Variation in Forming Forces Due To Different Tool Movements for PVC Sheet in Incremental Sheet Forming Process

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1 IJSRD - International Journal for Scientific Research & Development Vol. 5, Issue 02, 2017 ISSN (online): Variation in Forming Forces Due To Different Tool Movements for PVC Sheet in Incremental Sheet Forming Process Rajender Singh 1 Ravi Kumar 2 Vinod Kumar 3 1 Assistant Professor 2,3 Student 1,2,3 Department of Mechanical Engineering 1,2,3 Guru Jambheshwar University Science and Technology Hisar-(125001), India Abstract Incremental sheet forming (ISF) is a promising manufacturing process in which flat material sheets are gradually formed into 3-Dimentional (3D) shapes using a generic forming tool. Since the process features benefits of reduced forming forces, enhanced formability and greater process flexibility, it has a great potential to achieve economic pay off for rapid prototyping applications and for small batch production in various applications. Although substantial research has been done in the past decades on ISF, there is still a lack of an efficient prediction of forming force to facilitate the production design and optimization of the process. Also, unsatisfactory part is quality obtained still hampers its wide use in industrial applications. In past the force prediction is done for considering different parameters i.e. feed, speed, depth of cut, sheet thickness, tool radius etc. But work done in the field of force prediction by different tool s is very less. Therefore, the work presented in this thesis is mainly focused on efficient forming force prediction for different tool s and its improvement. The force prediction is done by experimental method in which tool is changed by taking the other parameters constant. Forces are find out in the different directions on CNC milling machine using force sensor. By this work the efficient condition of less force and better formability is find. This work also helps in decreasing the time and increasing the surface finishing during the process. The limits of the proposed model are also identified and the potential of future improvements are suggested. Key words: Incremental Sheet Forming, Different Tool Movements, PVC, Force Measurement I. INTRODUCTION During the past few years there has been increasing the demand for the need of development of manufacturing technologies that are both agile and be able to handle with the market requirements, that it should be also adaptable for new product development so that introduction of new products in the markets could be easily achieved. Single point incremental forming (SPIF) is a new innovative and feasible solution for the rapid prototyping and the manufacturing of small batch sheet parts. This process requires a CNC machining center, a hemispherical headed tool and a simple support to fix the sheet being formed. The flexibility of the process is mainly related to the fact that SPIF does not require a dedicated die to operate as compared to other forming processes. As a result, the leadtime and cost of tooling along with the die cost can be avoided. This technique allows a relatively fast and cheap production of small batch of sheet metal parts. This process starts from a flat sheet metal blank, clamped on a sufficiently stiff rig and mounted on the table of a CNC machine. It can be used for forming of symmetric and nonsymmetric parts in a wide range of thicknesses from 100 microns to several mm. Y.H. Kim et al. [1] (2002) study the effect of process parameters tool type, tool size, feed rate, friction at the interface between tool and sheet, planeanisotropy of sheet on the formability by experiments and FEM analyses. It was found that the formability is improved when a ball tool of a particular size is used with a small feed rate and a little friction. J. Kopac et al. [2] (2005) study the process controlled by CNC milling machine-tool together with CAD/CAM Master Cam system and a smooth forming tool. In this paper with experimental testing and measurements the limits of forming without a full-size model were defined. N. Bay et al. [3] (2008) presents a closed-form theoretical analysis modelling the fundamentals of single point incremental forming and explaining the experimental and numerical results available in the literature for the past couple of years. Petek et al. [4] [2009] in this paper the forming forces and deformation were measured using specially designed force measuring system which is connected with the CNC milling machine. They find that the deformations and forces distribution are mostly dependent on the size of the wall angle of forming, tool diameter and vertical step sizes of the tool. Kwiatkowski L. et al. [5] (2009) This paper is concerned with these issues and is focused on the possibility of employing the single point incremental forming technology currently being developed for flexible sheet metal forming polymeric sheet components. The Results show that single point incremental forming of commercial PVC sheets at room temperature seems promising for the manufacture of complex polymer sheet components with very high depths applications, for producing low cost, small-batch, high-quality. Silva M. B et al. [6] (2010) this experimental is based on research work makes use of polyvinyl chloride (PVC) sheets and was carried out on a CNC milling machine, equipped with conventional SPIF set-up Benchmark tests were performed on cones with varying wall angle and results confirm that SPIF of PVC sheets at room temperature has potential for the manufacture of complex parts with very high depth. M. Hrairi et al. [7] (2011) Incremental sheet forming (ISF) is an emerging metal-forming technology in which the tool motion is controlled numerically. The process is economical to form complex parts in small to medium batches and provides a short and inexpensive way of forming products having a relatively simple but interesting shape. In this article, a review of the present state-of-the-art technologies and the potential applications of incremental sheet metal forming are presented in brief. This article seeks to address the approaches and methods that are prevalently applied. Tânia A. F. Marques et al. [8] (2012) focuses on the determination and experimental validation of the formability limits, evaluating the incremental forming application potential. In order to fulfill the aforementioned objectives All rights reserved by 189

