Effect of Forming Parameters in sheet Hydro Mechanical Deep Drawing Process Vplyv parametrov tvárnenia pri hydromechanickom procese hlbokého ťahania plôch D Rajenthirakumar, G Chandramohan Abstract Advanced manufacturing technology, which is the basis of modern industries, is very important The technology of hydro mechanical deep drawing combines the features of conventional deep drawing and hydroforming and widely used in many industries, especially automobile and aircraft industry In this process, the punch deforms the blank to its final shape by moving against a controlled pressurized fluid The objective of this work is to develop a method to analyze the effects of the forming parameters on the quality of the part formability and determine the most significant forming parameter affecting the hydroformability Experimental analysis and Taguchi method are used to study the effect of forming parameters Experiments have been carried out on Inconel 625, a nickel-based super alloy sheets by varying the process parameters such as chamber internal pressure, drawing ratio, punch geometry and friction coefficient To design an orthogonal experimental array in order to study the effect of each forming parameter Taguchi method is used In this work Inconel 625 sheet cups with drawing ratios of 2.5 and 2.6 are obtained to study the effect of forming parameters for the lowest thinning ratio The results obtainned from this work are useful for forming quality parts in terms of uniform thickness distribution Keywords: hydro mechanical deep drawing, thinning ratio, Taguchi method Abstrakt Vyspelá technológia výroby, ktorá je základom moderného priemyslu, je veľmi dơležitá Technológia hydromechanického hlbokého ťahania kombinuje prvky konvenčného hlbokého ťahania a hydrotvárnenia a je široko vyžívanou technológiou hlavne v automobilovom a leteckom priemysle Pri tomto procese ťažník deformuje materiál jeho výsledného tvaru pohybom proti kontrolovanej stlačenej kvapaline Cieľom tejto práce je vyvinúť metódu na analyzovanie vplyvom parametrov formovania na kvalitu formovateľnosti objektu a stanoviť parameter, ktorý najvýznamnejšie vplýva na hydrotvárnenie Na vyhodnotenie parametrov tvárnenia boli použité Taguchiho metóda a experimentálna analýza Pokus sa realizoval na tabuli Inconel 625, super zliatina na báze niklu, spơsobom variácie procesných parametrov akými boli napríklad vnútorný tlak komory, pomer ťahania, geometria tažníka a koeficiente trenia Pre návrh ortogonálného experimentálneho poľa za účelom štúdia jednotlivých parametrov ťahania bola použitá Taguchiho metóda V tomto príspevku bolo realizované téglikové ťahanie s pomerom vytiahnutia s pomerom vytiahnutia 2,5 a 2,6, na ktorých následne prebehla analýza vplyvu parametrov ťahania pre najnižší pomer hrúbky Výsledky získané z tejto práce sú požité pre tvorbu kvalitatívnych dielov v zmysle rovnomernej distribúcie hrúbky Kľúčové slová: hydromechanické hlboké ťahanie, pomer ztenčenia, Taguchiho metóda Introduction Special deep drawing processes have been developed in the past years in order to overcome some problems inherent in the conventional deep drawing process The objective of such processes is to increases the drawing ratio; minimize thickness variation of the drawn cups, reducing the tooling cost In the special drawing processes only one half rigid tool of either the punch or the die is used for forming the sheet metal to the required shape The shape of this rigid tool should be similar to the shape of the drawing component [1] The hydro mechanical deep drawing process is one of the special drawing processes in which the bottom of the sheet is supported with a bed of pressurized viscous fluid during the forming process Fig represents a schematic of this process used for forming deep-drawn cups The punch deforms the sheet to its final shape by moving against a controlled pressurized fluid The aim is to form deep drawn cups without any kind of forming instability such as buckling, wrinkling or bursting In order to successfully obtain the final desired parts, it is necessary to study the influence of the forming parameters on the hydroformability The influence of process parameters and material properties on the hydroforming process has been studied by means of analytical models and experiments Amino et al [2] found that limiting drawing ratio (LDR) improved significantly in case of hydro mechanical deep drawing when compared with conventional deep drawing Elsebaie and Mellor [3] determined that high chamber pressure is required to achieve maximum possible LDR, but when the chamber pressure is too high blank may be ruptured at the die profile Zhang et al [4] using finite element simulation showed that prebulging pressure has greater influence on the thickness distribution along the cup wall Kim et al [5] performed hydro mechanical forming and concluded that the hydro mechanical forming process could produce part with more uniform and sound thickness distribution com-pared to stamping operation Consideration of the influence of the geometry, material and process parameters simultaneously in one process has