©Copyright 2010 BlueSwarf LLC

Introduction toMACHINING DYNAMICS

BlueSwarf® Technical Series

The science of Machining Dynamics is

the vibration or frequency of the tool point self-generated

during machining often resulting in chatter.

Understanding Machining Dynamics will have the SINGLE GREATEST IMPACT on

your milling operations

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To begin to understand machining dynamics, you must recognize that the cutting tool is part of an

entire cutting system

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1

The cutting tool is gripped in a

toolholder

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2

The toolholder is pulled into a

spindle

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3

The spindle is rotating on

bearings and is mounted into a the headstock

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4

The headstock slides up and down

on guide ways

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4

Each of these connections

creates a flexible joint

3

2

1

Force is applied when a tooth of the tool makes

contact with the workpiece

The flexibility of the system allows it to

deflect. The amount of the deflection, or the

amplitude, is determined by the force applied

which is in proportion to the depth of cut

When the tooth releases the tool then rebounds, or responds, back in the opposite direction, past the center line. Think of

Newton’s third law of motion, “For every action

there is an equal and opposite reaction”

Then the tool continues to vibrate back and forth until it is fully dissipated. The rate and duration of the vibration is the tool

point’s natural frequency

An example of natural frequency is to hang a

ruler over the edge of a table and flick the end with your finger. The

ruler will vibrate at its natural frequency

The vibration is not allowed to fully dissipate. The next tooth impacts the workpiece and the process starts all over

again. For example a four flute tool, running at

15,000 RPM, will have 1000 impacts per second

There is an up and back vibration and the tool is also rotating. If not perfectly in sync each tooth

will impact the workpiece at different points within the up and back cycle.

If the rotating tool tooth passing frequency is not perfectly in sync with the back and forth natural frequency, each tooth will impact the part at a

different depth, changing the force applied

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Here is the programmed chip thickness that is provided by the

cutting tool manufacturer for maximum tool life

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If the tool rotation is not in sync one tooth will have a

much smaller “instantaneous “

chip thickness

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Another tooth will have a much larger instantaneous chip

thickness

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Tool Life

This excessive instantaneous chip thickness will cause

premature tool failure

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Energy Use

The excessive instantaneous chip thickness will also increase spindle load and energy

consumption

One revolution of the cutter looks something like this. These rapid frequency change caused by the chip thickness variation results in audible

chatter or feedback like a microphone

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Because the unequal cuts leave a wavy surface, each subsequent pass

creates even greater chip thickness variations and the chatter gets much,

much worse. We call this regenerative chatter

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The BlueSwarf® Tool Dashboard™ enables users to determine the maximum stable speeds, cutting depths

and feed rates for any milling tool in any material

We do this by measuring the tool point and synchronizing the tooth passing frequency (RPM) with the cutting system’s natural frequency

Results

• Up to 5X increase in metal removal rate• DOUBLE tool life• Reduce energy consumption by up to 75%Plus• Improved Surface Finishes• Reduced Maintenance Costs• Lower Scrap Rates

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Any change to any component of the cutting system will change the tool point frequency and its performance

Factors Include:•Cutter Length•Cutter Diameter•Cutter Projection•Number of Teeth•Spacing of Teeth•Tool Coating•Workpiece Material•Gripping Force of Toolholder•Weight of Toolholder•Run-out•Imbalance•Drawbar Force•Bearing Preload…and many more

No paper speed and feed chart can

accurately predict the performance of every

different cutting system combination and its unique tool

point frequency

For more information:

www.BlueSwarf.com