2 four different polymers were selected and independent calibration of physical, mechanical properties and formability limits were performed under laboratory controlled conditions. The study allows the confirmation that SPIF can be successfully extended to polymers. M.A. Dittrich et al. [9] (2012) Using the concept of exergy analysis, two ISF technologies, namely single sided and double sided incremental forming, are investigated and compared to conventional forming and hydroforming. A second exergy analysis is carried out with the purpose of examining the environmental impact of different forming technologies from a supply chain perspective. The results of both analyses suggest that ISF is environmentally advantageous for prototyping and small production runs. Nandedkar V.M. et al. [10] (2013) Incremental sheet forming has demonstrated its great potential to form complex three dimensional parts without using a component specific tooling. The die-less nature in incremental forming provides competitive alternative for economically and effectively fabricating low volume functional sheet products. Incremental sheet metal forming has the potential to revolutionize sheet metal forming, making it accessible to all level of manufacturing. This paper describes the current state of the art of Incremental sheet metal forming. P. A. F. Martins et al. [11] (2014) study the methodology to determine the in plane stresses and the accumulated damage at various positions over the surface of conical a pyramidal PVC parts directly from the experimental strain measurements until failure of material occurs. Yogesh Kumar et al. [12] (2015) study the use of 3D complex shapes in ISF for larger forming angles with proper forming methodology by using motion card. The strain distribution over the length of deformation has been computed, and it has been found to be distributed over the length of the deformation. Nasri S. M. Namer et al. [13] (2015) the aim of this work is to study the influence of different oil lubricant on the surface roughness of polymer material by single point incremental forming process (SPIF). In this research incremental forming work were performed on polyethylene (PEHD) and polyvinylchloride (PVC) sheets to create a cone shape. Roughness was studied by different variables (oil lubricant, tool diameter, spindle speed and feed rate). From this study, it was found that the surface roughness was improved as oil viscosity, tool diameter, spindle speed and feed rate increases. a] e test) test) PVC Table 2: Representative summary of the mechanical properties of the PVC Sh To Tool Shee Wal eet Mat Spe Too ol dia t Feed l siz erial ed l len met thick (M angl e of (R mat gth er ness MP e (m shee PM erial (m (mm m m) ) (mm M) (deg t ) ) ree) ) HS S PV C 1200 Table 3: Values of Parameters Taken III. RESULTS AND DISCUSSION In the incremental sheet metal forming process of PVC sheets, a number of parameters affect the forming forces. In this work forming forces are calculated by different tool s. So other parameters i.e. tool radius, sheet thickness, wall angle, depth of cut, feed, speed are taken constant. A. Different Tool Movements Are 1) Outer to inner spiral path tool 2) Inner to outer spiral path tool 3) Outer to inner straight path tool 4) Inner to outer straight path tool 1) Outer to inner spiral path tool : The outer to inner spiral path tool shown in figure 1. The cycle completes in 30 minutes. As the tool moves towards the inner direction the depth of cut also increases. In starting, the tool touches sheet at very small area so the force in z-direction is very less. With increases in time contact area increases and force also increases. Force increases from 0 to 150N in sec. After this the force in z-direction is approximately constant. The value of forces in other two directions (x and y) also increases but this value is very less as compared to z-direction. The graph is plotted between force (N) and time(s) as shown in figure II. EXPERIMENTAL SETUP The entire experiment was carried out on Agni BMV 45 TC 24 machining center. Hemispherical tool of high speed steel (HSS), Fixture of size mm to hold the sheet and sheet of PVC material is used for operation. Force sensor is used for measuring the forces. Element W Cr V C Fe Percentage Table 1: Composition of HSS Poly mer Elastic ity Modul us E [MPa] Yiel d tensi le Stre ss [MP Effect ive strain at fractur e (tensil Effect ive strain at fractur e (bulge Fractur e Toughn ess [kj/m 2 ] Dens ity [kg/ m 3 ] Fig. 1: Outer to Inner spiral path tool S.N. Time (s) Fx (N) Fy (N) Fz (N) All rights reserved by 190

