FORGING IN CLOSED DIES

[Music] we take you now on an exciting tour of an industry that forges parts out of hospitals to make them safer and more dependable for airplanes autos beans and tools down through the ages when something made of metal to stand shock and strain and take hard punishment it was always for verged this is the story of how forged parts are made [Music] there what time when the ring of the anvil was a familiar sound in every town and village but that was a long time ago so long in fact that some might think the blacksmiths craft is one of the lost arts and belongs to the days of our grandfathers actually this is far from true although the art of forging is as old as history itself its practices have been transformed to fit our modern needs today's Forge is a modern oil or gas burning furnace where billets of special quality steel are brought to forging Heat the blacksmith's hammer has grown to a powerful machine that multiplies the strength of his muscles a thousand four [Applause] his crude anvil now appears as it carefully may die that shapes the hot metal with Swift precision [Applause] thus the skill of the Smith as important now as it ever was has been aided and abetted by many other skills so that now we can forge the mettle faster reproduce the desired contours exactly and as many times as may be needed a fundamental fact about forging is the quality improvement that hot working imparts to the metal this is a natural consequence of the forging process itself which allows the original grain flow of the metal to conform to the contours of the finished piece it works in our favor equally well whether the forging blow was struck by the hand hammer of the blacksmith or a thousand-pound board drop hammer or a 50,000 pound steam-driven giant but huge forgings like this are the exception not the rule to learn what forgings really mean to us in our daily lives let's take an example we all know about for instance the family car it's a convenience we all take for granted and one would have a tough time getting along without it takes a lot of forgings to build a car normally of course they're concealed beneath the handsome exterior but if we just dissolve that exterior away leaving only the vital chassis then we can take a really good look at its works let's start with the engine whose component parts are made of many materials and by many processes the cylinder block and manifolds are cast iron in the distributor we find a shaft that is machined to size and shape from solid bar stock fan blades are stamped from sheet steel and so are cylinder head cars valve rocker arms are steel forgings and so are many of the vital parts that transmit the engines power connecting rods crankshaft and transmission gears Universal joined yokes and crosses and differential gears and pinions and in the chassis the steering knuckle arm and kingpins are all forgings our car is thus a beautifully integrated whole built up from many kinds of parts each suited to its particular kind of service where maximum strength and toughness are essential these parts of forgings because forging develops the utmost quality in the metal through refining and controlling its grain structure a connecting rod is a first-class example of this here is the die in which the rod is made its to matching halves contain the impressions that correspond to the shape the rod in use the dies amounted in a drop forging hammer the lower half fixed while the upper half is fastened to the RAM which can fall freely to bring the two matching halves together the connecting rod starts as a steel blank of the proper size called in the trade a multiple which is heated in the furnace until the steel becomes somewhat plastic and will flow under the blows of the hammer [Applause] here's what the rod looks like after trimming and cleaning this one has been cut in two and the exposed surface polished then fetched with acid this reveals how the grain structure conforms to the shape of the piece concentrating the grain density and fiber formation at the points of greatest stress most forgings are made in drop hammers one widely used type is the board drop hammer it gets its name from the hard maple boards that are attached to the RAM at the top of the frame they pass between but do not quite touch continuously running rollers whenever the ram has fallen to deliver a blow to the work the rollers automatically press against the boards and drive them upward carrying the RAM up to its top position the boards are caught and held by wedge action until the hammer man releases them for the next blow this cycle will repeat itself automatically as long as the treadle is held down this hammer is rated at 2500 pounds that being the weight of the RAM board hammers run up to about 7500 pounds and make forgings up to about 30 pounds another kind of gravity drop hammer is the airlift hammer instead of boards to raise the round and air cylinder and piston do the work operating the treadle lets the RAM fall freely of its own way an important feature of the airlift is that that how a man can control the length of stroke varying the blow from light to heavy this is a steam drop hammer they are usually built bigger and heavier than gravity hammers run in falling weight up to 50,000 pounds and use a double-acting steam cylinder to raise the RAM and to drive it downward so that the force of the blow is greatly increased the RAM is automatically kept moving up and down between working strokes in order to prevent condensation of steam in the cylinder and valves by varying the steam pressure the hammer man can deliver a light or heavy blow as required the hot steel multiple usually has some surface scale as a result of heating and this is removed by an air jet or steam nozzle steam hammers using closed eyes produce drop forgings weighing up to several tons you've probably noticed how the hammer man uses different cavities in the