6 Lee, E. H. and Shaffer, B. W. " The Theory ofPlasticity applied to a problem of Machining."J. App. Mech. 18 (4), 1951: 405-413-

7 Hill, R. " The Mechanics of Machining: A newapproach." J. Mech. Phys. Sol. 3, 1954: 47-53.

8 Goddard, J. " Basic Theory and ExperimentalTechnique in Machining and the Application ofMetal-Cutting Fluids." (Unpublished.) College ofAeronautics, Cranfield, Diploma thesis. 1955.(See Aircraft Production, Oct. 1955, p. 420, forsummary.)

9 Merchant, M. E., Ernst, H. and Krabacher, J." Radioactive Cutting Tools for Rapid Tool-LifeTesting." Trans. A.S.M.E. 75 (4) 1953: 549.

10 Boston, O. W. " Metal Processing." John Wiley& Sons, Inc., N.Y., 1941.

11 Wolfe., K. J. B. and Robinson, I.R. "The Effect ofManganese Segregations on Machinability" Met-allurgia, 43, 1951: 3.

12 Galloway, D. F. "Machine Tool Research &Development." Research Dept., Institution ofProduction Engineers, 1945.

13 Cherry, J. Report on the Machinability of AircraftSteel. D.T.D. 331 (B.S.S. 99) using H.S.S. tools.Note No. 24, April, 1955. College of Aeronautics,Cranfield.

REPORT AND DISCUSSION

Mr. D. A. Oliver, in presenting the Paper, saidit might have been noticed that in the preliminaryannouncement the title had been given as " MachineResearch and its Impact on Speeding Production "as distinct from " Machining Research ". It wasscarcely necessary to say that there was a big differ-ence between those two words, and, while some peoplemight regret that the title as given in the finalprogramme of the Conference was correct^ he wouldlike to make it clear that in his view the finest found-ation for future research in machine tools themselveswas a wider and deeper knowledge of the conditionsof practical machining or of metal removal in general.That point would be brought out by his colleague andco-author, Dr. Fitzgeorge, who would give a summaryof the Paper. Mr. Oliver wished to make a fewgeneral observations which might be of interest to theConference before the formal presentation of thePaper. He hoped that in the discussion which was tofollow they might receive some stimulating and help-ful advice.

It was generally known that the Mechanical Engin-eering Research Board took a great interest in theadvancement of knowledge of the machining processas applied to materials generally, and that work wasbeing undertaken at M.E.R.L., East Kilbride, whichmight be described as a gigantic offshoot of theoriginal Engineering Division of the National PhysicalLaboratory. Due to a number of circumstances, thevolume of work conducted there had been limited,but the quality had been high, and the work wasnow gathering momentum.

The Mechanical Engineering Research Board hada Committee devoted to the mechanics of formationand machine shaping of metals. That Committee,of which Mr. Oliver happened to be Chairman, metabout four times a year, and at alternate meetingsendeavoured to discuss problems relating to machiningand machinability. The Committee itself formeda national focal point for work on this subject, with-

out claiming, of course, to be exhaustive. NaturallyP.E.R.A. was represented on the Committee, and theuniversities and large industrial organisations whichwere interested in this broad subject.

He mentioned that to give the assurance that,however small the scale of the work which was beingundertaken, a sense of responsibility to the subject hadbeen shown and had been maintained for seven oreight years, and indeed ever since the MechanicalEngineering Research Board had been formed.

They would all remember the late Dr. Schlesingerwho, with Dr. Galloway, at Loughborough Collegestarted a school of research on the machining ofmaterials in Great Britain. Before this ProfessorWright Baker, of Manchester University, had under-taken cutting tool researches, and these had beenreported to a Committtee of the Institution of Mech-anical Engineers which Mr. Oliver believed startedthis work about forty years ago. He thought, however,that the first serious effort could be traced toSchlesinger and Galloway and their early team, whodid such excellent sample researches at LoughboroughCollege and later at Melton Mowbray, therebyopening the eyes of production engineers to the typeof work which could be done and to the value of thedata which became available.

