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Internship at LMTG


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Internship at LMTG

  1. 1. INTERNSHIP AT LMTG Presented by: Ashish Sethi Indian Institute of Technology (Banaras Hindu University), Varanasi (May-June 2013)
  2. 2. Steam Turbine • Thermal energy from pressurized steam does mechanical work on a rotating output shaft. • Drives an electrical generator which produces power. • Increase in thermodynamic efficiency by using multiple stages in the expansion of steam.
  3. 3. Projects: Past and Present Projects Undertaken By LMTG Power Rating APPDCL-1 800 MW APPDCL-2 800 MW JP-1 660 MW MH-1 660 MW Rajpura-1 700 MW JP-2 660 MW MH-2 660 MW Rajpura-2 700 MW MH-3 660 MW USA 660 MW Rabigh IWSPP 120 MW RRVUNL-1 660 MW RRVUNL-2 660 MW • Supercritical range: 5001000 MW • Refers to main steam operating conditions being above critical pressure of water (221.5 bar) • At a pressure of 242 bar, main steam and reheat steam temperatures are 565ºC and 593ºC respectively.
  4. 4. The Process Flow Fabrication Heat Treatment Shot Blasting Assembly Machining Painting Shot Blasting Painting
  5. 5. Layout of the Production Department
  6. 6. Machine Shop T3 • Planomillers: Gen 6 and ST 13 Planing Milling Planomilling  Axes are X, Y, Z, W and C.  Bed moves, columns are stationary.  Attachments include right angle, universal, extension and surfacing. • Horizontal Boring Machines (HBMs): UDM 1, UDM 2, UDM 5, ST 15  Operations such as drilling, boring, facing, back spot facing, turning, etc. can be performed.  Possible axes include X, Y, Z, W, V, B.  Attachments include right angle, universal, facing and profiling, offset.
  7. 7. Machine Shop T3 (contd.) • Vertical Turning Lathes (VTLs): Gen 7 and ST 9  Facing, ID turning, OD turning, chamfering etc. performed using a single point tool.  Axes are X, Z and W. • Electric Discharge Machine:  Used for machining thin slits in blades and grooves for caulking.  Used for machining hard materials like HSS.  Copper electrode is used.  Job is completely submerged in dielectric oil, which acts as a capacitive medium.  When voltage is sufficiently high, electric arc is generated which jumps across dielectric medium and erodes metal.
  8. 8. Machining Tools and Operations Operation Purpose Tool Facing Generation of a flat surface Face mill, Shoulder mill Turning Generation of a cylindrical surface Single point cutting tool Drilling Making holes Drills Boring Enlarging holes, ID machining Boring tool Tapping Making internal threads Taps Reaming Finishing of holes Reamer Chamfering Generation of Chamfering tool angled surfaces to remove sharp edges Slot Milling Machining of slots End mills
  9. 9. Cutting Parameters • where, V is the cutting velocity N is the required rpm D, for turning – diameter of job for facing – diameter of cutter for drilling – diameter of drill bit For tools with multiple inserts, where, Feed rate is in mm/min fz is the feed/revolution/tooth
  10. 10. PROJECT I: TOOL DEVELOPMENT Objective: Developing tool for back spot facing of diameter 46 mm for “D4” detail in ash lock
  11. 11. Challenging Aspects of Ash Lock Machining • Ash lock has two openings (A1 and A2). The machine ram cannot enter A2. • Large spindle overhang makes it difficult to maintain concentricity of various IDs. • Vibrations arise as machining operations take place at very large distances from the ram. • Not possible to mount the ash lock at the centre of the table. On rotating the rotary table, the centre of various IDs gets displaced.
  12. 12. Common Back Spot Facing Tools • Centric Tool:  Rotates about its centre.  Has a removable head.  Suitable in situations where back spot diameter is much more than passing diameter. • Eccentric Tool:  Insert is offset from the central axis of tool.  Efficient as no manual intervention is required.  Suitable when difference between spot face diameter and passing diameter is less. • Tool with HSS Bit:  Boring bar with slot at its end to hold the HSS bit.  Similar to centric tool, as bar is first passed through the bore and then the bit is inserted. • Butterfly Tool:  Has a foldable wing.  No manual interruption.
  13. 13. The D4 Detail
  14. 14. Problems Faced and Possible Solutions • Unavailability of tool of sufficient length and required passing diameter. Length of the tool should be more than (1350 + 50 + 50 – 1000) = 450 mm Maximum spindle travel Clearance between ram and A2 Minimum thickness of the flange Distance between A2 and D4 • Vibrations in the tool because:  Spindle would be at close to its maximum extension.  The length of the tool is large.  The diameter of the bar is small.
  15. 15. Problems Faced and Possible Solutions (contd.) Suggested solution: • The bar of the tool to be in the form of a stepped shaft. • The bar of the centric tool is internally threaded at its end, for attaching the removable head. • A short tool of this type with a large passing diameter could be attached to another with a passing diameter less than 27 mm, creating a stepped bar. • External threads would have to be machined on the tool with smaller diameter, to mesh with the internal threads present in the first tool.
  16. 16. Problems Faced and Possible Solutions (contd.) • Problem of chip evacuation because of large depth of back spot. Suggested solution:  Using a tool with HSS bit. Proper angles can be provided to guide chip flow.  Machining of a helical path in the removable head of centric tool. • If we use a tool with HSS bit, setting the bit to make the required back spot diameter is time consuming. Suggested solution:  Step to be created on the bit at a pre-determined distance from the cutting tip.  Stepped part will not enter the slot.
