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A new technology of sheet-metal flexible-die forming using a viscoplastic pressure-carrying medium
Journal of
ELSEVIER
Journal of Materials Processing Techology 52 (1995) 359-367
Materials Processing Technology
A new technology of sheet-metal flexible-die forming using
a viscoplastic pressure-carrying medium Ming-Wang Fu a'*, Si-Quang Lu a, Mao-Heng Huang b Nanchang Institute of Aeronautical Technology, Nanchan9 330034, People's Republic of China b Governor Office of Jiangxi Province, Nanchang 330046, People's Republic of China
Received 13 January 1994
Industrial Summary The conventional pressure-carrying media of sheet-metal forming are solid materials (a rubber or polyurethane pad), liquid (oil and water) and gas (pressured air and expanding air). The various flexible-die forming methods using the above pressure-carrying media have a lot of different characteristics and have promoted the development of sheet metal forming technology. There are, however, a lot of disadvantages in using these pressure-carrying media. In order to explore a new pressure-carrying medium, numerous experiments have been undertaken, as a result of which a new type of pressure-carrying medium called a viscoplastic pressure-carrying medium (VPCM) has been synthesized. In this paper, a new kind of flexible-die forming technology using VPCM has been put forward and used to manufacture many different workpieces. The experimental results have shown that this kind of technology has a lot of advantages, such as a small drawing coefficient, good surface fineness, high dimensionalaccuracy, and a simple and a general-service die structure. Moreover, This technology can also be used to manufacture complicated workpieces with a large degree of deformation or substantial local deformation. According to the practical uses of this technology, three sets of die are described also in this paper.
1. Introduction Sheet m e t a l w o r k i n g is the b a c k b o n e of m a n y i n d u s t r i a l fields such as electronics, a u t o m o b i l e s , a g r i c u l t u r e m a c h i n e s a n d the a e r o n a u t i c a l a s t r o n a u t i c a l industry. Since the r e q u i r e m e n t s for d i m e n s i o n a l accuracy, surface fineness a n d shape c o m p l i c a t i o n of sheet m e t a l p r e s s - w o r k i n g w o r k p i e c e s are b e c o m i n g increasingly higher, m o r e lowplasticity a n d b a d - f o r m a b i l i t y sheet m e t a l s need to be formed. C o n c e r n i n g the third r e q u i r e m e n t , the m a n u f a c t u r i n g field has c o m e b a c k to the state of m o r e types a n d less
*Corresponding author. 0924-0136/95/$9.50 (~ 1995 Elsevier Science S.A. All rights reserved SSDI 0 9 2 4 ~ 0 1 3 6 ( 9 4 ) 0 1 6 1 8 - B
360
M.-W, Fu et al. /Journal (?[Materials Processing Technology 52 (1995) 359 367
output, especially in the aeronautical and astronautical industry. Conventional pressworking technology does not satisfy the needs of industrial development. Flexible die forming (FDF) is an important technology of sheet metal forming. It uses the pressure-carrying medium (PCM) to replace a rigid punch or die. The conventional pressure-carrying medium is liquid (water, oil), gas (pressured or expanding air) and an elastic body (a rubber or polyurethane pad). Thus, F D F uses a different PCM and has different characteristics. Liquid is used as the PCM for hydro-mechanical drawing [1,2]. Although it has been used widely, there are some disadvantages such as liquid splash when forming fails and difficulty in controlling the liquid pressure during forming. Thirdly, it is troublesome to perform the pressing operation due to concern about possible liquid leakage. Rubber is used as PCM for the Guerin process and polyurethane is often used as the PCM for F D F [3 7], but deep-drawing parts and complicated workpieces, however, cannot be produced by this F D F technology because of the deformation limit of PCM itself. Rubber-pad forming is also used widely in aeroplane factories. Its equipment, however, is very expensive and workpieces with great local deformation can not be manufactured by this process. Gas is used as the pressure-carrying medium for superplastic bulging and explosive forming, but its efficiency is low and its thickness reduction is great. Kurosaki et al. have used a viscoplastic medium (VM) to replace the rigid punch to pierce very small holes in sheet metal [8 11 ], which is another good use of FDF. On the basis of the above statement, an attempt is made in an exploratory way to discover a new process of sheet-metal flexible-die forming using a new kind of viscoplastic material synthesized by the present authors as the PCM. This PCM has a viscoplastic mechanics behaviour and it is called a viscoplastic pressure-carrying medium (VPCM). A great deal of effort has been put into both exploring the principles and experimental study. A lot of workpieces with a low drawing coefficient and a complicated shape have been formed by this technology. The workpieces shown in Fig. 4 have been manufactured by flexible die forming using the VCPM. These workpieces are manufactured in the same die, by means of changing the punch, the blank-holder and the flange.