Mr. Oliver was glad to take the opportunity ofpaying tribute to the help which they had receivedfrom Dr. Galloway and his colleagues in the earlystages of setting up the B.S.A. Machinability Labor-atory round about 1946, which had made it possibleto save a year or so of preliminary work. A briefhistorical survey of machining research in this countrywas given in the Paper, and he would not elaborateon those aspects.

Turning to the impact of the findings of machiningresearch on machine tool design, he wished to expressthe following opinions. The modern machine toolincorporated the production experience of manygenerations of engineers and machinists, rather than

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being the direct and logical expression of basicscientific principles. For example, experience hadshown that massive slides on the average performedbetter than those of more slender proportions, andeven if slender parts were made which were otherwisesuitable, they might have different vibrationcharacteristics and usually lower internal damping. Allthis had encouraged engineers to be conservative andto welcome only small changes in design, drawingheavily on what had been found empirically to besuccessful.

A new challenge had now arisen with materials sotough and strong as to be classed as non-machinableaccording to ordinary standards, while new needswere arising such as servo-controlled and motor-drivenparts which must have minimum slide friction,minimum backlash and other fresh features whichstruck at the very roots of orthodox practice as judgedby ordinary standards.

The Authors were primarily concerned with thosemachine tools such as single-spindle and multi-spindleautomatics which were not generally subject to muchchange, and therefore on some of the newer machinetools for the aircraft industry they spoke more asobservers than as actors in the piece. They were,however, concerned very much with the design andperformance of small tools and with the machiningprocess generally, and thus were far from indifferentas to what the machine tool of the near future shouldand must be. Perhaps the advent of automationwould give them all a fresh start in this field.

With those preliminary remarks Mr. Oliverproposed to give way to his co-author, Dr. Fitzgeorge,but before doing so he would like to mention that allthe Authors were present on the platform and wouldbe available to answer points raised in the discussionin accordance with their experience of the questionsraised.

Dr. D. Fitzgeorge then gave a summary of thePaper, and showed slides of some of the machinesat the B.S.A. Group Machinability Laboratory. Indoing so he gave correct figures for the Adcock andShipley drilling machine, which differed from thosegiven in the preprint. The main drive, he said, wasby a 40-h.p. motor, giving about 460 spindle speedsbetween 30 and 1,350 r.p.m. It was virtually acontinuously-variable machine. A 2-h.p. motorprovided the feed, and the value of the feed rate couldbe chosen from 578 alternatives between 0.8 in. and65 in. per minute.

Mr. J. Gregson (Development Engineer, TheFairey Aviation Co. Ltd.) said he had three questionsto put to the Authors. The first arose from theircomments on the machining of high-strength steelswhich were mostly concerned with milling and turn-ing. He suggested that drilling, reaming and tappingalso presented a considerable problem. There was thequestion of reaming to get finish on holes on highstrength steels, and using reamers for more than onehole without regrind. Had any work been done onthis? Information had been quoted in regard to theseproblems on titanium.

His second question was the important one at thepresent stage of what materials should be used tomake machine tools. It had been suggested thatspheroidal cast iron might be better than ordinarycast iron, because of the decrease in deflexion due tothe higher modulus. A very important point therewas the effect of decreasing the damping character-istic. Was any effective work being done to considerthe relationship between damping, weight anddeflexion for the three materials which were available,namely cast iron, spheroidal graphite cast iron andwrought steel? If it was possible to give way on thesuperior damping characteristics of cast iron, it mightbe advisable to turn attention to wrought steel ratherthan spheroidal graphite cast iron with which it ispossible to get a better structure in terms of weight.

The third question was whether the Authors sus-pected that the fatigue strength of tungsten carbidemight have some effect on the life of the carbideunder conditions where the rigidity was sufficient togive stress reversals when cutting. Some of the testswhich Mr. Gregson's company had carried out oncutting light alloy gave reversals in terms of a millionan hour on the tip-edge of the cutter, which was avery high reversal rate. He did not know of any workwhich had been carried out on the fatigue life oftungsten carbide, and it would be interesting if theAuthors had any information on that point.

