ComputerAided_Design_Engineering_amp_Manufactur.pdf

FIGURE 4.1(a)
A typical configuration for computer-aided inspection system of mold manufacturing.
integration for parts having sculptured surfaces with some basic features, such as holes, slots, and bosses.
Features to be inspected are chosen in the CAD environment, and inspection planning is performed for
each feature. Sampling-point strategies are (1) uniform distribution; (2) curvature dependent distribution;
or (3) hybrid distribution of the two, depending on the complexity of the sculptured surface. Line
and plane features are divided into subintervals, and measurement points are distributed at random
positions in the subinterval. Prime numbers of subintervals are considered for a circle feature, in order
to avoid possible periodic distortion of the measurement features.
Prior to measurement path planning, alignment procedures which will relate the workpiece coordinate
system (CAD coordinate system) to the CMM coordinate system are generally required. In this chapter, the
techniques of two-stage alignment procedures are introduced, enabling alignment even for the products of
very thin and sharp geometry, such as turbine blades. The two-stage alignment procedures comprise the
rough phase alignment, based on six points probing on clear cut surfaces, and the fine phase alignment,
which uses the least squares method based on measurement feedback. For accurate tolerance evaluation, an
improved evaluation method is introduced: the actual measurement points are obtained as the closest points
on the CAD geometry by the subdivision technique, and the Chebyshev norm is applied iteratively to get
optimum alignment of the measurement datum, giving an accurate profile tolerance. Figure 4.1a shows a
typical CAD/CAI integration system around networks of computers and machine tools. Figure 4.1b shows
the conceptual framework of the inspection system demonstrated in this chapter. 1,5,10
4.2 Geometric Features and Tolerances for Inspection
Features and Tolerances Defined by ISO
In order to achieve a computer integrated inspection system, a feature-based inspection technique is
applied, in which the features to be inspected are chosen in the CAD environment, and several key