The document discusses various aspects of fillet welds, including their shapes and profiles, with emphasis on throat thickness and leg length calculations necessary for achieving effective weld strength. It covers specific calculations for determining design throat thickness from leg length and vice versa, while highlighting the significance of proper fillet weld dimensions in resisting fatigue loading. Additionally, it advises against using standard calculations for certain angles and emphasizes the importance of ensuring adequate weld volume for strength.

1. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Welding Technology
THE HEAT AFFECTED ZONE (HAZ)
tempered zone
grain growth zone
recrystallised zone
partially transformed zone
Maximum
Temperature
solid-liquid transition zone
solid
weld
metal
unaffected base
material

2. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Features to Consider
Fillet welds - Toe Blend

3. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Mitre Fillet Convex Fillet
Concave Fillet
A concave profile is
preferred for joints
subjected to fatigue
loading
Fillet Weld Profiles
Fillet welds - Shape

4. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
b. = Horizontal leg length
a. = Vertical leg length
b
a
Fillet Weld Leg Length
Note: The leg length should be approximately equal to the
material thickness

5. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Fillet Weld Features
Design
Throat
Vertical
Leg Length
Horizontal leg Length
Excess
Weld Metal

6. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Fillet Weld Throat Thickness
b
a
b = Actual Throat Thickness
a = Design Throat Thickness

7. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
b
a
b = Actual Throat Thickness
a = Design Throat Thickness
Deep Penetration Fillet Weld
Features

8. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Fillet Weld Sizes
Calculating Throat Thickness from a known Leg Length:
Design Throat Thickness = Leg Length x 0.7
Question: The Leg length is 14mm. What is the Design Throat?
Answer: 14mm x 0.7 = 10mm Throat Thickness

9. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Fillet Weld Sizes
Calculating Leg Length from a known Design Throat Thickness:
Leg Length = Design Throat Thickness x 1.4
Question: The Design Throat is 10mm. What is the Leg length?
Answer: 10mm x 1.4 = 14mm Leg Length

10. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Features to Consider
1200
600
Throat
Thickness
is smaller
Throat
Thickness
is larger
Fillet welds connecting parts with fusion faces with an
angle more than 1200 or less than 600 should not use
the previous calculations.

11. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Features to Consider
Approximately the same weld volume in both Fillet Welds, but
the effective throat thickness has been altered, reducing
considerably the strength of weld B
Importance of Fillet Weld Leg Length Size
2mm
(b)
4mm
8mm
(a)
4mm

12. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Fillet Weld Sizes
Importance of Fillet weld leg length Size
Question: How larger in c.s.a. is (b) comparable to (a)?
4mm 6mm
6mm
4mm
(a) (b)

13. Copyright © 2006, TWI Ltd World Centre for Materials Joining Technology
Fillet Weld Sizes
Area = 4 x 4 = 8mm2
2
Area = 6 x 6 = 18mm2
2
The c.s.a. of (b) is over double the area of (a)
without the extra excess weld metal being added
4mm 6mm
(a) (b)
Importance of Fillet weld leg length Size
4mm 6mm
(a) (b)