November, 1938 AIRCRAFT ENGINEERING Workshop and Production Section By J. G. Waterhouse and A. R. Mowbray* H E subject of welded structures in aircraft a s compared with that of riveted ones necessarily affects two schools of de signers. It is contended that under modern conditions and requirements the welded structure has definite merits over its rival, provided that it is tackled with the correct technique. Therefore it should be borne in mind that the welded structure must be designed for the process and not, as some designers suppose, be improvised for jobs where riveting or bolting was previously employed. Even with this limitation, there is great scope in many fields of metal construction for the use of welding. Bearing in mind the fact that both in aircraft and automobile construction the weight-to-strength ratio is ever important, the fabrication of parts by welding has many advantages. But, the best results can only be obtained by correct design for the processing of the job and the efficiency of the lead to distortion than the longer application of a weld without arriving at the melting temperature. welder. While the latter may be a first-class man less concentrated flame. A test was carried out Furthermore , owing to the localizing of the heat on repetition work, he requires a knowledge of on these lines which is shown in the sketches in th e adjacent metal is not raised in temperature metallurgy and the behaviour of the various metals Fig . 2. Four plates, 6 in. by 3 in. by 16 s.w.g. of sufficiently to cause undue expansion and con under the applied heat to tackle vicarious jobs mild steel plate, were joined as follows. Two were traction . With this point in mind, and assuming successfully. The operator may be conversant welded with the pipe at 45 deg., a gap of 1/16 in . tha t the operator is aware of the behaviour of with the means of dealing with the numerous being left at the finishing end ; the result was the variou s metals under the heat, it remains for him metals, but the success of the job lies in his distorted weld shown, with its overlap 1/16 in. t o be acquainted with methods whereby he can best practical knowledge of a method of approach for Th e second pair was welded with the same gap, but eliminat e distortion ; that is, by knowing a recom the multitudinou s shapes t o be met with in designs th e blowpipe was held at an angle of about 80 deg. mended procedure for the individual job in hand. and also in his rate of executing the job. In view Th e plates on completion were found to butt I t is in an endeavour to give such odd " wrinkles " of this , it can t e seen that a set procedure cannot correctly and to be without buckling, with its tha t the writers hav e ventured on th e presen t article. be laid down for all and sundry operations, and it consequen t internal stresses. is for this purpose tha t the following methods arc Fro m the illustration (Fig. 3a) it is apparen t that given with a view to assisting the welder in the th e joint is caused to open to its maximum, owing many problems which he has to face. t o the heat being delivered over a greater length, whereas with the pipe in an upright position The average welder is in the habit of practising (Fig. 3b) th e exten t of th e expansion (and subsequent the leftward method of welding, but there is an possible distortion of the plate) can ' be more outstanding advantage to be obtained from the effectively controlled. more recently introduced rightward method. The Havin g dealt with this problem, attention must latter involves the opposite directional movement, be drawn to the question of penetration of the as may be seen from the illustration (Fig. 1) where weld. In this respect, it is most essential that the the filler rod travels in advance of th e flame. One joined parts must be formed in the most homo point tha t should be borne in mind regarding this geneous way and the parent metals fully united. method is that it is impracticable to apply it to Th e absence of this, where the two parts are in materials of less than a/16- in. thickness. This is contac t on the reverse face to the weld and not wing to the fact that the cone of the flame, pro joined, is definitely liable to lead to fracture,' ceding as it does in advance of the filler rod, is startin g at the point where the metals are not approaching the two edges of the parent metal, completely fused. Another common tendency is hich if of a light gauge have a tendency to burn for welders to assume that by having a proud away. It is, of course, this limiting factor of deposit of filler rod on the joint a weld giving thickness which curtails the use of the leftward continuit y of the material has been effected. This method in aircraft work to certain special cases. is not the case, for the parent metal has not been It is a definite fact tha t with the rightward method heate d to fusion point and the resulting weld, far he welder protects his welds from the atmos from being a bonding of surfaces, is little more phere, owing to the outer flame covering the welded tha n an overlaid strip of ornamental metal! This portion and allowing it to cool more slowly. This fault also can be overcome by holding the blowpipe permits th e grain formation to re-form in practically a t a steeper angle. ts normal state and retain its physical According to the usual handbook information, characteristics. Moreover, on many jobs it is th e welder is invariably advised to offer the flame mpossible to see the underside of the welded to the job at 45 deg. inclination. structure, and ascertain whether the correct Whil e admitting that this has a definite applica INSPECTION IN THE MIDLANDS penetration and deposit have been homogeneously tion in some instances, it has a tendency to allow O mee t the needs of its growing member applied. With the leftward method, there is a th e outer cone to play on the adjacent metal and shi p in th e Midlands, th e Institution of tendency by the welder, owing to the outer cone keep it at its maximum expansion. This intro Engineerin g Inspection is establishing preheating his job, to effect penetration partially duces undue heating and consequently excessive before the bottom of the vee at the joint has distortion . It has been found that by altering the tw o new Branc h centres, one a t Mancheste r and reached melting point. Whereas with the right- angle of th e nozzle t o a more nearly vertical position, th e other a t Coventry. ard method the operator has an unobstructed thi s fault can be eradicated, inasmuch as the heat Th e inaugural meeting of the Coventry and iew of the joint and cannot possibly complete the is localized and thereby concentrated on the parts Distric t Branc h took place on Octobe r 28, 1938, where most required. a t 7.30 p.m . a t th e Coventry Technical College. Fro m this it appears that, contrary to general * Mr. Waterhouse and Mr. Mowbray are instructors at The Th e chair was taken by Mr. C. Grad, Chief Collegc of Aeronautical Engineering, Chelsea. belief, the concentration of heat is less likely to Inspecto r a t the Rugby Works of the British Thomson-Housto n Co., Ltd. , and a member of th e Nationa l Council of th e Institution. Lt.-Col . H. W. S. Outram, C.B.E., T.D., A.R.S.M. , F.R.Ae.S., A.M.I.E.E., Director of Aeronautica l Inspection to th e Air Ministr y and Presiden t of the Institution was the principal speake r a t this meeting. Colone l Outra m will also addres s th e opening meetin g of the Manchester Branch on Novembe r 8, 1938. On this occasion the meetin g will be held a t Manchester College of Technolog y a t 7.30 p.m . with Mr. L . Nicholson, Chief Inspector of Metropolitan-Vickers Electrica l Co., Ltd. , in th e chair.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Nov 1, 1938
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