Diamond turn machining

Shri Ramdeobaba College of Engineering and
Management, Nagpur.
Department of Mechanical Engineering
(2020-21)
DIAMOND TURN MACHINING
(DTM)
PRESENTED BY COURSE COORDINATOR
Abhishek Shahu (Roll no.-13) Dr.A.D.Urade
Sangeet Khule (Roll no.-60) (Dept. of Mechanical Engg.)
Sannidhya Shegoankar (Roll no.-61) Course Code : MET 452-6
Mechanical 4th year
1

Content
2
● Introduction
● Components and machine structure ● Advantages and disadvantages
● Different types of equipments ● Applications
● Tooling specifications ● Advancement in DTM
● Tolerance and aspect ratios ● Machine characteristics
● Working principle ● Machine tool requirement
● Control systems and power requirement ● Bar graphs and tables
● Process parameters ● Conclusion
● Material to be machined ● References
● MRR and surface finish ● Animation video

Introduction
● Diamond turning is turning using a cutting tool with a diamond tip. It is also
known as single point diamond turning.
● It is a process of mechanical machining of precision elements using lathe or
derivative machine tools (e.g., turn-mills, rotary transfers) equipped with natural
or synthetic diamond-tipped tool bits.
● Diamond turning is an ultraprecision machining technology for the generation of
complex functional surfaces and extremely fine microstructures with the use of
geometrically defined diamond cutters. The cutters can be natural diamond or
synthetic diamond depending finishing scale of machining and finishing
requirements.
3
Fig : This axiconical mirror
was cut from 6061-T6
Aluminum with no subsequent
polishing.

Classification of Diamond Turn Machines
Classified based on their number of axes and their configurations.
● Type A: X, Z Lathe machines
● Type B: X, Z, C Lathe machines
● Type C: X, Z, C, B Lathe machines
● Type D: X, Y, Z, A, B Milling machines
5
Fig : Classification of DTM.

Classification of Diamond Turn Machines
● Type A machines are similar to conventional lathe machines wherein, both the X-axis,
which carries head stock with spindle, and the Z-axis carrying the tool can be
programmed for simultaneous movements and axisymmetric features can be generated.
With appropriate fixtures, off-axis parabolic surfaces can also be generated on this
machine.
● Type B machines have additional control on the spindle (C-axis) and this enables it to
generate non-axisymmetric features. When used along with attachments like fast tool
servo, multiple features like lenslet arrays can be generated on this type of machine.
● Type C machines are provided with control on the B-axis, which holds the cutting tool
and enables it to remain normal to the surface being machined. For spherical surface
machining, this type of machine is most preferred.
● Type D machines are similar to milling machines; however, these machines employ a
6

Two Basic Types of SPDT Machines
7
Fig : Lathe type
Fig : Fly cutter type
Lathe type:
● Workpiece rotates & diamond tool translates
● Axisymmetric surface
● Off-axis optics
Fly cutter type:
● Diamond tool rotates & work piece translates
● Flats
● Multi-faceted prisms

Components of Diamond Turn Machine
8
Fig : Diamond Turn Machine.

Functional Elements and Components
9

Working Principle
● At the core of each is the fundamental accuracy of the diamond turning machine,
which can position a tool with an uncertainty of better than 100 nanometers.
These basic approaches include traditional turning, off-axis turning, fly-cutting,
and free form machining.
● An ultra sharp diamond of extremely accurate nose radius is used to turn and face
the part. The CNC interpolation of the X and Z axis of the machine can produce
arbitrary rotationally symmetric parts. In principle it is just as easy to produce the
parabola of a reflecting telescope as it is to produce a basic cylindrical shape.
● Fly-cutting and milling reverses the position of work and tool. The tool is
mounted to the spindle and the work is mounted to the slide. This allows the
generation of flat or elliptical surfaces.
10

Working Principle
● DIAMOND as cutting tool in CNC turning and grinding machines.
● Ultra precision cutting tool required to be hard and sharp, superior thermal
properties, which are properties of diamond.
● Achieves tolerances upto 0.01 to 0.001 microns.
11
Fig : Finished job of DTM.