2. The characteristics and advantages of this new technology by comparison with conventional FDF F D F using the VPCM has a lot of advantages: (1) The main characteristics of the die are a simple structure, low cost, a short manufacturing period and universal usage, so that different workpieces can be manufactured in the same die set by changing the punch, the flange and the blankholder. (2) Great formability. Because the VPCM changes the flow pattern and stress states of the sheet metal, the formability can be improved greatly. For example, the drawing coefficient of 08AI is 0.57-0.58 for conventional drawing, 0.41 for hydro-mechanical drawing, but is 0.38 for this kind of FDF. For the hemi-spherical workpiece of stainless steel sheet metal with a barrel-shaped bottom in Fig. 4(a), the drawing
M.-VK Fu et al./Journal of Materials Processing Technology 52 (1995) 359 367
361
coefficient of the barrel is 0.21. This illustrates that sheet metal formability using this new technology is much better than that of conventional drawing and hydro-mechanical drawing. (3) Increasing of the dimensional accuracy of products and decreasing of the spring-back. The VPCM of this technology improves the stress state and the stress distribution, so that it increases the dimensional accuracy. For FDF, the dimensional accuracy can reach IT 9-10, but its value is only ITll-12 for conventional drawing technology. (4) Good surface fineness. In conventional drawing, the sheet metal is deformed by the way of flowing along the corner of the rigid die, so that the surface of sheet metal is easily scratched. However, for this technology, the sheet metal is deformed by the way of forming a "convex ridge" in the drawing process. Therefore, the sheet metal do not flow along the corner of flange and its surface is not scratched and retains the original surface fineness of the sheet metal. (5) Small wall-thickness reduction. The high pressure generated by VPCM makes the sheet metal wrap the punch tightly and the frictional effect between the punch and the sheet metal makes the radial tensile stress decrease. On the other hand, the strain-rate sensitivity of VPCM makes it easy to set up high pressure in the medium container and to increase the visco-friction effect between the VPCM and the sheet metal, which produces the resistance to the wall-thickness reduction of the sheet metal. On account of the above, the wall-thickness reduction is small in this technology. For the flat cupping of 08A1 sheet metal for which the drawing coefficient is 0.57, the maximum wallthickness reduction is about 15 20%, but the maximum wall-thickness reduction is only 8% when the drawing coefficient is 0.38 for the present technology. The drawing coefficient of the cone-shaped workpiece in Fig. 4(f) is 0.40 and the maximum wallthickness reduction at the top of the workpiece is less than 34%. (6) A lot of low-plasticity and bad-formability materials or high-strength materials can be deformed by this technology. (7) Workpeices with complicated or unusual shapes can be manufactured by this technology, such as the workpieces shown in Figs. 4 (d), (f)-(i).
3. The requirements for a viscoplastic pressure-carrying medium In view of the disadvantages of the PCM of conventional F D F and the experiences of hydro-mechanical drawing research, the authors think that the ideal VPCM should meet the following requirements: (a) relatively high strain-rate sensitivity; (b) low adhesion to the metal surface and a good ability to be easily shed from the surface of the workpieces and the die; (c) good sticky ability and stability; (d) proper stickiness and cohesion, i.e., difficult to splash; (e) harmless to human health and non-polluting of the environment; (f) good repeatability in use: On the basis of the above requirements and numerous experimental results, the authors have synthesized a kind of viscoplastic pressure-carrying medium. Experimental results have shown that the VPCM meets the above requirements.
