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Simulation of a hydraulic short-stroke device for deep drawing
ELSEVIER
J. Mater. Process. Technol. 43 (1994) 305-315
Journal of Materials Processing Technology
Simulation of a hydraulic short-stroke device for deep drawing S. T h i r u v a r u d c h e l v a n School of Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 2263
(Received March 24, 1993; accepted October 20, 1993)
Industrial summary A novel hydraulic short-stroke device for the deep drawing of cylindrical cups has been designed, fabricated and experiments conducted with it recently. This device reduces the cycle-time and the stroke needed by 50 percent, and also applies automatically a blank-holder force that is approximately proportional to the draw force. Wrinkle-free cups of aluminium, copper and brass of diameter 100 mm and thickness between 0.8 and 1.0 mm were drawn successfully with this device at a draw ratio of 1.85. A software was developed for simulating this process, its features being presented and discussed in this paper. The software presents the user with several windows (on a Macintosh Computer) containing text, theoretical derivations, diagrams, animation of the process, and provision for the user to interact by feeding process parameters of different values, these parameters including the draw ratio, the thickness of the cup, material properties, various dimensions such as the punch and die radii, important dimensions of the device, spring constants, etc. After inputting the parameters, the user can calculate various related quantities including the draw force, the blank-holding force, the fluid pressure, etc., at any value of the punch stroke. These forces and the fluid pressure are presented to the user in graphical form also. Thus, the software can be used to enable thorough study and understanding of the process and to select the various parameters in the design of such a device for drawing cylindrical cups of desired specifications. Key words: Deep drawing; Short-stroke-device
1. Introduction Deep drawing is used widely in industry to form cup-shaped articles from sheet metal, several variations of the basic deep-drawing process being employed. After the initial drawing process, re-drawing is usually carried out to deepen the cups further. F r o m the results of several investigations on deep drawing [1-41 it has been found that a blank-holding force that is approximately proportional to the punch force is 0924-0136/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0 9 2 4 - 0 1 3 6 ( 9 3 ) E 0 1 2 6 - Z
306
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
Fig. 1. Photograph of a window with the first-stage animation of the process.
Fig. 2. Photograph of a window with the second and third stages of animation of the process.
advantageous compared with constant-force blank-holding, a blank-holding force that is approximately proportional to the punch force being similar in shape to the critical variation [5] needed to suppress wrinkling. The present short-stroke device incorporates also a blank-holding force that is proportional to the punch force: however, in the present device the blank-holding force is generated by hydraulic pressure rather than by friction. A short-stroke device aims at reducing the stroke needed to draw a cup, thereby reducing the cycle-time and increasing the machine productivity. A mechanical
S. Thiruvarudchelvan/Journal of Materials Processino TechnolooY 43 (1994) 305-315
307
Fig. 3. DesignDrawingof the device.
Fig. 4. Close-upviewof the blank-holderregion of the device.
short-stroke device [6], using a rack and a pinion, can reduce the stroke of the press needed to about one-and-a-half times the height of the cup to be drawn, which means that the stroke and the cycle-time needed are both reduced by 25%. A theoretical analysis and details of the development of the present short-stroke device are presented in Ref. [7], whilst the experimental results from the device are reported in Ref. [8]. In parallel with the theoretical and experimental research on metal forming problems, the author has embarked also on the development of software for metal-forming problems. A research-ware on the semi-continuous extrusion of round bars has already been developed [9]. Softwares on sheet-metal
308
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
Fig. 5. Views of the hydraulic components and the draw die.
Fig. 6. First window of the section 'Theory'.
forming and forming with flexible tools will also be published in the near future. These softwares are being developed to enhance computer-aided learning, and research and development in the field of metal forming. The software described in this paper is aimed at helping to enhance the understanding of the short-stroke device developed, whilst for those interested in developing such a device, it enables calculations to be performed interactively to determine the appropriate process parameters for the design of the device.
S. Thiruvarudchelvan/Journalof Materials Processing Technolooy43 (1994) 305-315
309
Fig. 7. A typical windowon Theory.
