Bruschi, Stefania

Francesco Bariani, P.

Ghiotti, Andrea

Regazzo, Paolo

English

GHIOTTI, ANDREA

BRUSCHI, STEFANIA

Archivio istituzionale della ricerca - Università di Padova

Original Citation:Reduction of vibrations in blanking by MR dampersSpringer Berlin HeidelbergPublisher:Published version:DOI:Terms of use:Open Access(Article begins on next page)This article is made available under terms and conditions applicable to Open Access Guidelines, as described athttp://www.unipd.it/download/file/fid/55401 (Italian only)Availability:This version is available at: 11577/3215429 since: 2016-11-30T13:08:50Z10.1007/978-3-662-46312-3_31Università degli Studi di PadovaPadua Research Archive - Institutional RepositoryA. Erman TekkayaWerner HombergAlexander Brosius Eds.60 Excellent Inventions in Metal FormingID: 10.1007/978-3-662-46312-3 – 031 Date: March 31, 2015 Proof number: 1Reduction of Vibrations in BlankingbyMR DampersAndrea Ghiotti, Paolo Regazzo, Stefania Bruschi, and P. Francesco Bariani1 IntroductionBlanking and, more generally, shearing operations are the most common operations inthe process chains for sheet metal parts. Looking at a typical punch force vs. penetrationcurve in blanking (Fig. 1), two main phases can be distinguished. In the former (from A toB in Fig. 1a), the punch penetrates the material causing the sheet metal to deform until theshearing starts. In this phase, the press and die set store up elastic energy. In the secondphase (from B to C in Fig. 1a), the shear strength of the material is exceeded and a fracturestarts causing the sudden release of the energy that dissipates through the high frequencyoscillations (the tail end of the curve in Fig. 1a). This break through shock generates un-Fig. 1 a The reverse load phenomenon in blanking, b Sketch of MR damper, c MR fluid dampersAndrea Ghiotti ! ! Paolo Regazzo ! Stefania Bruschi ! P. Francesco BarianiUniversity of Padova, Padova, Italye-mail: andrea.ghiotti@unipd.it199© Springer-Verlag Berlin Heidelberg 2015A. E. Tekkaya et al. (eds.), 60 Excellent Inventions in Metal Forming,DOI 10.1007/978-3-662-46312-3_31ID: 10.1007/978-3-662-46312-3 – 031 Date: March 31, 2015 Proof number: 1200 A. Ghiotti et al.controlled high reverse loads, mechanical vibrations and loud noise that may cause seriousproblems such as fatigue cracks in the ram, drive linkage, crown, housings and, in the bedof the press, premature wear in punches and dies and great discomfort for press opera-tors. The break through shock in blanking operations has been considered by a numberof researchers, most notably for modelling the ductile fracture that causes surface separa-tion and the associated energy release [1–3] or for correlating the stiffness of the systemcomponents (press, stripper and die set) and their vibrations during the break through [4–6]. However, few contributions in the scientific literature have dealt with new possiblesolutions to effectively reduce the reverse load, vibrations and noise. Murakawa [7] de-veloped a “hydraulic inertia damper” that proved to be effective in lowering the punchforce reduction rate, thereby causing a reduction in vibration and noise. Osakada [8]demonstrated that the noise level accompanying the break through shock can be signifi-cantly reduced if an accurate control of the punch motion – such as that allows by servocontrolled presses – is combined with a “continuous two-steps blanking”, where the punchis stopped just before the fracture starts. In this research, the application dampers basedon magneto-rheological (MR) fluids to reduce the shock response of press systems dur-ing blanking operations is considered. Compared to most conventional dampers, whichare passive hydraulic devices, MR dampers are semi-active devices where the dampingcapacity can be modulated either gradually or in real-time based on the system response.MR fluids are suspensions of micron-sized ferromagnetic particles in a liquid carrier thatpresents controllable and reversible changes in its rheological properties, from free flow-ing linear viscous liquids to semi-solids, having controllable yield strength when activatedby an external magnetic field. Thanks to these features, they offer relevant performancesin the typical working conditions of metalworking presses, where long working strokesare required and the vibrations caused by break through shocks present high frequenciesand small-amplitude vibrations. The aim of the investigation described in the paper was toevaluate, through full-scale experiments, the feasibility and practicability of implementingMR dampers and to understand the potential benefits when they are used in a semi-activemanner in comparison with