Materials

www.elsevier.com/locate/matdes

Materials and Design 28 (2007) 889–896

& Design

Design and applications of a pneumatic acceleratorfor high speed punching

Suleyman Yaldız *, Hacı Saglam, Faruk Unsacar, Hakan Is�ık

Mechanical Department, Technical Education Faculty, Selcuk University, 42031 Konya, Turkey

Received 8 April 2005; accepted 14 October 2005Available online 29 November 2005

Abstract

High speed forming is an important production method that requires specially designed HERF (high energy rate forming) machines.Most of the HERF machines are devices that consist of a system in which energy is stored and a differential piston mechanism is used torelease the energy at high rate. In order to eliminate the usage of specially designed HERF machines and to obtain the high speed form-ing benefits, the accelerator which can be adapted easily onto conventional presses has been designed and manufactured in this study.The designed energy accelerator can be incorporated into mechanical press to convert the low speed operation into high-speed operationof a hammer. Expectations from this work are reduced distortion rates, increased surface quality and precise dimensions in metal form-ing operations. From the performance test, the accelerator is able to achieve high speed and energy which require for high speed blankingof thick sheet metals.� 2005 Elsevier Ltd. All rights reserved.

Keywords: C-pneumatic accelerator; G-high speed shearing; G-data acquisition

1. Introduction

High speed forming technique is divided into twogroups; the first group covers the forming desired compo-nents with sufficient kinetic energy being imparted to thehammer as suddenly releasing compressed gas, the secondgroup covers the forming of metals in machines or devicesin which the force necessary to form the materials isobtained directly from such energy sources as the pressureof an explosive charge or a sudden electrical discharge. Inthis case, the energy is transferred directly to the metal tobe formed without any intermediate stage [1].

In the early development of high speed forming pro-cesses, many conflicting and exaggerated claims were made.Subsequent research on metals deformed at high straightrates and development work on high speed forming

0261-3069/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.matdes.2005.10.009

* Corresponding author. Tel.: +90 332 223 23 49; fax: +90 332 241 0185.

E-mail address: syaldiz@selcuk.edu.tr (S. Yaldız).

machines themselves has shown that many of these claimswere unfounded [2].

Nevertheless, in many cases, there are certain advanta-ges of using high speed. The products manufactured byconventional methods can be manufactured at high speedforming in same cost, with higher quality and they donot need finishing process [1]. It is observed that the qualityof shear-fractured surface improved and the amount of dis-tortion was reduced as a result of the use of high punchspeeds. This improvement is significant, particularly in caseof mild-steel, while with non ferrous metals marginalimprovement is obtained [3].

In high speed metal cutting processes, the required form-ing energy for metals is obtained by realising stored energysuddenly [4]. In the form of chemicals such as explosives andpetrol, electrical energy such as electromagnetic formingand compressed air, the early Dynapak high energy rateforming machine have been employed for forming the met-als [5]. The process of high speed forming involves the defor-mation of the metal at very high rate under impact load.

Nomenclature

A1 area of clearance between hammer cover and pis-ton head (mm2)

A2 area of flange of the piston (mm2)A3 area of top surface of hammer (mm2)A4 area of flange of the hammer (mm2)Fmax maximum press force (kN)Pin inlet pressure to piston chamber (bar)Pp pressure at compressed state in piston chamber

(bar)Ph1 pressure at expanded state in hammer chamber

(bar)Ph2 pressure at compressed state in hammer chamber

(bar)Phf pressure at the flange of the hammer (bar)Ph-exp pressure at explosion state in hammer chamber

(bar)Fh-exp force at explosion state in hammer chamber (N)

th acceleration time of the hammer (s)mh mass of the hammer (kg)ah acceleration of the hammer (m/s2)vh velocity of the hammer (m/s)ve experimental velocity of the hammer (m/s)Vp1 volume of piston chamber before compression

(m/s)Vp2 volume of piston chamber after compression (m/

s)Vh1 volume of hammer chamber before compression

(mm3)Vh2 volume of hammer chamber after compression

(mm3)Wk work done in compressing the air in the piston

chamber (J)c ratio of specific heatg gravitational acceleration (=9.81 m/s2)

Table 1Properties of material to be cut

Descriptions Properties

Material Mild steelUltimate shear strength, r (N/mm2) 300Penetration percentage, d (%) 38Clearance (%) ±5–10Diameter of punched hole (mm) 30Sheet thickness, c (mm) 10

890 S. Yaldız et al. / Materials and Design 28 (2007) 889–896

The common specifications of high speed formingmachines are that can convert any type of energy into thekinetic energy. If an accelerator which can be adapted onmechanical press is designed at high speed shearing, itcan be useful to take advantages of high speed shearing [6].

