What is Brazing-Principles

Discovering Brazing (Braze Welding)


Brazing is a gas welding process in which you join metals by using heat that surpasses the 800 degree Fahrenheit mark and a nonferrous (iron-free) filler rod with a melting temperature below that of the base materials. The most important point about brazing is that you can use it to join dissimilar metals — cast iron to steel, brass to steel, or copper to steel, just to name a few examples.

Keeping a few brazing rules in mind
A successful brazing job requires that you stick to a few rules, as follows:

✓ The surfaces of the metals must be free of contaminants. Use steel wool to clean off all the metals, and use flux (a material that dissolves or removes oxides and other contaminants from the surface during brazing) for additional cleaning when the surfaces are heated.
✓ The joint to be brazed must have a tight fit. You use two basic joints for brazing: the butt joint (two pieces of material lying together on the same plane) and the lap joint (two pieces of material overlapping each other, usually in a parallel plane). If the joint has sizeable gap, brazing just doesn’t work. But if the joint is too tight, the melted filler rod can’t penetrate the entire joint, and you get a weak, ineffective weld.
✓ The base metals you’re brazing must remain stationary during the
heating and cooling process. If the base metals move while you’re welding or before everything has cooled off after welding, the joint’s integrity will likely be compromised


Giving brazing a try
If you’re trying brazing for the first time, I recommend going with an oxyacetylene torch in the flat position and using the forehand method I discuss in “Making the weld” earlier in the chapter. You can start by creating a brazed corncob, which is a piece created when you join two different metals,
following the steps in this section.

Brazing principles 

1. Acquiring a section of carbon steel pipe 1 inch in diameter and five inches long, as well as four 1⁄8-inch fluxed brazing filler rods that are 36 inches long.

2. Clean the pipe thoroughly with steel wool to remove any contaminants on the surface.

3. Lay the pipe between two fire bricks, leaving a 3⁄4-inch space between the bricks.
Fire bricks are special bricks that can withstand extremely high temperatures; find them at your welding supply or hardware store.
4. Set up and light the oxyacetylene torch, using the steps I describe in “Working through the Basics of Welding with Gas” earlier in this chapter, and adjust the torch so you have a neutral flame.
5. Preheat the pipe to burn off any grease or varnish that may be left on
the surface.
6. If you’re right-handed, start on the right end of the pipe and melt off a small portion of the filler rod onto the end of the pipe. If you’re left-handed, start on the left end of the pipe. The molten puddle should be very fluid. Be sure that when you use more of the filler rod, you let only the molten puddle (not the flame from the torch) melt the rod. If you notice white smoke coming from your molten puddle, that means you’re burning the zinc out of your filler rod, which will result in a poor
weld. Avoid that problem by welding at a lower temperature or moving more quickly with the molten puddle. When you’re practicing the brazing process, you can quench the metal between passes with the torch. Use pliers to pick up the section of pipe you’re practicing on and place it in a tank of water to cool it very quickly. Quenching isn’t good for the integrity of the brazed weld, though, so don’t quench unless you’re just practicing.

7. After you make your first pass with the torch, start a second pass by pointing the tip of the flame at the edge of the previous pass; when part of the first braze starts to melt, add some of your filler rod and proceed. This pass laps over the first braze bead 1⁄3 to 1⁄5.

8. When you’ve completed your second pass, quench the welded metal (or allow it to cool) and go ahead and start on a third pass. When you’re finished with the third pass, you should have a finished
product that resembles the brazed corncob in Figure 13-3. For some brazing projects, you may need to make even more passes. (For example, projects involving thick pieces of metal definitely require more than three passes.)

Please Read :

• Different types of welding defects.
• How to easily understand TIG welding Basics 
• Advantages of TIG welding 
• TIG welding Principles in Easy language 
• Welding Electrodes Explained 
• MIG welding principles 
• Aluminothermic or Thermit Welding Principles  
• Submrged Arc Welding 
• Flux shielded metal arc welding process principles 
• Resistance Projection Welding 
• Resistance Spot Welding 
• Resistance Seam Welding 
• TIG Aluminum Welding Advantages  made easy !
• Advanced TIG welding operations 

Read full post »

Electrical Discharge Machining (EDM) Principles

EDM is a non-conventional machining technique uniquely used for cutting metals which are not possible to cut with traditional methods. EDM only works with materials which are electrically conductive. Delicate cavities and intricate contours which are difficult to produce with a grinder or other machines can be done with Electrical Discharge Machining or EDM. The cutting tool for EDM may be made of hardened too steel, titanium carbide or inconel or kovar.  

