EPP 212 Advanced Manufacturing Technology Group Seminar

L B L B AASSEERR EE AAMM M ACHIINNG ACHININ MG

Process Capability

Laser beam machining process uses highly coherent light source. This beam can be focused by means of a lens on a very small spot in the work piece. The high power radiation of laser gives rise to high temperature on a small area of work piece. This initiates the cutting process in the work material. The equipment consists of ruby crystal placed inside a flash lamp. The flash lamp is used to produce high intensity light rays.

 The ruby crystal is thus simulated and this produces highly spatial laser beam. When the rays hit the work surface it causes partial or complete vaporization of surface material.

Design Consideration

 Non-reflective workpiece surfaces are preferable  Sharp corners are difficult to produce; deep cuts produce tapers  Consider the effects of high temperature on the workpiece material

 Laser Beam Machining (LBM) is thermal processes considering the mechanisms of material removal.  Laser Beam Machining or more broadly laser material processing deals with machining and material processing like heat treatment, alloying, cladding, sheet metal bending.  Laser stands for light amplification by stimulated emission of radiation.  As laser interacts with the material, the energy of the photon is absorbed by the work material leading to rapid substantial rise in local temperature. This in turn results in melting and vaporisation of the work material and finally material removal.

Similarly as can be seen in Fig , laser beams can be focused over a spot size of 10 – 100 μm with a power density as high as 1 MW/mm 2. Electrical discharge typically provides even higher power density with smaller spot size. EBM and LBM are typically used with higher power density to machine materials. The mechanism of material removal is primarily by melting and rapid vaporisation due to intense heating by the electrons and laser beam respectively.

 Laser can be used in wide range of manufacturing applications Material removal – drilling, cutting and tre-panning Welding Cladding Alloying  Drilling micro-sized holes using laser in difficult to machine materials is the most dominant application in industry.  In laser drilling the laser beam is focused over the desired spot size. For thin sheets pulse laser can be used. For thicker ones continuous laser may be used.

Typical Application and Product Made

4 Typical application ○ Material removal-Cutting ○ Welding ○ Cladding ○ Soldering

Method used in laser cutting  vaporization  melt and blow  melt blow and burn  thermal stress cracking  scribing  cold cutting  burning stabilized laser cutting

Laser Beam welding  LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium  The weld quality is high.

Laser Cladding  A method of depositing material by which a powdered or wire feedstock material is melted and consolidated by use of a laser in order to coat part of a substrate or fabricate a near-net shape part.  It is often used to improve mechanical properties or increase corrosion resistance, repair worn out parts, and fabricate metal matrix composites.  The powder used in laser cladding is normally of a metallic nature, and is injected into the system by either coaxial or lateral nozzles.

Laser Soldering  A technique where a laser is used to melt and solder an electrical connection joint. Diode laser systems based on semiconductor junctions are used for this purpose.  The beam is delivered via an optical fiber to the workpiece, with fiber Since the beam out of the end of the fiber diverges rapidly, lenses are used to create a suitable spot size on the workpiece at a suitable working distance. A wire feeder is used to supply solder.

Product made by LBM

Advantage of Laser Beam Machining

Easier workholding Reduced contamination of workpiece Reduced chance of warping the material that is being cut High precision (more precise and using less energy when cutting sheet metal compared to plasma machining)

Limitation of Laser Beam Machining

 Consume electricity (eg. A typical 1500-watt CO 2 laser will have a running cost in the region of £10 - £20 per hour.)  High initial capital cost  High maintenance cost  High purity gas (for the laser generating chamber)  Limited thickness of sheet metal can cut out compared to plasma machining  Presence of Heat Affected Zone – specially in gas assist CO2 laser cutting  Thermal process – not suitable for heat sensitive materials like aluminium glass fibre laminate

Alternative Method

 Press tools (working on the shearing principle) are a very quick and efficient way to produce components from sheet or strip stock in large quantities, they are however time consuming to set up and expensive to tool.  Machining and forming process, such as combining of laser cutting and punching of sheet metal  eg. turret punch presses have been equipped with an integrated laser head; the machine can punch or laser cut, but it cannot do both simultaneously

New laser cutters have positioning accuracy of 10 micrometers and repeatability of 5 micrometers. This process is capable of holding quite close tolerances, often to within inch (0.025 mm) Part geometry and the mechanical soundness of the machine have much to do with tolerance capabilities. The typical surface finish resulting from laser beam cutting may range from 125 to 250 micro-inches (0.003 mm to mm)

Surface roughness is an effective parameter representing the quality of machined surface. surface roughness value reduces on increasing cutting speed and frequency, and decreasing the laser power and gas pressure surface roughness value was found to be reduced on increasing pressure in case of nitrogen and argon but air gives poor surface beyond 6 bar pressure. Also, surface finish was better at higher speeds.