3 Table 4: Forming forces for outer to inner spiral tool Fig. 2: Force V/S Time graph for outer to inner spiral process 2) Inner to Outer Spiral Path Tool Movement The inner to outer spiral path tool s are shown in figure 3. In these tool s tool starts at the center and moves in outer direction with spiral path. Here we took two cases for force prediction. In case (a) the tool moves only in horizontal direction during the process as shown in figure 3(a). Forces increases in the same way but force in z- direction is very less as compared to horizontal (x and y) direction because tool does not move in z-direction. So main component of force occurs in x and y direction. Value of forces for x and y-direction changes alternatively positive or negative. In this process chances of sheet failure is more due to more resistance in horizontal direction. In case (b) tool moves in horizontal as well as in vertical direction. Due to feed in z-direction normal deformation takes place for some time but after this sheet elongation starts and fracture occurs because sheet deformation is not uniform. Elongation is more at the deformed sheet and less at the corner where deformation starts. So more stress occurs at deformed surface and causes the failure of sheet. Fig. 3: Inner to outer spiral path tool for case(a) and case(b) S.N. Time (s) Fx(N) Fy (N) Fz(N) Table 5: Forming forces for inner to outer spiral case (a) All rights reserved by 191

4 Fig. 4: Force V/S Time graph for inner to outer spiral case (a) S.N. Time (s) Fx(N) Fy (N) Fz(N) Table 6: Forming forces for inner to outer spiral case (b) S.N. Time (s) Fx (N) Fy (N) Fz (N) Table 7: Forming forces for outer to inner straight path tool Fig. 5: Force V/S Time graph for inner to outer spiral case(b) 3) Outer To Inner Straight Path Tool Movement In outer to inner straight path tool tool moves outer to inner direction with increases in depth of cut. Force generated is less as compared to spiral path. Tool moves only in one direction at a time. Due to this at one time only two component of forces occurs (x,z or y,z). Horizontal forces occur in positive and negative direction alternatively. In this process chances of failure is more at corner points. Fig. 6: Outer to inner straight path tool Fig. 7: Force V/S Time graph for outer to inner straight path tool 4) Inner to outer straight path tool In inner to outer straight path tool process tool moves inner to outer in bidirectional. Here we also consider two cases. In case (a) tool moves in horizontal (x and y) direction only without giving feed in z-direction. Force generation in horizontal direction is more as compared to vertical direction. Like spiral inner to outer starting force generation is same but after half cycle (approx.) deformed sheet weakens due to more stresses. It does not withstand forming forces and fracture occurs. Due to this it does not complete cycle and limits the All rights reserved by 192