In order to take advantage of the high speed effects,presses with operational speed of about 10 m/s have tobe used. Conventional mechanical machines such as crankpresses operate at speeds ranging from 0.06 to 1.5 m/s.Compressed air, steam and gravity drop hammers to oper-ate at speeds (ranging from 4 to 10 m/s) approaching therequirement; however, their bulky structure made themunsuitable for blanking of metals. In connection with thedevelopment of high speed metal forming, a number ofhigh speed machines such as Dynapak [5], Petro Forge[7] and special air hammers which are generally called highenergy rate forming (HERF) machines, have been devel-oped in the last 30 years.

As they require high rate of energy, the high energyforming machines led the engineers to develop acceleratorsthat can be adapted easily onto the conventional presses toincrease high speed and energy about 10 m/s [7].

The design and development of an energy acceleratorwas first reported by Yanagihara et al. [8] for high speedcropping.

In this study, the pneumatic accelerator was designed,manufactured and tested on a conventional press. Also,some punching applications on different kind of parts werecarried out, the pressure occurred in cylinder and hammervolume and the speed of piston and hammer were mea-sured in operation. The advantages of the pneumatic accel-erator can be stated that the distortion rate is reduced incutting and stamping and surface quality is increased. Inthe usage of the same or similar tools on conventional

presses, provide comparatively longer tool life and alsomore precise dimensions as it is adapted onto conventionalpresses and is not required special tools, accelerator isbecame an economic solution on forming. It is also notrequired especially experienced operator. The needed com-pressed air (8 bar) can be supplied by an ordinary air com-pressor. The speed and kinetic energy to be applied onmaterial can easily be adjusted. This is not possible on anordinary conventional press [5].

2. Development of high speed pneumatic accelerator

2.1. Initial conditions

The purpose of this work is to design and manufactureof a pneumatic accelerator that would be adapted to theconventional press machine which has 400 kN punchingcapacity. The diameter of punch will be used is 30 mmand the blank thickness is 10 mm. The properties of mate-rial to be cut are shown in Table 1.

The accelerator contains two chambers; the pistonchamber (Vp) and the hammer chamber (Vh). For deter-mining piston and hammer chamber by considering therequired work (Wk) and hammer speed (vh); the piston

Ø255

Ø210

Ø156

Ø300

80

40

8045

Ø90

Ø84

Ø70

Ø60

30

280

180

175

A

B

C ED

F

GC

DIE

Air

Ø260

35

inlet port

A: PistonB: Lifting rodC: Check-valveD: CylinderE: Hammer cover F: Base plateG: Hammer

Fig. 1. Designed pneumatic accelerator.

S. Yaldız et al. / Materials and Design 28 (2007) 889–896 891

and hummer area and their strokes are used. The dimen-sions of the accelerator that includes these values of vol-umes are given in Fig. 1.

2.2. Design considerations

Considering the properties of the press in Table 2 to beused, some design criterions predefined and essentialdimensions are given in Fig. 1. It must be taken intoaccount that the minimum initial pressure should be ableto push and hold the hammer in the top position afterthe lifting rod disjoints itself from the hammer. In addition,the initial pressure must also be able to push the piston,including the lifting rod and hammer back to the initialposition. There should be no violations to the workingprinciples of the accelerators. Also, the energy of the accel-eration hammer must be high enough to perform highspeed forming of metals of various thicknesses. The speedof the hammer should be about 10 m/s in order to takeadvantage of high speed effects [6].

Table 2Technical specifications of the mechanical press

Descriptions Properties

Capacity of press (kN) 400Stroke range (mm) 10–70Number of stroke (stroke/min) 72Morse diameter (mm) 35Dimensions of table (mm) 420 · 540Hole diameter of the table (mm) 140Distance between table and head (mm) 450Motor power (kW) 4Speed (rpm) 1400Speed of the hammer (m/s) 0.14

An initial design was conceptualised, which included theconsiderations such as the tightening means for joining,chose of seals and check valve. The basic dimensionaldesign of essential components that conformed to alldesign criteria was made.

