conventional and unconventional contact lens manufacturing systems

8/10/2019 Conventional and Unconventional Contact Lens Manufacturing Systems

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Conventional and Unconventional ContactLens Manufacturing Systems

By Mocan Tudor Cristian

Industrial Design, 2ndyear


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A lens is a transmissiveoptical device which affects the focusing of alight

beam throughrefraction.Asimple lens consists of a single piece of material, while

acompound lens consists of several simple lenses (elements), usually along a

common axis. Lenses are made fromtransparent materials such asglass,ground

and polished to a desired shape. A lens can be used to focus light to form animage,unlike aprism which refracts light without focusing. Devices which

similarly refract radiation other than visible light are also called lenses, such as

microwave lenses or acoustic lenses.

The word lens comes from the Latin name of thelentil,because a double-

convex lens is lentil-shaped. The genus of the lentil plant isLens,and the most

commonly eaten species is Lens culinaris. The lentil plant also gives its name to a

geometric figure.

The oldest lens artifact is theNimrud lens,dating back 2700 years to

ancientAssyria.Another early reference tomagnification dates back toancient

Egyptianhieroglyphs in the 8th century BC, which depict "simple glass meniscallenses".

The earliest written records of lenses date toAncient Greece,with

Aristophanes'playThe Clouds (424 BC) mentioning a burning-glass (abiconvex

lens used tofocus thesun's rays to produce fire). Some scholars argue that the

archeological evidence indicates that there was widespread use of lenses in
http://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Light_beamhttp://en.wikipedia.org/wiki/Light_beamhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Simple_lenshttp://en.wikipedia.org/wiki/Lens_%28optics%29#Compound_lenseshttp://en.wikipedia.org/wiki/Transparency_%28optics%29http://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/Prismhttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Lentilhttp://en.wikipedia.org/wiki/Lens_%28genus%29http://en.wikipedia.org/wiki/Lens_%28geometry%29http://en.wikipedia.org/wiki/Nimrud_lenshttp://en.wikipedia.org/wiki/Assyriahttp://en.wikipedia.org/wiki/Magnificationhttp://en.wikipedia.org/wiki/Ancient_Egypthttp://en.wikipedia.org/wiki/Ancient_Egypthttp://en.wikipedia.org/wiki/Egyptian_hieroglyphshttp://en.wikipedia.org/wiki/History_of_Ancient_Greecehttp://en.wikipedia.org/wiki/Aristophaneshttp://en.wikipedia.org/wiki/The_Cloudshttp://en.wikipedia.org/wiki/Lens_%28optics%29#Types_of_simple_lenseshttp://en.wikipedia.org/wiki/Lens_%28optics%29#Types_of_simple_lenseshttp://en.wikipedia.org/wiki/Focus_%28optics%29http://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Focus_%28optics%29http://en.wikipedia.org/wiki/Lens_%28optics%29#Types_of_simple_lenseshttp://en.wikipedia.org/wiki/Lens_%28optics%29#Types_of_simple_lenseshttp://en.wikipedia.org/wiki/The_Cloudshttp://en.wikipedia.org/wiki/Aristophaneshttp://en.wikipedia.org/wiki/History_of_Ancient_Greecehttp://en.wikipedia.org/wiki/Egyptian_hieroglyphshttp://en.wikipedia.org/wiki/Ancient_Egypthttp://en.wikipedia.org/wiki/Ancient_Egypthttp://en.wikipedia.org/wiki/Magnificationhttp://en.wikipedia.org/wiki/Assyriahttp://en.wikipedia.org/wiki/Nimrud_lenshttp://en.wikipedia.org/wiki/Lens_%28geometry%29http://en.wikipedia.org/wiki/Lens_%28genus%29http://en.wikipedia.org/wiki/Lentilhttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Prismhttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Transparency_%28optics%29http://en.wikipedia.org/wiki/Lens_%28optics%29#Compound_lenseshttp://en.wikipedia.org/wiki/Simple_lenshttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Light_beamhttp://en.wikipedia.org/wiki/Light_beamhttp://en.wikipedia.org/wiki/Optics


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antiquity, spanning several millennia. Such lenses were used by artisans for fine

work, and for authenticatingseal impressions. The writings ofPliny the Elder (23

79) show that burning-glasses were known to theRoman Empire,and mentions

what is arguably the earliest written reference to acorrective lens:Nero was said

to watch thegladiatorial games using anemerald (presumablyconcave to correctfornearsightedness,though the reference is vague). Both Pliny andSeneca the

Younger (3 BC65) described the magnifying effect of a glass globe filled with

water.

