PhoenixII Coniflex Technical
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Transcript of PhoenixII Coniflex Technical
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Straight Bevel Gears onPhoenix Machines Using
Coniflex Tools
Dr. Hermann J. StadtfeldVice President Bevel Gear Technology
January 2007
The Gleason Works__________________________________________________________________________________________________________________
1000 University AvenueP.O. Box 22970Rochester, New York USA 14692-2970
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Straight Bevel Gears on Phoenix MachinesUsing Coniflex Tools
Dr. Hermann J. Stadtfeld, Vice President - Bevel Gear TechnologyThe Gleason Works, Rochester, New York
Introduction
Manufacturing of straight bevel gears was in the past only possible on specially
dedicated mechanical machines. Such machines are by nature difficult to set up with
limited ability to precisely repeat the setup. Mechanical machine setup has been
historically slow and time consuming. New developments allow the use of the straight
bevel gear cutting system known as Coniflex on the Phoenix free form machine. This
patent pending methodology takes advantage of the Phoenix free form flexibility and
reduces setup time to a minimum while applying the Coniflex cutting system used
previously on mechanical machines.
Figure 1: Interlocking Coniflex cutters
Coniflex straight bevel gears are cut with a circular cutter with a circumferential blade
arrangement. The Coniflex cutters are arranged in the machine under an angle of e.g.
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24to a plane which is perpendicular to the genera ting plane or cradle plane. The upper
cutter disc is inclined to point down with the cutting zone of the blades and the lower
cutter is inclined to point up (Figure 1). The blades of the lower cutter move through the
gaps between the blades of the upper cutter while rotating (and vice versa). This pair of
cutter disks and the arrangement in the cutting machine is called interlocking cutter
system.
The upper cutter cuts the upper flank only and therefore is equipped with blades that
have their cutting edges towards the top of the figure. The lower cutter in turn cuts the
lower flank and is equipped with blades that have their cutting edges towards the bottomof the figure. The two cutters generate a combination of profile and length crowning in the
flank surfaces. A side effect of the cutter arrangement is a curved root line, depending on
the cutter diameter.
The two cutters represent one tooth of a generating gear which subsequently requires
the setup possibilities for a variety of job designs. The cutters can be moved away from
the center of the cradle to achieve a certain mean cone distance. Since the Coniflex flank
line tangents point to the pitch apex, it is necessary to adjust the angle of the flank line
tangent with the so called space angle. To control the slot width using existing cutters the
cutters can independently be shifted apart or towards each other. Some Coniflex
machines allow an additional freedom to adjust both cutters in order to modify the length
crowning (swing angle). Coniflex is a completing process which, compared to spiral bevel
gear wet cutting is considered a rather fast process. Figure 2 shows a Gleason No. 2A
Coniflex generator with the interlocking cutters engaged in a slot of a ring gear.
In case of a 20pressure angle system and a tilt a ngle of 20for each cutter the planes
of the cutter disks would generate flank surfaces which consist of precise spherical
involutes. However, also in straight bevel gears a located flank contact is desired which
lead to a modified cutter and cutter tilt design. If in the case of a 20pressure angle
system the tilt angle of the cutter disks is 24an d the cutting edge, rather then being part
of the cutter disk plane, form an internal cone of 86cone angle (90- 4), then the
internal cone generates a certain length crowning. This effect in connection with curved
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cutter blades is used to produce the crowning in straight bevel gears. As mentioned
before, it is always a pair of cutters, one left hand and one right hand cutter, required to
realize the interlocking arrangement in the cutting machine in order to cut both flanks of a
slot at the same time.