The surface roughness is minimum and laser power has a small effect on surface roughness but no effect on striation frequency Micromachining of 0.5 mm thick NdFeB ceramic (magnetic material) using pulsed Nd:YAG laser gives better surface finish in water as compared to air

LBM economics  Depend on number of parts manufactured on that machine  One laser produced and used in different machine, can reduce investment costs of laser  Reduce time of production of laser, hence reduce steps to setting up machine  By increasing the technological compactness, different machining process can be done in one machine  Since the machining procedure is done continuously, the total time to produce is reduced, less time for more production

LBM economics(cont.)  Time for laser use is less than cutting times  Laser is shared on different machine, production rate increase  Time-sharing will lead to reducing cost  If we adjust intensity or power of laser, it is possible to be used based on different technology on different machines, for the same laser source

LBM economics(cont.)  Hardening process was replaced by laser– hardening.  Cost is saved due to integration of process.  Less reworking because less distortion occurred when hardening in final processing.  It is beneficial if the production can be taken in integrated process as switching half-finished product to another station for finishing will waste time.

F UTURE USE OF LBM

 Perspectives of applications of micro- machining utilizing water jet-guided laser. - It is accurate, produce small cutting radius - temperature-controlled which no burns on work piece - without producing impurities  3D LDM machining such as turning and milling - controlling different/ many laser in different angles  Improving laser quality to cut difficult-to-cut materials

 Develop the models with no or very few assumptions to get the real solution of the LBM problems quantitatively. - optimization of process variables. - consider about beam spot diameter, thermal conductivity and reflectivity of work piece material  Hybrid or integration of LBM with other machining methods.  Solve the weakness of laser : thermal process - burns on material hence affect mechanical properties. - surface is not perfect from aspect of roughness, parallelism and flatness due to burining.

Case Study

COHERENT Laser Beam Machining Centre (LMC)

It’s Applications  Architectural models  Precision sheet metals  Acoustic guitar fabrication  Trophies and awards  Medical part fabrications  Printing and nameplates  Rapid prototypes

Extremely reliable, inexpensive to run, provide over 20,000 hours of cutting before requiring service. It’s Laser Technology Sealed CO 2 Laser Compared to Flow-through Gas Lasers require an external gas source to supply gas flowing through the laser Use only 100 to 500 Watt sealed CO2

Combination of a beam with a low M2 Allowing smaller focus spot sizes (highly focused spot (.004” diameter) Allow square-wave pulsing characteristics Allows a 500W model, which generates 1500W peak power, to produce instantaneous intensities of up to 0.3 MW/mm2 at the material reduces the Heat Affected Zone due to lower thermal conduction Pulsing gives accurate and essential control over how much and how fast energy is delivered for material processing by using dedicated microprocessor Control to harness the power of each pulse and maximize material processing efficiency Less charring when cutting materials such as paper, and less melting when cutting materials such as polymers. faster vaporization of materials, higher processing speeds and deeper cuts.

Far- infrared light at a wavelengt h of 10.6 microns. Produce high- frequency pulses with extremely fast rise-and-fall times (opposite). for cutting or drilling, rather than for merely heating the material to be processed.

Slab-discharge CO2 Laser Conventional CO2 Laser Slab-discharge CO2 Laser VS Conventional CO2 Laser Permanently confines the lasing gas mixture between two rectangular plate electrodes (opposite) No replacement gas and no scheduled maintenance to the laser head for up to 25,000 hours (roughly two-and-a-half years) of continuous operation lower electrical and cooling-water requirements than conventional lasers that flow consumable gases through the laser head. Cost Productivity

from group D….