Tooling Specifications of DTM
● To give a perfect edge or shine to precious metals [gold, silver, or platinum] and
other metals [ brass, copper or aluminium] you need more ideal diamond cutting
tools [faceting tools]. These tools are used for faceting & designing non-ferrous
metals too.
● Diamond as Tool.
● Tool Radius = 0.2 to 0.4 mm.
12
Fig : Concave diamond tool.

Various Diamond Cutting Tools
13
Fig : Differents diamond tools with same internal angle. Fig : Schematic of the typical structure
of a single crystal diamond tool and
holder.

Internal structure of DTM tool
15
(a) Single crystal tool. (b) poly crystalline tool. Fig : Enlarge view of tool tip.

(a) Sintered diamond tool. (b) Diamond coated (WC) tool. (c) Titanium nitride interlayer tool.
16
Diamond Coated Tools

Tool Geometry
The most common cutting edge shape is triangular with the nose radius at one apex
of the triangle. Other edge shapes include:
● Flat rectangular shape used in grooving applications with customised groove
widths down to a few micrometres.
● Two straight cutting edges meeting at an obtuse angle – used for nano-milling.
● Single arc cutting edges – used for milling.
● Multiple discontinuous connected arcs – used for nano-milling applications.
● Elliptical arc shape.
17
Fig : Schematic showing (top view of the rake face, showing cutting edges)
various geometries in which diamond tools are available.

Nomenclature of tool
Besides the overall cutting edge profile, other geometrical parameters of interest are:
Top Rake Angle, Cylindrical/Conical Edge, Tool Nose Radius, Cutting Arc, Offset
Angle, Included Angle, Front Clearance, Second Clearance, Primary Depth, Diamond
Depth, Total Cutting Height and Tool Nose Waviness.
18
Fig : Microdrilling on soda lime glass (thickness - 0.13 mm, diameter = 0.1 mm,
rpm-30,000, cutting speed 9,42 m/min, feed 0.25 μm/rev)

Control Systems and
Power Requirement
19

Process Parameters
Spindle Speed
● Usually low.
● High speed causes more vibration and increases surface roughness.
Feed rate
● Affects surface quality significantly.
● Increases Feed force and tool wear.
Depth of cut
● Less effect on surface quality.
Coolant
● Most heat is carried away by microchips.
● Diamond tool also helps.
● Evaporative coolant is sprayed to remove adhered chips.
20

Process Parameters
Spindle Head
● Aerostatic bearing for smooth motion.
● Housing of epoxy granite reduces.
● Thermal and vibration effect.
● Brushless DC motor drive is used.
Tool Post
● Required to have sufficient stiffness.
● Should have micro height adjustment.
Slide Ways
● Hydrostatic bearings give smooth precise and repetitive motion.
● Linear motors are used for table drive.
● Linear motors with minimum moving parts provide smooth motion.
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Granite Bed
● Epoxy granite reduces thermal and vibrational deformation.
Tool Measurement(For Feedback purposes)
● Optical LVDT.
● Precise tool setting.
● Tool Shape monitoring.
Control Panel
● Precise positioning of tool and work.
● Uses linear encoders and laser interferometer feedback.
● Controls spindle speed, feed and direction of machining.
22
Process Parameters

Effect of Spindle Speed on Surface Finish
23
Fig : Effect of spindle speed on surface finish.

Effect of Feed on Various Output Parameters
24
Fig : Effect of feed on various output parameters.

Effect of Tool Shank Overhang on Surface
Finish
25
Fig : Effect of tool shank overhang on surface
finish.

Surface Finish
Final finish of a diamond-turned surface is affected by a variety of factors. Surface finish
is described as the presence of defects with length scales of below 0.8mm in the machined
surface.
● Workpiece Material : Compatibility of the material for the diamond turning process is
crucial to achieve clean cutting with reduced surface damage. Grain structure and the
presence of impurities in the material affect surface finish. Hence, selecting an
appropriate material is important to attain the desired surface finish.
● Diamond Tool : Diamond tools used in the turning process need to be sharp without
chips on the nanometer scale. It is necessary to optimize the tool rake angle and tool
radius for a given workpiece or material for a better surface finish. Proper tool lubrication
and provisions for chip removal also help achieving better finish.To avoid vibration in
the diamond tool and workpiece, the diamond needs to be rigidly attached to a stiff tool
shank.
26

