Steel Metal

For aerospace component makers, a 5-axis, long-bed, 90kW/20,000 rev/min machining centre offers high aluminium metal removal rates - reducing cycle times by up to 40%

Chiron has developed new high-power, long-bed, five-axis machining centre concepts that are specially tailored to customers in the aerospace sector. These include 5-axis Chiron Mill machining centres with a 90kW, 20,000 rev/min spindle that allow customers to explore new possibilities in highly productive aerospace machining.

The massively powerful spindle allows major savings in cycle times - with aluminium removal rates of around 2.1/2 lb/min.

As Chiron’s managing director Richard Blake explained, ‘One of the major issues within the aerospace industry is that maybe only 2% of the billet material ends up as product.

The rest has to be removed.

That’s why poundage is the key to being cost-effective.

Most machines currently in use in the aerospace sector only have 40kW spindles.
Further reading

Turning centre has Y-axis on three turrets
Among eight super high-precision turning centres is a machine with Y-axis on three turrets, while pallet handling and bar-feeders will also be shown including a serv0-driven type

Vertical machining centre has swivelling head
A 5-axis vertical machining centre features a thermally stabilised head with motor spindle that swivels about the B-axis, while the fifth CNC axis is provided by a horizontal rotary table

Five-axis vertical machining centre is affordable
Offering simultaneous 5-axis machining at an affordable price, a vertical machining centre gives maximum versatility, as the trunnion table can be quickly, and easily, removed for 3-axis work

The latest Chiron machines with spindles in the 90 to 100kW range allow you to cut faster for the more cost-effective manufacture of components.

On wing components, for example, it would not be unreasonable to expect a 40% reduction in cycle times.’ He said that many of the high-volume machine tool makers aren’t interested in offering this kind of special capability, and that Chiron has set out to offer something over and above other suppliers.

This is also true of the long bed sizes available in Chiron’s Mill range.

A typical specification might include a 3m overall bed length with a twin rotary table configuration, where each table could take components up to 1.25m in the X axis.

This compares to a maximum of around 800mm on most mass-market machines - and many wing components will not fit on this size table.

The Mill series machines also offer 60m/min rapid travels in all axes, spindle speeds up to 20,000 rev/min, HSK63 taper spindle nose and 30 bar through spindle coolant.

With its long bed, the machine layout is designed for optimum spindle utilisation.

The moving column, with vertical fixed spindle or tilting fifth-axis head can, for example, serve two rotary tables on either side of a mechanically operated dividing door.

While the components on one table are being machined the other table is being loaded and unloaded, so maximum uptime is achieved.

To support this high level of utilisation the Mill machine is fitted with a background tooling magazine holding 92 tools that works in conjunction with a tool changer within the machining column to give chip-to-chip times of less than 2.9s irrespective of where on the bed the column is.

Rather than simply supplying a machining centre, Chiron UK and its parent company, The Engineering Technology Group, can deliver a turnkey package, with zero point hydraulic or vacuum fixturing supplied by its sister company Hyfore Engineering, complete with all programs written, parts proved out and with guaranteed cycle times.

‘We believe that this ability of Chiron and The Engineering Technology Group to offer a total package is a major benefit for our customers - a total philosophy that other companies can’t offer,’ said Blake.

‘To stave off overseas competition we need to be at the forefront of technology in the UK.

If we are not exploiting it to its optimum effect then we will lose out to Third World labour rates.’

Intended for precision 250mm diameter x 250mm component manufacturers, an advanced 5-axis machining system, with 40 pallets allows long unmanned operation

Matsuura has released the latest version of our globally acclaimed 5 axis CNC machine, the MAM72-25V. (MAM = Matsuura Advanced Manufacturing) Configured with 40 pallets in an exceptionally small machine footprint, this incarnation of the MAM72-25V is aimed at precision component producers who require proven unmanned running capability over long production runs.

Maximum component size is 250mm diameter x 250mm height (300mm diameter is optional).

APC (automatic pallet changer) options are: twin pallet/10 pallet/40 pallet.

A dedicated single table version is also available.
Further reading

Toolholders offer high speed machining accuracy
CNC machine tool spindle toolholding products for high speed machining, suit the most arduous machining environments that require proven tooling and absolute accuracy

Five-axis machining used for cylinder blocks
A V8 cylinder block, machined from solid in one hit and possessing a near perfect surface finish was machined in a 5-axis machining centre working to tight tolerances

The MAM72-25V (all versions) is capable of holding up to 240 tools in its ATC (Automatic Tool Changer).

The PC40 and PC10 machines can be assigned to hold a variety of different jobs in the fully integrated high speed APC.

The NC is the powerful Matsuura G-Tech (Fanuc) 30i as standard, with the option of a Matsuura G-Tech (Siemens Yaskawa) 840Di.

As ever with Matsuura Products, all spindles available across the range are designed and built by in house by a dedicated team in a clean room facility in Fukui, Japan, a facility which is mirrored at Matsuura’s UK Operation in Leicestershire.

A BT40 15,000 rev/min Matsuura Hi-Tech Spindle comes as standard with the MAM72-25V, with 20,000 rev/min and 33,000 rev/min spindles available as options.

The MAM72-25V has proven to be a firm favourite with UK precision subcontractors and OEMs alike, with the majority of supplied machines being configured with either a 10 pallet or twin pallet APC.

Due to the growing requirement in the UK to compete with ‘low cost’ overseas operations, Matsuura has seen a dramatic rise in the number of multi pallet machines capable of proven and reliable unmanned operation supplied in the UK.

We consider our full range of machine tools to be at the leading edge of proven unmanned running technology.

On April 17-19, 2007, Matsuura will hold its annual Open House - theme being ‘Lights Out Manufacturing’.

Practice covers the procedure for sorting ferrous metals using the electromagnetic (eddy-current) method. The procedure relates to instruments using absolute or comparator-type coils for distinguishing variations in mass, shape, conductivity, permeability, and other variables such as hardness and alloy that affect the electrical or magnetic properties, or both, of the material. The selection of samples to determine sorting feasibility and to establish calibration standards is also included.

Sorting Practice
The two techniques that are primarily used in electromagnetic sorting employ the absolute (single-) and comparative (two-) coil methods. The decision of whether to use single-coil or two-coil operation is usually determined by empirical data.

In the absolute-coil method, the equipment is calibrated by placing standards of known properties in the test coil. The value of the tested parameter (for instance, hardness, alloy, or heat treatment) is read on the scale of an indicator. In the comparative-coil method, the test piece is compared with a reference piece and the indication tells whether the piece is within or outside of the required limits.

In absolute coil method, a sample of known classification is inserted in the test coil, and the controls of the instrument are adjusted to obtain an indication. The test is then continued by inserting the pieces to be sorted into the test coil, and observing the instrument indication.

In comparative coil method, known reference pieces representing the minimum or maximum limits of acceptance, or both, are inserted in the reference coil and test coil. The instrument controls are adjusted for appropriate indications. The test is then continued by inserting the pieces to be sorted in the test coil, leaving a known reference in the reference coil, and observing the instrument indication.

