Tungsten Arc Welding (TIG)

Gas tungsten arc welding (GTAW) also known as tungsten inert gas (TIG) welding is a process that melts and joins metals and heating them with an arc established between a no consumable tungsten electrode and the metals. There are shielded gases which act as a protector for welded part from atmospheric contamination. Shielded gas commonly used is an inert gas such as argon, and a filler metal is normally used, even though, auto-genous welds do not require it. A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and plasma

The GTAW is suitable to weld thin sections such as stainless steel and light metals for instances aluminum, magnesium, and copper alloys. The GTAW is comparatively more complex and difficult to master and it needs some skills or technique from welder and furthermore, it is significantly slower than other welding techniques.

 

Figure 3.0.1: GTAW weld area

 

Manual gas tungsten arc welding is often considered the most difficult of all the welding processes commonly used in industry. This is because the welder must use two hands and it’s very difficult to maintain a tungsten electrode and filler rod simultaneously in order to prevent contact between the electrode and the work piece.  The welder has to feed a filler metal into the weld area manually with one hand while, the other act to manipulate welding torch. However not all welds need filler metal for example auto-genous welds which is combining thin materials most notably edge, corner and butt joints.

The separation between the electrode and the work piece is approximately 1.5-3 mm (0.06-0.12 in). Getting both into contact also serves to strike an arc, but this can cause contamination of the weld and electrode. Once the arc is struck, the welder moves the torch in a small circle to create a welding pool, and depends on the size of the electrode and the current. In order to maintain a constant separation between the electrode and the work piece, the operator should moves the torch back slightly and tilts it backward about 10-15 degrees from vertical. 

Welders often develop a technique of rapidly alternating between moving the torch forward and adding filler metal. The filler rod is withdrawn from the weld pool each time the electrode advances, but it is never removed from the gas shield to prevent oxidation of its surface and contamination of the weld. Filler rods composed of metals with low melting temperature, such as aluminum, require that the operator maintain some distance from the arc while staying inside the gas shield. If held too close to the arc, the filler rod can melt before it makes contact with the weld puddle. As the weld nears completion, the arc current is often gradually reduced to prevent the formation of a crater at the end of the weld.

 

 

 

Working Principle

In gas tungsten arc welding operation, the equipment required is includes, a constant-current welding power supply, welding torch utilizing a non-consumable tungsten electrode and also a shielding gas source.

           

a)      Welding torch

     

            Tungsten inert gas (TIG) welding torches are designed for both automatic or manual operation and it was attached with cooling systems whether air or water. The manual torch has a handle while the automatic torch comes with a mounting rack. But both have similar in construction. The angle between the centerline of the handle and the centerline of the tungsten electrode, known as the head angle, which can be varied on some manual torches according to the comfortable of the operator. Air cooling systems are usually used for low-current operations, while water cooling is needed for high-current welding (up to about 600 A). The torches are connected with cables to the power supply and shielding gas source hoses.

The internal metal parts of a torch are made from hard alloys which are copper or brass. This is because to transmit current and heat effectively. The tungsten electrode must be detained definitely in the center of the torch with properly sized collets, and ports around the electrode offer a constant flow of shielding gas. The body of the torch is made of heat-resistant, insulating plastics which casing the metal components, providing insulation from heat and electricity to protect the welder.

The size of the welding torch nozzle depends on the size of the preferred welding arc, and the inside diameter of the nozzle is usually at least three times the diameter of the electrode. The nozzle must be heat resistant and thus is normally made of alumina or a ceramic material, but fused quartz, a glass-like substance offers better visibility. Devices can be inserted into the nozzle for special appliance, such as gas lenses or valves to control shielding gas flow and switches to control welding current.

The filler metals are similar to the metals to be welded, and flux is not used. The shielding is usually argon or helium (or a mixture of the two). Welding with GTAW may be done without filler metals- for example, in the joining of close-fit-joints.

