Page 248 - Modular design for machine tools

208 Engineering Design for Machine Tool Joints

before with the enhancement of the machine tool technology and the
advent of new technologies available for the related engineering activities.
For further understanding, now let us look at an example of the prob-
lem of the taper connection. As already shown in the research history in
Fig. 5-26, the first facing problem was fretting corrosion, and the engineer
endeavored to clarify its cause. In this regard, it is very interesting that
the machine tool even in the 1990s suffered from fretting corrosion at the
tapered hole of the main spindle. Actually, some of the representative MCs
have employed the ceramic tapered hole as one of the remedies. Next, the
stiffness of the taper connection was investigated including the rein-
forcement effect of the tapered bush press-fitted on the main spindle [26].
On that occasion, the fitting tolerance of the taper connection became
crucial. To improve the machining accuracy, it is necessary to use tight
fitting by having the bearing area extended across the whole joint surface;
however, this leads to greater difficulty in the release of taper shank. For
instance, the two-stepped taper was widely employed for jig borers. The
MC was furthermore requested to enhance its cutting performance in
considering that the tapered connection between the main spindle and the
end mill is the weakest within the machine-tool-work system, during
machining the plastic injection mold. Within an engineering design con-
text of the tapered connection, one remedy is to produce smooth and full
contact around the larger end diameter of the tapered hole.

Research activities in the 1990s. In the late 1990s, research into the
machine tool joint became less active compared to the first and second
phases. This observation is acceptable in part; however, we have to pay
the special attention to the changing trend of the structural design.
Importantly, an emerging trend is the wider application of higher- speed
cutting, for instance, face milling of mission casing made of Mg alloy and
end milling of plastic injection molding die in the industrial sector. The
joint design is thus forced to change, and new research subjects are
suggested according to new requirements based, e.g., on the fast-growing
employment of the linear motor to the table traveling system, linear
roller guideway, and HSK.
The higher- speed table system consists of a combination of (1) ball
screw-nut and linear roller guideway, (2) linear motor and roller guide-
way, or (3) linear motor and hydrostatic guideway. As is widely said, the
linear motor and rolling guideway have less damping capacity than the
ball screw-nut driving system and slideway, and thus at issue is how to
increase the damping capacity of table traveling system. In retrospect,
the damping problem of the joint was vigorously investigated in the
first phase, and the connecting mechanism of the table and its driving
system was investigated in the second phase. In this context, some grass
root-like subjects are being investigated such as the following.