This document discusses various failure modes and repair methods for machine elements. It covers failures in gears, guideways, spindles, lead screws, bearings, and machine beds. The main causes of failure include wear, fatigue, overload, and corrosion. Repair methods depend on the type and extent of damage, and may include grinding, welding, bush fitting, replacement of parts, and preventing future failures through improved maintenance and design. Failure analysis techniques help identify root causes and prevent recurrence.

1. Repair Methods for Basic
Machine Elements
UNIT-4

2. Failures
It refers a deterioration , Malfunctioning ,
stoppage and crash of any system or element

3. Causes of failures

4. .

5. Main -Classification of failure
System Failure
Component Failure
Example- Failure of any component
in an aero plane makes it
completely in-operable
Example- Failure of air-conditioner
in an automobile will not affect the
running condition of the vehicle.

6. Classification of failure
Intermittent Failure
Permanent Failure
-Failure of any component occur
with in short period due to few
problems
-Example – over heating of parts
This Failure result permanent
damage to the system.
So replacement is the only
solution

7. Sub- classification
• Complete failure
• Partial Failure
Catastrophic Failure – Tyre bursting
Degradation Failure – Brake shoe worn out

8. Basic Failure Mechanism
or
Categories of Failure
• Failure due to Distortion
• Failure by overload or Fracture
• Failure due to fatigue
• Failure due to stress concentration
• Failure due to impact loading
• Failure due to creep
• Failure due to Corrosion
• Failure due to Contamination of unwanted things

9. Failure type
predictable Un-predictable

10. Predictable Failure Model
(Age –Dependent Failures)

11. Failure at any time Survival at running
time

12. Unpredictable Failure (Purely Random Failure)
Some of the machine elements failed with in a week of
time due other reasons

13. FAILURE ANALYSIS
• It’s a reliability and safety analysis
• Logical gates (AND , OR gates) are used.
• Event blocks are also used to do the analysis.
FAUT TREE ANALYSIS (FTA)

14. Example
• Consider two events (blocks) occurrence.
• Chances of one event occur use OR gate
• Chances of both occur use AND gate

16. Example

17. Fault Tree Structure

19. Benefits of Fault Tree Analysis

20. .
EVENT TREE ANALYSIS (ETA)
It’s a visual representation of all
events which can occur in a system

21. EVENT TREE ANALYSIS (ETA)
Example

22. .
Root Cause Analysis (RCA)

23. failureRoot
Cause
Analysis
(RCA)
Cause of Failure
Route cause of
failures
Route cause of
failures
Route cause of
failures
Previous Causes Previous Causes Previous Causes
Evidence Evidence Evidence
Final Solution for future correction
Brainstorming by 3 -6 Peoples

24. Route Cause Failure Analysis
(RCFA)
Same like Route Cause Analysis (RCA)

25. Cause and effect Analysis

26. .
Failure Mode Effective Analysis
(FMEA)

27. • FMEA used to identify Potential Failures and their
effect on product
• FMEA is a tool to identify and prevent problems
from occurring.
• It help the design engineer to make safe and
reliable product from the historical data.
Failure Mode Effective Analysis (FMEA)

28. Types of FMEA

29. FMEA
Flow
Diagram
RPN–
Risk
Priority
Number

30. Failure Mode Relationship in FMEA

31. Inputs and outputs of FMEA

32. Benefits of FMEA

33. Applications of FMEA
• In Manufacturing and assembly
• In Design Process
• Equipment design and Purchase
• Service

34. Failure Mode, Effect and Criticality
Analysis (FMECA)

35. • It’s the extension of FMEA analysis.
• Here , we are ranking the failures depend on
the criticality
Failure Mode, Effect and Criticality
Analysis (FMECA)

36. Criticality index
• Each Failure data are listed with their danger
rating called criticality index.
• Depend on this number they can judge the list
the hazards and its risks

37. Types of FMECA
Design FMECA Process FMECA System FMECA
Eliminate
Failure
during
Equipment
Design
Eliminate
Failure right
from m/c
manufacturing,
Maintenance
Eliminate
Failure right
from
production
lines

38. Approaches to
FMECA
Bottom up Approach Top Down Approach
All Components right
from bottom are taken
to study one by one
This analysis Start
from Early Stage of
Design.