 

b)      Shielding gas

 

 

As with other welding processes such as gas metal arc welding, shielding gases are necessary in GTAW to protect the welding area from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. The gas also transfers heat from the tungsten electrode to the metal, and it helps start and retain a stable arc.

            The selection of a shielding gas depends on several factors. That’s the type of material being welded, joint design, and desired final weld form. Argon is a shielding gas that most normally used for GTAW, it will helps to prevent defects due to a varying arc length. Using argon with alternating current will produce high weld quality and good appearance. Another common shielding gas is helium, which is normally used to increase the weld penetration in a joint, to boost the welding speed, and to weld light metals such as copper and aluminum. A major disadvantage is the difficulty of striking an arc with helium gas, and the decreased weld quality related with a variation of arc length. Argon-helium mixtures are also commonly utilized in GTAW, since they can improve in controlling the heat input while maintaining the benefits of using argon.        

            Usually, the mixtures are made with primarily helium (often about 75% or higher) and a balance with argon. These mixtures will increase the speed and quality of the AC welding of aluminum, and also ease to strike an arc. Another shielding gas mixture, argon-hydrogen, is used in the mechanized welding of light gauge stainless steel, but it utilize are limited because hydrogen will cause porosity, it utilize are limited. In the same way, nitrogen can be added to argon to help stabilizing the austenite in austentitic stainless steels and increase penetration when welding copper. Due to porosity problems in ferritic steels and limited benefits, however, it is not a popular shielding gas additive.

 

Advantages

 

            There are several advantages to GTAW as well.  The welds created by the GTAW process are suitable for high quality and can be achieved in almost every alloy or metal.  Secondly, the welds need little or no cleaning after they are finished.  The precision of the welds is increased due to the fact that the welder can see the arc and the weld pool easily.  The idea that no filler material is transferred during welding is there area minimal amount of spatter.  Welding of this type can be done in numerous positions, and there is no slag produced to leave impurities in the weld

 

Limitation

            Everything is not perfect including GTAW. The GTAW required greater welder deftness than MIG or stick welding and it’s also need lower deposition rates. And finally, for welding thick sections there need more cost.

 

 

Shielded Metal Arc Welding (SMAW)

 

Principle of Process

 

The heat generated melts a portion of the tip of the electrode, of its coating and of the base metal in the immediate area of arc. A weld forms after the molten metal, a mixture of the base metal (workpiece), the electrode metal and substances from the coating of the electrode, solidifies in the weld area. The electrode coating deoxidizes the weld area and provides a shielding gas to protect from oxygen in the environment.

A bare section at the end of the electrode is clamped to one terminal of the power source, while the other terminal is connected to the workpiece being welded. The current usually used in ranges between 50 A and 300 A, power requirement are less than 10kW. The current maybe AC or DC. For sheet metal welding, DC is preferred because of the steady arc is produced.

The polarity of the DC current, the direction of the current flow is very important because the selection is depends on the type of electrode to be welded and the depth of the heated zone. In straight polarity the workpiece is positive and the electrode is negative because it is preferred for sheet metals to produce shallow penetration and for joint with very wide gaps. In reverse polarity, the electrode is positive and deeper weld penetration is possible. In the AC method is suitable for welding thick section and for large diameter electrodes at maximum currents.

 

 

 

 

 

 

 

 

Figure 1: Principle of Shielded Metal Arc Welding (SMAW) Process

 

 

 

 

 

 

Figure 2: SMAW circuit

 

Equipment

Shielded metal arc welding equipment typically consists of a constant current welding power supply and an electrode, with an electrode holder, a work clamp, and welding cables (also known as welding leads) connecting the two.