EDM is also known as "Spark Machining" . Such name has been given for the fact that it removes the metal by applying a rapid series of repetitive electrical discharges. An electrode and the work piece is used for the conducting path of these electrical discharges. A continuously flowing fluid is always flowing to flush away the little amount of material that are removed. Repetitive discharge gives the workpiece a desired shape.

Please Read :

• Abrasive Jet Machining Process 
• Water Jet Machining Process .
• Ultrasonic Machining Principles 
• Laser Beam Machining

Two primary EDM methods are

Ram EDM and
Wire EDM.

Between this two methods the main difference is found in the electrodes. In ram EDM graphite electrodes are used. These electrodes are machined in traditional tools and a special shape is given which is connected to the power source. The electrodes are also connected to a ram. When all the arrangements are ready the electrodes are fed into the workpiece. The entire process is performed under a submerged fluid bath. In Wire EDM the electrode it self is a thin wire. Specially processed brass wires are used for feeding into the material. Electrical discharges cut the w/p according to desired shape. Wire EDM is generally done while submerged in a bath of water.

Ram Electro-Discharge Machining (EDM) Process: 

Rapid recurrence of spark produced between the two electrodes (tool & w/p) controls the metal erosion. It is to be noted that the workpiece must be an electrically conducting metal. An appropriate gap is necessary which is usually approximately 0.025 to 0.075 mm known as spark gap. The gap must be maintained between the w/p and the tool by a servo motor which runs by the difference between a reference and gap breakdown voltage. The tool moves upwards and downwards by this operating motor.
The rate of metal removal depends on the spark gap. If both the electrodes are made of same materials then the highest erosion is found on the positive electrode or the anode. So logically to get a high metal removal rate and a greater tool life the tool is made as cathode and workpiece works as anode, The two electrodes are kept apart and are separated by a dielectric fluid. A transient electric discharge is found across the gap between the two electrodes in the form of spark. When the potential difference between the electrodes is sufficient, the dielectric fluid is ionized and break down which in terms produces an conductive spark channel. The current is discharged across the channel by the condensers as spark. If the potential difference is less than or equal to 12 volts the dielectric fluid is deionized. The process is repeat itself as the condensers start to recharge. The spark interval is generally 10 to 30 microseconds and the current density ranges from 15-500 am/mm2. The energy is released from the sparks in the form of local heat and eventually local temperature found is in the order of 12000°C. Such high temperature and pressure melts and erodes some metals some of which is vaporized and other fine material particles are carried by the fluid circulating around the electrodes which creates a crater on the w/p. As the time interval of the sparks is very low the heat doesn't get time to conducted between the tool & workpiece. Fig below shows a schematic diagram of the whole process.

How to choose the Tool Material
Many factors are needed to be taken into consideration while selecting the tool material.

• Low erosion rate and decent work to tool wear ratio
• good electrical conductivity 
• good machinability 
• low electrical resistance 
• high melting point . 
• high rate of electron emission  

EDM has one major drawback and it is the wear ratio of the tool. Different material has different wear ratio. For Brass it is 1:1 . For metallic electrodes it is found 3:1 or 4:1 . For high melting point electrode graphite it ranges from 5:1 to 50 :1 . 

Tool Wear

While applying EDM the tool or cathode also erodes which is not desirable. It is unavoidable but remains in tolerable limit as the wear of the cathode is much less than the anode. This occurs because -

• Positive ions from the dielectric fluid hit the cathode but electrons strikes the anode. Though electrons are much lighter than the positive ions it possesses more energy as it moves it greater velocity. So anode gets more eroded. 
• At the time of spark a compressive force is created at the cathode which reduces the cathode erosion. 
• Fluid medium is generally hydrocarbon. Due to pyrolysis gases are produced which produces carbon particle and these particles create a thin layer of protection on the cathode. Thus the cathode is much safer than anode. 

