Note: Descriptions are shown in the official language in which they were submitted.
1046807
BACKGROUND OF THE INVE~TION
This invention relates generally to machine tools and
more particularly to machine tools which are capable of cutting
accurate circular flanges in one or more ends of a relatively
large workpiece. In the past, accurate circular flanges were
cut on workpieces in lathes, the workpiece being rotated about
the axis of the desired flange while a fixed cutting tool is
engaged with the workpiece and is moved over the end of the
workpiece in a sequence of axial feed movements and cross-
feed movements which cut the rim, the front face, and therear face of the desired flange. However, for relatively
large workpieces, such as cast steel axle housings for trac-
tors or large earth moving machines, machining the flanges in
a lathe is difficult due to the size and weight of the work-
pieces, and also due to their unsymmetrical shape. Therefore,it is desirable to provide a machine tool which is capable
of accurately cutting circular flanges in relatively large un-
symmetrical workpieces while the workpiece is held in a sta~
tionary fixture. It is also desirable to provide a machine
tool of the above-described type which is also capable of
machining axially curved surfaces on such a workpiece.
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SUMMARY OF THE INVENTION
~.
In accordance with this invention, the foregoing problem
has been solved by providing a machine tool having one or more
rotary tool heads which are each slidably mounted for linear
movement along a first axis and are journalled for rotation about
the first axis. ~ne or more tool slides are slidably mounted on
the face of each tool head for cross-feed movement transverse
to the first axis. Toolholders are mounted on the tool slides
to support cutting tools thereon. Means is provided for moving
- lO each tool slide along its cross-feed axis while the tool head is
rotating. A fixture is provided to hold the workpiece in a pre-
determined stationary position relative to the tool head, and a
; controller is provided for controlling the rotation of the tool
head, the axial feed movement thereof, and the cross-feed move-
ment of the tool slide to machine the desired surface of the
; workpiece. In the preferred embodiement, when the tool slide is
moved along its cross-feed axis, the rotary speed of the tool
head can be automatically varied by the controller in accordance
with variation in the radius of the circular path followed by the
point of the cutting tool so as to maintain a constant cutting
surface speed in spite of the cross-feed movement of the tool
slide. Also, as the tool slide is moved along its cross-feed
,l axis, the cross-feed rate can be automatically varied by the con-
troller in accordance with variation in the rotary speed of the
tool head to maintain a constant chip thickness per revolution.
In addition, the tool head can preferably be simultaneously moved
along its linear feed axis and cross-feed axis simultaneously at
predetermined feed rates while the tool head is rotating to ma-
chine a predetermined axially curved surface on the workpiece.
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DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevation view of an embodiment of the
invention which utilizes two counterposed rotary tool heads for
machining flanges on opposite ends of an axle housing;
Fig. 2 is an axial sectional view of the tool drum and tool
drum housing of one of the rotary heads shown in Fig. l;
Fig. 3 is an axial sectional view of one of the tool heads
and a portion of the tool drum therefor;
Fig. 4 is an axial sectional view of the slip-ring assembly
for the rotary tool head disclosed in Figs. 2 and 3;
Fig. 5 is a side elevation view of an axle housing mounted
in a fixture between the two rotary tool heads and showing the
fixed toolholders on the tool heads which machine the circular
rim of the flanges on the axle;
Fig. 6 is a side elevation view similar to Fig. 5 but showing
the movable tool slides on the rotary tool heads which machine the
outer and inner faces of the flanges and the curved bell surface
adjacent to the inner faces;
Fig. 7 is a front elevation view of one of the tool heads
i 20 showing the fixed and movable tool slides thereon;
Fig. 8 is a front elevation view of the other rotary tool
head showing the fixed and movable tool slides thereon;
Fig. 9A is a block diagram of the NC processor, along with
the input/output section and power distribution panel section
for one of the rotary tool heads of the machine tool shown in Figs.
1 through 8; and
Fig. 9B is a block diagram and diagrammatic representation of
one of the rotary tool heads along with the electric motors, slip-
rings, tachometers, and resolvers which control the operation of
the tool head in conjunction with the electrical circuit shown in
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Fig. 9A, the conductors identified by the same letter in Figs.
9A and 9B being connected together.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows an embodiment of the invention which utilizes
two counterposed rotary tool heads mounted on diametrically opposed
sides of an index table for simultaneously machining opposite ends
of a stationary workpiece on the index table. This embodiment of
the invention includes a conventional bed 10 which is divided into
a central portion 12 which supports the rotary index table 14, and
two diametrically opposed outer portions 15 and 16, each of which
carry ways 18 and 20, respectively, upon which saddles 22 and 24,
respectively, are slidably movable. Ways 18 and 20 and saddles
22 and 24 define a common horizontal Z axis which is perpendicular
to the vertical Y axis about which index table 14 is rotatable.
