Indian Journal of Engi neering & Materials Sciences Vol. 10, April 2003. pp. 11 3- 122

Analysis on a flexible forging cell

Bunyamin Aksakal

Ataturk University. Mechanical Engineering Faculty. 25240 Erzurum. Turkey

Received 3 .lillie 2002; accepted 2 Febnwrv 2003

Forging and press ing in manufacturing industry has not been adapted to flexible manufacturing systems (FMS). Predicti ons on the metal flow and requ ired power ha ve been made here through the upper bound analysi s by applying vari ous amounts of deformation in an incremental manner. In order to observe the final dimensions and the structural

ch:l11ges during open die forging. the 6082 alum iniu m billets (annealed at 425°C for two hours and cooled in the air) have been subjected to cold deformation between simple flat tools. The TEM observations have been made for different parts of the locally deformed aluminium billets to show dislocati on behaviour during multi-cyc le co ld open die forging process. Formation of a flexible forging cell (FFC). as an initi al step to FMS is also descri bed here. A simple contro l system is proposed to enable a communica ti on link between computer, press and robot arm . The robot arm manipulates workp iece between upper and lower dies. where fixed on the press. to run multi compression and rotation cycles in forging of simple rectangular and square cross-secti on components.

Production methods throughout industry have recentl y undergone radical changes covering the computer integrati on resu lting in increased competitiveness for companies, as reported by Fosterl and Schonberger2

.

The forging industry has to make signi ficant improvement to accommodate shorter production runs with a greater variety of parts. The small-batch manufacturing mode is becoming common to meet changing customer requirements. Accordingly, fl ex ibility and cost effectiveness are becoming important in the utili sation of forging equipment}.

For manipulating the workpiece by robots , a feas ibility study was undertaken by Appleton el 01 .4-6.

Tomlinson and Stringer's7 formulae were used for the prediction of spread . Thi s led to a computer technique for generating an optimum forging schedule which can be used as a basis for robot programming introduced by Appleton el 01.(' The study used the software developed in the interactive graphi cs unit by Heginboth alll e l 0 1.8.

9 Pahnke 1o.

11 produced a robot and press combination which can be used for automation of open die forging but whil st the facility is programmable, it has yet to learn the appropri ate sequence of steps based on experience and trial and error in order to produce a particular shape.

The working forces can be red uced in open die forming since only a small part of the workpiece is subjected to deformation. Also, hi gh productivity, continuous production, and automation are attainable. A method involv ing accurate and rapid metal flow

and power predictions was developed for the formation of a process planning routine I2

.1'. Sengupta

ef 0 1. 14 used a robot for ring forging and pointed out that it was necessary to break the forging procedure into elements and to programme the robot usi ng a seri es of mod ules . The importance of Flexible Automation was reported by Bauer l 5 which deals with theoretical proposals for the economic survi val of the process. Also, Schmoechel 16 presented a theoretical work regarding flexibility and control in Forming Machinery. The work was purely related to the description of the development of forming machinery. The creation of a Flexible Forging System (FFS) would greatly reduce the number of pre-form ing operations and would increase a company's fl exibility by allowing smaller batch sizes to be economically produced 17 .

The evalu at ion of microstructure can be criti cal for certain types of components, e. g. forged marine shafts, di scs and blades for gas turbine engines. No studies are reported that deal with microscopic and TEM observations relating to deformat ion in open die metal forming operati ons satisfac torily . TEM provides information about the dislocati ons that occur during multi cyc le deformation processes. Different grain and defect structures in AI alloys have been

1 H observed by through hot and cold rolling processes ' . Wang and Lee l

'! reported microstructural characteri sti cs in AI all oys showi ng hi gh and low density of di slocati ons in the as-quenched and as-aged

