DEPARTMENT OF MECHANICAL ENGINEERING

BATCH - 10

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

Gate valve

Connecting

Rod

Wedge

In BHEL gate valve has wedges from 3” to 32”.

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.

Side view of wedge

Problem while machining

Solution

Components of fixture

Base plate

Angle plate

Heat treated plate

Strap Clamps

Rest screw

Fasteners

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)

Contd.,

Angle plate:

To make the parallel machining surface to the machine bed the inclination of the angle plate is set to 4.50.

Material: IS 2062 (carbon steel)

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.

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 =

=

= 7.5398 X 103 mm/s

Contd.,

Fc =

=13,428.7 N.

Clamping force should be greater than the cutting force

So, Let as assume clamping force is 40000 N. (3 times of cutting force)

Total no of clamps = 4

For each clamp clamping force should be 10000 N.

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 8227.23 – 11454.55 N. For this range the bolt diameter is 22.23 mm. From standard bolt table from DDB 5.49.

From the above M24 bolt is selected Material: SA193 B7 .(medium carbon steel)

Strap design

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

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 = 133.33 ~ 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,

Contd., Width (w)

w = 2.3 d +1.5748

=2.3 X 24 + 1.5748

= 56.7748 mm ~ 57mm. Thickness(t)

t2= 0.85 d A [1- (A/B)]

= 0.85 X 24 X 133[1-(133/200)]

t2 = 908.4196

t=30.14 mm ~ 30 mm. Slot width (c)

c=d+1.5748

=24+1.5748

=25.5748 ~ 26mm.

Strap clamp Orthographic view

Strap clamp isometric view

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.

Reference Design of Jigs, Fixtures and Press tools

by c.elanchezhian.

A Hand book of Fixture design- BHEL.

PSG Design data book.