  17. 17. Problems Faced and Possible Solutions (contd.) Cutting Force • Large spindle overhang results in drooping of machine spindle. • Cutting forces on the bit tend to reduce the diameter of the back spot. • Difficult to accurately predict the diameter formed for a particular length of tool bit cutting edge. Suggested solution:  Preparation of tool bit for a slightly larger diameter.  Modification to length of cutting edge depending on outcome of trials.
  18. 18. The Final Tool • Boring bar of length 450 mm and passing diameter 26 mm used. • Longer adaptor not originally meant for this boring bar used. • Slot of 9.5 x 9.5 mm for housing HSS bit. • Outer part of the bar is ground to smaller diameter.
  19. 19. The HSS Bit Diameter of the boring bar = 26 mm Radial distance between the bore and the bar = 0.5 mm Difference between spot face diameter and bore diameter = 19 mm So, Radial distance between bore and OD of spot face = 9.5 mm Allowance for cutting force problem = 0.5 mm So, distance from step to tip of tool = 26 + 0.5 + 9.5 + 0.5 = 36.5 mm • Three relief angles – rake angle, clearance angle, end cutting edge angle • Step was removed one side and pushed inwards.
  20. 20. Machining of HSS Bit Step was created on VMC in T6 Required angles were given on Tool and Cutter Grinder in T6 Required length (including the step) was cut off from the bar on EDM in T3 Step was pushed inward on required side on Tool and Cutter Grinder in T6
  21. 21. Trials Conducted Distance from step Spindle to cutting extension tip (mm) (mm) Diameter of back spot formed Remarks 0.7 mm material was subsequently ground off from the end of the bit. 0.1 mm material was subsequently ground off from the end of the bit. Very long chips were formed and good surface finish was obtained with coolant. Surface finish without coolant was not very good. Repeatability of the bit was confirmed. Long chips and good surface finish was obtained with a feed rate of 1 mm/min. Increasing the feed rate to 1.5 and 2 mm/min degraded the surface finish. Repeatability of the second bit was confirmed. 36.9 500 48.4 36.2 500 46.8 36.1 500 46.4 36.1 1100 46.2 Bit II 36.1 36.2 1100 800 46.2 46.8 (for clockwise spindle rotation) 36.2 800 46.8 Bit I (for counter clockwise spindle rotation)
  22. 22. PROJECT II: SURFACE FINISH ANALYSIS Objective: Analyzing surface finish obtained using wiper cutter on Horizontal Boring Machine (of Collet make) – UDM 1
  23. 23. Wiper Cutter • Used for finishing of plane surfaces. • Not a single point cutting tool. Whole cutting edge ‘wipes’ off the high points. • Can be done using a single insert, or more than one. • If more than one insert is used, one forms the roughing edge and the other forms the finishing edge. • The finishing edge is placed 10-20 microns below the roughing edge. • The finishing edge is radially inward in comparison to roughing edge. • Mitsubishi wiper cutter can hold 2 inserts, Dijet can hold 4. Operation of wiper cutters with single insert on UDM 1 is generating extensive back cut marks on the surface.
  24. 24. Trials Conducted Machine Make of Cutter Cutting Parameters Back Cut UDM 1 Mitsubishi 100 rpm Clearly visible back cut A face out of 0.04 mm was observed on the cutter. Less back cut A face out of 0.16 mm was observed on the cutter. Less back cut Cutter was removed and set again. A face out of 0.12 mm was observed on the cutter. Possible reasons for this face out were discussed: 125 mm/min feed UDM 1 Dijet 100 rpm 125 mm/min feed UDM 1 Dijet 100 rpm 125 mm/min feed Remarks • Face out in the cutter itself • Face out in the cutter due to run out of the spindle
  25. 25. Machine Gen 6 Gen 6 Make of Cutter Mitsubishi Cutting Parameters 220 rpm Mitsubishi 300 mm/min feed 220 rpm 300 mm/min feed Gen 6 Mitsubishi 220 rpm 300 mm/min feed Gen 6 Mitsubishi 250 rpm 300 mm/min feed Back Cut Remarks Visible back cut Face out on the cutter observed. Visible back cut A different Mitsubishi cutter was used. Face out of 0.08 mm observed. Insert was kept on the lower end of the cutter. Replaced insert. Other conditions same as before. Visible back cut Slightly less back cut Concluded that problem not with the cutter. Insert position changed from lower end to upper end. Possible reason for back cut could be spindle run out. • Spindle run out of UDM 1 is 0.5 mm. • ST 13 Mitsubishi 300 rpm 350 mm/min feed No back cut Spindle run out of Gen 6 is 0.25 mm. No spindle run out on ST 13. Reason for back cut found to be spindle run out.
  26. 26. Suggestions for Improvement in Shop Reasons for formation of such an irregularly shaped pit were discussed: • If the table of EDM is not locked, it can deviate slightly if a jerk is encountered for any reason. • There may be an error in initial setting of the electrode by the operator. Suggestion: Job could be covered with an insulating material in areas where no cutting is to take place.
  27. 27. Suggestions for Improvement in Shop (contd.) • Using ATC (Automatic Tool Change) in Gen 6 Planomiller machine.  Offset of tools needed for the next planned job can be taken and their values stored in the ATC beforehand.  Tools can be stored in the ATC.  Time required for completion of job can be reduced. • Leakage from the roof over Machine Shop T6.  Machines such as Tool and Cutter Grinder can not be used at times.  Possibility of damage to the machine.