Axle Shop Processes - PDF

36 Axle Shop Billet Cutting Billet heating in Forging in LFM RHF Normalising Cooling on the End Cutting and Bed Hot Stamping of Axle no Air Cool R16 Polymer...

36 Axle Shop Billet Cutting Billet heating in Forging in LFM RHF Normalising Cooling on the End Cutting and Bed Hot Stamping of Axle no Air Cool R16 Polymer Tempering Axles Quenching for R43 Axles Machining Sampling for Air Cool mechanical & metallurgical test  37 Axle Shop The Axle shop is the second unit of RWF. An axle is a central shaft for a rotating wheel. RWF produces an axle every 5 minutes. Rail Wheel Factory is having three axle machining lines out of which 2 are CNC machines to convert these forgings to the axle. RWF converts BOX N, Coaching and Container Axles to wheel sets. Loco axles are generally sent in rough turned condition to the Production Units and Railways workshops for converting to wheel sets. RWF produces 16 Axels according to the requirement. The Plant converts steel blooms to axles through a series of forging, heat treatment and machining processes. Blooms cut to the required sizes are heated in Rotary Hearth Furnace up to 1200 degree Celsius. These are carried to the precision Long Forging machine where the hammers convert billets into the required shapes through computerized control program. The Forging Machine having multiple hammers is used to get required sizes of forgings. After end cutting, the rough forged axles are subjected to heat treatment in normalizing and tempering furnaces. It undergoes machining, finishing and inspection tests to satisfy the customer requirements.  38 The railway axle is a long, thick cylindrical rod made up of alloy steel and weighs about 500 kg. The axles mainly consist of 4 parts – body, wheel seat, dust guard and journal. Major portion of the axle is the body whose length is fixed and is equal the distance to be maintained between two parallel wheels. Hence, the length of the body which is the center portion of the axle varies for different types of axle. The portion of the axle where the wheels of the train is fixed is the wheel seat. The curved portion between the wheel seat and the journal is the dust guard. The two ends of the axle after the dust guard is journal. The journal is the main portion which is required in a perfect smooth finished surface state. The bearings of the train wheels occupy this place. The axle shop is divided into three portions and they are:  Forging shop  Machining shop  Assembly shop  39 FORGING SHOP  Billet cutting : The long bar with square cross section is called a bloom and they are cut into small length pieces by gas welding. The blooms are obtained from Durgapur (SAIL), Maharashtra (MUSCO) and Pune (Kalyani forging) steel plant. The billet cutting machine is an automated machine and it takes three minutes to cut a billet from a bloom. The fuel used is a mixture of Oxygen and LPG. According to the various cross section area, the axle are divided into the following types: Types Area(mm2) Materials used Locomotive axles 340 R43 BOX-N 300 R16 Coaching axles 287 R16 Brief procedure  The bloom is carried in a conveyor to the billet cutting machine.  The operator marks the points at which the flame cutting will take place. The marking depends on the type of axle to be manufactured.  The machine is switch ON and the gas flame of O2 and LPG at a suitable pressure is directed on the work piece and cutting operation is performed. The cutting is based on length to weight ratio.  40  Heating : Heating of billets is done in Rotary Hearth Furnace (RHF). The billet after being cut must be heated so that it can be forged. The RHF having four furnaces namely – preheating zone, heating zone, soaking zone I and soaking zone II – is used for heating the billets to a temperature of 1200 °C. Zone Total no of burners Preheating 6 Heating 9 Soaking I 3 Soaking II 2 Total 20 Brief procedure  A robot arm inserts the billet into the RHF. The billet enters the preheating zone where the heating process begins.  The billet moves into the heating zone. This zone takes the longest time.  41  In the soaking zone I and II, the heat is spreads to the core of the work piece.  The RHF has a capacity of 80 billets and the cycle time is 6.5 hours. *NOTE: Quality parameters of Billet Heating Zones Upto 250 sq per 272/287/300 340 sq/round with round (with sq/round (with tolerance tolerance) tolerance) Pre heating Zone 1100-1170 1150-1200 1170-1210 Heating Zone 1100-1170 1180-1200 1180-1210 Soaking zone I 1125-1170 1180-1200 1180-1210 Soaking zone II 1125-1170 1180-1200 1180-1210  Forging : Forging is a mechanism used to make or shape a metal object by heating in a fire furnace and hammering it to the required dimensions. The forging machine called Long forging machine consists of four hammers of about 800 tons capacity each with two motors subjected to the power supply of 400KW power. The hammers are placed diagonally to each other. The operation is brought about based on the set of instructions (program) given by the operator.  