Advances in micro milling: From tool fabrication to process outcomes.

1. Article covers all the aspects of “A state of art review on micromanufacturing : Design and testing of micro-products”
Advances in micro milling: From tool fabrication to process
outcomes
Ni Chen, Hao Nan Li , Jinming Wu, Zhenjun Li, Liang Li, Gongyu Liu, Ning He
DOI : https://doi.org/10.1016/j.ijmachtools.2020.103670
Impact factor : 10.331
Term Paper Presentation on
Presentation By:
Shivendra Nandan (M21ME009)
Srikant Padmanabhan (M21ME004)
Rahul A Makadia (M21ME014)
Sujay B J (M21ME003)
Under the guidance of:
Dr. Ankur Gupta
Course Instructor
Department of Mechanical Engineering
Indian Institute of Technology Jodhpur

2. ‘
GRAPHICAL ABSTRACT
 In this article, Authors have presented the comprehensive and up-to-date review of micro milling cutters in terms of their uniqueness, material removal
mechanisms, materials and compositions, structures and design, fabrication techniques and machining performances, to provide adequate guidance for
interested involvers.
 They also outline and discuss several possible future research directions to offer potential insights for the micro milling community and future
researchers.
Objectives:

3. INTRODUCTION TO MILLING CUTTERS
Hard magnetic soft materials
Conventional
Milling
Micro-Milling Applications
Cited from: https://tenor.com/en-GB/view/cnc-machining-gif-23989014

4. MICRO-MILLING CUTTER GEOMETRY
Cited from: https://www.fraisa.com/en/products/fraisa-microhx

5. ‘ ‘
MATERIAL REMOVAL MECHANISM
Minimum undeformed chip
thickness (hm)
‘
Chip formation might not
occur when the UCT in micro
cutting is smaller than a
certain value.
• In micro machining, the UCT value (denoted as h) of 0.1–50 μm is much smaller than
that used in macro process (0.1–10 mm).
• When the UCT becomes smaller than hm, workpiece materials would, instead of
being removed in the form of chips as in macro machining, experience either rubbing
or ploughing.
• This also results in different and even more complicated material removal behaviors
in the micro cutting process because of not only diverse h–hm relationships but also
different loading conditions in each relationship based on the geometrics of the
contact zone between the cutting edge tips and workpiece.
Elastic Deformation: h < hm
Elastoplastic Deformation: h ~ hm
Chip Formation: h > hm
Orthogonal Micro-cutting
 
1 cos
m m
e
h r 
 

6. ‘
‘
MATERIAL REMOVAL MECHANISM
C
‘
Side micro milling process: two-tooth micro milling cutter
:
entrance
UCT MUCT
 Chip begins to form; :
UCT MUCT
 Chip generation would stop;
After the micro milling cutter is Passed
• A part of workpiece material will elastically recover while other
material will undergo plastic deformation.
• The machined surface in side micro milling includes both the
theoretical residual height (Rtheoretical) and the residual height
(Rmax) left by the existing MUCT.
• The point where the material flow separates to form the chip and
machined surface is stagnation point.
2
8
z
theoretical
f
R
r

   
 
2
2
max 2
1
1
1
8 2
m
m
z
z
k h
k h
f
R
r f
 


 
  
 
 
Fz : Feed per tooth
hm : MUCT
κ : Constant percentage of recovered machined
materials
‘
Cutting force in micro milling:
• Cutting force-based models defined the MUCT based on
the resultant cutting force along the direction normal to the
workpiece surface
• The transition point of the force from upward to downward
directions was considered as the MUCT
‘
Principle - 1 ‘
θm based on horizontal force (Fx), vertical
force (Fy), and friction coefficient between
the tool and workpiece (μ) .
It based on the friction angle (β) between the
workpiece and rake face.
Principle - 2
Sometimes an ultra-precision dynamometer is required to detect small variations in cutting forces when the UCT is close to the MUCT.
(i) The tool runout cannot be
avoided in the fabrication
process,
(ii) The tool runout for micro
mills would be at the same
length scale as the feed per
tooth, and
(iii) The tool runout significantly
affects the micro process,
from process kinematics, via
chip thicknesses to forces.
Assumptions

7. MATERIALS FOR MICRO MILLING CUTTERS

8. MATERIALS FOR MICRO MILLING CUTTERS
Toughness and hardness of micro milling cutter materials
Scanning electron microscopy (SEM) images, schematic of chemical components
ND Natural diamond
MCD Monocrystalline diamond,
CVD Dimond- chemical vapor deposited diamonds
PCBN Polycrystalline cubic boron nitride
PCD Polycrystalline diamond

9. ‘
MATERIALS OF COATINGS
• Coatings have been commonly applied to cemented carbide micro milling cutters
to reduce tool wear and improve their cutting performance.
• The most commonly used metal coatings for micro milling cutters are TiN, AlCrN,
CrN, AlTiN, and TiAlN. However, TiN and CrN coatings were found to have
insufficient hardness for difficult-to-machine materials.
• To improve coating hardness, aluminum was introduced to TiN and CrN coatings,
resulting in coatings such as AlCrN and AlTiN which increased tool life and reduced
cutting edge chipping and wear rate.
• Despite these improvements, metal coatings have limitations due to droplets on
the flank face decreasing surface quality and coating defects increasing cutting
forces and surface ploughing.
• Diamond coatings were proposed to improve the hardness and wear resistance of
metal coatings and prevent droplets and coating defects.
• Fine-grained diamond (FGD) and nanocrystalline diamond (NCD) coatings were
effective in increasing tool hardness and wear resistance. A bilayer coating of SiC
and diamond was proposed to solve this problem, which significantly reduced
cutting forces, and improved surface quality.
SEM images of coatings for micro milling cutters

