Laser bending presentation.pptx

A Lecture

on “Laser Beam Machining

(LBM)”

By:

Dr. Arun Kumar Pandey Assistant Professor (SG)

Mechanical Engineering Department

LASER BEAM MACHINING (LBM)

It is a non contact type thermal energy based advanced machining process.

Disadvantages of LBM- • High specific energy. • Material damage. • Initial investment is high. • Tapers are normally

encountered.

Advantages of LBM- Non contact type process. Versatile process Flexible process Narrow Kerf width Machining is extremely

rapid.

Beam Generation Unit

Motor

CNC Controller(X – Y axes)

Supply of gas jet to nozzle

Chiller Unit

Bending Mirror

Focusing optics

Workpiece

Fig.1. Block Diagram of Laser beam machining system

CNC Controller(Z-axis)

Fig. Schematic of laser cutting system

Nd:YAG Laser Cutting System:

Beam delivery unit

Beam Generation Unit

Bending Mirror

Assist gas Supply unit

Workpiece

Laser Beam

NozzleStand offdistance

Focal length

CoolingUnit

CNC Table

Beam Generation Unit

Workpiece positioning system

XY

Z

Focusing lens

The beam delivery unit consists of different optical components which are used to focus the laser beam on the workpiece.

The main components of beam delivery unit are mirrors, beam splitters, focusing lenses and fiber optic coupling.

Mirrors are used to direct, reflect or bend the laser beam in the desired direction.

For this purpose, generally metallic mirrors are used, as these mirrors pass high reflectivity, minimal energy losses, and withstand high energy density without thermal damage due to their high thermal conductivity.

Copper is most commonly used material for making the mirrors and it can withstand energy densities above100 kW/cm2 without any thermal damage.

Beam splitters are used to distribute the incident laser power among the different workstations.

Focusing lens focuses the laser beam into a very small area.

The common lens materials for CO2 and Nd:YAG lasers are

Sodium Chloride (NaCl), Potassium Chloride (KCl), Zinc Selenide, Gallium Arsenide, and Germanium.

The lens material must have high transmissivity or low reflectivity to the laser light wavelength.

The beam spot diameter can be changed by changing the focal length of the lens as by increasing the focal length, the working distance as well as spot diameter of the laser beam can be increased.

For the laser cutting of thin workpieces, it is advisable to use minimal focal length in order to obtain maximum material removal rate with narrow kerf.

Beam delivery systems based on mirrors assembly have certain advantages such as geometric flexibility, integration of laser beam to the multi degree of freedom devices such as robots, and movement of laser beam along the complicated and complex profile path.

For such situations, fiber optic coupling may be used to transfer the laser beam between the laser output and laser head.

The main problem with the optical fiber is the limit of power that can be transmitted through it, as a fraction of beam energy is absorbed by optical fibers.

The maximum power transmitted through the optical fibers depends upon the dielectric breakdown at the entrance.

Beam powers upto 100W and 500W may be transmitted through optical fibers in CW mode and pulsed mode, respectively.

Focusing head

Nozzle

Assist gas supply pipe

Workpiece

CNC table

Molten material

Fig. Pulsed Nd;YAG Laser Cutting Setup

Fig. Dimensional tolerance obtained with various manufacturing processes

Fig. Surface roughness obtained with various manufacturing processes

Laser Parameters: Power, Type, Frequency, Mode (CW or pulsed), Pulse duration.

Process Parameters: Speed, Focal plane position, Assist gas type and pressure, Beam angle.Material Parameters: Thickness, Geometry, Composition, Surface Condition

PERFORMANCE CHARACTERISTICS

- Material Removal Rate (MRR)- Surface roughness- Kerf width/ taper/ deviation-Thickness of heat affected zone (HAZ) - Recast layer thickness- Mechanical Properties (e.g. hardness)

PROCESS PARAMETERS

Fig. 7. Schematic illustration of various cut quality attributes of interest . Kentry: kerf width at entry side; Kexit: kerf width at exit side; Ra: surface roughness; S: thickness of material; 1: oxidized layer; 2: recast layer; and 3: heat affected zone (HAZ).