114 INDI AN 1. ENG. MATER. SCI.. APRIL 2003

samples respec ti ve ly. It has a lso been detected 19 that need le like and lathlike prec ipitates probably grow from direct nucl eat ion o n the di slocations. However, the work done by Ringer el af. 20 using TEM reveals th at e levated temperature age ing leads to the forma tio n of spherica l particles in AI a lloys. It has been show n th at prec Ipitati on nuc leates heterogeneously on these particles . Muka i2 1 reported that aluminium alloys with fine grain , inte rmediate grain and coarse grain can be developed by a combinat ion of mechanical properties at dynami c strain rates and a quasi-stati c strain rate . Raughunath an and Sheppard22 investi gated the factors th at affec ted spread during slab ro lling in two com merci a l AI-M g a lloys (AA 5056 and AA 5083) with a new spread fo rmulae which was de rived through the ir experiments. Oyekanmi el al. 23

introduced an experimental technique which is genera lly applicable to the evaluati o n of s tra in in metal-forming processes. The ultimate objective was to have a system which for a given required component shape could automatically prescribe a sequence o f incremental deform ati on steps and workpi ece manipul ati ons. At the core of thi s was the need to have a sys tematic model for the prediction of spread, e longatio n and microstructure analyses in open die forging .

The main goal of thi s paper is to integrate the previous work done by Aksakal el o f. 12.13, which was re lated particul arly o n incre menta l meta l fl o w and fo rming load analyses in open di e forging , with those of the microstructure and di slocation analysis in which 6082 AI alloy deformed continuously through multi cycle compression-rotation fo rging operations. Theoretical and experimental analysis are described here on metal flow and TEM analysis during cold open die forging process and the essential steps in the fo rmatio n of a FFC. The sys tem consists of a press, a robot arm as manipulator and a hos t computer as network controller. They are interfaced to each other to produce a number of geometrically different simple components using a set of open di es. Also, a control system is proposed to enable the press to run multi­cycles for only particular s impl e forging shapes such as rectangular and square bars.

Methodology The mos t beneficial area, in which such a system

could be incorporated, would be to rep lace the initi a l pressing to a "retrofi tting" computer control system.

The commercial viability of such a system depends o n constraining and identifying the areas where the sys tem can be used effectively. A large proporti on of this work in vo lves creating a communication link be tween the press, robot arm , and a Pc. The construction , imple mentation, and running of the inte rface are a lso described here. A FCC would typica lly consist of a CNC press, a robot a rm and a common compute r to coordinate the operatio n as sho wn sche matically in Fig I.

The following subjects have been studi ed and tes ted for the system: Robot arm sensing and control , the Communication Link between Press and PC, instrumentati o n and measuremen t, material deformation and metal flow , programming and inte rfac ing between Press and Robot ann.

]n order to achieve a number of geometri cally varying components from a pair of simple open di es with high production rates , an accurme measurement system is needed. As the material is deformed, the metal flows in a number o f different directions, e.g. axial , lateral and vertical. These flows will have to be monitored and informatio n recorded and fed back such that the cycle can be altered according to the material used . There are a number of di fferent ways in which the data can be gathered either by mechanical and electrical means .

One of the essential parts of thi s work was to develope a communication link between the press and Pc. For thi s, a program written in the C language is used to transmit the data between the PC press and robot. When a long quadrapiped billet is pressed in an open di e forg ing process by the action of top cushion , there is naturally a change in the form o f the billet. The bar will be subjec ted to a drop in centre line,

Fig. I - Model for the Flex ible Open Die Forging Ce ll (FPC)

AKSAKAL: ANA LYSI S ON A FLEXIBLE FORGING CELL 115

elongati on in the ax ial direction and spreading in the side ways and poss ibl e sagging which cannot be predicted eas ily. The change of ori entation of the end of the bar during pressing has been fo und to be sufficient In magnitude to cause problems In work pi ece that is gripped in the end effector of a robot arm. Large forces w ill be transmitted to the robot if it does not attempt to fo llow the motio n. Several methods of overcom ing this problem have been consldered utilising stra in gauges, pressure pads and flex ible and effec to r. An outpu t signal , when ampli fied, is interpreted by the robot contro ller to provoke motion of the workpiece and strain gauges are mounted on the workpi eces to be forged. If the program is not supported by a metal fl ow analys is then the robot arm grippers are like ly to be forced and sagged.