Excavations at theViking harbor town ofFrjel,Gotland,Sweden

discovered in 1999 the rock crystalVisby lenses,produced by turning onpole

lathes at Frjel in the 11th to 12th century, with an imaging quality comparable to

that of 1950saspheric lenses.The Viking lenses were capable of concentrating

enough sunlight to ignite fires.

Lenses came into widespread use in Europe with the invention of

spectacles,probably inItaly in the 1280s. This was the start of the optical industry

of grinding and polishing lenses for spectacles, first in Venice and Florence in the

thirteenth century, and later in the spectacle-making centers in both the

Netherlands and Germany. Spectacle makers created improved types of lenses for

the correction of vision based more on empirical knowledge gained from

observing the effects of the lenses (probably without the knowledge of the

rudimentary optical theory of the day). The practical development and

experimentation with lenses led to the invention of the compoundoptical

microscope around 1595, and therefracting telescope in 1608, both of which

appeared in the spectacle-making centers in theNetherlands.

With the invention of the telescope and microscope there was a great deal of

experimentation with lens shapes in the 17th and early 18th centuries trying to

correct chromatic errors seen in lenses. Opticians tried to construct lenses of

varying forms of curvature, wrongly assuming errors arose from defects in the

spherical figure of their surfaces. Optical theory onrefraction and

experimentation was showing no single-element lens could bring all colors to a

focus. This led to the invention of the compoundachromatic lens byChester

Moore Hall inEngland in 1733, an invention also claimed by fellow Englishman

John Dollond in a 1758 patent.
http://en.wikipedia.org/wiki/Seal_%28emblem%29http://en.wikipedia.org/wiki/Pliny_the_Elderhttp://en.wikipedia.org/wiki/Roman_Empirehttp://en.wikipedia.org/wiki/Corrective_lenshttp://en.wikipedia.org/wiki/Nerohttp://en.wikipedia.org/wiki/Gladiatorhttp://en.wikipedia.org/wiki/Emeraldhttp://en.wiktionary.org/wiki/concavehttp://en.wikipedia.org/wiki/Myopiahttp://en.wikipedia.org/wiki/Seneca_the_Youngerhttp://en.wikipedia.org/wiki/Seneca_the_Youngerhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Vikinghttp://en.wikipedia.org/wiki/Fr%C3%B6jelhttp://en.wikipedia.org/wiki/Gotlandhttp://en.wikipedia.org/wiki/Swedenhttp://en.wikipedia.org/wiki/Visby_lenseshttp://en.wikipedia.org/wiki/Pole_lathehttp://en.wikipedia.org/wiki/Pole_lathehttp://en.wikipedia.org/wiki/Aspheric_lenshttp://en.wikipedia.org/wiki/Spectacleshttp://en.wikipedia.org/wiki/Italyhttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Optical_microscopehttp://en.wikipedia.org/wiki/Optical_microscopehttp://en.wikipedia.org/wiki/Refracting_telescopehttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Achromatic_lenshttp://en.wikipedia.org/wiki/Chester_Moore_Hallhttp://en.wikipedia.org/wiki/Chester_Moore_Hallhttp://en.wikipedia.org/wiki/Englandhttp://en.wikipedia.org/wiki/John_Dollondhttp://en.wikipedia.org/wiki/John_Dollondhttp://en.wikipedia.org/wiki/Englandhttp://en.wikipedia.org/wiki/Chester_Moore_Hallhttp://en.wikipedia.org/wiki/Chester_Moore_Hallhttp://en.wikipedia.org/wiki/Achromatic_lenshttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Refracting_telescopehttp://en.wikipedia.org/wiki/Optical_microscopehttp://en.wikipedia.org/wiki/Optical_microscopehttp://en.wikipedia.org/wiki/Netherlandshttp://en.wikipedia.org/wiki/Italyhttp://en.wikipedia.org/wiki/Spectacleshttp://en.wikipedia.org/wiki/Aspheric_lenshttp://en.wikipedia.org/wiki/Pole_lathehttp://en.wikipedia.org/wiki/Pole_lathehttp://en.wikipedia.org/wiki/Visby_lenseshttp://en.wikipedia.org/wiki/Swedenhttp://en.wikipedia.org/wiki/Gotlandhttp://en.wikipedia.org/wiki/Fr%C3%B6jelhttp://en.wikipedia.org/wiki/Vikinghttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Seneca_the_Youngerhttp://en.wikipedia.org/wiki/Seneca_the_Youngerhttp://en.wikipedia.org/wiki/Myopiahttp://en.wiktionary.org/wiki/concavehttp://en.wikipedia.org/wiki/Emeraldhttp://en.wikipedia.org/wiki/Gladiatorhttp://en.wikipedia.org/wiki/Nerohttp://en.wikipedia.org/wiki/Corrective_lenshttp://en.wikipedia.org/wiki/Roman_Empirehttp://en.wikipedia.org/wiki/Pliny_the_Elderhttp://en.wikipedia.org/wiki/Seal_%28emblem%29


