GB1571634A - Machine tool with counterposed rotary toohlheads carrying cross-fed tool slides - Google Patents

Abstract

The lathe has two rotatable and axially displaceable tool heads (34, 36) coaxially facing one another, on which tool slides (50, 54) for fastening the cutting tools are arranged. A clamping device (264, 266) for holding the workpiece (262) is arranged between the two tool heads. The tool slides are displaceable at right angles relative to the workpiece during the turning. The rotation of the tool heads, the displacement of the tool heads and the displacement of the tool slides are effected by drive devices (126, 28, 42, 44, 58, 60, 62, 69) which are numerically controlled in order to obtain a constant cutting speed as well as a constant chip thickness. It is thus possible to simultaneously machine a workpiece at opposite sides. <IMAGE>

Description

(54) MACHINE TOOL WITH COUNTERPOSED ROTARY TOOLHEADS CARRYING CROSS-FED TOOL SLIDES (71) We, KEARNEY & TRECKER COR- PORATION, a corporation organised and existing under the laws of the State of Wisconsin, United States of America, of 11000 Theodore Trecker Way, West Allis, Wisconsin, 53214, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 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 have been 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 crossfeed movements which cut the rim, the front face, and the near face of the desired flange. However, for relatively large workpieces, such as cast steel axle housings for tractors or large earth moving machines, machining the flanges in a lathe is difficult due to the size and weight of the workpieces, and also due to their asymmetrical shape. Therefore, it is desirable to provide a machine tool which is capable of accurately cutting circular flanges in relatively large asymmetrical workpieces while the workpiece is held in a stationary fixture. It is also desirable to provide such a machine tool which is also capable of machining axially curved surfaces on such a workpiece.

In accordance with this invention there is provided a machine tool comprising a bed; a first toolhead mounted for slidable movement on said bed for linear movement along a first axis and journalledfor rotation about said first axis; a second toolhead mounted for slidable movement on said bed for linear movement along said first axis and journalled for rotation about said first axis; said second toolhead being spaced from said first toolhead and counterposed thereto; fixture means in the space between said first and second toolheads for holding a workpiece in a fixed position relative to said toolheads, so that said workpiece presents a first portion facing said first toolhead and a second portion facing said second toolhead; means for rotating said first toolhead; means for rotating said second toolhead; means for moving said first toolhead along said first axis while it is rotating; and, means for moving said second toolhead along said first axis while it is rotating; a first tool slide slidably mounted on said first toolhead for cross-feed movement along a second axis which is transverse to said first axis; first cross-feed means for moving said first tool slide along said second axis while said first toolhead is rotating; a first toolholder on said first tool slide for holding a first tool for rotation in an orbit to cut said workpiece; a second tool slide slidably mounted on said second toolhead for crossfeed movement along a third axis which is transverse to said first axis; and second cross-feed means for moving said second tool slide along said third axis while said second toolhead is rotating; a second toolholder on said second tool slide for holding a second tool for rotation in an orbit to cut said workpiece; and controller means for independently controlling the rotation of said first and second toolheads; the axial feed movement of said first and second toolheads along said first axis, and the cross-feed movement of said first and second tool slides along said second and third axes, respectively, to perform machining operations on said first and second portions of said workpiece.

In a preferred embodiment, 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 means 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 axis, the cross-feed rate can be automatically varied by the controller means 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 machine a predetermined axially curved surface on the workpiece.

In the accompanying drawings: Fig. 1 is a side elevation view of an embodiment of the invention which has 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. 1; 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 slipping assembly for the rotary tool head shown 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 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 an 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 to 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 Fig. 9A, the conductors identified by the same letter in Figs. 9A and 9B being connected together.

Figure 1 shows an embodiment of the invention which has 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 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 which carry ways 18 and 20, respectively, upon which saddles 22 and 24, respectively are slidably movable. The ways 18 and 20 and the saddles 22 and 24 define a common horizontal Z axis which is perpendicular to the vertical Y axis about which the index table 14 is rotatable. The saddle 22 is moved along the ways 18 by a Z axis drive motor 26 which is mechanically coupled to the saddle 22 through a conventional ball screw mechanism (not shown). The saddle 24 is moved along the Z axis by a similar Z axis drive motor 28 which is mechanically coupled to the saddle 24 through a conventional ball screw mechanism (not shown). Bolted to the top of the saddles 22 and 24 are hollow tool drum housings 30 corresponding tool heads 34 and 36 are journalled for rotation about the Z axis.