Purpose of Dielectric Fluid 

• Effective Coolant for the workpiece and the tool . 
• It works as an insulating material during the charging of the condenser as a result perfect condition for efficacious spark discharge and its conduction when ionized is obtained. 
• The eroded materials are carried away by this medium. 
• It is a coolant in quenching the spark and prevents the arcing. 

Essential Requirements for dielectric fluid 

• Optimum Viscosity is necessary . If the viscosity is low then the fluid will not be able to carry the metal particles. On the other hand if the viscosity is high then it will restrict the flow of the liquid. 
• It should be non-reactive with the work piece, container or the tool material. 
• Non-expensive, easily available and inflammable. 
• It should not produce toxic gases or vapors during the operation. 
• It should be a hydrocarbon compound. 

Different dielectric fluids are : transformer oil, spirit (white), oil and kerosene etc. If some conducting power like aluminum or light graphite is added to the fluid then the metal removal rate increases. 

Advantages of EDM

• Metal having any hardness or brittleness and toughness can be machined. 
• Harder materials such as steel alloys or tungsten carbides which are used for molding and other non-conventional machining like forging and press tools can be reproduced. 
• Dies can be machined at hardened condition. 
• Complicated shapes can be reproduced. 
• Very fine holes can be done very accurately . 
• The accuracy is very high. Tolerance of 0.005 mm can be achieved. 
• Wear resistance surface can be made because workpieces produced with EDM have micro-craters which can contain lubricants effectively. 
• The physical contact between the tool and w/p is avoided. No cutting force other than blasting pressure is exerted. So fragile jobs and cylinders can be machined without causing any damage. 
• Harder metals can be machined very quickly in comparison to the conventional machining process. 

Disadvantages Electrical Discharge Machining 

• The power required for machining is much higher compared to the conventional machining. (120J/mm2)
• There are chances of surface cracking when the materials become brittle at room temperature. 

• A thin layer usually ranging from 0.01 mm to 0,10 mm containing 4 % carbon may be deposited on the workpieces made of steel 
• The Material Removal Rate  (MRR) is comparatively low (75 mm3/sec)
• Reproducing sharp corners is difficult in EDM. 
• Sometimes the micro-structures are distorted and subsequently etching occurs. 

Applications of EDM 

Generally EDM is hugely used for machining burr free intricate shapes as well as narrow slots and blind cavities. Sinking of dies , plastic molding, die casting compacting, cold heading, extrusion, press tools, wire drawings are some of the examples of its application. Negative tool geometry can also be generated on a w/p if suitable tool can be made. EDM is very useful for machining small holes. It is also used to cut slot in diesel fuel injection nozzles. It is also used in air crfat engines and brake valves etc.

Wire Electrical Discharge Machining

A very thin wire of diameter ranging from 0.02 to 0.3 mm is used as an electrode in wire cut EDM. It cuts the workpiece with electrical discharge just like a band saw. In this process either workpiece or the wire is moved. The spark discharge phenomenon is used for eroding the metal which is same as the conventional EDM. In wire cut EDM the wire acts as an electrode as a result complicated shapes can be cut easily without forming electrode. Basically the wire-cut EDM consists of a machine which has a workpiece contour movement control unit ( NC tension : a power supply which supplies electrical energy to the wire and has a unit ) . It also has workpiece mounting table and a wire driver section. The wire driver section is use for moving the wire accurately at a constant tension. Another important part is the dielectric fluid (distilled water) supplier having constant specific resistance. Wire EDM has the following features -   

•  No forming electrode is necessary. 
• electrode wear is very negligible. 
• Smooth machined surface. 
• Tight geometrical and dimensional tolerances . 
• Extremely high tolerances between punch and die. Extended die life. 
• Straight holes are possible to produce. 
• Machine can be operated without any regular supervision for long time at high operating rates. 
• No skill is needed to run the machine. 

Advantages

• Because of the absense of the split lines in the die, savings of the stages in the sequential tools occurs. It permits more punch opening per stage. 
• There will no flashes on the molded parts because the molds with draught  can be arranged without vertical divisions. 
• To necessity for tool manufacturing and storing. 
•  Workpieces are hardened before cutting . So no heat treatment distortion is not present. 
• Whole work is done in one machine . So die manufacturing cycle time is short. 
• Lesser inspection time because of single piece construction of dies with high accuracy. 
• Time is utilized perfectly as the wire cut EDM can cut throughout the day. 
• Very economical even for small batch production. 
• low thermally affected zone. High surface finish. 
• Number of rejected workpieces are very small. 

