The Laser Machining Engineering Essay

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Laser machining consists of the removal of material brought about by laser material interaction. Laser machining is a term that encompasses laser drilling, laser cutting, laser grooving, laser marking and laser scribing. These processes remove material by melting and blow away or by direct vaporization. Due to the precision of the lasers, cut edges do not need to be refinished and are ready for assembly. Laser machining can also handle a limitless array of product designs from ranging from simplistic to intricate. From sheet metal cutting to part identification, laser machining has become an industry standard. It is also utilized in serialization, bar coding, calibration and the engraving of logos or labels.

A laser light beam has several properties that distinguish it from other forms of light. It is monochromatic (theoretically, the light has a single wave length) and highly collimated (the light rays in the beam are almost perfectly parallel). These properties allow the light generated by a laser to be focused, using conventional optical lenses, onto a very small spot with resulting high power densities. Depending on the amount of energy contained in the light beam, and its degree of concentration at the spot, the various laser processes identified above can be accomplished. There are many types of laser machining that are commonly used in Industry and technology processing. Each type has its own applications and uses that differ from other types. This unit will discuss four types of machining process.

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3. Recognize the suitable applications for suitable type of laser machining.

3.3 LASER MACHINING CAPABILITIES

3.3.1 ALS EXPRESS 3000 WATT CO2 LASER CUTTER (3SYSTEMS)

Capable of holding 5' x 10' sheets

Continuous wave or pulsed laser capabilities

Cuts up to ¾ thick on carbon steel

Precision cut parts with tolerances held to ± 0.005" (depending on material and thickness)

Special beam conditioning which allows for better cuts on thick sheets

Contouring speeds of 1,000 in/min

Linear motor drives

1.33 G acceleration

High production run capability

3.3.2 ALS EXPRESS 6000 WATT CO2 LASER CUTTER

Capable of holding 5' x 10' sheets

Contouring speeds of 1,000 in/min

Cuts up to 3/4" thick on carbon steel

Precision cut parts with tolerances held to ±0.005" (depending on material and thickness)

Special beam conditioning which allows for better cuts on thick sheets

Linear motor drives

2.5 G acceleration

High production run capability

3.3.3 MITSUBISHI 2000 WATT CO2 LASER CUTTER

Capable of holding 5' x 10' sheets

Continuous wave or pulsed laser capabilities

Cuts up to 1/2" thick on mild steel

Precision cut parts with tolerances held to ± 0.005" (depending on material and thickness)

3.3.4 MITSUBISHI 1600 WATT CO2 LASER CUTTER

Capable of holding 4' x 4' sheets

Continuous wave or pulsed laser capabilities

Cuts up to 3/8" thick on mild steel

Precision cut parts with tolerances held to ±0.05" (depending on material and thickness)

Low volume, small parts production.

Non-metal capabilities: plastic, plexiglass, wood etc.

3.3.5 LUMONICS 400 WATT & 500 WATT YAG LASER SYSTEMS (2 SYSTEMS)

Laser welder/cutter

Utilizes fiber optics beam delivery to produce exceptionally precise, clean welds

Pulsed laser cutting

Laser welding with minimal heat distortion of parts

Precision cut parts with tolerances held to ±0.002"

Precision hole drilling

Flat and rotary welding capabilities

3.4 LASER MACHINING OPERATIONS AND MACHINES

Laser machining has been introduced in different ways. For example, there is laser cutting, laser welding, laser drilling, laser heat treating, laser scoring and laser scribing. Each of these ways has a different definition from each other according to the task that will be performed in the process.

3.4.1 LASER BEAM MACHINING PROCESS

Laser beam machining uses the light energy from a laser to remove material by vaporization and ablation. The setup for LBM is illustrated in Figure 3.1. The types of lasers used in LBM are carbon dioxide gas lasers and solid states lasers (of which there are several types). In laser beam machining, the energy of the coherent light beam is concentrated not only optically but also in terms of time. The light beam is pulsed so that the released energy results in an impulse against the work surface that produces a combination of evaporation and melting with the melted material evacuating the surface at high velocity.

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LBM is used to perform various types of drilling, slitting, slotting, scribing and marking operations. Drilling small diameter holes is possible. For larger holes, above 0.50 mm diameter, the laser beam is controlled to cut the outline of the hole. LBM is not considered a mass production process, and it is generally used on this stock. The range of work materials that can be machined by LBM is virtually unlimited. Ideal properties of a material for LBM include high light energy absorption, poor reflectivity, good thermal conductivity, low specific heat, low fusion heat and low vaporization heat. Of course, no material has this ideal combination of properties.

The actual list of work materials processed by LBM includes metals with high hardness and strength, soft metals, ceramics, glass and glass epoxy, plastics, rubber cloth and wood. Figure 3.2 shows schematics of a mask projection technique that can be used to define machining geometries. The mask is inserted into the expanded part of the beam where the laser fluence is too low to ablate the mask. The mask geometry is de magnified through the lens and projected onto the work piece. This approach can be used to machine multiple holes simultaneously.