conventional dampers.2 MRDampersThe MR dampers designed and developed by the Authors are presented in Fig. 1b and c(details of the design and manufacture in [9] and [10]). The prototypes consist of single-hand dampers designed to withstand the break through shock generated during blankingin a long-stroke hydraulic press. A 1 mm thick annular orifice between the piston rod andthe liner allows the fluid to flow through the entire annular region as the piston moves.The inner shaft prevents possible misalignments from arising due to high-frequency vi-bration and reverse load and, at the same time, works as a volume compensator to balancethe volume change during the rod stroke. The electrical coils embedded into the pistongenerate a uniform magnetic field across the 240 mm long gap and perpendicularly to theID: 10.1007/978-3-662-46312-3 – 031 Date: March 31, 2015 Proof number: 1Reduction of Vibrations in Blanking by MR Dampers 201Fig. 2 Force vs. current inten-sity curves of the MR dampersfor a fixed value of the punchspeeddirection of the MR fluid flow. Figure 1c shows the four dampers in the working area ofthe press.The damping force of the four MR dampers for different values of the current intensitywas measured through laboratory experiments. Figure 2 shows the curves of the force vs.current intensity of the MR dampers for a fixed value of the punch speed. For the fourdampers, the damping force is constant along the entire testing stroke and presents a goodlinearity with the current intensity.3 ExperimentsIn the experiments three damping systems were compared: (a) the MR dampers abovedescribed, (b) conventional hydraulic cushions, and (c) commercially available hydraulicdampers. The damping system based on hydraulic cushions consisted of four hydrauliccylinders whose chambers were connected in parallel to a common manifold. The work-ing stroke and maximum counter force were 40 mm and 80 kN, respectively. The system,based on hydraulic dampers, consisted of four shock dampers providing a counter pres-sure generated by an internal orifice and a flow control valve. The working stroke andmaximum counter force were 20 mm and 200 kN, respectively. The experiments werecarried out on a four-column double-effect 2500 kN hydraulic press. Figure 3a–c showsthe machine and the details and the sketch of the tooling.Data regarding the pressure and acceleration were acquired during the experiments:the former was monitored inside the manifold of the upper actuator of the press, the lattermeasured on four points of the frame, respectively located on the die plate, on the ramand on one of the columns of the press. The blanking experiments were conducted on2 mm and 3 mm thick C40 steel sheets with a constant punch-die clearance of 0.2 mmand two different speeds of the press ram (20 mm/s and 50 mm/s). The experiments wererepeated for four different configurations of the press: with no damping device, with MRdampers, with hydraulic cushions and with hydraulic dampers. The experiments with theMR dampers were carried out using four levels of current intensity: 0.4 A, 0.6 A, 1.1 Aand 2 A. All the experiments were replicated to assure the repeatability of results.ID: 10.1007/978-3-662-46312-3 – 031 Date: March 31, 2015 Proof number: 1202 A. Ghiotti et al.Fig. 3 a The 2500 kN hydraulic press with indication of the accelerometers, b Detail and c sketchof the tooling, d Accelerations for different electrical currents with the MR shock dampers4 ResultsFigure 3d shows the effect of the current intensity in the MR damper circuits on the re-sponse of the press system to the break through shocks. Damping performance increaseswith the current intensity until a critical value of 3 A generates the saturation of the mag-netic circuit and the permanent magnetization of the particles in the MR fluid. A value of1.1 A proved to be a good compromise between damping performance and system stabil-ity. Figure 4 shows the acceleration-time response over the duration of the break throughshock when the press system is equipped with the hydraulic cushions (Fig. 4a), the hy-draulic dampers (Fig. 4b) and the MR dampers (Fig. 4c).Each of the three responses is compared to the one measured on the press without anydamping device. Reductions in the peak acceleration are achieved by using both the hy-draulic cushions and the MR dampers. Compared to the response of the system equipped26,025,0Time [s]No dampingMR damper26,025,0Time [s]No dampingHydraulic damper-40-30-20-100102026,025,0Time [s]No dampingHydraulic cushionAcceleration [m/s2 ]Punch speed 20mm/s Sheet thickness 2mm Relaxation t. (0.562s) Relaxation t. (0,585s) Relaxation t. (0.555s) a b cFig.4 Accelerations measured