BURR MINIMIZATION IN DRILLED HOLES THROUGH DRILL GEOMETRY INNOVATION

Introduction

Objectives Experimental Results

• Conduct research into the current methods and ideas of reducing burr formation through

changes in drill geometry. Conditions: • Have two innovative drills configured based on this research. Drill: SD Spindle Speed: 4000 rpm Observations & Analysis • Test the above mentioned drills as well as the standard twist drill so that their effectiveness of Coolant: ON Work piece: Clamped • Increase in Feed Rate resulted minimal burr formation can be evaluated at different input parameters. in an increase in Axial Thrust • Study the drill chip morphology and drilling mechanism. • Step Drill resulted in lowest • Draw conclusions based on the above evaluation. Axial Thrust • Make recommendations based on the knowledge gained and conclusions made. • Point Drill and Step Drill resulted in a reduction in burr height Burr Formation

In Engineering, a “burr” refers to the raised edge on a metal part often generated during cutting or punching. More specifically, burrs are unwanted material remaining after a process such as drilling, grinding, or . These are undesirable projections of materials Drilling Conditions: on the edge of the surface arising because of plastic deformation during Feed Rate: 200 mm/min Spindle Speed: 4000 rpm machining operations. Coolant: ON Work piece: Clamped Burrs are created in most machining operations, and are only considered to be intolerable protrusions when the shape or size hinders the function of the part. The magnitude of the burr can be defined by its height (h) and Figure 1: Cross Section Showing Burr Height thickness (w) as shown in Figure 1.

Drill Configurations

Geometry Standard Drill Point Drill Step Drill Analytical Results Point Angle 114° 117° 124° Analytical Results

Step Angle - - 90°

Helix Angle 30° 32° 27°

Drill Diameter 8.8 mm 8.8 mm 8.8 mm

Overall Length 122 mm 99.3 mm 104.3 mm

Flute Length 79 mm 52.5 mm 45.8 mm

Step Length - - 0.87 mm

Margin Width 797.95 μm 761. 71 μm 672.44 μm

Web Thickness 1728.81 μm 371.17 μm 329.80 μm

Tungsten Tungsten Material HSS Carbide Carbide

Gashing NO YES YES

Experimental Setup & Testing Conditions

Testing Setup: • KM 100 CNC Machining Centre • Kistler Type 9257A Dynamometer • Kistler Type 5001 Channel Amplifier Conclusions • DSO 3062A Oscilloscope • PC with DSO3000 software Two drills with innovative geometry were developed and tested for the purpose of reducing the exit burr height when cross-drilling Aluminium. They were compared to a standard HSS twist drill which produces exit burr that requires extensive post-cleaning operations when drilling cross-holes. The Point and Step Drills CNC Machine produced substantially smaller burrs compared to the Standard Drill. The Step Drill produced the smallest burr height of 79.89 μm at a feed rate of 200 mm/min. Although the smallest burr was formed at 200 Connecting Cable mm/min, the burr height at 500 mm/min was only slightly greater. In terms of increased productivity, a feed rate of 500 mm/min is the most beneficial. Computer There was a clear trend which resulted in smaller burr size and Step Drill suitability. The Step Drill was System configured with a smaller web thickness, gashing, a larger point angle and a step. This resulted in Oscilloscope substantially smaller axial thrust when drilling which in turn produced less plastic deformation. The drill Charge Amplifier geometry also assured better coolant penetration and hence the drill chips produced were smoother and more uniform. The end result was smaller uniform burr formation and better suitability for burr minimization Test Components: Standard Drill Point Drill Step Drill Al 6068 with 8% Silicon Recommendations for Future Work Test Hole Burr Spindle Speed 4000 rpm 4000 rpm 4000 rpm Ø 8.8 mm Surface Feed Rate 200 – 800 mm/min 200 – 800 mm/min 200 – 800 mm/min •A full wear analysis of the drills should be completed. This will justify the manufacture of the Step Drill or Point Drill for use in manufacturing. Coolant ON ON ON •The drill tip geometry configuration of the Step Drill could be altered to include the tip geometry used for Pre-Drilled the Point Drill. This would possibly minimize the burr height even more than that of the Step Drill tested in Hole Work-piece Clamped Clamped Clamped Ø 19 mm this thesis.

Author: K.G. Thorpe Supervisor: Associate Prof. R. Kuppuswamy Project Number: 54 Year: 2009