2.3. Working principles of the pneumatic accelerator

Compressed air at preset pressure is charged into the pis-ton chamber through the check valve as resulting the pistonto move upwards, and at the same time lifting the hammerthrough the lifting rod as shown in Fig. 2(a). When themechanical press is triggered on, the press hammer descendsto push the piston downwards and this will compress the airin the piston chamber (see Fig. 2(b)). At the same time, thelifting rod is dislodged from the hammer but the hammer isheld in position due to the pressure action on the under sideof the flange of the hammer (see Fig. 2(c)).

When the piston closes to the end of the stroke (seeFig. 2(d)), the highly compressed air in the piston chamberrushes into the hammer chamber through the neck of thelifting rod. This situation is similar to the situation of airrushing from a high pressure chamber through a nozzleto a low pressure chamber. This flow condition can beassumed to be adiabatic transformation. This sudden expo-sure of the large area to the high-pressure air causes thehammer to move downward. Once, the top of the hammerclears the port holes of the hammer cover, the high pressureair rushes into the hammer chamber through the portholes, thereby, forcing the hammer downwards in very highspeed which is more than enough for high speed forming.

On the return stroke of the press hammer, the piston(which is not attached to the press hammer) forces the press

F2e

Fp

F

Fp

exp

F

80

F

A ,V

A

p

1 1 p

2 3 h

4

in

2A

40

,VA

pF

F

F

1I

2I

3

I

75

F

pFa b

c d

Fig. 2. Operation principle of the pneumatic accelerator.

892 S. Yaldız et al. / Materials and Design 28 (2007) 889–896

hammer upward because the pressure in the piston cham-ber is still very high. At the same time, the lifting rod liftsthe hammer upward causing the air in the hammer cham-ber to flow into the piston chamber through the checkvalve that is attached to the hammer cover (see Fig. 2).The cycle repeats itself and the number of strokes per min-ute of the energy converter will be the same as the numberof strokes per minute of the press.

2.4. Theoretical calculations of the pneumatic accelerator

There are different methods of working on sheet metalsin press. Fig. 3 shows the progressive deformation and thedevelopment of a shear fracture during the shearing pro-cess, together with a typical load penetration sketch. Theeffect of clearance of on the piercing of a moderately ductilemetal which work hardens and begins to develop cracks atan early stage of penetration. The work done in shearing is

PIERCING

DIE

PUNCH

t

CLEARANCE

PE

NE

TR

AT

ING CLEARANCE

Fig. 3. Influence of clearance when piercing a hole [9].

somewhere near minimum, but the maximum load on thepunch is almost independent of the clearance and is givenby [9]

F max ¼ c � lc � rs; ð1Þwhere c is metal thickness, lc is cutting perimeter and rs isultimate shear stress of metal. Applying the predefineddimensions in Table 1 to Eq. (1), required maximum pressforce to punch the mild steel material is found as

F max ¼ 282 kN.

The estimated value of work required for shearing opera-tion, is given by

W k ¼ F max � d � c; ð2Þwhere the percentage penetration (d) represents the propor-tional depth to which the tool sink into the metal beforecracks run into the other.

Applying the values of Fmax, and d, c from Table 1 toEq. (2), the work can be calculated as

W k ¼ 1071:6 J.

While the volume of piston chamber depends on areas ofA1 and A2, the hammer volume depends on A3 and A4

(see Fig. 2). Compressed air at preset pressure (Pin) ischarged into the accelerator when the system is initial posi-tion and acts A1 and A2 areas and while the pressure createsa force moving the piston upward, the pressure in hammerchamber and the hammer weight creates a force down-ward, as a result, the both forces are equal to each other.In addition, the compression of air in piston chamber takesplace in only fraction of a second, thus, it can be assumedthat the compression is an adiabatic transformation:

S. Yaldız et al. / Materials and Design 28 (2007) 889–896 893

F 1 ¼ F 2;

P inðA1 þ A2Þ ¼ P h1A3 � P inA4 þ mhg.ð3Þ

The areas of the piston and the hammer are found as fol-lows by using the dimensions in Fig. 1: A1 = 50,265 mm2,A2 = 17,593 mm2, A3 = 30,788 mm2, A4 = 15,523 mm2,and mh = 14.84 @ 15 kg.

