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Proc. of. Int. Conf. on Advances in Mechanical Engineering 2010

Sheet Metal Micro Forming: Future Research Potentials Manish Oraon1; Vinay Sharma2 Asst. professor; university polytechnic; B.I.T. mesra, ranchi, india Manish_oraon@yahoo.com Department of production engg.; B.I.T. mesra, ranchi, india vinay1970@gmail.com Abstract - The paper is aimed to discuss some relevant issues concerning an innovative sheet metal forming technology, namely Single Point Incremental Forming. The advantages of this technology are addressed, including its capability to provide effective answers to some impellent industrial requirements: process flexibility, strong customer orientation, production of highly differentiated goods at low industrial costs. As well some relevant drawbacks are highlighted, mainly as concerns the level of accuracy permitted by the process. A wide recognition of the research efforts in this field is presented, taking into account some general considerations on the difference sources of shape and dimensional errors, as well as the influence of the most relevant parameters. Finally, some strategies for error minimisation are presented and discussed

methods but the surface of finished part will smoother than previous one. The forming paths are generated directly from the 3D CAD file, and often no tooling is needed. If a support tool is required, the same 3D CAD file can be used for making the support tool. In many cases the support tool is not needed and the process is shorter. The comparison between them can be easily understood by the block diagram. II. FORMING METHODOLOGY The methodology uses in micro forming is shown as in fig.2. Firstly the help of CAD/CAM determines the tool path which gives an idea about the movement of the tool. With generated tool path from CAD, the CNC milling

Keywords: Microforming; Incremental forming; Laser; Micro machining.

I. INTRODUCTION A substantial mutation is occurring in sheet metal forming companies basically oriented to the development of more efficient strategies in terms of flexibility and cost reduction. Sheet forming companies attempt to satisfy market demands by producing highly differentiated products, with small lot sizes. Customers, in fact, ask for exclusive products and they are driven to invest more if this aspect is taken into account. Furthermore, due to the market competition, a low production cost is strictly required with the aim to improve the margin of profit even if the sale price reduces. In the incremental forming of sheet metal, a simple-shaped tool imposes deformation locally on the sheet in a consecutive manner. In this process, the ball tool moves on the sheet according to a programmed tool path on a CNC milling machine. The sheet is located with the periphery fixed by bolts on a die, which is hollow and square in cross section. The basic idea of single point incremental forming (SPIF) processes is that the final shape of the component is obtained by the relative movement of a simple and small punch with respect to the blank, rather than by the shape of the dies. Such process is carried out on CNC machines, where it is possible to assign and control the punch movement according to fixed paths. The production process of sheet metal microforming is slower than in conventional production

Fig 1. production process of deep drawing

machine makes the product in precise form. Here the tool geometry is different from the milling cutter, the tool is a cylindrical rod with hemispherical head in few millimeter diameter. Among the different possibilities, incremental sheet forming (ISF) has proved to be a very reliable solution as shown in many different works carried out by Kim and Park [1,2] investigate the formability of an aluminum sheet under various forming conditions was assessed and difficult-to-form shapes were produced with the ISF technique. The machine setup for the experimental work as shown in fig.3. He also investigated the forming limit curve for the formation of the desired shape. Ambrogio et al.[3] and Kopac and Campus [5] investiated 32

Proc. of. Int. Conf. on Advances in Mechanical Engineering 2010

Different process configurations, both by numerical and experimental approaches, taking into account. They considered two different shapes, namely truncated cones and pyramids. The simulated figures of the cones were as shown in figure3. F. Micari et. al. [6] investigated on some general considerations related to the difference sources of shape and dimensional errors as in figure 4, as well as the influence of the most relevant parameters. Finally, some strategies for error minimization are presented and discussed. E. Maidagan et. al. [7] proposed a new method; the Sculptor process (fig. 5) which aims at developing a new concept of sheet metal forming in small and medium Sculptor process proposed an additional substituting upper and lower dies with two

influential parameters affecting the forming process through experimental comparison of the two observed methods. V. Franzen et al.[10] researched on the PVC sheets where the experimentation is based on the

Fig.3:[Ref 3 ]Incremental forming of an aluminum incremental sheet on CNC milling machine.

