This ppt file is about the third session of smart material class, which is about the machining difficulties of SMAs. At last, there is a case study with an experimental and simulation investigation.

1. Special Technologies
Machining of Shape Memory
Alloys (SMAs)
Mehrshad Mehrpouya
mehrshad.mehrpouya@uniroma1.it
Sapienza University of Rome
Department of Mechanical and Aerospace Engineering

2. Department of Mechanical and Aerospace Engineering
Special Technology

3. Department of Mechanical and Aerospace Engineering
Special Technology
https://it.linkedin.com/in/mehrpouya

4. Department of Mechanical and Aerospace Engineering
Special Technology
Machining of Nickel-Titanium Alloy
Machining has a main characteristic in a wide complex of manufacturing
processes how it is designed for removing material from workpiece. The
basic machining operation can be categorized to milling, drilling, turning,
sawing, shaping, broaching and abrasive machining.

5. Department of Mechanical and Aerospace Engineering
Special Technology
Machining of Nickel-Titanium Alloy
 Drilling, as with turning,
requires careful control of feed
and speed, and the use of
chlorinated lubricant is
recommended.
 Cylindrical centerless grinding is
a useful process for developing a
good surface on tubing and wire.

6. Department of Mechanical and Aerospace Engineering
Special Technology
Machining of Nickel-Titanium Alloy
 Abrasive methods such as abrasive
wheel cut off and abrasive water jet
cutting are also used in processing
Nitinol.
 Electro-discharge (EDM) machining is
quite useful, although not really suitable
for volume production.

7. Department of Mechanical and Aerospace Engineering
Special Technology
Laser cutting and machining
has become a preferred method for
creating stents from Nitinol tube.
Very complicated geometries are
produced using CNC controlled part
motion and finely focused pulsed
Nd:YAG laser beams. Laser cutting
is fast and very flexible, and cut
geometry is readily changed
through reprogramming of the CNC
control.

8. Department of Mechanical and Aerospace Engineering
Special Technology
OrthogonalMachining

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Special Technology
The mechanism of a machining process
Nomenclature
𝑽 𝑪 Cutting Speed
FC Cutting Force
𝒉𝒄 Chip Thickness
h Depth of cutting
𝜸 𝟎 Rank Angle
𝜶 𝟎 Clearance Angle
𝒌 𝒓 Tool Cutting Edge Angle
Φ Shear Angle

10. Department of Mechanical and Aerospace Engineering
Special Technology
Problem Statement
Machining of Nitinol is very difficult by reason of the
very rapid work hardening of this alloy. Although with
proper carbide tooling and control of tool geometry,
speed and feed, excellent tolerance and finish can be
achieved in turning operations.
NiTi alloy cannot be machined easily because of high
tool wear, high cutting force, huge hardness and
surface defects are made many problems into their
machining.

11. Department of Mechanical and Aerospace Engineering
Special Technology
Surface defects
Investigation in micron precision shows plenty
surface defects in machining process, something
like;
 High Tool Wear
 Chip layer formation
 Burrs Formation
 Lay Pattern
 Debris of microchips
 Feed marks
 Tearing surface
 Deformed grains
 Material cracking
 Smeared Material
 Feed Marks after Turning
 Build-up edge (BUE)

12. Department of Mechanical and Aerospace Engineering
Special Technology
Some Problems in the Machining of NiTi: a) High Tool Wear, b)
Adverse Chip Form, c) Burrs Formation After Turning, d) Grinding
(Weinert and Petzoldt 2004).

13. Department of Mechanical and Aerospace Engineering
Special Technology
Surface Damages in
Machining of Nickel-Titanium
Alloys: (a) Metallographic
Microstructure after Turning
(b) Lay Pattern after Dry
Milling (c) Metal Debris after
Turning, and (d) Smeared
Material and Feed Marks after
Turning (Ulutan and Ozel 2011).

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Special Technology
The schematic of
the build-up edge
(BUE) in the
machining process

15. Department of Mechanical and Aerospace Engineering
Special Technology
There are a lot of parameters that have influence on the workpiece’s
surface quality. workpiece parameters (material, grain size), tool
parameters (edge radius, rake angle, wear shape, coating) and cutting
parameters (feed, cutting speed and depth of cut) (Falvo 2007, Ulutan and Ozel
2011, Mackerle 2003; Sun and Feng 2006).
Feed Rate Cutting Speed Tool Wear
Tool Geometry
and Properties
Cutting Depth
Workpiece
Materials and
Properties

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Special Technology
Case Study

17. Department of Mechanical and Aerospace Engineering
Special Technology

18. Department of Mechanical and Aerospace Engineering
Special Technology
 Nickel-Titanium shape memory alloy
 Ni50.9 Ti49.1.
 Cutting tool, TiCN/TiAlN multilayer
coating (is chosen as the appropriate
with capability of utilizing in high cutting
speed processes)
 At room temperature
The experimental machining (Turning Process)

19. Department of Mechanical and Aerospace Engineering
Special Technology
The optimum cutting speed is investigated as a
considerable parameter and a principle factor in
applied stress to obtain a better machining
quality of NiTi. The interaction between various
cutting speeds and the temperature rise of the
workpiece has attracted much attention. High
stress can increase the hardness of NiTi due to
its specific thermo-mechanical properties.

20. Department of Mechanical and Aerospace Engineering
Special Technology
Generally, the lower cutting force and
consequently lower stresses in the
machining process improve the
mechanical properties, as well as
reduction in hardness, distortion and
residual stress.

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Special Technology
Experimental results

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Special Technology
FEM provide suite powerful offers and
complete solutions for both routine and
sophisticated engineering problems covering
a vast spectrum of industrial applications. In
the automotive industry engineering work
groups are able to consider full vehicle
loads, dynamic vibration, multibody systems,
impact/crash, nonlinear static, thermal
coupling, and acoustic-structural coupling
using a common model data structure and
integrated solver technology.
Finite Element Method (FEM)

23. Department of Mechanical and Aerospace Engineering
Special Technology
Generally, a complete simulation process
based on finite element method (FEM)
enables to predict a comprehensive model
for machining optimization and effectively
reduces the cost of experimentation
effectively. Particularly, numerical modeling
of the cutting operation reveals that the
stress-strain rate, chip formations and tool
statement are costly and time consumable to
determine experimentally
Finite Element Method (FEM)

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Special Technology
JC constitutive material model

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Special Technology
Finite Element Method (FEM)
Mesh ModelSchematic of the machining modeling

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Special Technology
SimulationofMachiningbasedonFEM

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Special Technology
Von Mises stress contour
plots in cutting speed, (a)
20, (b) 80, (c) 100, (d)
110, and (e) 130 m/min

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Special Technology
Shear stress contour
plots in cutting speed,
(a) 20, (b) 80, (c) 100,
(d) 110, and (e) 130
m/min

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Special Technology
Von mises stress-Cutting speed

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Special Technology
Shear stress-Cutting speed

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Special Technology
Resultant stress-Cutting speed

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Special Technology
As it clear, the value of micro-hardness has reduced remarkably, when the cutting speed
has risen. Additionally, this diagram depicts 100 m/min as the acceptable amount of
cutting speed where the lowest value of hardness is 240 HV ± 7.5 (Kaynak et. al.).
Hardness-Cuttingspeed

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Special Technology
The obtained cutting speed, as shown
in the resultant graph of FEM, would
be acceptable since it has only 9%
variation in comparison with the
experimental cutting force (100
m/min).
Final result

34. Department of Mechanical and Aerospace Engineering
Special Technology