The pressure in the hammer chamber (Ph1) at the initialposition is found by using Eq. (3) for 4 bar inlet pressure(Pin) as Ph1 = 10.84 bar.

When the system has completed the high speed formingin each cycle that is when the hammer has reached to thelowest point, the pressures in each chamber (piston andhammer chamber) is equal to inlet pressure (see Fig. 2(d)).While the lifting rod lifts the hammer upward for a newoperation, the volume of the hammer decreases and thepressure increases in the volume. When the lifting rodreaches to the highest point, the rate of the hammer volumesfor the beginning and after forming can be obtained fromthe following equation:

P h1 � V 1;4h1 ¼ P in � V 1;4

h2 . ð4Þ

The rate of the hammer volumes (Vh1/Vh2) for the initialand final position of the system is

V h1

V h2

¼ 2:03.

Depending on the volume situations, when the air inletports are being 80 mm below from the bottom face of thepiston cover and the distance between hammer cover andthe top face of the hammer is 40 mm the condition ofVh1/Vh2 = 2.03 is provided.

In this situation, while the press moves downward, boththe lifting rod and the hammer move down, too. When theupper surface of the hammer is at the distance 5 mm to theinlet port the hammer starts to move upward because ofincreasing pressure in the piston chamber (see Fig. 2(b)).In this case, pressure variation in the hammer chambercan be calculated as by the following equation:

P h2 � ðA3 � h1Þ1;4 ¼ P in � ðA3 � h2Þ1;4. ð5Þ

When the distance between lower surface and upper sur-face of the hammer cover is 75 mm the pressure in the ham-mer chamber is given as

P h2 ¼ 4:38 bar.

At the same time the downward force (F2) created by thehammer would be as

F 2 ¼ P h2A3 þ mhg; F 2 ¼ 13:626 kN. ð6Þ

When the hammer creates downward force F 02 the pressurein the piston chamber creates also upward force F 01

F 01 ¼ F 02. ð7Þ

From Eq. (7), the pressure at the flange surface of the ham-mer ðP hf

Þ when the hammer starts to move upward is:

P h1 ¼F 2

A3

; P h1 ¼ 8:78 bar.

When the pressure at the initial position in piston chamber(4 bar) is increased to 8.78 bar, the rate of volumes wouldthen be as

P in � V 1:4p1 ¼ P p � V 1:4

p2 ; P p ¼ 1:76.

At the initial position the volume of piston chamber(Vp1(80)) at stroke of 80 mm (in addition to the volume ofinlet ports calculated as 40,000 mm3) is

V p1ð80Þ ¼ 6; 952; 677 mm3.

When the piston moves downward by the press, the liftingrod together with the hammer is also moved downward. Inorder to reach of the hammer to inlet port, the piston mustbe descend down 40 mm and by means of increasing pres-sure in the piston chamber, the hammer again moves backupward before it reaches to the inlet ports. In this case,when the piston at the stroke of 40 mm it should beVp1(80)/Vp2(40) > 1.76 so the hammer can start to move up-ward before it reaches to the inlet ports.

The piston volume (Vp2(40)) for 40 mm stroke is foundas

V p2ð40Þ ¼ 3;735;891 mm3.

Now the rate of piston volumes at the initial position for40 mm stroke would then be

V p1ð80Þ

V p2ð40Þ¼ 1:86;

1.86 > 1.76, this means that it will be suitable to place theinlet ports at 40 mm below. The volume of piston chamber(Vp2(70)) at full stroke (for 70 mm stroke length) is found as

V p2ð70Þ ¼ 2;274;061 mm3.

The pressure at compressed state in piston chamber(Pp) for variation of the stroke from 80 to 70 mm is foundas

P p � V 1;4p2ð70Þ ¼ P inV 1;4

p1ð80Þ; P p ¼ 19:12 bar. ð8Þ

The pressure in hammer chamber (Ph2) can be found as fol-lows by using Eq. (9) at 70 mm stroke which is the criticalpoint just before the explosion when the forces acting onhammer surface are equal (see Fig. 2(c))

P pA4 ¼ P h2A3; P h2 ¼ 9:64 bar. ð9ÞThe volume of hammer chamber (Vh) in this pressure isfound by using the following equation:

