In general, this invention relates to an alignment device used for temporary alignment of two or more workpieces having holes within them that must be positioned in a precise relationship while some other operation is performed upon the workpieces. More particularly, this invention relates to an alignment device adapted to precisely position two or more workpieces by radially expanding to contact and align the holes' inside surfaces about a single longitudinal axis.
In industry, and in particular, the aerospace industry, it is desirable to have a simple mechanism for temporarily aligning parts in a desirable relationship such that some interim operation such as riveting, can be performed upon the parts. Typical of the situations in which such mechanisms find application is the process of temporarily attaching aircraft skins to each other or to structural members while they are being permanently fastened together to form an assembly.
If the parts to be aligned each have at least one generally cylindrical hole of relatively small diameter, the alignment can be accomplished by means of a device that has a hollow cylindrical body defining a longitudinal axis and an end including a relatively small cylindrical post mounted between two expandable arms having enlarged ends. The arms and the post are generally aligned with the longitudinal axis of the cylindrical body. The arms are connected to a drive nut in the body that, when actuated, causes the arms to longitudinally retract or extend relative to the post.
In operation, the arms are initially extended beyond the end of the post and have a width sufficiently small to enable the arms and the post to be inserted into the workpiece holes. The arms and post are inserted through the holes until the body of the device abuts an outer surface of the outermost workpiece. The drive nut is then rotated, causing the enlarged ends of the arms to move longitudinally toward the post. When the arms contact the post, the arms are forced radially outward as they move toward the inner surface of the innermost workpiece. The rotation of the nut is stopped when the enlarged ends of the radially-expanded arms abut the inner surface of the innermost workpiece. In such a position, the workpieces are compressed between the body of the device and the enlarged ends of the radially-expanded arms. When the interim operations are completed on the workpieces, the device can then be withdrawn by a reversal of the above steps and re-used on other workpieces.
While the prior art discussed above is generally effective in clamping two parts or workpieces together, it does not lend itself well to precisely aligning the holes of the workpieces. More particularly, the radial expansion of the arms of the device causes the arms to have an angled orientation as compared to the cylindrical inner surfaces of the holes. Accordingly, the arms contact only a relatively small portion of the hole in the innermost workpiece, namely that portion of the hole adjacent to the inner surface of the innermost workpiece. Such contact is not sufficient to ensure that the holes of the workpieces are aligned along the same axis to provide a finished assembly with high tolerances now desired by manufacturers. Further, high friction forces can develop between the arms and the holes during retraction of the arms causing the device to stick in its fastened position, thereby requiring the user to forcibly remove the device by other means, such as hammering, which can damage the workpieces.
To remedy these problems, another alignment device was developed to temporarily and precisely align holes within associated workpieces. This device featured cooperating, precisely machined male and female sleeves mounted in a longitudinal series on a pin that has a lower, enlarged end to engage the lowermost sleeve. Both the female and the male sleeves have cam surfaces that interact to expand the female sleeves. The upper end of the pin is mounted to a body that includes a drive cam configured to bear on a thrust washer riding on the uppermost sleeve. The female sleeves are split and the male sleeves move longitudinally to expand the female sleeves in response to compression from the lower end of the pin and the thrust washer.
In operation, this device is initially inserted into two or more workpiece holes. The drive cam is then actuated to move the thrust washer toward the enlarged pin end. Such movement reduces the distance between the thrust washer and the enlarged pin end thereby driving the male sleeves into the female sleeves. The tapered ends of the male sleeves then radially expand the female sleeves to contact and align the inner surfaces of the holes of the workpieces. These steps can be reversed to remove this device from the holes when desired.
While this device is generally effective in aligning holes in workpieces in a precise relationship, the cam surfaces of the male and female sleeves must be precisely toleranced to provide for the uniform expansion of the female sleeves. Accordingly, the male and female sleeves are relatively expensive to manufacture. Further, to avoid their permanent deformation, the expandable female sleeves must be confined to the area within the workpiece holes. As compared to the other confined female sleeves, an exposed female sleeve encounters no resistance and, therefore, can expand to a greater extent in response to the retraction of the enlarged pin end. Such unrestrained expansion can plastically deform the female sleeve, thereby preventing removal and reuse of the device. Accordingly, for each different length of the aligned workpiece holes, a different length device must be purchased, resulting in undesirable costs.
Another drawback of this device is associated with its shorter length when it is expanded. Because the distance between the thrust washer and the enlarged pin end is reduced when the female sleeves are compressed, a possibility exists that a user may mistakenly assume that the device can be used to align holes having a total length of the uncompressed sleeves. Accordingly, the device could be inserted into the holes and then compressed, resulting in the longitudinal withdrawal of the female sleeves from a hole in an innermost workpiece. This innermost workpiece can then be in a nonaligned position during the rest of the process, resulting in undesirable loss of tolerance for the final assembly.
Accordingly, there is a definite need for an expansion pin that does not shorten or permanently deform during use. Further, there also is a definite need for an expansion pin that is relatively simple to manufacture and, therefore, relatively inexpensive.