The range of instrument indication must be so adjusted in the initial step that the anticipated deviations will be recognized within the range of readout according to whether two- or three-way sorts are to be accomplished.

Both absolute and comparative methods require comparing the pieces to be tested with the reference piece(s). Two or more samples representing the limits of acceptance may be required. In the absolute method the electrical reference is generated by a test piece. In the comparative method any electromagnetic condition that is not common to the test specimen and the standard will produce an imbalance in the system. The comparative method is usually more stable, as it normally suppresses all internal and external disturbances.

The testing process may consist of manual insertion of one piece after another into the test coil, or an automated feeding and classifying mechanism may be employed. In automated setups, it is sometimes necessary to stop each piece momentarily in the test coil while the reading is being taken, especially if low test frequencies are employed.

Significance and Use
Absolute and comparative methods provide a comparative measure for sorting large quantities of ferrous parts of stock with regard to composition; condition; and structure or processing, or both.

The comparative or two-coil method is used when high-sensitivity testing is required. The advantage of this method is that it almost completely suppresses all internal or external disturbances such as temperature variations or stray magnetic fields. The two-coil method is normally used when harmonic evaluation is employed for sorting.

The ability to accomplish satisfactorily these types of separations is dependent upon the relation of the magnetic characteristics of the ferromagnetic parts to their physical condition. These methods may be used for high-speed sorting in a fully automated setup where the speed of testing may approach ten pieces per second depending on their size and shape.

The success of sorting ferromagnetic material depends mainly on the proper selection of magnetic field strength and frequency of signal in the test coil, fill factor, and variables present in the sample. The degree of accuracy of a sort will be affected greatly by the coupling between the test coil field and the tested part and the accuracy with which the tested part is held in the test coil field during the measuring period.

When high currents are used in the test coil, a means should be provided to maintain a constant temperature of the test standard in order to minimize drift of the test results.

Needs for cost reduction in military and civil production of large tubes led to the development of the new manufacturing processes. Large losses in production of large-caliber cannons and other tubes forced factories to develop and apply manufacturing processes that permit fabrication of parts closer to required net shape.

The state-of-the-art improvement in technology is made possible through a major change in forging methods for large, hollow, high-strength steel alloys by use of a rotary forge machine developed by the Austrian firm GFM (Geselschaft für Fertigungstechink und Maschinebau AG).

The machine was capable of both hot and cold forging of hollow or solid cylinders having maximum starting diameters of 22 inches and a minimum hole size of 2.5 inches and will forge cannon tubes up to a maximum length of 33 feet. It was the largest machine of its kind - 195 feet long and weighing 935 tons.

The machine was located in the USA. This machine has a self-contained forging box in which the work piece is formed by four forging hammers that are axially symmetric and synchronized in such a way that rotational motion of the work piece is interrupted to permit hammer-to-metal contact while the work piece is immobile in order to avoid shearing or surface tearing of the forging. The forging hammers are mechanically driven, generating a maximum force of 1100 tons per hammer. The reaction forces are absorbed in the forging box and are not transmitted to the foundation as with conventional open-die forge presses. This results in a significant reduction in noise level with the foundation remaining vibration-free.

The complete forging sequence, including loading and unloading, is accomplished through use of a numerical control system. This provides a greater dimensional precision than is possible with conventional forging presses, as the latter are completely operator-skill dependent. With the use of a mandrel device on the machine, the cannon tube is forged with the proper size hole for subsequent finishing operations. Cannon tubes cannot be hot formed as hollows with open-die press forging methods.

Machine has two large chuck-jaw heads on each side of the forging box. Initially, the work piece is held by only one chuck-jaw. As forging proceeds, the chuck-jaw on the opposite side of the forging box picks up the partially completed forging and finally supports it entirely as the forging is completed. This permits cannon tube forging to be worked its full length in a single pass with minimum material loss.

Practice showed that material losses in rotary forge are around 8 times less then in conventional practice. It should be noted that "loss" does not imply discarding all the material, as most of it is remelted and recast to produce additional cannon tubes or other items. Since that rotary forge process begins with a hollow work piece that will be obtained from an electroslag refined (ESR) cast ingot, the material loss is markedly less than that for the conventional process.

In order to obtain an evolution of how well the rotary forge operation is controlled, the tolerances achieved during hot forging were measured. Wall thickness variation ranged between 0.044 to 0.060 inch. The repeatability was excellent since that machine is numerically controlled. To place these values in proper perspective, it should be realized that tolerances maintained for the conventional forging practice are achieved as a consequence of subsequent machining operations which include finish turning the external surface and then trepanning the hole in the solid forging. Rotary-forged internal diameter variations are small and less than one-half of those resulting from conventional practice.

Since that these methods were used also for production of cannon weapons, where the principal concern are material characteristics of the high-strength steel alloys employed, the influence of the rotary forge process on the material properties was an important consideration. A comparison was made of the properties obtained after heat treatment from conventional and rotary forged tubes for cannons. The mechanical property variations from tube to tube and also within a tube along its length have been determined. It would appear that there is a tendency for the rotary-forged material to display somewhat more uniform mechanical properties. It is equally apparent that the toughness values are consistently higher, and that, too, is beneficial since a greater toughness is associated with a higher fatigue life limit.

Experiments also were conducted to evaluate the cold forging operational capabilities of this rotary forging machine. It has been done in a single pass reduction of 17 per cent. In this case, the mandrel over which material was formed contained a mirror image of the desired geometry and the proper helix angle of rifling. The rifling form dimensions and tolerances were equal or better than those achieved by conventional rifling practice. In addition, the bore surface finish was better than that achieved through standard practice. The external finish obtained would be adequate with no further machining required as there are no detrimental surface discontinuities.

Tests were also conducted to determine feasibility of cold forging thick wall cannon tubes. Full size howitzer tubes were successfully cold forged from materials having initial yield strength of 176 ksi (12 bar). This was accomplished in a single pass with an average reduction of 15 per cent. The transverse yield strength is of most importance because the maximum firing stresses are operable in the transverse (hoop) direction. The cannon tube material specification requirements for yield strength and ductility have been met.

However, the toughness values achieved were only marginal and somewhat below specifications requirements. Additional work is required in terms of tooling optimization, thermal treatment, and the amount of metal flow required in order to achieve satisfactory mechanical properties throughout the finished cannon tube.

It is obvious that tremendous economic advantages and benefits can be derived from both hot and cold forging of cannon tubes. From the hot-forging application alone, it has been showed that costs of cannon tube forging was reduced by 50 per cent using this process. In the cold forging applications for thin wall tubes, where the rifling can be put in as part of the forming process, reductions of up to 40 per cent in fabrication times were achieved. There are also significant reductions possible in finishing operations of all large diameter and cannon tubes using the machine in the cold-forging mode, and such reductions reflected at lower costs.

