Introduction to Machining Dynamics

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

4/18/2010To begin to understand machining dynamics, you must recognize that the cutting tool is part of an entire cutting system

4/18/2010The cutting tool is gripped in a toolholder1

4/18/20102The toolholder is pulled into a spindle

4/18/20103The spindle is rotating on bearings and is mounted into a the headstock

4/18/20104The headstock slides up and down on guide ways

4/18/2010324Each of these connections creates a flexible joint1

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

Here is the programmed chip thickness that is provided by the cutting tool manufacturer for maximum tool life4/18/2010

4/18/2010If the tool rotation is not in sync one tooth will have a much smaller “instantaneous “ chip thickness

4/18/2010Another tooth will have a much larger instantaneous chip thickness

4/18/2010Tool LifeThis excessive instantaneous chip thickness will cause premature tool failure

4/18/2010Energy UseThe 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

4/18/2010Because 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

4/18/2010The BlueSwarf® Tool Dashboard™ enables users to determine the maximum stable speeds, cutting depths and feed rates for any milling tool in any materialWe do this by measuring the tool point and synchronizing the tooth passing frequency (RPM) with the cutting system’s natural frequency

ResultsUp to 5X increase in metal removal rateDOUBLE tool lifeReduce energy consumption by up to 75%PlusImproved Surface FinishesReduced Maintenance CostsLower Scrap Rates

4/18/2010Any change to any component of the cutting system will change the tool point frequency and its performanceFactors Include:Cutter Length

Introduction to Machining Dynamics

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Introduction to Machining Dynamics