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CONSTRUCTION OF SIMPLE LENSES

Most lenses are spherical lenses: their two surfaces are parts of thesurfaces of spheres. Each surface can beconvex (bulging outwards from the lens),

concave (depressed into the lens), or planar (flat). The line joining the centers of

the spheres making up the lens surfaces is called the axis of the lens. Typically the

lens axis passes through the physical center of the lens, because of the way they

are manufactured. Lenses may be cut or ground after manufacturing to give them

a different shape or size. The lens axis may then not pass through the physical

center of the lens.

Toric or sphero-cylindrical lenses have surfaces with two different radii of

curvature in two orthogonal planes. They have a differentfocal power in different

meridians. This forms anastigmatic lens. An example is eyeglass lenses that are

used to correctastigmatism in someone's eye.

More complex areaspheric lenses.These are lenses where one or both

surfaces have a shape that is neither spherical nor cylindrical. The more

complicated shapes allow such lenses to form images with lessaberration than

standard simple lenses, but they are more difficult and expensive to produce.
http://en.wiktionary.org/wiki/convexhttp://en.wiktionary.org/wiki/concavehttp://en.wikipedia.org/wiki/Toric_lenshttp://en.wikipedia.org/wiki/Focal_powerhttp://en.wikipedia.org/wiki/Astigmatismhttp://en.wikipedia.org/wiki/Astigmatism_%28eye%29http://en.wikipedia.org/wiki/Aspheric_lenshttp://en.wikipedia.org/wiki/Optical_aberrationhttp://en.wikipedia.org/wiki/Optical_aberrationhttp://en.wikipedia.org/wiki/Aspheric_lenshttp://en.wikipedia.org/wiki/Astigmatism_%28eye%29http://en.wikipedia.org/wiki/Astigmatismhttp://en.wikipedia.org/wiki/Focal_powerhttp://en.wikipedia.org/wiki/Toric_lenshttp://en.wiktionary.org/wiki/concavehttp://en.wiktionary.org/wiki/convex


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Types of simple lenses

Lenses are classified by the curvature of the two optical surfaces. A lens is

biconvex (or double convex, or just convex) if both surfaces areconvex.If bothsurfaces have the same radius of curvature, the lens is equiconvex. A lens with

twoconcave surfaces is biconcave (or just concave). If one of the surfaces is flat,

the lens is plano-convex or plano-concave depending on the curvature of the

other surface. A lens with one convex and one concave side is convex-concave or

meniscus. It is this type of lens that is most commonly used incorrective lenses.

If the lens is biconvex or plano-convex, acollimated beam of light passing

through the lens will be converged (or focused) to a spot behind the lens. In this

case, the lens is called a positive or converging lens. The distance from the lens to

the spot is thefocal length of the lens, which is commonly abbreviated f in

diagrams and equations.
http://en.wiktionary.org/wiki/convexhttp://en.wiktionary.org/wiki/concavehttp://en.wikipedia.org/wiki/Corrective_lenses#Lens_shapehttp://en.wikipedia.org/wiki/Collimated_lighthttp://en.wikipedia.org/wiki/Focal_lengthhttp://en.wikipedia.org/wiki/File:Large_convex_lens.jpghttp://en.wikipedia.org/wiki/File:Lens1.svghttp://en.wikipedia.org/wiki/File:Lenses_en.svghttp://en.wikipedia.org/wiki/Focal_lengthhttp://en.wikipedia.org/wiki/Collimated_lighthttp://en.wikipedia.org/wiki/Corrective_lenses#Lens_shapehttp://en.wiktionary.org/wiki/concavehttp://en.wiktionary.org/wiki/convex


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If the lens is biconcave or plano-concave, a collimated beam of light passing

through the lens is diverged (spread); the lens is thus called a negative ordiverging lens. The beam after passing through the lens appears to be emanating

from a particular point on the axis in front of the lens; the distance from this point

to the lens is also known as the focal length, although it is negative with respect

to the focal length of a converging lens.