 

Evaluation of Result

The preferred polarity of the SMAW system depends primarily upon the electrode being used and the desired properties of the weld. Direct current with a negatively charged electrode (DCEN) causes heat to build up on the electrode, increasing the electrode melting rate and decreasing the depth of the weld. Reversing the polarity so that the electrode is positively charged and the work piece negatively charged increases the weld penetration. With alternating current the polarity changes, creating an even heat distribution and providing a balance between electrode melting rate and penetration.

 

 

 

 

 

 

 

Figure 3: 1) DCEN welding result, 2) DCEP welding result

 

The quality problems associated with SMAW include weld spatter, porosity, poor fusion, and shallow penetration. Weld spatter, while not affecting the integrity of the weld, damages its appearance and increases cleaning costs. It can be caused by excessively high current, a long arc, or arc blow, a condition associated with direct current characterized by the electric arc being deflected away from the weld pool by magnetic forces. Porosity, often not visible without the use of advanced nondestructive testing methods, is a serious concern because it can potentially weaken the weld. Another defect affecting the strength of the weld is poor fusion, though it is often easily visible. It is caused by low current, contaminated joint surfaces, or the use of an improper electrode. Shallow penetration, another detriment to weld strength, can be addressed by decreasing welding speed, increasing the current or using a smaller electrode. Any of these weld-strength-related defects can make the weld prone to cracking, but other factors are involved as well.

 

Advantages of the Shielding Arc Welding

a)      The welding process is very simple and versatile.

b)      The process is suitable for workpiece thickness of 3mm-19mm.

c)      The process does not required high skills welder.

 

Limitations of the Shielding Arc Welding

a)      The welding processes are required to clean the slag after each weld bead.

b)      The solidified slags are cause of several corrosion of the weld area and lead to failure of the weld.

c)      The cost and material in the welding process are very high.

 

 

 

 

 

 

 

Safety Aspects of Welding

             

Although welding and cutting operations require special considerations, personnel should be aware of the general health and safety requirements of related fabrication activities. Safe places and systems of work include handling and housekeeping.

 

                               

Figure 1 : The wrong (left) and right (right) way to carry out arc welding processes.

 

Personal Protection.

            Fume will have to be controlled at source, perhaps by local ventilation. Respiratory equipment should not be used until all other possibilities have been eliminated. In general, respiratory protective equipment is used only as an interim measure but there will be circumstances where, in addition to ventilation measures, personal protection may be necessary.

 

Protective Clothing.

Protect persons in the vicinity of the arc by means of non-reflective curtains or screens .

 

 

Figure 2 : Protective Screens.

 

Figure 3 : Protective Clothings.

 

 Arc radiation

            The arc can generate three types of radiation; ultra-violet, visible and infra red (heat) radiation which can be injurious in the following ways,

1. ultra-violet: damage to skin and eyes(inflammation of the cornea and cataracts)
2. visible light: dazzle eyes and impair vision infra-red: damage skin and eyes

Radiation may be direct or reflected from shiny or other reflective surfaces.

 

 

 

Fire and Explosion Hazards

 

There is an inherent hazard associated with gas processes. Additionally, both flames and arcs in welding and cutting may create a fire hazard. When fighting a fire, the appropriate fire extinguisher for the type of material must be used. Class C fires, for example those involving flammable gases such as acetylene, are best extinguished by cutting off the gas supply. Water and foam extinguishers should not be used on fires near to live electrical equipment.

 

Safe Practice and Accident Avoidance

 

            Remove flammable material from the welding area

Cover remaining flammable material with fire resistant material

Before welding, check that the appropriate fire fighting equipment is at hand

After welding, observe surrounding area of the work for an adequate period of time

 

Welding in Confined Spaces.

 

            Special care should be taken in case toxic fumes or gases build up. In gas shielded welding operations, there may be a danger from asphyxiating because of oxygen deficiency. A suitably qualified person should assess the risk, determine the steps required to make the job safe and recommend precautions to be taken during the welding operation itself.

 

Check Equipment for Gas Leaks.

