Surface Roughness Measurement

Abstract          :

 

            This report is to obtain the value of surface roughness of the piston cylinder. In the order to gather necessary information about this laboratory report, some procedures were carried out at the Metrology laboratory. The result of the surface roughness is obtained by the Centre Line Average (CLA) or Roughness Average (R_a) method using a computerize Roughness Measuring Machine.

 

Introduction    :

 

The development of modern technologies has called not only for improved control of dimensional accuracy but also of the texture and geometric from of both working and non-working surfaces of components. There are three main factors which have made the control of surface texture important: fatigue life, bearing properties and wear. Most bearing are rotary in nature and it is obvious that roundness is an important geometric property of the component parts and roundness can be controlled only by measurement.

 

Types of Surfaces

 

Surface

A surface is a boundary that separates an object from another object or substance.

 

Nominal Surface

A nominal surface is the intended surface. The shape and extent of a nominal surface are usually shown and dimensioned on a drawing. The nominal surface does not include intended surface roughness.

 

Real Surface

A real surface is the actual boundary of an object. It deviates from the nominal surface as a result of the process that created the surface. The deviation also depends on the properties, composition, and structure of the material the object is made of.

 

Measured Surface

A measured surface is a representation of the real surface obtained with some measuring instrument. This distinction is made because no measurement will give the exact real surface. Later portions of this manual describe many different types of measuring instruments.

 

 

 

 

 

 

Objective        : To obtain the value of surface roughness of a component by Centre Line

                           Average (CLA/Ra) method using Computerized Roughness Machine.

 

Apparatus :

 

 

 

                     

 

   Roughness Measuring Machine                                    Specimen  (cuboids block)

                      System.

1. A Roughness Measuring Machine System (Surface GV-600; Mitoyo Auto Leveling Table.
2. A Specimen-Piston.
3. A Planimeter.

 

Theory           :

 

                  A surface can never be perfectly smooth and will always have two components of surface texture namely roughness and waviness as shown in Figure 1. They may vary from fine to coarse according to the machining.

 

                 

 

 

Surface texture includes roughness and waviness. Many surfaces have lay: directional striations across the surface.

 

Roughness

Roughness includes the finest (shortest wavelength) irregularities of a surface. Roughness generally results from a particular production process or material condition.

 

Waviness

Waviness includes the more widely spaced (longer wavelength) deviations of a surface from its nominal shape. Waviness errors are intermediate in wavelength between roughness and form error. Note that the distinction between waviness and form error is not always made in practice, and it is not always clear how to make it. New standards are emerging that define this distinction more rigorously as developed in later sections.

 

Lay

Lay refers to the predominant direction of the surface texture. Ordinarily lay is determined by the particular production method and geometry used.

Turning, milling, drilling, grinding, and other cutting tool machining processes usually produce a surface that has lay: striations or peaks and valleys in the direction that the tool was drawn across the surface. The shape of the lay can take one of several forms as shown below. Other processes produce surfaces with no characteristic direction: sand casting, peening, and grit blasting. Sometimes these surfaces are said to have a non-directional, particulate, or protuberant lay.

 

A means of measuring surface finish that is normally used by ISO is the CLA method. It measures the average values of the departures of both what are above and below the centre line of the surface through a prescribed sample length L. The mean result of several sampling length taken consecutively will give the actual roughness value of the surface of the component.

 

 

Center Line

The center line of a profile is the line drawn through a segment (usually a sample length) of the profile such that the total areas between the line and the profile are the same above and below the line.

This concept is little used in modern instruments; it mainly served as a graphical method for drawing a mean line on the output of a profile recording instrument with no built-in parameter processing.

                                       Formula used

 

=Sum of Area above and below centerline

L     = Sample Length

 Vertical Magnification.

 

 

Procedure       :

1.      Select a cut off wavelength of 0.8mm on the machine. Set the machine to a Vertical Magnification of 2000 and Horizontal Magnification of 50.

2.      Place the component on the Auto Leveling Table at a suitable position such that when the pick-up head is lowered, its stylus contacts the surface of the specimen.