Saddle 22 is moved along ways 18 by a Z axis drive motor 26 which
is mechanically coupled to saddle 22 through a conventional ball
screw mechanism (not shown). Saddle 24 is moved along the Z axis
by a similar Z axis drive motor 28 which is mechanically coupled
to saddle 24 through a conventional ball screw mechanism (not
shown). Bolted to the top of each of the saddles 22 and 24 is
a hollow tool drum housing 30 and 32, respectively, within which
the corresponding tool heads 34 and 36 are journalled for rota-
tion about the Z axis. Each of the tool heads 34 and 36 are
bolted to the end of a corresponding tool drum 38 and 40 which
extends within the tool drum housings 30 and 32 and is jour-
nalled therewithin. Mounted on the top of the tool drum hous-
; ings 30 and 32 are tool head motors 42 and 44 which are mechan-
ically coupled to their respective tool drums 38 and 40 through
drive belt assemblies 46 and 48.
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Referring to Figs. 7 and 8, which show the front face of
tool heads 34 and 36, respectively, two movable tool slides
50 and 52 are moun~ed on the front face of tool head 34 for
sliding movement along X and U axes, respectively, and two tool
slides 54 and 56 are slidably mounted on the front of tool head
36 for sliding movement along X and U axes, respectively. Tool
slides 50 and 52 are moved along their respective X and U axes
by two DC motors 58 and 60 (Fig. 1), which are mounted on tool
drum 38 and rotate therewith. Motors 58 and 60 are mechanically
coupled to their respective tool slides 50 and 52 through ball
screw mechanisms and are electrically coupled to conductors
on tool drum housing 30 through a slip-ring assembly described
hereinafter. Tool slides 54 and 56 are similarly driven by DC -
motors 62 and 64 which are also coupled to their respective
slides 54 and 56 through ball screw mechanisms and are elec-
trically coupled to conductors on tool drum housing 32 through
a slip-ring assembly.
;Fig. 2 i8 an axial sectional view of tool drum housing 30,
tool drum 38 and tool head 34. Tool drum housing 30 is a
¦20 hollow cylinder which is bolted to saddle 22 by bolts 66. Tool
drum 38 is also cylindrical in shape and.is ,~ournalled within
tool drum housing 30 by tapered roller bearings 68. Tool drum
38 has a drive gear 70 on its outer end which is driven by a
matching gear 72 on a drive shaft 74 journalled to tool drum
housing 30 through bearings 76 and 78. Drive shaft 74 has a
drive wheel 80 rigidly attached thereto which is rotated by
drive belts 81 from tool head drive motor 42 (Fig. 1). Tool
slide drive motor 58 is mounted on a plate 82 (Fig. 2) which
is bolted to the outer end of tool drum 38 by bolts 84 and
rotates with tool drum 38. Motor 58 turns a drive shaft 86
which is mechanically coupled to another drive shaft 88 through
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gears 90 and 92. Drive shaft 88 is journalled to the interior
of tool drum 38 by means of bearings 91 and is mechanically
coupled to its corresponding tool slide by means described
hereinafter. Although only the mounting and drive shaft 88
for tool slide motor 58 is shown in Fig. 2, it will be under-
stood by those skilled in the art that a similar mounting and
drive shaft are included within tool drum 38 for the other
tool slide motor 60. However, since these two motor mountings
and drive arrangements are alike, only one will be shown and
described in detail.
Fig. 3 shows the mechanical connection between the tool
slide drive shaft 88 and the corresponding tool slide 50. As
can be seen in Fig. 7, the front face 93 of tool head 34 is
slotted at g4 to slidably receive tool slide 50 and to accurately
guide it in its movement along the U axis. Front face 93 is
bolted to the body 95 (Fig. 3) of tool head 34 by bolts 96 and
the body 95 of tool head 34 is bolted to the end of tool drum
38 by bolts 98 so that tool drum 38 and tool head 34 rotate to-
gether as a rigid unit. Tool slide drive shaft 88 is coupled by
a splined coupling 99 to the input shaft 100 of a spiroid re-
ducing gear assembly 102 which is journalled within the hollow
interior of tool head 34 by bearings 104, 106, 108, 110, 112
and 114. The output shaft 116 of spiroid reducing gear assembly
102 is threaded and forms part of a conventional ball screw
mechanism which includes a ball screw nut 118 attached to tool
slide 50 by bolts 120.