Multilayer material is obtained by joining different metals producing a range of different good properties of the constituent metals in the obtained material, like:

good structural properties of one constituent metal,

good anticorrosive property, shearing and sliding properties or abrasive hardness of the other constituent metal,

good conductivity of one metal, and

good heat resistance of the other constituent metal.

It should be noted that price of the article made of multilayer material becomes quite low due to substitution, even up to 90%, of high grade alloys and scarce materials with cheap structural steel.

Low Carbon Steel – Stainless Steel

Bimetal in this particular combination, absolutely substitutes stainless steel in all types of steel structures, securing absolute corrosion resistance in the aggressive environments and very high toughness of the structure at the same time, the quality that stainless steel it self does not possess.

Selection of the basic layer of a bimetal depends on the following working conditions of the equipment made of that specific bimetal: temperature, working pressure and impact load. In most cases carbon and low-carbon steel with high yield points and steels resistant to ageing and so called "creeping deformation" are used as the basic layers of this kind of bimetal.

The secondary layer, i.e., the adherent layer secures high resistance to corrosion in the aggressive ambient and frequently chrome-nickel (Cr-Ni) steels are used as the adherent layers.

Technological character of bimetal considerably widens the scope of use of stainless steel in different industries. In comparison to stainless steel, bimetal is more successfully used in the construction of: reservoirs, tanks for aggressive liquids and gases, heat exchangers, digesters, mixers, agitators, hydroelectric power stations (turbine blades) dam gates, pipeline components, steam pipeline components, steam separators and many others.

Carbon Steel – Titanium

With the development of processing and chemical industry, high alloy Cr-Ni steels proved to be not enough resistant in many cases. Advantage of titanium over other anticorrosive metals is that when titanium corrodes, corrosion does not take place at some individual area or areas of the metal but uniformly over the whole area of the metal. Pitting or intracrystal corrosion is a very rare case.

Titanium its alloys in combination with structural steel, besides securing high anticorrosive resistance in an aggressive ambient, considerably improve the structure of the equipment working in acid-baths, like, hydrochloric acid, sulphuric acid and sodium chloride.

Steel Sheet Joined to Copper Sheet or Tombac (CuZn10)

The bimetal obtained by combining copper or brass with steel has a wide range of application in industry.

Three-layer bimetal strips are of special interest, they are used for making ammunition. These bimetal strips are also used in the automobile industry for production of cooling radiators, reservoirs and gaskets for motor-heads.

Bimetal Industrial Cutters

Bimetal cutters, compared to cutters made of uniform steel only, have many technical, technological and economic advantages. Firstly, in bimetal 90% cheaper structural steel substitutes for expensive tool steel and high speed steel.

In the case of bimetal only the cutting edge of a tool is made of quality steel. Use of bimetal makes the heat treatment, straightening, grinding and sharpening processes easier and similar.

In the event of bimetal cutters the possibility of burning of cutting edge during hardening is excluded because the heat is intensively transferred to the structural steel side. Hardness of the cutting edge of a cutter of this kind is high and so is the necessary toughness of the body made of structural steel. That is why they are absolutely safe for exploitation and safe even when they are in direct contact with any worker. These cutters are used in industries, like: paper, metal, wood, textile and similar.

Bimetal Sliding Bearing (Steel-AlSn20Cu)

A bimetal bearing comprises of a steel shell with high modules of elasticity, shell which makes a rigid bearing assembly, and a layer of the alloy used which makes the inside wall of the bearing. The hard components are capable of bearing shocks or impacts without causing any deformation while the soft base (plays the role of a shock absorber) absorbs those impacts or shocks and adapts to the journal.

Sliding bearing alloy has the following characteristics: ability of surface adaptation, ability of adhering to oil layer, small coefficient of expansion, good thermal conductivity, good resistance to corrosion in fatty medium and less sensitive to deformation at edge. These bearings are mounted to diesel motors of locomotives, ships, to compressors, aggregates, cranes, heavy vehicles and similar.

Bimetal Kitchen Utensils

Multilayer materials have bright prospects in manufacturing metal kitchen utensils because they have considerably higher thermo-mechanical properties compared to those properties of single-layer materials.

Manufacturing of bimetal kitchen utensils differs from the manufacturing of present generation metal kitchen utensils only in deep drawing of bimetal straight into utensils without any subsequent welding of heavy thermo-bottoms. By bimetal kitchenware has a very artistic look, its inside is made of 18/10 stainless steel while the outside is made of a high-polished copper or brass layer.

Heat Exchangers

Heat exchangers, particularly tubular heat exchangers are very frequent components of equipment used in processing industry. Generally, most of these heat exchangers are in direct contact with aggressive mediums during exploitation, so it is essential that their parts are made of stainless steel or titanium. Due to heavy consumption of high alloy and scarce materials, it is economic that massive heat exchangers are made of bimetal.

In the case of tubular exchangers, welding of pipes to the pipe wall of exchangers is a bottle-neck in the manufacturing process. Technology of welding by explosion energy secures absolute homogeneity of the joint, because it creates a genuine metallic connection between the pipe and the pipe wall of the exchanger where toughness of the joint is higher than toughness of the weaker metal.

Welding of metal by explosion energy is widely used for manufacturing different types of panel or plate heat exchangers also. Cooling ducts are cut on a steel plate first, over which a thin plate layer of stainless steel or copper is built-up (welded). Deformation of ducts during exploitation itself is negligible because they cool intensively during exploitation. Repairing of heat exchangers (due to wear of the thin plate of stainless steel or copper during exploitation) heads to welding of a new plate by explosion energy.

Electro Contacts

Bimetal Steel-Aluminum serves as the intermediate joint of steel and aluminum in the structures for obtaining aluminum. Today bimetal, obtained using explosion energy, is the only dependable solution for electrolysis of clay, because use of this type of bimetal reduces electrical resistance of the contact even five times and extends the exploitation time more than double compared to these factors of bimetals obtained with other technologies of joining aluminum and steel.

Trimetal Sheet (Steel-Al-Alma4.5) for Shipbuilding

Aluminum and its alloys have a very bright future in making different structures which are exposed to sea or salt water ambient. Lately aluminum alloys are more and more used as structural material in shipbuilding where the lower construction or hull of a ship is made of steel but the inside metal sheet of hull is aluminum.

This type of construction considerably increases the carrying capacity of a ship and its maneuvering capability. It is of particular importance that the navigation system of a ship is located in an antimagnetic field.

Rolling is an indirect compression process. Normally the only force or stress applied is the radial pressure from the rolls. This deforms the metal and pulls it through the roll gap. The process can be compared to compression or forging but differs in two respects in that compression takes place between a pair of platens at various inclinations to each other, and that the process is continuous, Fig. 1.

Fig.1.

Rolling is the most widely used deformation process and for the reason that there are so many versions the process has its own classification. This can be according to the arrangement of the rolls in the mill stand or according to the arrangement of the stands in sequence. Rolling mills are classified as in Fig. 2.