42 Brief procedure:  The billets from the Rotary hearth furnace at a temperature of about 1100 - 1150 degree Celsius are subjected to forging process. This is done to bring the billet.  The forging process in axle shop is based on cams, which in turn is controlled by PLC (Program Logic Control) and CNC (Computer Numerically Controlled) for the control of movements and dimension specifications (measurements) respectively.  It consists of two chuck head named A and B related to the movement of expansion and R which is used as a reference for diameters.  The hydraulic pressure in the machine generates mechanical power to bring about the process. As a result the axles of required dimensions are obtained based on the requirement.  Thus the forged axles of specified dimension are now subjected to End cutting process. *NOTE: The cycle time of the process ranges from 4.5-5 minutes per axle.  43 SPECIFICATIONS: 1.Force 800tons 2.Eccentric stroke(hammer 14mm length) 3.Stroke 270strokes/min 4.Hydraullic pressure 90-100bar 5.Lubricant pressure 5bar 6.Damping pressure 80bar 7.Ring space pressure 70-80bar  End Cutting: The metal cutting process used in the removal of excess material at the ends to obtain metal component with required dimensions is termed as end cutting. During the forging process, the billet deforms to the required axle shape, and since at the ends the material is deformed and in an irregular shape, it needs to be eliminated. Thus, end cutting is done. Basic procedure:  The forged axles after forging is subjected to end cutting process termed as Axle end cutting.  High flame gas of oxygen and LPG mixture from the nozzle with a diameter of about 25mm at high pressure is forced on both the sides hence the removal of metal.  The cycle time of the process is less than a minute due to high temperature of the forged axle.  The high temperature axles are now subjected to normal Air cooling process, wherein the axles are arranged in an open area hence the cooling takes for about half an hour duration.  44  Heat Treatment:  Normalising : It consists of heating steel about 40-50°C above its upper critical temperature and if necessary holding it at that temperature for a short time. Brief procedure:  Once the axles are air cooled, they are sent into the normalizing furnace.  These axles are placed on the base of the furnace and fire is set on the sides of the furnace. The fuel used is High Speed Diesel. Around 90 axles can be accommodated in the furnace.  Normalizing furnace consists of three zones namely pre-heating, heating and soaking.  The cooled axles regain their grain structure by the end of normalizing process.  The type of structure obtained will depend largely on the thickness of cross section as this will affect the rate of cooling. Thin sections will give a much finer grain than thick sections.  45  Quenching : It is simply defined as sudden cooling of heated metal by dipping in cooling agent or spraying cooling agent in order to obtain the work piece in a stable state which induces certain properties like hardness etc to the work piece. Brief procedure:  Not all types of axles require quenching.  Only a few types of diesel axles are quenched in quenching agent.  The quenching agent used is a mixture of polymer oil and water in the ratio 1:20.  The quenching agent is present in a tank about 10 feet depth where quenching takes place.  Quenching is done for about 25-30 minutes depending on the carbon content present in the material of the particular axle. It is done for 4 to 5 axles at a time.  The axles which do not require quenching are sent directly to tempering furnace after normalizing. Diesel axles are sent into tempering furnace after quenching.  Tempering : Tempering is a heat treatment technique applied to ferrous alloys, such as steel or cast iron, to achieve greater toughness by decreasing the hardness of the alloy. The reduction in hardness is usually accompanied by an increase in ductility, provides softness and machineability to the metal thereby decreasing the brittleness of the metal.  46 Brief procedure:  Axles enter the tempering furnace where they are heated below their critical temperature in order to achieve softness so that they can be machined with ease.  The tempering furnace also consists of three zones i.e.; pre- heating, heating and soaking. Heating is done at around 600 to 650°C.  Around 118 axles can be placed in the tempering furnace.  Tempering reduces internal stresses in the axles which may have induced during heating, forging or quenching.  Those axles which have acquired the required composition and properties are sent to the axle machining shop for machining while others are sent back for re-heating.  Sampling: After tempering, the axles are cooled for 24 hours and then taken for testing. The axle is taken for destructive testing where it is cross-sectioned and checked if it is suitable for operating and its other functions. Axle Machine Shop  Station 1:End milling, centering and Cup turning : End milling can be defined as removal of metal with the help of rotating end mill. An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, a milling bit can generally cut in all directions, though some cannot cut axially. And end mill is a multi-point cutting tool. Because the forged axles undergo various hat treatment processes, it has excess length. This must be cut with little amount of tolerance for further machining.  