die as the work progresses the most important reason for this is that full development of proper grain flow in the metal requires progressive forging steps to show how this works out here's a typical die it's two halves laid out so we can study these steps and here we have a number of partly finished forgings to show what each step does this is the fullering impression and is the first one used holding the multiple in this position reduces the section of the metal for the shank of the rod the edging impression is next it is used to gather the stock where it will be needed for the largest sections such as the big boss on the crank end in blocking the next step several blows form the hot metal into approximately its final shape the final operation is done in the finishing impression now all details of the final shape appear the maximum improvement in the quality of the metal has been achieved and the piece is ready for trimming here is a set of trimmer dies consisting of the die and the punch when set up in a press it will shear the flash off cleanly leaving a finished forging of the exact shape required needing only a bare minimum of machining before assembly some forgings are made in another type of equipment called a forging machine or upsetter of which this is an example in upset forging the hot metal has worked not by hammer blows but by applying squeeze pressure to the heated portion of a bar of stock displacing the metal and forcing it to fill a cavity in the dye the dye itself is made in two halves which open to admit the stock and close to Grippit I played on each work stroke of the machine the finished forging appears on the end of the bar of stock and needs only to be cut off a job usually done with speed and accuracy by a fast cutting hot saw looking down into the machine from above we can see that the actual displacing of the metal is done by a ram or header that moves into the die cavity on each work stroke these wooden models show how the header operates moving into the cavity from the rear of the machine this is called a three pass die with three cavities and three headers corresponding to three progressive stages in forming the metal to its final shape the first two headers are hollow removing a portion of one will let us see just how it works the blank is merely a bar of forging steel heated to working temperature it is inserted in the die cavity which then closes around it gripping the bar tightly at this point now let's look inside the die and see what happens when the heading tool is brought into position pressing on the end of the bar with great force it shortens and expands it to fill the hollow in the header then withdraws now the piece is transferred to the second cavity and the Rann moves in again this further shortens and expands the piece now it is ready for the finishing cavity or the final pass this time the header a solid bar expands the stock to the full diameter of the finishing cavity when it withdraws the completed forging may be removed from the die to make larger or more complex parts dies with more cavities and headers are used this one with four passes produce this forged blank for a gearshift counter shaft this gear cluster forging was made in a similar set of die cutting it at 2:00 and etching with acid shows the control of grain structure and fiber formation achieved by upset forging which results in a finished part of maximum strength and durability another means of forging by the use of squeezed pressure is the mechanical press presses like this are capable of exerting up to several thousand tons of pressure on the hot metal this press is making shell casing basis the simple round shape is very well adapted to high speed press production only one die cavity is needed for this forging although two strokes of the press are required the first one upsets the metal blank breaks the scale and partly positions the grain flow on the second stroke the upset blank is forced into the dye impression which gives it its final form and finish for large forgings of aluminum or magnesium a hydraulic press is often used this one is capable of exerting 18,000 tons of pressure and even larger ones are being built here we see aluminum alloy being worked into an impeller wheel for a jet engine right now a billet of the alloy heated to forging temperature is being pre worked between flat dyes to improve its grain structure next comes the first pressing or blocking that brings the billet roughly to shape then in a second I the finishing strokes give the forging its final form as in any other kind of closed die forging the hot plastic metal is forced to flow step-by-step into the contours of the finished piece with its grain structure developed and improved at each step in addition to hammers and presses auxiliary forging equipment is often used for example forging rolls reduce a short thick section to a long thin one or modify the cross section of the stock prior to forging in this case partly finished forgings are being elongated and tapered to make tractor gear shift levers some preparatory forging is done with plain flat dies the method is called Smith forging and is here being used to make a tongue hold on this billet to prepare it for a closed die hammer this is a trip hammer or held hammer another type of auxiliary equipment a typical use is drawing out and tapering large stock preparatory to finish forging in a closed eye thus making for a simpler die in the drop hammer this like all other auxiliary equipment is one more means of utilizing closed dies to the best advantage because it's the closed die and all the technology that goes with it that combines the benefits of mass production with the fine quality of forged metal so the die itself is the focal point of the whole process and the making of the dies a vital part of any forging plant die blocks are made from special alloy steel forged to the dimensions needed for each die