The workpi ece manipulator used for this work is a six-ax is revolute robot arm, which is eq uipped with a simple paralle l-jawed end effector opera ted by a selenoid va lve and contro lled by a pneu matic actuato r. Opening and closing the jaws within a controlling program is possible by sending a com mand through the analogue o utput. Additional hardware can communicate with the contro ller via either analogue or digital input and output ports. The ana logue output can be set to give a O+qV supply and the analogue input can be read in voltages between 0 and +5 V, resu lting in digital values of 0 to 225 after going through the A to D converter. Motion of the robo t arm can be affected through the controlling programme from the computer to g ive a target poi nt

(i) (ii)

Strain gauges

a)

(iii)

Fi g. 2a- Pressure pad and strain gauge local ions

or by using a teach pendant with joystick and toggle button .

Robot arm sensing and its control Several mechanisms were investigated and due to

the simplic ity and economic reasons the pressure pads-strain gauges were used for such a sys tem . In using pressure pads on the jaws of the gripper, a signal could be read to ana lyse the pressure vari ation a long the two gripper faces and thus to calcu late the direction and magnitude of the workpi ece moti on. Disadvantages of this part wou ld include sufficient sensitivity of pads, robustness and durability and thermal or chemical attack. The re levant pressure pad and strain gauge locati ons are shown schematically in Figs 2a and 2b show ing the stra in gauge tes t rig and bridge. As shown in the Figs, the s trai n gauge bridges were used to monitor the bending of the gripper jaws. If the gauges are mounted away fro m the contact faces of the jaws, the possible mechanical damages could be avo ided. Compared to more complex measurements, thi s is simple r and a lso economica l.

Communication link between press-robot arm and computer When a system is insta lled, it has to be 'tailored ' to

the requirements of the indi vidual eq uipment at each end of the link line. To es tabli sh a reasonab le and adequate system, the problem can be devided into various aspects, e .g. control , mode of transmissio n and to establi shing the optimum solutio n. As the press has its own micro-processor, the PC can e ither have direct control (i.e., disabling the press micro processor), or the s impl y 'slave' the press controller. Slaving the press processor enables the contro ller to fo rce the registers held within the press thus altering the cycle parameters.

Direct contro l would effecti vely nullify the press micro-processor and the PC would have a complete control over the press, i.e. a ll va lves, switches , relays

B01lom j ow 1 Of t per J(1W

Gauge

b)

Fig. 2b-Strain gauge lest ri g and bridges

116 INDIAN 1. ENG. MATER. SCI., APRIL 2003

and encoders would be open, closed and read by the Pc. The main advantage of this method is its high speed. However, the di sadvantage with this type of control is the lack of safety . For example, the PC could switch off to limit switches and send the top ram through the base of the machine.

The mode of data transmi ss ion is a sort of numbering sys tem in which the structure of the individual units of information loaded within a message. The mode used is ASC II and the interface RS 232 link as a socket for such a sys tem which is incorporated into the press. To achi eve multi-cycling, the information is needed to be transmitted as a number of single cycles on a set time interval. The pos iti on control would be through setting va lve ON/OFF switches if needed. incorporating the machine offsets. In order to ensure correc t data trans mi ss ion , a system protocol has been used to assist the preparing, sending and decoding of the informati on when passed betwen the two machines.

In order to enable sending massages over the data lines, the massage is programmed into an envelope. The envelope leaves the device throug h a port and is carri ed to the addressed dev ice. The receiver then processes thi s information and checks for errors. If the informati on is correct, it pe rforms the req uired task and returns to the sender for a new response. However, if the in fo rmation is corrupted , then no response will be returned. The response to such a request will contain the machine address, function code and the number of data bytes returned to the system.