The tool heads 34 and 36 are bolted to the end of respective tool drums 38 and 40 which extend within the tool drum housings 30 and 32 and are journalled therewithin. Mounted on the top of the tool drum housings 30 and 32 are tool head motors 42 and 44 which are mechanically coupled to their respective tool drums 38 and 40 through -drive belt assemblies 46 and 48.

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 mounted on the front face of tool head 34 for sliding movement along X and U axes, respectively, the 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 ;K 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 electrically coupled to conductors on tool drum housing 32 through a slip-ring assembly.

Fig. 2 is an axial sectional view of tool drum housing 30, tool drum 38 and tool head 34. Tool drum housing 30 is a hollow cylinder which is bolted to saddle 22 by bolts 66. Tool drum 38 is also cylindrical in shape and is journalled 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 Motor 58 turns a drive shaft 86 which is mechanically coupled to another drive shaft 88 through 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 understood 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 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 94 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 together as a rigid unit.

Tool slide drive shaft 88 is coupled by a splined coupling 99 to the input shaft 100 of a spiroid reducing 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 coupling is shown in Fig. 4.

Two slip-ring units are used, a large slipring unit 122 and a smaller slip-ring unit 124. Slip-ring 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 slipring 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 cable or sliding contacts to couple conductors 136 to the machine 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, tool slide motors, and sliprings is the same as tool head 34, it is not illustrated or described in detail herein.

Figs. 9A and 9B show a block diagram of the electrical control circuits for rotary tool head 34. This particular control 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, tachometers and slip-rings for rotary tool head 34, along with the conductors for coupling these electrical elements to the controller circuits shown in Fig. 9A, are shown in Fig. 9B, which is 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 con ventional 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 control the operation of rotary tool head 34 in the manner described hereinafter.

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 drawings. 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 conventional 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 include a digital Z word specifying the position along the Z axis to which the 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 movement 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 desired positions of saddle 22 are compared and if they are different, a drive signal is applied to digital to analog converter 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 predetermined tolerance of the desired federat. When saddle 22 reaches the desired position along the Z axis, this information is applied by the Z axis resolver 186 to feedback counter and oscillator 192 which applies the corresponding digital number to following 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 difference 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 respective 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.

U axis motor 58 is controlled 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 tachometer 228, U axis resolver 170 and slip-ring brush connectors 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 circuits for rotary tool-head 36 which are also controlled by digital output signals from the logic circuits 178. In addition, 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 unclamping 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 shown 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 above 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 of each other and can be moved simultaneously to make cuts with both cutting tool 256 and 258. How ever, in this particular embodiment of the invention, tool slides 50 and 52 are moved separately in accordance with a machining program in 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 ma chining 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 constitu tes a cast steel tractor axle housing shown in its entirety in Figs. 5 and 6. Axle hous ing 262 is held in a fixture 264 which is at tached to a pallet 266 which, in turn, is clamped to the top of index table 14 (see Fig. 1). This particular embodiment of the invention is adapted to machine flanges on both ends of axle housing 262 in a manner to be described more particualrly herein after.

As tool slides 50 or 52 are moved in wardly 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 corresponding cutting tool 256 or 258 will decrease with the inward move ment 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 opera tion in which the rotary speed c9 of tool head 34 at any given time is varied in ac cordance with the formula d = SS/(2 7r Re) where SS = the desired cutting surface speed, and Re = the radius of the circle de scribed 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 cutting that surface regardless of the cross-feed movement-of the cutting tool.