Comparison of FLCs in both and conventional forming methods production process of micro forming

utilization of an ordinary CNC milling machine and a single point forming tool to shape commercial PVC sheets and the overall investigation is centered on the characterization and evaluation (fig.7) of the formability limits of the process as a function of the major operating parameters. J.R Duflou et. al. [11] carried the analysis of forming a series of cones. The experiments were conducted to determine the influence of dynamic, local heating respectively on the process forces, the process accuracy, the formability and the residual stresses in formed workpieces. Guoqiang Fan et. al.[12] proposed a new method for hot incremental forming. The method is based on simple tooling and is easy to employ.

generic forming tools placed in on both sides of the blank, giving rise to a flexible die system. This way a truly dieless forming process is obtained. G. Ambrogio et al.[8] focused on the investigation of the influence of the process parameters on accuracy through a reliable statistical analysis. The obtained models permit to implement some effective actions to improve the accuracy taking into account a simple case study.

Fig. 2: steps for single point sheet metal microforming Fig. 4. [ Ref. 5] Geometrical errors during the SPIF process.

A. Petek et. al [9] investigate An interesting alternative is to substitute the rigid tool with a high velocity water jet (WJ). The comparison between using a rigid tool and a water Jet forming shown in fig 6.The aim to identify the most

It makes use of electric current for heating hard-to-form sheet metals at the tool–sheet interface in order to fully utilize the formability of these materials. The potential 33

Proc. of. Int. Conf. on Advances in Mechanical Engineering 2010

effect of processing parameters, namely current, tool size, feed rate,

Working principles and relevant process RTSPIF and WJSPIF.

Fig.5[Ref. 6] Incremental Sheet Forming processes

parameters of

J.R. Duflou et al.[13] proposed an experimentally explored multi-step toolpath strategy is reported and the resulting part geometries compared to simulation output. Sheet thicknesses and strains achieved with these multi-step toolpaths were verified and contribute to better understanding of the material relocation mechanism underlying the enlarged proess window.

SCULPTOR processes

and step size, on the formability are investigated. They conclude that electric hot micro forming technique is feasible and easy to control. Probably the process could be used for other hard-to-form materials and asymmetric parts (such as pyramids) show more distortion than axisymmetric parts (cones).

Fig. 7 [Ref. 9] Formability limits and defects in SPIF of PVC sheets. (a) Schematic illustration of the typical modes of failure. (b) Picture showing a crack (mode 1) and a surface defect. (c) Picture showing wrinkling along the wall thickness (mode 2) followed by a crack (mode 1).

G. Hussain et al. [14] targeted the investigation on the effect of wall angle (θmax) in single point incremental forming of sheet metals. Two tests were carried out in order to evaluate the formability of an aluminum sheet. In the first test, conical frustums and square pyramids (fig. 9), a set of each, were produced by systematically varying the wall angle in order to investigate θmax. The result obtained from the experiment as shown in table 2

Fig. 6: [ref.8] The main tool in RTSPIF and WJSPIF.

Proc. of. Int. Conf. on Advances in Mechanical Engineering 2010

Fig.8 [ref. 11] The structure of the machine laser-assisted

Table 1: Formability test results of various incremental forming processing

Table 2: Systematic investigation of θmax

Experimental investigations (fig.10) were carried out to determine the workpiece temperature by varying laser power at constant heating time.

Fig. 9 [ref. 13]. Some parts formed in the Test-1: (a) representative conical frustums and (b) representative square pyramid

Fig. 10 [ref. 14]. Laser-assisted micro forming

III. PROCESS ADVANTAGES AND LIMITATIONS The advantages and disadvantages of SPIF are as follows [4]. Advantages:

J.P. Wulfsberg et. Ai. [15] makes an approach to solve the problems (size effects related to small dimensions). He found that, the laser assistance of the micro forming process to benefit from e.g. the growing influence of thermodynamic aspects.

Useable parts can be formed directly from CAD data with a minimum of specialized tooling. These can be either Rapid Prototypes or small volume production runs. The process does not require either positive or negative dies hence it is dieless. However it does

Proc. of. Int. Conf. on Advances in Mechanical Engineering 2010

Development of computational techniques using Finite Element Method ¾ Fast calculation of plastic deformation, Process optimization To simulate the actual manufacture of parts using numerical modelling techniques

need a backing plate to create a clear change of angle at the sheet surface. ¾ Changes in part design sizes can be easily and quickly accommodated, giving a high degree of flexibility. ¾ Making metal Rapid Prototypes is normally difficult, but easy with this process. ¾ The small plastic zone and incremental nature of the process contributes to increased formability, making it easier to deform low formability sheet. ¾ A conventional CNC milling machine or lathe can be used for this process. ¾ The size of the part is limited only by the size of the machine. Forces do not increase because the contact zone and incremental step size remain small. ¾ The surface finish of the part can be improved. ¾ The operation is quiet and relatively noise free. Disadvantages: ¾ The major disadvantage is the forming time is much longer than competitive processes such as deep drawing. ¾ As a result the process is limited to small size batch production. ¾ The forming of right angles cannot be done in one step, but requires a multi-step process. ¾ springback occurs, however algorithms are being developed to deal with this problem.

