lecturer 1 machining

MECHANICAL & INDUSTRIAL ENGINEERING DEPARTMENTMECHANICAL & INDUSTRIAL ENGINEERING DEPARTMENT

INDIAN INSTITUTE OF TECHNOLOGY ROORKEEINDIAN INSTITUTE OF TECHNOLOGY ROORKEE

Chapter 1. Machining

08/30/14 Dr. Kaushik Pal



M.Tech 1st year


• MI 572 MI 572 : : Advanced Manufacturing Processes

• L:T:PL:T:P 3 : 1 : 2/2 3 : 1 : 2/2

• Weight-ageWeight-age : : Mid term – 20% Mid term – 20%

End term – 40%End term – 40%

Practical & class work– 20%+20%Practical & class work– 20%+20%

• Credit: 0404



DIAMOND TURNING•




INTRODUCTION


• Diamond turning is a process of mechanical machining of precision elements using lathes or derivative machine tools (e.g., turn-mills, rotary transfers) equipped with natural or synthetic diamond-tipped tool bits.

• The process of diamond turning is widely used to manufacture high-quality aspheric optical elements from crystals, metals, acrylic, and other materials.



PROCESS• Diamond turning is a multi-stage process.

• Initial stages of machining are carried out using a series of CNC lathes of increasing accuracy.

• A diamond-tipped lathe tool is used in the final stages of the manufacturing process to achieve sub-nanometre level surface finishes and sub-micrometre form accuracies.




• Quality of surface finish and form accuracy is monitored throughout the manufacturing process using such equipment as contact and laser profilometers, laser interferometers, optical and electron microscopes.

• Temperature control is crucial, because the surface must be accurate on distance scales shorter than the wavelength of light. Temperature changes of a few degrees during machining can alter the form of the surface enough to have an effect.




TYPES OF TURNING

• TRADITIONAL TURNING is a turbocharged version of classic lathe work. The part is chucked on a lathe having an incredibly accurate spindle and slides. 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.




• OFF-AXIS TURNING is an approach where a workpiece is mounted to the spindle in an asymmetric fashion. This allows cutting of multiple parts simultaneously or producing contours whose rotational center is not coincident with the center of the part. Certain optical configurations take advantage of this approach.




• 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.




MATERIAL THAT CAN BE MACHINED USING SPDT

• Plastics– Acetal– Acrylic– Nylon– Polycarbonate– Polypropylene– Polystyrene– Zeonex




• Metals– Aluminum and aluminium alloys– Brass– Copper– Gold– Electroless nickel plating on other materials– Silver– Tin– Zinc




• Infrared crystals– Cadmium sulfide – Cadmium telluride– Calcium fluoride– Cesium iodide– Gallium arsenide– Germanium– Lithium niobate– Potassium bromide– Potassium dihydrogen phosphate (KDP)




APPLICATIONS• The process of diamond turning is widely used to

manufacture high-quality aspheric optical elements from crystals, metals, acrylic, and other materials like:-– assemblies in telescopes– video projectors– missile guidance systems– Lasers– scientific research instruments – numerous other systems




DRAWBACK• 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.




HYBRID MACHINING•




INTRODUCTION• Technological improvement of machining processes can be

achieved by combining different machining actions or phases

to be used on the material being removed for eg:-

• A mechanical conventional single cutting or MA action process can be combined with the respective machining phases of electrodischarge (ED) in electrodischarge machining (EDM)




NEED OF HYBRID MACHINE• To make use of the combined advantages and to avoid or

reduce some adverse effects the constituent processes produce when they are individually applied.

• The performance characteristics of a hybrid process are considerably different from those of the single-phase processes in terms of:-– Productivity– Accuracy– Surface quality




DIFFERENT PROCESS COMBINATION AND APPLICATION




HYBRID CHEMICAL AND ELECTROCHEMICAL

PROCESSES.•




• In this family of hybrid machining processes, the major material removal phase is either CD or ECD.

• machining action can be combined with the thermal assistance by local heating in case of laser-assisted electrochemical machining (ECML).




HYBRID THERMAL MACHINING PROCESS

•




• the main material removal mechanism is a thermal one.

• The combination of this phase with the ECD phase, MA action, and ultrasonic (US) vibration generates a family of double action processes.

• The triplex hybrid machining is also achievable by combining the electrodischarge erosion (EDE) phase, the ECD action, and the main grinding (G) as shown in above fig 1.9.




•




MICRO MACHINING•




INTRODUCTION• Refers to techniques for fabrication of 3D structures on the

micrometer scale

• Applications include MEMS devices e.g. airbag sensor, medical devices, micro-dies and molds, etc.

• Most methods use silicon as substrate material




BASICS OF MICROMACHINING• Two Different Approaches of Micromachining• Bulk or Surface• Fundamental Four Techniques of Micromachining

– Thin Film Deposition– Photolithography– Etching– Sacrificial Release




PHOTOLITHOGRAPHY•




• The wafers are chemically cleaned to remove particulate matter, organic, ionic, and metallic impurities

• High-speed centrifugal whirling of silicon wafers known as "Spin Coating" produces a thin uniform layer of photoresist (a light sensitive polymer) on the wafers

• Photoresist is exposed to a set of lights through a mask often made of quartz

• Wavelength of light ranges from 300-500 nm (UV) and X-rays (wavelengths 4-50 Angstroms)




ETCHING• Process Variations:

– Wet etching– Dry etching




WET ETCHING• The key ingredients are:

– Oxidizer (e.g. H2O2, HNO3)– Acid or base to dissolve the oxidized surface (e.g. H2SO4,

NH4OH)– Dilutent media to transport the products through (e.g.

H2O)




DRY ETCHING•


THE ABOVE FIG SHOWS PLASMA BASED ETCHING PROCESS PRODUCTS MANUFACTURED BY ETCHING



THIN FILM DEPOSITION• Chemical Vapor Deposition




• sputtering




• evaporation




BULK OR SURFACE• Process for producing 3D MEMS structures – older process• Uses anisotropic etching of single crystal silicon




SURFACE• Newer process for producing MEMS structures• Uses etching techniques to pattern microscale structures

from polycrystalline (poly)silicon, or metal alloys




APPLICATIONS• MEMS (Microelectromechanical systems)

• medical device

• Fabrication etc.


lecturer 1 machining

Documents

process of diamond turning

kaushik pal diamond

sharp diamond

kaushik pal mi

diamondtipped lathe

traditional turning

mid term

end term