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Aviation History
1955
1955 - 0152.PDF
152 FLIGHT PRODUCTION CONFERENCE . . . G. W. RICHARDS, replying: forging pressures might, at an indeter-minate date, be reduced to about 12-14 tons/sq in. Information on large slabs was limited; it was difficult to produce slabs in certain alloys, buthe thought rolled slabs were generally preferable. Cu-Al alloys might be better for thin pieces. A. MENZIES, also replying, agreed that steel was preferably cut fast,but cited the case of a 90-ton spar on which a fast cut was impossible. W. E. GOFF (Aircraft Production) asked for opinions on the relativemerits of forming panels with thin surface stiffeners by close forging or by "hogging."G. W. RICHARDS, replying, said that this problem was governed by stiffener pitch (which might not allow room for a tool); it was difficult toobtain sufficient die accuracy, but an improvement might result from heating the whole die to forging temperature. A. VINES (Fairey) asked what was a "large" forging by 1955 standards?He contrasted the requirements for a prototype "or, now, 20 prototypes" with those for production, and then discussed ^he work required toimprove mechanical properties of slabs, particularly elongation. He called for stress-free (stretched) stock. G. W. RICHARDS, replying, noted that one could obtain a cast (rolled)ingot weighing five or six tons and a forged billet of roughly half the weight. It was difficult to control the quality of such large pieces, theproblem being the mechanical one of extracting the heat. Elongation became poorer in such sizes, particularly across the shorter transversedirection; 10 per cent could not be seen yet, but 4 or 5 might be attained. J. F. M. ORAM (Bristol) inquired about bulbed, legged or D-sectionstiffeners, possibly combined with transverse ribs. Bristols had found distortion negligible (0.040in on a 6ft slab, for example) and askedNorthern Aluminium whether there could be an expansion in slab production. D. F. MITCHELL (Northern Aluminium) noted that Bristol's plate hadbeen stretched (i.e., stress-free) and promised that an expansion of business would follow firm orders. L. G. BURNARD (Vickers-Armstrongs) cited the manufacture of9ft x 2ft x Jin aileron skins, with stiffeners, accurate to 0.018in; panting was found between the stiffeners, which was overcome by using Farnhamrolls to alter the stress distribution. R. D. EDWARDS (Vickers-Armstrongs) pointed out that, with forgingpressures set at 20 tons/sq in, his company would need a 300,000-ton press to do what they wanted; he preferred machining and extrusion.He also brought up the subject of machining in the flat and then forming to contour by shot-peening (as is done on the Super Constellation). E. D. KEEN, replying, spoke of "the difficulty of getting people to doextrusions which can be stretched-formed." Aircraft for Mach 1 to 1.5 required wing-skins of half-inch light-alloy sheet, very highly loaded butwithout stiffeners; he doubted if such skins could be shot-peened. PROF. CONNOLLY said that, with care, panels could be stretchedwithout waisting becoming a problem. W. G. HORTON (Gloster) inquired of the importance of surface finish.A. MENZIES, replying, said that surface finish raised a huge problem; the polishing of flat surfaces was much less important than ensuring thatall radii and changes of section were of the highest accuracy and finish. E. D. KEEN also emphasized the importance of stress-raisers, and ofthe effort in the micro-inch field being transferred to considerations of fatigue.J. HALL (Blackburn and General) complained that present stretching equipment could not handle cross-sections exceeding 60 sq in, and thatnothing bigger would be available for two years. Could solution heat-treatment at elevated temperatures help?G. W. RICHARDS agreed that this might be the case. High-speed Machine Tools for Aircraft Production was the title of the third paper, and this was one of the few occasions uponwhich the author was able to report solid, tangible progress towards the provision of machine tools tailored to the requirementsof the aircraft industry. The author was Mr. S. Radcliffe, B.Sc.(Tech.), A.M.I.Mech.E.,M.I.Prod.E., technical director of Wadkin, Ltd., of Leicester. He began by recalling the paper by Mr. S. P. Woodley (Supermarine)at the 1954 conference, suggesting the adaptation of "the ease, cheapness and versatility of the router technique to the problemsof skin milling and many other components." He and Air. Woodley had since gone far in installing new developments ofconventional routers in the Supermarine South Marston works [referred to in Flight of January 1st, 1954 and also in AircraftProduction, August 1954 and February 1955]. The machine now in use had a very substantial superstructurecarrying an overhead template. Mounting the template above the work had already been proved to offer great advantages,including greater flexibility in choice of cutter diameter and guide- bush rollers, height clearances and range of operations possible;the fact that the template could be left in place throughout a pro- duction run; and elimination of the risk of cutter damage to thetemplate. The machine has now been at work for some four months, with great success. Developments along this general line included machines capableof accepting much larger work. Whereas the machine shown had a table 10ft by 2ft 6in arranged to traverse, the next stage would bea unit with a fixed 25ft table overhung by a pair of routers mounted on power traverses. Hydraulic control from the overhead