Burr Formation And Minimisation In Drilling

FORMATION AND MINIMISATION OF BURR IN DRILLING

[email protected] Bhubaneswar

What is a burr? • Unwanted material remaining after a machining operation • Undesirable projections of materials beyond the edge of the work-piece arising because of plastic deformation during machining.

Why remove burr ? • Accounts for a significant portion of machining costs • Cause Of Many Industrial Problems. • Inspection • Assembly • Automated Manufacturing Of Precision Components

• Reduce the quality of machined parts • Can cause interference, jamming and misalignment • A safety hazard to personnel

•Estimates of between 10% and 30% of the total cost of a part •In 1977 estimated cost of deburring $100 million in Canada alone

Classification of burr According to height of the burr •Uniform burr Type 1-The height of burr varies upto 0.150 mm Type 2-The height of burr varies in between 0.150 to1.1mm . Also reffered as transient burr

•Crown burr Height varies in between 1.1 to 1.5 mm .Burr is not uniform

Uniform burr Type 1

Uniform burr Type 2

Crown burr

According to location of burr, •Entrance burr Produced on the side of the work piece where the drill enters Smaller than the exit burr Usually of little concern

•Exit burr Is formed on the opposite side of the work piece They are more challenging to remove

•Interlayer burr Drilling Through A Number Of Layers

Entrance burr, Interlayer burr and Exit burr

Mechanism of burr formation Uniform burr Small feed force condition this type of burr is formed. Fracture takes place at the chisel edge

Crown burr Large feed condition this type of burr is formed initial rupture will occur at the center

Entrance burr Material bumped up on the perimeter of the drill engaging region As more part of cutting edge engages small amount of bumps of material is always observed on the perimeter of the hole When almost all cutting edges are engaged, the shape of bump on the perimeter starts to change

Interlayer burr

Exit burr The mechanism of formation of exit burr is same as that of uniform burr or crown burr depending on feed condition

MINIMIZATION OF BURR 2-Axis Drilling Burr Control Charts •(DBCC) can be used to predict what type of burr will be formed given certain drilling parameters. •feed rate and thrust force with varying drill diameters can be approximated by applying the shear plane model •Merchant equation, φ = π / 4 + (α-λ) / 2 and the expression for the rake angle varying with relative radius, R. •thrust force

•stress that directly influences the burr formation,

•Another important parameter is cutting speed N •Depending on the cutting speed, the amount of heat generated at the cutting edge change greatly. •Finally, the parameters for the chart are:

Pre-drilling and pre-chamfering

Burr minimization through drill tip design

•Gillespie found that increasing helix angle will reduce burr height by up to 50%, thickness by up to 20% •Sofronas increase helix angle and harden the exit surface •by changing the tip of the drill it is possible to minimize the burr

• Plastic deformation region is formed by the stress caused by cutting resistance in the slant section • The position at which bending deformation starts is determined by the rigidity of the remained part • When the stiffness of the part which is bent by thrust force imposed in drill cutting edge is large enough, no bending occurs and cutting is continued

Observation of burr formation in chamfered drill

Observation of burr formation in round drill

Observation of burr formation in step drill

METHODS OF DEBURRING Ultrasonic vibration in drilling The distribution of the ultrasonic vibration pressure depends on •the properties of the medium, • initial speed, • density of slurry • frequency

Results of Ultrasonic vibration in drilling

Before

After

Integrated drilling and deburring tools

Burr off tools: One-Pass Hole-Deburring tool which can remove both Entrance and exit burr .Simple and Rugged One-Piece Construction Allows cutting chips to clear easily

References • Sung-lim ko1, Jae-eun Chang1 “Development of drill geometry for burr minimization in drilling” • P. Stringer, G. Byrne and E. Ahearne “Tool Design For Burr Removal In Drilling Operations”. • Jinsoo Kim “Development of a drilling burr control chart for stainless steel”. • H. Z. Choi, s. W. Lee, y. J. Choi, s. L. Ko “Study on technology using Ultrasonic Cavitations”

deburring

• Jihong Choi ,Sangkee Min, David A. Dornfeld “Finite Element Modeling of Burr Formation in Drilling of a Multi-Layered Material” • Choi, Sangkee Min ,David Dornfeld ,Mahboob Alam, T. Tzong “ Modeling of Inter-Layer Gap Formation in Drilling of a Multi-Layered MaterialJihong ”

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