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Aviation History
1958
1958 - 0043.PDF
FLIGHT, 10 January 1958 The Aircraft Production Conference—1 45 British Manufacturing Practice TO Mr. L. G. Bumard, M.I.Prod.E., A.F.R.Ae.S., much creditis due for reviewing in a single paper nearly all the currentmanufacturing techniques in use and under development by the British aircraft industry. Formerly chief development engineer at the South Marston factory of Vickers-Armstrongs (Aircraft), Ltd., he is> now assistant to the general manager of that company. Machining. After some preliminary remarks on routing, Mr. Burnard described various types of routers, including overhead template, link arm, and servo-operated machines. Contour etch- ing could often take the place of routers for skin-milling operations; some skins, however, were too large to be produced in this way and routers had been adapted to deal with jobs of this kind. A number of firms were attempting to develop the routing of high-tensile steels. Using tungsten carbide cutters and CO* cool- ing, router heads had been run at 6,000 r.p.m., but cutter life was very short. Ceramic cutters had also been tried, but broke down almost immediately; whether this was due to thermal or mechanical shock was not yet known. Milling Wing Skins. Many British designs called for the use of integrally stiffened wing skins. In a milling machine made by Blackburn and General Aircraft (and used, incidentally, for the milling of NA.39 wing skins) a 26ft fabricated beam was supported at each end by two travelling vertical members. These were accommodated in slideways at each end of the machine bed, and were adjustable separately, making it possible to machine con- verging or angular stiffeners in the component. The beam carried a 50 h.p. Onsrud cutter head controlled in the vertical plane by means of a hydraulic copying device. High-tensile Steels. Many airframe components were now being made from high-tensile steels of the order of 80-100 tons and these presented a difficult problem, particularly with profiling and pocketing, for which long slender cutters were necessary. A very efficient machine recently developed was the Strasmann- type cutter. This had a helical thread form machined on it and was made of high-speed cobalt steel. The peculiar form of the cutter lengthened the cutting edge, broke up the chips from the long acicular form which normal slab mills produced, and reduced the tooth loads. Very heavy cuts could be taken with impunity. Numerical Control. Many firms were experimenting with numerical control for machine tools. A number of systems had been applied to standard milling machines, but in the future it would be necessary to consider the design of the actual machine tool in relation to the electronics. Numerical control offered many advantages. In the aircraft industry it offered the means by which the lead time on aircraft could be considerably reduced. Numeric- ally controlled machines needed very little in the way of com- plicated tooling—all that was necessary was a fixture which would hold the workpiece in the correct position in relation to a fixed datum, and a punched paper tape or magnetic tape. Modifications were easily incorporated by changing the information on the tape. Aircraft Pipework Manufacture. Mr. Burnard said that in order to produce a pipe by mechanical means it was necessary that every bend should be to a true radius, and to standard radii for which there were bend-blocks available. If these requirements were adhered to, it was possible to machine-bend almost every pipe in an aircraft run. Among the bending devices described was an automatic machine by Vickers-Armstrongs (Aircraft), which extruded a pipe through a die to the required form. The pipe was located in a collet mounted on a carriage moving along the bed of the machine. It passed first through a fixed die and then through a movable one. When the latter was displaced in rela- tion to the fixed die, the pipe emerged in the shape of a bend —the greater the displacement the greater the bend. Control of the amount of bend was by means of a countershaft containing a number of cams set numerically, and actuated in sequence by "U.S.-U.K. PRACTICE" was the theme of the sixth conference on theproblems of aircraft production, held at Southampton University on January 2 to 3. The conference was organized by the Institution ofProduction Engineers and three papers were presented, one of which, on certain aspects of English Electric P.I production, is reported atsome length on pages 47-51. Of the two papers summarized here and on the following page, the first is a review of British manufacturingpractice, and the second, from the other side of the Atlantic, deals with the problems set by the new age of supersonic aircraft and guidedmissiles, and the means by which the American aircraft industry is meeting the challenge. A note on the discussions held on the threepapers appears on page 61. the moving carriage. It was intended eventually to replace this system by electronic control by means of punched tape. Titanium. So far, said the lecturer, titanium had mainly been used to replace stainless steel where heat- and corrosion-resistant properties were necessary. No difficulty had been experienced in forming commercially pure titanium. The English Electric Co., Ltd., were hot-forming alloyed titanium; a die press was used, with a silicone rubber insulating blanket to protect the rubber bolster. Titanium parts and form blocks, the latter being made in steel, were heated to about 300 deg C. Titanium welded quite well in an inert atmosphere, but an argon torch was necessary to prevent contamination. For com- plicated components it was necessary to use a welding box. This was provided with a Perspex window through which the com- ponent could be viewed, and before welding was exhausted of air and filled with argon. Stress-relieving was most important with titanium, and was generally carried out at between 450 and 500 deg C for a period dependent on the gauge of the material. Sheet-metal Forming. There had been few developments in sheet-metal working during the last decade, but two minor develop- ments were perhaps worth mentioning. The first was the stretch- forming of magnesium alloys on heated blocks by the Folland Aircraft Co., Ltd. The formula of 5 kW per 100 lb of tool-weight was used, and the material was formed at 280 deg C. Blackburn and Vickers-Armstrongs were both using Hufford machines with articulated jaws. Considerable saving in material was possible, as the work could be made to assume the required curves prior to forming; this was not possible with flat jaws. Assembly Methods. Aircraft assembly methods varied from company to company, according to their individual design philo- sophies. Fairey had designed three-dimensional lofting equipment which provided accurate means for the full three-dimensional laying-out of component assemblies. Handley Page had adopted the spot-welding philosophy, for which they claimed the advan- tages of cheapness, higher surface-finish and lighter assemblies. Puddle welding had been developed by Bristol Aircraft. Chemical Production Methods. Most British aircraft firms, said Mr. Burnard, were experimenting with, or were in production with, contour etching. One considerable advantage of this tech- nique was that parts could be etched in the formed condition, thus avoiding the difficulties experienced in forming a component with a non-uniform cross-sectional area. A tailplane skin produced by this method was illustrated in the paper. The etched areas were of different depths, achieved by progressive de-mas Ring. Other processes in use included the chemical reclamation of work files, electrolytic profiling, and spark erosiot —used for the production of dies, drilling of holes in hard materials, and other small-scale machining operations; even the hardest materials could be machined provided they were electrically conductive. Relief of Stress-raisers. The lecturer described two techniques for the relief of stress-raisers, the first of which was barrelling, where the components were located in fixtures and loaded into a A tailplane skin by Vickers- Armstrongs (Aircraft), Ltd., produced by contour etching. It »os been etched to varying depths by means of progressive de-masking.
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