Please Read : 

• Different types of welding defects.
• How to easily understand TIG welding Basics 
• Advantages of TIG welding 
• TIG welding Principles in Easy language 
• Welding Electrodes Explained 
• MIG welding principles 

Read full post »

Electrochemical Machining (ECM) Principles

Electrochemical Machining (ECM) is based upon Faraday's law of electrolysis. Faraday's law states that the the mass of a metal altered by the electrode is proportional to the quantity of electrical charges transferred to that electrode.

• In ECM the removal of metal is controlled by the anodic dissolution in the electrolyte. 

In ECM -

•  The workpiece acts as the anode
• The tool act as cathode.
• The electrodes should be placed closely with a gap of about 0.5 mm .
• The anodes and cathodes should be immersed into electrolyte. (Here Sodium Chloride)

Please Read : 

• Abrasive Jet Machining Process 
• Water Jet Machining Process .
• Ultrasonic Machining Principles 
• Laser Beam Machining
• Electrical Discharge Machining (EDM) Principles 

Schematic illustration of the electrochemical-machining (ECM) process

The main principles of ECM are as follows - 

• A potential difference is maintained between the electrodes as a result ions existing in the electrolytes migrate towards the electrodes. 
• Conventionally positively charged ions are attracted towards the cathode and negative ions are attached towards to the anode. And thus flow of current is initiated in the electrolyte. 
• The set-up is kept stationary and tool is fed linearly. 
• The desired amount of metal is removed because of ion migration towards the tool. 
• For keeping the tool safe from damage a continuous supply of electrolyte is ensured by pumping it at high pressure (15kg/cm2). 
• In this process the temperature generated is very low and no spark is produced and thus there isn't any scope of metallurgical changes in the job. 
• When electricity is supplied to the metallic ions of the w/p is pulled out. The positive ions of the metal reacts with the negative ions present on the electrolytic solution and hydroxides of metal and other components. This hydroxides are precipitated and washed away by the electrolytic solutions.  
• In Electrochemical Machining the tool and workpiece doesn't come in direct contact with each other so negligible wear and tear is observed. 
• Metal removal rate is high and voltage supplied is very low. 
• The metallic workpiece is not damaged due to thermal stresses. 
• Dimensions up to 0.05 mm can easily machined . 

Examples of parts made by ECM 

Different parts made by electrochemical machining.  (a) Turbine blade material :  nickel alloy (b) Thin slots on a 4340-steel roller-bearing cage.  (c) Integral airfoils on a compressor disk.

 Electrochemical Grinding  (ECG) Principles  

(a) Schematic illustration of the electrochemical-grinding process.  (b) Thin slot produced on a round
nickel-alloy tube by this process.

        Functions of Electrolyte

•           The current is carried between the tool and the w/p through electrolyte.
•           The produced heat is dissipated by the liquid electrolytic solution.
•           The product of machining is removed by the solution.               
•            It keeps the reactions continuous by supplying the elements necessary for the reaction.  

What Should be The Criteria of Selecting Electrolyte in Electrochemical Machining  (ECM) and Grinding (ECG)

The selection of the electrolyte should be done by considering the following matters - 

·         Required Machining rate 

·         Required Dimensional Accuracy 

·         Surface Texture and Integrity  

            

      The properties of Electrolytes 

•            High Electrical Conductivity 
•            High Current Efficiency for machining 
•            Good Surface finish and integrity is necessary
•            Composition of the electrolyte and structure of the material controls the final surface texture. 

 Flow Arrangement of the Electrolyte in  ECM / ECG 

       Perfect electrolyte flow across the machining tool is mandatory for proper machining.

      cavitation is likely to be occurred in the tool so proper care is necessary to keep the 

      tool in shape. Tool design must ensure the uniform flow of electrolytic solution in all

      the machining areas. Optimum flow of the electrolyte is desired because excessive

      flow can cause erosion of the tool. 
      
     Mainly two types of flows are used –

     1.     Divergent flow

     2.     Convergent flow

     Convergent flow provides a smoother flow of electrolytes. At first the electrolyte has to pass a

     chamber known as ‘dam’. The dam is used to pressurize the are outside  the working tool. 

