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Abstract Briefly reviewed in this paper is the development of
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an expert system for the fixture set-up and for gearbox casings to
be machined on machining centres. The set-up and fixture plan-
ning involves the definitions of operation sequence, workpiece
orientation, locating type, locating surfaces, clamping type, and
clamping surfaces. In this paper, the development of the system
and a more detailed description of the locating solution is pre-
sented.9578
Keywords Expert systems · Fixture planning · Locating ·
Process planning1 Introduction
The conceptual design of fixtures is one of the most complex in-
tellectual tasks in the process of industrial design [1]. This early
stage of design can be automated with the application of expert
systems.
An expert system for set-up and clamping fixture planning is
developed for machining of gearbox casings, which belong to the
class of prismatic workpieces.
For machining prismatic workpieces, the most suitable ma-
chine tool is the horizontal machining centre [6]. Depending on
the workpiece complexity, the complete machining is feasible in
one or two clamping operations. In the process of fixture design,
the technological process is reduced to operations, and general
solutions for clamping fixtures are generated for every clamping.
The basic operation functions of clamping fixture are the locat-
ing and clamping of the workpiece [8]. Locating can be pided
into plane locating and side locating, and side locating is further
reduced to endwise locating and guiding (Fig. 1).The general solution for the fixture requires the following
points to be defined: clamping sequence, plane locating type,
plane locating face, plane locating surface, type of side locating,
locating surfaces, clamping type, and clamping surfaces.
2 Inputs to system for set-up and fixture planning
2.1 Geometric model
A geometric model is formed by the principle of workpiece re-
duction [11]. The workpiece is first reduced to six faces (top,
bottom, left, right, front, back), which are further reduced to typi-
cal forms (features). Features are defined by a series of attributes,
which include dimensions, initial state, roughness, and dimen-
sional accuracy.
2.2 Functional characteristics of workpiece
The functional surfaces of a workpiece, besides the tolerance
of features themselves, are “interconnected” with tolerances be-
tween features. These relationships can be further pided intodistance tolerances and locating tolerances. The type of distance
and locating tolerances, which are used in gearbox casings are
presented in Fig. 2 and Fig. 3. The features whose location is de-
termined by distance or locating tolerances are called “connected
features”.
2.2.1 Classification of functional characteristics with regard to
fixture solution
The location of functional surfaces in the workpiece structure
and the type of interconnections have a great influence on the
selection of the workpiece location in the machine workspace
and on the reduction of the technological process involved into
clamping operations. From a technological viewpoint, the ma-chining of all the connected faces in one clamping operation is
the ideal case. However, there are cases when this is impossible
and in such cases one is forced to machine the functionally con-
nected faces of the workpiece in separate clampings. In such
cases, a high accuracy of fixture and a high accuracy of the lo-
cating surfaces are needed to realize the prescribed workpiece
accuracy. Some of connecting types are relatively easy to access
when the connected faces are machined in separate clampings,
but there are also types for which machining in separate clamp-