Page 134 - Modular design for machine tools

94 Modular Design Guide and Machine Tools Description

Head changer. The head changer was contrived in the late 1970s and
in fact was already patented in 1978 by Kearney and Trecker Co., as
shown in Fig. 2-18(a), under the commercial name of Multiple Spindle
Machine Tool (U.S. Patent No. 4,125,932, Nov. 21, 1978). As already
shown in Fig. 1-6, the head changer can machine the work by changing
the gang head and single spindle head in accordance with the machin-
ing sequence, where the head is stored in the head magazine located in
both flanks, rear side or rear top of the machining space. A crucial prob-
lem is that the machining flexibility is dependent upon the preparation
plan and changing program of the head. In addition, the head itself is
very expensive, e.g., at a cost of several million Japanese yen per head.
In contrast, the head changer shows very high machining efficiency,
and thus it can be employed as an entity of the FMS for large volume
and large batch size production as well as medium volume and medium
batch size production. Figure 2-18(b) reproduces the head changer of
Heller make in the mid-1970s. This head changer displays the typical
structural configuration of that time, and it was widely applied to the
production of automobile parts.
Figure 2-19 is an interesting head changer (commercial name: CNC
Station) developed by Ford Co. The machine is applicable to even
small batch size production and can be characterized by the function
for the single tool changing system. The square turret facilitates the
layout of the head with the assistance of a robotlike changer, and
some tools within a head can be changed by another ATC between the
square turret and the tool magazine. In short, the ATC enables the
single tool within a gang tool cassette to be changed independently to
reinforce the tooling flexibility. In addition, the machine is equipped
with both the tool life control function achieved by detecting the feed
component of cutting force and the tool damage detection with TV
camera or ultrared beam [28].
On that occasion, KTM (Kearney Trecker and Marwin) employed a
strategy by which the machining function in the factory was able to
expand from the stand-alone operation to FMC of pallet pool type, and
even to the FMS. Based on such an idea similar to the modular prin-
ciple, KTM produced a head changer called the KTM Multiple-Head
changer, which was capable of stand-alone machining and of playing
the role of increasing the productivity in the FMS, as shown in Fig. 2-20.
In addition, this head changer can be characterized by an additional
40-tool magazine, which is on the top of the column, although not
shown in Fig. 2-20. As a variant of these head changers, an interest-
ing concept is that of tool cassette changing type, which is, in princi-
ple, the smaller size of head changer, i.e., the changing head being
compact [29].