Contents introduction

ABSTRACT
In the past engineering industries have witnessed a rapid growth in the development of harder and difficult-to-machine materials such as hastalloy, nitralloy, waspalloy, nimonics, carbides, stainless steel, heat-resisting steels, and many other high-strength-temperature-resistant (HSTR) alloys, These materials find wide application in aerospace, nuclear engineering, and other industries owing to their high strength-to-weight ratio, hardness, and heat-resisting qualities. For such materials the conventional edged tool machining, in spite of recent technological advancement, is highly uneconomical and the degree of accuracy and surface finish attainable are poor. Besides, machining of these materials into complex shapes is difficult, time-consuming and sometimes impossible. Recent Trend Manufacturing of Smart Material are in the sense that they do not employ a conventional or traditional tool for metal removal, instead, they directly utilize some form of energy for metal machining.

CONTENTS

• 
  INTRODUCTION
  
• 
  TYPES OF UNCONVENTIONAL MACHINES
  
• 
  LASER BEAM MACHINING
  
• 
  WORKING PRINCIPLE
  
• 
  MACHINING PROCESSES USING LASER TECHNOLOGY
  
  • 
    Laser cutting
    
  • 
    Laser bending
    
  • 
    Laser tube cutting
    
  • 
    Laser engraving
    
  • 
    Diamond drilling
    
• 
  ADVANTAGES OF LASER
  
• 
  APPLICATIONS OF LASER
  

• LASER CUTTING vs. WATER JET CUTTING

• LASER CUTTING vs. PLASMA CUTTING

• 
  CONCLUSION
  

INTRODUCTION

The basic principle of metal removal in the conventional methods of machining involves the use of some sort of tool which is harder than the workpiece and is subject to wear. The metal removal is by mechanical energy through the use of physical force (the tool and the workpiece being in direct contact with each other) which shears the chips. That is, the conventional machining methods involves removal of metal by compression shear chip formation.

• 
  Metal removal by chip formation is an expensive and difficult process.
  
• 
  Proper holding of the work piece and to avoid its distortion are very important, due to the very large cutting forces involved.
  
• 
  Due to the large cutting forces, and large amount of heat gene-rated at the tool-work piece interface, undesirable deformation and residual stresses are set up in the work piece. These undesirable effects have to be removed afterwards.
  

Unconventional machines are generally non-mechanical don’t produce chips or a lay pattern on the work surface and often involves new energy modes. There is no direct physical contact between the tool and the work piece and so, the tool need not be harder than the job.
TYPES OF UNCONVENTIONAL MACHINES

Mechanical

1. 
   Abrasive jet machining
   
2. 
   Ultrasonic machining
   

Chemical

1. 
   chemical machining
   

Electro chemical

1. 
   electro – chemical matching
   
2. 
   electro - chemical grinding
   

Thermoelectric

1. 
   ion-Beam machining
   
2. 
   plasma arc machining
   
3. 
   electrical discharge machjining
   
4. 
   electron-beam machining
   
5. 
   laser – Beam machining
   

LASER BEAM MACHINING

A laser (light amplification by stimulated emission of radiations) is a device which produces a beam of light. Laser light can be a very powerful sources of power. In LBM, exceedingly high electromagnet energy densities (of the order of 105 kw/mm²) are focused on the surface of the work piece (in air or vacuum) to remove metal by melting and evaporation.

There are many types of lasers used for different purposes, e.g., solid state, gas, liquid and semi-conductor. For machining and welding, high power lasers are required and, in general, only the solid state lasers can provide the required power levels.
WORKING PRINCIPLE

The most commonly used solid-state laser is the ruby laser (crystalline aluminium oxide or sapphire). These lasers are fabricated into rods about 150 mm long and their ends are finished to close optical tolerance. The ruby crystal is doped with a small amount of chromium oxide. The laser is “pumped” by a flash of high intensity light (a xenon-filled flash lamp). The xenon lamp is fired by discharging a large capacitor through it (electric power of 250 to 1000 watts may be needed for this). The intense radiation from the lamp excites fluorescent impurity atoms (chromium, at – ohms) to a higher energy level. When the atoms fall back to the original energy level through a series of energy levels, an intense beam f visible light is emitted. When this light is reflected back from, the coated rod ends, more atoms are exited and stimulated