Surface Finish
● Cutting Forces and Dynamic Forces :
○ A diamond turning machine is affected by a variety of dynamic
forces that are much higher than the cutting forces. The ability to
defy these dynamic forces determines the surface finish capability of
a diamond turning machine and is defined as dynamic stiffness.
● Environment and Peripheral Devices :
○ A diamond turning machine is affected by a variety of other dynamic
forces caused by the machine environment, such as machine
vibrations due to sound pressure and seismic forces.
○ These environmental influences can be isolated by employing
pneumatic vibration isolators and acoustic enclosures. However,
these measures are required only for machines having a low dynamic
stiffness.
27

Surface Finish
● Sensor Resolution :
○ A diamond turning machine slide is capable of only holding position as
well as sensing it. Hence, the noise level or resolution of the position
sensing system needs to be low.
○ Achieving a very fine resolution is possible with high levels of
interpolation between grating lines on a scale.
○ However, these interpolation techniques are erroneous, thus causing finish
problems different from those caused by electrical noise. In the case of
diamond turning, sensor resolution is smaller by several orders of
magnitude than the accuracy of the sensors over their entire range, or of the
rest of the machine. In diamond turning, the sensor noise/resolution has a
small effect on surface finish, as it is small.
28

Requirements of Diamond Turn Machines
The ultimate requirement of an ultra-precision machining process is to generate the
desired surface profile with deviation in the order of a few nanometres (nm) or less.
PM - Conventional precision machines.
29
Fig : Factors contributing to the inaccuracies on generated surfaces.

Accuracy of diamond turn machines depends on the following factors in a significant
way:
● Positional accuracy and repeatability of moving elements
● Vibration effects
● Thermal effects
● Balanced loop stiffness
30
Positional accuracy and repeatability of diamond turn machines are affected by
the following factors:
● Degree of freedom of moving elements
● Geometrical accuracy of the axis of moving element and its datum
● Friction between moving elements
● Scale, drive and feedback elements
The resulting vibration at the interface of tool and workpiece is due to
● Tool and tool tip vibration
● Spindle vibration
● Material-induced vibration
● External vibration

Balanced Loop Stiffness
Loop stiffness in a diamond turn machine indicates the equivalent stiffness values of
different machine elements during machining. Elements forming the loop stiffness in
Type A machines can be represented as follows:
31
Thermal Effects
Due to the heat generated by drivers, friction generated by the rotation of the spindle
and movement of the slides and cutting process, thermal drift takes place and it
causes differential expansion of various machine elements. Expansion due to
thermal drift causes many undesirable effects.
As the loop stiffness of the
machine is affected by the
individual stiffness and
damping values of different
machine elements, any
variations in them result in
generating vibration and
chattering on the machined
surface.

Characteristics and Capabilities of DTM
32

Technologies Involved in DTM Building
33

Environmental Requirements for DTM
Environmental conditions severely affect the accuracy, performance and life of the
machine. Diamond turn machines are very sensitive for the following environmental
conditions:
● Temperature and humidity
● Ground vibration
● Acoustic
● Dust
34
● Diamond turn machines are housed in a clean room with temperature and
humidity control as well as a dust-free environment. Temperature control in
the order of ±1°C and humidity control of ±5%.
● Work-pieces in general are thermally stabilised by keeping them in the same
environmental conditions before machining.
● Transmission of ground vibration to the diamond turn machine is minimised
by vibration isolators.
● Noise levels near the machine need to be controlled properly.

Case Study
Place of DTM in the Process Chain
Typical process chain for manufacturing optical components.
35

Figure
Surfaces dealing with infrared waves can be processed via DTM, while those dealing
with visible light require subsequent polishing and surface deflect X-ray beam require
several iterative rounds of polishing and measurement after DTM processing. 36

Fig : Schematic diagram of glass lens formation. (a) Molds and glass gob, (b) Heating, (c)
Heating and pressing, (d) Cooling and release.
37

Tolerance and Aspect Ratios with Examples
Radius of curvature
● Typical tolerance for radius of curvature:
±0.05%
● Relatively short radii : Limits of spherometer
● Accuracy: about 0.005%
● Long radii (> 2 m) : lower accuracy, error in the
order of 0.1 – 1.0%
38
Fig : Lens