5 performance of this process. In case (b) tool also gives feed in z-direction and that force elongates the sheet more. Due to this cycle failure occurs at early stage than case (a). Variation in Forming Forces Due To Different Tool Movements for PVC Sheet in Incremental Sheet Forming Process Fig. 8: Inner to outer straight path tool for case(a) and case(b) S.N. T (s) Fx(N) Fy (N) Fz(N) Table 8: Forming forces for inner to outer straight path case (a) Fig. 9: Force V/S Time graph for inner to outer straight path case (a) S.N. T (s) Fx(N) Fy (N) Fz(N) Table 9: Forming forces for inner to outer straight path case (b) Fig. 10: Force V/S Time graph for inner to outer straight path case (b) B. Comparison between Different Tool Movements 1) Comparison between Outer To Inner and Inner To Outer Spiral Tool Movements In the comparison table 10 forces Fx 1, Fy 1 and Fz 1 are considered for outer to inner spiral tool and forces Fx 2, Fy 2 and Fz 2 are considered for inner to outer spiral tool on PVC sheets. Here we compared outer to inner spiral path tool and inner to outer spiral path tool when no feed given in z-direction during the process. The average value of force Fz 1 is 390N which continuously deforms the PVC sheet. The force Fz 2 is around 130N which is less than force Fz 1. The horizontal forces are less in outer to inner spiral tool than inner to outer spiral tool. The overall forces generated in inner to outer spiral tool are less than outer to inner spiral tool but the deformation is more in outer to inner spiral tool. Also the thickness and surface finish of deformed product is more in outer to inner spiral tool. Lesser thickness decreases the strength and increases the chances of failure of the product. The surface finish in outer to inner spiral tool is more than inner to outer spiral tool. So, outer to inner spiral tool process is more preferable for ISF work on PVC sheets as compared to inner to outer spiral tool. S.N. T (s) Fx1 Fy1 Fz1 Fx2 Fy2 Fz2 (N) (N) (N) (N) (N) (N) All rights reserved by 193

6 Table 10: Forming forces comparison in spiral path tool Table 11: Forming force comparison in straight path tool Fig. 11: Force V/S Time graph for comparison of spiral tool 2) Comparison between Outer To Inner and Inner To Outer Straight Path Tool Movements Straight path tool process is mostly used according to requirement of product shape. Here the forces Fx 1, Fy 1 and Fz 1 are generated in outer to inner straight path tool and forces Fx 2, Fy 2 and Fz 2 are generated in inner to outer straight path tool. In straight path tool the pattern of force generation is same but the value of forces are different from spiral path tool. Also in inner to outer straight path tool sheet failure occurs before completing the process. In straight path tool the forces are generated alternatively in x and y direction. The force Fz 1 act in vertical direction and Fx 1 and Fy 1 are generated in horizontal direction which deformed the sheet in required profile by completing the cycle. The forces Fx 2, Fy 2 and Fz 2 deforms the sheet but sheet sustain force for short time and failure occurs at half of process cycle. These failure occurs at different point of time with changing the speed, feed etc. So, the possibility of deformation process by inner to outer straight path tool is negligible. We should prefer outer to inner straight path tool for ISF process. Fx1 Fy1 Fz1 Fx2 Fy2 Fz2 S.N. T (s) (N) (N) (N) (N) (N) (N) Fig. 12: Force V/S Time graph for comparison of straight path tool IV. CONCLUSION AND FUTURE SCOPE The deformation behaviour in the Incremental sheet forming process is a combination of stretching, bending and shearing. Outer to inner tool is more effective than Inner to outer tool because there are less chances of sheet failure. Force increases continuously at starting but after some time it is approximately constant. In outer to inner tool vertical force is more but in Inner to outer horizontal forces are more. Increasing the cycle time increases the surface finish. So this parameter affect this process for large batch production. If speed increases, surface roughness decreases but the temperature at the tool contact increases. So process speed should be in limits. All rights reserved by 194

7 V. SCOPE OF FUTURE WORK In future Force prediction can be done by changing the tool diameter with different tool s considering the surface finish. The other extension of the force prediction model to capture the changing of local curvature and wall angle during forming to suit more complex shapes. Although it is widely accepted that different types of deformation modes are involved during the ISF process, there is still uncertainty as to how different process parameters affects these deformation modes. Forming forces for two-point incremental forming can be investigated since current force study is mainly based on SPIF process. REFERENCES [1] Kim, Y. H., & Park, J. J. (2002). Effect of process parameters on formability in incremental forming of sheet metal. Journal of materials processing technology,130, [2] Kopac, J., & Kampus, Z. (2005). Incremental sheet metal forming on CNC milling machine-tool. Journal of Materials Processing Technology, 162, [3] Martins, P. A. 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