 

            Ensure trained personnel are in attendance to deal with any emergency

Check by rehearsal that the worker can be rescued, should an emergency arise

At the end of work periods, shut off all gas supply valves and withdraw hoses and equipment

 

 

 

 

Awareness of Welding Environments.

 

Noise

            As a general guideline, wherever it is difficult to carry on a conversation, it is likely the noise level is unacceptable. HSE recommendations are that when the noise reaches 85dB(A), employers are required to offer hearing protection to their employees. As continuous exposure for 8 hours or more to a noise level at or above 90dB(A) is injurious, hearing protection is mandatory when this level is reached. Higher levels can be tolerated for short periods but impulsive or peak noise in excess of 140 dB should not, where practicable, be exceeded.

As damaging noise levels can be generated from some welding processes and allied activities, welders will usually need hearing protection. For example, hand grinding may emit noise levels of the order 108dB(A).

 

Vibration

 

            Portable tools which produce excessive vibration, may cause damage to the hands, often called 'white finger' (Raynaud's phenomenon). As the hazard is particularly acute with tools such as chipping hammers which rely on impact, their use must be minimised.

 

Designation of hazardous areas

 

            It may be necessary to restrict entry to the work area to authorised persons wearing suitable protection. Warning signs will be required for the following hazards:

For welding and cutting processes, where the arc is exposed, the warning for eye protection should refer to the hazard of arc radiation

'Ear Protection Areas' where 8 hours exposure to noise levels is at, or above, 90 dB(A).

 

 

 

 

 

Plasma – Arc Welding

          Plasma – arc welding (PAW) developed in the 1960s, is produced a concentrated plasma arc and aimed at the weld area. The temperature of this process is stable and reaches as high as 33,000 ^oC. A plasma torch is ionized hot gas, composed of nearly equal numbers of electrons and ions. Plasma cutting usually used to cut steel and other metals using a plasma torch. In this process, an inert gas is blown at high speed out of a nozzle or orifice, at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut, turning some of that gas to plasma. This plasma is sufficiently hot to melt the metal and moving sufficiently fast to blow molten metal away from the cut. The result is very much like cutting butter with a hot jet of air.

Working Principle

There are two methods of plasma arc welding. Firstly, transferred – arc, the process happened which the workpiece made the part of the electrical circuit, so the transferred arc from electrode to the workpiece occurred. Meanwhile for second process is non – transferred, the arc occurred between the electrode and the nozzle, and the heat is carried to the workpiece by the plasma gas. The arc used a two cycle approach to producing plasma. First, a high-voltage, low current circuit is used to initialize a very small high intensity spark within the torch body, thereby generating a small pocket of plasma gas. This is referred to as the pilot arc. The now conductive plasma contacts the workpiece, which is the anode. The plasma completes the circuit between the electrode and the workpiece, and the low voltage, high current now conducts. If the plasma cutter uses a high frequency/high voltage starting circuit, the circuit is usually turned off to avoid excessive consumable wear. The plasma, which is maintained between the workpiece and electrode, travels at over 15,000 km/h. For new types plasma welding machines operational capabilities. There are likes,

Ø      Manual plasma-arc welding is usually modified to non key hole fusion type welding.

Ø      Mechanized plasma-arc welding is required for high current plasma-arc applications such as making key hole-mode welds or high current filler passes. Metals welded by these processes: Weld unalloyed, low alloy and high alloy steels, nickle, copper, titanium, zircon and their alloys and special
materials.

Ø      Powder Surfacing (PTA) is used for wear facing and corrosion resistance applications using a wide variety of cobalt, nickel, tungsten carbide, stellite and iron based alloys in powder form.

Figure 1 : Two types of plasma arc welding, left picture transferred arc, right picture non – transferred arc.