47 Centering is the process of producing a center hole in the axle in order to hold the axle in further machining process. This is followed by cup turning where excess material is removed and smoother surface finish is done only at the ends. The centering tool and cup turning tool is made out of HCS. The tool life of centering tool is 200 axles. These operations are performed by CNC machines of Siemens technology. Brief procedure  The end mill cutter has a number of inserts which does the actual cutting job. The axle is brought close to the end mill and machined.  It consists of two chucks each powered by a motor. They remove 0.7 mm of material from each side.  The inserts that are used for milling have four cutting edges and are made of Carbide. Each edge may be used for operating 60 axles.  Then it is switched to another set of two chucks that is again powered by a motor (each). The same set of chucks performs both centering and cup turning.  Centering is done for a hole diameter of 28mm (Box-N axle)  Cup turning is done for a diameter of 148mm(Box-N axle)  Ultrasound inspection : Ultrasound inspection is done to detect internal defects. This inspection is done from one face to another. After calibrating the ultra sound flow detector the couplant is applied to obtain proper coupling for conductance. On inspection, of the axle does not meet the conditions even after heat treatment, the axle is rejected.  48  Station 2: Rough turning: Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helical tool path by moving more or less linearly while the work piece rotates. The tool used here is a single point cutting insert made of Carbide. They are called nest inserts. In order to remove the excess material and bring it to the required dimensions, rough turning is carried out. The exact shape of axle is brought to in this process and later machined to obtain a smoother surface finish. During this process the axle is fixed between the chucks and made to rotate at very high speeds. The carbide insert is fixed to a cassette and it is fitted into the tool holder. Hence the tool holder is more permanent and the cassettes are replaced. Each cassette has an L and R side. According to their function, they will be selected. There are five chucks used for this operation.  49 The rough turning operation also uses CNC technology. Brief procedure  The axle is divided to four sections – 1, 2, 3 and 4. 1 and 4 for the body. 2 and 3 for journal.  Rollers are used for long turning to avoid vibrations.  After lifting rollers, channels 1 and 4 take place.  Coolant is not used in this process since carbide inserts are used.  15 axles can be machined with the same insert for journals and 8 to 10 axles can be machined in case of longer lengths.  Station 3 : Drilling, countersinking, Tapping and Recentering : After rough turning of the axle, threaded holes are drilled at the two end surfaces in order to fix the bearing to the axle. Drilling is a machining operation of producing a cylindrical hole in a solid work piece by means of a revolving tool called the drill bit. Drill bit is called as twist drill since it has sharp twisted edges formed around a cylindrical body. It is made up of HCS (High Carbon Steel).  50 A countersink is a conical hole cut into a work piece. It is used to allow the dead center to support the axle for further machining processes. Tapping is the operation of producing internal threads in a previously drilled hole by means of a tool called tap. The tap had threads cut on its periphery and is hardened to improve its properties. The threads cut on the tap form the replica of the threads to be produced in the work piece. Brief procedure  An overhead crane transfers the rough turned axle to station 3.  Prior to the operation the pitch circle diameter (PCD) and the angle at which the holes are to be drilled is checked.  The axle is subjected to drilling operation where the drill bit is held in the chuck of the machine and is rotated by a spindle at high speeds of 198 rpm.  The drill bit is forced to move against the rigidly clamped axle.  In the case of BOX-N axles three holes are drilled at an angle of 120o and 22.5 mm drill by the sharp cutting edges of the rotating drill bit.  Excess material removed (i.e; chips) gets curled and escapes through the helical grooves provided in the drill bit.  Countersinking is done with the help of a countersink tool of conical shape for the axles to be supported.  To perform the tapping operation the tool held rigidly in the spindle is rotated at a speed of 90 rpm. The rotating tap is fed slowly in the hole of axle to cut the material and produce threads.  During the tapping process, eight threads are formed for each inch.  51  Operations are carried out on both sides. A continuous supply of coolant is required in order to reduce the heat production and wash away the chips. Operation Speed Feed Depth of Coolant Insert Rev/min mm/min cut mm Drilling 198 50 72 Flood dia 27.5 coolant twist drill Countersinking 198 1 Flood Dia 28 coolant twist drill Tapping 90 52 Flood 1”, 8 (+0.5, -1.0) coolant threads CNC M/C tap.  