P inV 1;4h1ð80Þ ¼ P h2V 1:4

h2 ; V h ¼ 1;313;977 mm3. ð10Þ

The pressure in the hammer chamber (Pexp) just afterexplosion is found by using the following equation (seeFig. 2(c)):

P pV 1:4p1 þ P hV 1:4

h1 ¼ P expðV p2 þ V h2Þ1:4; P exp

¼ 15:74 bar. ð11Þ

894 S. Yaldız et al. / Materials and Design 28 (2007) 889–896

The force created on the hammer (Fexp) after explosion isfound as

F 2- exp ¼ P 2- expðA3 � A4Þ; F 2- exp ¼ 24:024 N. ð12ÞBy means of force effect, the hammer is moved downwardat very high speed, the acceleration of the hammer (ah) isfound by using the following equation (Fig. 2(d)):

ah ¼F 2- exp

mh

; ah ¼ 1602 m=s2. ð13Þ

As taking the distance 50 mm, the acceleration time for thehammer (th) is found as:

x ¼ 1

2ah � t2;

th ¼ 0:0079 s.ð14Þ

At the end of the explosion stroke, the velocity of the ham-mer (vh) is found by using the following equation:

vh ¼ ahth; vh ¼ 12:66 m=s. ð15ÞSince potential energy should be equal to kinetic energy(Wk = Wp) from the principles of energy conservation,the velocity of the hammer (vhg) is found by using the fol-lowing equation:

1

2mhv2

hg ¼ mhgx; vhg ffi 1 m=s. ð16Þ

The total velocity of the hammer (vt) is found as

vt ¼ 13:66 m=s.

The kinetic energy created by the hammer is found as:

W k ¼1

2mhv2

t ; W k ¼ 1399 J.

X1

X2

oscCounter

Photocell

Fig. 4. Experimental set up for measuring the str

3. Experimental study

3.1. Test setup

In order to investigate the performance of the designedpneumatic accelerator, the measurement of pressure andspeed variations in operation is essential. For this purpose,a pressure regulator is fitted to air inlet to supply at con-stant pressure to the desired level. The pressure in the pis-ton chamber and the hammer chamber were measured bypressure transducers. To measure the hammering time,two photocells were used, one of which was fitted at the ini-tial position of the hammer end and the other was fitted tothe end of the stroke of the hammer as shown in Fig. 4. Thesignal taken from two photocells was transferred into thecounter. According to the signal values taken from thecounter, the speed of the pneumatic accelerator wascalculated.

The analog signals taken from the pressure transducerand the counter are converted into digital signals and trans-ferred to PC for evaluation. By using the speed values, thekinetic energy of the accelerator was calculated.

3.2. Materials and methods

The designed accelerator was manufactured and incorporatedonto a conventional press. The technical specifications of the pressare shown in Table 2. Various cutting operations were carried outon different kind of metals such as mild steels and copper. Theproperties of mild steel material punched are given in Table 1.

The inlet pressure was changed in range of 2–8 bar and pres-sure variations in piston and hammer chamber and also the ham-mering times were measured.

Y1

Y2

A/DConverter

0-5 V

PCL 818HG

Data AcquistionCard

PC

Pneumatic accelerator

and die set on the press

oke time of the hammer, pressure and speed.

Table 3Theoretical and experimental data for 2–10 bar

Pin (bar) Ph2 (bar) F2 (N) Pp (bar) Pexp (bar) F2-exp (N) ah (m/s2) th (s) vh (m/s) Wc (J) ve (m/s)

4 4.38 13,626 19.12 15.74 24,024 1602 0.0079 12.66 1399 11.025 5.47 16,996 23.90 19.49 29,757 1984 0.0071 14.08 1704 12.046 6.57 20,366 28.68 23.25 35,484 2366 0.0065 15.38 2010 13.297 7.66 23,736 33.46 27.00 41,211 2747 0.0060 16.58 2314 14.438 8.76 27,106 38.25 30.75 46,939 3129 0.0057 17.69 2617 15.219 9.85 30,476 43.03 34.50 52,666 3511 0.0053 18.74 2919 16.70

10 10.95 33,845 47.81 38.25 58,393 3893 0.0051 19.73 3220 17.85

S. Yaldız et al. / Materials and Design 28 (2007) 889–896 895

4. Results and discussion

In order to design the accelerator; the blanking diame-ter and sheet metal thickness were defined and therequired energy and maximum cutting force were calcu-lated to cut blanking. To provide the required energyand maximum force, some optimisations were performedfor the calculation of the dimensions of piston and ham-mer. The calculated and experimental values of the pres-sures in the piston and the hammer chamber and theforces on the piston and hammer surface and also the

0

5

10

15

20

25

30

35

40

45

15.7 19.5 23.2 27.0 30.7 34.5 38.3

Ph (bar)

F

(kN

)2-

exp

-exp

Fig. 5. Variation of the force by the pressure in explosion conditions.