2. Features of the software
The software was developed using the pictorial programming language Prograph 2.0 on an Apple Macintosh Computer. The programming language allows easy use of the hyper-media concepts of windows, buttons, texts, pictures, animations, calculations, etc. For ease of interacting with the software, the windows in the software may be divided into three sections, these being described as follows. 2.1. Principle and design aspects of the device
The underlying principle of operation of the short-stroke device is illustrated by text, multi-coloured engineering drawings and an animation of the device. To enable the user to gain a clearer understanding of the dynamics of the device, the animation is divided into three stages. Figure 1 shows the photograph of a window of the software dealing with stage 1, presenting a textual description of this stage. Also, on the right hand side of the window a schematic drawing of the device is presented: by pressing the button named 'STAGE 1', an animation of stage 1 will replace the drawing. Figure 2 shows the window with the text that describes stages 2 and 3; and also the drawing which presents the animations of these two stages. Figures 3, 4 and 5 are photographs of windows showing the design drawings of the device in colour, the use of different colours helping the user to read these engineering drawings with ease. Descriptive information is presented also in these windows. Figure 4 is a close-up view of the blank-holder region of the device, whilst Fig. 5 shows the hydraulic components of the device and the draw die, etc. in magnified
310
S. Thiruvarudchelvan/Journal of Materials Processin# Technology43 (1994) 305 315
I ~'°w~c-~°r
I
,k
PtmchForceList --- 0 Pressure ,v-- 0 Y-value BHforoe ~ 0 TotalForceList --- 0 ro
",-- 0
if'lace Stroke value in 1st colunm L of 'Calculation' window I"~
I
Stroke ~ Stroke + 4'"'~
t
Stroke > 76 ?
Yes
I
S~o~e--0
I
Read input values:
6 Fig. 8. Flow chart for computing the theoretical forces, etc.
views. With these drawings, descriptions and labelling, the design of the device is illustrated clearly. 2.2. Theory, derivations and computations The theory section of the software has seven windows showing the derivation with text, equations and explanations. Figure 6 shows the first window of the section on theory. To aid the user, a N o t a t i o n window has been included, which can be accessed
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
311
[ Store result in ro list
[ ~t.
St,.n a~dicthroat ]
Yes
Yes
V
t
throat using equation 2";
throat using equation 24 !
No throat *--
01
Fig. 9, Flow chart (continued).
by clicking on the 'NOTATION' buttons provided on all the windows containing the theory. Figure 7 is a typical window on theory with equations and text. The flow chart used for the theoretical computations of the draw force blank-holding force, etc. at various values of the punch stroke are shown in Figs. 8-10, whilst Fig. 11 shows a section of the pictorial program used in the computations of the forces, etc. For example, the rectangle named "Stress at die throat" calculates the yield stress at the die throat for the particular value of the stroke. By 'opening' the method called "Equivalent stress" the details of this method can be seen.
312
S. Thiruvarudchelvan/Journal of Materials Processing Technology43 (1994) 305-315
Strain > 0.26 ?
0.07 < Equivalent Strain < 0.26 ? ! Yes~
Yes
.
CalcuiateEquivalent I Stress using equation23
I CalculateEquivalent I Stress using equation 24
I
I I
Collectdata and I efloJlat¢Draw Force
CalculatedHydraulic Pressure,P I
+ Store Pressurevalue in
CalculateBlankHolderFtm=e]
i
Store Draw force valuein ] Y-valueBHfo~:e List II ] Reverseorderof data stored ] in all~ lists
V
]
S~ke=Srtok+ .~tl-No~ 2, Yes
Fig. 10. Flow chart (continued).
~,alentSta'ess",- 0
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994,) 305-315
313
DRAWFORCE1:I
]~stra;n at die thr0at ~ I \ I~.stre~s at d,e t"roat ~Jl /
I~r-Equ'va'e!~ strain ~ L~
/
Fig. 11. A typical block of a pictorial program used in the computation of forces, etc.
Fig. 12. A typical 'calculation' window enabling the input of various quantities for the process calculations.
2.3. Interactive input and output A section called c a l c u l a t i o n s is p r o v i d e d in the software with three windows. I n this section, the user can key in all the r e l e v a n t d a t a for the s i m u l a t i o n of the process.
314
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
Fig. 13. A window showing the output of the calculations in tabular form.
Fig. 14. The forcesand the hydraulic pressure in presented graphical form.
Figure 12 shows a calculation window, where in the fight-hand side box various values are entered into the text fields. The Notation window can also be accessed from the calculation windows to ascertain the notations of the quantities to be entered. After entering all the data, by pressing the 'DO ALL C A L C U L A T I O N S ' button the appropriate quantities are calculated and stored, and also displayed on the left-hand side of the same window. Figure 13 shows the output of the calculations in tabular form. The calculated values can be plotted in a graphical form as shown in Fig. 14. In this window, by pressing the appropriate button, the forces can be plotted against stroke. A summary
S. Thiruvarudchelvan/Journal of Materials Processino Technolooy 43 (1994) 305-315
315
window provides the values of the maximum draw force, the blank-holder force and the hydraulic pressure computed at the end of the interactive session.
