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. Diamond turn machining is a well-established and affordable process for the fabrication of highly accurate optical components as well as mechanical components requiring micro inch dimensional tolerances. 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.

1. DIAMOND TURNING FOR
OPTICALAPPLICATIONS
PRESENTED BY
RAHUL R
S2 MTECH
CIM
ROLL NO : 9

2. Introduction
 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.
 Diamond turn machining is a well-established and affordable process for the
fabrication of highly accurate optical components as well as mechanical
components requiring micro inch dimensional tolerances.
 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.
2

3.  Applications 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.
 As the technology becomes more mature diamond turning was applied to
manufacture mold inserts for the mass production of high-quality plastic
lenses with injection molding.
 The process of diamond turning is widely used to manufacture high-
quality aspheric optical elements from crystals, metals, acrylic, and other
materials.
 Optical elements produced by the means of diamond turning are used in
optical assemblies in telescopes, video projectors, missile guidance
systems, lasers, scientific research instruments, and numerous other
systems and devices.
3

4. Diamond Turning Vs Traditional Optical
Fabrication
 In diamond turning , the final shape and surface of the optical produced
depends on the machine tool accuracy , whereas , in traditional optical
fabrication , the final shape and surface of the optical element are produced
by lapping and polishing with an abrasive loaded lap .
 The differences between diamond turning and traditional optical fabrication
can be summarized by describing diamond turning as a displacement -
controlled process versus a force - controlled process for traditional optical
fabrication .
 The goal in diamond turning is to have a machine tool that produces an
extremely accurate path with the diamond tool , hence a displacement-
controlled machine .
4

5.  A traditional polishing machine used for optical fabrication depends on the
force being constant over the area where the abrasive-loaded lap or tool
touches the surface being worked .
 The stiffness of a diamond-turning machine is important because , to control
the displacement , it is important that cutting forces and other influences do
not cause unwanted displacements .
 Feeds, speeds and depth of cut are typically much lower in diamond turning
than conventional machining , thus giving lower forces .
5

6. Components of DT Machine
6
Fig.1 : Components of diamond turning machine

7. Basic Types of SPDT Machines
 Lathe Type
 Work piece rotates and diamond tool translates
 Axisymmetric surface
 Off axis optics
7
Fig.2 : Lathe type SPDT machine

8.  Fly cutter type
 Diamond tool rotates and workpiece translates
 Flats
 Multi faceted prisms
8
Fig.3 : Fly cutter type SPDT machine

9. Materials
 Generally, diamond turning is restricted to certain materials. Some of the
materials that are readily machinable include:
9

10.  The most often materials that are not readily machinable are:
 Ferrous materials (steel, iron)
 Beryllium
 Titanium
 Molybdenum
 Nickel
 Ferrous materials are not readily machinable because the carbon in the
diamond tool chemically reacts with the substrate, leading to tool damage and
dulling after short cut lengths.
 Several techniques have been investigated to prevent this reaction, but few
have been successful for long diamond machining processes at mass
production scales
 Tool life improvement has been under consideration in diamond turning as the
tool is expensive. Hybrid processes such as laser-assisted machining have
emerged
10

11. 11
Fig.4 : Diamond turning of an acrylic dome
Fig.5 : Aluminum Mirror

12. 12
Fig.7 : A lens mold and the injection-molded camera
lenses for mobile phones
Fig.6 : A contact lens fabricated by diamond
turning.

13. Diamond Turning RSA905 Optical Aluminium
 Ultra-high precision machining is used intensively in the photonics industry for
the production of parts for optical devices and high accuracy measuring systems.
 Single point diamond turning (SPDT) is an ultra-high precision machining
technique that employs diamond as the cutting tool for turning optical
engineering materials.
 Diamond tools have the ability to retain their cutting edge for virtually most of
their useful life and are capable of machining up to 100 times the number of
parts than conventional high-speed steels or carbide tools.
 Aluminium alloys are commonly used in this industry as they cause less tool
wear and are relatively cheaper in comparison to other optical metallic alloys.
13

14.  Newly modified grades of aluminium alloys have recently become sought after
by the industry. The newer grades are produced by rapid solidification in the
foundry process and are characterized by their finer microstructures and
refined mechanical and physical properties.
 Traditional aluminium alloys, such as AA 6061, are produced through
conventional foundry processes that involve slow solidification resulting in a
coarse microstructure and relatively large grain sizes.
 Diamond turning of AA 6061 results in surface roughness values of
approximately 5-8 nm.
 RSA 905 is produced by melt spinning that rapidly cools the molten alloy at a
rate of up to 106 K/s, resulting in ultra-fine microstructure and enhanced
physical and mechanical properties.
 Therefore, RSA 905 exhibits better mechanical and physical properties
compared to traditional optical aluminium alloys.
14

15.  Here we investigates the surface roughness achievable by diamond turning of
rapidly solidified aluminium RSA 905 over a range of different diamond
cutting parameters.
 The RSA grade selected in this study is a modified version equivalent in terms
of composition to the traditional optical aluminium AA 6061 which is a
common optical material.
15

16. Experimental Setup
 The diamond machining tests were carried out on a Precitech Nanoform 250
Ultra grind machining centre, a high performance four axis ultra-high precision
machine designed for turning and grinding applications.
 Diamond turning was carried out on flat 60-mm diameter RSA 905 workpieces
produced by RSP Technology.
 The workpiece was fitted in an adapter designed for easy
attachment/detachment and centering on the machine’s vacuum spindle. A new
diamond insert was used for each experiment.
 Odourless kerosene mist was used as a coolant and lubricant in the
experimentation.
16