Advantages

         i.            Adding filler metal is accomplished more easily with Paw than LBW or EBW, during process in tolerance to joint gaps and misalignment. It is because although the arc is constricted, the plasma column has a significantly larger diameter than the beam. 

       ii.            Reduced weld time results in less embrittlement by carbide and complrx intermetallic compounds for stainless steel and super alloys.

      iii.            Equalization of distortion stresses results in less residual stress.

     iv.            Weld in a single pass up to 6mm plates in squre butt position and 10mm plates in only two passes.

       v.            Less filler metal required in keyhole mode significantly reduces porosity and less sensitivity in arc length.  

Limitations

           i.            The equipment of plasma welding is more complex and costly, and the need for water cooling of the torch limits how small the torch can be made compare to GTAW (GTAW torches may be gas-cooled and can be made to fit into smaller areas).

         ii.            The process plasma welding is its greater heat input, which produces wider welds and heat-affected zones than LBW and EBW. This may result in more distortion and loss of mechanical properties.

        iii.            Plasma torches need to be bulky, making them uncomfortable for precision manual use.

       iv.            For the plasma welding, a careful balance of current, plasma and filler control is needed.

 

Metal Inert Gas (MIG)

      Gas Metal Arc Welding or GMAW is also known as Metal Inert Gas (MIG). It is an arc welding process which produces coalescence of metals by heating them with an arc between continuous filler metal (consumable) electrode and the work.  Shielding is obtained entirely from an externally supplied gas or gas mixture.  Originally developed to weld aluminum, it has become one of the most popular arc welding processes.

Working Principle     

      This system of welding was developed to weld metals thicker than ¹/₄" that Tungsten Inert Gas (TIG) welding could not weld.  Despite of this matter, MIG welding was limited to only thick metal applications.  However, some adjustments were made and the possibilities for welding various metals were gained. This welding procedure is very close to TIG welding in that an inert shielding gas is used to protect the weld and the arc is maintained between the electrode and the work piece. The difference comes from the fact that the electrode is consumed in MIG welding.  The electrode is actually a long wire that is fed through a hole in the tip of the handle that carries the current to the work piece and supplies a filler metal. The fact that the electrode is continuous makes the welds that are produced very well in quality. There is no need to start and stop to replace an electrode as in SMAW and long welds can be completed in one step.  The entire process can be automated and all welding positions can be used on any thickness of metals.  The process is easy to learn and there is little or no spatter and no slag is created in MIG welding which makes surface preparation for painting very easy.

                         

Figure 1 Welding power Supply and Gas supply (left) and Welding Gun (right)

Advantages

            The usage of MIG brings a lot of advantages that might not be achieved in other welding processes. These advantages really benefits and ease the usage of this welding method. Some of the advantages are listed as below;

a)      Able to be welded on stainless steel, aluminium and mild steel.

b)      Do not require any cleanup as the fusion is clean.

c)      By using this method, it can weld metals at any positions.

d)      The method is simple. First hand user will not have any problem as only one hand is require, no need to hold the filler metal.

e)      Production rate is high, as the process can be continuous; the spool of filler metal will flow continuously during the welding process.

Limitations

            Despite of the advantages carried out by MIG, there are several limitations which make it undesirable under certain circum stances. The limitations of MIG are listed as below;

a)      More expensive and is less portable than some other types of welding, such as SMAW.

b)      Requires shielding gas commonly helium.

c)      The gun is large and the cable is stiff which makes welding tight spaces hard and the gun's size makes it hard to see the arc, which leads to poor welds

d)      For outdoor MIG welding, the breeze must not exceed 5 miles per hour with no screen, or the shielding gas will blow away and will not protect the weld surface.

e)      Not good for thick steel because it doesn’t get the proper penetration.

 

Gas Metal Arc Welding (GMAW)

Introduction

Gas Metal Arc Welding or GMAW is an arc welding process that produces the coalescence of metals by heating them with an arc between continuous filler metal electrode and the workpiece.  Shielding is obtained entirely from an externally supplied gas or gas mixture. The weld area is that shielded by an effectively inert atmosphere of argon, helium, carbon dioxide or various other gas mixtures. The consumable wire is fed automatically through a nozzle into the weld arc. Originally developed to weld aluminum, it has become one of the most popular arc welding processes.