3. Conclusions The simulation of the deep-drawing process with the short-stroke device allows a comprehensive study of the process to be made without actually drawing the cup experimentally. The variation of the punch force, the blank-holder force and the hydraulic pressure with punch stroke are determined theoretically: these values are presented in tabular form and are displayed also as graphs. The software allows the user to feed in the various quantities and calculate the relevant parameters for the design of such a device. Note: copies of the program can be obtained from the author at cost.
References I-1] W.G. Lewis, Friction-activated blank holding in deep drawing, M. Phil. Thesis, University of the West Indies, Trinidad, 1987, pp. 1-137. I-2] S. Thiruvarudchelvan and W.G. Lewis, Friction-actuated blank holding in deep drawing, J. Mech. Work. Tech., 17 (1988), 108-112. 1-3] S. Thiruvarudchelvan and W.G. Lewis, Deep drawing with blank-holder force approximately proportional to the punch force, Trans. ASME, J. Eng. Ind., 112(3) (1990), 278-285. [4] S. Thiruvarudchelvan and N.H. Loh, Drawing of cylindrical and hemispherical cups using an improved tooling for friction-actuated blank-holding, J. Mats Proc. Tech., 36 (1992) 69-78. I5] N. Kawai, Critical conditions of wrinkling in deep drawing of sheet metals, Reports 1, 2 and 3, Bull. JSME, 4 (1961) 169-192. 1"6] Private communication, Joseph Rhodes Ltd., U.K., 1986. I-7] S. Thiruvarudchelvan, A hydraulic short-stroke device for deep drawing with blank holder force proportional to the punch force, J. Mats. Proc. Tech. (paper submitted). I-8"1 S. Thiruvarudchelvan and F.W. Travis, Experimental investigation of a short-stroke device for deep drawing, J. Mats. Proc. Tech., 36 (1992) 69-78. 1-91 S. Thiruvarudchelvan, Semi-continuous extrusion of round bars, J. Mats. Proc. Tech., 31 (1992) 441-443.
J. Mater. Process. Technol. 43 (1994) 305-315
Journal of Materials Processing Technology
Simulation of a hydraulic short-stroke device for deep drawing S. T h i r u v a r u d c h e l v a n School of Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 2263
(Received March 24, 1993; accepted October 20, 1993)
Industrial summary A novel hydraulic short-stroke device for the deep drawing of cylindrical cups has been designed, fabricated and experiments conducted with it recently. This device reduces the cycle-time and the stroke needed by 50 percent, and also applies automatically a blank-holder force that is approximately proportional to the draw force. Wrinkle-free cups of aluminium, copper and brass of diameter 100 mm and thickness between 0.8 and 1.0 mm were drawn successfully with this device at a draw ratio of 1.85. A software was developed for simulating this process, its features being presented and discussed in this paper. The software presents the user with several windows (on a Macintosh Computer) containing text, theoretical derivations, diagrams, animation of the process, and provision for the user to interact by feeding process parameters of different values, these parameters including the draw ratio, the thickness of the cup, material properties, various dimensions such as the punch and die radii, important dimensions of the device, spring constants, etc. After inputting the parameters, the user can calculate various related quantities including the draw force, the blank-holding force, the fluid pressure, etc., at any value of the punch stroke. These forces and the fluid pressure are presented to the user in graphical form also. Thus, the software can be used to enable thorough study and understanding of the process and to select the various parameters in the design of such a device for drawing cylindrical cups of desired specifications. Key words: Deep drawing; Short-stroke-device
1. Introduction Deep drawing is used widely in industry to form cup-shaped articles from sheet metal, several variations of the basic deep-drawing process being employed. After the initial drawing process, re-drawing is usually carried out to deepen the cups further. F r o m the results of several investigations on deep drawing [1-41 it has been found that a blank-holding force that is approximately proportional to the punch force is 0924-0136/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0 9 2 4 - 0 1 3 6 ( 9 3 ) E 0 1 2 6 - Z
306
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
Fig. 1. Photograph of a window with the first-stage animation of the process.
