Page 236 - Modular design for machine tools

196 Engineering Design for Machine Tool Joints

ability of exciting force should be employed together with the dynamic
stiffness, if necessary, to correctly represent the dynamic behavior of the
joint. In addition, it is worth suggesting that the concept of complex
damping might be applicable to an expression of joint behavior [18].
Reportedly, the complex damping is caused by the hysteresis property of
the spring, which appears as viscous damping.

5.3 External Applied Loads to Be Considered
and Fundamental Factors Governing Joint
Characteristics
In the design and manufacture of the structural body component of the
machine tool, the bending and torsional loads are of great importance
and should be taken into consideration, whereas the axial load has, in
general, no significant effects on the static and dynamic behavior of the
machine tool. Because the joint is regarded as a structural body com-
ponent, in nearly all the machine tool joints, the bending and torsional
loads are important. In contrast, the axial load becomes dominant as a
leading factor for joints comparatively rarely. Actually, when the rela-
tive microslip occurs between the two mating joint surfaces, the normal
load governs the energy dissipation at the joint, e.g., the damping capac-
ity of the bolted joint. Although some loading conditions for the bolted
joint have already been displayed in Fig. 5-16, these examples are not
sufficient to understand the various loading conditions of the joint. The
further knowledge for this issue will be grasped by referring to the suc-
ceeding chapters, in which the actual loading conditions are demon-
strated precisely. In this context, note that an optimum design of joint
under several different kinds of the load is very difficult at present.
In addition to the loading condition, many factors need to be consid-
ered in the designing and production procedures of the joint. Although
the importance of each influencing factor varies according to the kind
of joint, in general, these factors can be classified into the following
three categories.
1. Factors concerned with the applied load, i.e., magnitude, kind, and
type of applied load. For the dynamic load, its frequency and static
preload should be considered.
2. Factors concerned with the joint surface, i.e., physical properties of
joint material, macroscopic and microscopic topographies, machining
method, surface roughness, waviness and flatness deviation, inter-
facial layers (oil, plastic, and metallic shims).
3. Factors concerned with the jointing method, i.e., size and shape of
joint surface, number of contact entities across a whole joint surface,
machined-lay orientation, size and shape of joint surroundings and