I nstrumentali on and measurement

To achieve the fl ex ibility of the curren t FFC mode l, first co mponents of eas il y gripped lo ng quadropiped bi llets and a simpl e set of open dies were taken for initial experiments. In order to make the workpiece ready for the fina l pressing operati o n and to cooperate within the sys tem, decent control is necessary. For this, a number of measuring sys tems were considered, e.g. touch probes, plug and go/not go gauges, encoder fitting , and as a result the li ght based sys tems such as infra red and laser system. These systems can measure dimensions extremely accurately over long and short di stances. As the system uses an e lectrica l signal to express the measurement it could be directly incorporated into the controll er enabling the prog ram to be insta ntl y updated . They could be fixed to the press table and linked to the contro ll er through an 110

port after pass ing through an A to D converter. One of the problems with measuring the component with any device is the undesired conditions of the workpiece surface where could lead the measured dimensi ons to be incorrect.

Experimental Analysis The material used for experiments is the extruded

6082 half hard a luminium alloy (Fe 0.5 %, Si 0.7 %. Cu 0.1 %, Mn 0.4%, Mg 0.6%, .Cr 0 .25 %, Zn 0.2%, Ti 0. 1 %) bar stock. The recei ved material is named "hardened" material because its hardness is e·qui va lent to half-hard material. The initial forg ing ex periments were performed using a 1000 kN Rhodes hydraulic press. The forging tools were mo unted on a two pi liar Desoutter die set. The billet dimension s fo r the initi a l open di e fo rging experiments were sq uare secti ons ( 15x 15mm2

) to fac ilitate the workpiece a li gnment and location between increments. The billets/workpieces

were then annealed at 425°C fo r two ho urs before applying deforming loads up to 200 kN by depending o n height reducti o n. Annealing treatment was followed by a ir cooling to chemically ho mogeni ze the mate rial , and to obtain fairly uniform gra in size di stributio n throughout the bar.

I n order to work out the flow stress o f the mate rial. co mpression tests was carri ed o ut using a number of cylindrical specimens having 30 mm height and 25 mm diameter. These specimens were a lso annealed at the same conditions as menti o ned above. The output from the load cell and the change of spec imen height from a displacement tran sducer were recorded simultaneously. Since the volume rema ins constant during deformation. the continuous reduction in he ight can be converted into the contact area. Thus, the s tress was dete rmi ned and hence the progressi ve stress-strai n curve of the material was plotted as shown in Fig. 3.

As illustrated in Fig. 4, the samples take n from the no n-deformed (zone- I) and incrementa ll y deformed parts (zone- II and zone- III ) of the billets were prepared for T EM ana lys is. For the micros truc tural analysis o f AI billets, pieces were c leaved 2x2 mm" in s ize and thinned using a chemical e tch following mechanica l po li shing. T EM samples were prepared by chemical po li shing using a solution of 2 mL HF, 5 mL HNO} and 3 mL Hel In 190 mL water. Image and diffracti on experiments were carried o ut us ing a JEOL EMIOOSX operating at a vo ltage up to 100 kV. Detail s about TEM samp le preparation and diffracti on

AKSAKAL: ANALYSIS ON A FLEXIBLE FORGING CELL 117

350 r---------------------~--_;

300

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OJ

c7) 150

OJ

2 100 I-

50

0

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0 0.2 0.4 0 .6 0.8 1.2 1.4 True Strain

Fig. 3- Stress strain curve of AI6082

f Zone I

Fig. 4- Deformation zones for microscobic in ves ti ga ti on

contrast experiments are already reported by Atici and Ch 24-27 . d·f> . I I . erns uSIng t .erent matena s, e.g. super attlces , multi-quantum well s and thin films.