Figure 2: View into the work chamber of a Gleason No. 2A Coniflex Machine
There is still a considerable demand for straight bevel gears and machines for their
manufacturing. However, there was never a full CNC machine developed to satisfy the
present demand. Manufacturers of straight bevel gears were relying on remanufactured
mechanical machines, some of which are equipped with partial CNC functions like cradle
roll, sliding base, ratio of roll and indexing. The reason why no Coniflex CNC free form
machine was designed becomes evident after studying the geometrical concept in Figure
2. It is not possible to utilize a 6-axis machine because of the double tilted cutter spindles
and the interlocking cutter arrangement. To configure a regular 6-axis free form machine
with the Coniflex double spindle head including an automated head setup would have
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introduced 6 additional axes with complicated setup actuators. The cost to build such a
machine is between 150 and 200% of a regular todays Phoenix II free form generator.
Motivation of Coniflex Cutting on Free Form Machines
Manufacturers of straight bevel gears are processing mostly low quantities and a high
variety of different designs. The applications are differential gears for special equipment,
electrodes for forging dies and powder metal dies, machine tool applications etc. The
demand for higher quality straight bevel gears has been raised together with the desire to
apply a defined hard finishing method such as grinding.
Manufacturers with a high job variety and many changeovers between jobs would invest
in a modern machine tool for their straight bevel gear needs if it was also possible to put
the machine to different uses e.g. to cut spiral bevel gears. A six axis free form machine
can present a tool in every desired position and angular inclination to a work. This is the
basis for the ideas that realized Coniflex cutting on Phoenix free form machines. It is onlypossible to use one cutter which makes the completing process semi completing. The
cycle time is still acceptable since the free form machine with direct spindle motors
indexes extremely fast and since the higher stiffness of a Phoenix machine allows a cycle
of rapid plunge and limited roll.
There are additional features like independent correction of upper and lower flank (even
using different ratio of roll, root angle, tilt angle and more), summary storage and fast
setups and the possibility to implement cutter disks with carbide tips, that would allow a
high speed dry cutting of Coniflex gear sets.
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Conversion of Coniflex Summaries to PhoenixII Machines
Coniflex summaries which have been calculated for the Gleason machine Nos. 2A, 102,
104 and 114 can be converted to general basic settings in order to perform Coniflex
cutting on Phoenix II free form machines. The procedure that has been developed
follows the list of steps below:
Conversion of Coniflex summary into general basic settings
Conversion of upper and lower Coniflex cutter separately
Transformation of basic settings into free form motions
Reverse mount Coniflex cutter on the free form machine to avoid too negative
machine root angles
Rolling of root only to the bottom of the involute (avoids undercut and reduces
negative machine root angle), rolling face like on Coniflex machine
Calculate work phase angle set over between upper and lower cutting in order to
manufacture correct slot width Use vector feed to allow cutting slot from solid with outside blades only (no
alternating blades)
Coniflex straight bevel gear cutting summaries that use interlocking cutters contain the
following gear geometry relevant settings. The settings of group 1 are initially identical for
the upper and lower cutter but may be changed in the course of contact optimizations on
the mechanical machine. The settings of group 2 are always identical for the upper and
lower cutter in the mechanical machine. In a free form machine all settings of group 1
and 2 may be changed in order to optimize a pinion or gear:
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Figure 3: Vector diagram of Coniflex setup (upper cutter)
Summary Settings Group 1
Space Angle
Cutter Offset
Cutter Cone Distance
Cutter Swing Angle
Summary Settings Group 2
Cradle Test Roll
Work Test Roll
Start Roll Position
End Roll Position
Machine Root Angle
Sliding Base
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For the correct positioning of the cutter in the machine the tool related dimensions of
group 3 are required:
Summary Settings Group 3
Actual Cutter Diameter
Cutter Reference Height
In order to convert a summary of a mechanical machine into basic settings the machine
constants of group 4 are additionally required:
Summary Settings Group 4
Cutter Tilt Angle
Swing Axis Constant
Cutter Gage Reference Radius
With all information of groups 1 through 4 available, the basic machine setup can be
calculated according to the vector diagram in Figure 3. The first step, after the cutter is
positioned with the tip of the RW vector in the origin of the coordinate system (cutter axis
parallel to Y-axis) is a cutter tilt rotation around the Z-axis, followed by a movement of
the cutter tip Rw to the cutter cone distance (vector Rm1). Then the cutter tip is moved in
X-axis direction about the cutter offset ET and rotated around the Y-axis about s to
achieve the space angle inclination. The lower diagram in Figure 3 shows the movement
XB in direction of the Y-axis to the proper sliding base position. In some cases there is a
swing angle setting (not shown in Figure 3) which requires an additional rotation of the
cutter around the X-axis. Also the adjustment of the work root angle is not shown in the
diagrams, it requires a rotation of the work around the X-axis. A similar conversion is
done for the lower cutter setup. Although initially the lower cutter arrangement is a mirror
image of the upper cutter setup (mirror in a horizontal plane that contains the cradle
axis), the conversions are done separate and independent. If corrections have been
made to the theoretical summary, the upper and lower cutter setup may differ from each
other and the independent conversion will correctly transfer those corrections into the
free form machine setup.
