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several difficult research issues such as costs, joints, accuracy and dynamic structural response。  Nevertheless, the concept of an RMT brings many of the potential advantages of an RMS to the component level。 Thus, it is useful to conduct research on RMTs, to assess weather some of the basic research challenges can be addressed, and if attractive application niches for RMTs can be developed。 Consequently, our research group has designed and built several RMTs, including a table-top  Cartesian 3-axis RMT, a reconfigurable inspection machine, and an arch- type RMT [3,15–20]。

The purpose of this paper is to describe the so-called arch-type RMT, first demonstrated at the 2002 Interna- tional Manufacturing Technology Show in Chicago, and to provide a brief description of the design concept, the design and construction, and dynamic characteristics of the machine。 This paper describes the frequency response functions (FRFs) and experimentally verified analytical stability lobes for the machine at different reconfiguration positions。 Cutting model estimation has also been carried out to evaluate the stability lobes of the machine。 Contrary to predictions during the design stage of arch-type RMT [15,18], the dynamic performance of the machine does not vary significantly with reconfiguration position。 The reason for this is discussed in the  paper。

2。 Background  and methodology

2。1。 Arch-type RMT: design and construction

The characteristics of customized flexibility on which the arch-type RMT design is based, makes the design procedure more involved than the design of a dedicated machine tool or a flexible CNC machine tool [17,20]。 The functional design of the arch-type RMT is focused on the finish milling of cylinder head inclined surfaces。 The tooling tolerances and process parameters were the same for all inclined surfaces。 However, the surfaces to be milled

are at different angles with respect to the horizontal: 301 (for V6 cylinder heads) and 451 (for V8 cylinder heads)。  A

dedicated machine tool solution would need a customized station for each member of the part family。 If a commercial CNC machine solution is sought, one would  have  to choose from available 5-axis CNC machines with ortho- gonal kinematics。 In the arch-type RMT an alternative reconfigurable solution is presented where the machine is capable of 3-axis kinematics with one passive degree-of- freedom  available for reconfiguration。

A detailed evaluation of various possible conceptual machine tool configurations was undertaken by Katz and Chung [15]。 Based on workspace evaluation, finite element analysis (FEA) and research considerations the decision to go ahead with a side-mounted arch-type  RMT  (Fig。 1a) was taken。 A detailed FEA analysis (Fig。 1b) was carried out   on   the   final   design   and   the   calculated    natural

frequencies for lower structural modes of 451  reconfigura-

tion position are shown in Table 1 [18]。 Some of the alternative solutions to arch-type RMT considered were to achieve the passive degree for reconfiguration by pivoting the spindle housing or pivoting the worktable。 The pivoted spindle housing designs (shown in Fig。 2) were not selected because of the limited workspace achieved by such machines at higher reconfiguration angles。 The pivoted worktable was not chosen because of the concerns of compatibility of such a machine with most  conveyor system environments in industry。 The  arch-type  RMT (Fig。 3) was built by a commercial machine tool manufacturer, and was showcased in the International Manufacturing Technology Show, September 2002, Chicago [13]。