Equipment

 Gas metal arc welding equipment consists of a welding gun, a wire-drive system, a shielding gas supply, and a power supply which pulls the wire electrode from a spool and pushes it through a welding gun. A source of cooling water may be required for the welding gun. In passing through the gun, the wire becomes energized by contact with a copper contact tube, which transfers current from a power source to the arc. A system of accurate controls is employed to required the initiate and terminate the shielding gas and cooling water, operate the welding contactor, and control electrode feed speed. The basic features of MIG welding equipment are shown in figure below. The MIG process is used for semiautomatic, machine, and automatic welding. Semiautomatic MIG welding is often referred to as manual welding.

 

Principle of process

This system of welding was developed to weld metals thicker than ¹/₄" that Tungsten Inert Gas (TIG) welding could not weld.  Despite of this matter, MIG welding was limited to only thick metal applications.  However, some adjustments were made and the possibilities for welding various metals were gained. This welding procedure is very close to TIG welding in that an inert shielding gas is used to protect the weld and the arc is maintained between the electrode and the work piece. The difference comes from the fact that the electrode is consumed in MIG welding.  The electrode is actually a long wire that is fed through a hole in the tip of the handle that carries the current to the work piece and supplies a filler metal. The fact that the electrode is continuous makes the welds that are produced very well in quality. There is no need to start and stop to replace an electrode as in SMAW and long welds can be completed in one step.  The entire process can be automated and all welding positions can be used on any thickness of metals.  The process is easy to learn and there is little or no spatter and no slag is created in MIG welding which makes surface preparation for painting very easy.

 

Evaluation of Result

Two of the most prevalent quality problems in GMAW are dross and porosity. If not controlled, they can lead to weaker, less ductile welds. Dross is an especially common problem in aluminum GMAW welds, normally coming from particles of aluminum oxide or aluminum nitride present in the electrode or base materials. Electrodes and workpieces must be brushed with a wire brush or chemically treated to remove oxides on the surface. Any oxygen in contact with the weld pool, whether from the atmosphere or the shielding gas, causes dross as well. As a result, sufficient flow of inert shielding gases is necessary, and welding in volatile air should be avoided.

 

In GMAW the primary cause of porosity is gas entrapment in the weld pool, which occurs when the metal solidifies before the gas escapes. The gas can come from impurities in the shielding gas or on the workpiece, as well as from an excessively long or violent arc. Generally, the amount of gas entrapped is directly related to the cooling rate of the weld pool. Because of its higher thermal conductivity, aluminum welds are especially susceptible to greater cooling rates and thus additional porosity. To reduce it, the workpiece and electrode should be clean, the welding speed diminished and the current set high enough to provide sufficient heat input and stable metal transfer but low enough that the arc remains steady. Preheating can also help reduce the cooling rate in some cases by reducing the temperature gradient between the weld area and the base material.

 

Safety Aspect

Gas metal arc welding can be dangerous if proper precautions are not taken. Since GMAW employs an electric arc, welders wear protective clothing, including heavy leather gloves and protective long sleeve jackets, to avoid exposure to extreme heat and flames. In addition, the brightness of the electric arc can cause arc eye, in which ultraviolet light causes the inflammation of the cornea and can burn the retinas of the eyes. Helmets with dark face plates are worn to prevent this exposure, and in recent years, new helmet models have been produced that feature a liquid crystal-type face plate that self-darkens upon exposure to high amounts of UV light. Transparent welding curtains, made of a polyvinyl chloride plastic film, are often used to shield nearby workers and bystanders from exposure to the UV light from the electric arc.