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Reverse Coniflex Cutter Mounting
Figure 4 demonstrates that the slot width taper and additionally the work root angle leads
in case of a regular mounted cutter to highly negative machine root angles in a free form
machine (center roll position is shown). By reversing the cutter disk such that the cutting
edges point away from the cutter spindle the cutter finishes the right flank in the left slot
in Figure 4, which swings the cutter axis in the positive direction. The common limitation
of = -3on free form machines would present a proble m with regular cutter mounting.
This problem is completely eliminated without any negative side effect if the cutter is
used in the reverse mounting arrangement.
Figure 4: Machine root angle in case of reverse cutter mounting
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Cutting Cycle and Generating Roll Strategy
A basic cycle comparison is shown in Figure 5. The upper diagram in Figure 5
represents the cycle of a No. 102 Coniflex machine. Roll angle changes are plotted along
the abscissa, plunge advances of the cutter are plotted along the ordinate. The cycle
starts with a first plunge, followed by a rough roll to the start roll position. The next step is
a set in plunge to full depth, followed by a finish roll from start roll to the end roll position.
Then the cutter is withdrawn to the index position, the cradle rolls back to center of roll
and the indexing to the next slot occurs.
Figure 5: Cycle diagram mechanical machine and free form machine
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The lower diagram shows the cycle of cutting the same bevel gear on a free form
machine. The red vectors represent the cutting of the first cut lower slots. It begins with a
plunge to full depth (at the root roll position), followed by the finish roll to the top of the
profile. Then the cutter withdraws, rolls to the start roll position and indexes to the next
slot. After all flanks in the lower position are finished a setover of the cutter in the upper
position and a setover rotation of the work occurs. Now the cutter approaches the full
depth with rapid plunge feed, since the slotting operation had already been conducted in
the lower position and immediately the finish roll begins and rolls the second flank from
root roll position to the top of the flank.
The lower diagram in Figure 5 leaves some question unanswered such as how a cutter
with only outside blades can perform a slotting operation without damage and why the
roll angle required for one flank is only about 65% of the roll travel of a mechanical
machine with interlocking cutters.
Figure 6: Vector feed approach
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As the lower slot is cut first in the presented example it is important to approach the work
with the cutter in a manner to prevent the clearance side of the cutter from any cutting
action. Figure 6 shows schematic the cutter in the start roll position. The feed vector is
derived in the final plunge position at the start roll position attached to the clearance
corner of the cutter at the center face width such that enough stock is left on the not yet
generated flank 2. The feed vector is preferably perpendicular to the root at the mean
face width. If the cutter follows with the clearance cutting edge side the vector shown in
Figure 6, then only the cutting edges and the blade tips are subjected to any chip load,
which prevents damage to the clearance side blade edges and leads to an efficient and
smooth cutting action.
