M ATERIAL R EMOVAL P ROCESSES

For industry to operate effectively, the material that produces the final product must be machined and formed quickly and accurately. The key factors that affect the efficiency of a metal-removal process are the machine tool, the controller, spindle, toolholder, cutting tool, and CNC programming. High Speed Machining (HSM) uses high spindle speeds, high feed rates, and light depths of cut to increase productivity, reduce lead time, reduce warping, increase part accuracy, and improve surface quality.

In virtually all metal-removal operations, manufacturers are trying to reduce the amount of time a part is moved from machine to machine and perform more operations in a single workpiece setup. This has led to the development of new machine tools such as the turning center with live tooling and special workholding fixtures where both turning and milling operations can be performed in one part setup.

Grinding is a metal-removal process that uses an abrasive cutting tool to finish a part to an accurate size and produce a high surface finish. The most common abrasive tool used is a grinding wheel that consists of many thousands of abrasive grain bonded together. In a grinding process, a revolving grinding wheel is brought into contact with the surface of the part to be ground. As each abrasive grain on the periphery of the wheel contacts the part surface, it acts as a cutting tool and removes a minute (very small) chip of metal, Fig. 2-3-1.

Fig. 2-3-1 The cutting action of abrasive grains in a grinding wheel. (Carborundum Abrasives, Div. Saint-Gobain Abrasives.)

Cylindrical grinding may be defined as grinding the periphery of a rigidly supported, revolving part. Cylindrical grinders fall into three general classes: plain cylindrical, universal cylindrical, and special cylindrical grinders. The centerless grinder, one of the special grinders, makes it possible to grind cylindrical parts without supporting the part between centers or holding it in some from of fixture, Fig. 2-3-2. Centerless grinders are precision machine tools capable of mass-producing countless numbers of parts held to close tolerances of size, shape, and surface finish. The modern grinding machine is capable of finishing soft or hardened parts to tolerances of .0002 in. (0.005 mm) or less on high-production machines, while producing

very fine surface finishes.

Fig. 2-3-2 Parts pass between the grinding and regulating wheels during Thrufeed grinding. (Cincinnati Machine, A UNOVA Co.)

The goal of every manufacturing operation is to produce quality products as quickly and accurately as possible. To accomplish this goal, it is important that every component in the manufacturing process be in top condition so that inaccurate parts are not produced. Inaccuracies in manufacturing result in parts that may have to be repaired, replaced, or scrapped, which affects the productivity and profitability of any operation.

Virtual Reality and certain software programs can be used to simulate a manufacturing operation on a computer before starting to actually manufacture a product. This allows any potential manufacturing errors or operational sequences to be corrected before spending time, material, and labor on a process that may not produce satisfactory results.