LATEST TRENDS IN MACHINING
Latest Trends in Machining machine was fully automatic that provided the manufacturing solution to bevel gearing used in differentialdrive. The most advanced gear cutting machine of the molding generating type was Fellows’ gear shaperof 1897 (Fig.1.6) that was invented just in time to produce gears that would be needed for automobiles.Edwin Fellows designed the teeth of his cutter in such a way that one cutter could be used to makegears of any diameter provided the pitch was the same. The only qualification was that its teeth mustbe of the specific helix angle the cutter was designed to produce. To make hardened cutters for hisshaping machine, Fellows created another machine. Hobbing was the last to come. The first attempt to cut gears by using a worm with teeth on it wasmade perhaps by Ramsden in England in 1766. In 1835, Josheph Whitworth produced a machinethat would hob spiral gears. But the hobber did not become practical until Pfauter, working in Germanybuilt a machine with a cutter axis that was not at 900 to the gear axis. There were many problems indeveloping the process, but by 1909, there were at least 24 firms manufacturing gear-hobbing machines.CUTTING TOOL MATERIALS Robert Mushet first produced the improved tool steel in 1868 in England. That proved to be far superiorto carbon steel used for tool earlier. With this new tool steel, John Fowler & Co. of Leeds turned ironshafts in the lathe at the rate of 75 feet per minute, and when machining steel wheels in their boring mill theycould make roughing cuts 1/2 inch deep. Frederick W. Taylor (1856-1915) is credited with the revolutionaryresearch on cutting tool materials. In 1900 Paris Exhibition, Taylor amazed the visitors with chips peelingaway at blue heat from an American lathe while the tip of the cutting tool was red hot. Taylor was the first to carry out methodical experiments with cutting tools that lasted over 26 years andcost over $ 200,000 - a large R&D expenditure for the time. Mushet’s steel contained 7% tungsten, 2%carbon and 2.5% manganese. Taylor with Maunsel White in the Bethlehem Steel Works discovered thatchromium was an effective substitute for manganese used to give the steel self-hardening character, whilegiving better performance. They then increased both the chromium and tungsten (the tungsten to 14%)and added silicon, which was found to increase shock resistance. They found that if a tool is heated to20000 F (just below fusion point) instead of 15500 F, cutting speed would be increased to 80 to 90 feetper minute (as against 30 feet per minute in earlier case) before failure occurred in the same time. Additionof 0.7% vanadium produced further improvement. But with this radically improved new cutting material, all the existing machine tools were to becomeobsolete. As proof of this, the Ludwig Loewe Company, A.G., a reputable German machine-tool builder,tested the new steel tools in one of their lathes and drilling machines, running them so as to give maximumperformance. In four weeks both machines were reduced to junk! Main drive spindles were twisted;thrust bearings were destroyed; keys fell out of gears and shafts; cast gears were broken and the lubricationsystems proved inadequate. Taylor had not only given the machine designer a new tool but also thespecifications by which its performance could be translated into terms of tool pressure, speed and feed.Cemented tungsten carbide was first produced by Krupps of Essen, Germany in 1926. After the LeipzigFair in 1928, where the carbide tool was demonstrated under working conditions, it was an instantsensation. The introduction of tungsten carbide tools resulted in second machine tool revolution. this newcutting tool material also made possible the new machining technique offine boring. In Germany, ernstKrause used tungsten carbide to bore iron cylinders. He patented his process, which was adopted by themotor industry supplanting the planetary grinding machine that was used before it. 6
MACHINING - LATEST TRENDS SOME PRODUCTION MACHINE TOOLS In 1903, A. B. Landis patented an automatic magazine feed release for short cylindrical parts enabledefficient production grinding of connecting-rod pins. L.R.Heim obtained his patent for the centreless grindingprinciple in 1915. In 1922, Cincinnati Milling Machine Co. acquired Heim’s invention and introduced itsfirst production centerless grinder. The machine gained immediate acceptance in the automobile industry,where its 20in. diameter wheel was used to grind shoulder work like push rods and valve tappets. By1925, automobile valve stems were being finish ground on centerless machines at the rate of 350 an hour.It was necessary to plunge cut and retract the regulating wheel to release the workpiece. In 1905, bothNorton Co. and Landis Tool Co. offered specialized grinding machines for automobile crankshafts thateliminated torsion in the shaft by mounting the work on two live heads, counterbalanced by the journalbearings. A.B. Landis brought out his 1912 camshaft grinder that provided automatic feed from one cam to the nexton a shaft. Master camshafts were geared to the workpiece and were larger than the workpiece, thusreducing error. Norton also developed the camshaft grinder at about the same time. The machine enabledengine designers to specify one-piece camshafts of hardened alloy steel instead of having to build up thesecontrolling mechanisms from individually ground pieces. Broaching as production technique though probably dated back to Englishman Josheph Whitworth wasredeveloped in 1873 by Anson P. Stephens in America for its present potential in automobile industry. In1898, John N. Lapointe obtained the patent for pull-broaching which was till date being done by pushingthe serrated tool through a hole in the workpiece that was severely limited by the physical strength of thebroach under compression. In 1918, special form-grinding machines for broach production were developed,and the first hydraulic broaching machine was produced in 1921. Later, in 1934 external or surface broachingwas introduced. The automakers made strong impact on machine tools. With cut in assembly time for Model T from a dayand a half to an hour and a half, it was realized no machine shop could supply components that fast.E.P.Bullard Jr set about designing a new machine for multi-station manufacture. When it was ready, Bullardheaded for Detroit, and arranged for an appointment with Ford. Seated beside Ford was C. Harold Wills,chief of car design and factory operations. The two men listened attentively to Bullard, but, when they bothexpressed their skepticism, the machine-tool builder unleashed his strongest argument. “ Mr. Ford,” saidBullard, “How long does it take you to make a flywheel?” “Eighteen minutes,” was the reply. Willsnodded. “Will you test our machine if I guarantee to cut that down to two minutes?” Bullard asked. Fordsmiled, “Cut our time in half, and we’ll do business.” The first Bullard Mult-Au-Matic to arrive at the Fordfactory in Highland Park was subjected to a test run that lasted 54 days and nights. Finished flywheelswere taken off the machine at intervals of just over a minute.EVOLUTION OF NEW MACHINE TOOLS The history of manufacturing was marked by the development of mass production first in the automotiveindustry and was followed by the improvements in machine tools and cutting tools, and the introduction ofnew and better materials with which to manufacture the cars and other consumer goods. By early 1920smachine tool builders competed fiercely with one another in bringing out machines of higher productioncapacity, especially for the auto industry. The methods of transmitting power to machine tools were 7