Figure 7: Roll angle ranges of mechanical machines and free form machines
The plunge position in Figure 6 forms already the root of flank 1. The cutting edge
generates a zero degree pressure angle area which generally is not part of the operating
portion of the flank anymore. Zero degree is sufficient to form the trochoidal part of the
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root, below the flank yet it will avoid undercut in cases where it would be generated while
rolling in negative direction, away from the flank. Not rolling beyond zero degree pressure
angle will therefore eliminate the risk of undercut and mutilation and reduce the cycle
time on the free form machine.
Figure 7 shows the roll diagram for both cutters drawn in the top roll position. To fully
generate both flanks in case of two connected interlocking cutters like in the mechanical
machine it is required to roll from position 1L to 3U which amounts to a roll range of 40.
In a free form machine it is only necessary to roll either cutter through the required range
for the particular flank, which is for the lower cutter from 2L to 1L, which is 20of roll andfor the upper cutter from 2U to 3U, also 20of rol l. The bottom diagram in Figure 7 shows
the different possibilities of roll ranges:
Free Form Machine-Seamless rolling between -20to 0of lower posit ion and 0to +20of upper position-Gap between lower and upper roll range-Overlap between lower and upper roll range
Mechanical MachineOnly one roll range from -20to + 20of interlock ing cutters
Figure 8: Comparison of cycle times
Cycle times on modern free form machines are always expected to be lower than the
times on older mechanical machines. The interlocking cutter arrangement of the Coniflex
machines involve two cutters simultaneously in the chip removing action. The free form
machine uses only one cutter and has therefore only half the number of cutting edges in
action (applying in both cases the same surface speed). This relationship would basically
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tell that the cutting time on a free form machine is about twice of that of a mechanical
machine. However, the two cutters of a mechanical machine are not always both part of
the active chip removal except during the plunge part of the cycle. During the roll of flank
No. 1, the opposite lower cutter idles with respect to chip removal. In case of rolling flank
No. 2. the upper cutter does not remove any chips. The free form machine on the other
hand has only cycle parts, where the one cutter which is used removes chips on its
cutting edges and during the plunge additionally on the tips. The table in Figure 8 shows
a cycle time comparison of four different Coniflex gears (pinions):
13 tooth pinion No. 102 compared to Phoenix II 275HC20 tooth pinion No. 104 compared to Phoenix II 275HC
16 tooth pinion No. 114 compared to Phoenix II 600HC
83 tooth gear No. 114 compared to Phoenix II 600HC
In this comparison the cycle times in the free form machines are 11 to 25% greater than
on the comparable mechanical machine. In the ongoing developments coated Coniflex
cutters with full blade point and different side rakes are tried in order to increase the
productivity of the new free form process.
Calculation of Work Phase Angle Setover
Figure 9 shows the upper cutter as positioned in the mechanical machine and
represented by the basic settings in a front view as well as a top view. A first rotation
around the x-axis of the indicated coordinate system about the machine root angle m
lines up the work axis with the y-axis of the coordinate system. A second rotation around
the y-axis, until the cutter axis vector is horizontal and does not contain a component in
x-axis is necessary to determine the angle WZU. This is the position cutter and work
have in the free form machine with respect to the relationship between work and cutter
while the cutter axis is horizontal. In case of cutting the first (lower) flank, this is not
significant. In case of cutting the second (upper) flank it is important in order to achieve
the correct slot width to rotate the work back into the neutral position about WZL and
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after that about WZU in direction of the rotation vector indicated in the center of the work
in Figure 9 to the correct upper position.
The set over rotation between the upper cutting of flank 1 and the lower cutting of flank 2
in order to cut the correct slot width in the correct position is therefore calculated as:
WZ = WZU + WZL
Figure 9: Calculation of work phase angle rotation between upper and lower cutting
It has to be mentioned, that one cutter in the free form machine can represent both
cutters of the mechanical machine. The lower portion of the cutter represents the upper
cutter and the upper portion of the cutter represents the lower cutter. This is the reason,
why one single cutter is moved in the free form machine (after conversion to basic
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settings and transformation of the basic settings in free form coordinates) in the upper
position, using the summary of the mechanical machine for the upper cutter and in the
lower position, using the summary of the lower cutter of the mechanical machine.