0

5

10

15

20

25

15.7 19.5 23.2 27.0 30.7 34.5 38.3

Phexp (bar)

Vh

(m/s

)

0

500

1000

1500

2000

2500

3000

3500

Wc

(J)

Vh

Wc

Fig. 6. The speed and kinetic energy variation with the pressure inexplosion conditions.

kinetic energy were performed for 5–10 bar, are given inTable 3.

The variation of the force by pressure in explosion con-dition is shown in Fig. 5, the speed and kinetic energy var-iation with pressure are shown in Fig. 6.

The theoretical and experimental speed variations withpressure are given in Fig. 7. It shows that the theoreticalcalculations have given a good fit with experimental resultsobtained.

The same cutting operations were performed on the samepress for the same metal, with and without pneumatic accel-

1

5

9

13

17

21

15.7 19.5 23.3 27.0 30.8 34.5 38.3

Phexp (bar)

Vh

(m/s

)

1

5

9

13

17

21

Ve

(m/s

)

VhVe

Fig. 7. The theoretical and experimental speed variation by the pressure inexplosion conditions.

Fig. 8. Mild steel blanks produced by conventional method (on the left)and by high speed forming (on the right).

896 S. Yaldız et al. / Materials and Design 28 (2007) 889–896

erator and then the surface quality of work parts obtainedfrom two kinds of cutting methods were compared. Thephotograph of low-carbon steel blanks cut by conventionalmethod and high speed forming are shown in Fig. 8.

High speed forming is not a unique answer to metalmachining problems and most high speed forming processeshave their own particular difficulties. But there are definiteadvantages in using high speed for some metal working oper-ations, and is probably that high speed methods will becomeincreasingly acceptable alongside existing techniques.

5. Conclusions

The aim of this study was to design and manufacture anaccelerator as an energy converter to form the differenttypes of metals in high speed. Most significant outcomesof this study can be summarised as follows:

1. Instead of using high speed forming machines, develop-ing some energy converter systems that convert differenttypes of energy into mechanical energy are preferable.

2. Conventional mechanical presses can operate at speedsranging from 0.06 to 1.5 m/s. However, designed pneu-matic accelerator can operate at speeds at 10 m/s.

3. The products manufactured by utilising the pneumaticaccelerator have higher surface quality then the surfacesof products produced in conventional presses and theydo not need finishing process. Comparing two samplesproves that satisfactory results have obtained.

Acknowledgement

This experimental study was supported by Scientific Re-search Projects coordinator. The authors would also like tothank Scientific Research Projects coordinator of SelcukUniversity for providing the machine and materials forconducting the experiments.

References

[1] Davies R, Austin ER. Developments in high speed metal forming. NewYork: Industrial Press Inc.; 1970.

[2] Tobias SA. Survey of the development of Petro-Forge formingmachines. Oxford: Pergamon Press; 1985.

[3] Davies R, Dhawan SM. Further developments in high speedblanking of metals. In: Proceedings of 7th International machinetools design research conference, University of Birmingham,September, 1966.

[4] Bruno EL. High Velocity Forming of Metals. Revised Edition.ASTME; 1968.

[5] Mang WG. In: Special conference on high energy-rate forming, SheetMetal Industries; 1962.

[6] Chan LT, Ong NS. Design and development of an energy converter fora mechanical press and its application to high speed forming. Int JMach Tool Manufact 1988;29:161–9.

[7] Chan LT, Bakhtar F, Tobias SA. Design and development of petraforge high energy rate forming machines. Proc Inst Mech Eng1966;180.

[8] Yanagihara N, Saito H, Nakagawa A. A pneumatic accelerating deviceinstalled on press machine and its application to high speed cropping.Plast Process 1981;22:242.

[9] Lissaman AJ, Martin SJ. Principles of engineering production.London: ELBS Edition; 1983.