3.      Set the machine ready to record the measurement.

4.      Obtain the roughness profile graph for the specimen.

5.      Manual process:

                                                                                I.            Draw the centerline on the profile graph.

                                                                             II.            Measure the areas above and below the centerline using a digital planimeter. Take at least two measurements.

                                                                           III.            Calculate the CLA value.

6.      Compare the computerized with the manual the calculated result.

 

Result        :

 

Result of value of Roughness Average (R_a) using a computerized Roughness Measuring Machine:

1.      Speed              = 0.500mm/s

2.      Length (L)        = 0.8mm

3.      Range               = 600µm

4.      Pre-travel length           = 0.400mm

5.      Amplitude transmittance            = 50%

6.      Low-band cut off                      = 0.800mm

7.      Filter                                        = Gauss

8.      R_a                                             = 3.40µm

 

 

 

 

Result of Roughness Average (R_a) using by the Centre Line Average (CLA)

 

Aa (cm2)	Ab (cm2)
5.2	5.3
5.3	4.5
4.7	5.0

 

 

 

 

 

Length = 14cm

 

For Aa = 5.2 and Ab = 5.3,

Center Line Average                = ∑A / (L × M_V)

                                                = (5.2 + 5.3) / (14 × 2000)

                                                = 3.75 × 10^-4 cm

                                                = 3.75µm

 

For Aa = 5.3 and Ab = 4.5,

Center Line Average                = ∑A / (L × M_V)

                                                = (5.3 + 4.5) / (14 × 2000)

                                                = 3.5 × 10^-4 cm

                                                = 3.5µm

 

For Aa = 4.7 and Ab = 5.0,

Center Line Average                = ∑A / (L × M_V)

                                                = (4.7 + 5.0) / (14 × 2000)

                                                = 3.46 × 10^-4 cm

                                                = 3.46µm

 

 

 

 

Discussion      :

 

1.      Comment on any vibrations in the results for the measured profile?

The roughness profile includes only the shortest wavelength deviations of the measured profile from the nominal profile. The roughness profile is the modified profile obtained by filtering a measured profile to attenuate the longer wavelengths associated with waviness and form. Optionally, the roughness may also exclude (by filtering) the very shortest wavelengths of the measured profile which are considered noise or features smaller than those of interest.

 

2. What are the possible errors involved?

Errors result from large scale problems in the experimental such as errors in machine tool ways, guides, or spindles, insecure clamping, inaccurate alignment of a work piece, or uneven wear in machining equipment. Error is on the dividing line in size scale between geometric errors and finish errors.

 

3. What are the necessary precautions?
• During the experimental some precautions must be taking such as setting up the specimen from moving during the experiment.
• Make sure the trace profile just nice on the line of the specimen surface if not this will affect the resultant or may damage the trace profiling instrument.
• By using this Computerized Roughness Measuring Machine the operator should knows to operate this machine to make this experiment easier.

 

 

Conclusion         :

 

Roughness is of significant interest in manufacturing because it is the roughness of a surface (given reasonable waviness and form error) that determines its friction in contact with another surface. The roughness of a surface defines how that surfaces feels, how it looks, how it behaves in a contact with another surface, and how it behaves for coating or sealing. For moving parts the roughness determines how the surface will wear, how well it will retain lubricant, and how well it will hold a load.

 

 

References         :

1. Metrology of Engineers; J.F.W.Galver & C.r shotbolt.
2. Industrial Metrology: Surfaces and  Roundness. G.T. Smith. Springer-Verlag, 2002. 
3. Manufacturing Engineering and Technology: Serope Kalpakjian.
4. Metrology and Properties of Engineering Surfaces : Evaristus Mainsah, Jim A. Greenwood, Derek G. Chetwynd - Technology & Engineering - Kluwer Academic Publishers (1998)

 

TOOL ENGINEER

 

INTRODUCTION

 

 

            What is a tool engineer? Since the advent of modern mass production a new field in engineering has become more and more apparent. Today it has attained a professional recognition comparable to that of older fields in engineering. This new field is called tool engineering.