not been found in the literature The Taguchi method adopts a set of orthogonal arrays to analyze the effect of parameters on specific quality characteristics to determine the optimal combination of parameters [6] Considering the wide application of super alloy in the fields of aviation and spaceflight, in this work, a method is developed to analyse the effects of the forming parameters on hydroformability of Inconel 625 by combining experimental analysis and the Taguchi method First, the quality characteristics and the forming parameters are selected, and the appropriate orthogonal array is constructed Experimen- 29 tal investigation is performed based on the arrangement of the orthogonal array and the results are then transformed into the Taguchi signal-to-noise (S/N) ratios Statistical ana-lysis of variance (ANOVA) is performed to see which are significant Fig Experimental setup Obr Experimentálna zostava Tooling and material for study The experimental apparatus was built around a 60 tone hydraulic press, shown in Fig In hydro mechanical deep drawing process, when the fluid pressure in the chamber is too high, it results in premature rupturing of the sheet material On the other hand if the fluid pressure is too low, it leads to wrinkling Hence the process pressure has to be maintained in a safe working zone between the ruptures and wrinkling zones to ensure a defect free part To maintain the fluid pressure – punch travel path in the working zone, material specific wrinkle and rupture governing equations were formulated by Yossifon S and Triosh J [7] In this work, the safe working zone was established by interfacing the punch travel by means of Linear Variable Transducer (LVDT) with the Pressure Relief Valve (PRV) of the hydro mecha-nical deep drawing system (Fig 3) This interface was controlled by a Personal Computer (PC) with the help of commercial software LabVIEW [8] Experiments are car-ried using sheets of mm thick sheet metal of nickel based super alloy (Inconel 625) Fig Arrangement of valves and electronic data acquisition system Obr Usporiadanie valcov a elektronického systému na zber dát 30 Table Parameters used Tab Použité parametre Results and Discussions Based on the experimental results, the forming quality characteristic thinning ratio is studied using Taguchi method The signal-to-noise (S/N) ratio and analysis of variance (ANOVA) are considered for analysis For a successful deep drawing process, the maximum value of thinning is not beyond 20% When drawing ratio reaches 2.6, the thickness distribution is shown in Fig Along the cup wall the thickness strain varies from negative values at the most wall height to positive values at the top of the cup 30 25 20 Geometry parameters, material parameters and process parameters are the three categories of parameters influencing hydroformability Tab shows the forming parameters selected for study and their levels Based on Taguchi method, the experimental layout of an L18 orthogonal array (Tab 3) is selected considering the eight parameters and three levels of each parameter Although there are many different proposed criteria for predicting fracture in metal forming processes, there is no standard approach Therefore, the commonly used thinning ratio criteria is used as a measure of forming quality The successfully formed cups are sectioned at 90° and thickness is measured at several po-ints along the cup wall from the top of the cup to center of the cup bottom Table Forming parameters selected for study and their levels Tab Vybrané parametre tvárnenia a ich úroveň Thining ratio (%) 2.1 Design of Experiments 15 10 -5 -10 -15 -20 -25 12 16 20 24 28 32 36 40 Curvelinear distance to the cup center (mm) Fig Distribution of thickness thinning ratio (to=1mm) Obr Rozloženie pomeru zmenšenia hrúbky(to=1mm) 3.1 S/N analysis In the Taguchi method, the S/N ratio is defined by S/N = -10 log (Mean square deviation for the quality characteristic) - (1) Generally there are three categories of quality characteristic in the analysis of the S/N ratio, i.e the-lower-thebetter, the higher-the-better, and the-nominal-the-better Thinning ratio is the quality characteristic with the objective “the-lower-the-better” The mean square deviation (MSD) for the lower-the-better quality characteristic is defined by n MSD = 1/n ∑ yi2 - (2) i=1 Table Taguchi’s L18 orthogonal array Tab Taguchiho ortogonálne pole L18 Trial No 10 11 12 13 14 15 16 17 18 K 1 1 1 1 2 2 2 2 L 1 2 3 1 2 3 Forming parameters M N X U 1 1 2 2 3 3 1 2 2 3 3 1 3 3 3 2 1 3 2 1 3 3 3 3 2 V 3 2 3 1 2 W 3 2 3 3 Where yi is the value of the-lower-the better quality characteristic and n is the number of tests for a trial condition Regardless of the category of the quality characteristic, a greater S/N ratio corresponds to better quality characteristics After conducting experiments and applying S/N analysis, the results of the thinning ratio and its S/N ratio in the 18 trial conditions are shown in Tab The average S/N ratio of the thinning ratio for each parameter at levels to are shown in Tab and plotted in Fig Table Thinning ratio values and S/N ratio Tab