17. 17
Fig.8 : Experimental setup

18.  The cutting parameters varied were the cutting speed, feed rate and depth of
cut.
 The feed rate was varied between 5 and 25 mm/min, the cutting speed between
500 and 3000 rpm while depth of cut between 5 and 25 μm.
 The workpiece was machined a distance of approximately 4 km for each
experiment and the surface roughness (Ra) was measured at various intervals.
 The surface roughness was measured on a high precision profilometer, Form
Talysurf PGI Optics 3D by Taylor Hobson.
 The machined workpiece was placed on the high precision air-bearing spindle
on the profilometer table and an automated probe dragged along the surface to
sense roughness measurements.
18

19. 19
Fig.9 : Surface roughness measurement setup

20. Results and Discussions
 Table 1 shows the average surface roughness results of each experiment at various
distances.
 The results as shown in Table 1 had a common trend of decrease in surface
roughness with increasing cutting distance.
 The results generally indicate the high surface quality that could be produced on
RSA 905 aluminium. This could be mainly attributed to the ultra-fine
microstructure of RSA 905.
 Changes in feed rate suggested that lower feed rates produced finer surfaces.
20

21. 21 Table 1. Surface roughness results

22.  Experiment 1 with cutting speed of 1750 rpm and 25 μm depth of cut, resulted in
7 nm roughness for 25 mm/min feed rate and 3.2 nm roughness for 5mm/min
feed rate after 4 km.
 Experiment 2 with 1750-rpm cutting speed and depth of cut 5 μm, had Ra 6.6 nm
at 25 mm/min feed rate and Ra 3.3 nm at 5 mm/min feed rate after 4 km.
 Experiment 3 and experiment 4 also produced finer surfaces at the lower feed
rates after 4 km of cutting.
 Higher feed rates meant slower and more effective material removal as the
diamond tool cut through the workpiece radius in its entirety with each pass. As a
result this contributed to improved surface quality.
 Lower feed rates when face turning would cause the tool to follow a less spiral
path creating a surface made up of multiple evenly distributed grooves and thus
reducing the average surface roughness.
22

23.  Figure below charts the feed rate against surface roughness for the various
experiments.
23
Fig.10 : Surface roughness vs feed rate

24.  When cross-observing the experiments, the combination of lower cutting speeds
and high feed rates showed drastic differences in roughness. This can be seen by
the steepest slope in chart.
 Experiment 4 at 500 rpm cutting speed and 25 mm/min feed rate produced the
highest surface roughness measurement (Ra 31.2 nm) while reducing the feed
rate down to 5 mm/min returned the surface roughness back down to the 4 nm
range. This showed that cutting speed had a significant effect on surface
roughness.
 When a high cutting speed was maintained (3000 rpm in experiment 3) the
surface roughness was considerably maintained at a very low value of
approximately 4 nm, regardless of feed rate changes. This can be seen as the
almost flat slope in chart.
24

25.  When comparing experiment 1 and experiment 2, it can be seen that changes in
depth of cut has a minimal effect on the resulting surface roughness. This can be
clearly seen by the slopes in chart which are almost identical.
 The surface profile charts show that high Ra value produced a more periodic
profile with higher amplitudes than the lower Ra value.
 Higher surface roughness values were generally associated with a higher
number of amplitude peaks of higher magnitude that were more closely packed.
 Lower surface roughness values had profiles with a lower number of amplitude
peaks of lower magnitude and a wider spread.
25

26. 26
Fig.11 : Surface profile chart for lowest roughness Ra 3.2 nm at v = 1750 rpm, f = 5 mm/min and d
=25 μm

27. 27
Fig.12 : Surface profile chart for highest roughness Ra 31.2 nm at v = 500 rpm, f = 25 mm/min and d
=15 μm

28. Conclusion
 Single point diamond turning of RSA 905 generally produced an average
surface roughness of Ra 3-5 nm within 4 km of cutting distance.
 Experimental results revealed that low feed rates produced better surface
quality, and this, combined with high cutting speeds produced the best
results.
 The high surface quality achieved was associated with smaller amplitude,
widely spread peaks along the surface profile.
 The optical surface quality achieved was mainly attributed to the ultra-fine
microstructure of RSA 905.
28

29. References
1. Otieno, T., and K. Abou-El-Hossein. “Surface Roughness Analysis When Diamond
Turning Optical Grade Rapidly Solidified Aluminium RSA 905.” Journal of Optics,
no. 4, Springer Science and Business Media LLC, June 2017, pp. 446–55. Crossref,
doi:10.1007/s12596-017-0405-2.
2. Taniguchi, Norio. “Current Status in, and Future Trends of, Ultraprecision
Machining and Ultrafine Materials Processing.” CIRP Annals, no. 2, Elsevier BV,
1983, pp. 573–82. Crossref, doi:10.1016/s0007-8506(07)60185-1.
3. Tang, Longlong, et al. “Research on Single Point Diamond Turning of Chalcogenide
Glass Aspheric Lens.” Procedia CIRP, Elsevier BV, 2018, pp. 293–98. Crossref,
doi:10.1016/j.procir.2018.05.023.
29