V. APPLICATION OF MICROFORMING There are a number of areas where high precision of the product is required for the accuracy of the performance. Some of the following area where these types of product can manufacture by microforming . ¾ ¾ ¾

Aerospace: Instrument panel, Body panel, Passenger seat cover etc. Automobile: Door inner/outer panel, Hood panel, Engine cover etc. High customized products: Denture plate, Ankle support, Metal helmet etc. VI. CONCLUSION

As can be seen from the large amount of research activities in the field of microforming, some aspects are already identified and described, but several problems are still unsolved. Thus, only a few applications in this relatively wide field are already industrially applicable (especially in the field of microelectronics), other applications are close to a breakthrough. In most research areas great effort has been made to identify the size effects, now these effects must be described and solutions must be proposed to solve the problems that occur. This can be done purely academically, but considering the great advantage of the forming process for serial manufacturing, it will also be reasonable to start future research activities together with industry, not only to enhance process knowledge but also its usability and stability.

There are lots of research is going on to minimize the problem associated with the microforming / ISMF. L. Kwiatkowski et.al [16] developed a concepts to decreasing the main process time by applying several forming zones on the part through multiple tools working in parallel which gives the improved the surface finish as well as the formability of the sheet metal. J.P. Wulfsberg et al.[15] introduce the laser to enhancing the stretching capability and formability of sheet.

REFERENCES IV. FUTURE RESEARCH SCOPE

[1] Y. H. Kim & J. J. Park., Effect of process parameters on formability in incremental forming of sheet metal. Journal of Materials Processing Technology130-131, (2002) pp 42-46. [2] Y. H. Kim & J. J. Park. Fundamental studies on the incremental sheet metal forming technique. Journal of Materials Processing Technology 140, (2003) pp 447-453. [3] G. Ambrogio, L. Filice, L. Fratini, F. Micari, Some relevant correlations between process parameters and process performance in incremental forming of metal sheets, Proc. of 6th ESAFORM: (2003) pp175- 178. [4] Jadhav S., Goebel R., Homberg W., kleiner M; process optimization and control for incremental sheet metal forming, Proceedings of the International Deep Drawing Research Group Conference, IDDRG, ( 2003)pp. 165171. [5] J. Kopac, Z. Kampus, Incremental sheet metal forming on CNC milling machinetool, Journal of Materials Processing Technology 162–163 (2005) 622–628.

In industrial implementations of micro forming, it is very important to know the limiting factors of the process. The limiting factors may be due to special features of the micro forming. There are lots of research is going on related to the improvement of micro forming process such as ¾ Construction of forming limit criteria in incremental forming process I. Forming Limit Diagram, II. Ductile fracture criteria ¾ Improvement of formability using Preform design ¾ Warm incremental sheet metal forming technology I. Lightweight materials (Al, Mg) using halogen heating device II. Electric heating based micro forming III. Laser assisted micro forming 36 ©2010 AMAE DOI: 02.AME.2010.01.35

Proc. of. Int. Conf. on Advances in Mechanical Engineering 2010

Formability and Accuracy Improvement Annals of the CIRP Vol. 56/1/2007. [12] Guoqiang Fan; L. Gao; G. Hussain; Z haoli Wu b; Electric hot incremental forming: A novel technique, International Journal of Machine Tools & Manufacture (2008), pp. 1688–1692 [13] J.R. Duflou , J. Verberta, B. Belkassem , J. Gu, H. Sol, C. Henrard, A.M. Habraken; Process window enhancement for single point incremental forming through multi-step toolpaths; CIRP Annals - Manufacturing Technology 57 (2008) pp. 253–256 [14] G. Hussain , L. Gao, N.U. Dar; An experimental study on some formability evaluation methods in negative incremental forming; Journal of Material Processing Technology 186 (2007) pp. 45–53 [15] J.P. Wulfsberg, M. Terzi; Investigation of Laser Heating in Microforming Applying Sapphire Tools, Annals of the CIRP Vol. 56/1/2007 [16] L. Kwiatkowski ; M. Urban ; G. Sebastiani ;A. E. TekkayaTooling concepts to speed up incremental sheet forming Prod. Eng. Res. Devel. (2010) pp.57–64

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