Likewise the correct work rotational position has to be established with a phase angle
rotation of WZ.
Hard Finishing of Coniflex Gears
This method can be applied to grinding also because it converts a method of using
interlocking cutters into a method of cutting with a single cutter. It seems not practical to
use segmented grinding wheels which is why in the past never a grinding method was
developed for Coniflex gears. Even with a single grinding wheel that duplicated the
enveloping internal cone surface of the cutting edges a major obstacle occurs with
respect to the dressing removal and the compensation thereof. The cutting edges of a
Coniflex cutter form an internal cone which makes dressing in radial direction impossible
(even if a diameter change was acceptable within limits). Also dressing in axial directionis not a possibility because the difference between maximal and minimal blade point
would allow a few redressings only.
Since the geometry changes due to redressing eliminate the possibility of dress able
grinding wheels a permanent CBN coated grinding wheel seems the only realistic tool for
the task of grinding Coniflex gears. A CBN galvanic ally coated steel wheel can be
manufactured to duplicate the enveloping surface of the cutting edges in a free form
grinding machine which allows a defined hard finishing of straight bevel gears preserving
the identical flank form. This is a planned future development which will allow the use of
Coniflex gears in many applications where grinding as a hard finishing process is
required like in many aircraft gears. Often when straight bevel gears are the gears of
choice for a certain application but grinding is required to fulfill the requirements in
accuracy, Zerol gears are used instead because they are the closest to straight bevel
gears. Ground straight bevel gears have been machined in the past on Maag two wheel
generators or on Heidenreich & Harbeck grinders until those mechanical vintage
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machines were not available anymore. The todays demand in ground straight bevel
gears could be covered with the possibility of Coniflex grinding. Coniflex gear sets
present many advantages in their geometry which contains length crowning and
controllable contact size and location. With the future possibility of grinding Coniflex
gears a complete new field of applications will be open up for this revitalized and well
established process.
AbstractManufacturing of straight bevel gears was in the past only possible on specially
dedicated machines. One type of straight bevel gears are the gears cut with a circular
cutter with a circumferential blade arrangement. Figure 10 shows a pair of 4.5 inch
Coniflex cutters as they are used on the Gleason machines Nos. 2A, 2E and 102. The
Machines and cutters used to manufacture these gears are known by the Gleason
trademark Coniflex. The cutters are arranged in the machine under an angle in an
interlocking arrangement which allows a completing cutting process. The two interlockingcutters have to be adjusted independently during setup which is complicated and time
consuming.
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Figure 10: Pair of 4.5 inch diameter Coniflex cutters
The outdated mechanical machines have never been replaced by full CNC machines but
there is still a considerable demand in a high variety of low quantities of straight bevel
gears. Just recently it was discovered that it is possible to connect one of the interlocking
straight bevel gear cutter disks to a free form bevel gear generator and cut straight bevel
gears of identical geometry compared to the dedicated mechanical straight bevel gear
generator. A conversion based on a vector approach delivers basic settings as they are
used in modern free form machines. The cutter is mounted to a shaft which is connected
to the cutter spindle. Additional features like reverse cutter mounting, vector feed and
root limited roll finally enabled the straight bevel cutting process on modern free form
machines.
The advantages are quick setup, high accuracy, easy corrections and high repeatability.
Because of the use of a single cutter disk, it will be possible to grind Coniflex bevel gears
on standard free form grinding machines. The grinding technology of straight bevel gears
whose geometry bases on an interlocking cutter system is being developed in the next
development step.
Literature
[1] N.N. Operating Instructions for No. 2A Straight Bevel GeneratorThe Gleason Works, Rochester, New York, 1961
[2] N.N. Calculating Instructions Generated Straight Bevel CONIFLEX Gears(No. 2A, 102, 104, 114 and 134 Straight Bevel CONIFLEXGenerators)The Gleason Works, Rochester, New York, 1961