Fig.2.

The two-high mill was the first and simplest but production rates tended to be low because of the time lost in returning the metal to the front of the mill. This obviously led to the reversing two-high mill where the metal could be rolled in both directions. Such a mill is limited in the length that it can handle, and if the rolling speed is increased, the output is almost unchanged because of the increased time spent in reversing the rotation at each pass. This sets an economic maximum of about 10 meters.

The next obvious development was the three-high mill, which has the advantages of both the two high reversing and non-reversing mills. Such a mill must, of course, have elevating tables on both sides of the rolls. The roll gap on a three-high mill cannot be adjusted between passes, therefore grooves or passes must be cut into the roll face to achieve different pass reductions.

All three kinds of mill suffer from the disadvantage that all stages of rolling are carried out on the same rolled surface and the surface quality of the product tends to be low. Roll changes on such mills are relatively frequent and time consuming. This type of mill is therefore used for primary rolling where rapid change of shape is required, even at the expense of surface quality.

Four-high mills are a special case of two-high, and in an attempt to lower the rolling load, the work roll diameter is decreased.

There is, however, a risk of roll bending which is avoided by supporting the small work rolls by larger backing rolls. The backing roll diameter cannot be greater than about 2-3 times that of the work rolls, and as the work roll diameter is decreased more and more (to accommodate processes with exceedingly high rolling loads) the size of the backing rolls must also decrease. A point is reached when the backing rolls themselves begin to bend and must be supported hence the ultimate design - the cluster mill.

The principal criticism of the traditional mill is this tendency for roll bending due to its inherent design - the beam principle. Sendzimir proposed a design which eliminated this limitation based on the castor principle where the work roll is supported over ali its face by an array of backing rolls. This principle can be applied to much mills and an installation for rolling stainless steel 1600 mm wide is fitted with work rolls 85 mm diameter.

Continuous rolling mills can be classified according to the arrangement of stands or passes. These are in line in a continuous mill and line abreast in a looping or cross-country mill. Looping and cross-country mills require the workpiece to be bent or turned between stands and are used therefore for rolling rods, rails or sections. Continuous mills are used for plates, strip or sheets. They all require a large capital outlay and are only justified when a large demand for the product is guaranteed.

It is possible to derive an expression for this friction force. Pressure acts radially on the ends of this element, and if the element is located between the point of entry and the neutral point a frictional force acts toward the neutral point. The radial pressure has a horizontal component which tends to reject the metal and prevent it from entering the rolls, whilst the friction force has a horizontal component dragging the metal inward. Whether the metal passes through the rolls depends upon the values of the two horizontal force components.

Primary rolling is a process where large maximum reductions are required in order that the metal can be deformed quickly and cheaply. Such mills have large diameter rolls with surfaces that are roughened or ragged to increase the coefficient of friction.

The rolling load can be minimized by making the radius as small as possible and the roll surface as smooth as possible. This principle is used in the design of cluster mills which are used extensively for foil rolling and consist of small work rolls supported by larger back-up rolls to prevent bending. Even with such mills the rolling loads can still be excessive and recourse is made to devices which apply front and back tension to the metal being rolled.

Foil rolling and finishing mills are generally very different from primary mills which as already seen tend to use large diameter rolls with roughened surfaces.

It is an essential of metal-deformation processes that the tool is only loaded elastically, while the workpiece is flowing plastically. This elastic deformation is generally so small that it can be ignored, but this is not the case in rolling. There are two reasons. One is that rolling loads and stresses can be very large, especially when the workpiece is thin and work-hardened. The other is that the tool in rolling comprises the whole mill-rolls and housing with overall dimensions measurable in meters. This combination can result in very large strains due to elastic deformation divided between mill stand extension "mill spring", roll flattening and roll bending.

Roll flattening. The workpiece passing between a pair of rolls is compressed by the radial stress in them, but the reaction is transferred to the mill bearings and housing, which are capable of only limited yield because of their large dimensions. If an attempt is made to compress thin hard material further, the reaction becomes so large that the rolls deform elastically and the radius of curvature of the arc of contact is increased. The extent of this flattening depends on the magnitude of the reaction stress and the elastic constants of the rolls.

Roll flattening has another effect in that for a given mill there is a minimum gauge below which it is not possible to roll. Any attempt to do so results in greater deformation of the rolls, without any plastic deformation of the strip. With thin gauges as already seen the friction hill becomes very large producing reaction stresses in the arc of contact which exceed the yield stress of the rolls, therefore it is easier to deform the rolls than the metal. As long as the mill is running the rolls will remain circular, but if the load is not removed when it is stopped, deformation will take place to flatten the surface over the area of contact between the rolls.

Attempts to avoid or limit roll bending have involved ways of decreasing the rolling load. This has resulted in small work rolls and four-high mills. But even with these mills a certain amount of roll bending still occurs and is accommodated by cambering the rolls, i.e. making them barrel shaped. With multistand continuous rolling, interstand tension is adjusted to maintain the rolling load to a constant value and so achieve a flat surface. This is an important aspect of shape control in the rolling of strip.

A recent development has been the introduction of hydraulic jacks onto the roll necks thereby altering the roll camber by actually bending the rolls. Results to date indicate that this method will be very successful in controlling strip shape.

All the methods described so far have involved continuous rolling where front and back tension or interstand tension can be used. With single sheet rolling this technique for controlling rolling load cannot be used and therefore the problem of shape control is tackled in another way.

Mill spring or plastic distortion. The reaction to rolling load is called the roll separating force and if the rolls were not held in the mill housing they would indeed separate and reduction of metal would not be possible. The upper roll pushes the top of the housing upwards whilst the bottom roll pushes the base of the housing downwards. The housing is therefore subjected to a tensile stress, which is obviously below the yield stress of the cast steel normally used, but there is a measurable elastic deformation.

The extent depends upon (a) the rolling load, (b) the cross-sectional area of the housing, and (c) the height of the housing. If the extent of this deformation is small the mill is said to be hard or rigid, whilst if it is large, the mill is said to be soft or springy.

It is a characteristic of the mill and can be determined in the following way. The mill is set to a constant roll gap and a series of different pieces of metal are rolled. These produce different rolling loads which are measured. The rolling loads can be varied either by using different gauges of the same metal or by using different metals. A graph is drawn relating rolling load to gauge, the gauge being found by measuring the thickness of the rolled pieces.

Specification according to the Standard F 2282, establishes quality assurance requirements for the physical, mechanical, and metallurgical requirements for carbon and alloy steel wire, rods, and bars in coils intended for the manufacture of mechanical fasteners which includes: bolts, nuts, rivets, screws, washers, and special parts manufactured cold.

The term "quality" is being used to designate characteristics of a material which make it particularly well suited to a specific fabrication and/or application and does not imply "quality" in the usual sense.