362
~L-W. Fu et al./Journal qf Materials Processing Technology 52 (1995) 359 367 Punch
Upper' b o l s t ~'r
I
"
St
Scre~ 2 Fig. 1. Rigid b l a n k - h o l d i n g s t r u c t u r e .
4. D i e structure
As stated above, flexible-die forming uses a pressure-carrying medium to replace the rigid-punch or rigid-die, Fig. 1 is the F D F die for using the VPCM. In the figure, the sheet metal is placed on the medium container which is full of VPCM. After the punch has been inserted into the container, the high pressure of the VPCM is created, whereupon the VPCM presses the blank against the surface of the punch to form the workpiece to the shape of the punch. The characteristics of the die structure are as follows: (1) General service. Different workpieces can be manufactured using a different punch, blank-holder and flange. The workpieces shown in Fig. 8 have been manufactured by this way. (2) Blank-holding Force. The blank-holding force for the die set is generated by a rigid blank-holding structure and can be controlled according to the sheet metal and the workpieces. (3) Filling of VPCM. For large mass production, the VPCM does not flow out from the container. After the punch has been inserted into the container the pusher bar moves down, and after deformation has ceased the pusher bar moves up to let the VPCM rise up to the flange plane. For small mass production, the VPCM can flow out of the container through the throtting set mounted in the throtting hole. The filling of the VPCM is finished by manual operation. (4) Controlling of the pressure. As the filling of VPCM is performed by the movement of the pusher bar, the pressure of the VPCM inside the container is controlled by the throtting, set according to the strength, the formability of the sheet
M.-W. Fu et al. / Journal of Materials Processing Technology 52 (1995) 359-367
363
tpperbolster
Sprin9 2 ~ ,
Sprin91 ~ Blank holder / ~ / Flan9e
2.~
Sealri~19
•
~ ~i/li
o lt,q]olJtI
Seal r i n g ~
Fig. 2 Elastic blank-holding structure.
Bar l:0~e;'!mlsl,,;,
F
Pu,,~,
V
"/-'fl/A
IF5117"./'71 B;a;~k hinter,
//IVA
~V/A----~
~ Pressure
meask~ l r~v~
iIil~COIla~iltel'
h
e
r
Fig. 3. Die suitable for a twin-drive press,
metal and the workpieces shape. The handling of the blank-holder in Fig. 1 must be performed for every forming operation. The production efficiency is low and it takes 3-5 min to perform one forming operation. Thus it cannot be suitable to large mass production. The blank-holder in Fig. 2 is elastic. The blank-holding force can be controlled by holding down the spring of the blank-holding set. The filling of the V P C M and the controlling of its pressure are the same as for the first die set. The main characteristic of this die set is that it is more efficient than the first die set. Fig. 3 is
364
M.-W, Fu et al./Journal of Materials Processing Technology 52 (1995) 359 367
(e)
(a)
(b)
(c)
(d)
(f) Fig. 4. Workpieces manufactured by the new technology.
M.-W. Fu et al. /Journal of Materials Processing Technology 52 (1995) 359-367
(g) (h)
(i)
(J)
(k)
(0 Fig. 4. (Continued)
365
366
M.-W. Fu et al./Journal ojMaterials Processing Technology' 52 (1995) 359 367
a further die set, suitable for twin-drive press, and it can be used to press automobile parts. The pressure measurer is mounted in the throtting holes.
5. Applications The workpieces shown in Fig. 4 are applications of this new technology to the manufacturing of actual workpieces and complicated parts. All of the workpieces have been manufactured in one operation. Workpieces (a) (c) are helicopter parts, (a) being a hemispherical part with a barrel bottom. Its material is stainless steel and the conventional drawing coefficient is 0.56-0.58, but the drawing coefficient of its barrel bottom is about 0.21. Parts of (b) and (c) have a high requirement for surface fineness and dimensional accuracy. The workpieces from (d)-(l) are either of complicated shape or have a small drawing coefficient. The drawing coefficient of(e) is 0.38, but the conventional drawing coefficient and hydro-mechanical-drawing coefficient are 0.58 and 0.40 respectively for this material. The workpiece in (f) has the property that the flange plane is at an angle to the drawing axis. The drawing coefficient (defined as d/D, where d is the maximum diameter of the workpiece and D is the original blank diameter) is 0.40, but the conventional drawing coefficient is 0.56-0.58. It is reported that this kind of workpiece with such a degree of deformation need eight die sets for drawing. All of the workpeices in Fig. 4 have been manufactured using the same die sets, so the new process saves at least thirty to forty die sets that would be required to produce these workpieces with conventional technology.