Figure 3.1: Laser Beam Machining

Figure 3.2: Schematic of excimer laser and mask projection technique

Example 3.1

Describe the principle of Laser beam machining (LBM).

Solutions:

Laser beam machining (LBM) uses the light energy from a laser to remove material by vaporization and ablation. The types of lasers used in LBM are carbon dioxide gas lasers and solid states lasers (of which there are several types). In laser beam machining, the energy of the coherent light beam is concentrated not only optically but also in terms of time.

Example 3.2

What are the ideal properties of a material for LBM?

Solutions:

The ideal properties include high light energy absorption, poor reflectivity, good thermal conductivity, low specific heat, low fusion heat and low vaporization heat. The actual list of work materials processed by LBM includes metals with high hardness and strength, soft metals, ceramics, glass and glass epoxy, plastics, rubber cloth and wood.

3.4.2 LASER CUTTING PROCESS

This process is defined as a machining process in which a laser passes over the material being cut. The beam vaporizes the material and the path of the beam determines the shape that is cut. There are two variables that should be considered in this process which are the specification of the object that will be cut and the speed of cutting.

 

(a) (b)

Figure 3.3: (a) Laser cutting equipment and (b) laser cutting process

Figure 3.3 shows a laser cutting process that is used in labs and industry usages. This particular machine is used primarily to create architectural models out of plastic. It has a cutting area of 3 feet by 2 feet, but larger machines have cutting areas of 8 feet by 4 feet. The major components are the gas tanks, the laser plotter itself and the controller. The gas tanks are provided with a nitrogen gas that breaches through the material. The laser cutting process starts with creating a drawing object on a PC using graphic software (mostly Corel software). Also, objects can be created by using Auto Cad program and save the file as a DXF format file. After the object is created, the process is ready to perform after setting up the laser cutting machine. The laser cutting is used in different applications in the industry and technology. Some examples include, flat panel displays, optical glass, telecommunications, hard disks/storage disks, biotechnology, glass wafer, cuts to final size in online glass production and other types of flat glasses.

Example 3.3

Describe the laser cutting process that involves in industry.

Solutions:

The laser cutting process starts with creating a drawing object on a PC using graphic software (mostly Corel software). Also, objects can be created by using Auto Cad program and save the file as a DXF format file. After the object is created, the process is ready to perform after setting up the laser cutting machine.

3.4.3 LASER DRILLING PROCESS

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Laser drilling is the process of repeatedly pulsing focused laser energy at a specific material. The drill beam can drill in every difficult locations or areas of materials and the holes that are made by the laser drilling process can be drilled with reliable and consistently good in quality or performance. The picture below illustrates the laser drill process. There are many benefits associated with the use of laser drilling. First of all, with laser drilling there is no drill breakage or tool wear. Also with laser drilling these are no limitations on the hole sizes or shapes that the operator can create. Laser drilling, also allows the operator to drill on angled and curves surfaces as well as on both hard and soft materials. The common applications of laser drilling are in aerospace where cooling holes needs to be formed, nozzle guide vanes, combustion rings and engine blades are common components drilled with lasers. The programmable nature of laser drilling allows for every high speed drilling applications where many thousands of holes are required in short cycle times. By this, laser drilling acquits a very important role in industry and technology due to the mass usage of it in these fields.

Figure 3.4: Laser Drilling Process

3.4.4 LASER HEAT TREATING PROCESS

A surface alteration process created to change the microstructure of metals by controlled heating and cooling. The laser, because of its ability to pinpoint focus its energy, can heat treat small sections or strips of material without affecting the metallurgical properties of the surrounding area. Laser heat treating is best known in the use of industry due to its advantages and benefits. Some of the advantages include precision control of heat input to localized areas minimum distortion, minimum stress and cracking, self quenching, requires no quenching medium and inherently time efficient process. These advantages make this process to be used widely in industry and technology.

Figure 3.5: Laser heat treating process

Example 3.4

What is the advantage of using laser heat treating on the workpiece?

Solutions:

The advantages include precision control of heat input to localized areas minimum distortion, minimum stress and cracking, self quenching, require no quenching medium and inherently time efficient process.

EXERCISE 3.1

1. What is the purpose of using laser drilling?

2. What is the advantage of using laser cutting compare to other cutting method?

3. Why laser beam machining cannot be used for larger holes?

SUMMARY

In this chapter, we have studied the types of laser machining including laser beam machining, laser cutting, drilling and heat treating process. This unit also discusses the suitable applications on each laser machining types. For an example, Laser Beam Machining can perform various types of drilling, slitting, slotting, scribing and marking operations. This type of machining can be used in electronic industry and sheet metal industry because it can help reduce a cost of the operations.