Results and Discussion Among the various methods of solutions, the upper

bound method appears to be used in metal formin g ·d I 11 14 b f . . I·· II - more WI e y .. ecause o · ItS sImp IClty as we as

accuracy and modest use of computationa l time. In this work a lso, the upper bound method was used to calculate the load and dimensional changes which occur incrementally after each compression step. During analysis, the most probable bulging shape of a partially forged long quadrapiped billet was assumed to be of parabolic form. The spread and elongation were predicted after every compression step using a kinematically admi ss ible optimi sed velocity fields, yielding the minimum power requirements.

Fig . 5 describes the distortion , sagging and spread in material deformation using the current open die forging cell. Flow occurs in the longitudinal and lateral directi ons, x and y respecti vely as the height of workpiece and thus the c ross secti on is reduced

L,q,q-0'ff~~,q,q,q,q,q,q,q,q", ..L : • .. . .. : L,q,q,q-0'"ij'h/~<!w,q,q,q,q,q,q", l·jioF)(;r.: IJror :". b · .. : .

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Fig. 5- An illustrati on of pressing action possible to produce sagg ing and d istorti ons

between flat tools. The actual bulge shape in thi s type of forming operations is normally of an approximate parabolic type and is affected by forming conditions, friction , structural behaviour, aspect ratio and tool width . The internal plastic and friction power were calculated over the area of contact with the tool through various friction conditions(l<m<O). The final energy formulae was then optimised numerically with respect to an independent pseudo parameter and required tota l load and final dimensions were then predicted. The CPU time required for ten incremental steps was fo und to be less than half a minute on a SUN SPARC+ workstation with 12 MB of memo ry. Such speeds would enable the proposed on-line application using a faster PC and incorporating a feed back mechanism to reschedule the sequence at each inc rement if necessary.

For a given penetration level, the program predicts the fi nal maximum width of a partially compressed bille t in an incremental manner. The dimensions of the workpiece after compression become the initi a l dimensions for the next compression stage of the process. The second part of programming deals wi th prediction of load, dimensions and in addition enables to determine the effect of various tool widths of billet and friction factors m on metal flow for various aspect rat ios. To change the aspect ratio, the height hI! was fixed and the width Wo of the billet was varied for each compression cycle. The third part of the programming is not only to predict load and meta l

118 INDI AN J. ENG. M ATER. SCI.. APRIL 2003

flow for a given penetration in height at varying aspect ratios but also to ana lyse the workpiece as it is subjected to a multi cycle of compress ion-rotation through 90° again for various friction conditions. The relevant theoretical computing program optimises the total energy dissipation, compri sing the deformation and friction power and gives the optimum relati ve pressure. If the flow stress of the material is know n, the fo rging load requirement can then be computed by usi ng relati ve pressure va l ue and the contact area between workpiece and tool. For a given deformati on, billet/workpiece height reduces and the program also predicts all the final dimensions in an incremental manner for various fr iction conditi ons.

The defl ection of the robot arm, when loaded up to its des ign limits, was inves ti gated in order to ca li brate the req uired motions in the three dimensional material fl ow directions. The robot ann was fully extended and was loaded in 2 kg increments up to 20 kg suspended from the end of the grippers. The defl ecti on was recorded usi ng a dial test indicator. Some dev iation from this path was observed when the arm was unloaded which could have been due to flex ing of the robot joints. The gain of the amplifier was adj usted so as to gIve approx imate saturated readings at maximum loading.