Material is furnished in many application variations. The purchaser should advise the supplier regarding the manufacturing process and finished product application as appropriate. Five application variations are:

    * Cold heading
    * Recessed head
    * Socket head
    * Scrapples nut
    * Tubular rivet

Forming is the primary manufacturing operation in the fastener industry and the term includes heading, upsetting, extruding, and forging. These formed parts are produced at very high speeds by metal flow due to machine-applied pressure.

The primary forming operation self-inspects the quality of the raw material and imperfections such as seams, laps, and internal pipe which may not be visible are revealed when the material is upset. The absence of bursts, forging cracks, and open seams is strong evidence that the quality of material selected was that intended for the severe upsets of today’s fastener manufacturing.

Manufacture
Melting Practice:     The steel shall be melted in a basic oxygen or electric furnace process.
Casting Practice:     Steel shall be ingot cast, or continuous cast with controlled procedures to meet the requirements of this specification.
Deoxidation Practice
and Grain Size:     The material shall be furnished in one of the deoxidation and grain size. When not specified, the practice shall be at the option of the manufacturer.
Silicon killed fine grain shall be produced with aluminum for grain refinement. The material purchaser’s approval shall be obtained for the use of vanadium or columbium for grain refinement.
Silicon killed coarse grain practice.
Silicon killed fine grain practice.
Aluminum killed fine grain practice.
Hardenability:     Hardenability for steels with a specified minimum carbon content of 0.20% or greater shall be determined for each heat and the results furnished to the purchaser when requested on the purchase order.
Thermal Treatments:     The purchaser shall specify one of the following options for thermal treatment on the purchase order:

    * No thermal treatment.
    * Annealed.
    * Spheroidized.
    * Drawn from annealed rod or bar.
    * Drawn from spheroidize annealed rod or bar.
    * Spheroidized at finished size wire.
    * Annealed-in-process wire.
    * Spheroidized annealed-in-process wire.

Rimmed or capped steels are characterized by a lack of uniformity in their chemical composition, especially for the elements carbon, phosphorus, and sulfur, and for this reason product analysis is not technologically appropriate unless misapplication is clearly indicated.

Coarse Austenitic Grain Size: When a coarse grain size is specified, the steel shall have a grain size number of 1 to 5 inclusive. Conformance to this grain size of 70 % of the grains in the area examined shall constitute the basis of acceptance.

Fine Austenitic Grain Size: When a fine grain size is specified, the steel shall have a grain size number greater than five. Conformance to this grain size of 70 % of the grains in the area examined shall constitute the basis of acceptance. When aluminum is used as the grain refining element, the fine austenitic grain size requirement shall be deemed to be fulfilled if, on heat analysis, the total aluminum content is not less than 0.020 % total aluminum or, alternately, 0.015 % acid soluble aluminum. The aluminum content shall be reported.

Materials and Processing
While standard steel grades for rods and bars have been in existence for many years, and have, with modifications or restrictions of one or more elements, long been used for cold forming, ASTM standard presents a distinct selected series of twenty steel grades for cold forming. These have been jointly developed by steel producers and cold heading and forging users under the aegis of the Industrial Fasteners Institute. These twenty grades are designated steel grades and the ranges and limits for the thirteen carbon steel grades for carbon, manganese, phosphorus, and sulfur and alloy steels with copper, nickel, chromium, molybdenum, tin, and silicon.

A significant area of improvement is in the decarburization control and measurement for cold heading rods and bars.

To prepare a material for cold forming it is often spheroidized, which is an annealing treatment that transforms the microstructure of steel to its softest condition with maximum formability. In the hot rolled or normalized condition, steels containing less than 0.80 % carbon consist of the microconstituents pearlite and ferrite. Pearlite, the harder of the two constituents, causes the steels to resist deformation. The harder pearlite is comprised of alternating thin layers or shells of ferrite and cementite, a very hard substance.

In spheroidize annealing, the cementite layers are caused by time and temperature to collapse into spheroids or globules of cementite. This globular form of cementite tends to facilitate cold deformation in such processes as cold heading, cold rolling, forming, and bending.

Boron is extremely effective as a hardening agent in carbon steels, contributing hardenability which generally exceeds the result of many commercial alloying elements. It does not adversely affect the formability or machinability of plain carbon steels. Actually, the reverse is true since boron permits the use of lower carbon content which contributes to improved formability and machinability.

In its early development, some unsatisfactory results produced product which did not have uniform hardness or toughness along with reduced ability to resist delayed fracture. However, many of these problems were overcome by exhaustive research which demonstrated that for boron to be effective as an alloying agent, it must be in solid solution in a composition range of 0.0005% to 0.003%. During deoxidation, failure to tie up the free nitrogen results in the formation of boron nitrides which will prevent the boron from being available for hardening. Research also revealed boron content in excess of 0.003% has a detrimental effect on impact strength because of the precipitation of excess boron as iron borocarbide in the grain boundaries. Many European steels contain higher boron levels than in North America.

When producing a boron steel, titanium and/or aluminum is added and the resulting product is subjected to thermal processing. These two additions are designed to tie up nitrogen to stop it from reacting with boron. The resulting free boron is available to provide excellent hardenability in steel. Both titanium and aluminum nitrides reduce the machinability of the steel, however, when the nitrogen becomes tied up, the formability of the steel is improved.

Silicon and aluminum act as somewhat similar elements with respect to their behavior when added during the steel making process. They both have a high affinity for oxygen and are, therefore, used to deoxidize or "kill" the steel. Deoxidation or "killing" is a process by which a strong deoxidizing element is added to the steel to react with the remaining oxygen in the bath to prevent any further reaction between carbon and oxygen.

When carbon and oxygen react in the bath a violent boiling action occurs which removes carbon from the steel. When the bath or heat reaches the desired carbon content for the grade being produced, the carbon-oxygen reaction must be stopped quickly to prevent further elimination of carbon. This addition is accomplished by the addition of deoxidizers such as silicon and aluminum which have a greater affinity for oxygen than does carbon. This effectively removes oxygen, eliminating the "carbon boil" and killing the heat. Elements other than silicon and aluminum can be used, but these are the most common.

Silicon and aluminum can be added together or individually. This is determined by the type of steel desired. If silicon only is added, that particular batch of steel is referred to as a silicon killed coarse grain practice grade because silicon acts as a deoxidizer without the formation of fine precipitates allowing the formation of large or coarse austenitic grains.

Austenitic grain size is not usually a factor for consideration in cold forming, but has a significant effect in subsequent fastener heat treatment. Aluminum, on the other hand, not only deoxidizes the steel, but also refines the grain size. Like silicon, aluminum removes oxygen from the bath, effectively killing the heat. Aluminum also reacts with nitrogen in the steel to form aluminum nitride particles which precipitate both at the grain boundaries and within the austenitic grains thus restricting the size of the grains; even when the steel is reheated for carburizing or neutral hardening, hence the term fine grain.

When aluminum only is added, the steel is referred to as aluminum killed, fine grain. A third group of steels are referred to as silicon killed, fine grain. In steels of this type, silicon is added as the deoxidizer followed by the addition of aluminum for grain size control.