Mr. Kinman, referring to the drilling, reamingand tapping of high tensile materials, said that theirown practical experience was that the drilling pre-sented no problem at all. It was a question of theright design and lubricant and the correct cuttingspeed. With reaming, if a tungsten carbide reamerwas used there was no trouble. Tapping, on the otherhand, was extremely difficult. In the high tensilerange (85—tons and over), surface treated taps wereneeded, such as were abtained by nitriding. It wasa question of one tap, one hole, and blind holes werealmost impossible. It was necessary to have severalthreads lead or a series of taps, or one would failcompletely.

With regard to tool life with tungsten carbide andthe question of fatigue, the Authors believed thatwhat had been said was correct. It seemed thatunder conditions of great rigidity with the minimumof deflexion on the carbide entering and leaving theworkpiece, cutting speeds could be greatly increasedand tool life would go up enormously. The questionof rigidity seemed to be the main point in machiningthese high tensile materials. With ultra-rigid con-ditions an entirely different conception was obtained.

Mr. Oliver, referring to Mr. Gregson's questionon damping and the use of spheroidal graphite ironin place of cast iron, sail the Authors had hadsome practical experience of fabricated machine toolbases. They looked very attractive and were easilymade when the steel plate could be obtained, but inpoint of fact they were markedly worse with regardto noise and vibration and had to be stiffened anddamped, as compared with the ordinary cast-ironbase. The cast-iron base was not unduly porous, but

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it did its job well with regard to damping. Theirgeneral experience was, however, that there was noneed to be worried very much by the different intrin-sic damping characteristics of materials, becausethere was nothing like a very close joint to providedamping of the order of ten times the inherentamount, so that if it was necessary to put damping in-to a machine tool it would only be necessary to makeone very carefully-designed joint and shrink one parton to the other. That joint would then introduce,say, tenfold the damping inherent in the unmodifiedstructure.

Mr. J. Glennie (Planning Engineer (Weston Fac-tory), Bristol Aircraft Ltd.) said that productionengineers appreciated the importance of the problemsinvolved in using cutting tools with high tensile steels,and apparently the B.S.A. Group were facing thoseproblems in their research work. He would like toknow whether the Authors considered it to be import-ant, apart from the design and the manufacture of thecutting tool, to maintain that tool properly from theshop production point of view. Perhaps they mightgive the Conference the benefit of their experiencesin respect of the lapping of such tools, and saywhether they preferred metal or Resinoid bondedwheels, particularly in the case of offhand lapping. Itwould be interesting to know whether they would usea mist coolant or a flow coolant.

Tapping had been dealt with, but he thought ratherloosely. Were the manufacturers facing the problemof producing a tap for these materials? They werecarrying out research work on milling cutters and soon, but he thought that the tapping problem wasgreater. Were they doing any research which wouldenable them to give the production engineer a suit-able tap which would satisfactorily produce a tappedhole in high tensile steel, and could such a tap beused in a tapping attachment or must it be used onan orthodox tapping machine?

Mr. Kinman, referring to the grinding of carbidetools, said that many claims were made for theadvantages to be obtained from high finishes, but ifthe finish was reasonable the Authors thought thatwas sufficient. They considered that a finish of be-tween 3 and 5 micro-inches was satisfactory. Anyfurther finish did not show a profitable return. Withregard to the wheels used, it was a question of con-venience. For offhand lapping, a metal-bondedwheel was more resistant to misuse, but a Resinoidbonded wheel, if carefully used, would give greaterlife and faster carbide removal.

With regard to cooling, whether it was done byflow or mist was again a question of convenience. Anoffhand grinding machine was generally adequatelyguarded and a copious supply of coolant was no dis-advantage, but where that was a disadvantage mistcooling should be used.

With regard to tapping, they were working veryhard in trying to develop taps for the high tensilematerials, and also for titanium, which presentedeven more difficulty than high tensile steel; but, asmentioned in the Paper, to some extent designers

must co-operate. Tests had shown that a nut tappedto 60% full depth of thread was quite as strong asone tapped to 100%, and that made a tremendousdifference in tap life.