   Advantages of convergent flow system.  

  

•         Improved Surface finish 
•         Improved Uniform and predictable side over cut as well as front machining gap. 
•         Less prone to arcing. 
•         Clean operating environment 
•         Stray currents make it possible to eliminated unwanted machining.  

But it is also to be mentioned that machining in convergent flow is much expensive than divergent flow. 

Advantages of Electrochemical Machining (ECM)

1. Accurate Machining 
2. No direct contact between tool and job. 
3. Negligible wear and tear of the tool. 
4. Environment friendly 
5. no thermal or mechanical stress is induced on the tool.
6. There is no contact between worpiece and the tool so its is possible to machine non-rigid and open w/p. 
7. Jobs with complex geometric shapes can be machined with ease accurately and repeatedly. 
8. ECM is a time saver when compared to conventional machining. 
9. During drilling several holes can be done at once.  
10. Deburring can be done in hard to access areas. 
11. Fragile and brittle materials which are prone to damage can be machined easily in ECM without cracking or breaking. 
12. Surface finish up to 25 μ in can be achieved. 

Disadvantages of Electrochemical Machining (ECM)

1. Sometimes this process is costly because the equipments are expensive. 
2. Continuous supply of electrolytic solution is mandatory. 
3. Steady voltage or potential difference should be maintained. 
4. Rigid fixturing is required to withstood the high flow rate of electrolytes. 
5. Designing the tool is arduous because it must be insulated to maintain the perfect conducting paths towards the workpiece. 
6. Corrosion free material is needed for the structure and the electrolyte handling unit. 
7. If hydrogen is liberated at the tool surface then it is possible to suffer from hydrogen-embitterment of the surface. 
8. There is possibility of damages because of sparks. 
9. Conventional machining techniques produce more improved fatigue properties than ECM.  

Applications of Electrochemical Machining ECM 

• ECM is mainly used in the areas where conventional machinig techniques are not feasible . One of the main applications of ECM is found in the aerospace industries where accuracy is very important when complex shaped difficult to machine materials are needed to be machined. 
• Different Industrial techniques have been developed on the basis of Electrochemical Machining Such as 

                a. Electrochemical Cutting 

                b. Electrochemica ECM 

                c. Electrochemica broaching 

                d. Electrochemica drilling 

                e. Electrochemica deburring 

Please Read : 

• Different types of welding defects.
• How to easily understand TIG welding Basics 
• Advantages of TIG welding 
• TIG welding Principles in Easy language 
• Welding Electrodes Explained 
• MIG welding principles 

Read full post »

Match Plate Pattern - Used in Casting (With diagram)

What is Match - Plate Pattern 

The match plate pattern is almost similar to the mounted pattern but it can have part of the casting in the cope and part in the drag like split piece pattern. These parts are generally attached to the plate / board in opposite sides in the perfect positions. When the plate is removed and mold is in close position the cavities in the cop and drag match perfectly. The mounting procedure matches the procedure of one sided mounted plate.

schematic of match plate pattern

Characteristics of Match Plate Pattern 

• It is split pattern 
• Cop and Drags on the opposite site of the metallic (generally) plate. 
• The gates are runners are on the match plate. 
• Can be used for large number of casting with very little hand work. 
• A match plate can be single pattern or a combination of many small patterns
• Example : IC engine piston rings can be produced by match plate pattern 

Important parts of Match Plate Patterns  

Cope and Drag Mounts

• Two separate pattern mounts are there.
• One is fitted to the female guides (for drag) other is fitted with pins (for cope). This must match the profile of the flask that is used.
• The half part of the pattern associated by the cope is attached to the cope mount and drag part pattern is attached to the drag mount.
• Cope and drag portions are manufactured disparately and combined together for pouring.
• Generally one molder makes copes other makes drags.
• Cope and drag mounts are also known as tubes.
• These (cope and drag mounts) are very similar when producing large castings. 

cope and drag mounts in match plate pattern 

Follow board

• It is a board with a cavity or socket.
• The cavity must conform to the shape of the pattern.
• It also defines the parting surface of the drag.
• Materials: It can be made of plaster or metal. If sand is used to manufacture follow board then it is called dry sand match.
• When the drag half of the mold is made the pattern rests on the follow board.
• It creates the correct sand parting.
• Pattern is rammed in the drag and follow board is removed.
• The follow board is replaced by the cope.
• A simple follow board may have a hole in it so that the pattern rests firmly when the drag is being rammed.   

follow board

simple follow board

Please Read :

• Different types of casting defects 
• What is casting ? Main application of castings 
• different types of patterns that are used on the sand casting process. 
• different types of molding sand
• properties of various natural and synthetic molding sands
• Comparison of different casting processes. 
• Advantages and disadvantages of centrifugal castings.  