To return to their ground level. This chain reaction results in a stimulated avalanche of light, some of which is transmitted through the reflecting coatings (about 80% reflective). This light is highly coherent in time and space, that is, it has a very narrow frequency band is highly in phase, and is quite parallel. When this light is focused with ordinary lense at spot on the workpiece, high energy density is obtained which will melt and vaporize the metal. It is clear that LBM is a pulsed operation.
MACHINING PROCESSES USING LASER TECHNOLOGY

• 
  Laser cutting
  
• 
  Laser bending
  
• 
  Laser tube cutting
  
• 
  Laser engraving
  
• 
  Diamond drilling
  

LASER CUTTING

Laser cutting is a technology that uses a laser programmed by a computer to cut materials, which is used in the production line and is typically used for industrial manufacturing applications. Laser cutting works by directing the output of a high power laser, by computer, at the material to be cut. The material then either melts, burns, vaporizes away, or is blown away by a jet of gas, leaving an edge with a high quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.

Comparison to mechanical cutting

Advantages of laser cutting over mechanical cutting vary according to the situation, but two important factors are the lack of physical contact (since there is no cutting edge which can become contaminated by the material or contaminate the material), and to some extent precision (since there is no wear on the laser). There is also a reduced chance of warping the material that is being cut, as laser systems have a small heat-affected zone. Some materials are also very difficult or impossible to cut by more traditional means. One of the disadvantages of laser cutting includes the high energy required.

Types:

Both gaseous CO₂ and solid-state Nd:YAG lasers are used for cutting, in addition to welding, drilling, surface treatment, and marking applications. Common variants of CO₂ lasers include fast axial flow, slow axial flow, transverse flow, and slab.

Processes in laser cutting:

There are many different methods in cutting using lasers, with different types used to cut different material. Some of the methods are vaporization, melt and blow, melt blow and burn, thermal stress cracking, scribing, cold cutting and burning stabilized laser cutting.

Vaporization cutting:

In vaporization cutting the focused beam heats the surface of the material to boiling point and generates a keyhole. The keyhole leads to a sudden increase in absorbability quickly deepening the hole.

Thermal stress cracking:

Brittle materials are particularly sensitive to thermal fracture, a feature exploited in thermal stress cracking. A beam is focused on the surface causing localized heating and thermal expansion. This results in a crack that can then be guided by moving the beam. The crack can be moved in order of m/s. It is usually used in cutting of glass.

LASER BENDING

Tube bending

The numerically controlled multi-radial tube-bending machine makes it possible to bend products of geometry composed of straight sections, arcs and spirals in three dimensions. It also makes it possible to bend pipes as well at a fixed radius (with use of a mandrel) as at changing radii (rolling) in one work cycle. It is also possible to enter 3D geometry that is recorded in the IGES format. A built-in patented MINIMES system ensures high repeatability of products made by this bending machine.

LASER TUBE CUTTING

These laser tube cutting systems have brought significant process and economic benefits to the fabrication and assembly of mechanical tubing into a wide range of end use products. Those benefits are found in three primary areas:

• 
  Dramatic improvements in labor productivity with users reporting increases of 70% to 80% compared to conventional methods.
  
• 
  Reductions in downstream assembly costs due to the ability to hold tighter fabrication tolerances resulting in better fit up, easier assembly, and simpler assembly fixturing.
  

The high efficiency of the tube cutting and its broad flexibility puts additional degrees of design freedom into the hands of new product designers that can enhance innovation in new product development and reduce the time to market of new products

LASER ENGRAVING

Laser marked electronic part Numbers Printing On Mobile Phones

Laser engraving is the practice of using lasers to engrave or mark an object. The technique can be very technical and complex, and often a computer system is used to drive the movements of the laser head. Despite this complexity, very precise and clean engravings can be achieved at a high rate. The technique does not involve tool bits which contact the engraving surface and wear out. This is considered an advantage over alternative engraving technologies where bit heads have to be replaced regularly.

The material removal process provides typical depths from 0.001 inch to 0.002 inch. Heavier marks can be made from 0.003 inch to 0.004 inch with depth of 0.005 inch.