Fig. Kerf width and Kerf deviation

Fig. Typical striation patterns formed during the laser cutting Fig. Heat affected zone (HAZ) laser-cut titanium alloy

Fig. EPMA image of laser cut surface of Titanium alloy at A=6 kg/cm2, B=1.4 ms, C=6 Hz and D= 20 mm/min

Top 1.5 mm Bottom

Fig. Kerf width measured and predicted with the focus setting for different workpiece thicknesses

Fig. Variation of kerf width with the focus setting for different workpiece thicknesses.

Effect of focal plane position on kerf width

The influences of cutting parameters on HAZ

Fig. Variation of HAZ layer thickness with pulse parameters: (a) 25 Hz and (b) 1 J (1.0 mm/s; argon; 0.8 Mpa)

Fig. Variation of HAZ layer thickness with cutting speed (2.0 J; 25 Hz; argon; 0.8 MPa).

Fig. Variation of HAZ layer thickness with gas pressure (2.0 J; 25 Hz; argon; 1 mm/s).

Effect of assist gas-

Fig. Comparison of laser cuts made with different assist gases (a) top surface and (b) bottom surface.

Fig. Titanium nitride layer on the laser cut surface made with nitrogen as the assist gas.

Fig. Effect of assist gas on the waviness of laser cut kerf (a) assist gas = He; (b) assist gas = Ar; (c) schematic illustration of waviness.

Fig. Effect of laser power on the (a) kerf width and (b) roughness of cut edge for three different cutting speeds during laser cutting of 1.2 mm austenitic stainless steel by continuous Nd:YAG laser

Fig. Effect of laser power and feed rate (cutting speed) on (a) top kerf width and (b) surface roughness during CO2 laser cutting of 4130 steel

Fig. Effect of laser power and feed rate (cutting speed) on (a) striation frequency and (b) average heat affected zone (HAZ) during CO2 laser cutting of 4130 steel.

Laser Turning and laser milling

Fig. Schematic of Laser Grooving

Thanks

A Lecture

on “Laser Bending”

By:

Dr. Arun Kumar Pandey Assistant Professor (SG)

Mechanical Engineering Department

Laser FormingIntroduction:

Forming techniques, in a broader sense, comprise a variety of metal working processes in which the material is shaped in solid state by plastic deformation.

The forming techniques are generally classified as bulk forming and sheet forming processes.

Common bulk forming processes are rolling, extrusion, drawing, forging, etc., whereas common sheet metal forming processes are bending, surface contouring, linear contouring, shallow recessing, etc.

The end products of forming processes can either be final components or basic shapes such as rods, bars, tubes, sheets, plates, etc.

In the present context, forming process is primarily referred to as sheet material forming such as bending.

Conventional mechanical bending process for a sheet material involves a set of bending die and punch with a sheet material placed between them.

Fig. Schematic of sheet metal forming process for typical V-bend

Limitations of conventional forming:

For a rapid production of few parts such as those required for test prototypes and special shapes, the conventional sheet metal forming processes are often uneconomical due to high cost of dies, and longer time for the fabrication and error corrections of dies.

Also, the mechanical sheet metal forming processes are often associated with the inherent effects such as spring-back effects where the actual bending angle is always less than the desired bending angle defined by the dies.

Laser Forming Process (Laser bending)

The idea of using lasers for forming of sheet material was first conceived by Kitamura in Japan.

This is followed by successful bending of 22 mm thick steel plates using a 15 kW CO2 laser (Kitamura 1983). During laser forming, the surface of the sheet material is scanned with a defocused laser beam such that laser–material interaction causes localized heating of the surface without melting.