In the two types where silicon is added, the silicon content can have several ranges with the most common being 0.15 % to 0.30 %. When aluminum is added to these steels for grain size control, the aluminum content is generally in the 0.015 % to 0.030 % range. The aluminum content in fully aluminum killed steels is generally 0.015 % to 0.055 %, somewhat higher on average since the aluminum must both deoxidize and control grain size at the same time.

In selecting the type of deoxidation practice for a particular carbon grade of steel to be used in fastener manufacturing, a number of factors should be considered, such as, heat treated property requirements, heat treat conditions, fastener size, and steel availability, to name a few. Silicon acts as a ferrite strengthener and, therefore, in the absence of aluminum, has somewhat greater hardenability. For the same carbon grade and heat treat conditions with and without aluminum, complete transformation of the fastener core during heat treatment can take place in a larger section using a coarse grain steel.

The disadvantage of silicon killed steels can be reflected in reduced ductility and tool life during cold heading because of its ferrite strengthening characteristic. Aluminum killed steels are usually more formable and hence provide somewhat improved tool life but reduced heat treatment response during heading, particularly in larger size fasteners. For this reason, the recommended maximum diameter for oil quenched aluminum killed carbon grades is typically 0.190 in.

The future developments in mechanical engineering, vehicle and energy system engineering must concentrate on solutions for processes, machines and materials which carefully treat resources and energy and at the same time keep the technical lead with new and innovative products. Lightweight construction concepts are able to be maintained and operated costs efficiently, reduce production costs, increase the product life for economic reasons reliability of use or optimize the freight of payloads.

Steel has become less favorable in previously dominated areas, e.g. in the automobile industry since lightweight materials such as aluminum and magnesium based alloys as well as synthetic materials and composite materials have gained a broad range of acceptance.

Steels with a higher strength and a higher young modulus than conventional steel cannot quite compensate the advantage of these materials for lightweight construction, despite the advantage of a lower price, a better forming behavior, a higher strength and the possibility of recycling without problems. A trend-setting solution for a higher demand of steel use seems possible by the development of high-strength, austenitic steels with a large manganese content. These steels show comparable mechanical qualities, and at the same time are more economical and in addition permit lightweight construction.

Sandwich systems represent an interdisciplinary concept by combining the areas of material choice, production engineering, design and function integration for the fulfillment of the high demands on modern materials. The sandwich material connects the advantages of miscellaneous materials (e.g. low density, high bend resistance, sound and vibration insulation, energy absorption, high load-capacity at a low weight, need adapted qualities) with each other.

Applications
Nowadays these new materials and designs are appreciated as key technologies for innovative research and development. The further development of the materials, the optimization of material applications and the necessary manufacturing method with reduced costs and time are permanent research objectives.

These new compound systems open new, future-oriented applications. The weight reduction is considerable for this task. A combination of steel/synthetic material/steel has the advantage of a higher strength opposite to corresponding steel and, depending on the choice of the steel grade, a high corrosion resistance. These sandwich materials find their way in more and more industrial applications such as automotive-, building-, transport-, chemical-, aerospace- and airplane industry.

The first essays and theoretical based works from to the "sandwich" topic are from 1935-1945. Applications are found not only in aircraft construction but also in the automobile manufacturing industry, in architecture, in shipbuilding engineering as well as in the sports and leisure industry. Some examples are described in the following.

Sandwich sheet metals increasingly find their way into the automobile industry. They are used for car bodies both for of lightweight reasons and for sound reduction. Sandwich materials are used with a homogeneous or inhomogeneous core of foams and other hard materials.

Examples of components of sandwich constructions are cowl application, gear box covers, hoods, car boot covers, oil pumps and chassis frame components. A well known example for the use of sandwich sheet metals in the automobile industry is the lightweight construction bodywork (Ultra Light Steel Auto Body).

Some of the components, such as spare wheel hollow and cowl application were manufactured of steel sandwich sheets. These components can be executed up to 50% lighter with the same properties concerning geometry and function than with normal deep drawing steel. The material consists of two thin steel sheets which are bonded with a thin polypropylene material layer as core material.

Material manufacturing
In one investigation sandwich materials with high-grade steel sheets were researched. They combine a good corrosion behavior and acid resistance with good damping behavior and noise reduction. For the production of the sandwich materials a 0.5 mm thick polyolefin foil was used.

The first manufacturing method to be tested was a press-joining process. This was performed discontinuously by an 8" and 10" rolling stand. The high-grade steel sheet metals [X2CrNiMo17 12-2 (1.4404) and X6CrNiMoTi17 12-2 (1.4571)] with a thickness of 0.5 mm were first cleaned and degreased. The steel was than coated with a defined layer of adhesive. The used adhesive agent is a conventional product based on epoxy with resin. After activating the adhesive the upper sheet metal was joined with a 0.5 mm thick PP/PE-foil in a rolling process. During the next step the produced upper sandwich was bonded with the lower sheet metal, also by rolling. For durable and reproducible adhesive bonding an activation temperature of the adhesive of 254°C +/-2°C was needed. The necessary dwell time of the coated sheet metals was 30 seconds in a stationary convection oven.

The other way to produce sandwich material is the discontinuous method. This manufacturing method was carried out with a cooling and heating system deduced in a laboratory press system. For the sandwich production a sufficient set of the granular material was mixed with the adhesive agent. This mixture was inserted as a packed bed between the cleaned and degreased sheet metals. At temperatures between 260 to 300°C the sandwich materials were then pressed for about 60s. To reach an even core layer thickness, the sandwich material was pressurized at 445 MPa. After the press process the sandwich material annealed to room temperature with a cooling rate of 10°C/min. For adjusting the core layer thickness and the thickness of the complete sandwich material a metal frame was used as a spacer.

These sandwich materials were examined in different tests for the bond strength of the individual layers and for their forming behavior. Deep drawing behavior is for example examined in the Erichsen Test. The height of the cup is a reference value to compare different sheet materials.

The difficulties in the deep drawing process of sandwich systems dwells from the different behavior of the used materials, e.g. polymer and high-grade steel.

The wrinkling of the metal can be counteracted with blank holders for mono materials. The material is forced into the desired flow direction. With sandwich systems, e.g. metal/PP/PE/metal the metal layer can flow despite a blank holder in the polymers, so that it can come to wrinkling in the metal layer. The higher the resistance of the polymer is brought into line with that of the metal, the bigger the resistance is against wrinkling.

For the deep drawing process of sandwich materials the knowledge about the blank holder pressure and force was necessary. Too little blank holder pressure increases the risk of wrinkling.

Conclusion
If some years ago sandwich systems were used only in individual sections, then they will find the way to more and more industry areas today. By the combination of construction and material they offer the substitution of classic mono materials, because next to lightweight construction they offer quantities like anti-corrosion protection and damping.

