Technical Information

Dynamic Efficiency – Working Efficiently and with
Process Reliability
Considerable potential lies in the efficient heavy machining—roughing at high cutting speed—but also in the machining of hard-to-cut
materials like titanium alloys, nickel-based materials or stainless steel, which are standard materials in the aviation and aerospaceindustry. Heavy machining is primarily about removing as much material as possible in the shortest time. This is where many
components of the machining process are pushed to their limits. So for this type of high-performance cutting, comprehensive process
management is an indispensable prerequisite for quality and economy. The forces that result from the cutting process place an extremeload on the machine and tool. The goal must therefore be to optimize metal removal rates, maximize tool service life and minimize themachine load.
With the concept of Dynamic Efficiency, HEIDENHAIN offers innovative TNC functions that help the user to increase process reliability
in heavy machining and roughing in order to improve efficiency. Dynamic Efficiency comprises these three TNC functions:• Active Chatter Control (ACC): This option reduces chatter tendencies and permits greater infeeds• Adaptive Feed Control (AFC): This option controls the feed rate depending on the machining situation• Trochoidal milling: Cycle for the roughing of slots and pockets in a way that eases the load on the tool and the machine

Each function in itself provides advantages
in the machining process. However, they
can also be ideally combined to achievedecisive improvements.
• Reduced machining time thanks tohigher material removal rates (ACC, AFC,trochoidal milling)• Tool monitoring (AFC)• Longer tool service life (ACC, trochoidalmilling)
With Dynamic Efficiency, yourmanufacturing process becomes faster,easier on the machine and tool, and as aresult, more efficient and economical.

September 2013

Dynamic Efficiency
More efficiency in heavy machining and roughing

Dynamic Efficiency focuses on allprocesses with high cutting forces andhigh metal removal rates. These include
roughing processes in general, but also themachining of hard-to-cut materials such astitanium, corrosion-resistant nickle-based
alloys (such as Inconel) and many othermaterials that are used in the tool and die
making business, the aviation andaerospace industry, and in medical andenergy technology. The forces that result
from machining place an extreme load on
the machine and tool. This high load isoften observed as process-induced
vibrations that occur during machining. The
goal of improvement must therefore be toincrease metal removal rates while at thesame time extending tool service life andreducing the machine load.
Dynamic Efficiency from HEIDENHAIN
addresses exactly these points.

With the concept of Dynamic Efficiency,
HEIDENHAIN combines innovative TNC
functions that help the user to make heavymachining and roughing more efficientwhile also enhancing its process reliability.
Because these are software functions,they require no intervention in themechanics of the machine. Dynamic
Efficiency helps to to increase the metal
removal rate and reduce machining time.
Dynamic Efficiency comprises threefunctions:• Active Chatter Control – The ACC option
reduces chatter tendencies and permits
greater infeeds• Adaptive Feed Control – The AFC option
controls the feed rate depending on themachining situation• Trochoidal milling – A function for theroughing of slots and pockets that eases
the load on the tool and the machine2Each solution in itself offers decisive
advantages in the machining process. But
the combination of these TNC features, inparticular, exploits the potential of themachine and tool and at the same time
reduces the mechanical load. Changing
machining conditions, such as interrupted
cuts, various material dipping treatments or
simple clear-out also show that thesefeatures pay for themselves. In practice,
removal rate increases of 20 to 25 percent
are possible.
Dynamic Efficiency permits higher
removal rates and therefore increases
productivity without making the user resort
to special tools. The avoidance of tool
overload and premature tool wear as wellas the additional gain in process reliability
contribute considerably to improved
economy.
A significant gain in efficiency can beexpected if trochoidal milling is combinedwith adaptive feed rate control. Because
the tool moves into the material on acircular path, the load tool and machine isconsiderably reduced. However, a part ofthis movement is in the air. In this situation,
AFC moves the tool at a much higher feedrate. These features add up duringmachining with the HEIDENHAIN cycle toenormous time savings.

In comparison, the same slot is machinedwith trochoidal milling together withadaptive feed rate control AFC. Trochoidal
milling is considered a particularly
protective technology for the tool andmachine, but alone is provides little
advantage in speed. This is where AFC canbe especially effective. During the air cutsof the circular milling process, AFCsignificantly increases the feed rate andreduces it as soon as the cutter meets thematerial. In this way, Dynamic Efficiency
achieves dramatic time savings in thismachining example.

Conventional milling
1 Full cuts in four infeed depths
2 Partial cut
Machining time 96 sVorschub
Feed rate

Machining example
This application example clearly illustrates
the benefits of Dynamic Efficiency. This
slot is machined first with the conventional
method and then with trochoidal milling
combined with AFC.
In conventional machining slot machining
begins by plunging into the middle of theslot. Because of technological characteristics (of the material or cutter) each cut canremove only a fourth of the required depth.
Once the desired depth is reached, the slot
is expanded in a working step to the desired width (green line). The line colors indicate the feed rate achieved.

Trochoidal milling with AFC
Machining time 58 sVorschub
Feed rate

In this machining example, compared with conventional machining methods, Dynamic Efficiency
increases productivity by 40 %.

