Patent Number: 051851245
Section: summary

The present invention relates to gauging the dimensional characteristics of manufactured parts and particularly to quality assurance gauges for determining if piece parts have been manufactured in compliance with specified dimensional tolerances. BACKGROUND OF THE INVENTION There are numerous piece part manufacturing situations where the dimensional characteristics of the finished part are critical. That is, after a part has exited a manufacturing process, such as machining or forming, dimensional characteristics imparted thereto by the process must fall within predetermined design limits, which may have a tolerance on the order of several mils or less. When such parts are manufactured in large quantities on an automated production line basis at high piece count rates, quality assurance inspection of the parts for dimension accuracy must be performed on a frequent basis to detect process excursions, caused by, for example, worn tooling, before large quantities of unacceptable parts are manufactured. One example of a part whose dimensional characteristics are of critical importance is the spacer cell in a nuclear fuel rod assembly or bundle. Each spacer includes a multiplicity of conjoined tubular cells arrayed in matrix or egg crate fashion, where the bore of each cell provides a passage for receiving a nuclear fuel rod. A fuel rod is centered in each cell by at least one spring acting to bias the rod against axially spaced pairs of stops formed as inwardly projecting dimpled or fluted wall segments of the cell. These stops not only determine the positions of the rods in their cells, but also the critically important spacings between fuel rods in an assembled fuel bundle. If quality assurance inspection of rod to rod spacing is performed by inserting fuel rod simulating pins into the cells of a completed spacer, considerable manufacturing effort and material expense goes for naught if it is then found that rod spacing is out of tolerance. SUMMARY OF THE INVENTION It is accordingly an objective of the present invention to provide apparatus for gauging the dimensional characteristics of individual cells prior to their incorporation in a nuclear fuel bundle spacer. The gauging apparatus includes a gauging fixture having a planar base and upstanding perpendicular sidewalls. The spacing between the parallel sidewalls is equal to the nominal width of a cell. The height of the sidewalls is also equal to the nominal cell width. If a cell can be placed in the fixture between the sidewalls with minimal play, its width dimension in the horizontal direction is acceptable. A plate is rested on the tops of the fixture sidewalls, and, if the cell fits between this plate and the fixture base with minimal play, its width dimension in the vertical dimension is acceptable. If the cell fits between two steps upstanding from the fixture base, its length dimension is acceptable. To check the dimensional characteristics of the fuel rod positioning stops of a cell, a first pin is inserted through the cell to rest on the stops. This pin is of a diameter equal to the nominal diameter of a fuel rod, but is relieved so as not to be in contact with the springs of the cell. The gaps between this first pin and each of the base and two sidewalls represent one-half of the rod-to-rod spacing the cell will establish when incorporated in a spacer, and the dimensions of the gaps between the fixture base and the pin and between one fixture sidewall and the pin are checked using a pair of "go, no go" feeler gauges. If these two gaps are within prescribed tolerances, a fuel rod will be centered in the cell with acceptable spacings with all neighboring fuel rods. The first pin is replaced by a second pin whose diameter is slightly less than the fuel rod nominal diameter, so that the cell springs should just contact this second pin. If the springs in their relaxed positions, do contact the second pin, the springs are deemed capable of exerting requisite spring forces to center a fuel rod in the cell against the stops. The invention accordingly comprises the features of construction, combination of elements and arrangement of parts, all as detailed hereinafter, and the scope of the invention will be indicated in the claims.