Since the tool slide motors 58 and 60 rotate with tool head
34, it is necessary to use a slip-ring coupling for applying the
exciting signals to the motors 58 and 60. This slip-ring coup-
ling is shown in Fig. 4. Two slip-ring units are used, a large
slip-ring unit 122 and a smaller slip-ring unit 124. Slip-ring
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unit 122 has an outer housing 126 which is rigidly mounted on
a collar 128 which, in turn, is rigidly attached to tool drum
housing 30 by conventional means not shown in the drawings.
Slip-ring unit 122 has a central rotatable portion 130 upon
which the slip-rings 132 are mounted. Brushes 134 are mounted
on the stationary outer housing 126 and bear against the slip-
rings 132 to make electrical contact therewith. Conductors
136 are coupled to the brushes from the machine controller and
conductors 138 are coupled from the slip-rings to the motors
58 and 60. The inner rotatable portion 130 of slip-ring unit
122 is journalled to the outer portion 126 thereof by bearings -
140 and is rigidly attached by bolts 142 to a disc 144 which,
in turn, is attached by bolts 146 to a collar 148 which is
attached to and rotates with tool drum 38. -
The second slip-ring unit 124 is smaller in size than the
unit 122 but is constructed similarly and has an outer housing
150 which is attached by bolts 152 to a collar 154 which, in
turn, is attached by bolts 156 to the housing 126 of the larger
slip-ring unit 122. The inner rotatable portion of the small
slip-ring unit 124 is driven by a shaft 158 which is rigidly
attached at its right end in Fig. 4 to plate 144 and rotates
therewith. Shaft 158 is journalled within collar 154 by means
of bearings 160 and 162 and has a gear 164 rigidly attached
thereto which engages a matching gear 166 on the shaft 168 of
a resolver 170. The shaft 168 of resolver 170 is journalled
to collar 154 by bearings 172 and 174. Resolver 170 generates
electrical signals which identify the angular position of tool
head 34.
The conductors 136 which are attached to the brushes of
slip-ring unit 122 move with tool drum housing 30 along the Z
axis and it is therefore necessary to use either a long flexible
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1046807
cable or sliding contacts to couple conductors 136 to the ma-
chine controller. Conductors 138, which rotate along with
tool drum 38, can be attached directly to their respective
motors 58 and 60. Since tool head 36, along with its mounting,
5 tool slide motors, and slip-rings is the same as tool head 34, -
it is not illustrated or described in de,tail-herein.
Figs. 9A and 9B show a block diagram of the electrical
control circuits for rotary tool head 34. This particular con-
trol system utilizes a computerized numerical control system
(CNC) which includes a tape reader, CNC processor, CNC input/
output section (I/O), and power distribution panel (PDP) section,
all of which are shown in Fig. 9A. The motors, resolvers, tacho-
meters and slip-rings for rotary tool head 34, along with the
conductors for coupling these electrical elements to the con-
troller circuits shown in Fig. 9A, are shown in Fig. 9B, whichis a continuation of Fig. 9A. Referring to Fig. 9A, the NC
controller includes a tape reader 176 which reads the program
tape for the machine and applies the corresponding digital
signals to conventional data processing circuits 178 which
store, read and write the signals and perform the conventional
arithmetic and distributive functions therewith. Logic circuits
of this type are well-known in the art and are therefore not
shown or described herein in detail. Logic circuits 178 are
coupled to a core memory 180 which stores the specific program
for a plurality of different parts which may be machined by
' rotary tool head 34 on this particular machine. The output of
logic circuits 178 is a plurality of digital signals which con-
trol the operation of rotary tool head 34 in the manner de-
scribed hereinafter.