Fig. 2. Photograph of a window with the second and third stages of animation of the process.
advantageous compared with constant-force blank-holding, a blank-holding force that is approximately proportional to the punch force being similar in shape to the critical variation [5] needed to suppress wrinkling. The present short-stroke device incorporates also a blank-holding force that is proportional to the punch force: however, in the present device the blank-holding force is generated by hydraulic pressure rather than by friction. A short-stroke device aims at reducing the stroke needed to draw a cup, thereby reducing the cycle-time and increasing the machine productivity. A mechanical
S. Thiruvarudchelvan/Journal of Materials Processino TechnolooY 43 (1994) 305-315
307
Fig. 3. DesignDrawingof the device.
Fig. 4. Close-upviewof the blank-holderregion of the device.
short-stroke device [6], using a rack and a pinion, can reduce the stroke of the press needed to about one-and-a-half times the height of the cup to be drawn, which means that the stroke and the cycle-time needed are both reduced by 25%. A theoretical analysis and details of the development of the present short-stroke device are presented in Ref. [7], whilst the experimental results from the device are reported in Ref. [8]. In parallel with the theoretical and experimental research on metal forming problems, the author has embarked also on the development of software for metal-forming problems. A research-ware on the semi-continuous extrusion of round bars has already been developed [9]. Softwares on sheet-metal
308
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
Fig. 5. Views of the hydraulic components and the draw die.
Fig. 6. First window of the section 'Theory'.
forming and forming with flexible tools will also be published in the near future. These softwares are being developed to enhance computer-aided learning, and research and development in the field of metal forming. The software described in this paper is aimed at helping to enhance the understanding of the short-stroke device developed, whilst for those interested in developing such a device, it enables calculations to be performed interactively to determine the appropriate process parameters for the design of the device.
S. Thiruvarudchelvan/Journalof Materials Processing Technolooy43 (1994) 305-315
309
Fig. 7. A typical windowon Theory.
2. Features of the software
The software was developed using the pictorial programming language Prograph 2.0 on an Apple Macintosh Computer. The programming language allows easy use of the hyper-media concepts of windows, buttons, texts, pictures, animations, calculations, etc. For ease of interacting with the software, the windows in the software may be divided into three sections, these being described as follows. 2.1. Principle and design aspects of the device
The underlying principle of operation of the short-stroke device is illustrated by text, multi-coloured engineering drawings and an animation of the device. To enable the user to gain a clearer understanding of the dynamics of the device, the animation is divided into three stages. Figure 1 shows the photograph of a window of the software dealing with stage 1, presenting a textual description of this stage. Also, on the right hand side of the window a schematic drawing of the device is presented: by pressing the button named 'STAGE 1', an animation of stage 1 will replace the drawing. Figure 2 shows the window with the text that describes stages 2 and 3; and also the drawing which presents the animations of these two stages. Figures 3, 4 and 5 are photographs of windows showing the design drawings of the device in colour, the use of different colours helping the user to read these engineering drawings with ease. Descriptive information is presented also in these windows. Figure 4 is a close-up view of the blank-holder region of the device, whilst Fig. 5 shows the hydraulic components of the device and the draw die, etc. in magnified
310
S. Thiruvarudchelvan/Journal of Materials Processin# Technology43 (1994) 305 315
I ~'°w~c-~°r
I
,k
PtmchForceList --- 0 Pressure ,v-- 0 Y-value BHforoe ~ 0 TotalForceList --- 0 ro
",-- 0
if'lace Stroke value in 1st colunm L of 'Calculation' window I"~
I
Stroke ~ Stroke + 4'"'~
t
Stroke > 76 ?
Yes
I
S~o~e--0
I
Read input values:
6 Fig. 8. Flow chart for computing the theoretical forces, etc.
views. With these drawings, descriptions and labelling, the design of the device is illustrated clearly. 2.2. Theory, derivations and computations The theory section of the software has seven windows showing the derivation with text, equations and explanations. Figure 6 shows the first window of the section on theory. To aid the user, a N o t a t i o n window has been included, which can be accessed
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
311
[ Store result in ro list
[ ~t.
St,.n a~dicthroat ]
Yes
Yes
V
t
throat using equation 2";
throat using equation 24 !
No throat *--
01
Fig. 9, Flow chart (continued).
by clicking on the 'NOTATION' buttons provided on all the windows containing the theory. Figure 7 is a typical window on theory with equations and text. The flow chart used for the theoretical computations of the draw force blank-holding force, etc. at various values of the punch stroke are shown in Figs. 8-10, whilst Fig. 11 shows a section of the pictorial program used in the computations of the forces, etc. For example, the rectangle named "Stress at die throat" calculates the yield stress at the die throat for the particular value of the stroke. By 'opening' the method called "Equivalent stress" the details of this method can be seen.