 

 

THE DEVELOPMENT OF TOOL ENGINEER

 

 

            Modern mass production dates from the first decade of this century. It replaced the long established factory system, which was a mere massing of men and tools with little emphasis on planning and engineering principles. At first, this new system caused bitter social and political hostility but it’s basic worth was soon recognized. This led to an efficient movement in industries and time-study and similar methods became prominent.

 

            This new field is essential in metalworking industries, such as automobile and aircraft manufacture. It is also important in industries that manufacture plastics and textile goods, and other non-metal products. Furthermore, mass production is no longer necessary for its application. Now in moderate production good use can be made of the methods of tool engineering. In fact, different branches of industry are constantly applying these methods for better efficiency and greater profit.

 

            In this age of specialization, the tool engineer has broad and vital duties, although tool engineer is considered a specialist. Their importance makes them a respected member of the engineering profession. Most significantly, the field of tool engineering is never static. It is constantly improving and the tool engineer must grow with it or risk becoming a liability.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TODAY’S TOOL ENGINEER

 

 

            According to Webster’s New International Dictionary, second edition, tool engineer is ‘ a division of industrial engineer whose function is to plan the processes of manufacture, develop the tools and machines, and also integrate the facilities required for producing given products with minimal expenditure of time, labor and materials’.

 

            This definition was interpreted at through consultation of the dictionary’s editors with officials of the American society of Tool Engineers, an organization founded in 1932. There are three basic parts that require expansion and they are;

 

1. Planning the processes of manufacture.

i.                     Studying the design of the products with a view toward improving the product’s economical manufacture.

ii.                   Determining the most suitable materials for the product.

iii.                  Roughly developing the best arrangement of equipment and sequence of operations for efficient processing the product.

iv.                 Estimating the rough costs of materials, tools, machines, and production techniques, and holding them to a minimum level.

 

2. Developing the tools and machines.

 

i.                     Determining if machines and tools on hand can be used or adapted for efficient processing of the products.

ii.                   Adapting those machines and tools found usable.

iii.                  Designing new machines and tools as necessary for the job.

iv.                 Investigating the market for machines and tools necessary to the job and purchasing them.

 

 

3. Integrating the facilities required for producing given products with minimal expenditure of time, labor, and materials.

 

i.                     Developing detailed arrangements and sequence of operations.

ii.                   Scheduling rate of production and significant dates, including starting and completion dates.

iii.                  Making route sheets that completely describe the sequence of operations and desired flow of work.

iv.                 Making operator instructions sheets that completely describe the steps of operation of each machine.

v.                   Assembling bills of material that give all the information necessary for purchasing or drawing from stock.

       

            Even though the duties listed as above are in the realm of tool engineering, they overlap into other fields as well. Product engineering, machine, tool, and gage designing, metallurgical engineering, cost accounting, purchasing, plant layout and methods engineering are all distinct activities in quantity manufacturing, yet the tool engineer has a hand in each. They must therefore have a working knowledge in other fields, especially in plant layout and applied mechanics, besides having a thorough background in the design of tools, machines, and other production equipment, and their many applications.

TOOL ENGINEER’S DUTIES

 

 

From Design to Finished Products

 

 

            At this point, a brief narrative of the tool engineer’s duties is necessary to show his relationship with others in production and to emphasis their overall importance.

 

            An idea of a product is conceived and presented to the product engineer, who designs a product based on the idea. The idea may come from a member of the sales force, engineering staff, and production department or from any responsible source. Arriving at decision as to whether the proposed product has a market is a subject in itself. Surveys of the public usually conducted and information gathered concerning competitive products, existing patents, and any available technical data. Even at this stage, tool engineer may be brought in for technical advice.

 

            The design of products nowadays entails a great amount of research and development. During the latter stages of development, the tool engineer is usually consulted. After studying the design of the product, tool engineer may suggest changes to promote a more economical manufacture, for instance, standardizing hole dimension or gear size. Tool engineer may also advise that manufacture of the product would not be wise, due to excessive production costs.