6. Conclusions (1) The new technology of sheet-metal flexible-die forming using the VPCM has a lot of advantages over other flexible die forming methods, such as a small drawing coefficient, good surface fineness, high dimensional-accuracy and a simple and general-service die structure. (2) The new technology need not impose any extra requirements for forming equipment over those for conventional drawing. (3) The new technology has a great ecomonic potential and great prospects for application. (4) The VPCM is suited to mass production and its cost is reasonable.
References [1] Japanese Patent, No. 36-200010. [2] H. Amino, K. Nakamura. T. Nakagawa, Y. Kurosaki, Y. Mizukusa, Y. Miyake, Hydraulic drawing and its application on the forming of automobile parts, J. Mats. Proc. Tech., 23 (1990) 243 265. [3] Japanese Patent, No. 57-55493. [4] German Patent~ No, 2601423.3. [.5] Soviet Union Patent, No. 1156774. [6] S. Thiruvarudchelvan and J.G. Gan, Drawing of hemispheric cups with an annular urethane pad, J. Mals. Proc. Techn., 36 (1992) 43 55.
M.-W. Fu et al. / Journal o f Materials Processing Technology 52 (1995) 359-367
367
[7] S. Thiruvarudchelvan and J.G. Gan, Deep drawing of conical cups using friction-actuated blank holding, J. Mats. Shaping Tech., 9 (2) (1991) 59-65. [8] Y. Kurosaki, I. Fujishir, Y. Miyake, Y. Fayukawa, A simple piering process applicable to brittle materials, J. Eng. lnd. 12 (May 1990) 155-160. [9] Y. Kurosaki, l. Fujishir., Y. Miyake, Y. Fayukawa, A piercing technique for glass sheets by the impact compression of a viscoplastic pressure medium, JSME lnt, J., 32 (2) (1989) 330 337. [10] Y. Kurosaki, studies on microplastic working, Adv. Tech. Plasticity, 2 (1990) 105%1064. [11] Y. Kurosaki, 1. Fujishiro, K. Bann and A. Kamoto, A manufacturing process using the impact compression of a viscoplastic pressure medium-application to the piering of fine holes, JSME lnt J., 30, (2621 (1987) 653 660. [12] Mao-Heng Huan, Sheet metal flexible die forming technology by using the viscoplastic pressurecarrying medium. Proc. 2nd Int. Conf. on Die and Mould Tech., Singapore; (1992) 247-254.
ELSEVIER
Journal of Materials Processing Techology 52 (1995) 359-367
Materials Processing Technology
A new technology of sheet-metal flexible-die forming using
a viscoplastic pressure-carrying medium Ming-Wang Fu a'*, Si-Quang Lu a, Mao-Heng Huang b Nanchang Institute of Aeronautical Technology, Nanchan9 330034, People's Republic of China b Governor Office of Jiangxi Province, Nanchang 330046, People's Republic of China
Received 13 January 1994
Industrial Summary The conventional pressure-carrying media of sheet-metal forming are solid materials (a rubber or polyurethane pad), liquid (oil and water) and gas (pressured air and expanding air). The various flexible-die forming methods using the above pressure-carrying media have a lot of different characteristics and have promoted the development of sheet metal forming technology. There are, however, a lot of disadvantages in using these pressure-carrying media. In order to explore a new pressure-carrying medium, numerous experiments have been undertaken, as a result of which a new type of pressure-carrying medium called a viscoplastic pressure-carrying medium (VPCM) has been synthesized. In this paper, a new kind of flexible-die forming technology using VPCM has been put forward and used to manufacture many different workpieces. The experimental results have shown that this kind of technology has a lot of advantages, such as a small drawing coefficient, good surface fineness, high dimensionalaccuracy, and a simple and a general-service die structure. Moreover, This technology can also be used to manufacture complicated workpieces with a large degree of deformation or substantial local deformation. According to the practical uses of this technology, three sets of die are described also in this paper.