The heating of the material causes the expansion of the material in a confined region.

Due to continuity of the heated region with the surrounding material, the free expansion of the hot region is resisted, resulting in bending of the part.

Even though flame bending has been extensively used in the shipbuilding industry.

The Flame bending is often associated with the difficulties in bending thin sections of materials and sections of high-conductivity materials.

With the development of high-power lasers with an enhanced ability to deliver intense beam on highly localized regions, steep temperature gradients can efficiently be established in the materials for bending action.

Laser forming of sheet materials is generally free from spring-back effects and also associated with typical advantages of laser materials processing such as rapid manufacturing, ease of automation, and flexible manufacturing.

Depending on the nature of the thermal effects during laser forming, the strains can be induced either within or out of the sheet plane.

Fig. (a) Out-of-plane and (b) in-plane deformation during laser forming

If the strains induced are uniform throughout the thickness of the material, the material tends to shrink or shorten in length.

whereas, if the strains are not uniform throughout the thickness, the material tends to deflect resulting in out-of-plane deformation or bending.

Fig. Mechanical analogy of three laser forming mechanisms

The figure indicates that shape change during bending is associated with stresses perpendicular to the neutral axis. The shape change can also be induced if the stresses are parallel to the neutral axis.

The three mechanisms of shape change during laser forming can be identified as bending, buckling, and upsetting mechanisms.

Bending or Temperature Gradient Mechanism (TGM)

Among the various mechanisms of laser forming, TGM is most extensively studied and reported in the literature.

Fig. Schematic of the laser bending setup

Fig. Effect of temperature on yield strength of a material

Fig. Thermal gradient mechanism of laser bending: (a) heating process and (b) cooling process

Fig. Sequence of various effects taking place during temperature gradient mechanism of laser bending

Buckling Mechanism (BM)

When the diameter of the laser beam is significantly larger than (nearly 10 times) the thickness of the sheet (i.e., for thin sheets) and when the ratio of thermal conductivity to the thickness of the material is large, negligibly small temperature gradient is developed in the thickness direction.

The condition of negligibly small thermal gradient in thickness direction is also favored where the ratio of the thermal conductivity to the thickness of the material is large. Such conditions facilitate the deformation by BM.

The various steps in laser forming by BM can be summarized as:

1. Initial Heating2. Bulging3. Growth of buckle4. Development of bending angle

Fig. Steps in the laser forming of sheet by buckling mechanism (BM)

Buckling force prop. to t2

Fig. Factors influencing the bending direction during laser forming by buckling mechanism

Prebending of sheet almost always tends to increase the initial bending angle during subsequent laser forming.

The forming of the prebend sheets may be positive or negative depending on the prebend angle.

Generally, the positive bending of concave sheets and the negative bending of convex sheets are most easy cases.

However, the positive bending of convex sheets and the negative bending of concave sheets may be possible by controlling the laser forming parameters such as laser power, scan speed, and beam size and shape.

The other important factor influencing the bending direction during laser forming is the presence of preexisting residual stresses in the sheet.

If the surface of the sheet has preexisting compressive stresses as in the case of rolled sheets, the subsequent laser forming facilitates the positive bending by relieving the surface compressive stresses during heating.

Upsetting Mechanism

Fig. Laser forming by upsetting mechanism (UM): (a) Initial heating, (b) cooling, and (c) final shape

Fig. Schematic of the influence of interaction between the various buckling mechanisms (TGM and BM) on final bending angle

Applications:

• Thermal processing tools

• Bending of pipes and extrusions

• Rapid prototyping and shape alteration in the aerospace, marine and automotive industries

• A forming tool for astronauts

• Adjustment of sealed electric contacts

• Straightening of rods

Effect of Process Parameters on Bending angle

Effect of Power

Fig. Influence of the laser power on the bending angle for AlMg3 (open squares,1 mm thick, speed 25 mm/s) bent by the buckling mechanism and plain carbon steel, St12 (closed squares, 2 mm thick, speed 83 mm/s) bent by the temperature gradient mechanism