templatewould be another advantage. Mr. Radcliffe went on to discuss rate of metal removal, cutterdesign, life and lubrication, methods of working, and similar prob- lems. Metal could now be removed at rates very much greaterthan before, and a 20 h.p. router head was being designed which would roughly double the output at present possible. Somehigh-speed-steel cutters were still being used (in spirals) but even these would shortly give way to carbides. Pocketing cutters usingmolybdenum disulphide lubricants were now running on con- tinuous production for a week without being touched. Wadkins had designed a new skin-milling machine with a fixedtable 16ft by 5ft, the cutter head (a 20 h.p., 20,000 r.p.m. router) being carried on a gantry cross-slide. Power feed would be pro-vided along the length, working in conjunction with double-acting pneumatic cylinders at right angles to the feed to keep the guideroller up to the profile plate. The template would be overhead, and stepped templates or packing on the table would be used forstepped pockets or tapered skin. Another new machine was a universal miller, capable of rapidthree-dimensional work on large components. The prototype would be finished in a few weeks, and would be an open-sidemachine, with longitudinal traverse on the table, cross-traverse on the cross-beam, power-feed table rotation and a spindle headcanting through 120 deg. The machine would take work up to 5ft x 3ft x 3ft, or up to 7ft diameter for simple circular-milling.A hydraulic copying tracer would be an optional fitment, and a great range of desirable features would be standard. One of the largest new Wadkin machines was a spar millerspecially developed for the aircraft industry. It marked an abandonment of open-side construction, being of a more rigidbridge-type. On the other hand, the travelling outboard arm could be removed for wide material.The pivot-point for the canting horizontal spindle had been carefully chosen to ease calculations for the canting copy bar.Vertical and horizontal slides in front of the canting slide mechanism would permit re-positioning of the cutter after regrind-ing, and it was proposed to control the canting and rise-and-fall by independent hydraulic servo mechanisms. Three sets of copybars would be used, all mounted at the rear. The spindle would be driven by a motor giving up to 60 h.p. at 3,000 r.p.m., and themachine would be able to work on steel or light alloy. The table width would be 24in (new for British-built machines) and thelength any multiple of 14ft. Mr. Radcliffe discussed the problem of clearing away the swarffrom a spar mill of this type, and then suggested that a useful additional feature might be a radial-arm router. If such a unitwere fitted, in conjunction with drop-on templates, tapering, and possibly additional pocketing, could be carried out at one settingof the spar. Spar mills were, in any case, expensive, and it was doubtful whether it was worth while having all machines of theuniversal type. Another illustration showed an aluminium-plate sawing machinenow being developed. It comprised a circular saw mounted on a power traverse across a table 76ft by 26ft, the table consistingof powered conveyors. The maximum size of billet would be 45ft x 10ft x 5in, the saw having a 44in wheel driven by a 75 h.p.motor at a feed of up to 10ft per minute. Swarf would be exhausted by a drag-link conveyor capable of removing up to 120 cu ft perhour, running on to a belt elevator to lift the swarf into bins. The last section of Mr. Radcliffe's paper dealt with the sawingof expanded honeycomb sections. The biggest problem was to make cuts over 4ft across and to generate accurate curves forproducing aerofoil sections. A drawing showed a suggested band- saw driven at 8,000 ft/min by a 5 h.p. motor, the work beingmounted on a fixed table—if possible in a rigid frame—and the horizontal blade traversed over the work under the control of camsof suitable profile. Mr. Radcliffe concluded with a note on the future, endingwith the words: "I hope that in this great step forward to electronic control the British machine-tool industry will play itspart and give the aircraft industry the equipment it needs to produce its products. Discussion. H. A. CHAMBERS (Rockwell Machine Tool) noted that,in America, a wing skin 25ft by 5ft could be machined in 25 to 30 hours. C. BROMAGE (Gloster) expressed concern over the disposal of swarfin spar milling, to which Mr. Radcliffe replied that it was less of a problem if an exhauster of up to 8,000 ft/min speed were fitted and ifdowncutting was adopted. J. C. KING (English Electric) pleaded for stress-free stock—"themissing link" being the means of stretching it. A. VINES (Fairey) believed that the preceding 12 months had been"the turning point" and that firms were at last showing an interest in the special requirements of the aircraft industry. MESSRS. FRANKLAND AND FROST (Westland) brought up the subject ofspindle moulding, and called for larger equipment of this type with dynamic balancing. Mr. Radcliffe replied that one could design routersto accept an out-of-balance force. P. V. BROWN (M.O.S.) spoke of the possibility of a variable-angle headon a Wadkin WT router, and Mr. Radcliffe cited the special rocking head supplied to Shorts for prototype aircraft work.W. J. MORGAN (M.T.T.A.) hinted at the possibility of a link betweenMr. Keen (whose paper mentioned machining on virtual centres) and Mr. Radcliffe. The latter thought that three-dimensional problems hadby no means all been solved.
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