1. Introduction Sheet m e t a l w o r k i n g is the b a c k b o n e of m a n y i n d u s t r i a l fields such as electronics, a u t o m o b i l e s , a g r i c u l t u r e m a c h i n e s a n d the a e r o n a u t i c a l a s t r o n a u t i c a l industry. Since the r e q u i r e m e n t s for d i m e n s i o n a l accuracy, surface fineness a n d shape c o m p l i c a t i o n of sheet m e t a l p r e s s - w o r k i n g w o r k p i e c e s are b e c o m i n g increasingly higher, m o r e lowplasticity a n d b a d - f o r m a b i l i t y sheet m e t a l s need to be formed. C o n c e r n i n g the third r e q u i r e m e n t , the m a n u f a c t u r i n g field has c o m e b a c k to the state of m o r e types a n d less
*Corresponding author. 0924-0136/95/$9.50 (~ 1995 Elsevier Science S.A. All rights reserved SSDI 0 9 2 4 ~ 0 1 3 6 ( 9 4 ) 0 1 6 1 8 - B
360
M.-W, Fu et al. /Journal (?[Materials Processing Technology 52 (1995) 359 367
output, especially in the aeronautical and astronautical industry. Conventional pressworking technology does not satisfy the needs of industrial development. Flexible die forming (FDF) is an important technology of sheet metal forming. It uses the pressure-carrying medium (PCM) to replace a rigid punch or die. The conventional pressure-carrying medium is liquid (water, oil), gas (pressured or expanding air) and an elastic body (a rubber or polyurethane pad). Thus, F D F uses a different PCM and has different characteristics. Liquid is used as the PCM for hydro-mechanical drawing [1,2]. Although it has been used widely, there are some disadvantages such as liquid splash when forming fails and difficulty in controlling the liquid pressure during forming. Thirdly, it is troublesome to perform the pressing operation due to concern about possible liquid leakage. Rubber is used as PCM for the Guerin process and polyurethane is often used as the PCM for F D F [3 7], but deep-drawing parts and complicated workpieces, however, cannot be produced by this F D F technology because of the deformation limit of PCM itself. Rubber-pad forming is also used widely in aeroplane factories. Its equipment, however, is very expensive and workpieces with great local deformation can not be manufactured by this process. Gas is used as the pressure-carrying medium for superplastic bulging and explosive forming, but its efficiency is low and its thickness reduction is great. Kurosaki et al. have used a viscoplastic medium (VM) to replace the rigid punch to pierce very small holes in sheet metal [8 11 ], which is another good use of FDF. On the basis of the above statement, an attempt is made in an exploratory way to discover a new process of sheet-metal flexible-die forming using a new kind of viscoplastic material synthesized by the present authors as the PCM. This PCM has a viscoplastic mechanics behaviour and it is called a viscoplastic pressure-carrying medium (VPCM). A great deal of effort has been put into both exploring the principles and experimental study. A lot of workpieces with a low drawing coefficient and a complicated shape have been formed by this technology. The workpieces shown in Fig. 4 have been manufactured by flexible die forming using the VCPM. These workpieces are manufactured in the same die, by means of changing the punch, the blank-holder and the flange.
