1. A.V.C.COLLEGE OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
BATCH - 10

2. Design and fabrication of wedge milling fixture
Presented by,
M. Chandru
G. Muthuthiyagarajan
C. Padmanabha
B. Prakash
Internal guide,
M. Varatharajulu, B.E.,M.B.A.,
Asst. professor.
External guide,
S. Sivananainthaperumal,A.M.E
Manager(Tool Engg),
BHEL.

3. Objective
Design and fabrication of a wedge fixture for ‘T’ slot and guide slot milling for gate valve component.

4. Gate valve
wedge

5. Wedge
In BHEL gate valve has wedges from ” to 32”.

6. Contd.,
The wedge is made by casting process.
Then the ‘T’ slot and guide slot are made by milling process in vertical milling machine and horizontal milling machine.
The ‘T’ slot is used to hold the wedge by means of a stem which is normally connected with actuator or hand wheel.
Guide slot is used for up and down motion of wedge inside the valve.

7. Side view of wedge

8. Problem while machining

9. Solution

10. Components of fixture Base plate Angle plate Heat treated plate
Strap Clamps
Rest screw
Fasteners

11. Design
Base plate:
Base plate is designed according to the milling machine bed dimensions and angle plate dimension. The base plate is fastened with the bed by using ‘T’ bolts.
Dimension: 1484 X 1484
Material: IS 2062 (carbon steel)

13. Contd.,
Angle plate:
To make the parallel machining surface to the machine bed the inclination of the angle plate is set to
Material: IS 2062 (carbon steel)

15. Contd.,
Heat treated plate: It is a circular thin plate of thickness 10mm. It has the same diameter of the Angle plate . This is gas carburized plate . Use of the plate is to reduce the fixture wear due to continuous loading and unloading of work piece. Clamp: For this fixture we select the strap clamp. We design the strap clamp. The calculations are as follows.

16. Clamping force calculations
For any fixture the clamping force should be greater than the cutting force, so we calculate the cutting force by the following formula.
CUTTING FORCE (FC) =
Here, K=material constant (KN/mm2), f = feed(mm/s)
d =depth of cut (mm),b =width of cut (mm)
Cs = cutting speed (mm/s).
cutting speed Cs = =
= X mm/s

17. Contd.,
Fc =
=13,428.7 N.
Clamping force should be greater than the cutting force
So, Let as assume clamping force is N (3 times of cutting force)
Total no of clamps = 4
For each clamp clamping force should be N.

18. Contd.,
To get the 10000N clamping force chose the bolt diameter from the force exerted by bolts table.(table 3.1,design of jigs, fixtures and press tools by C.Elanchezhian book)
The range is – N. For this range the bolt diameter is mm. From standard bolt table from DDB 5.49.
From the above M24 bolt is selected
Material: SA193 B7 .(medium carbon steel)

19. Strap design
For effective clamping the one third of the clamp length provided in between bolt and work piece.

20. Contd., From the above d = 24 (d = diameter of the bolt)
From DDB, for M24 bolt the total length of the clamp, B = 200 mm.
And the 2/3 of B is the distance between rest screw and the bolt .
A = 2/3 B
= 2/3 (200)
A = ~ 133mm.
And the chamfer values are taken from the DDB
Values of A , B , d are used to find the thickness and width, slot. The calculations are as follows,

21. Contd., Width (w) w = 2.3 d +1.5748 =2.3 X 24 + 1.5748
= mm ~ 57mm.
Thickness(t)
t2= 0.85 d A [1- (A/B)]
= 0.85 X 24 X 133[1-(133/200)]
t2 =
t=30.14 mm ~ 30 mm.
Slot width (c)
c=d =
= ~ 26mm.

22. Strap clamp Orthographic view

23. Strap clamp isometric view

27. conclusion
Thus the wedge milling fixture is designed and fabricated according to the above discussion.
The above said problem was rectified by our fixture.
Using this fixture the T slot and guide slot are milled without any difficulties.
The need is fulfilled by our project.

28. Reference Design of Jigs, Fixtures and Press tools by c.elanchezhian.
A Hand book of Fixture design- BHEL.
PSG Design data book.