Fig. Variation of bending angle with laser power during laser forming of 0.8 mm thick mild steel plate

Effect of Speed – “Line Energy”

Fig. Variation of bending angle with laser traverse speed during laser forming of 0.8 mm thick mild steel plate

Fig. Bending angle versus velocity for a constant line energy of 33 J/mm and a single scan. Laser power 250–1,300W, beam diameter 10 mm

Fig. Bending angle versus line energy for α – β Ti alloy showing the effect of phase changes. Laser power 1,300W, beam diameter 10mm, materialTi–6Al–4V,thickness 1mm, graphite-coated, five scans

Effect of Materials

Fig. Effect of thermo-physical properties of materials on bending angle

Fig. Effect of (a) thermal conductivity, (b) density, (c) specific heat, and (d) thermal expansion coefficient on the bending angle during laser forming

Effect of Mechanical Properties

Fig. Effect of (a) yield strength, and (b) Young’s modulus on the bending angle during laser forming

Effect of Sheet Geometry

Fig. Influence of laser scanning path curvature on the bending angle during laser forming of 0.8 mm Ti-6Al-4V sheets

Fig. Effect of (a) sheet thickness, and (b) sheet width on the bending angle during laser forming of Ti-6Al-4V sheets with laser intensity of 3.33 J/mm2 and sheet length of 50 mm

Effect of other parameters

Fig. Variation of bending angle with laser beam diameter during laser forming of 1.5 mm mild steel plate with laser power of 760 W and traverse velocity of 30 mm/s

Fig. Effect of dwell time between the successive passes on the variation of bending angle with the number of passes during laser forming of 0.2 mm mild steel

Thanks

A Lecture

on

“Laser Welding”

By:

Dr. Arun Kumar Pandey Assistant Professor (SG)

Mechanical Engineering Department

Laser welding has evolved as an important industrial manufacturing process for joining a variety of metallic and nonmetallic materials.

With the developments in the high-power laser technology over the past few decades, laser welding is now capable of joining thicker sections with higher processing speed and better weld quality.

Due to the noncontact nature of laser processing, high degree of automation is possible providing economic advantages in the typical industrial environment.

Even though, laser welding seems to be a simpler process, it presents significant challenges to produce defect-free welds at high speed and under reproducible conditions.

Laser Welding

Fig. General arrangement for laser welding

Process Arrangement

Fig. Arrangement for welding a pipe from the inside using metal optics

Fig. Conduction-limited and “keyhole”-type welds. HAZ heat-affected zone

Laser Welding:

Conduction-limited welding occurs when the power density at a given welding speed is insufficient to cause boiling and therefore to generate a keyhole.

In Conduction-limited welding, the laser processing conditions are such that the surface of the weld pool remains unbroken. In this approach the energy transfer into the depth of the material takes place by conduction.

The weld pool has strong stirring forces driven by Marangoni-type forces resulting from the variation in surface tension with temperature.

The second and the most important approach referred as key-hole welding corresponds to the laser processing conditions which create a “keyhole” in the weld pool.

Generally, the transition from the conduction mode to the key-hole welding is associated with the increase in laser power intensity or irradiation time.

The alternative mode is “keyhole” welding, in which there is sufficient energy per unit length to cause evaporation and hence a hole in the melt pool.

This hole is stabilised by the pressure from the vapour being generated. In some high-powered plasma welds there is an apparent hole, but this is mainly due to gas pressures from the plasma or cathode jet rather than from evaporation.

The “keyhole” behaves like an optical black body in that the radiation enters the hole and is subject to multiple reflections before being able to escape.

In consequence, nearly all the beam is absorbed.

This can be both a blessing and a nuisance when welding high-reflectivity materials.