Hodnoty pomerov ztenčenia a pomery S/N Trial No Thinning ratio 0.254 0.496 0.435 0.399 0.565 0.312 0.484 0.338 0.456 S/N ratio 10.722 6.127 6.978 7.015 5.678 10.543 6.987 10.643 7.556 Trial No 10 11 12 13 14 15 16 17 18 Thinning ratio 0.365 0.439 0.355 0.321 0.436 0.543 0.477 0.362 0.451 S/N ratio 8.345 7.786 8.742 9.567 7.893 5.934 6.784 8.416 7.324 31 Table Forming parameters and average S/N ratio Tab Parametre tvárnenia a priemerné pomery S/N wed by friction coefficient The effect of thickness of the sheet and die profile radius are relatively small compared to that of internal pressure Conclusions ¾ ¾ ¾ ¾ Fig Effect of forming parameters on the thinning ratio Obr Vplyv parametrov na pomer zmenšenia hrúbky ¾ 3.2 Analysis of variance (ANOVA) ANOVA is carried out to fine the effect of forming parameters quantitatively By comparing variances, ANOVA tests for significant differences between the parameters The overall average S/N ratio is given by _ m S/N = 1/m ∑ (S/N)i - (3) i=1 Where m is the number of tests in the orthogonal array and (S/N)i is the S/N ratio of the ith test The sum of the squares due to the variation from the overall average S/N ratio is m The following conclusions are made: In this work, a method to study the effect of forming parameters in sheet hydro mechanical deep drawing process has been developed Experiments designed based on the orthogonal array of the Taguchi method can used to identify the most significant forming parameter affecting the hydroformability The greatest effects on thinning ratio in sheet hydro mechanical deep drawing is contributed by internal pressure The second greatest effect is from friction coefficient The results from this work open the avenue of determining the optimal internal pressure range for better quality products The forming parameters except internal pressure and friction coefficient not contribute much to the hydroformability As a result other insignificant forming parameters like thickness of the sheet and die profile radius etc can be eliminated from the optimization study which will results in significant saving of computational time Acknowledgements This work was carried out in the Net shape Manufactuing Lab, Department of Mechanical Engineering, PSG College of Technology, Coimbatore, India The authors wish to thank all the faculty and staff members for their contribution D Rajenthirakumar, Lecturer, Tele Phone: 91 9486382138, 91 422 2572177 E-mail: d_rajentkumar@yahoo.co.in G Chandramohan, Professor, Tele Phone: 91 9443723728 Department of Mechanical Engineering, PSG College of Technology, Peelamedu Coimbatore – 641004, Tamil Nadu, India _ SS = ∑ [(S/N)i – S/N]2 - (4) i=1 The sum of the squares due to the variation from the average S/N ratio for the ith factor is _ t SSi = ∑ Tt X [(S/N)it – S/N]2 - (4) t=1 Where t is the number of the factor levels, Tt is the number of the tests of the ith factor at the tth level (S/N)it is the average S/N ratio of the quality characteristic for the ith factor at the tth level The percentage contribution of the ith factor is defined by Pi(%) = (SSi/SS ) X 100 - (5) Table ANOVA for thinning ratio Tab ANOVA pre pomery stenčenia References [1] LANGE K.: Handbook of metal forming: McGraw-Hill, New York, 1985 [2] AMINO H, Nakamura K, Nakagawa T.: Counter-pressure deep [3] [4] [5] [6] [7] The result of ANOVA for thinning ratio is shown in Tab Tab shows that the internal pressure is the most significant forming parameter affecting the thinning ratio follo- 32 [8] drawing and its application in the forming and automobile parts: Journal of Material Processing Technology, 1990:23, 243-265 EL-SEBAIE M G, Mellor M G.: Pressure assisted deep drawing: Ann CIRP, 1973: 22(1), 71-72 ZHANG S H, Danckert J.: Development of hydro mechanical deep drawing: Journal of Material Processing Technology, 1998:83, 14-25 KIM J, Son B M, Kang B S, Hwang S M, Park H J.: Comparison stamping and hydro mechanical forming process for an automobile fuel tank using finite element method: Journal of Material Processing Technology, 2004:153/154, 550-557 KO D, Kim A, Kim B.: Application of artificial neural network and Taguchi method to perform design in metal forming considering workability: International Journal of Machine Tool Manufacturing, 1999:39, 771-785 YOSSIFON S, Tirosh J.: On the permissible fluid-pressure path in hydro forming deep drawing processes-analysis of failures and experiments: Journal of Engineering for Industry, 1988: 110, 146152 Lab VIEW 7.1 Users Manual: National Instruments, 2002 ... the top of the cup 30 25 20 Geometry parameters, material parameters and process parameters are the three categories of parameters influencing hydroformability Tab shows the forming parameters... (PC) with the help of commercial software LabVIEW [8] Experiments are car-ried using sheets of mm thick sheet metal of nickel based super alloy (Inconel 625) Fig Arrangement of valves and electronic... the top of the cup to center of the cup bottom Table Forming parameters selected for study and their levels Tab Vybrané parametre tvárnenia a ich úroveň Thining ratio (%) 2.1 Design of Experiments