Page 13 - Electric Drives and Electromechanical Systems

Chapter 1 Electromechanical systems 5

The demands of the market place for cost reductions and the requirement for
increased product quality has led to dramatic changes in all aspects of manufacturing
industry, on an international scale, since 1970. These changes, together with the intro-
duction of new management techniques in manufacturing, have necessitated a
considerable improvement in performance and costs at all stages of the manufacturing
process. The response has been a considerable investment in automated systems by
manufacturing and process industries. To fully appreciate the complexities found in
modern machine tools, we will consider a number of the processes in detail, firstly
subtractive machining processes and then additive manufacturing.
1.2.1 Conventional subtractive machining processes

Subtractive machining is the global term for a range of processes in which the geometry
of a workpiece is modified by the controlled removal of material. This approach to
machining is highly versatile since it can produce a wide variety of shapes and surface
finishes. To fully understand the requirements for controlling a machine tool, the in-
dividual machining process must be considered in some detail. Machining can be
classified as either conventional subtractive machining, where material is removed by
direct physical contact between the tool and the workpiece, or non-conventional sub-
tractive machining, where there is no physical contact between the tool and the
workpiece.
In a conventional subtractive machining operation, material is removed by the
relative motion between the tool and the workpiece in one of five basic processes:
turning, milling, drilling, shaping, or grinding. In all machining operations, several
process parameters must be controlled, particularly those determining the rate of ma-
terial removal; and the more accurately these parameters are controlled the higher is the
quality of the finished product (Waters, 1996). In sizing the drives of the axes in any
machine tool, the torques and speed drives that are required in the machining process
must be considered in detail.
Fig. 1.2 illustrates the turning operation, found in a lathe, where the tool is moved
relative to the workplace. The power required by the turning operation is of most

FIG. 1.2 The turning process, where a workpiece of an initial diameter D is being reduced to d; F c is the
tangential cutting force, F f the feed force, N is the spindle speed, and f the feed rate. In the diagram the depth
of the cut is exaggerated.