Since much power is needed to start the “keyhole”, but as soon as it has started then the absorptivity jumps from 3 to 98% with possible damage to the weld structure.

There are two principal areas of interest in the mechanism of keyhole welding.

The first is the flow structure since this directly affects the wave formation on the weld pool and hence the final frozen weld bead geometry. This geometry is a measure of weld quality.

The second is the mechanism for absorption within the keyhole which may affect both this flow stability and entrapped porosity.

Fig. Approximate shape and flow pattern in laser welds

The absorption of the beam is by Fresnel absorption (absorption during reflection from a surface) and inverse stationary relative to the laser beam but varies in intensity with the laser power and welding speed.

Fig. The variation of the metal and shroud gas plasmas from a laser keyhole weld

Fig. Side-view illustration of the keyhole shape and beam absorption

The vapour in the keyhole consists of very hot vapour from the material being welded together with shroud gas that has been sucked in owing to the pulsation of the keyhole.

This vapour may be sufficiently hot to be partially ionised, forming a charged plasma.

The flow of vapour out of the keyhole is fast, approaching sonic speeds, and hence it makes a snarling noise.

This flow through the neck at the throat of the keyhole would be expected to show Helmholtz instabilities (similar to a flag flapping), with the higher velocities in the throat creating a low-pressure zone that would tend to close the throat.

This may be one of the causes of the fluctuation noted, the other being the rapid fluctuation in fluid flow around the keyhole, driven by surface tension variations and sporadic boiling within the keyhole. The boiling reaction is very vigorous and causes a spray to form. This emerges as particles and dust.

Deep penetration laser welding

Fig. Deep penetration laser welding showing various effectsFig. Schematic of the deep penetration welding process

Flow Chart

Operating Characteristics:

Fig. Welding speed versus power for Ti–6Al–4V

Fig. Effect of power modulation on porosity in 20mm deep welding with 20kW peak pulses from a CO2 laser

Fig. Welding speed versus penetration for a fast axial flow CO2 laser

Fig. Variation of the penetration and depth of focus achievable with pulsing using a spot size of 0.3mm on 304 stainless steel

Quality Aspects in Laser Welding

Laser welding is attracting increased interests for welding of various materials in automotive and aerospace industries.

These applications necessitate very high quality of the welds to ensure the desired performance of the laser-welded components.

Due to the complexity of the effects involved in the laser welding process, it is often associated with various geometric and metallurgical defects.

This section discusses various common laser welding defects.

Porosity

Porosity is one of the major defects associated with the laser welding process.

There are various sources of porosity in the laser welds.

Porosities appearing in various locations of the weld may be characterized by distinct morphologies and distributions.

For example, large voids are commonly formed at the bottom of the weld, whereas small distributed voids are formed towards the surface of the weld.

The formation of porosity is greatly influenced by a number of laser processing parameters such as laser power, focusing conditions, welding speed, shielding gas, etc.

Fig. Formation of large and small voids (bubbles) in the weld microstructure of tantalum (laser parameters: Nd:YAG laser; power 3 kW; spot size 300 µm)

Fig. Schematic showing the formation of large void due to incomplete filling of keyhole during laser welding.

Fig. Number of cavities per weld length as a function of the welding speed and the beam quality (K) in laser welding of Al–Mg–Si alloy with CO2 lasers

Cracking

Cracking in the weld structures is one of the most serious laser welding defects.

Most of the cracks in the welds originate from the restrictions to the free contractions of the material during the cooling cycle. Such restrictions result in the setting up of high tensile stresses causing cracking.

Hot cracking in the weld can either be solidification cracking or liquation cracking.

Cracking in the fusion zone during solidification is called solidification cracking.

Cracking may be caused due to the liquation of low melting components in the partially melted zone (liquation cracking).

Liquation cracking is susceptible in the heat-treatable alloys which may form eutectic phases with low melting point during laser welding.