 

            This conclusion is based on a rough estimate of such costs as tools, machines and other production equipments including raw materials. Also involved is a rough layout (on paper) of the best equipment arrangement and sequence of operations. With the help of the plant layout engineer, methods engineer, and others, an experienced tool engineer can readily collect the data on which to make this decision.

 

 

Providing the Equipments

 

 

            Once a product is designed and considered economically or manufacture, the tool engineer must provide the tools and machine equipment to process it. This phase of production is crucial and complex. Two major factors affect tool engineer’s judgments are, the ultimate total volume of the product and its quality in the sense that the degree of tolerance and grade of materials desired. By knowing the volume and quality of the products, tool engineer can decide whether or not new machinery and tools better suited for production that what the tool engineer has been constructed to do.

 

            For instance, high volume requirements would mean that the tool engineer could purchase comparatively expensive equipments which would process the products more efficiently and economically in the long run than his their own equipments. In the other hand, if high quality is also required, probably the tool engineer would decide that they must adapt the tools and machines at their disposal to keep overall production economically. Tool engineer’s next problem then would be to adapt their equipments to meet the high quality requirements. If the tool engineer fail to do this, they are forced to purchase what they need.

 

            However, no outside source may be able to meet their specifications and they must draw up plans for the manufacture of new design equipments. Sometimes, tool engineer might not find an outside source to build their new design equipments. So, they must do with what they have by making arrangement and modification. Many other problems arise during this phase of production that requires the tool engineer to bring all their experience and knowledge into play.

 

 

Planning the Final Phase

 

 

            After the necessary equipments have been provided, the final phase of production planning begins. Adequate floor space, lighting, and power are allotted. A detailed arrangement of machinery and sequence of operations is established and the equipments installed. Here, the tool engineer works with the process engineer. Their chief aim is to build in coordination so that neither time nor manpower is wasted. Working plans, bills of material, operator instruction sheets, route sheets, and many more are drawn up and distributed. Men are selected and if necessary will be given training.

 

            Actual production can commence when the raw material for the product, and all other needed materials, are on hand. The tool engineer’s duty now is to follow up on their work, making changes wherever he sees room for improvement, until they are really satisfied.

 

 

Equipments Selection

 

 

            All equipment used in the manufacture of a product is called production equipment. Power-driven machinery is an outstanding example of production equipment.

 

 

 

 

Idea for product

                       

Finished product

Processing the product

Developing and selecting the production equipment

      

 

Figure 1. Operations flow from the initial idea to the finished product.

 

 

 

 

 

            Tools are called production equipments. Besides machine tools, they include jigs, fixtures, patterns, moulds, dies, cutting tools, tool holders, checking fixtures, gages, and a number of small auxiliary tools necessary for a complete tooling-up operations. Materials handling equipment, such as hand trucks, cranes, hoists, and conveyors are also classified as production equipments. Development of machines and tools is based initially on product volume and product quality desired. When these factors are decided upon-usually by management and a range of equipments, based on cost and general performance is thereby determined, selection of equipments within this range can be made.

 

 

Influencing Factors for Tools Selection

 

 

            The following considerations greatly affect any decision the tool engineer makes. They are stated as below,

 

 

1.       Sufficient production capacity. In the context of power driven machinery especially, careful study of setup, loading, and cycling time is indicated.

2.       The best possible way of operation. In other words, the equipment must be as simple and functional as it can be, with only minimum moving parts.

3.       Providing necessary accuracy. The product must meet the required tolerances by the product engineer.

4.       Acceptable depreciation and upkeep costs

5.       Adaptability for future processing of products with a different design. .

6.       Requirement of a minimum labor, especially skilled labor. For many applications nowadays, machines are sought that have a maximum number of automatic devices, which reduce the chance of human error.