Convex-concave (meniscus) lenses can be either positive or negative, depending

on the relative curvatures of the two surfaces. A negative meniscus lens has a

steeper concave surface and will be thinner at the centre than at the periphery.

Conversely, a positive meniscus lens has a steeper convex surface and will be

thicker at the centre than at the periphery. An idealthin lens with two surfaces of

equal curvature would have zerooptical power,meaning that it would neither

converge nor diverge light. All real lenses have nonzero thickness, however, which

causes a real lens with identical curved surfaces to be slightly positive. To obtain

exactly zero optical power, a meniscus lens must have slightly unequal curvaturesto account for the effect of the lens' thickness.
http://en.wikipedia.org/wiki/Thin_lenshttp://en.wikipedia.org/wiki/Optical_powerhttp://en.wikipedia.org/wiki/File:Concave_lens.jpghttp://en.wikipedia.org/wiki/File:Lens1b.svghttp://en.wikipedia.org/wiki/Optical_powerhttp://en.wikipedia.org/wiki/Thin_lens


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CONTACT LENSES

A contact lens, or simply

contact, is a thin lens placed directly

on the surface of the eye. Contactlenses are considered medical

devices and can be worn to correct

vision, or for cosmetic or therapeutic

reasons. In 2004, it was estimated

that 125 million people (2%) use

contact lenses worldwide, including

28 to 38 million in the United States. In 2010, worldwide contact lens market was

estimated at $6.1 billion, while the U.S. soft lens market is estimated at $2.1

billion. Some have estimated that the global market will reach $11.7 billion by

2015. As of 2010, the average age of contact lens wearers globally was 31 years

old and two thirds of wearers were female.

People choose to wear contact lenses for many reasons. Aesthetics and

cosmetics are often motivating factors for people who would like to avoid

wearing glasses or would like to change the appearance of their eyes. Other

people wear contacts for functional or optical reasons. When compared withspectacles, contact lenses typically provide better peripheral vision, and do not

collect moisture such as rain, snow, condensation, or sweat. This makes them

ideal for sports and other outdoor activities. Contact lens wearers can also wear

sunglasses, goggles, or other eyewear of their choice without having to fit them

with prescription lenses or worry about compatibility with glasses. Additionally,

there are conditions such as keratoconus and aniseikonia that are typically

corrected better by contacts than by glasses.

Typically, soft contact lenses are mass-produced, while rigid lenses are

custom-made to exact specifications for specific individual patients.

Spin-cast lensesA spin-cast lens is a soft contact lens manufactured by

whirling liquid silicone in a revolving mold at high speed.


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Diamond turningA diamond-turned contact lens is cut and polished on a

CNC lathe. The lens starts out as a cylindrical disk held in the jaws of the lathe.

The lathe is equipped with an industrial-grade diamond as the cutting tool. The

CNC lathe may turn at nearly 6000 RPM as the cutter removes the desired

amount of material from the inside of the lens. The concave (inner) surface of thelens is then polished with some fine abrasive paste, oil, and a small polyester

cotton ball turned at high speeds. In order to hold the delicate lens in reverse

manner, wax is used as an adhesive. The convex (outer) surface of the lens is thus

cut and polished by the same process. This process can be used to shape rigid

lenses, but can also be used to make soft lenses. In the case of soft lenses, the

lens is cut from a dehydrated polymer that is rigid until water is reintroduced.

MoldedMolding is used to manufacture some brands of soft contact

lenses. Rotating molds are used and the molten material is added and shaped by

centrifugal forces. Injection molding and computer control are also used to create

nearly perfect lenses. The contact lens is kept moist throughout the entire

molding process and is never dried and rehydrated.

CONVENTIONAL MANUFACTURING OF CONTACTING LENSES

The precise meaning of the term machining has evolved over the past one

and a half centuries as technology has advanced. In the 18th century, the word

machinist simply meant a person who built or repaired machines.

This person's work was done mostly by hand, using processes such as the

carving of wood and the hand-forging and hand-filing of metal. At the time,

millwrights and builders of new kinds of engines (meaning, more or less,

machines of any kind), such as James Watt or John Wilkinson, would fit the

definition. The noun machine tool and the verb to machine (machined,machining) did not yet exist.