The tendency to crack during laser welding can be minimized by various ways such as careful design of the material, optimization of laser processing parameters, additional designs (such as welding fixtures and joint design).

Other defects associated with laser welding may include incomplete penetration, spatter, etc.

Heat-Affected Zone

The regions adjacent and below the fusion zone of laser weld may undergo some transformations due to the heating and cooling cycles (maximum temperature less than melting point).

This area is referred as heat-affected zone (HAZ).

HAZs often show the altered properties and microstructure and mark the transition region between the fusion zone and the bulk material.

The extent of HAZ can be characterized by the width of the altered region between the fusion zone and the bulk material.

Also, the extent of HAZ is expected to be influenced by various laser processing parameters such as laser power, welding speed, etc.

Fig. Microstructure of single-pass laser weld in steel showing heat-affected zone (HAZ). Arrows indicate the location of fusion line.

Mechanical Properties of Laser Welds

Various mechanical properties such as hardness, tensile strength, fatigue strength, formability of the laser-welded joints have been extensively studied.

The mechanical properties of the weld joints are significantly influenced by various welding defects such as cracking and porosity.

Also, other parameters such as laser joint configuration, laser welding parameters, material composition play an important role in determining the mechanical strength of the joint.

Due to the complexity of the parameters involved in laser welding, the reported mechanical properties should not be regarded as general trends.

Hardness of the weld zone may be higher, lower, or equivalent to the base material depending on the type of material.

In general, the hardness of the laser weld zone in non heat-treatable alloys is generally higher than the base material with an intermediate transition zone corresponding to HAZ.

The increase in the hardness of the weld zone may be due to refinement of the microstructure.

Some of the heat treatable alloys show reduction in hardness in the weld joints due to the loss of precipitates in the weld and overaging in the HAZ

Fig. Tensile strength of aluminium–lithium welds produced by various welding processes

This figure compares the tensile properties of an aluminum–lithium alloy joint welded by various processes. The better tensile strength of the laser-welded joint is primarily due to the small HAZ and the finer structure in the weld zone

LASER WELDING ADVANTAGES

•Deep narrow welds •Low heat input •Minimal distortion •High joint completion rates •Joint design flexibility •Ease of automation

LASER WELDING DISADVANTAGES

Welding speed is very slowIt is limited up to the depth of 1.5 mm.The maximum joint thickness that can be welded by laser beam is somewhat limited

CONVENTIONAL MACHINING PROCESS:-

a) Lower capital cost.

b) Easy setup of equipments.

c) Less skilled labours can easily perform operations on the machines.

NEED FOR UNCONVENTIONAL MACHINING PROCESS:-

1. Emergence of advanced engineering materials

2. Requirement of precision cutting with good surface quality

Hybrid Machining

Unconventional Machining Process

a) There is no direct contact between tool and workpiece, therefore the heat affected zone is less as compared to conventional machining process

b) Tool life is more

c) Higher accuracy and good surface finish is obtained

d) Low wastage of material

e) Difficult- to- machine materials may be easily machined

f) Precision cutting may be done easily

• Technological improvement of machining processes can be achieved by combining different machining actions or phases to be used on the material being removed.

• Hybrid machining is the combination of two or more than two machining processes.

• These processes are combined in order to harness the advantages of different process and to remove the limitation of individual process, if any.

• The processes may be combination of conventional and

unconventional machining processes or combination of different unconventional machining processes.

Introduction of Hybrid Machining

• The main reasons of using hybrid machining processes are;

1. The reason for such a combination and the development of a hybrid machining process is mainly to make use of the combined advantages of the conventional and non conventional process.

2. To avoid or reduce some adverse effects the constituent processes produce when they are individually applied.

3. The performance characteristics of a hybrid machining processes are considerably different from those of the single-phase processes in terms of productivity, accuracy, and surface quality.

Needs of Hybrid Machining

4. The quality of machining is also improved by hybrid machining process. The aspect ratio and the wall surface finish of the micro holes are also improved.