 

 

Concession of Tool Engineer

 

 

            Sometimes tool engineers are not able to purchase or adapt production equipment to suit their entire initial requirement. They must always be prepared to make concessions. A detailed analysis will usually show what requirements can be overlooked without seriously raising the overall cost or threatening the quality of the product. Since there is a host of variables involved, a good tool engineer must exercise careful judgment and, again rely on their knowledge and experiences.

 

 

 

 

 

 

 

 

 

 

 

 

TOOL ENGINEER’S APPROACH

 

 

Empirical Versus Analytical Approach

 

 

            The emergence of tool engineering as a field into itself implies the use of exact methods in solving problems within its field. The passage of time and division of job responsibility will tend to cause the development of exact methods. In the early years of mass production, shop supervisors, tool room foreman, master mechanics, and acted like tool engineer, as a matter of course. In general, what they accomplished did not call as tool engineering and also did not recognize their collateral work could be approached anilitycally. In that respect, they were not tool engineer.

 

 

            As a result of production planning was often incomplete, inexact, and devious, especially as compared to present standard. Coordination among the various shops and on the assembly line itself was often less than smooth, with much wasted motion and loss of time. This inefficiency and lost of time meant rising costs. We must remember, however, that thirty to forty years ago total quantities produced weren’t so great, nor labor so costly, as they are presently. More, men in industry then did not have the means at their disposal to measure and compare with a view towards their production equipments and processes.

 

 

Recognition of Planning and Analysis

 

 

            When problems arose in tool engineering before it became a distinct field, the men involved would rely on their experience and knowledge in their own specialties to solve problems. Even though sometimes these solutions weren’t excellent, often they were makeshift, and good solutions weren’t recorded in detail. As time passes, these all will change. Slowly, the values of careful planning and analysis were recognized. It became economical to do what tool engineer proposed. They presented figures and plans that clearly showed why one production process or machine was better than another for manufacturing the product under considerations. Tool engineer reduced guesswork to a minimum and removed most of the gamble in production planning. When management found that they could even improve the quality of the product with no increase in cost, tool engineering was here to stay.

 

            Naturally we are indebted to the pioneers in tool engineering for advancing the analytical approach to quantity production. Today, however the tool engineer has not abandoned the empirical approach. Sometimes it is more advantageous for tool engineer to experiment than analyze. As for an example, when adapting their production equipment it might prove simpler to try various setups than work them out on a drawing board.

 

            Since tool engineering is comparatively new, any gaps in analytical methods must be bridged by using empirical methods. Also, there may be some production problems where solution by detailed planning and analysis isn’t warranted. An approximate solution by practical methods might be more satisfactory. Cost is usually the reason, since more expense is involved in conducting the analytical method.

 

 

Combination of Analytical and Empirical

 

 

            Today, the wise tool engineer combines the analytical approach with the empirical. Always, they strive to manufacture their product to be quantity required as economically as possible without endangering its quality. By whatever means, this manufacture can best be accomplished, is the duty of tool engineer.

           

SUMMARY

 

            Tool engineering is classified under mechanical engineering as a whole. It is one of the most important fields which make that particular person to be known as a tool engineer. Nowadays, the development of tool engineer is increasing radically. More and more machinery are invented each days to improve the productivity and also to ease human work. So, the presence of tool engineer made these developments a reality. Even though the title given to the engineer is specifically as a ‘tool engineer’, it does not mean that they are only involved with tools and machines.

 

What lies beyond the title ‘tool engineer’ is more that what we could have expected. As mentioned above, the work of a tool engineer is not a one man job, but dramatically the burdens are carried by a single person. It is the same person who carries out multi task job with full responsibility and this is what made them the respected person among all. Lastly, engineers are the one who becoming the backbones of a country.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Laser-Beam Machining (LBM)

Introduction

 

Recently, laser beam machines have been widely used for cutting a metal. In the case where the metal is made of nonferrous metals such as aluminum, brass, stainless steel, the machining condition for executing the cutting operation is modified when piercing is executed at the cutting start point, and when the cutting operation after that is executed. For example, an oxygen gas is used as an assist gas in piercing; on the other hand, an inert gas such as nitrogen gas is used as an assist gas in cutting.