Mr. L. J. Bolton (Production Superintendent(Hydraulics), The Sperry Gyroscope Co. Ltd.) com-mented on the fact that the Authors had not men-tioned any experiments in the use of liquid carbondioxide as a coolant, and asked whether they hadcarried out any experiments on this and come to anyconclusions about it.

Mr. Kinman replied that they had not carried outany experiments on carbon dioxide, but they were inclose touch with the carbon dioxide suppliers and withother users and would shortly be carrying out experi-ments. It would appear that carbon dioxide waspurely a coolant and not a lubricant, and their testshad shown that in certain conditions one requiredlubrication and in others one required a coolant.Under conditions where a coolant was necessarylubrication without cooling was ineffective. In suchconditions the use of carbon dioxide might be profit-able.

Mr. L. G. Burnard (Chief Development Engin-eer, Vickers-Armstrongs (Aircraft) Ltd) asked whetherthe capri-honing or vapour-blasting of a ground toolhad any effect on its life. Some experiments had beencarried out, he said, on the honing of a cutter in thisway after it had been ground, and it had been foundthat this had increased its life considerably.

He had read Mr. Cherry's report on D.T.D. 331,and the rake angles in question, whilst all very wellon turning tools, had no real application, at presentat any rate, on end mills which must be used forsculpturing the very complicated components in pre-sent designs. He would like to know whether the toolmanufacturers were going to provide the aircraft in-dustry with end mills with these very high rakeangles and, if so, how they would get the strengthinto the tip, because this was going to make the tipextremely weak. With an inserted tooth cutter it waspossible to alter the rake angles considerably, but withan end mill it was necessary to use the rake angleprovided by the tool manufacturer.

Mr. Kinman said that the Authors had triedhoning and found that it was particularly beneficialon high-speed steels. Unless they were very carefullyground, the surface layer was austenitised. Honingremoved that surface layer, with consequent benefitto tool life.

On the question of high rake end mills, there was aweak point there and work would have to be done tosee whether cutters could be made with these ex-tremely high rakes. Failing that, it would be necessaryto use much lower cutting speeds with conventionalcutters. With these cutting speeds, cutting oils wereextremely important. Many people did not realisethe effect of lubrication on these difficult materials.It was not possible to select a particular oil and saythat that was what was going to be used for difficult

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materials. All the cutting oils had different activecharacteristics, and they worked by forming a metal-lic compound which acted as a lubricant; but theformation of this compound would attack the cutter,and too active an oil would give a short tool life byattacking the cutter and giving an impression ofwear. It was necessary to select a cutting oil of theright activity for the particular operation.

Mr. S. W. Potter (Development Engineer, RoyalAircraft Establishment) congratulated the B.S.A.Group on doing so much research on the cutting func-tions of machine tools. This was obviously, he said,one of the major considerations; before it was pos-sible to start on the development of a machine tool,they must be clear in their minds about the function-ing of the machine tool and know whether in fact itwas going to be a milling principle or a grindingprinciple, and so on. That was relevant to the designof the machine tool.

The emphasis of the present Conference was rightlyon the production of aircraft parts, but there was therelated problem of the production of models of air-craft for wind tunnel testing. It was well known thatsuch models had taken far too long in the past toproduce, and that had had its repercussions rightthrough the production stage. Here the emphasiswas not on rate of metal removal from those models,but rather on metal removal with the minimumamount of induced stress in the material left in themodel itself.

He was gratified to learn that the B.S.A. Grouphad removed metal by the fly cutting process, evenon 100-ton tensile material. This was an aspect ofthe subject which was relevant to the job whichR.A.E. had to do. They felt that the minimum lengthof tool-work contact time inherent in single-pointmachining against, say, a grinding technique wouldimpart a lower stress in the resulting shape, and theywere therefore interested in these single-pointmachining tests. He would like to ask whether anyresearch had been carried out on single-point toolmachining in comparison with grinding. It seemedto him that the negative rake of the grinding tech-nique, due to crystal formation, although giving abetter surface finish, may, in fact, impart greaterstress in the thin aerofoil sections. The surface finishresulting from single-point cutting was still the sub-ject of tests and it seemed to him a major problemto get down to a reasonable surface finish on thesemodels.