The development of new materials and technologies still stands at the beginning. New adapted material systems like natural fiber composites, hybrid structures of metals, polymers and ceramics increasingly gain meaning in future. The development for adapted composites, the processing of a material construction matrix for composite materials as well as the improvement on the adhesion and cohesion qualities by shift transitions graduated are future design objectives. Furthermore at the beginning of the material design process the aspects of the environmental protection and recycling have to consider.

Tool concepts and procedures should also be reconsidered for the component production from sandwich materials or be developed newly or adapted to the materials.

Aspects of the environmental protection and recycling are getting more important in these considerations from the beginning of the development. The use of natural fibers can serve as reinforcements in a matrix material between two metal sheets.

The interest in research and development in the area of these new materials has increased strongly during the last few years. In combination with other fields of research, like the nanotechnology, the biotronics, the mechatronics and the material development, the sandwich materials offer a large and important spectrum for the future.

Several types of hot-rolled dual-phase sheet steels prepared by simple temperature control in hot strip mill or by heat treatment on a continuous annealing line have been compared in this article with conventional micro alloyed steels through various forming tests.

Thickness of these steels ranges from 1.8 to 2.5 mm and yield strength from 300 to 520 MPa. Forming tests employed include stretching, drawing, flange stretching or hole expansion, and simulative model forming of automotive parts such as rear axle housing and spring support, and the behavior of these sheets is discussed.

Interest in high-strength steel has a lengthy history in the steel industry. Recent development of high-strength low-alloy (HSLA) sheet steel depends upon the large amount of technical information available in this field. In response to the automobile industry’s demand to reduce overall vehicle weight and thereby improve fuel economy, and to satisfy safety and crash-worthiness requirements, the steel industry has developed a large variety of steels and processes for producing high-strength hot-rolled and cold-rolled steel sheets.

The overall suitability of various steels for automobile body panel applications is assessed by evaluating their characteristics with regard to the performance requirements (formability, weldability, paintability, etc.). The formability of the steel sheets is perhaps the most important requirement for automotive component applications.

The aim of this article is to shed some light on the properties of steels which are controlled by the manufacturing conditions, and to recover the loss of formability that occurs as strength increases. The possible applications to automotive parts can be divided into two general categories, namely body panels and structural and safety-related parts. This article describes the formability of hot-rolled high-strength sheet steels for the latter category and the principal material properties which become the indication when producing such materials.

Dual phase steels, which have much better ductility for a given strength than conventional high-strength steels, have been developed. They have microstructures consisting of two major phases: martensite and ferrite. The suitable method of making these steels is to roll to the required thickness and then make use of heat treatment on a continuous annealing line. Another method is to find out the cooling condition and steel compositions which achieve typical dual phase properties directly from a continuous hot strip mill. These lead to the availability of hot-rolled dual phase steels made by two different methods and substantially different compositions.

Despite the differences between the steels, it is necessary for the automotive industry that they should have similar forming behavior and performance. This study therefore compares some of the properties for nine as- hot-rolled dual phase steels, two continuously heat treated dual phase steels, two conventional high-strength steels, and a commercial low carbon steel with yielding strength of 300 to 520 MPa.

The press forming of these steels is studied to gain an understanding of the influence of increasing strength on formability parameters. The formability investigation is performed through an evaluation of the response of the sheet steel in three deformation modes in the forming limit diagram: stretching, plain strain, and drawing.

Stampings are judged acceptable if there are no obvious tears, cracks, buckles, wrinkles, or necks in the finished stamping. In the forming of hot-rolled steels applied to the frame members of automobiles, which generally require thicker sheet than that of exposed panels, it is important that the steels exhibit good stretch flanging and punch stretching ability.

Tension testing is performed on parallel-sided specimens with a nominal width of 25 mm. Testing is carried out using a constant cross head speed, and elongation to fracture measured with a 50-mm gage length extensometer. Average mechanical properties are obtained from a minimum of five specimens in three test directions.

Hole expansion testing is carried out as follows: a 20-mm hole is punched into the sheet before deformation and is expanded with a conical punch. The expansion of this hole prior to the point of failure is referred to as the ratio of hole expansion.

The stretch forming test is performed with a hemispherical and flat bottom punch in which 400 and 450 mm square blanks are held in the die.

Simulative model forming is carried out with two types of dies. One is a spring support of which a character is stretching, and the other is a rear axle housing of which a character is drawing.

Springback is measured after a simple bending over three dies of different radius of curvature. Thickness of specimen is reduced to 1.7 mm by surface grinding in order to establish a constant strain of bending.

Formability parameters affect the ability of a material to be transformed from its original shape into a defined final shape by a specific forming process. Material, process, and shape interact in forming parts; therefore, they must be considered simultaneously in a formability study.

Mechanical properties such as yield strength, tensile strength, total elongation, work hardening exponent, plastic strain ratio, and strain rate sensitivity exponent, which are determined in the tension test, generally indicate the forming behavior of the material. The importance of these material parameters, which all interact in forming processes, depends upon the shape of the part and the manufacturing processes. Better understanding and accurate determination of these forming parameters help to predict the behavior of these steels in stamping operations.

The work hardening behavior of sheet steels is often characterized by the n-value, defined as the exponent in the Ludwig’s equation. For most dual phase steels, and also for highly formable interstitial free steels, the stress-strain curves do not conform to the Ludwig’s equation. To compare the work hardening behavior of the steels, it is suggested that the most useful parameter is the instantaneous work hardening rate normalized with respect to the flow stress. The distinct expression of the work hardening behavior is obtained by this parameter. However, it is tedious to establish the curves of the normalized work hardening rate in the function of the tensile strain.

Hole expansion ratio is influenced by the plastic strain ratio, by total elongation (which affects the critical hole expansion), and by quantity and shape of inclusions (which cause cracks). Results indicates that the hole expansion ratio decreases with the increase of total quantity of inclusions.

As reported previously, sulfide shape control becomes important in achieving a higher ductility along the sheared edge. Without sulfide shape control in these hot-rolled steels, lower expansion can occur due to the tearing which initiates on the punched edge at elongated sulfide inclusions. However, even in a material with sulfide shape control, there is a rather important degradation of sheared edge ductility as strength increases.

It is noted that a high-strength material which has a hole expansion ratio of more than 1.5 may be considered satisfactory, compared with the low-carbon steels. An investigation is made of the influence of the clearance between punch and die when a hole is punched into the sheet. It is indicated that the clearance has relatively little effect on the hole expansion ratio.

For automotive components the formability of sheet steel is determined principally by biaxial stretchability and deep draw ability. The total elongation and work hardening exponent are measures of the biaxial stretchability of sheet, and these parameters decrease as the yield strength of the sheet steel increases. As a general rule, the average plastic strain ratio, which is a measure of deep draw ability, also decreases as strength increases. For all the steels examined, the values are in a very narrow range and similar to those for low-carbon steel.

