Design and Fabrication of Wedge Milling Fixture
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Transcript of Design and Fabrication of Wedge Milling Fixture
DEPARTMENT OF MECHANICAL ENGINEERING
BATCH - 10
Design and fabrication of a wedge fixture for T slot and guide slot milling for gate valve component.
In BHEL gate valve has wedges from 3 to 32.
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
Components of fixtureBase
AngleHeat Strap Rest
treated plate Clamps
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
= =13,428.7 N.
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.
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.
the above M24 bolt is selected Material: SA193 B7 .(medium carbon steel)
effective clamping the one third of the clamp length provided in between bolt and work piece.
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,
(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
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
A Hand book of Fixture design- BHEL. PSG Design data book.