Around the middle of the 19th century, the latter words were coined as the

concepts that they described evolved into widespread existence. Therefore,

during the Machine Age, machining referred to (what we today might call) the


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"traditional" machining processes, such as turning, boring, drilling, milling,

broaching, sawing, shaping, planing, reaming, and tapping. In these "traditional"

or "conventional" machining processes, machine tools, such as lathes, milling

machines, drill presses, or others, are used with a sharp cutting tool to remove

material to achieve a desired geometry.

Since the advent of new technologies such as electrical discharge

machining, electrochemical machining, electron beam machining, photochemical

machining, and ultrasonic machining, the retronym "conventional machining" can

be used to differentiate those classic technologies from the newer ones. In

current usage, the term "machining" without qualification usually implies the

traditional machining processes.

The three principal machining processes are classified as turning, drillingand milling. Other operations falling into miscellaneous categories include

shaping, planning, boring, broaching and sawing.

Turning operations are operations that rotate the work piece as the

primary method of moving metal against the cutting tool. Lathes are the principal

machine tool used in turning.

Milling operations are operations in which the cutting tool rotates to bring

cutting edges to bear against the work piece. Milling machines are the principal

machine tool used in milling.

Drilling operations are operations in which holes are produced or refined by

bringing a rotating cutter with cutting edges at the lower extremity into contact

with the work piece. Drilling operations are done primarily in drill presses but

sometimes on lathes or mills.

Miscellaneous operations are operations that strictly speaking may not be

machining operations in that they may not be swarf producing operations but

these operations are performed at a typical machine tool. Burnishing is anexample of a miscellaneous operation. Burnishing produces no swarf but can be

performed at a lathe, mill, or drill press.

An unfinished work piece requiring machining will need to have some

material cut away to create a finished product. A finished product would be a

work piece that meets the specifications set out for that work piece by


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engineering drawings or blueprints. For example, a work piece may be required to

have a specific outside diameter. A lathe is a machine tool that can be used to

create that diameter by rotating a metal work piece, so that a cutting tool can cut

metal away, creating a smooth, round surface matching the required diameter

and surface finish. A drill can be used to remove metal in the shape of a cylindricalhole. Other tools that may be used for various types of metal removal are milling

machines, saws, and grinding machines. Many of these same techniques are used

in woodworking.

Machining requires attention to many details for a work piece to meet the

specifications set out in the engineering drawings or blueprints. Beside the

obvious problems related to correct dimensions, there is the problem of achieving

the correct finish or surface smoothness on the work piece. The inferior finish

found on the machined surface of a work piece may be caused by incorrect

clamping, a dull tool, or inappropriate presentation of a tool. Frequently, this poor

surface finish, known as chatter, is evident by an undulating or irregular finish,

and the appearance of waves on the machined surfaces of the work piece.

Lathe cutting

In this process, non-hydrated disks (or "buttons") of soft contact lens

material are individually mounted on spinning shafts and are shaped with

computer-controlled precision cutting tools. After the front and back surfaces areshaped with the cutting tool, the lens is then removed from the lathe and

hydrated to soften it. The

finished lenses then

undergo quality assurance

testing.

Though the lathe

cutting process has more

steps and is more time-

consuming than an

injection molding process,

over the years the


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process has become more automated. With computers and industrial robotics, it

now takes only a few minutes to create a lathe-cut soft contact lens.

Diameter of the button is 12 to 15 mm and thickness is 4,5mm.

Polishing is usually done less than 50 seconds because of heating dangerand change of curvature.

The semi-finished button is then cleaned in an ultrasonic bath.

The advantages are that the lens are thicker and relatively easier to handle,

the lens also have a better movement and centration when compared to the spin-

cast lens.

The disadvantages to this process are the time consumption, intensive

labor and difficult to reproduce lens due to each lens being individually made.


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UNCONVENTIONAL MANUFACTURING OF CONTACTING LENSES

An unconventional machining process (or non-traditional machining

process) is a special type of machining process in which there is no direct contact

between the tool and the work piece. In unconventional machining, a form ofenergy is used to remove unwanted material from a given work piece.

Injection molding (spin casting)

Molding the lens can be carried out in several different ways. The lenses

first developed in Prague were spin-cast. Three different fluids were poured into

open rotating molds. The outside curvature of the lens was shaped by the mold,

and the inside curvature was formed according to the speed of the rotation of the

mold.