Read full post »

Ultrasonic Machining (USM) Working Principles

In this process the material of the workpiece is removed by the repetitive impact actions of abrasive particles. The erosion takes place by the abrasive particles which are carried by a liquid medium in the from of a slurry . A shaped vibrating tool is used to produce the impact. The term shaped is used to explain that the process is capable enough to create 3D profiles in correspondence to the tool shape which is not possible in AJM. The tool gets the vibrating motion from the vibrating mechanical horn.  Here is a schematic diagram of the basic system.   


Please Read : 

• Abrasive Jet Machining Process 
• Water Jet Machining Process .
• Laser Beam Machining
• Electrical Discharge Machining (EDM) Principles 

Ultrasonic Machining (USM) Principles

Working principle of Ultrasonic Machining  or Ultrasonic Impact Grinding is described with the help of a schematic diagram. The shaped tool under the actions of mechanical vibration causes the abrasive particles dipped in slurry to be hammered on the stationary workpiece. This causes micro-indentation fracture on th material. 

Small abraded particles are removed along the surface which is perpendicular to the direction of the tool vibration. When the material is removed a cavity of the same profile of the tool face is formed. The abrasive particles gradually erodes as the machining process continues. As a result fresh abrasive particles are needed to be supplied in the machining zone. Abrasive particles associated with the liquid is fed to the m/c zone and it ensures the removal of the worn out grains and material. 

Machining Time 

The machining time of the ultrasonic grinding depends on the frequency of the vibration, material properties and grain size.  The amplitude of the vibration may vary from 5 to 75 µm and frequency may vary from 19~25 kHz. Ample static force is also required to hold the job against the machining tool . A continues flow of abrasives suspension is also mandatory.

  

Advantages of USM:

1. It can be used to drill circular or non-circular holes on very hard materials like stones, carbides, ceramics and other brittle materials.
2. Non-conducting materials like glass, ceramics and semi precious stones can also be machined. 

Disadvantages of Ultrasonic Machining  :

1. It can be proved slower than the conventional machining processes. 

2. Creating deep holes is difficult because of the restricted movement of the suspension. 

3. It is arduous to select the perfect tool geometry for creating hole of certain dimension. The holes created may be of larger sizes because of side cutting.  

4. High tool wear because of continues flow of abrasive slurry. 

Applications:

1. Hard and brittle materials can be machined like tungsten carbide, diamond and glass. These are difficult to machine in conventional m/c-ing process.
2. Wire drawing dies of tungsten carbide can be drilled by this process.  

3. Circular as well as non-circular holes can  be done with straight or curved axes.
4. It has been proved successful in machining geranium, silicon quartz and synthetic ruby etc. 

Please Read : 

• Different types of welding defects.
• How to easily understand TIG welding Basics 
• Advantages of TIG welding 
• TIG welding Principles in Easy language 
• Welding Electrodes Explained 
• MIG welding principles 

Read full post »

Water Jet Machining (WJM) Advantages and Disadvantages

        In Water jet Machining no abrasive is used. Water jet alone is used for cutting. In WJM, materials like concrete, asbestos, wood, rocks, coal, textiles and leather can be cut. The material is removed by means of erosion. These days hydraulic coal mining as well as tunneling, descaling and cleaning is also done by this process. 

         Water Jet Machining (WJM) Principles 

As the name suggests the water jet machining process involves the use of high velocity  and high pressure thin jets of water to cut the job. Water Jet is the stream of high velocity water coming out from the nozzle. When high pressure water jet comes out of the nozzle it gains a large kinetic energy. After striking the work piece this kinetic energy is converted to pressure energy inducing high stress on the material. When this induced stress surpasses the ultimate stress of the material, removal starts. 