 

Laser-beam machining (LBM) is accomplished by precisely manipulating a beam of coherent light to vaporize unwanted material. LBM is particularly suited to making accurately placed holes. It can be used to perform precision micromachining on all microelectronic substrates such as ceramic, silicon, diamond, and graphite. Examples of microelectronic micromachining include cutting, scribing & drilling all substrates, trimming any hybrid resistors, patterning displays of glass or plastic and trace cutting on semiconductor wafers and chips.

 

A laser beam machine can make quality of machining almost constant in such manner that a first reflecting means in a first beam guide portion is moved and driven so as to maintain a length of an optical path of laser beam to be almost constant in spite of a moved position of a machining head. According to the invention, a second reflecting means for catching laser beam in a second beam guide portion is located at a position facing the first reflecting means, thereby relatively shortening a length of the optical path between the first and second reflecting means and shortening the whole length of the optical path, and maintaining quality of machining with laser beam good.

 

 

 

 

Lasers can be used to cut, drill, weld and mark. LBM is particularly suitable for making accurately placed holes. A schematic of laser beam machining is shown in Figure below:

 

 

 

 

Fig : (a) Schematic illustration of the laser-beam machining process. (b) and (c) Examples of holes produced in nonmetallic parts by LBM.

 

 

 

 

 

 

 

 

 

 

 

 

 

General Applications of Lasers in Manufacturing

 

 

 

 

 

 

 

 

 

How Laser Beam works

 

The solid-state laser utilizes a single crystal rod with parallel, flat ends. Both ends have reflective surfaces. A high-intensity light source, or flash tube surrounds the crystal. When power is supplied by the PFN (pulse-forming network), an intense pulse of light (photons) will be released through one end of the crystal rod. The light being released is of single wavelength, thus allowing for minimum divergence.

 

One hundred percent of the laser light will be reflected off the rear mirror and thirty to fifty percent will pass through the front mirror, continuing on through the shutter assembly to the angled mirror and down through the focusing lens to the workpiece.

 

The laser light beam is coherent and has a high energy content. When focused on a surface, laser light creates the heat used for welding, cutting and drilling.

 

The workpiece and the laser beam are manipulated by means of robotics. The laser beam can be adjusted to varying sizes and heat intensity from .004 to .040 inches. The smaller size is used for cutting, drilling and welding and the larger, for heat treating.

 

Types of Laser

 

The types of laser used in LBM are basically the carbon dioxide (CO2) gas lasers. Lasers produce collimated monochromatic light with constant wavelength. In the laser beam, all of the light rays are parallel, which allows the light not to diffuse quickly like normal light. The light produced by the laser has significantly less power than a normal white light, but it can be highly focused, thus delivering a significantly higher light intensity and respectively temperature in a very localized area.

 

Lasers are being used for a variety of industrial applications, including heat treatment, welding, and measurement, as well as a number of cutting operations such as drilling, slitting, slotting, an marking operations. Drilling small-diameter holes is possible, down to 0.025 mm. For larger holes, the laser beam is controlled to cut the outline of the hole.

 

The range of work materials that can be machined by LBM is virtually unlimited including metals with high hardness and strength, soft metals, ceramics, glass, plastics, rubber, cloth, and wood.

 

LBM can be used for 2D or 3D workspace. The LBM machines typically have a laser mounted, and the beam is directed to the end of the arm using mirrors. Mirrors are often cooled (water is common) because of high laser powers.

 

  

Laser cutting

 

Different types of lasers are available for manufacturing operations which are as follows:

·        CO₂ (pulsed or continuous wave): It is a gas laser that emits light in the infrared region.  It can provide up to 25 kW in continuous-wave mode.

·         Nd:YAG:  Neodymium-doped Yttrium-Aluminium-Garnet (Y₃Al₅O₁₂) laser is a solid-state laser which can deliver light through a fibre-optic cable. It can provide up to 50 kW power in pulsed mode and 1 kW in continuous-wave mode.

 

 

Below is a simple representation of how a CO₂ laser beam is generated.