Station 4: Smooth turning : The rough finished axle is now given a good surface finish by turning operation. A carbide tool with Titanium coating (heat proofing) is fixed in the tool holder and is fed against the rotating work piece. Brief procedure  Bypass the axles that have defects. The type of rejections maybe journal undersize, dust guard undersize, wheel set undersize and body undersize.  The process consists of two channels. CH1: T1 Journal T3 Body T5 Wheel seat  52 CH2: T4 Journal T2 Body T6 Wheel seat  The axle is rotated at a speed of 350 rpm and the operation is carried out at a feed rate of 0.66 mm/rev.  The coolant used during the process is servo oil mixed with water. And the cycle time is 20 minutes.  Change the inserts when required.  Station 5 : Cylindrical grinding : Grinding is an abrasive machining process which uses a grinding wheel as a cutting tool to produce finished surface. The journal is the most important part of the axle since the bearing is seated on it. Hence, the journal is given a perfect finish. This is done by grinding. Brief procedure  53  Two grinding wheels are kept on both the ends at an angle of 45o to finish both the sides of the axles. They operate one after the other.  The work piece (axle) comes near to the wheel and gets fixed.  The high speed grinding wheel rotating at 1240 rpm approaches the axle due to which very fine material layer is removed from the axle due to the action of abrasive particles fixed on the grinding wheel. In the same manner the other side of the axle is also finished.  The time taken for grinding one axle is 8 to 8.5 minutes. *NOTE : The tool used here is a diamond wheel dresser of 700 mm diameter. The depth of cut lies between 0.12 to 0.125 mm.  Magnaglo testing : This is a fluorescent magnetic particle inspection method. This test is conducted for detecting surface cracks. Brief procedure  The operator uses a pipe that consists of magnetic flux powder and carrier oil to wet the axle.  The axle under the black light fluoresces bright yellow green.  Due to accumulation of magnetic flux in cracks, they appear brighter.  The magnetizing time before switching on the black light is 20 seconds.  If the crack is lesser than 21.88 mm, the axle is passed otherwise it is rejected.  Ultrasonic testing : Ultrasound testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. This test is performed to detect interior defects/flaws.  54 Brief procedure  The axle is dipped in the water bath of volume 4000 ltrs.  A transmitter moves above the axle along its axis. It is also called diametric probing.  The frequency used is 5 MHz.  The internal defects can be detected because of acoustic mismatch. This is due to difference in density.  The results are displayed on a CRT screen.  The time taken for ultrasound inspection is 5 to 6 minutes.  Wheel Seat Measuring Station: Since the axle and wheel are brought separately from two shops, during assembly the type of fit maintained is interference fit. The wheel seat is measured with gauges to allow the wheel to be pressed on to it.  Wheel Boring: The wheel boring in the Wheel shop is a rough finishing process. The wheel has to be bored for a smoother finishing and to the specification of the wheel seat. The wheel seat specifications are obtained from the measuring station. The manufactured wheels from the wheel shop for the particular axle is center bored to the measure axle’s wheel seat diameter by the vertical boring machine using Octagon shaped carbide tool.  Wheel mounting : Wheel mounting is the process of pressing the two wheels onto the wheel seat of the axle using mounting press to form a wheel set.  55 Brief procedure  After the smooth surface finish boring operation, the two wheels for the particular axle are sent for pressing. Boring of one wheel consumes 4 minutes. For BOX-N wheel set Bore diameter = 211.917 mm Wheel seat diameter = 212.32 mm  The two wheels are hydraulically pressed so that the two wheels sit on the wheel seat of the axle by using pressing machine one wheel after the other.  Castor oil/double boiled linseed oil is applied on the axle during pressing to reduce the pressure on the axle.  The wheel set obtained is measured by various gauges. Example : offset gauge.  The track gauge measurement and the offset measurement are done. The track gauge is important since the wheels sit on the track. Thus their measurement is essential. And the offset allows the bearing to sit properly.  56  In case the distance between the wheels is to be altered or any other minor corrections need to be done, it is corrected by DEMOUNTING machine.  Good sets are rolled onto the inspection line.  It is painted to prevent the surface of the axle from rusting and the journal is covered and then transported to place where rest of the body parts of the train is manufactured. Pressing tonnage for wheel sets Wheel set type Tonnage Range (metric) BOX-N 78 – 136 BGC 72 - 117.5 BLC 78 – 136 25 T 85 - 128