Surface Figure Test
39
● Talysurf contacting profilometer
○ Scan the part
○ Measure the departure of the surface from theoretical
shape
● Interferometer
○ Overall performance
○ Null test
Aspect ratio
● Aspect ratio is the relationship of center thickness to
diameter.
● Ideal aspect ratios are less than 6:1 for precision.
● Aspect ratios greater than 10:1 will be more problematic and
therefore more costly

Materials Machinable by DTM
Diamond turn machining can be carried out on metals, polymers and crystals.
● Metals that can be diamond turn machined are as follows:
Copper, brass, aluminum alloys, electroless nickel, bronze, copper beryl
lium, tin, antimony, silver, gold, zinc, magnesium, lead and platinum.
● Polymers that can be diamond turn machined are as follows:
PMMA (Chemical & Scratch resistance), Polycarbonate (Impact strength/temperature
resistance), Polystyrene (Low cost/highly transparent), PolyEtherimide (High
Thermal/chemical/Impact resistance/high index) etc.
40

Materials Machinable by DTM
● Crystals that can be diamond turn machined are as follows:
Barium Fluoride (BaF2), Cadmium Telluride (CdTe), Cesium Bromide(CsBr), Cesium
Iodide (CsI), Chalcogenide Glass, Gallium Arsenide(GaAs), Germanium (Ge), Lithium
Fluoride (LiF), Magnesium Fluoride (MgF2), Potassium Bromide (KBr), Potassium
Chloride(KCl), Silicon (Si), Sodium Chloride (NaCl), Thallium Bromoiodide(KRS-5),
Zinc Selenide (ZnSe), Zinc Sulfide.
41

Material removal rate (MRR)
● DTM is a near perfect marriage of ultra-precision vibration-free equipment, stiff
tool holder and a well-chosen fixture, a diamond tool of prescribed geometry and
orientation, to initiate and maintain a calibrated material removal rate with
minimal cutting forces.
● Typical material removal rate (MRR) for the turning process is expressed by the
following equation:
● MRR =d* f* v mm3 /min
● where d = depth of cut in mm; f = feed in mm/revolution; v = cutting velocity in
mm/min.In this type of process, prediction of precise material removal rate is
difficult and varies in a nonlinear fashion. MRR is higher in the DTM. It also
depends on DOC , Spindle speed and surfaced finished required.
42

Ductile Regime Machining of Brittle Materials
● The mechanism of material removal is identified by the occurrence of radial,
lateral cracking, chipping, and pileup formation on the surface level.
● The ductile regime machining of brittle materials produces the material removal
in the plastic deformation zone when the applied stress is below the critical stress
of the material, which is insufficient to cause the macrocrack formation.
● When the depth is below the critical depth of cut, it leads to a ductile regime of
machining, where the material removal takes place by plastic deformation. On the
other hand, when the depth of cut exceeds the critical depth, it removes the
material by brittle fracture.
43

Material Removal Process in Machining of
Brittle Materials
44
Fig : Material Removal Process in Machining of Brittle
Materials.

Brittle Material Machining
Formation of discontinuous chips in brittle material processing.
45
Fig : Formation of discontinuous chips in brittle material processing.

Materials having a Fine Grain Structure
● When the single grit comes in contact with the fine-grained material, it leads to
the plastic deformation based on the shape of the diamond grit and the shear
stress level of the material.
● While the applied stress exceeds the critical stress of the material, the lateral
cracks are formed parallel to the scratch direction. This is associated with the easy
material removal during the scratch test.
46

Materials having a Fine Grain Structure
Fig : Different Crack System and Plastic Deformation in the Fine-Grained Structure.
47

Materials having a Coarse Grain Structure
● The material removal observed in the coarse structure takes place in a dissimilar
way,where the single grit with sharp edges plastically split the grains and the
cracks are formed along the grain boundary.
● This leads to the break-off or chipping near the edges of the scratch. The grit with
blunt edges forms a plastically deformed zone at a higher scratch depth due to the
increase in shear stress.
48