3

ACC
Active chatter control (option)

Strong milling forces come into play during
roughing (power milling). Depending on thetool spindle speed, the resonances in themachine tool and the chip volume (cutting
power during milling), the tool cansometimes begin to “chatter.” Because
chattering places an extreme load on boththe tool and the machine, it is considered
one of the factors that limit the metal
removal rate.
Limits of the metal removal rates
Three main factors limit the metal
removable rates attainable in a millingmachine for a given material: the thermal
and mechanical stability of the tool, theavailable spindle power and the occurrenceof chatter. In itself, the occurrence ofchattering is not a sign of machine defects.
When tool stability and spindle power aresufficient, it cannot be avoided as the limitof cutting performance.
Causes of chatter
Chatter is the term or a dynamic instabilityof the cutting process due to vibrations
during cutting. High cutting forces comeinto play during roughing and particularly
here during machining of hard-to-cut

materials. The periodically occurring forces
result in vibration between the tool andworkpiece. If feedback develops between
the vibration and the cutting process, moreenergy is put into the process as friction
than can be converted to heat. The
vibration is amplified and chatter ensues.
Whether feedback develops depends on
various factors, which include dynamic
compliance of the machine at the tool
center point (TCP), the tool and the cuttingparameters.
Because chatter is a self-generated
oscillation, chatter frequencies are always
near to the natural frequency of themachine.

The effect of ACC is particularly positive
during heavy cutting:• Significantly better cutting power• Higher metal removal rates (up to 25%
and more)• Low forces on the tool thereby
increasing service life
• Smaller load on the machine.
• Higher process reliability

Conventional measures
Chatter puts excessive stress on the tooland the machine. It is therefore usually
avoided. The occurrence of chattervibrations depend among other things on
the selection of the cutting qualities (chipthickness, chip width, cutting velocity, etc.).
To prevent it in practice, the cutting data
(cutting depth, spindle speed and feed rate)
have to be reduces, which however resultsin lower productivity.

Operating principle of ACC
Because active chatter control (ACC) isentirely a software solution, it requires nochanges in the machine. Additionalsystems (such as sensors or actuators) that
increase the complexity and therefore theprobability of total system failure areunnecessary. ACC detects chatter throughthe measuring signals of the drives anduses the machine’s own feed drives towithdraw energy from the vibration.

Part milled without ACC: Chatter marks are clearly visible.

4Benefits of ACC
With its TNC option Active Chatter Control(ACC), HEIDENHAIN now offers aneffective control function to reduce amachine’s inclination to chatter. ACC uses
damping to increase the cutting rate at
which chatter arises.

Part milled with ACC: At the same feed rate and cutting depths the surface
shows no chatter marks. The machining process took placed with reduced
loads on the tool and machine.

Application of ACC
ACC operates in a certain frequency range
below the tool’s tooth engagement
frequency. The user defines whether ACC
become active by simply selecting the tool.
Because the respective tool geometry has
effects on the cutting forces and therefore
influences the characteristics of any
ensuing chatter vibrations, a separate
parameter set can be configured for eachtool. The tools are changed, the control
automatically switches the tool-specificparameter sets.

10005000-500-1000
0Cutting forces
during chatter

0.05

0.1

0.15

0.2

Time [s] Force [N] Impact in practice
In milling experiments on a large numberof various materials with differing cutters, it
proved possible to significantly increase
the metal removal rate (by up to 25 % andmore) in cases in which chatter was aprocess-limiting factor. In addition, theprevention of chatter greatly reduces theforces affecting the tool and the machine.
This increases tool service life andpositively affects the life cycle of machinecomponents (main spindle, guideways, ballscrews and bearings).

Force [N] However, this also places limits on thechatter phenomena that can be counteredwith ACC. The feed drives can only remove
enough energy in a frequency range up to
100 Hz of the chatter vibration. Higherfrequency vibrations are not sufficiently
damped. In individual cases, some chattervibration below 100 Hz also cannot be
damped, for example because it is limited
to the tool while the drive affects the table.

10005000-500-1000

Cutting forces
with ACC

00.05

0.1

0.15

0.2

Time [s] Because of differing machine geometries,
the machine tool builder can also
separately configure the ACC parametersspecifically for all feed axes. In certain
cases, this additional parameter
assignment can improve the effect of theACC algorithm.

Simulatedmachining5

AFC
Adaptive feed rate control (option)

The feed rate during milling operations isusually chosen depending on the material
to be machined, the cutting tool and thecutting depth. It is specified for therespective milling operation. If the cutting
conditions change during the operation, forexample due to fluctuations in cutting
depths, tool wear or in material hardness,this has no influence on the feed rate. On
the one hand, for example if the material
thickness decreases, this can mean thatthe feed rate that is at times lower thannecessary. The machining time is therefore
higher than it need be. On the other hand,a high programmed feed rate—particularly
if the chip volume increases—can result in
spindle and tool overload.
Benefits of AFC
Adaptive feed rate control option (AFC)from HEIDENHAIN optimizes the feed rateby taking the spindle power and further
process data into consideration. AFCensures that the maximum possible feed
rate and thereby increases efficiency. It
offers a number of benefits.