Please Read :  

•         Abrasive Jet Machining Process 
•          Laser Beam Machining
•          Electrical Discharge Machining (EDM) Principles 

         Schematic Diagram of WJM 

        The schematic diagram of  WJM process is very similar to that for AJM. To raise the pressure of the water a pump or intensifier is used. The system pressure ranges from 1600 to 4000 N/mm2. The accumulator used in the system act as a pulsation remover and an energy reservoir. Water passes through the accumulator and then nozzle through a high pressure thick tube. The tube material may be stainless steel jacketed with carbon steel. Sintered diamond , sapphire or tungsten carbide may be used as the nozzle material. The exit dia. of the nozzle may vary from 0.05 to 0.35 mm. 

a. Schematic of Water Jet Machining b. Example of workpiece machined by WJM

Advantages of Water Jet Machining Process 

1. Here water is used for cutting which is cheap, non-toxic and readily available. 
2. The water jet keeps the job clean and dust free. 
3. The only moving part used is the pump, therefore the operating and
maintenance expenses are low. 
4. The process is very safe to use. 
5. Very complicated designs and detailed work can be done. 
6. There is no damage of the workpiece due to thermal stress. Very little heat is
generated. 
7. Soft rubber like materials can be cut through this process where saw teeth
gets clogged. 

          

Disadvantages of WJM.

1. Hard Materials cannot be cut. 

2. The initial cost is high. 

Applications:

1. Cutting 

2. Milling 

3. 3D Shaping

4. Turning

5. Piercing

6. Drilling

7. Polishing 

Please read :

•          Different types of welding defects.
•          How to easily understand TIG welding Basics 
•          Advantages of TIG welding 
•          TIG welding Principles in Easy language 
•          Welding Electrodes Explained 
•           MIG welding principles 

Read full post »

ADVANTAGES AND DISADVANTAGES OF WELDING

Like all joining processes (in fact, like all processes!), welding offers several advantages but has some disadvantages as well. The most significant advantage of welding is undoubtedly that
it provides exceptional structural integrity, producing joints with very high efficiencies. The strength of joints that are welded continuously (i.e.,full length, without intentional skipped areas) can
easily approach or exceed the strength of the base material(s). The latter situation is made possible by selecting a joint design that provides greater cross-sectional area than the adjoining joint elements and/or filler that is of higher strength than the base material(s). Another advantage of welding is the
wide range of processes and approaches that can be selected and the correspondingly wide variety of materials that can thus be welded.

Advantage of Welding 

Almost all metals and alloys, many (thermoplastic) polymers, most if not all glasses, and some ceramics can be welded, with or without auxiliary filler. Still other advantages of welding are that -

(1) there are processes that can be  performed manually, semi-automatically, or completely automatically; (2) some processes can be made portable for implementation in the field for erection of large structures on site or for maintenance and repair of such structures and
equipment; (3) continuous welds provide fluid tightness (so welding is the process of choice for fabricating pressure vessels);(4) welding (better than most other joining processes) can be performed remotely in hazardous environments (e.g., underwater, in areas of radiation, in outer space) using robots; and (5) for most applications, costs can be reasonable. The exceptions to the last statement
are where welds are highly critical, with stringent quality requirements or involving specialized applications (e.g., very thick section welding).

Disadvantage of Welding 

The single greatest disadvantage of welding is that it precludes disassembly. While often chosen just because it produces permanent joints, consideration of  ultimate disposal of a product (or structure) at the end of its useful life is causing modern designers to rethink how they will accomplish joining.
A prime example is the need for the regulatory authorities in former West Germany to  dismantle the nuclear reactors in former East Germany that have designs similar to the reactor that failed in Chernobyl in the former USSR.

A second major disadvantage of many welding processes is that the requirement for heat in producing many welds can disrupt the base material microstructure and degrade properties. Unbalanced heat input can also lead to distortion or the introduction of residual stresses that can be problematic from
several standpoints.

A third serious consideration, but not necessarily a  disadvantage, is that welding requires considerable operator skill, or, in lieu of skilled operators, sophisticated automated welding systems. Both of these, along with the aforementioned specialized applications, can lead to high cost.