Tn model manufacture they were concerned withshapes which were flexible. They were machiningdown at trailing edges to a knife edge of say, 0.004in. thickness, and must balance the upward anddownward cutting loads, thereby giving greaterrigidity to the workpiece and stability to the result-ing model. He had already emphasised that it wasnecessary to determine the tool geometry before pro-ceeding to the development of special machine tools.There was the ability in Britain to develop thesespecial machine tools when the users knew what theywanted. The R.A.E. were getting to the stage nowwhere they were ready to go ahead with such develop-

ments, and had found some support in the machinetool industry.

In reply to Mr. Kinman, Mr. Potter said that themodels were made in anything from light alloy to the100-ton steel which had already been mentioned.

Mr. Kinman, on the question of finish, said thatthey had found light alloy was not a particularly goodmaterial for getting a good finish. The extent towhich the single-point cutting tool could be used waslimited. It was not possible to take a chip of infinitelysmall section. For reasonable cutting conditions therewas an optimum, and above it and below it therewould be a bad cutting condition and therefore abad finish. He would be inclined to favour grindingwith a soft wheel; he thought it would mean lesspressure, though he had no actual evidence for that.

Mr. E. B. Loewendahl (Assistant General Man-ager, Central Tool & Equipment Co. Ltd.) said thatmention had been made of lubricants for the cuttingoperations themselves, but there had been no referenceto any kind of new lubricating methods for machinetool slides. For example, the use of molybdenum di-sulphide had recently been introduced by a number ofpeople, and he would like to ask to what extent thatimproved the stability of slides when tightening closeron the slide gibs, exploiting the improved lubricatingpossibilities given by materials such as molybdenumdisulphide, either in solution or applied in a pasteor solid compound. Had the Authors had any exper-ience in that direction, or carried out experiments?

Mr. Kinman said that they had done so and hadfound that the use of molybdenum disulphide appliedto the slideways before lubrication was of consider-able benefit, and reduced the co-efficient of friction by50%, and therefore, stickslip was reduced. They hadalso obtained better results by using lubricating oilscontaining active polarised additives which wouldadhere to the slides by creating an adsorbed layereven if the pressure on the slideways forced the lubri-cant out. A combination of molybdenum disulphideand a correct lubricant would undoubtedly effect abig improvement.

Mr. W. S. Hollis, B.Sc.(Eng.), A.F.R.Ae.S.,(Assistant Director, Aircraft Production DevelopmentDirectorate, Ministry of Supply), raised the questionof temperatures at the tool face. He thought it wasnow fairly well known that machining speeds and theconsequent temperature had an effect on tool wear.Work done by Dr. Bowden at Cambridge had shownthat there could occur on the tool face formations ofintermetallic compounds which were knocked off bythe oncoming chip stream. Trigger in the U.S.A. hadshown that temperatures on the tool face could reach1000° - 1100°C. The junction between the chip andthe tool face at those temperatures caused a migrationof the metallic binder to the chip, thus acceleratingcrate ring of carbide tools. Obviously the B.S.A.Group must have investigated similar work and mightbe able to comment on it. The Authors had given, itwas thought, a temperature of 500°C. without anyrelation to the higher speeds of cutting.

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Mr. Kinman replied that they had given thematter attention in an empirical way, and their find-ings on the high rake tools tended to confirm the workof other investigators. Failure occurred by mechanicalbreakdown of the cutting edge due to its fundamentalweakness. They also found, in the field of lubrication,that when using a high rake with steel a plain coolantwas the most effective and an active cutting oil was ofno use. In the mists which they used for cooling theywent from a high concentration to plain water andobtained the best results from plain water.