39. Failure Reporting And
Corrective Action System
(FRACAS)

40. FRACAS
• It’s a closed loop system that is used
to manage failure throughout the
Product life cycle

41. How it works ?
• The owner of FRACAS is responsible to give a
elaborated statement of how failure
happened, date of failure and conditions .
• Then it goes to an engineer to find out fault
and its solution

42. .
Maintenance in Gear

43. • Periodic maintenance
• Proper Lubrication
• Proper loading
• Proper design and installation
Maintenance in Gear

44. Failure Analysis of Gears
1. Inspect the failed gear
2. Identify the nature of failure
3. Analyzing time constraints
4. Preparing for inspection
5. Failure Inspection at site

45. Steps
• Visual Examination
• Document observations
• Calculations of gear geometry
• Specimens for lab tests
• Determine type of wear
• Test and calculate Aid Analysis
• Conduct NDT test
• Report the results

46. Causes of gear teeth surface Deterioration

47. Gear failure - Wear

48. • Ridging – formation of diagonal lines on tooth
surface
Gear failure – Plastic Flow
(surface Yielding)

49. Gear failure - Scoring
• A sudden removal of material from tooth surface

50. Gear failure – Surface Fatigue
• A failure due to repeated stress on a particular area
For small cavities – grinding or polishing tooth surface
Pitting , Spalling – do surface hardening
Maintenance

51. Tooth Breakage

52. Tooth Breakage

53. Repair of Tooth
Deposition of weld
metal on crack portion

54. Repair of gear meshing area

55. Repair of damaged rim or bore of the
gear

56. Gear Inspection

57. GUIDEWAYS

58. GUIDEWAYS - Classification

59. • Load carrying capacity
• Position of transmission
• Wear type
• Ease of chip disposal
GUIDEWAYS –
Design Based on

60. Factors - Guide ways wear

61. Methods of Repairing – Guide ways

62. Methods of Repairing – Guide ways
Scraping

63. Methods of Repairing – Guide ways
Grinding

64. Methods of
Repairing –
Guide ways
Grinding
In Different Position

65. Methods of
Repairing –
Guide ways
Machining

66. Checking of Guide ways
• Straightness
• Flatness
• Parallism of surfaces

67. Lathe Bed
Repair

68. SPINDLES

69. Parts of Spindle

70. Wears on Spindle

71. Repair Standards (references)
• The dimension of the existing state of the
spindle are compared with the reference
dimensions called repair standards

72. Repair Standards for shanks and bearing seats

73. • Chrome plating
• Metallization
• Fitting compensating bush
Repair methods for shanks and bearing seats

74. Chrome plating
• Initial clamping at both ends are done
• Proper metal finishing is done on lathe
i.e …for avoid eccentricity
• Then the spray type or dip type deposition is done on
metal to be coated.
• Chromium can with stand high temp
• It’s a `Wear – Corrosion resistant
• But not with stand knocks
• It’s a Costly and time consuming Process
When the wear is up to 0.2mm

75. Metallization When the wear is more than 0.2mm
• Initial groundings are done to avoid taper and eccentricity
• Initial pre heating is done on metal surface

76. Fitting Compensating Bush
• Its done when the wear is more than 1mm in dia

77. Repair methods for Bush Bearing seats
• Its done when the wear is b/w 0.1mm – 0.2mm in dia
Lapping
A bush with the
internal thread is
fastened with the
bearing by layer of glue

78. • When the wear is in 0.2 mm in diameter
Grinding
Here the shanks are ground to the required size

79. Repair methods of taper bore of
spindles
• Grinding
• Fitting Compensating Bush
• Spindle Reversal (boring a new taper hole at other end)

80. Repair methods for Threads of Spindle
• Metal deposition & thread cutting
it’s the only way to build a new
thread on the surface

81. Repair methods for Keyways of Spindle
• Over sizing (keyway is made to next std. value)
• Cutting new keyway (Cutting keyway in opp.side of
spindle)
• Weld deposition (Metal Deposit & key way milling)

85. Repair standards
• The permissible bending or eccentricity
relative to the axis of rotation in a length of
500mm is 0.03mm to 0.06mm

86. Repairing methods for wear up to 0.3mm
• Both sides of the threads turned slightly
• Reduce diameter and cutting new threads

87. Repairing methods for wear over 0.3mm
• Worn out lead screw replaced by a new one.
• Partial replacement of Parts

88. Repairing methods for Lead screw nut
• When ever a lead screw has been replaced or
repaired, the matching nut also replaced or
repaired according to the thread of the screw
METHODS
Depositing Metal

89. BEARINGS
.

90. Bearing
It’s a element used for frictionless shaft Rotation
Plain Bearing Roller Bearing
Bearing
Light Loads Heavy Loads

91. Requirements Bearings

92. Basic Requirements - Bearings

93. Bearing Material

94. Plain Bearing –
Factors influence performance

95. Plain Bearing –
Factors influence performance

96. Plain Bearing –
Factors influence performance

97. Plain Bearing – Factors influence performance

98. Plain Bearing –
Factors influence performance

99. Plain Bearing –
Factors influence performance

100. Repair Methods of Bush Bearings
Bush Bearing
Solid Bush Bearing Split Bush Bearing
•Full Replacement
• Grinding
• Using Proper Bush Locking screws
• Use Proper thickness of
Packing material
• Give proper Gap b/w materials

101. Inspection of Bearing failure

102. Inspection of Bearing failure

103. Inspection of Bearing failure

104. Inspection of Bearing failure

105. Bearing Failure
- Classification

106. MACHINE BED
.

107. MACHINE
BED
Riveting

108. MACHINE
BED
Hot
Clamping
Clamping and Weld deposition