This table summarizes the major advantages and disadvantages or limitations of welding as a means of joining materials or parts into parts or assemblies or structures.

advantages  and disadvantages of welding

Advantages and Disadvantages of Welding as a Joining Process

Advantages	Disadvantages
I. Joints of exceptional structural  integrity and efficiency, will not accidently loosen or disassemble  2. Wide variety of process embodiments  3. Applicable to many materials within  a class  4. Manual or automated operation  5. Can be portable for indoor or  outdoor use  6. Leak-tight joints with continuous welds 7. Cost is usually reasonable	1. Impossible to disassemble joints without  destroying detail parts  2. Heat of welding degrades base properties  3. Unbalanced heat input leads to  distortion or residual stresses  4. Requires considerable operator skill  5. Can be expensive (e.g., thick sections)  6. Capital equipment can be expensive (e.g.,  welds electron-beam guns and vacuum chambers)

Please Read : 

• TIG welding Basics 
• Advantages of TIG welding 
• TIG Aluminum Welding 
• MIG Welding Principles 
• Submrged Arc Welding 
• Flux shielded metal arc welding process principles 
• Resistance Projection Welding 
• Resistance Spot Welding 
• Resistance Seam Welding 
• Different types of welding defects
• Aluminothemic Welding or Thermit Welding Principles 
• LaserBeam Machining/Welding

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Magnetically Impelled Arc Butt Welding Principles

Magnetically impelled arc butt (MIAB) welding (sometimes referred to as rotating arc welding) is a rapid, clean, and reliable arc welding process that employs forging to produce  the finished weld. As such, it is classified as an electric arc welding process since that is the energy source for producing melting or fusion, even though pressure from forging is needed to complete the weld. It is thus a fusion arc pressure welding process, and, in that way, is related to arc stud welding  ( not described in this article. )

The MIAB welding process is well established in Europe (especially Eastern Europe) and the independent  states of  the  former Soviet Union, finding application in  the  automotive  industry for  the fabrication of tubular-section butt welds and, to a lesser extent, tube-to-plate welds. Tubes can have circular or non-circular cross sections, with walls ranging from 0.5 to 5 mm or more (0.020 to 0.200 in.) thick. Steel as well as aluminum alloy has been  welded successfully in mass production, producing welds with exceptional quality even for safety-critical applications.

Magnetically Impelled Arc Butt Welding Principles 

In practice, MIAB welding  is fully automated. An arc drawn between aligned but properly gapped tube ends is impelled to move (rotate) around the joint  line by an interaction of  the arc current  and  an externally  applied magnetic field , hence the name. Once the arc has heated the ends of the tubes to cause localized melting and adjacent softening in the heat-affected zone, the parts are forged together. This expels most of the molten metal present and a solid-phase  bond is formed. The principle of operation is shown  schematically in  Figure 1 ; typical placement of the magnets used to apply the propelling force to the arc is shown in Figure 2

Figure 1 : MIAB principles 

Figure 2 : MIAB schematic 

Benefits of MIAB

The  major benefits of MIAB welding are (1)  no rotation of either  component  (thereby  overcoming  problems  with  asymmetrical  parts  encountered with many friction welding processes), (2) short welding times (e.g., 2-4 s for 2 to 4-mm CO.040-  to 0.080-in.]-thick low-carbon steel tube), (3) low
material loss, (4) low fumes and  spatter, and (5) relatively low required arc current.

As opposed to flash and upset welding , MIAB welding does not use resistance to accomplish heating at the joint, but, rather, an electric arc. This makes  it an arc rather  than a  resistance welding process. The fact that forging  removes  most  molten  metal  suggests that  the  process  could  be considered non-fusion; after  all,  the role of the  liquid is  largely  fluxing . The  process is considered  a  non-consumable electrode arc process because the intent is not to consume the parts being welded and used as electrodes, but to preserve those parts.

Please Read :

• Different types of welding defects.
• How to easily understand TIG welding Basics 
• Advantages of TIG welding 
• TIG welding Principles in Easy language 
• Welding Electrodes Explained 
• MIG welding principles 
• Aluminothermic or Thermit Welding Principles  
• Submrged Arc Welding 
• Flux shielded metal arc welding process principles 
• Resistance Projection Welding 
• Resistance Spot Welding 
• Resistance Seam Welding 
• TIG Aluminum Welding Advantages  made easy !
• Advanced TIG welding operations 

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