The centrifugal force of the spinning mold led to the polymerization of the

fluids so that the molecular chains linked to form the required hydrophilic plastic.

A more reliable mass-production contact lens method is injection molding. In

injection molding, the molten plastic is injected into the mold under pressure.

Then the lens is removed from the mold and cooled. The lens is then finished on a

lathe. It is also possible to

produce lenses entirely through

molding, that is, they need no

lathe cutting. This is a recent

development, made possible

through highly automated,

computer controlled mold

production.

In this process, the soft

contact lens material is heatedto a molten state and is then

injected into computer-designed molds under pressure. The lenses are then

quickly cooled and removed from the molds. The edges of the lenses are polished

smooth, and the lenses are hydrated to soften them prior to undergoing quality

assurance testing.


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Most disposable contact lenses are

made with an injection molding process, as

this method is faster and less expensive

than lathe cutting processes.

Features and benefits of this process include:

-Tapered edge profiles and smooth surfaces;

-Back aspherical surface of the lens matches well with the aspheric profile

of the cornea;

-Has only one base curve;

-Enhanced comfort during lens wear;

-Minimal lens movement on the eye yet acceptable tear film dynamics;

-Easy to fit.

Why unconventional machining processes are used?

The answer is simple. In several industries, hard and brittle materials like

tungsten carbide, high speed steels, stainless steels, ceramics etc., find a variety

of applications. For example, tungsten carbide is used for making cutting tools

while high speed steel is used for making gear cutters, drills, taps, milling cutters

etc.

If such materials are machined with the help of conventional machining

processes, either the tool undergoes extreme wear (while machining hard work

piece) or the work piece material is damaged (while machining brittle work piece).

This is because, in conventional machining, there is a direct contact

between the tool and the work piece. Large cutting forces are involved and


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material is removed in the form of chips. Huge amounts of heat is produced in the

work piece. This induces residual stresses, which degrades the life and quality of

the work piece material.

Hence, conventional machining produces poor quality work piece with poor

surface finish (if the work piece is made of hard and brittle material).

To overcome all these drawbacks, we use unconventional machining

processes to machine hard and brittle materials.

We also use unconventional machining processes to machine soft

materials, in order to get better dimensional accuracy.


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References:

1.

NM Farandos, AK Yetisen, MJ Monteiro, CR Lowe, SH Yun (2014).

"Contact Lens Sensors in Ocular Diagnostics.".Advanced Healthcare

Materials.doi:10.1002/adhm.201400504.

2. Manufacture of soft contact lenses.

(http://www.lensfinder.co.uk/information/contact-lens-manufacturing-

process/)3. Aspheric Optics Simplified.

(http://www.slideshare.net/Eyenirvaan/aspheric-optics-

25387700?next_slideshow=1) .

4. How contacts are made.

(http://www.allaboutvision.com/contacts/faq/how-cls-made.htm).

5. Contact Lens. (http://www.madehow.com/Volume-2/Contact-

Lens.html)
http://onlinelibrary.wiley.com/doi/10.1002/adhm.201400504/abstracthttp://en.wikipedia.org/wiki/Digital_object_identifierhttp://dx.doi.org/10.1002%2Fadhm.201400504http://www.lensfinder.co.uk/information/contact-lens-manufacturing-process/http://www.lensfinder.co.uk/information/contact-lens-manufacturing-process/http://www.slideshare.net/Eyenirvaan/aspheric-optics-25387700?next_slideshow=1http://www.slideshare.net/Eyenirvaan/aspheric-optics-25387700?next_slideshow=1http://www.allaboutvision.com/contacts/faq/how-cls-made.htmhttp://www.allaboutvision.com/contacts/faq/how-cls-made.htmhttp://www.slideshare.net/Eyenirvaan/aspheric-optics-25387700?next_slideshow=1http://www.slideshare.net/Eyenirvaan/aspheric-optics-25387700?next_slideshow=1http://www.lensfinder.co.uk/information/contact-lens-manufacturing-process/http://www.lensfinder.co.uk/information/contact-lens-manufacturing-process/http://dx.doi.org/10.1002%2Fadhm.201400504http://en.wikipedia.org/wiki/Digital_object_identifierhttp://onlinelibrary.wiley.com/doi/10.1002/adhm.201400504/abstract

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