SMATI group - Study of innovative

SMATI group - Study of innovative manufacturing
processes using experimental test, material
characterization and numerical simulation
Di Michele G1, Guglielmi P1, Palumbo G1, Piccininni A1, Piglionico V1, Scintilla LD1,
Sorgente D1, Spina R1, Tricarico L1,*
1
DMMM – Politecnico di Bari, viale Japigia 182 – Bari, Italy
{gabriella.dimichele, pasquale.guglielmi, gianfranco.palumbo,
antonio.piccininni, vito.piglionico, donato.sorgente,
roberto.spina, luigi.tricarico1}@poliba.it
Abstract. The following research area are investigated: (i) Mechanical and
technological characterization of industrial materials (metals and polymers). (ii) Sheet
metal forming processes, assisted with flexible media, in warm/hot conditions and
plastic/superplastic behaviour. (iii) Modelling of manufacturing processes.
Keywords: Mechanical and Technological Characterization; Sheet Metal Forming;
Laser Material Processing; Plastic injection moulding; Casting processes
Introduction
Through a numerical-experimental approach, in the 2013-2014 biennium the research
group on MAterials and Innovative Technologies (SMATIgroup) of the Politecnico di
Bari has investigated different innovative manufacturing processes, mainly in the sheet
metal forming [1-3,12,13,15,17,18,26,27], laser material processing [4,7,8,10,11,14,16,
19-25, 28-31], plastic shaping [5,6,9,32] and casting processes [33,34]. In this paper,
some case studies are described.
1
Case studies
1.1
Warm Hydroforming tests on age hardenable Al alloys
The HydroForming process in Warm conditions (WHF) has been investigated using a
2500kN electro-hydraulic press machine specifically designed and produced as a
prototype by Gigant Italia. The 6xxx series Al alloy AC170PX (1mm thick), largely
Page 1 of 5
adopted for automotive applications, was purchased in the T4 condition and
characterized in terms of mechanical properties (flow stress curves according to
temperature and strain rate) and formability limits (Forming Limit Curves according to
temperature). Such experimental data were implemented in a Finite Element model
aimed at investigating the working range of the parameters affecting the WHF process
(temperature in the range 20 – 200C and pressure rate in the range 2.5 – 25 bar/s).
The investigated case study had a stepped geometry; as response variables the length
of the flat part of the deepest region of the die (Flatness%), the bursting pressure and
the sheet thinning were monitored.
Results from numerical simulations are presented in figure 1a: the adoption of the
highest pressure rate (the biggest bubbles ) coupled with the highest temperature (the
red bubbles) was predicted to determine the highest Flatness and Bursting pressure.
Figure 1. WHF working range from FE simulations (a); measured sheet thinning at 200C (b)
Experimental results confirmed the effectiveness of working at the highest
temperature level (200C); in addition in figure 1b the favourable effect of forming the
blank using elevated strain rates is highlighted: when setting the pressure rate at
25bar/s, both the Flatness% and the minimum thickness along the blank section were
increased.
1.2
Multiscale modeling of injection molding parts
Predicting the microstructure requires the simulation of the crystallization process
which is a complex problem because it is necessary to combine transport phenomena
of the multi-phase flow in non-isothermal conditions with crystallization kinetics. This
requires the calculation of polymer properties on a microscopic scale using
information from a macroscopic scale.
The simulation of the crystallization kinetics is performed by integrating COMSOL,
in-house future SphäroSim. thorough the OpenSource file format VTK. The
temperature and velocity in the nodes are transferred to SphäroSim where they are
used as boundary conditions for the simulation of the crystallization process.
Figure 2: Injection profile and microstructure formation
1.3
Steel surface structuring by high brightness pulsed laser
Laser hardening and remelting of a hypereutectoid steel (AISI 52100), has been
investigates using individual circular spots of a high brightness fiber laser working in
pulsed mode.
Hardned Diametr, micron
1500
750LP-20JP-num
1250
750LP-20JP-exp
500LP-20JP-num
M
1000
500LP-20JP-exp
750
250LP-20JP-num
H
500
250LP-20JP-exp
1200°C
250
1400°C
0
0
0.5
1
1.5
Spot Radius, mm
2
1800°C
Figure 3: Hardened diameters obtained using a pulse energy of 20J/pulse.
Investigated parameters were the laser power (LP: 250-750W), laser pulse energy (JP:
10-20J/pulse) and focusing distance (FD). A finite element model was developed and
model parameters were calibrated using the shape and size of the treated zone
measured in experimental tests. The figure 3 compares numerical and experimental
results obtained with a laser pulse energy of 20J/pulse. The process maps obtained by
the numerical model show the laser spot radius (related to the focal distance), and the
laser power ranges, which provide the substrate hardening without melting (H) or the
substrate melting without cracks occurrence (M). These maps are useful to design
pattern for the laser structuring of tool steel surfaces in pressure die-casting and metal
forming applications.
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Conclusions
Process window definition in the part manufacturing using new materials and/or
innovative technologies, need a deeper knowledge of material behavior and process
parameters impact. The results obtained in the 2013-2014 biennium by the SMATI
research group, highlight great advantages in the use of numerical-experimental
approach as shown by the case studies proposed in this paper.
Acknowledgements. The authors wish to thank the Italian Institutions Region
APULIA and MIUR (Ministry of Education, University and Research) for financing
the research activities published in the 2013-2014 biennium (projects: TRASFORMA,
PON01_02584, PON01_02238, PON02_00576_3333604).
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