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Int. J. Mech. Eng. & Rob. Res. 2014 D P Kute et al., 2014

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Vol. 3, No. 2, April, 2014

2014 IJMERR. All Rights Reserved

Research Paper

CAD MODELLING & CONCEPT DESIGN OF JIGFIXTURE FOR CONCENTRIC DRILLING

D P Kute1*, A V Gadge1 and A P Kedar2

*Corresponding Author: D P Kute, devprakashkute@yahoo.com

Due to todays heavy, growing competition environment, manufacturing companies have todevelop technologies to produce no scrap. Owing to the trend towards reducing lead time andhuman effort, fixture design is one of the options. This paper discuss about Jig and fixturedesign to drill five equidistant concentric holes on coupling hub.

Keywords: Jig and fixture design, Drilling concentric equidistant holes

INTRODUCTION

Anybody who has ever drilled on circularperiphery knows that it is extremely difficultto prevent the drill from slipping and goingoff to the side, leaving misshaped holes. Thisis of course not something that is acceptedin the industry. The tolerances are very highand mistakes are not allowed. For a singlehole to be drilled there is no problem, but forfive holes and that to concentric & equidistanton circular periphery of a coupling hub is abig problem. The process of drilling with thehelp of vertical drilling machine is all donemanually. So there is a scope to be mistakenfrom starting (i.e. from marking & punchingcenters for holes) to the end drilling. So theproject, to eliminate the rejection of fingercoupling hubs was done to solve the problemby designing the Jig & fixture for the same.

1 Asst. Professor, Mechanical Engineering Department, Priyadarshini Institute of Engineering & Technology, Nagpur.2 Professor & Head, Mechanical Engineering Department, Priyadarshini Institute of Engineering & Technology, Nagpur.

PROBLEM DEFINITION

The support roll & drive shaft assembly isused in the zinc pot of a galvanizing line. Thejaw coupling is fixed with the support roll whilethe finger coupling is fitted with the drive shaft.The figure will let us understand the positionof the jaw & finger coupling on the supportroll & drive shaft respectively.

The jaw is an imported component from otherindustry while the finger coupling is fabricated

Figure 1: Support Roll with Jaw Coupling& Drive Shaft with Finger Coupling

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Int. J. Mech. Eng. & Rob. Res. 2014 D P Kute et al., 2014

in the workshop of the galvanizing industry.The unavailability of finger coupling wasoccurring due to its improper fabrication. Thisresulted in non engagement with the jaw.This was the main problem which was to berectified.

Figure 2: Actual Photo of Jaw & FingerCoupling Assembly

Non engagement Proper engagement

PROCEDURE OF MAKING

FINGER COUPLING

Firstly the fingers are made from EN08 (mildsteel) round bar of 30mm. The 30mmround bar is turned into size of 25mm onlathe machine. Then external threading ofM24x24mm is done one the lathe machine.Then the bar is cut into length of 50mm & thefinger is ready. Then coupling hub is madefrom 100mm EN08 material round bar. The100mm bar is machined on lathe to give aspherical shape of 85mm upto width of50mm. Then a bore of 50mm is done. Atthe center of the bore a step of 60mm x30mm & the hub is ready. Marking & punchingof holes on the circular periphery. It is themost important & time consuming process.It requires highly skilled person to get thecorrect marking & punching. Then the hub istaken to the vertical radial drilling machine &fixed in the vise. This also requires high skillso as to place the marked hole position exactvertical to get the concentric drilling. After itis properly fitted in the vice, drilling is done atthe marked position with a twist drill of 21mmsize. In this too the procedure is critical &

requires skilled person since the surface isspherical. Then the drilled 21mm sizedholes are tapped manually with the help ofM24 size tap set. After making the fingers &the hub, the fingers are fastened into the hub& the finger coupling is ready to use for fittingit into the drive shaft. The complete fingercoupling fabrication procedure can be seenthrough the following photo.