2. The characteristics and advantages of this new technology by comparison with conventional FDF F D F using the VPCM has a lot of advantages: (1) The main characteristics of the die are a simple structure, low cost, a short manufacturing period and universal usage, so that different workpieces can be manufactured in the same die set by changing the punch, the flange and the blankholder. (2) Great formability. Because the VPCM changes the flow pattern and stress states of the sheet metal, the formability can be improved greatly. For example, the drawing coefficient of 08AI is 0.57-0.58 for conventional drawing, 0.41 for hydro-mechanical drawing, but is 0.38 for this kind of FDF. For the hemi-spherical workpiece of stainless steel sheet metal with a barrel-shaped bottom in Fig. 4(a), the drawing
M.-VK Fu et al./Journal of Materials Processing Technology 52 (1995) 359 367
361
coefficient of the barrel is 0.21. This illustrates that sheet metal formability using this new technology is much better than that of conventional drawing and hydro-mechanical drawing. (3) Increasing of the dimensional accuracy of products and decreasing of the spring-back. The VPCM of this technology improves the stress state and the stress distribution, so that it increases the dimensional accuracy. For FDF, the dimensional accuracy can reach IT 9-10, but its value is only ITll-12 for conventional drawing technology. (4) Good surface fineness. In conventional drawing, the sheet metal is deformed by the way of flowing along the corner of the rigid die, so that the surface of sheet metal is easily scratched. However, for this technology, the sheet metal is deformed by the way of forming a "convex ridge" in the drawing process. Therefore, the sheet metal do not flow along the corner of flange and its surface is not scratched and retains the original surface fineness of the sheet metal. (5) Small wall-thickness reduction. The high pressure generated by VPCM makes the sheet metal wrap the punch tightly and the frictional effect between the punch and the sheet metal makes the radial tensile stress decrease. On the other hand, the strain-rate sensitivity of VPCM makes it easy to set up high pressure in the medium container and to increase the visco-friction effect between the VPCM and the sheet metal, which produces the resistance to the wall-thickness reduction of the sheet metal. On account of the above, the wall-thickness reduction is small in this technology. For the flat cupping of 08A1 sheet metal for which the drawing coefficient is 0.57, the maximum wallthickness reduction is about 15 20%, but the maximum wall-thickness reduction is only 8% when the drawing coefficient is 0.38 for the present technology. The drawing coefficient of the cone-shaped workpiece in Fig. 4(f) is 0.40 and the maximum wallthickness reduction at the top of the workpiece is less than 34%. (6) A lot of low-plasticity and bad-formability materials or high-strength materials can be deformed by this technology. (7) Workpeices with complicated or unusual shapes can be manufactured by this technology, such as the workpieces shown in Figs. 4 (d), (f)-(i).
3. The requirements for a viscoplastic pressure-carrying medium In view of the disadvantages of the PCM of conventional F D F and the experiences of hydro-mechanical drawing research, the authors think that the ideal VPCM should meet the following requirements: (a) relatively high strain-rate sensitivity; (b) low adhesion to the metal surface and a good ability to be easily shed from the surface of the workpieces and the die; (c) good sticky ability and stability; (d) proper stickiness and cohesion, i.e., difficult to splash; (e) harmless to human health and non-polluting of the environment; (f) good repeatability in use: On the basis of the above requirements and numerous experimental results, the authors have synthesized a kind of viscoplastic pressure-carrying medium. Experimental results have shown that the VPCM meets the above requirements.
362
~L-W. Fu et al./Journal qf Materials Processing Technology 52 (1995) 359 367 Punch
Upper' b o l s t ~'r
I
"
St
Scre~ 2 Fig. 1. Rigid b l a n k - h o l d i n g s t r u c t u r e .
4. D i e structure
As stated above, flexible-die forming uses a pressure-carrying medium to replace the rigid-punch or rigid-die, Fig. 1 is the F D F die for using the VPCM. In the figure, the sheet metal is placed on the medium container which is full of VPCM. After the punch has been inserted into the container, the high pressure of the VPCM is created, whereupon the VPCM presses the blank against the surface of the punch to form the workpiece to the shape of the punch. The characteristics of the die structure are as follows: (1) General service. Different workpieces can be manufactured using a different punch, blank-holder and flange. The workpieces shown in Fig. 8 have been manufactured by this way. (2) Blank-holding Force. The blank-holding force for the die set is generated by a rigid blank-holding structure and can be controlled according to the sheet metal and the workpieces. (3) Filling of VPCM. For large mass production, the VPCM does not flow out from the container. After the punch has been inserted into the container the pusher bar moves down, and after deformation has ceased the pusher bar moves up to let the VPCM rise up to the flange plane. For small mass production, the VPCM can flow out of the container through the throtting set mounted in the throtting hole. The filling of the VPCM is finished by manual operation. (4) Controlling of the pressure. As the filling of VPCM is performed by the movement of the pusher bar, the pressure of the VPCM inside the container is controlled by the throtting, set according to the strength, the formability of the sheet
M.-W. Fu et al. / Journal of Materials Processing Technology 52 (1995) 359-367
363
tpperbolster
Sprin9 2 ~ ,
Sprin91 ~ Blank holder / ~ / Flan9e
2.~
Sealri~19
•
~ ~i/li
o lt,q]olJtI
Seal r i n g ~
Fig. 2 Elastic blank-holding structure.