The effect of lubrication was particularly marked inthe case of titanium. Their dynamometer readingswhen drilling titanium with an unsuitable lubricantshowed an extremely violent oscillation which in-dicated a very strong degree of stickslip. Correctlubrication removed that and gave them a smoothcurve. There was a high temperature at the interfacewhich could be reduced by using high rake tools or,to go to the other alternative, by using carbide toolswhere these were suitable, which would stand this hightemperature.

Mr. T. S. Lister said that in the case of the veryhigh tensile steels their chemical composition seemedto reduce the tendency to crater on carbide, and thathad enabled them to show that the cast-iron grades ofcarbide seemed to come back into their own. Hepointed out that there was no longer, therefore,the disadvantage of the rather poor mechanicalproperties with titanium. That was an indication ;he would not say that it was established.

Mr. Lister agreed with Mr. Hollis that 500°C.was not a true face temperature ; it was going to bemuch more than that.

Dr. D. Fitzgeorge said his personal opinion wasthat the temperature at the actual point of contact ofthe chip with the tool face was very high, and wellabove the melting point of the material. That was apet theory of his. The time of contact was so verybrief that the material could exceed the melting pointand yet retain its crystalline state. When chip sec-tions were examined, evidence of excessive shearingwas seen in the surface layers of the chip which hethought was due to the high temperature. In a thinlayer, he believed that the temperature was very highindeed.

Mr. Hollis remarked that he could confirm thatalso, because from work which he had seen there wasa distinct blueing of the chip on the underface com-pared with its top face, confirming that temperaturedid not persist as a bulk temperature throughout thechip; in other words, it was a surface temperaturerelating entirely to the sliding of the chip over the tool.

Dr. Fitzgeorge pointed out that Fig. 11in the Paper showed the result of a theoreticalinvestigation* into the chip temperature distribution,the information having been given to the Authors byM.E.R.L. That was interesting and showed thistemperature gradient.

*RAPIER, A. C. " A theoretical investigation of the tempera-ture distribution in the cutting process ".

Brit. Jour. Appl. Phys. 5, 11, 1954; 400.

Mr. Mark H. Taylor (Managing Director, Taylor,Taylor & Hobson Ltd.), commenting on theconcluding paragraphs of the Paper, said thatthere had been some moaning about the machinetool industry. A great deal of useful informa-tion had been brought to light in the very instructivePaper which the Authors had presented. They hademphasised how much there was that it was necessaryto know about requirements and performance beforeit was possible to deal with the machine tool problemproperly. He imagined that there were many peoplepresent who, having heard the Paper, now felt a greatdeal more confidence in what was being done thanthey had felt before. He suggested that there was nowa case for some group to come together representingthe machine tool trades on the one hand and the air-craft industry on the other to get down to the prob-lem and emphasise the most important needs of theindustry as a whole.

He thought that there were many problems. Forexample, the machine tool trade might have a de-mand for one particular machine, and it was difficultto see the justification in present circumstances for.setting a design team to work to meet the require-ments of one member of the industry. He thoughtthat there was a case, therefore, for a strong groupdrawn from both sides to work out what were themost important problems and see whether the machinetool industry could not provide a range of machineswhich would satisfy a large number of firms in theaircraft industry, and not just one or two. It mightwell be that, if anything substantial were to be done,some of the prototype machines would have to benationally supported.

Mr. Oliver said that Mr. Mark Taylor's remarksdid not call for a reply, but he thought that they werea most constructive underlining of the conclusion to-wards which the Authors had been fumbling. Themore experience he had in research and developmentthe more he felt that Lord Kelvin's dictum was appo-site, namely, if it was possible to specify a problemone was half-way towards its solution.