Figure 3: Finger Coupling Fabrication Sequence

GEOMETRICAL CONCEPT

GENERATION

First aim is to restrict all degrees of freedomof the object. This will be done with the helpof the fixture. But for this let us see first, thecurrent arrangement for holding the couplinghub.

Figure 4: Finger Coupling Clamping inDrilling Vice

Actual Job Holding Area for Clamping

For arresting its all degrees of freedom & forbetter clamping we will be using block typeof fixture. The fixture can be of Split type soas to fix the hub inside as shown in figure.

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Figure 5: Split Type Fixture Block

This type of fixture will arrest some of thedegrees of freedom of hub. But we will haveto arrest all the DOF. We will be evaluating itafter the complete fixture concept. Now gofor its indexing.

INDEXING CONCEPT GENERATION

For indexing, there can be automatedsystems but this will increase the cost. Andas per the consideration for achieving ouraims stated earlier, we will go designing theconcept for manual indexing.

Now the process of is of drilling fiveequidistant holes, so square block of thefixture will not solve our problem. Also ratherthan providing another jig, which will increasenumber of parts, cost, time for fabrication etc,for correct drilling we will try for the jig to bemade with the same fixture. It will providethe rigidity & ease of use by having fewerparts. For drilling five concentric & equidistantholes we can go for a regular pentagonalstructure. (James Waltman, 2006; Lonny LThompson et al., 1998). as shown in figure.

Figure 6: Pentagonal Fixture

But with this position it is not possible to drillat the corners of the pentagon. So the cor-rect position for drilling will be its invertedposition as shown in figure below. Now atthe plain surface we can provide jigs for drill-ing. We will provide five jig bushes, one oneach side. This will solve our problem of drill-ing five holes

Figure 7: Correct Position for thePentagonal Fixture

By rotating the fixture one by one such a waythat the plain surface will be always perpen-dicular to the drill, or we can say the surfaceshould be horizontal since we are using ver-tical drilling, can get the desired result. Butstill it can't be assured or it is difficult to keepthe fixture always in the correct position. Soas to have this we will be providing a basewhich will perform the task of correct index-ing of the fixture. It is shown in the figure

Figure 8: Base for Fixture Indexing

Now our concept is almost completed but tohave complete restriction of DOF of the hubwe will have to do further development in thebase. For this & correct positioning of thebase itself, we will provide it legs which willfit in the gap of the vice bed. It is shown infigure below.

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Figure 9: Fixture Indexing Base with Legs

WORKING WITH FIXTURE

Under this heading we will see, use of thefixture for proper drilling. A step by stepprocedure is given as below.

For first drilling

Keep the pentagonal fixture in horizontalposition.

Place the hub inside the cavity of fixture. Clamp the hub inside the pentagonal

fixture with the help of Clamp Plate & boltby tightening it properly by the alen key.

Take the fixture & keep it properly on thefixture base.

Clamp the whole fixture by vice jaw. Now adjust the drill to the center of the

jig bush & start drilling.

For second drilling After drilling first hole, release the jaw of

vice & take out the pentagonal fixture. Then keep it back on the fixture base by

keeping the next jig bush position on top& clamp the whole fixture by jaw of vice.

Now from the second drill place thelocating pin in previously drilled hole.

Adjust again the drill (if necessary) to thejig bush center & star drilling.

For third, fourth & fifth drill Repeat theprocedure as stated for the second drilling.

CAD MODELS

Figure 10: CAD Models of Drill Jig-FixtureParts Using AUTODESK INVENTOR

REFERENCES

1. Composite Hood Jig for Automotive As-sembly Process-James Waltman, AdamAircraft -Proceedings of the 2006 IJME -INTERTECH Conference

2. L Thompson, Jon K Lampert and E HarryLaw (1998), Design of a Twist Fixture toMeasure the Torsional Stiffness of a Win-ston Cup Chassis-Lonny. SAE Interna-tional Paper series.

3. Robin Aman (2006), Design of an EndEffector for Drilling in Automated Pro-cesses.

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