There is a good correlation between the forming index and work hardening exponent. This test is performed both parallel and transverse to the rolling direction, so the fracture properties of the sheet in both directions can be evaluated. There is a difference in formability due to the rolling direction.

The shape of automotive sheet components is apt to deviate from the design configurations because of various elastic recovery effects including springback. Defects in shape precision of finished parts are responsible for difficulties in assembly processes. Materials must be as uniform as possible with regard to thickness and properties in order to minimize springback after stamping.

Various types of hot rolled dual phase steels are examined by forming tests. Dual phase steels containing manganese and silicium are characterized by improved formability. Good correlation is obtained between the hole expansion ratio and inclusion shape control.

The work hardening exponent is the principal factor determining the press performance of hot-rolled dual-phase steels. In particular, n-value from 5 to 10 percent strain in tension testing is shown to have a good correlation with formability. This will allow the setting of guidelines for optimizing manufacturing conditions for these steels.

It is expected that the superior properties of dual phase steels will result in significant increases in their use for automotive applications in the immediate future.

Forging was the first of the indirect compression-type process and it is probably the oldest method of metal forming. It involves the application of a compressive stress, which exceeds the flow stress of the metal. The stress can either be applied quickly or slowly. The process can be carried out hot or cold, choice of temperature being decided by such factors as whether ease and cheapness of deformation, production of certain mechanical properties or surface finish is the overriding factor.

There are two kinds of forging process, impact forging and press forging. In the former, the load is applied by impact, and deformation takes place over a very short time. Press forging, on the other hand, involves the gradual build up of pressure to cause the metal to yield. The time of application is relatively long. Over 90% of forging processes are hot.

Impact forging can be further subdivided into three types:

    * Smith forging,
    * Drop forging,
    * Upset forging.

Smith Forging
This is undoubtedly the oldest type of forging, but it is now relatively uncommon. The impact force for deformation is applied manually by the blacksmith by means of a hammer. The piece of metal is heated in a forge and when at the proper temperature is placed on an anvil. This is a heavy mass of steel with a flat top, a horn which is curved for producing different curvatures, and a square hole in the top to accommodate various anvil fittings. While being hammered the metal is held with suitable tongs.

Formers are sometimes used; these have handles and are held onto the work piece by the smith while the other end is struck with a sledgehammer by a helper. The surfaces of the formers have different shapes and are used to impart these shapes to the forgings. One type of former, called fuller, has a well-rounded chisel-shaped edge and is used to draw out or extend the work piece. A fuller concentrates the blow and causes the metal to lengthen much more rapidly than can be done by using a flat hammer surface. Fullers are also made as anvil fittings so that the metal is drawn out using both a top and bottom fuller. Fittings of various shapes can be placed in the square hole in the anvil.

The working chisels are used for cutting the metal, punches and a block having proper-sized holes are used for punching out holes. Welding can be done by shaping the surfaces to be joined, heating the two pieces then adding a flux to the surfaces to remove scale and impurities. The two pieces are then hammered together producing welding.

The easiest metals to forge are the low and medium carbon steels and most smith forgings are made of these metals. The high carbon and alloy steels are more difficult to forge and require great care.

Drop Forging
This is the modern equivalent of smith forging where the limited force of the blacksmith has been replaced by the mechanical or steam hammer. The process can be carried out by open forging where the hammer is replaced by a tup and the metal is manipulated manually on an anvil.

The quality of the products depends very much on the skill of the forger. Open forging is used extensively for the cogging process where the work piece is reduced in size by repeated blows as the metal gradually passes under the forge.

The cogging of a prismatic bar can be used to assess the parameters involved and how they are controlled. The objective is to reduce the thickness of the work piece in a stepwise sequence from end to end. Several passes may be required to complete the work and edging is usually carried out to control the width. The reduction in thickness is accompanied by elongation and spreading. The relative amounts of elongation and spread cannot be calculated theoretically but they have been determined experimentally for mild steel.

Die drop forging. Closed-die drop forging is widely used and the tup and anvil are replaced by dies. Matching dies fit into the anvil and the tup. The dies have a series of grooves and depressions cut into them and the work piece is passed in sequence through a shaping series.

These stations have names such as fullering, blocking, edging, bending and cut off. Where several stages are involved, care must be taken to ensure that the metal does not become excessively chilled before the last station is reached. To ensure that the die cavity is completely filled the volume of the starting billet is greater than that of the final forging. The excess metal appears as a "flash" at each stage, this is a thin fin around the perimeter of the forging at the parting line. This flash is cut away in a further press operation generally at a high temperature. The weight of flash may be a small percentage of the total weight for forgings of simple shapes but may exceed the weight of the actual forging for those of complex shape.

Each size and shape of forging will thus require a separate set of forging and trimming dies. The production tolerance for the initial metal must involve excess, e.g. ~10 mm. The over-tolerance metal is accommodated by a gutter around the die cavity which allows the formation of the fin referred to earlier.

Upset Forging
This process was developed originally to gather, or upset metal to form heads on bolts. Today the purpose of this machine has been broadened to include a wide variety of forgings.

It is essentially a double-acting press with horizontal motions rather than vertical. The forging machine has two actions. In the first, a movable die travels horizontally towards a similar stationary die. These two dies have semi-circular horizontal grooves, which grip the bars. A bar heated at the end is inserted between the movable and stationary die. While thus held, the end of the bar is upset or pressed into the die cavity by a heading tool mounted on a ram, which moves towards the front of the machine.

If hexagon heads are desired, a heading tool will upset some of the metal into a hexagon-shaped die cavity. For more complex forgings, as many as six different dies and heading tools may be used in turn in a similar manner to the different stations in die drop forging.

Press Forging
Whereas impact forging usually involves a mechanical press, press forging, on the other hand, requires hydraulic power. The largest forgings are invariably produced on large hydraulic presses. These have vertically moving rams, which move down slowly under considerable pressure.

A typical press forge would be capable of loads of the order of 6000 to 10000 tones. Forgings up to 100 tones weight can be handled easily in this forge and the highest-quality products are manufactured by this technique.

Structure and Properties of Forgings
Forgings are invariably produced by the hot-working process and this controls the resultant structure and properties. There are, however, important differences in forgings produced by different techniques.

The fact that the impact forge applies a stress for a very short period compared to the long period for the press forge results in totally different structures in the product. In the case of impact, the mechanical working is concentrated in the surface layers, since rapid removal of the stress after the blow results in metal relaxation before the effect of the blow has penetrated into the center. Impact forging of a large "as cast" piece of metal at high temperature will result in a very inhomogeneous structure, the outside layers showing a typical hot-worked structure whilst the center is still as cast. Any attempt to achieve greater penetration by increasing the impact load usually leads to internal cracking. Impact forging is therefore limited to relatively small work pieces.

Press forging invariably results in total penetration of the effect of the applied stress into the center of the work piece. The process is generally less severe on the metal than impact. The end result is a more homogeneous product having very high quality. Since the process is much slower and the equipment used is much larger, press forged articles are more expensive than impact forged components.