Materials that can be engraved

Natural materials

Directly "burning" images on wood were some of the first uses of engraving lasers. The laser power required here is often less than 10 watts depending on the laser being used as most are different. Hardwoods like walnut, oak, mahogany and maple produce good results.

Plastics

Standard cast acrylic plastic, acrylic plastic sheet, and other cast resins generally laser very well.

Metals

The best traditional engraving materials started out to be the worst laser-engravable materials. This problem has now been solved using lasers at shorter wavelengths than the traditional 10,640nm wavelength CO₂ laser. Using Nd:YVO₄ or Nd:YAG lasers at 1,064nm wavelength, or its harmonics at 532 and 355nm, metals can now easily be engraved using commercial systems.

Coated metals

Much laser engraving is sold as exposed brass or silver-coated steel lettering on a black or dark-enamelled background. A wide variety of finishes is now available, including screen-printed marble effects on the enamel.

Stone and glass

Stone and glass do not turn gaseous very easily. As expected, this makes them generally a better candidate for other means of engraving, most notably sandblasting or cutting using diamonds and water. But when a laser hits glass or stone, it fractures. So lasers are indeed used to engrave on glass, and if the power, speed and focus are just right, excellent results can be achieved..

Jewelry

The demand for personalized jewelry has made jewelers more aware of the benefits of the laser engraving process. A laser can cut into both flat and curved surfaces. Jewelry contains both flat and curved surfaces. That points-up the reason why jewelers have welcomed all the adaptations for the creation of laser engraved jewelry.

Fine Art

Laser engraving can also be used to create works of fine art. Generally this involves engraving into planar surfaces, to reveal lower levels of the surface or to create grooves and striations which can be filled with inks, glazes, or other materials.
Common Laser Engraving Materials:

• 
  Acrylic
  
• 
  Anodized Aluminium
  
• 
  Ceramic
  
• 
  Cloth
  
• 
  Coated Metals
  
• 
  Cork
  
• 
  Delrin
  
• 
  Fiberglass
  
• 
  Glass
  
• 
  Leather
  
• 
  Marble
  
• 
  Matte Board
  
• 
  Melamine
  
• 
  Mylar
  
• 
  Paper
  
• 
  Plastic
  
• 
  Pressboard
  
• 
  Rubber
  
• 
  Wood
  
• 
  Wood Veneer
  

Laser Marking and Laser Engraving Attributes

• 
  A permanent mark
  
• 
  High density (characters as small as 0.012 high)
  
• 
  Non-contact (eliminates distortion of delicate parts and simplifies tooling.)
  
• 
  Marking of hard to reach areas.
  
• 
  Highly legible, even with small characters.
  
• 
  Typically does not need pre or post-processing.
  
• 
  A highly accurate and repeatable laser mark.
  
• 
  A wide variety of fonts and graphics via software.
  
• 
  Automatic sequential serializing.
  

DIAMOND DRILLING

• 
  Laser diamond drilling and machining is a well established process, but the availability of an excellent beam quality makes this technology even more attractive as smaller dimensions can be achieved, so smaller draw plates and tool features can be manufactured.
  
• 
  The high energy density of the beam and pulsed operation of this fiber laser system are key features to enable diamond machining at high erosion rates, making this processes cost effective for mass manufacturing.
  

ADVANTAGES OF LASER

• 
  Much wider range of machinable materials
  
• 
  Non-contact machining with almost no force impact to the surface
  
• 
  No tool wear
  
• 
  Material removal rate controllable down to the nanometer scale
  
• 
  Smaller heat affected zones and less sub-surface damage
  
• 
  Final quality machining in one process and with one tool only
  

APPLICATIONS OF LASER

• 
  Drilling small holes and apertures into difficult machinable materials (e.g. IC-boards, semiconductor substrates, bio-medical devices)
  
• 
  Micromilling (laminar material removal) of grooves, channels, webs, recesses (e.g. tiny moulds, fluid structures, lab-on-the-chip devices, miniaturized bio-chemical reactors, stents)
  
• 
  Production of micro-sieves
  
• 
  Cutting and structuring of thin foils
  
• 
  Marking and dicing of glass wafers and integrated circuits on semiconductor wafers
  