to be made and heat treated to assure maximum hardness and die where the face of each die block is dressed in a surface grinder this will result in a smooth accurate surface upon which to do the layout work now the die maker has begun the layout work the outlining of the die impression on the face of the block when this is completed the impressions are sunk into the die beginning with the finishing impression that gives the forging its final size and shape it is located near the center of the die so the weight of the falling Ram will be centered on the forging when the completed forging dies are finally installed in the hammer and lined up carefully for exact registration of the two halves then the painstaking work that went into the planning making and checking of the dies gives assurance that they'll do their work perfectly from the first forging on to make the enormous number of forgings in use today requires a vast variety of high-grade steels each different alloy designated by color code and SAE alloy number has been specified to meet the requirements of a particular forging application to make certain the requirements will be met samples of every lot are marked out for analysis by the forging quality control laboratory careful chemical analysis double checks the composition of the alloy physical properties are determined by harden ability and other mechanical tests microscopic analysis will reveal grain size and crystalline structure which have a lot to do with the behavior of the steel if a particular lot of Steel gets the nod from the metallurgist it is OK to cut up into multiples according to the size and weight of the forging to be made this is done by hearing the bars either hot or cold or sawing them when the bars are too big to shear or when squared ends are needed forging multiples cover a tremendous range in size and weight this little blank weighs about an ounce and will be forged into a carburetor link that weighs even less on the other hand this mass of multiple weighing well over a ton and requiring a crane to handle it will be hammered into a landing gear cylinder and struck for a big airplane nothing could be simpler informed then the multiples from which forgings are made yet from these elementary shapes a few swift blows of the hammer can produce an almost infinite variety of useful forms each with all the strength toughness and durability that is inherent in the process of forging hot steel over 600,000 different forgings are being made today and the number is constantly growing let's have a look at how some of the more interesting of these are made an automobile crankshaft is certainly interesting enough to start with here's the finished crankshaft forging alongside the billet from which it was made this is a crankshaft forging unit consisting of two steam hammers and their auxiliary equipment the hammer nearest us is the first one used and does the preliminary forging it's die carries the rolling impression and the first and second blocking impressions [Applause] [Applause] in the second hammer the die has only one impression thus the power of the hammer is concentrated on the forging during the finishing blow [Applause] the tremor press is located near the finishing hammer and the crankshaft is trimmed hot the flash remains on top of the die while the forging falls through tools for the dentist and surgeon are a far cry from the heavy crankshaft but the inherent strength and toughness of forged steel are as important to one as to the other these forceps are made from two similar forgings assembled together they start as a bar of special alloy of stainless steel and in a very short space of time the hammer has forged another pair of forceps small parts can often be produced economically by forging more than one from the same multiple this die has three identical cavities and makes three parts at once from each bar of stock the group of forgings together with their common flesh is called a platter one stroke of the trimmer punch suffice is to free all the forgings from the flash at once now let's look in on a really heavy forging job this billet of special alloy steel is about to be forged into a part of a catapult for launching jet planes from an aircraft carrier this is or will be a sizable fortune weighing some 1,300 pounds it's unusual shape calls for a die with a cavity 12 feet long the top half of the die weighs 14 tons the RAM weighs 20 a total of 68 thousand pounds of falling weight with the added force of a full head of steam behind it [Applause] well that will give you some idea of the size range of forgings but even in a whopper like this one the same principles of development of proper grain flow of improving the metal quality still hold one of the most interesting in spectacular uses of forgings is in the modern turbojet airplane engine here's how such an engine begins this block of Steel is about to be forged into one of the compressor wheels the stainless steel alloy used is very tough and resistant to defamation even one hot and calls for one of the biggest of the steam hammers [Applause] after being Finnish forged in another hammer this is what the wheel forging looks like here the blades for the engine are being finished Forge this is one of the forged blades after trimming here's how it looks after the finishing work is done and here's how it fits into the wheel of course there's a great deal more than forgings in a turbojet engine but just as we have found in other fields where conditions are most severe where stresses are the highest where human life depends on reliability there you're most likely to find forgings in use as the pilot starts his engine runs it up and takes off the sound and fury of the Jets can speak louder than any words for the ability of forgings to do the tough jobs well and for the contributions they make not only to our standards of living but to our very safety as a nation [Music]