Recently, processing in forging is most ly based on the indi vidual forge master's ex perience and observation, mainl y because each forging strike

a)

,. ,. j~--;

, I"i--. ;

Fig. 6a- Simple square cross-sec ti on bar products prodllced by curren t open di e forg ing cell (di storted and sagged specimens)

produce both elongat ion and sideways spreading as well as the possibility of material sagging where a dropping of the ends of the workpiece. As seen in Fi g. 6a in case of mi salignments, excessive deformation and false gripping cause sagging and di stotions in the bars . However, adeq uate contro l of the above factors enabl es to produce much bette r stepped bar formations usi ng the current open die fo rging cell , as seen in Fig. 6b. By thi s repeated mu lty-cycl e press ing, the current forg ing process resul ts in poss ibl e barrelled and radiused edges. However, the press ing operation would exert large forces on the bar, and when unavoidabl y transmitted to the robot, may lead to seri ous damages and voi late the system and di sable to continue the next press ing steps. Therefore, the undes ired deflections and sagging of the workpiece cause serious mi s-orrientat ions in the robo t arm , as a holder or manipul ator during continuous cyc lic press ing operations. The im pli cations of these effects have to be overcomed in the formation of a FFC. Therefore, a large scale of experiments were carri ed out to determine the optimum conditions required to avoi d the sagging/deflec ti on problems.

The prediction of final dimensions of long bars after cycl ic forging procedure through such a system is extremely important task in terms of evaluating the possible di splacements and so using th ese data as feed back in formation to avo id vital damages on the manipulating robot arm. The relevan t an alytical soluti ons used in thi s work are ex plained in detail in Aksakal ef a l . t3. Fig. 7 depicts the to tal amount of materi al volume di splaced or fl own horizontall y, in x direction for various aspect rati os and tool widths applying 25% penetration and fixed frict ion factor, Ill ,

of 0.5 . This material flow wi II directly effect the robot

"I

Fig. 6b- Spec imcns free of di stortion and sagging

AKSAKAL: ANALYS IS ON A FLEX IBLE FORGING CELL 119

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Initial Aspect Ratio(IAR) L-----O-'-5.---~ .-'---- ~_.J, ,-------"

Fi g. 7-The variation o r di spl aced material volume in the axia l direction

Initial Aspect Ratio(IAR)

6

5

E'4 5 -g3 ~ a.. Penetr;,ton

T~ary­

m=0 .5

wl1F0 .5 b=40mm

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Distance from the centre(mm)

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5 • whF1.4 • b=40mm 20% • 3

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OL-----~------________ ~ ____ ~ ___ OL-----~------~------~----~~

o 5 10 15 20 o 5 10 15 20

Distance from the centre(mm) Distance from the centre(mm)

Fig. 9- The variation of spread with with di stance from the centre

120 INDIAN J. ENG. M ATER. SCI.. APRIL 2003

arm and the amount of di splacement is surely needed to be determined. Despite the material flown in free sideways in y directi on, it does not seem to be affecting the robot arm.

However, the arm is affected when the bi lI et is rotated. Some adjustments are required in the hori za ntal direction. z, of th e robot ann. Therefore, the determination of maxi mum spreaded material in lateral direction is important fo r the nex t forg ing step, after ro tati on. Fi g. 8 shows the vari ati on of maximum percentage material flo wn in the sideway with aspect ratio and too l width during pressing action. Theoreti ca l predic iti on in comparison wi th experimental va lues are plotted in Fig. 9 in both free sideways, y direction , with di stance fro m the centre of the bar. The predi cti ons and experimen tal val ues of a quarter of spec imen material along the distance in x direction are show n for 0.5, 1.0. J .4 and 1.8 aspect ratios with fixed tool width and friction conditi ons. As seen from the figures, the theoretical predicti ons prove to be providing a good feed back data for the movement and readjustment of the robot arm .

The mi crostructure of cold-worked metal s can associate with rotated and elongated grain s, new dis locations wi th al igned structure28

. A study of electron diffraction has displayed distorted planes in the cold-worked all oy . Fig. to shows two di ffraction patterns taken from the undeformed (a) rthe first pattern 1. and the deformed (b) [the seco nd pattern]

Fig. lOa-Diffract ion patterns take n from undeformcd zone- I

reg ions (zone- I and III in Fig. 4) of the samples. Uniform spot rings in the first diffraction pattern (a). are ev idence of undi storted planes in the sam ple, that is, no deformati on. However, the second diffraction pattern (b) exhibits di storted rings due to the co ld deformation process. Some elongated grains were observed in the cold-worked TEM specimens and attributed to the co ld deformation as well.

