Fig. 15. Double edge shear cut-off mechanism. one can override a malfunction indicated by the control computer during operation, it is still a source of concern. Where possible, shielding has been provided to protect the most vulnerable limit switches. This has minimized the problem but has not eliminated it. Under consideration is the possible replacement of those limit switches which are still subject to damage by either larger units, photo-optical or magnetic proximity swtiches, where possible, to eliminate this troublesome problem altogether. 3. COMPOSITE BEAM BUILDER As the development efforts associated with the aluminum beam builder were nearing completion, attention was focused on what it would take to modify the design of the primary machine subsystems in order to produce composite beams. This new development effort focused on three items, as noted in Figure 16, while the remaining subsystems were considered to be usable as is or with slight modification to handle the new material. Beam Cap Processing Development In mid-1977, work began with a brute force approach of trying to roll form a graphite/polyethersulfone laminate using the aluminum beam cap development tooling with heaters added to soften the thermoplastic composite to forming temperature (Figure 17a). Figure 17d shows the result of these efforts. Disastrous, burnt toast, aptly described the product, but at the same time, much was learned. Such things as temperature control (polyethersulfone softens at about 260°C and has a forming range before it begins to sublimate of about 10°C), bend zone heating (heating the whole part resulted in severe rippling and deformation) and speed control between
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