5. In comparison to conventional and unconventional machining processes, it is quite suitable for cutting small and thin sheets with high cutting rates and can be applied to machine miniature objects.

6. Difficult- to- machine materials and very thick materials can be easily machined with the help of hybrid machining processes.

There are two ways of classifying hybrid machining process;

1. By combination of conventional and unconventional machining process

Example: EDG, EDDG, ECG, AEDM, LAT, LAG etc.

2. By combination of different unconventional machining processes

Example: EDMUS, EDML, ECDG etc.

Classification of Hybrid Machining Processes

Electro-chemical dissolution (ECD) Laser-assisted electrochemical machining (ECML)

Ultrasonic-assisted electrochemical machining (USMEC)Mechanical abrasion (MA)Ultrasonic (US)Fluid jet (FJ)Electrochemical buffing (ECB) Electrochemical grinding (ECG)Electrochemical honing (ECH)Electrochemical superfinishing (ECS)

Electro-discharge Grinding

Fig. AEDG machining system components

Fig. Electroerosion dissolution wire machining

Laser Assisted Machining (LAM)

LAM is a novel machining technique which combines the traditional machining methods such as turning, milling, grinding, etc. with the laser technology.

The process is specially developed for the machining of difficult-to-machine materials such as ceramics and hard metals.

Conventional machining of these materials is often costly due to slow machining speeds or is associated with machining defects such as surface and subsurface cracks, undesirable surface finish, etc.

It has been reported that conventional grinding and diamond machining of structural ceramics represent 60–90% of the total cost of the final product. In this context, LAM offers an attractive alternative for the cost-effective machining of ceramics.

In addition, due to recent developments in the high energy laser sources, energy delivery mechanisms, and process automation, LAM process can be configured to achieve higher material-removal rates, precise control over machined geometry, increased tool life, and significant reduction in man and machine time per part.

Fig. Laser Assisted Machining

Fig. Laser Assisted Turning

In laser-assisted turning, the laser heat source is focussed on the un-machined section of the workpiece directly in front of the cutting tool. The addition of heat softens the surface layer of difficult-to-turn materials, so that ductile deformation takes place rather than brittle deformation during cutting. This process yields higher MRRs while maintaining workpiece surface quality and dimensional accuracy. It also substantially reduces the tool wear and cost of machining by reducing man and machine hours per part.

Fig. Laser Assisted Grinding

Today, hardened and brittle work materials are mainly machined by grinding. In order to achieve high stock removal rates and high precision, diamonds and cubic boron nitride (CBN) are used as abrasives.

They permit grinding results which at most can be improved by integrating laser machining or combining it with the grinding processes.

Fig. Laser Assisted Machining Processes

Zheng and Huang found that both the aspect ratio (depth over diameter) and the wall surface finish of the micro-holes were improved by using the ultrasonic vibration-assisted laser drilling, compared to laser drilling without assistance of ultrasonic vibration.

Yue et al. have found the deeper holes with much smaller recast layer during ultrasonic-assisted laser drilling as compared with the laser drilling without ultrasonic aid.

Laser-assisted seeding (a hybrid process of LBM and electro-less plating) process have proven to be superior than conventional electro-less plating during plating of blind micro-vias (micro-vertical inter actions) of high aspect ratios in printed circuit boards (PCBs).

In LAECM, the laser radiation accelerates the electrochemical dissolution and localizes the area of machining by few microns size which enables the better accuracy and productivity.

De Silvaet al have found that L AECM of aluminium alloy and stainless steel have improved the MRR by 54% and 33%, respectively, as compared with electro–chemical machining alone. They also claimed that LAECM has improved the geometrical accuracy by 38%.

Li and Achara have found that chemical-assisted laser machining (laser machining within a salt solution) significantly reduces the heat-affected zone and recast layer along with higher MRR as compared with laser machining in air.

Thanks