Optimizing the machining time
Fluctuations in dimensions or material(blowholes) often appear particularly on
cast parts. By correspondingly adapting thefeed rate, the control maintains thepreviously “learned” maximum spindle
power during the entire machining time.
The total machining time is shortened byan increased feed rate in the machining
zones with less stock removal.
Tool monitoring
The TNC's adaptive feed rate control
continuously monitors the spindle power
required for the current feed rate. As a tool
becomes blunt, the spindle powerincreases. As a result, the TNC reduces thefeed rate. As soon as the feed rate falls
below a defined minimum, the TNC reacts
by switching off, with an error message, orby changing to a replacement tool. This
helps to prevent further damage after atool breaks or is worn out.

AFC adapts the feed rate to the various cutting conditions.

6

Protection of the machine mechanics
Reducing the feed rate down to thereference value whenever the learned
maximum permissible spindle power isexceeded also reduces the strain and wearon the machine. It effectively protects thespindle from overload.
Principle of function
The application is simple: before
machining, the maximum and minimum
limit values for spindle power can bespecified in a table. The values are
determined by having the TNC record themaximum spindle power consumed during
a teach-in cut. The adaptive feed control
then continuously compares the spindle
power with the reference power andattempts to maintain the reference powerby adapting the feed rate during the entire
machining period.

Trochoidal milling
Machining any contour slots with trochoidal milling

Tools and machine structures are
particularly challenged when they are called
upon to mill hard-to-cut, high-strength or
hardened materials. Particularly when end
mills are full-cutting slots, very strong
forces are at play because the tool andworkpiece form a contact arc of 180°. Thiscan result in the tool bending and thereby
causing geometric errors in the slot. To beable to attain the required component
accuracy, the axial cutting depth is often
limited to half the tool diameter. Deep slots
then have to be roughed in multiple, timeconsuming steps.

Advantages of trochoidal milling
The benefit of trochoidal milling is thecomplete machining of slots of all kinds ina way that reduces load on the tool andmachine. The roughing process is a circularmotion superimposed on a forward linearmotion.
With trochoidal milling, large cutting depths
are possible since the prevailing cutting
conditions do not increase the wear andtear on the tool. In most cases, this makes
it possible to use the entire length of thecutter to achieve higher chip volume per
tooth. Circular plunging into the material
places less radial force on the tool. This
reduces the mechanical load on themachine and prevents vibration. Enormous
time savings can be realized by combining
this milling method with the integrated
adaptive feed control (AFC) option.

Trochoidal milling as standard function
The slot to be machined is described in acontour subprogram as a contour train. You
define the dimensions of the slot and thecutting data in a separate cycle. Any
residual material remaining can then easily
be removed with a subsequent finishingcut.
The benefits include:• Engagement of the entire cutter length• Higher metal removal rate (incombination with AFC)
• Relief from mechanical load on themachine• Less vibration• Integrated finishing of the side wall

Trochoidal milling: ultraefficient machining of all kinds of slots

7

HEIDENHAIN controls

Contouring controls for milling, milling/turning, drilling, boring machines andmachining centers
The TNC controls from HEIDENHAIN cover
the whole range of applications: From thesimple, compact TNC 128 three-axis
straight cut control to the TNC 530 (up to18 axes plus spindle)—there's a TNC
control for nearly every application. The
TNC 640 is a control for milling machinesthat are also capable of turning operations.
HEIDENHAIN TNC controls are versatile:
They are workshop oriented and feature
both shop-floor and offline programming,and are therefore ideal for automatedproduction. They handle simple milling
tasks just as reliably as the TNC 640 andiTNC 530, for example, can handle highspeed cutting—with especially jerkreduced path control—or 5-axis machining
with swivel head and rotary table.
HEIDENHAIN combines innovative control
functions for efficient high-precision
machining under the hypernyms Dynamic
Efficiency and Dynamic Precision.
Dynamic Efficiency helps the user tomake heavy machining and roughing more
efficient while also enhancing its processreliability. Dynamic Efficiency is available
on the TNC 640 and iTNC 530 controls.
Dynamic Precision makes workpieces
more exact, with clean surfaces and highspeed machining, thereby providing highprecision and higher productivity. You can
use the Dynamic Precision software
options with the TNC 640, iTNC 530 andTNC 620.

TNC 640iTNC 530

TNC 620

TNC 640iTNC 530

TNC 620xxx

CTC – Compensation of position errors Option
through axis coupling

OptionOption

AVD – Active vibration damping

OptionOptionOption

PAC – Position-dependent adaptation of Option
controller parameters

OptionOptionLAC – Load-dependent adaptation ofcontrol parameters

OptionOptionOptionMAC – Motion-dependent adaptation of Option
control parameters

OptionOptionxx–ACC – Active suppression of chatter

OptionOptionOptionAFC – Adaptive feed control

OptionOption–Trochoidal milling•••

Dynamic Precision

Dynamic Efficiency

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For more information:• Catalog: TNC 640• Catalog: iTNC 530• Catalog: TNC 620• Technical Information:
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