Materials having a Coarse Grain Structure
Fig : Slight plastic deformation and break off in coarse grained structure.
49

Factors Affecting Ductile Material Removal
50

51
Advantages
● Toughness : Absorbs shock load,
reduces chipping and breakage.
● High Hot Hardness : sustain at
high temperature, lower tool
wear.
● High Thermal Conductivity.
● Crystalline Structure :Sharp
Edges.
● High Elastic and Shear Moduli :
limits deformation.
● Can withstand specific shear
energy of 100-1000 J/cc.
● Easy to program
● High degree of precisions in
Disadvantages
● Reacts with iron group elements :
poor toughness, low thermal
stability.
● Wears during nickel based alloy
machining.
● Can convert to graphite above 700
celcius .
● Expensive.
● Small size tool manufacturing is
comparatively difficult.
● The size of the work piece is
limited by the size of the SPDT
machine

Applications
● Microgrooves (2.5 micron wide and 1.6 micron deep on grating lens).
● Molds of lens manufacturing.
● Medical instrumentations (mostly glass).
● Reflecting optic instruments.
○ e.g. spherical lenses and mirrors for space applications, hybrid lenses for thermal
imaging or night vision.
● Complex profiles on aluminium alloys.
● Machining of substrates drums of photocopying machine.
52

Applications
● Diamond turning is used primarily to manufacture ultra precision parts for
advanced applications, those that call for extremely high levels of form accuracy
and surface ﬁnishing.
● There are various applications that can be found in a number of industry sectors,
including aerospace, defense, electronics, semiconductor, and biomedical.
● In the early days, a large fraction of the parts produced with diamond turning
were optical components like reﬂectors and lenses, mostly machined directly
from the stock material.
● Diamond turning is becoming more important in biomedical applications,
particularly in the mass production of contact lens.
● Diamond turning is also used to produce high-precision roller molds for large-
area printing, a process where additive materials are printed on engineering
substrates as microstructures.
53

Applications
Fig : Complex geometries with demanding surface smoothness needed in a variety of applications
from space and defence to medical. 54

Applications
55
Fig : A lens mold and the injection-molded
camera lenses for mobile phones.
Fig : A contact lens fabricated
by diamond turning.

Examples
● For example, brightness-enhancing films of are light crystal displays (LCDs) are
manufactured through large-area printing with the key ultraprecision roller molds
produced by diamond turning is gradually replacing conventional grinding and
polishing,as it is capable of producing highly accurate profiles and superior
surface finishing faster than traditional methods, and fabricating optical
components with special profiles and features like diffractive and hybrid systems.
56

Diamond Turning of Parabolic Mirrors
57
Fig : Diamond Turning of Parabolic Mirrors.

Advancement in DTM
Fig : Recent ongoing research on DTM for advancement in this field or domain.
58

DTM Process Monitoring
● The DTM group in Hong Kong Polytechnic (led by W. B. Lee) has reported
attempts in developing techniques to monitor surface roughness during the DTM
cutting process.Their goal is to effectively correlate force signals to suitable
surface profile signals.
59
Fig : Surface roughness profile along the cutting velocity path (spiral path)
shows better correlation to force and vibration signals.

Developments Related to Machine Tools
Fig : Structure of swing arm DTM machine.
60
Fig :Unique two-sided parallel machining to
reduce DTM process times.

Machine Characteristics
● The machine tool is an essential element of diamond turning. It commands the
highest levels of accuracy and repeatability that a mechanical system and
software can deliver –in short, an ultraprecision machine.
● The frame and structure of ultraprecision machine tools, as well as the
translational and rotational axes, are stiffened to minimize instability from the
surrounding environment.
● Sharp changes in humidity and atmospheric pressure will also affect the accuracy
of machining. To reduce the impact of this aspect, independent hydrostatic or
aerostatic bearing slides are incorporated to the linear axes to enhance the
dynamic stiffness and damping properties.
● A low-ﬂow and low-pressure hydrostatic oil bearing with closed-loop servo
control is preferred as it improves the stiffness of the machining axes while
simultaneously reducing external vibration.
61

Machine Tool Requirements
A qualiﬁed machine tool for diamond turning should possess the following merits:
● Vibration isolation and constant temperature control.
● High stiffness in both axial and radial directions for all axes.
● High sliding accuracy and assembly accuracy.
● High positioning and repositioning accuracy.
● High feedback and programming resolution.
● Sufficient spindle power for high-speed cutting.
● High servo performance.
● High-precision tool and workpiece setup.
● Complete process-monitoring system. 62
● Isolation from surrounding.
● Environment should be
controlled(Constant).