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The saddle 22 (Fig. 9B) upon which rotary tool head 34
is mounted is moved along the Z axis by Z axis motor 26 which
turns a shaft 182 which is mechanically coupled to saddle 22
through a ball screw mechanism which is not shown in the draw-
ings. The Z axis tachometer 184 and Z axis resolver 186 are
mechanically coupled to the shaft of Z axis motor 26 to perform
the conventional information feedback functions therefor. The
control circuit for Z axis motor 26 includes a conventional
axis interpolator 188 (Fig. 9A), a conventional following error
counter 190, a conventional feedback counter and oscillator 192,
a conventional digital to analog convertor 194, and a conven-
tional drive amplifier 196 which are coupled to Z axis motor 26,
Z axis tachometer 184, and Z axis resolver 186 in a conventional -
closed loop servo drive system. The operation of this servo -
drive system is controlled by three digital signals applied to
axis interpolator 188 by logic circuit 178. These signals in-
clude a digital Z word specifying the position along the Z
axis to which saddle 22 is to be moved, a digital feed rate
signal FR indicating the feedrate for the movement of saddle
22 towards its destination, and a digital function code G
which designates the function to be performed. In a typical
step of the operating program, where it is desired to move the
saddle 22 inwardly to a predetermined point, digital signals
are applied to axis interpolator 188 representing the direction
of rotation for Z axis motor 26, the point along the Z axis to
which saddle 22 is to be moved, and the feedrate for the move-
ment thereof. This information is applied to the following
error counter 190 where it is compared to digital feedback
signals from feedback counter and oscillator 192 which are
controlled by Z axis resolver 186 and contain a digital number
specifying the actual position of saddle 22. The actual and
.
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10468Q7
desired positions of saddle 22 are compared and if they are
- different, a drive signal is applied to digital to analog con-
verter 194 and drive amplifier 196 which drives Z axis motor
26 in the desired direction at the desired feedrate. Feedback
signals from Z axis tachometer 184 are used in a conventional
closed loop servo system to drive the Z axis motor 26 at the
proper speed to maintain the Z axis feedrate within a predeter-
mined tolerance of the desired feedrate. When saddle 22 reaches
the desired position along the Z axis, this information is ap-
plied by the Z axis resolver 186 to feedback counter and oscilla-
tor 192 which applies the corresponding digital number to follow-
ing error counter 190. Since, at this time, the actual position
of saddle 22 and the desired position therefor coincide, the
output of following error counter 190 will be zero which will
terminate the rotation of Z axis motor 26 until another command
is received to move to a different position.
X axis motor 60 is controlled by a similar closed loop
servo drive system which includes an axis interpolator 198,
following error counter 200, feedback counter and oscillator
202, digital to analog convertor 204, drive amplifier 206, X
axis tachometer 208 and X axis resolver 210. The only differ-
ence between the X axis drive circuit and the Z axis drive
circuit, apart from their relative power levels, is that the
X axis drive conductors D, E and F are coupled through slip-
ring and brush connections 212, 214 and 216 while Z axis drive
conductors A, B and C are connected directly to their respec-
tive motor, tachometer, and resolver. The slip-ring and brush
connection 212 is in the large slip-ring unit 122 while the
slip-ring connections 214 and 216 are in the small slip-ring
assembly 124.
,'~
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U axis motor 58 is contro~led by a similar closed loop
servo system which includes axis interpolator 218, following
error counter 220, feedback counter and oscillator 222, digital
to analog converter 224, drive amplifier 226, U axis tacho-
meter 228, U axis resolver 170 and slip-ring brush connec-
tors 230, 232 and 234. This servo drive system also operates
in the same manner as the Z axis motor drive system.
Tool drum motor 42 is driven by a similar closed loop
servo system which includes interpolator 236, following error
counter 238, feedback counter and oscillator 240, digital to
analog converter 242, drive amplifier 246, tachometer 248 and
resolver 250. This servo drive system also operates in the
same manner as the servo drive system for the Z axis motor 26.
In addition to the above-described control circuits for
rotary tool head 34, there is a duplicate set of the same cir-
cuits for rotary tool head 36 which are also controlled by
digital output signals from the logic circuits 178. In addi-
tion, there are other control circuits for controlling the
rotation of index table 14, for moving the pallet carrying the
workpieces onto the index table 14, and for clamping and un-
clamping the pallet. However, these circuits are conventional
and will not be disclosed in detail herein.
Referring to Fig. 9B, a toolholder 252 is mounted on tool -
slide 50 and a similar toolholder 254 is mounted on tool slide
52 for supporting cutting tools 256 and 258, respectively. As
best sho-~n in Fig. 7, toolholders 252 and 254 are shaped so as
to place tools 256 and 258 approximately on the same diameter
of rotary tool head 34 so that tools 256 and 258 move radially
inwardly and outwardly even though the slots 94 which guide
tool slides 50 and 52 are off-set from the radius of rotary
tool head 34. Tool slides 50 and 52 can be moved independently
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of each other and can be moved simultaneously to make cuts
with both cutting tool 256 and 258. However, in this particu-
lar embodiment of the invention, tool slides 50 and 52 are
moved separately in accordance with a machining program in
S which cutting tool 258 makes a rough cut in one step of the
machining program and cutting tool 256 makes the finish cut
in a subsequent step of the machining program. In the example
shown in Fig. 9B, cutting tools 256 and 258 are positioned to
cut the inner face 260 of a flange on a workpiece 262 which
constitutes a cast steel tractor axle housing shown in its
entirety in Figs. 5 and 6. Axle housing 262 is held in a fix-
ture 264 which is attached to a pallet 266 which, in turn, is
clamped to the top of index table 14 (see Fig. 1). This par-
ticular embodiment of the invention is adapted to machine
flanges on both ends of axle housing 262 in a manner to be
described more particularly hereinafter.
