam engine, that first pure machine tool was made in order to manufacture the bored cylinders in 1774 by John Wilkinson. Several centuries later MIT designed the first Numerical Control for a machining system with the binary number system punched on tape. This design also utilized their computer that they were also developing at the time. These innovations lead to how we seen CNC machine today with advanced computers and even built in CAD/CAM systems in some machines. A major factor that has lead to this advancement in recent years is the decline in the number of highly skilled machinists. Machinists help make the designs that engineers create a reality and can make a huge difference in the breakthroughs in the aerospace industry.
Traditional machining requires a tool that is harder than the workpiece being machined. This tool penetrates into the workpiece for a certain depth of cut. A relative motion between the tool and workpiece is responsible for form and generation of the cut to produce the required shapes, dimensions, and surface quality. The principle of machining is one of generating the surface required by providing suitable relative motion between the cutting tool and the workpiece. The cutting edge or edges on the cutting tool remove a layer of work material; the removed material is called a shaving or a chip. The simplest surfaces to generate are flat surfaces and internal or external cylindrical surfaces. The two main types of motion in machining are the primary motion and the feed motion. The primary motion is the main motion provided by a machine tool or manually to cause relative motion between the tool and workpiece so that the face of the tool approaches the workpiece material. The feed motion is a motion that may be provided to the tool or workpiece by a machine tool which, when added to the primary motion, leads to a repeated or continuous chip removal and the creation of a machined surface with the desired geometric characteristics.
Machining can generally be separated into three different categories: cutting, abrasion and erosion. In machining by cutting, a tool cuts the workpiece. A machine tool that controls the workpiece and tool motions required for the machining process.Turning and Milling are two common types of cutting machining. In abrasion machining, a small machining allowance is removed by a multitude of hard, small, angular abrasive grains of indefinite number and shape. Some typical abrasive processes are honing and lapping. Erosion machining removes the machining allowance by the removal of successive surface layers of the material as a result of dissolution or melting and vaporization of the material being machined. Laser Beam Machining and Electrochemical Grinding are nontraditional machining methods that are categorized as erosion type machining processes. The most common forms of machining are cutting and abrasion machining where as erosion machining are used for specialty applications.
Common types of machining that being used in the aerospace manufacturing industry are lathe machining and mill machining as these are some of the most versatile types of machining. Lathe type machining at its simplest can be broken down into four two-dimensional cuts: straight turning for machining the outside diameter of components, boring and internal grooving for finishing bores in components, drilling for the creations of bores and through holes in components, and threading for creating threads on the outside of components. Milling is one of the most versatile machining processes and is capable of producing a variety of shapes involving flat surfaces, slot, and contours. Milling machines use cutters with multiple teeth in contrast with the single-point tools of the lathe and planer. Milling can also be used to cut some gears and splines into workpieces.
Aerospace Machining unlike typical CNC machining processes are characterized by tighter tolerances and more difficult to machine materials. Along with large five-axis machines, turn-mill machines and precision grinders are among the high-value machine tools routinely used in this sector. Materials typical of aerospace machining include lightweight aluminum for structural members; hard and temperature-resistant metals including titanium and inconel alloys for engine parts; and carbon-fiber composites that are both hard and lightweight for outer skins. Aerospace machining can be very difficult for machinists as the dimensions being machined must be checked frequently and even the difference in temperature between morning and afternoon in the shop can affect some of the materials being machined.
Aerospace machining methods can also be applied to industries other than space travel and commercial aircraft construction. The medical instrumentation and optical industries also have a high demand for precision machining using difficult materials. At Marples Gears, we have even seen a demand for our level of precision in industries like commercial electrical fishing reels. The difficult to machine materials that can be found throughout aerospace manufacturing can also be used in the application of various industries because of their desirable engineering characteristics.