Mr. J. Cherry (Senior Lecturer, College, of Aero-nautics, Cranfield) congratulated the Authors on theirPaper and particularly on emphasising the advantagesof basic machinability research. They referred towork on machining 100-ton steel in which they hadincreased the angle beyond that which he had usedin his investigations, from 15° to 40°, increasing thetool life from 36 to 90 minutes. That did not surprisehim; it was probably the result which would beobtained when using that reduced feed rate. Thefeed rate had been reduced to just over .003". Hispoint was that if information was to be useful toproduction engineers it must be related to cutting con-ditions, such as depth of cut and rate of feed. Thelife of the tool would be governed by the heat gener-ated at the tool edge, as had already been pointed out,so that if the cutting conditions and the rate of feedaltered, the cutting life would alter.

At Cranfield what they were endeavouring to dowas to produce information of a nature which could

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be used practically by the aircraft industry. Theywere carrying out a research programme of machiningtough materials—titanium, Nimonics, S.90 and so on—in which they intended to produce data whichwould give machinability relationships with regardto a range of practical feeds and a range of practicaldepths of cut, so that planning and production engin-eers would be able to select the speeds and feeds forthe particular tool life which they required, and beable to specify standards of performance in the work-shop, which was most important. It meant that priorto the job being done on the shop floor, a reasonablestandard could be set as a target for the foremen andthe operators. He would, therefore, like to supportthe Authors in emphasising the advantage of this basicmachinability research and in showing how it couldeventually be given to production engineers and usedfor setting shop floor standards.

Mr. G. I. A. Spittle {Production Manager, Thede Havilland Engine Co. Ltd.), commenting on thereference in the Paper to ways in which metallurgicaltreatments could improve machinability, said thatvariations in machinability were obtained in steelswhich were nominally of the same physical propertiesand to the same specification. He would like to askthe Authors whether there was scope for improvingthe consistency of machinability by tighter grain-sizecontrol in the manufacture of the steel.

Mr. Lister replied that in his view there wasroom for something to be done in that direction.Moreover whilst there was a connection betweenphysical properties and machinability, it had also beenshown by some of their recent work that there wasan even more important connection between chemicalcomposition and machinability with these hightensile materials which were now of so much interest.For example, the work which they had done on the3% chromium steel would seem to indicate that atthe same tonnage it was very much more difficult tomachine than the 4£% nickel steel in the same con-dition, and that was probably more important thangrain-size. They were going to have to think veryhard about the possibility of making greater use ofalloying elements in those steels which the aircraftindustry found it necessary to machine under theseconditions.

Mr. N. Stubbs (Editor, " Metalworking Produc-tion "), on the question of ceramic tools, said he hadbeen astonished when he went to the Chicago Exhibi-tion to find that firms in America were now develop-ing ceramic cutting tools. A good deal of work hadbeen done on the subject in Britain, but he understoodthat it had been more or less dropped at the moment.It would be unfortunate if this were to become an-other example of something being started in thiscountry which the Americans took up and developed.It was also true that the Russians were doing a greatdeal of work on ceramic tools. Only the other daysomeone returned from the Prague Fair and aftervisiting various factories in Czechoslovakia where hefound that they were using Russian ceramic toolsactually in production. Mr. Stubbs had three of the

tips which this visitor had brought back with him.Mr. Oliver might like to comment on the point. Itseemed a pity that Britain should drop developmentwork on ceramic tools.

Mr. Oliver said that this was a very importantpoint, and a somewhat delicate one so far as he wasconcerned. Their laboratory had worked very hardon the ceramic tool problem for a number of years.They could never quite say that they had reachedthe point where they had overcome all the problems,or that they had one of those foolproof commercialtools which could be sold to everybody without quali-fication, but they did reach a point where the workwas of sufficient promise to justify increased interest.

The original stimulus to develop ceramic tools hadbeen the need for metal economy in view of shortages,at a time when they were wondering whether theywould have enough tungsten and what they would doif they had to put tungsten into other alloys. Apartfrom that, however, the ceramic tool had the tremen-dous advantage of possessing outstanding wear resist-ance. In some cases the wear resistance was aboutfour times that of the best tungsten-carbide hardmetal. There was the difficulty that, for instance,the chip coming from a high tensile steel (whenturning with a ceramic tipped tool) tended to attackthe edge of the ceramic tip and cause a certainamount of breaking along the free edge of the tooltip, and sometimes that spread to the cutting edge.If that happened, the tool was finished for the timebeing. To set against the attractive low cost, therewas the problem of fixing it to a shank. They hadovercome that after a good deal of hard work. Theynow found that American practice appeared to favoura clamped tool much more than was the case in thiscountry, and most people were getting successful re-sults by making a fairly massive bar of the ceramicand clamping it, and in that way by-passing some ofthe earlier problems.