It is know n29 that the grain si ze reach is maximum for pure AI after about 3% reducti on and then fall s progressive ly as the amount of cold work is increased. The degree of co ld work, however, often varies over different parts of deformed component. Defects . e.g. dis locati ons, move onl y a short distance before encountering a grain boundary as strength of the metal is increased and thus the properties of a metals can be contro lled by grain size strengt hening. The di slocati on behaviour during continuously multi­cyc led deformation of AI billets was observed using TEM to associate with many random ly ori ented grains and di slocations before and after cold defo rmation.

A pair of bright-fi eld electron-m icrographs whi ch show the gratns and dislocation structures of aluminium specimens are shown in Fig. II . The micrographs were taken from the undefonned (Zone­I) and deformed (Zone- III ) areas (see Fig. 4) of the alloy. The grain size meas urements were eva luated fo r the TEM mi crographs and the grai ns for the deformed and undefonned areas of all oy were found to be - 1500- 14000 A and 2000- 16000 A. respective ly.

Fig. IOb- DiffrJction patterns tak.:n from cl cf"r11ll:d 7()l1c- 1I 1

AKSA KAL: ANALYSIS ON A FLEX IBLE FORGING CELL 12 1

2 () O)l 1ll

h ) ;I)

Fi g. I I - (a) Electron micrographs showing dislocati ons in the incrementall y deformed bill et (deformed zone II ). (b) Electron micrographs showing dislocati ons in the incrementally deformed. zone III

As ex pected, the average grain size of the de formed part of alloy is smaller than the grain size of the undeformed part of alloy. Al so, higher di slocation densi ty was observed III the deformed TEM

specimens with nondeformed zone. It was detected that the stepped part (indicated in Fig. 4 zone- II ) that also can be named as deformed and di spl aced materia l between two fl at tools during compress ion of [he

122 INDIAN.I. ENG. MATER. SCI., APRIL 2003

alloy had lower di slocation density than the deformed part. Through the g.b analysis of di slocations27

.29

, it was found that the alloy had al2 < II 0> {III} slip systems for the di slocations. The differences between the micrographs are reduced di slocation densities in wh ich each sa mple were taken from the zone- III , (a)­normal to the x-z plane, and (b)-normal to the x-y planc of the continuously deformed billet, and the loca li sed hi gh strain rate which exists during the formation of deformation bands. It shows that the co ll ect ivc motion of di slocations, which occur to form bands. does not signi ficantl y change the microstructure seen after each incremental deformation cycle.

Conclusions Develop ment for the initial formation of a Flex ible

Forging Sys tem was dev ised using an FFC model for au tomati ng co ld forgi ng cell. From the theoret ical analysis and observations or material deformation, it was seen that a measuri ng system and material flow prediction to prov ide the movement of the robot arm, the workpi ece manipulator was imperat ive. Measurement devices were investigated and the pressure pads and strai n gauges were installed on the grippers of the robot arm sensing to prov ide a feed back information to the system. It was shown that such model, In wh ich computer-robot-press interfacing then coupling with material flow ca lculati on and measurements, was able to em ulate a simple shape production simultaneously. Finally, it was seen through the analysis end tests that if better monitoring system is provided, such system would enable to accommodate the full automation of a forgi ng process .

Acknowledgments The authors wish to thank Prof. A. . Bramley and

Dr F H Osman of the University of Bath ,UK, for supervi sing the initi al investigations and support received from the Turki sh Hi gher Education Council (YOK ). and to Prof. Y Atici for hi s help on the electron microscope at the A tati.i rk University, Turkey .

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