at the press ram with a the hydraulic cushions, b the hydraulic shockdampers and c the MR shock dampersID: 10.1007/978-3-662-46312-3 – 031 Date: March 31, 2015 Proof number: 1Reduction of Vibrations in Blanking by MR Dampers 203a b c0 250 500Frequency [Hz]No dampingMR damper0 250 500Frequency [Hz]No dampingHydraulic damper00,511,520 250 500Frequency [Hz]No dampingHydraulic cushionAmplitude Punch speed 20mm/s Sheet thickness 2mm Machine critical freq. Machine critical freq. Machine critical freq. Fig.5 Amplitude spectra of accelerations at press ram with a the hydraulic cushions, b the hydraulicshock dampers and c the MR shock damperswith the conventional dampers, the decay of residual vibrations that is observed for thesystem with the MR dampers is significantly faster (approximately a reduction of 30 %compared with hydraulic cushions and 10 % compared with hydraulic dampers). This isbecause the damping effect of the highly viscous MR fluid (when the magnetic field isactivated) predominates over the unavoidable elasticity of the fluid pressurized in the con-ventional dampers. Figure 5 shows the amplitude spectrum of the ram acceleration in thefrequency domain for the press system equipped with the hydraulic cushions (Fig. 5a), thehydraulic dampers (Fig. 5b) and the MR dampers (Fig. 5c). Each of the three spectra iscompared to the one measured on the press without any damping device. As expected, thespectrum for the press without any damper shows a high number of excited frequencies,with the highest values close to 25 Hz. Significant reductions of the number of the excitedfrequencies and the acceleration amplitudes are observed for the three kinds of dampers.However, the hydraulic cushions behave worse than the other two shock dampers typolo-gies since they are not able to damp the low frequencies vibrations that are typical of thetested hydraulic press. Among the latter, the amplitude of vibrations measured with theMR dampers is approximately 40 % less than the one obtained with the hydraulic dampers.5 ConclusionsMR dampers were developed for metalworking presses to withstand the break throughshock generated during blanking operations. Full-scale experiments were set up to un-derstand the potential benefits of MR dampers compared to conventional dampers. Theresults show that MR dampers can be effective in damping the vibrations induced by thebreak through shock and in limiting the number of excited frequencies. Thanks to theirshort response time they appear suitable to be implemented in processes where multipleblanking operations are required.ID: 10.1007/978-3-662-46312-3 – 031 Date: March 31, 2015 Proof number: 1204 A. Ghiotti et al.References1. Breitling J., Pfeiffer B., Altan T., Siegert K., 1997, Process control in blanking, Journal ofMaterials Processing Technology, 71 (1), 187–192.2. Stegeman Y.W., Goijaerts A.M., Brokken D., Brekelmans W.A.M., Govaert L. E., BaaijensF.P.T., 1997, An experimental and numerical study of a planar blanking process, J. of MaterialsProcessing Technology, 87 (1–3), 266–276.3. Stegeman Y. W., Goijaerts, D. Brokken, W. A. M. Brekelmans, L. E. Govaert, F. P. T. Baaijens,1999, An experimental and numerical study of a planar blanking process, Journal of MaterialsProcessing Technology, 87 (1–3), 266–276.4. Doege E., Seidel H.-J., 1985, Noise Reduction on Mechanical Punch Presses, CIRP Annals, 34(1), 507–509.5. Guo B., Chen W. M., Wang Z. R., 1998, Analysis of blanking vibration with consideration ofthe break-through state, Journal of Materials Processing Technology, Vol. 75 (1–3), 117–121.6. Bassiuny, A.M., Li, Xiaoli, Du R., 2007, Fault diagnosis of stamping process based on empiricalmode decomposition and learning vector quantization, Int. J. Mach. Tools and Manuf., 47 (15),2298–2306.7. Murakawa M., Mo J., Wakatsuki Y., Koga N., 2001, Investigation of blanking noise reductionusing a hydraulic inertia damper, J. of Materials Processing Technology, 112 (2–3), 205–213.8. Otsu M., Yamagata C., Osakada K., 2003, Reduction of blanking noise by controlling pressmotion, CIRP Annals, 52(1), 245–248.9. Regazzo P., Ghiotti A., 2008, Internal report in Italian, DIMEG 2008/56.10. Ghiotti A., Regazzo P., Bruschi S., 2014, Shear surface control in blanking by adaptronic sys-tems, Procedia Engineering, 81, 2014, 2512–2517.

Reduction of vibrations in blanking by MR dampers

Andrea Ghiotti

Paolo Regazzo

Stefania Bruschi

P. Francesco Bariani

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Reduction of Vibrations in Blanking by MR Dampers

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Reduction of vibrations in blanking by MR dampers

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