• 
  Cutting or repairing masks for processes in the semiconductor, display and OLED technologies
  
• 
  Marking or repairing lithograpy masks
  
• 
  Structuring semiconductor wafers and solar cells
  

Standard metal cutting processes: laser cutting vs. water jet cutting

Water jet cutting is a process used to cut materials using a jet of pressurized water as high 60,000 pounds per square inch (psi). Often, the water is mixed with an abrasive like garnet that enables more materials to be cut cleanly to close tolerances, squarely and with a good edge finish. Water jets are capable of cutting many industrial materials including stainless steel, Inconel, titanium, aluminium, tool steel, ceramics, granite, and armor plate. This process generates significant noise.

Precision of process

Minimum size of the cutting slit	0.006", depending on cutting speed	0.02"
Cut surface appearance	Cut surface will show a striated structure	The cut surface will appear to have been sand-blasted, depending on the cutting speed
Degree of cut edges to completely parallel	Good; occasionally will demonstrate conical edges	Good; there is a "tailed" effect in curves in the case of thicker materials
Processing tolerance	Approximately 0.002"	Approximately 0.008"
Degree of burring on the cut	Only partial burring occurs	No burring occurs
Thermal stress of material	Deformation, tempering and structural changes may occur in the material	No thermal stress occurs
Forces acting on material in direction of gas or water jet during processing	Gas pressure poses problems with thin workpieces, distance cannot be maintained	High: thin, small parts can thus only be processed to limited degree

Safety considerations and operating environment

Personal safety equipment requirements	Laser protection safety glasses are not absolutely necessary	Protective safety glasses, ear protection, and protection against contact with high pressure water jet are needed
Production of smoke and dust during processing	Does occur; plastics and some metal alloys may produce toxic gases	Not applicable for water jet cutting
Noise pollution and danger	Very low	Unusually high
Machine cleaning requirements due to process mess	Low clean up	High clean up
Cutting waste produced by the process	Cutting waste is mainly in the form of dust requiring vacuum extraction and filtering	Large quantities of cutting waste occur due to mixing water with abrasives

Standard metal cutting processes: laser cutting vs. plasma cutting

Plasma (arc) cutting was developed in the 1950s for cutting of metals that could not be flame cut, such as stainless steel, aluminum and copper. The plasma arc cutting process uses electrically conductive gas to transfer energy from an electrical power source through a plasma cutting torch to the material being cut. The plasma gases include argn, hydrogen, nitrogen and mixtures, plus air and oxygen.

Precision of process

Minimum size of the cutting slit (kerf width)	0.006", depending on cutting speed	0.002"
Cut surface appearance	Cut surface will show a striated structure	Cut surface will show a striated structure
Degree of cut edges to completely parallel	Good; occasionally will demonstrate conical edges	Fair, will demonstrate non-parallel cut edges with some frequency
Processing tolerance	Approximately 0.002"	Approximately 0.02"
Degree of burring on the cut	Only partial burring occurs	Only partial burring occurs
Thermal stress of material	Deformation, tempering and structural changes may occur in the material	Deformation, tempering and structural changes may occur in the material
Forces acting on material in direction of gas or water jet during processing	Gas pressure poses problems with thin workpieces, distance cannot be maintained	Gas pressure poses problems with thin workpieces, distance cannot be maintained

Safety considerations and operating environment

Personal safety equipment requirements	Laser protection safety glasses are not absolutely necessary	Protective safety glasses
Production of smoke and dust during processing	Does occur; plastics and some metal alloys may produce toxic gases	Does occur; plastics and some metal alloys may produce toxic gases
Noise pollution and danger	Very low	Medium
Machine cleaning requirements due to process mess	Low clean up	Medium clean up
Cutting waste produced by the process	Cutting waste is mainly in the form of dust requiring vacuum extraction and filtering	Cutting waste is mainly in the form of dust requiring vacuum extraction and filtering

CONCLUSION

Laser machining process has evolved into a reliable manufacturing process for precision .The broad range of lasers available for micromachining coupled with advances in control systems and micro positioning stages allows accurate and highly reproducible micromachining to be achieved. Additionally, the flexibility of laser micromachining allows adjustment of the prototype design to be accommodated without the need for expensive retooling.