Welders are also often exposed to dangerous gases and particulate matter. GMAW produces smoke containing particles of various types of oxides, and the size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, carbon dioxide and ozone gases can prove dangerous if ventilation is inadequate. Furthermore, because the use of compressed gases in GMAW pose an explosion and fire risk, some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.

 

Measuring Matrix screw thread dimensions

Figure 1.0 Profile Projector Machine.              Figure 1.1 Micro Profile Projector Machine

OBJECTIVE

Measuring certain dimension of a matrix screw thread

1. M24  3.0 ISO 6H
2. M5  0.8 6H

 

APPARATUS

Profile Projector Machine, Micro Profile Projector Machine, Specimen (matrix screw of M24  3.0 ISO 6H and M5  0.8 6H)

 

 

 

 

 

 

THEORY

The terminology of screw thread.

• The pitch is the distance between adjacent thread form measured parallel to the thread axis.
• The major diameter is the largest diameter of a screw thread.
• The minor diameter is the smallest diameter of a screw thread.
• Thread angle is fixed when the thread had its own standard angle. The angle is 60 degrees and the crest of the thread maybe either flat or rounded.
• The depth of cut is referred to the distance between crest and root of the thread.

   p = pitch

 

 

 

 

 

 

 

 

PROCEDURE

1. Place the screw M24  3.0 ISO 6H onto the Profile Projector Machine.
2. Set the height and location of the screw to be near the lens.
3. Suitable scale of projection is selected in order to determine appropriate projection on the screen.
4. Determine the:                                                                         
1. Major diameter
2. Minor diameter
3. Pitch
4. Thread angle
5. Depth of thread.
5. The readings for each of above are taken 5 times and the average values are calculated.
6. For the screw M5  0.8 6H, the procedure are the same as above just that it is measured using mini Profile Projector Machine.

 

RESULT

 

I. M24  3.0 ISO 6H

 

                                  Figure 1.3 Screw Matrix of M24  3.0 ISO 6H

 

 

 

 

Major	Minor	Pitch	Thread	Depth of Thread
23.992	19.841	2.996	5957’	2.083
24.069	19.792	2.998	59 29’	2.042
23.998	19.844	3.000	57 50’	2.072
23.990	19.813	2.997	59 43’	2.072
24.002	19.872	2.959	59 46’	2.064
24.010	19.832	2.990	59 21’	2.067

*all dimensions in mm

II. M5  0.8 6H

                                  Figure 1.4 Screw Matrix of M5  0.8 6H

 

Major	Minor	Pitch	Thread	Depth of Thread
4.965	3.73	0.805	57.3	0.442

*all dimensions in mm

 Figure 1.5 The projection of the screw profile.

DISCUSSION

 

            From the experiment above, both of the apparatus are used to determine the major diameter, minor diameter, pitch, thread angle and the depth of thread. The differences between these two apparatus are that the first one is used to measure bigger sample of screw and the profile is projected onto a screen which can be easily seen and measured. Whilst the second apparatus is used to measure and indicate smaller size of screw sample but the profile can only be seen through a lens such as a microscope. All of the measurements for the second apparatus are done only based on the projection through the lens. It is a little bit tougher as the scale is smaller and the adjustments of the micrometer must be done carefully and accurately to determine the deserved readings. Comparing to the first apparatus, the measurements are done easier as the readings can be taken directly from the big projection screen and the adjustment for certain axis is taken from a digital micrometer, means that the readings is more accurate.

 

CONCLUSION

 

Some of the readings for screw profile measurements vary due to several factors. One of the main factors that caused such matter is ralax parallax. Even some of the readings were taken 5 times, each of the readings show minor differences. It can be said that the person who operates the measurements did not measure accurately as sometimes mistakes happen when reading the measurements on the screen projection as it was not 100% clear and precise.  Besides that, it is said that the screw itself do not have consistent measurements, in order words the screw itself does not have the accurate readings as the given dimension and it is assumed to be under the permissible percentage of errors because the differences were very small.