Bar l:0~e;'!mlsl,,;,
F
Pu,,~,
V
"/-'fl/A
IF5117"./'71 B;a;~k hinter,
//IVA
~V/A----~
~ Pressure
meask~ l r~v~
iIil~COIla~iltel'
h
e
r
Fig. 3. Die suitable for a twin-drive press,
metal and the workpieces shape. The handling of the blank-holder in Fig. 1 must be performed for every forming operation. The production efficiency is low and it takes 3-5 min to perform one forming operation. Thus it cannot be suitable to large mass production. The blank-holder in Fig. 2 is elastic. The blank-holding force can be controlled by holding down the spring of the blank-holding set. The filling of the V P C M and the controlling of its pressure are the same as for the first die set. The main characteristic of this die set is that it is more efficient than the first die set. Fig. 3 is
364
M.-W, Fu et al./Journal of Materials Processing Technology 52 (1995) 359 367
(e)
(a)
(b)
(c)
(d)
(f) Fig. 4. Workpieces manufactured by the new technology.
M.-W. Fu et al. /Journal of Materials Processing Technology 52 (1995) 359-367
(g) (h)
(i)
(J)
(k)
(0 Fig. 4. (Continued)
365
366
M.-W. Fu et al./Journal ojMaterials Processing Technology' 52 (1995) 359 367
a further die set, suitable for twin-drive press, and it can be used to press automobile parts. The pressure measurer is mounted in the throtting holes.
5. Applications The workpieces shown in Fig. 4 are applications of this new technology to the manufacturing of actual workpieces and complicated parts. All of the workpieces have been manufactured in one operation. Workpieces (a) (c) are helicopter parts, (a) being a hemispherical part with a barrel bottom. Its material is stainless steel and the conventional drawing coefficient is 0.56-0.58, but the drawing coefficient of its barrel bottom is about 0.21. Parts of (b) and (c) have a high requirement for surface fineness and dimensional accuracy. The workpieces from (d)-(l) are either of complicated shape or have a small drawing coefficient. The drawing coefficient of(e) is 0.38, but the conventional drawing coefficient and hydro-mechanical-drawing coefficient are 0.58 and 0.40 respectively for this material. The workpiece in (f) has the property that the flange plane is at an angle to the drawing axis. The drawing coefficient (defined as d/D, where d is the maximum diameter of the workpiece and D is the original blank diameter) is 0.40, but the conventional drawing coefficient is 0.56-0.58. It is reported that this kind of workpiece with such a degree of deformation need eight die sets for drawing. All of the workpeices in Fig. 4 have been manufactured using the same die sets, so the new process saves at least thirty to forty die sets that would be required to produce these workpieces with conventional technology.
6. Conclusions (1) The new technology of sheet-metal flexible-die forming using the VPCM has a lot of advantages over other flexible die forming methods, such as a small drawing coefficient, good surface fineness, high dimensional-accuracy and a simple and general-service die structure. (2) The new technology need not impose any extra requirements for forming equipment over those for conventional drawing. (3) The new technology has a great ecomonic potential and great prospects for application. (4) The VPCM is suited to mass production and its cost is reasonable.
References [1] Japanese Patent, No. 36-200010. [2] H. Amino, K. Nakamura. T. Nakagawa, Y. Kurosaki, Y. Mizukusa, Y. Miyake, Hydraulic drawing and its application on the forming of automobile parts, J. Mats. Proc. Tech., 23 (1990) 243 265. [3] Japanese Patent, No. 57-55493. [4] German Patent~ No, 2601423.3. [.5] Soviet Union Patent, No. 1156774. [6] S. Thiruvarudchelvan and J.G. Gan, Drawing of hemispheric cups with an annular urethane pad, J. Mals. Proc. Techn., 36 (1992) 43 55.
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