As tool slides 50 or 52 are moved inwardly to make the cut
for the flat surface 260 on the flange of axle housing 262,
the relative speed between the surface being cut and the corres-
' 20 ponding cutting tool 256 or 258 will decrease with the inward
movement if the rotary speed of tool head 34 is held constant.
Accordingly, it is desirable to store in the CNC processor
memory portion 265 (Fig. 9A) a routine defining a constant
surface speed (CSS) mode of operation in which the rotary
speed ~ of tool head 34 at any given time is varied in accord-
ance with the formula ~ = SS/(2~R ) where SS = the desired
cutting surface speed, and Rc = the radius of the circle des-
cribed by the point of the cutting tool being used. When the
CSS mode of operation is used, it will automatically maintain
a constant relative speed between the surface being cut and
the cutting point of the tool cutti~g that surface regardless
of the cross-feed movement of the cutting tool.
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1046807
In the CSS mode of operation, if the cross-feed rate of
the tool slide being used to cut the flange is maintained at a
constant level, the thickness of the chip cut thereby will
vary as the rotary speed of the tool head is changed. If a
, 5 constant chip thickness is desired, it is preferable to store
in CNC memory portion 267 an inch per revolution routine (IPR)
- in which the cross feedrate FR of the tool slide at any given
time is defined by the equation FR = Q~ where Q = the desired
chip thickness per tool head revolution and ~ = the rotary
speed of the tool head at any given time. Both tool slides
50 and 52 can be controlled independently in the CSS and IPR
mode of operation and also in a fixed RPM and fixed cross-
, feed rate as desired.
Although toolholders 252 and 254 are shown in Fig. 9B as
being shaped to cut the inner face 260 of the flange on axlehousing 262, it will be understood by those skilled in the art
' that toolholders having different shapes are employed to cut
the rim 268 of the flange and the outer face 270 thereof as -
described hereinafter. In addition to the capability of ma-
chining flat surfaces on the workpiece perpendicular to the
axis thereof, or cylindrical surfaces coaxial therewith, this
embodiment of the invention also has the capability of machin-
ing axially curved surfaces such as the surface 272 in Fig. 9B
which is a portion of a circle tangent to the flat flange sur-
face 260 and contiguous therewith. The axially curved surface
, 272 is cut by simultaneously feeding the cutting tool-258
axially along the Z axis and radially along the X axis at
rates which are pre-calculated to produce the desired curve
which in this example is the arc of a circle but could also
be the arc of a parabola or any other desired curve. When the
inner face 260 of the flange is being machin~d, the machine
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:
1046~307
tool is normally operating in the CSS and IPR modes of opera- -
tion, but at the transition point 274 (Fig. 9B) from the flat
surface 260 to the curved surface 272, rotary tool head 34 is
switched from the CSS mode of operation to a constant speed
mode of operation designated as RPM, while the tool slide 52
is switched from the IPR mode of operation to a constant speed
cross-feed which is designated as the IPM mode of operation.
At the same time, a predetermined axial feedrate is initiated -
along the Z axis at feedrates which are predetermined to pro-
vide the desired curve 272. Normally, rotary tool head 34
will remain revolving during the transition from the flat sur-
face of the flange to the curved surface thereof and tool slide
52 will normally continue its cross-feed movement during this
transition period although both the rotary movement of rotary
tool head 34 and the cross-feed movement of tool slide 52 can
be stopped if desired at the transition point from the flat sur-
face 260 to the curved surface 272. In this case, a smooth
transition from flat surface 260 to curved surface 272 can still
be maintained as long as the radius of the cutting tool point
at the end of flat surface 260 is the same as the radius thereof
at the start of curved surface 272 and there is no movement of
the cutting tool point along the Z axis between the s~topping
and starting of rotary tool head 34.
