Maintenance of Machine Tools

1. Maintenance of Machine Tools -Presented By Bidve M.A.

2. Introduction of Maintnance • Introduction • Definition & Need • Causes • Importance • Types

3. Definition • Maintenance can be defined as a set of activities which are carried out to keep machine/device/equipment in good operating/working condition.

4. Need/Objective • To avoid breakdown of machine. • Replace and repair of parts. • Lubrication in sliding/moving parts. • To maintain accuracy and productivity. • To ensure longer service life. • To reduce non productive time. • To maximum use of machine & improve efficiency.

5. Causes • Insufficient Lubrication. • Overloading. • Misalignment. • Vibrations. • Improper handling. • Lack of preventive maintenance.

6. Importance • Safe & proper working of machines. • It helps to improve quality. • Control cost. • To develop market reputation.

7. Types • Unplanned Maintenance. • Breakdown 2. Corrective • Planned Maintenance. 1. Preventive 2. Predictive 3. Corrective 4. Routine 5. Design out 6. TPM

8. Unplanned Maintenance • In this type first breakdown or failure of machine tool take place and then maintenance will be carried out. • Emergency Maintenance. • Small scale Industry.

9. Breakdown Maintenance It is the conventional type of maintenance in which the breakdown of machine tool will occur and then maintenance is carried out. Not to do anything until and unless the machine stops its working. No plan for oiling, servicing. e.g. belt is broken, failure of joints, gears, couplings, springs, shafts, etc.

10. Advantages & Disadvantages of Breakdown Maintenance -Cost of maintenance is less. -No expert staff is required. Time delay. Life of components decreases b’coz of more wear & tear. Danger of accidents. Not suitable for mass production

11. Corrective Maintenance • It is the maintenance work that consists of replacement or repair of components. • Different sensors are connected to each machine to detect the performance. • It is pre-maintenance before breakdown or failure.

12. Planned Maintenance • In that the maintenance system is related for planning, scheduling, analysis of machine tool for its trouble free performance. • Schedule of maintenance activities are planned and followed strictly. • Problems may not occur.

13. Preventive Maintenance • Prevention is better than cure. • It is most popular maintenance system adopted by many industries. • It is as like regular body check up for blood pressure, sugar, etc by doctor. i.e. Lubrication, noise,vibration,oil change,belt & bearing replacement.

14. Advantages of Preventive Maintenance • Less production down time. • Repairs of parts are avoided. • Life of components increases. • Better quality control. • Less standby equipments. • Greater safety and protection. • Cost is control for maintenance.

15. Disadvantages of Preventive Maintenance • Not suitable for small scale industry. • More staff is required. • Cost of maintenance staff is more.

16. Predictive Maintenance • It is advanced maintenance method in which failure of the components can be determined or predicted so that repair can be done before failure. • Sensors, measuring and monitoring techniques are used. • Vibration analyser, wear monitoring devices, axial displacement monitors, non contact sensors are used.

17. Predictive Maintenance • Cost is more because of advanced electronic instruments. • It consists of three stages. • Detection b) Analysis c) Correction Predictive Maintenance includes • Scheduled Maintenance. • Condition based Maintenance.

18. Scheduled Maintenance • When maintenance is carried out as per the time table prepared in advance for the machine tool, it is known as scheduled maintenance. e.g. Cleaning of water tank, checking of pressure vessel, refilling of CO2 in fire extinguisher, calibration of measuring instruments,etc.

19. Advantages • Faults are detected correctly. • Improves service life of machine. • It prevents breakdown of machine. • It reduces the machine down time. • Safety and reliability is increased. • Minimizes the risk of failure. • Product quality is maintained.

20. Disadvantages • Use of sensors, meters increases cost of maintenance. • Not suitable for small scale industry. • Trained team of maintenance members is needed.

21. Condition based Maintenance • In this type, maintenance is done on the actual condition of the machine rather than on some preset schedule. e.g. instead of changing oil after 1000Km ,it is checked to determine actual condition and lubrication properties of oil and change.

22. Total Productive Maintenance • It is participative type maintenance technique in which responsibility of routine maintenance is shared by the operator himself rather than separate maintenance staff. • TPM increases the effectiveness of man machine system and it has objectives of zero maintenance and zero defects.

23. Objectives of TPM • Increase effectiveness and efficiency of machine. • Improve operator skills. • Minimize maintenance cost. • Minimize breakdown. • Improve quality of product. • Improve safety. • Improve reputation of company in market.

24. Basic Maintenance Practice • Bearing • Coupling • Shaft • Pulley • Gears • Chains • Belts

25. Bearing • It is medium of contact between rigid and movable parts. • Types: Ball bearing, Roller bearing • Subtypes: Thrust ball bearing, deep groove, angular contact ball bearing. They are used in power transmission by shafts, axles, spindles, chucks, etc

26. Failure Factor • 1. Dirt: It enters in the recesses in the bearing and causes rupture and removal of lining while rubbing. Maintenance: 1) Grinding and polishing of the journal surface. 2) Change oil and filters at regular intervals. 2. Fatigue: Fatigue crack occurs when running time is exceeded.

27. Failure Factor It is due to cyclic loads, load due to dirt accumulation, poor geometry of shaft, misalignment, etc Maintenance: 1) Proper Lubrication 2) Oil film thickness should be at desired level. 3. Hot shot phenomenon: Large area of lining gets removed from the steel back. Due to insufficient oil flow, dirt in oil, misalignment.