Latest Trends in Machining constantly improving. Helical gears for connecting parallel shafts were used more and more to providesmooth transmission. Special steels and heat-treated gears were common, hardened-and-groundgears were gaining favour where greater accuracy was required. The use of motor drives and of ballbearings and a growing trend toward hydraulic instead of mechanical transmissions were the outstandingdevelopments in machine tools of the 1920s. Centralized control became popular and, in severaltypes of machines, it was possible to shift speed instantaneously, without stopping the machines,through a combination brake-clutch. By 1927, another definite trend toward single-purpose equipmentof so-called manufacturing type and away from machine of a more universal naturebecame noticeable.The design of the single purpose machine was such that only a few key parts needed to be interchangedto make the machine adaptable to a wide variety of works. The interesting involvement of changes of equipment during a model change will be clear from thedetails of work done during a changeover from Model T to Model A by Ford in 1927. To do it, thecompany spent nearly $ 10 million for the purchase of 4500 new machine tools and alteration of15,000 more. Preparing to make the new rear axle alone necessitated construction of an entire groupof machine tools. Some 160 gear-generating machines were completely rebuilt, $3000 each, toproduce two gears for the new rear-axle assembly. Ford introduced a new V-8 model ($460-$650)to replace the Model A in 1932 and became the first company to use a cast alloy-steel crankshaft inplace of a forging. World War II put a stop to car industry, as most of the plants were requisitioned to produce war machineryand equipment. After the War, many automakers were in bad shape. But the effort of rebuilding theindustry started with a new zeal and many new technological strategy evolved for the manufacturing of‘The Machine that Changed the World’. It is evident from activities such as setting up of an AutomationDepartment in Ford in 1946 that devoted to making equipment operate at its maximum rate (whichusually can not be done without automatic loading and unloading) and to making work safer byeliminating hand loading of presses. By Oct.21, 1948, Automation Department had approved more than500 devices, costing $3 million, that were expected to increase production by 20% and to eliminate1,000 jobs. Most of the early work was on presses and included sheet feeders, extractors, turnoverdevices, stackers, loaders, unloaders, etc. Next automation project related to the machining line for engine block, where automation meant mechanicalhandling of blocks in, out, and between machines. Morris automobile plant in Coventry, England in 1924used a new approach to automation. A number of standard machines were attached to a continuous,13.8m long bed to perform 53 operations on engine blocks. The machine had a total of 81 electric motors.In 1929, Graham Paige installed in its cylinder department a system of operations that included automaticjigs and fixtures with transfer bars to move work from machine to machine; all the basic elements of themodern transfer machine were present in the system.With increased automation for higher productioncame the increasingly specialized machinery for manufacturing processes.NUMERICAL CONTROL AND COMPUTERISED MACHINING Shortly after World War II, John T. Parsons envisioned the use of mathematical data to actuate amachine tool. An electronic control system for machine tools was developed with the US Air Forcefunded program. The first commercial production based NC unit was built by Bendix Corp. and wasproduced in 1954 for machine tools introduced in 1955. By 1957, Barnes Drill Co. built a drilling 8
MACHINING - LATEST TRENDS machine with four parallel horizontal drilling spindles that moved on vertical ways to bring the desiredspindle into position, and only that spindle would then feed. In 1958, Hughes Aircraft and Kearney &Trecker worked together to develop a flexible automatic line comprising of three machines: one eachfor milling, drilling (and tapping), and boring. The three machines were tied together by handling equipment,and the whole system was under tape control. called a Digitape that was developed by Hughesaircraft. The entire line was called the Milwaukee-Matic Model I. In December 1958, a NC horizontalspindle multifunction machine ‘Milwaukee-Matic II’ was introduced. The machine was capable ofautomatically changing cutting tools in its spindle. The first numerically controlled machine or machiningcenter was born to make the beginning of the second industrial revolution. In 1960, the first controllerwith transistor technology was introduced. Integrated circuits (ICs) came in 1967 that permitted a 90%reduction in the number of components, as well as an 80% reduction in writing of program. NC andthen CNC have contributed immensely in changing the manufacturing practices in last decades.Today, even in automobile industry, dedicated machine tools are no more the preference. Flexibility forquick engineering/model change without any stoppage is becoming the basic demand from the manufacturingsystem. Computerized manufacturing provides the answer.
Latest Trends in Machining Section 2 MACHINING – LATEST TRENDS Quality characteristics in machining, General trends inmachining,Eemerging work materials, Machine tools-turning centers,machining centers, flexible manufacturing, agile manufacturing, Featureof advanced machine tools- main drive motors, spindles, linear motors;Modular design concept, CNC. , Tool condition monitoring, Accuracy ofmachine tools, Coolant management,Modular work holding systems,Automation.