Another interesting point was that there was atremendous range of new ceramics which could bedeveloped for this purpose. Some of them which hada very smooth, soapy appearance turned out in prac-tice to be superior on light alloys. Some which werewell known in this country, the Sintox type, turnedout in certain circumstances to show superiority incutting very abrasive material, and might come backinto their own in connection with atomic energy re-quirements for machining graphite. Graphite was verydifficult to machine, especially after it had been re-fired and recrystallised. When he had first thoughtof the problem he had imagined that it would beeasy, because it would be self-lubricating and every-thing would slip and slide all over the place, but itturned out to be quite the reverse, and due to internalchemical bonding graphite was one of the most diffi-cult materials to machine, as judged by tool wear.The tool wear in machining graphite was stupendous,and so far the atomic energy piles had been machinedby using inserted high-speed steel milling cutters ata very high rate of consumption.

The object of his remarks was not so much to saywhat the Authors knew about ceramic cutters or had

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done on them as to support Mr. Stubbs in his conten-tion that the ceramic cutter was by no means dead.It would undergo further development, and forspecialised applications it would come into its own,but there should be no attempt to make it do every-thing.

Mr. S. G. E. Nash {Deputy Chief DevelopmentEngineer, Bristol Aircraft Ltd.) supported verystrongly what Mr. Mark Taylor had said about thenecessity to get together on the question of machiningthe steels which were to form the structure of thenew generation of aeroplanes. There was a need, hesuggested, to implicate some more bodies in thismatter than the individual aircraft manufacturer andmachine tool maker, because it was fair to say thatthe requirements of the aeroplane would not be the

same for low Mach. Number and high Mach. Numberplanes, or for small research aeroplanes and bigbombers. On the other hand, they did not yet knowvery much about the structural properties of thosematerials in regard to such characteristics as highelastic modulus and the retention of it with increasingtemperature and so on. It would probably be neces-sary to bring in the steelmakers, because otherwisethere would be a great many development problemsto solve, which would take up a great deal of time.He thought, too, that the Ministry of Supply had apart to play in formulating the full range of aero-planes over which these materials were likely to beutilised, because otherwise there would be the dangeron which Mr. Mark Taylor touched, namely, of hav-ing ad hoc solutions to individual problems insteadof a general solution to the whole range of problems.

"CONTROL OF PRODUCTION PROCESSES"

Discussion -— concluded from page 252

The Chairman, in closing the session, said thatMr. Smith had brought to their notice some of thevarious processes with which they had to deal in themanufacture of aircraft. The theme of the Conferencewas speeding aircraft production. He felt that if theproduction side took these processes under their wing,and if the development engineers, the planning officesand so on became as interested in them as they werein cutting materials, assembly and all the otherproblems, they would make a large contribution to the.speeding up of production.

There was no doubt that these modern techniquesof X-rays, radiographic examination of materials andso on could be a means of saving a great deal of time.There was nothing worse for the production executivethan to have a complicated forging or casting 90%machined and then find a flaw in it and have to start

all over again. By the use of these processes and ofother facilities which were available they could havemuch more certainty of a production run.

Mr. Smith had also referred to cleanliness, whichwas certainly the key to the solution of manyproblems in the factory — surface adhesion, anodisingand plating problems and so on. This was mostimportant, and could be secured if the productionpeople would take an interest in it.

Interest-in these processes and the full use of themmust be initiated from the top and go right down tothe floor level, where everyone must realise theirimportance. It only remained for him to thank Mr.Smith on behalf of the whole Conference for a veryinstructive and comprehensive Paper.

The Conference then adjourned for half-an-hour.

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