In addition to the movable tool slides 50, 52, 54 and 56,
described above, this embodiment of the invention includes
fixed toolholders 276, 278, 280 and 282 (Figs. 7 and 8) which
are mounted on the faces of rotary tool heads 34 and 36 for
making the rough and finished cuts on the outer rim 268 of the
flanges on axle housing 262. When the fixed toolholders 276
through 282 are being used, as illustrated in Fig. 5, to cut
outer flange rim 268, the movable tool slides 50 through 56
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1046~7
are all moved to a position where their respective tools are
disengaged from the workpiece. On each of the tool heads 34
: and 36, one of the fixed tools makes the rough cut on flange
rim 268, while the other tool makes the finish cut. The
fixed tools 276 through 282 are preferably mounted on corres-
ponding slots 284 through 290 and are clamped to their respec-
tive rotary tool heads 34 or 36 by conventional clamps so that
they can be moved to different positions to accommodate differ-
ent flange dimensions. However, although the fixed toolholders
276 through 282 are adjustable they are called fixed toolholders
in this application because they are normally set in a fixed
position and clamped there for each different type of axle hous-
ing and do not move in and out during the machining operation
as do the movable tool slides 50 through 56.
A typical machining program for the above-described ma-
chine tool includes but is not limited to the following steps
'I or functions:
(1) A pallet 266 (Fig. 1) carrying a fixture 264 which
supports an axle housing 262 in a predetermined accurately de-
fined position is placed upon index table 13 and is clamped
thereto in a predetermined position which accurately locates
; the opposite ends of the axle housing with respect to the
rotary tool heads 34 and 36.
(2) Tool heads 34 and 36 are simultaneously rotated
and fed inwardly along the Z axis to machine the outer rim 268
of the flanges on both ends of axle housing 262 with fixed tool-
holders 276 through 282 as shown in Fig. 5.
(3) Tool heads 34 and 36 are then moved to the position
shown in Fig. 6 preparatory to machining the inner and outer
faces of the flanges.
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(4) Each of the tool heads 34 and 36 are then rotated
in the CSS mode of operation without movement along the Z axis
while one of the two tool slides thereon is operated in the --
IPR mode of operation to make a rough cut of the corresponding
flange face, the outer flange face 270 being cut by tool head
36 while the inner face 260 is cut by tool head 34.
(5) At the transition point 274 on the inner flange face
between flat surface 260 and curved surface 272, tool head 34
is switched from the CSS and IPR mode of operation to the CI
mode of operation without stopping rotation of tool head 34
or the cross feed movement of tool slide 52 to machine the curved
flange face portion 272 contiguous with and tangent to the flat
flange face portion 260.
(6) After the rough cuts of the inner and outer flange
15 ,faces are completed, the tool slides which were not used in the
rough cut are actuated in the same modes of operation specified
in steps (4) and (5) to make the finish cut on the rough cut
flange surfaces.
, (7) The tool heads 34 and 36 are then moved away from the
adjacent flanges to provide clearance for indexing axle housing
, 262.
(8) Axle housing 262 is then indexed about the Y axis by
180 degrees to interchange the flanges thereof with respect to
tool heads 34 and 36.
(9) Steps (3) to (6) are then repeated to machine the re-
; maining two flange faces.
(10) Tool heads 34 and 36 are then moved away from the
flanges to provide clearance for removing and replacing axle
housing 262.
(11) Pallet 266 is removed from index table 14 and is re-
placed by another pallet carrying an unmachined axle housing.
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The above described machining program is preferred for the
particular flange configuration and axle housing shown in the
drawings, but it should be understood that other programs may
be more suitable for other flange configurations and for differ-
ent machining operations on other workpieces.
Although both tool heads 34 and 36 rotate about and slide
along a common Z axis in the above-described embodiment, this is
not a necessary feature of the invention. With some workpieces,
it may be desirable to have the tool heads rotate about differ-
ent axes, which would not alter the essential operation of theinvention. Also, it is not necessary to have two rotary tool
heads, or two tool slides on each tool head. In some embodi-
ments, only one rotary tool head may be employed carrying only
one tool slide. In other embodiments, one or more rotary tool
heads may be employed with fixed toolholders but not slide-
able toolholders.
j Although the illustrative embodiment of the invention has
been described in considerable detail for the purpose of fully
disclosing a practical operative structure incorporporating the
invention, it is to be understood that the particular apparatus
shown and described is intended to be illustrative only and that
the various novel features of the invention may be incorporated
in other structural forms without departing from the spirit and
scope of the invention as defined in the subjoined claims.
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