 

 

 

 

 

Types of LBM

 

1- Laser Drilling

 

Drilling is one of the most important and successful applications of industrial lasers. Laser hole drilling in ceramic, silicon and polymer substrates is widely used in electronics industry. Laser drilling of metals is used to produce tiny orifices for nozzles, cooling channels in air turbine blades, via drilling of circuit board, etc.

 

Holes less than 0.25mm in diameter are difficult to drill mechanically, laser drilling offers good choices for small hole drilling, especially for hard and brittle materials, such as ceramics and gemstones. Large holes can be drilled by trepanning, i.e., by overlappingly drilling the circumference of a circle to form a large hole. High throughput of hole drilling are realized by mask projection and automation.

 

Table 3.1 compared laser drilling with electrical discharge machining (EDM) and traditional mechanical drilling. EDM is limited to electrically conductive materials, while drill wear and breakage is a big concern in mechanical drilling. Laser drilling is effective for small hole drilling, they can be flexibly automated.

 

	Mechanical Drilling	Laser Drilling
Advantages	Large diameter, large depth, low equipment cost	High throughput, no drill wear/breakage, noncontact, small HAZ, wide range of materials, low operating cost
Disadvantages	Drill wear/breakage, low throughput, difficult to drill small holes, limited materials	Hole taper, limited depth and diameter, recast layer

Comparison of  laser drilling and mechanical drilling

 

 

Laser drilled holes usually have tapers, in example the hole is not perfectly straight. Also a redepotion area may exist around the hole, because laser drilling is realized through violent phase change, the material becomes melted, then ablated, then cool down and become solid state again. Redeposition is serious for long pulses (pulse duration > 10 nanosecond. It was found that tapering and redeposition can be lowered by suitably choose shorter wavelengths and pulse durations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

How Laser Drilling works

 

 

In laser drilling, a short laser pulse with high power density feeds energy into the workpiece extremely quickly, causing the material to melt and vaporize. The greater the pulse energy is, the more material is melted and vaporized. Vaporization causes the material volume in the drilled hole to increase suddenly, creating high pressure. The vapor pressure expels the molten material from the hole. Spatter and vapor shoot upward in the direction of the processing optics. Once the laser beam breaks through to the other side, the spatter and vapor exit through the bottom. To prevent damage to the processing optics, manufacturers design the machines so that there is a large distance between the optics and the workpiece. A coaxial gas flow can also be used to shield the optics from spatter.

 

 

 

 

 

 

2- Laser Cutting

 

Laser cutting is a technology that uses a laser to cut materials, and is usually used in industrial manufacturing. 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,[1] 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.

 

Laser cutting machines can accurately produce complex exterior contours. The laser beam is typically 0.2 mm (0.008 in) diameter at the cutting surface with a power of 1000 to 2000 watts.

 

Laser cutting can be complementary to the CNC/Turret process. The CNC/Turret process can produce internal features such as holes readily whereas the laser cutting process can produce external complex features easily.

 

Laser cutting takes direct input in the form of electronic data from a CAD drawing to produce flat form parts of great complexity. With 3-axis control, the laser cutting process can profile parts after they have been formed on the CNC/Turret process.

 

Lasers work best on materials such as carbon steel or stainless steels. Metals such as aluminum and copper alloys are more difficult to cut due to their ability to reflect the light as well as absorb and conduct heat. This requires lasers that are more powerful.

 

 

 

 

 

 

 

How Laser Cutting Works

 

 

 

 

When a reactive gas such as oxygen is used, it also delivers additional exothermic energy through chemical reaction between the assist gas and the molten material. This chemical reaction produces additional energy that enhances the cutting process. This extra energy can be beneficial to cut thick sections of materials, however, catastrophic oxidation must be prevented to ensure final cutting quality. We see the efficiency and overall quality of laser machining is strongly dependent on the interaction of the gas jet with the workpiece. Also as we mentioned in section 3.1, inert gases are used in laser machining when oxidation need to be reduced.