312
S. Thiruvarudchelvan/Journal of Materials Processing Technology43 (1994) 305-315
Strain > 0.26 ?
0.07 < Equivalent Strain < 0.26 ? ! Yes~
Yes
.
CalcuiateEquivalent I Stress using equation23
I CalculateEquivalent I Stress using equation 24
I
I I
Collectdata and I efloJlat¢Draw Force
CalculatedHydraulic Pressure,P I
+ Store Pressurevalue in
CalculateBlankHolderFtm=e]
i
Store Draw force valuein ] Y-valueBHfo~:e List II ] Reverseorderof data stored ] in all~ lists
V
]
S~ke=Srtok+ .~tl-No~ 2, Yes
Fig. 10. Flow chart (continued).
~,alentSta'ess",- 0
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994,) 305-315
313
DRAWFORCE1:I
]~stra;n at die thr0at ~ I \ I~.stre~s at d,e t"roat ~Jl /
I~r-Equ'va'e!~ strain ~ L~
/
Fig. 11. A typical block of a pictorial program used in the computation of forces, etc.
Fig. 12. A typical 'calculation' window enabling the input of various quantities for the process calculations.
2.3. Interactive input and output A section called c a l c u l a t i o n s is p r o v i d e d in the software with three windows. I n this section, the user can key in all the r e l e v a n t d a t a for the s i m u l a t i o n of the process.
314
S. Thiruvarudchelvan/Journal of Materials Processing Technology 43 (1994) 305-315
Fig. 13. A window showing the output of the calculations in tabular form.
Fig. 14. The forcesand the hydraulic pressure in presented graphical form.
Figure 12 shows a calculation window, where in the fight-hand side box various values are entered into the text fields. The Notation window can also be accessed from the calculation windows to ascertain the notations of the quantities to be entered. After entering all the data, by pressing the 'DO ALL C A L C U L A T I O N S ' button the appropriate quantities are calculated and stored, and also displayed on the left-hand side of the same window. Figure 13 shows the output of the calculations in tabular form. The calculated values can be plotted in a graphical form as shown in Fig. 14. In this window, by pressing the appropriate button, the forces can be plotted against stroke. A summary
S. Thiruvarudchelvan/Journal of Materials Processino Technolooy 43 (1994) 305-315
315
window provides the values of the maximum draw force, the blank-holder force and the hydraulic pressure computed at the end of the interactive session.
3. Conclusions The simulation of the deep-drawing process with the short-stroke device allows a comprehensive study of the process to be made without actually drawing the cup experimentally. The variation of the punch force, the blank-holder force and the hydraulic pressure with punch stroke are determined theoretically: these values are presented in tabular form and are displayed also as graphs. The software allows the user to feed in the various quantities and calculate the relevant parameters for the design of such a device. Note: copies of the program can be obtained from the author at cost.
References I-1] W.G. Lewis, Friction-activated blank holding in deep drawing, M. Phil. Thesis, University of the West Indies, Trinidad, 1987, pp. 1-137. I-2] S. Thiruvarudchelvan and W.G. Lewis, Friction-actuated blank holding in deep drawing, J. Mech. Work. Tech., 17 (1988), 108-112. 1-3] S. Thiruvarudchelvan and W.G. Lewis, Deep drawing with blank-holder force approximately proportional to the punch force, Trans. ASME, J. Eng. Ind., 112(3) (1990), 278-285. [4] S. Thiruvarudchelvan and N.H. Loh, Drawing of cylindrical and hemispherical cups using an improved tooling for friction-actuated blank-holding, J. Mats Proc. Tech., 36 (1992) 69-78. I5] N. Kawai, Critical conditions of wrinkling in deep drawing of sheet metals, Reports 1, 2 and 3, Bull. JSME, 4 (1961) 169-192. 1"6] Private communication, Joseph Rhodes Ltd., U.K., 1986. I-7] S. Thiruvarudchelvan, A hydraulic short-stroke device for deep drawing with blank holder force proportional to the punch force, J. Mats. Proc. Tech. (paper submitted). I-8"1 S. Thiruvarudchelvan and F.W. Travis, Experimental investigation of a short-stroke device for deep drawing, J. Mats. Proc. Tech., 36 (1992) 69-78. 1-91 S. Thiruvarudchelvan, Semi-continuous extrusion of round bars, J. Mats. Proc. Tech., 31 (1992) 441-443.