28. Failure Factor Maintenance: 1) Temperature at the contact surface should not be more than desired level. 2) Ensure flow of oil free from dirt. 4. Fretting: It is rubbing of mating surface due to load. Wear occurs in the form of crushing area Maintenance: 1) Cleaning of the mating surface 2) Remove burrs while installation of bearing.

29. Failure Factor 5. Excessive Interference: Too tight fit at joints faces causes overheating due to excessive interference. Maintenance: Make proper fitting during mounting of bearing. 6. Corrosion: It removes outer surface of oxidation of lubricants Maintenance: 1) Prevent coolant leakage into oil 2) Consult oil suppliers.

30. Coupling • They are used to connect the shaft ends together for transmitting torques or rotary motion directly from one shaft to the other. • Types: Rigid coupling, Flexible coupling • Commonly used : Flanged coupling, Muff coupling, Bush pin coupling, Universal coupling, Oldham coupling.

31. Installation of Coupling • It is dismantled before installation and arrangement of the components noted carefully to assemble it again. • Cleaned properly to make free from dirt, burr, etc. • Keys are also checked for proper fit. • Hubs are fitted in shaft by heating water, oil • Alignment concentricity & balancing is checked.

32. Causes of failure of Coupling • Misalignment of mating parts. • Defective material during construction. • Improper fitting of coupling, improper tolerance. • Improper lubrication increases friction. • Improper selection of bearing.

33. Maintenance of Coupling • Noise of coupling due to misalignment, loose belts, etc. • Observe the vibration due to run out. • Visual inspection for misalignment. • Checking of lubrication regularly & change oil after certain interval. • Prepare maintenance report.

34. Shaft • It is a rotating member which transmits power from one place to another. • Causes 1. Misalignment 2. Run out 3. Friction and vibrations 4. Cyclic loads

35. Maintenance of Shaft • Check alignment of shaft by alignment testing method like dial indicator, straight edge, filler gauge. • Run out is checked by dial gauge axial & radial. • Shaft is properly balanced checked by static & dynamic balancing. • Design of shaft.

36. Pulley • It is a circular wheel which has a groove at the centre. • It is generally mounted on shaft for transmit the power. • Causes • Improper selection of pulley. 2. Improper rope/ belt size. 3. Tight fitting of belt. 4. Improper alignment, balancing with key & shaft

37. Maintenance of Pulley • Use pulley of correct size & standard mfr. • Check groove properly. • Dynamic balanced pulley must be used. • Proper alignment of pulley. • Lubricate moving part periodically. • Check tightness of belt on pulley.

38. Repair Cycle • The repetitive performance of maintenance activities in between two overhauling (Servicing) is called as repair cycle. • Inspection(I) • Minor repair(M) • Medium or Major repair(M) • Overhauling(O)

39. Repair Cycle Analysis • No of maintenance staff is needed. • No of small/minor repairs. • No of major repairs which are important and need more time and cost. • No of spare parts and their quantity. • To prepare budget of maintenance section.

40. Repair Complexity • It is defined as the extent of complexity of machine tool considered for the maintenance work which is represented by a index number. This number is called as repair complexity.

41. Use & effect of Repair Complexity • Use: To calculate maintenance staff size, To design inventory required for spares, To forecast the maintenance cost, To design repair cycle of machine tool, No of critical points can be find out. • Effect: It decides the time interval of repair cycle, When repair complexity no is large then repair cycle is longer & more time is required.

42. Maintenance Manual • We know that whenever we purchase any machine, vehicle then service or maintenance booklet is provided by the manufacturer which is called maintenance manual. • It is in printed format gives the user of the equipment about the preventive maintenance to be done w.r.t. time of that machine tool. • It is prepared based on vast experience of the manufacturer & feedback of customer.

43. Importance of Manual • Procedure for maintenance of different parts. • Maintenance schedule of different parts. • Safety precautions. • Instructions for safe handling. • Table showing trouble shooting of common parts. • Guarantee/ warrantee rules. • Service center details.

44. Maintenance Records • It is necessary to prepare documents for the improvements as well as to get history of maintenance. • The various reports/ charts are prepared by the maintenance staff. Which includes machine history card, preventive maintenance chart, breakdown report. • It is useful for making fast decision.

45. Machine History Card

46. Preventive Maintenance Chart

47. Breakdown Maintenance Chart

48. House Keeping • It is a practice or culture which arrange various facilities to create healthy & cheerful work environment. • In simple manner ‘Housekeeping’ is the culture to put right things at right place at right time. • Poor housekeeping increases the chances of breakdown, unsafe working condition & poor utilization of resources like man, machine & material.

49. Elements of House Keeping • Maintain easy and efficient flow of production • Adequate space is allotted for the storage. • Arrangement like ventilation, lighting, air circulation and exhaust system. • Clean & safe water supply, proper sewage disposal facility. • Cleaning, sanitary facilities, lockers, changing room, hygienic food canteens,etc.

50. Necessity of House Keeping • Make & maintain a clean, neat work area and surrounding. • Make work area look pleasant, more satisfying and motivate for quality work. • Minimize discomfort to the workers. • Minimize injury and accidents. • Increase the life of plant, building. • Avoid fire and other hazards.