10. Design Criteria:
 High stiffness to prohibit the micro milling cutter
breakage;
 Relief angles, tool peripherals, and tool bottom
surfaces should be considered to avoid the
unnecessary contact;
 Chip disposal spaces;
 Small cutting edge radius;
 Small positive rake angles.
STRUCTURES OF MICRO MILLING CUTTER GEOMETRY
Reference: https://youtu.be/IevJUD3puWs
Asymmetric tool geometry: Avoid Fabrication error
Symmetric tool geometry: Increase Machining efficiency

11. Solid Micro-milling Cutters
 Solid micro-milling cutters are mostly fabricated from non-ultra-hard materials;
 The 2D-profile of solid micro-milling cutters can be primarily classified into end
micro-milling cutters, ball micro milling cutters and profiled micro-milling
cutters;
 End micro-milling cutters have flat cutting teeth on both end and side surfaces
and have been commonly used to generate flat surfaces in vertical micro-milling;
 Ball micro-milling cutters have hemispherical cutting edges at the tool end;
therefore, they are ideal for machine parts with complex 3D contoured micro
features;
 Profiled micro-milling cutters are designed for specific micro structures.
STRUCTURES OF MICRO MILLING CUTTER GEOMETRY

12. Welded Micro-milling Cutters
 Fabricated by welding the ultra-hard head on the non-ultra-hard shank to
provide improved machining ability with an acceptable cost;
 Poor machinability of ultra-hard materials may limit the structure diversity
of welded micro milling cutters;
 Primarily simple geometries, such as circular, triangular, square, and conical
geometries, to reduce fabrication cost and increase efficiency owing to the
poor machinability of ultra-hard materials;
 Machining of difficult-to-machine materials such as hard and brittle crystals
and cemented carbides, while solid micro milling cutters are mostly used to
machine ductile metals or plastics;
 The cost of welded micro milling cutters is higher because of the use of
ultra-hard materials as the cutting edge.
STRUCTURES OF MICRO MILLING CUTTER GEOMETRY

13. • Reduced computational effort
• Full consideration of the effect of small cutting edge
structures in comparison with analytical calculations
• The poor match between simulations and experiments
in SFEM limits the applications of SFEM;
• Detailed FE simulations with consideration of dynamic
material behaviours such as plastic flows, strain-rate
hardening or softening, and dynamic mechanical and
thermal loading applied on micro milling cutters.
‘
DESIGN AND OPTIMIZATION
Static Finite Element Method (SFEM)
‘
Dynamic Finite Element Method (DFEM)

14. DESIGN AND OPTIMIZATION
References: 1. https://www.youtube.com/watch?v=U9LfdNmqM_Y&ab_channel=HongtaoDing;
2. Attanasio, Aldo, et al. "Finite element simulation of high speed micro milling in the presence of tool run-out with experimental validations." The International Journal of Advanced Manufacturing Technology 100 (2019): 25-35.
Von-mises Stress Distribution Contour Graphs

15. PERFORMANCES OF MICRO MILLING CUTTERS
Cutting Force Performance Comment
• Cutting forces are significantly different from those in milling in terms of size, morphology, and key factors owing to the size
effect.
• The cutting forces in micro milling, unlike hundreds of newtons generated in macro milling processes, are normally lower than 4 N
owing to only several micrometres of the UCT and feed per tooth.
Tool Wear Performance Check
• The micro milling cutter wear is closely related to the geometric
parameters of micro milling cutters, tool materials, workpiece materials,
cooling liquid, etc.
• The flank wear (the VB value) around the tooltip has been widely used as
the tool wear indication in micro-milling.
Optical images of micro milling cutters: (a), (b) new and worn cemented carbide micro milling cutters, (c), (d)
new and worn cemented carbide micro milling cutters; (e), (f) adhesive layers and microcracks on a used
Ti(C7N3)-based cermet micro milling cutter.

16. PERFORMANCES OF MICRO MILLING CUTTERS
Temperature Performances
• The cutting zone temperature is frequently below 100 ◦C,
whereas over 200 ◦C is frequently what is observed when
machining hard and brittle materials.
• Increasing the cutting speed in micro milling would
increase the number of workpiece materials with plastic
deformation per unit time; therefore, the consumed power
and micro milling temperature would increase.
Typical cutting temperature and machined surface morphology in micro milling: (a) response table of workpiece temperature change [209], (b)
numerical results of heat flux, (c) machined surface morphology, and (d) cutting temperature change of workpiece under different spindle speeds.
Surface Finish Performance Check
• High machined surface quality can be achieved in
micro milling with roughness Ra values typically
less than 100 nm, and a small cutting-edge radius
was required to select even a small feed rate, which
decreased the residual height on the machined
surface.
• Moreover, the unevenness of the cutting edge was
easily imprinted on the workpiece surface.

17. POSSIBLE FUTURE DIRECTIONS & CONCLUSIONS
The recent advancements in micro milling cutters by
detailing their uniqueness, material removal
mechanisms, raw materials, structures, design and
optimization methods, fabrication techniques, and
performances, and providing some possible future
directions.
The future can always be seen in how
past changes have been taken up and
what is the development rate of the
various changes.
Some of the points addressed are:
• Material removal mechanism
• Materials employed for
manufacturing
• Design and optimization for micro
milling cutter structures
• Fabrication techniques
• Tool performance

18. APPENDIX: COMMERCIAL SETUP FOR MICROMILLING
References: https://youtu.be/R6NbHSTfQwI.