Current and Future Trends in DTM
Large Optics Diamond Turning Machine :
● LODTM was capable of producing an extremely high-precision workpiece that
weighed 1360 kg with a diameter and length of 1650 and 500 mm, respectively.
● The tolerance could be maintained below 28 nm, approximately a thousand times
more accurate than conventional machine tools.
● LODTM is still in operation to this day, but many customized components that
were designed 30 years ago have been replaced with the standard ones to
facilitate its maintenance.
63

LODTM
64
Fig : Large Optics Diamond Turning Machine.

Graphs of Plane representing the Flank Wear
● It is due to work hardening.
● Flank wear occurs at the tool flanks, where it contacts with the finished surface,
as a result of abrasion and adhesion wear.
● The cutting force increases with flank wear. It affects the great extent of
mechanics of cutting.
65
Fig : Type of tool wear.

Graphs taken from Research Papers
66
Fig : Variation of flank wear with respect to
cutting distance.
Fig : (a) and (b) Measurement of cutting edge radius of fresh and
worn tool, respectively. by AFM. (c) Variation of cutting edge
radius with flank wear.

Conclusion
● After doing this research and study about this topic of DTM we are able to
understand different terms which are related to micro machining and we were
able to demonstrate all the required process which are taking place inside the
machines and some specifications of diamond turn machining.
● There are numerous opportunities for the advancement of machinery which are
related to micro fabrication/ machining. so this presentation will give us the
knowledge about the researches that we can explore and get some patents over it
because there will be disruption in the upcoming years corresponding to this type
of machining process in an industries 4.0.
67

References
Research papers:
1. A. Sharma, D. Datta, and R. Balasubramaniam, Journal of Micromanufacturing,
Published by journals.sagepub.com/home/jmf, TItle-Prediction of tool wear
constants for diamond turn machining of CuBe,2020.
2. Prasad, P.K. Brahmankar, R.Balasubramanian, Department of mechanical
engineering, Published by science direct in international conference on advances
in manufacturing and material engineering in 2014.
3. Xianqian J. Jiang,Duo Li, in hybrid machining, Title-Diamond Turning Machine,
published by science direct,2018.
68

References
Books :
1. Diamond turn machining theory and practices by R. Balasubramaniam,
ramagopal V. sarepaka,sathyan subbiah, published by CRC press New york.
2. Nanofinishing Science and Technology: Basic and Advanced Finishing and
Polishing Processes, by Vijay Kumar Jain, published by CRC press New york.
3. Significance of Diamond as a Cutting Tool in Ultra-Precision Machining Process-
By P. Suya Prem Anand,Submitted: March 11th 2019 Reviewed: May 15th 2019
Published: September 27th 2019.
4. Optical System Design by Robert E. Fischer and Biljana Tadic-Galeb, published
by SPIE Press and McGraw-Hill. It is titled ‘Optical Design Considerations for
Optics Fabrication.’
69

References
Websites :
● https://youtu.be/TJyxltsFKUo
● https://youtu.be/L2VWC6au5Dg
● https://books.google.com/books?hl=pl&lr=&id=JYlJbKw_azEC&oi=fnd&pg=PP
1&ots=EyM9KyrESR&sig=ke5EoRekL0uUw1pADZRr4SextNY#v=onepage&q
&f=false
● https://www.mecholic.com/2016/02/types-of-tool-wear-flank-crater-and-corner-
wear.html
● https://www.azom.com/article.aspx?ArticleID=11462
● https://wp.optics.arizona.edu/optomech/wp-
content/uploads/sites/53/2016/10/ZhouPresentation.ppt
● https://www.cncwmt.com/latest-news/what-is-the-working-principle-of-a-cnc-
and-types-of-cnc-
controllers/#:~:text=The%20principles%20of%20CNC%20operation,%2C%20de
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