 

In this section we give a brief review on the recent progress in other aspects of gas jet effects, focusing on nozzle design, jet alignment, effects of pressure and gas purity. Then we present a relative detail description on the effects of shock structure and standoff distance on laser cut quality.

 

 

 

3- Laser Beam Welding

 

Laser Beam Welding (LBW) is a modern welding process; it is a high energy beam process that continues to expand into modern industries and new applications because of its many advantages like deep weld penetration and minimizing heat inputs. The turnby the manufacturers to automate the welding processes has also caused to the expansion in using high technology like the use of laser and computers to improve the product quality through more accurate control of welding processes.

 

Operation

Like electron beam welding, laser beam welding has high power density (on the order of 1 Megawatt/cm²(MW)) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point: penetration is maximized when the focal point is slightly below the surface of the workpiece.

 

LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium. Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry.

 

A derivative of LBW, laser-hybrid welding, combines the laser of LBW with an arc welding method such as gas metal arc welding. This combination allows for greater positioning flexibility, since GMAW supplies molten metal to fill the joint, and due to the use of a laser, increases the welding speed over what is normally possible with GMAW. Weld quality tends to be higher as well, since the potential for undercutting is reduced.

Materials that may be cut

 

A wide range of materials may be cut using a laser beam, however care must be taken in choosing the correct type of laser. Below is a table outlining the suitability of both CO₂ and Nd:YAG lasers for materials likely to be encountered in the course of an average manufacturing business.

 

MATERIAL	CO2	Nd:YAG	BOTH
Mild and Carbon Steel			5
Stainless Steel			4/5
Alloy Steel			4/5
Tool Steel			5
Aluminium Alloys	2/3	4/5
Copper Alloys	1	3
Titanium			4
Plastics	5	0/1
Rubber	4	1
Paper (Gasket ETC)	5	¾
Ceramics			3/4

 

0=Impossible/Dangerous

5=Excellent

 

 

 

 

Safety on Laser Machining

 

    Even though there are advantages from using the laser machining processes in industry and technology, laser is one of the most dangerous tools that can kill users. Here is a list of the danger concerns that users should be aware of:

 

1. Working on Laser machines while the door open may cause damages in the eyes and burn hands. Therefore, a user should close the door of the machine before starts working.

 

2. Lasers produce coherent light which when looked at appears to the eye to have come from a very distant source. Consequently, the image formed on the retina by a laser source is always incredibly small and therefore of very high power density.

 

3. If a laser product is being used to process product, for example cutting, welding and surface treatments, there may also be chemical toxicity risk to address. The processing of organic materials such as thermoplastics is a particular risk that needs careful assessment in the context of local exhaust extraction (LEV) and personal protective equipment (PPE) provision.

 

4. The wavelengths of emitted radiation is determined by and a characteristic of the chemical composition of the ‘lasing’ medium. For example, carbon dioxide lasers emit in the far infrared at a wavelength of 10.6 microns. Some media are capable of being made to ‘lase’ at several wavelengths, organic dye lasers being one such example.

 

5. Additionally, since laser action is essentially an inefficient process, most lasers of class 3B and above will have significant electrical power needs, often at high voltage and three phase. Electrical safety, especially during maintenance and repair, is therefore a significant risk that needs to be adequately controlled by manufacturers and employers that use laser products.

 

Advantage of laser beam machining

 

·        No limit to cutting path as the laser point can move any path.

·        The process is stress less allowing very fragile materials to be laser cut without any support.

·        Very hard and abrasive material can be cut.

·        Sticky materials are also can be cut by this process.

·        It is a cost effective and flexible process.

·        High accuracy parts can be machined.

·        No cutting lubricants required

·        No tool wear

·        Narrow heat effected zone

·        Faster process

·        Useful with a variety of material : metals, composites, plastics, and ceramics

·        More precise

 

Limitations of laser beam machining

 

·        Uneconomic on high volumes compared to stamping

·        Limitations on thickness due to taper

·        High capital cost

·        High maintenance cost

·        Assist or cover gas required