In the CSS mode of operation, if the cross-fed 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 constant chip thickness is desired, it is preferable to store in CNC memory portion 267 an inch per revolution routine (IPR) in which the crossreed rate FR of the tool slide at any given time is defined by the equation FR = where Q = the desired chip thickness per tool head revolution and &commat; = 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 tool holders 252 and 254 are shown in Fig. 9B as being shaped to cut the inner face 260 of the flange on axle housing 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 machining 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 machining axially curved surfaces such as the surface 272 in Fig. 9B which is a portion of a circle tangent to the flat flange surface 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 machined, the machine tool is normally operating in the CSS and IPR modes of operation, 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 feed rate is initiated along the Z axis at feedrates which are predetermined to provide the desired curve 272. Normally, rotary tool head 34 will remain revolving during the transition from the flat surface 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 surface 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 stopping-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 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 corresponding slots 284 through 290 and are clamped to their respective rotary tool heads 34 or 36 by conventional clamps so that they can be moved to different positions to accommodate different flange dimensions. How- ever, 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 housing and do nowt 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 machine tool includes but is not limited to the following steps or functions: - (1) A pallet 266 (Fig. 1) carrying a fixture 264 which supports an axle housing 262 in a predetermined accurately defined 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 toolholders 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.

(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 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 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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. 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 surface 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 stopping-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 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 corresponding slots 284 through 290 and are clamped to their respective rotary tool heads 34 or 36 by conventional clamps so that they can be moved to different positions to accommodate different flange dimensions. How- ever, 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 housing and do nowt 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 machine tool includes but is not limited to the following steps or functions: - (1) A pallet 266 (Fig. 1) carrying a fixture 264 which supports an axle housing 262 in a predetermined accurately defined 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 toolholders 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. (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 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 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 remaining two flange faces. (l0) 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 replaced by another pallet carrying an unmachined axle housing. 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 different machining operations on other workpieces. WHAT WE CLAIM IS:-

1. A machine tool comprising a bed; a first toolhead mounted for slidable movement on said bed for linear movement along a first axis and journalled for rotation about said first axis; a second toolhead mounted for slidable movement on said bed for linear movement along said first axis and journalled for rotation about said first axis; said second toolhead being spaced from said first toolhead and coun

terposed thereto; fixture means in the space between said first and second toolheads for holding a workpiece in a fixed position relative to said toolheads, so that said workpiece presents a first portion facing said first toolhead and a second portion facing said second toolhead; means for rotating said first toolhead; means for rotating said second toolhead; means for moving said first toolhead along said first axis while it is rotating; and, means for moving said second toolhead along said first axis while it is rotating; a first tool slide slidably mounted on said first toolhead for cross-feed movement along a second axis which is transverse to said first axis; first cross-feed means for moving said first tool slide along said second axis while said first toolhead is rotating; a first toolholder on said first tool slide for holding a first tool for rotation in an orbit to cut said workpiece; a second tool slide slidably mounted on said second toolhead for cross-feed movement along a third axis which is transverse to said first axis; said second cross-feed means for moving said second tool slide along said third axis while said second toolhead is rotating; a second toolholder on said second tool slide for holding a second tool for rotation in an orbit to cut said workpiece; and controller means for independently controlling the rotation of said first and second toolheads, the axial feed movement of said first and second toolheads along said first axis, and the cross-feed movement of said first and second tool slides along said second and third axes, respectively, to perform machining operations on said first and second portions of said workpiece.

2. A machine tool according to claim 1, comprising a fixture support table supporting said fixture means, said fixture sup port table being mounted for rotation about a fourth axis perpendicular to said first axis and being rotatable through an angle of at least 1800 to interchange said first and second portions of said workpiece.

3. A machine tool according to claims 1 or 2 including a motor mounted to rotate bodily with said first toolhead; means mechanically coupling said motor to actuate said first slide in its cross-feed movement; and, a slip ring assembly connected to transmit electrical signals between said controller means and said motor for regulating the cross-feed movement of said first slide.

4. A machine tool according to claim 3 including a second motor mounted to motor to actuate said second slide in its rotate bodily with said second toolhead; means mechanically coupling said second cross-feed movement; and a second slip ring assembly connected to transmit electrical signals between said contollermeans and said second motor for regulating the cross-feed movement of said second slide; the said controller means including means for transmitting means including means for transmitting separate control programs to said first and second motors so that two different machining operations can be performed simultaneously on the same workpieces.

5. A machine tool according to claims 1 or 2 including a third tool slide mounted on said first toolhead for cross-feed movement along a fourth axis which is transverse to said first axis so that two separate tool slides are movably mounted on said first toolhead; a third toolholder on said third tool slide for holding a roughing tool for rotation in an orbit to cut said workpiece so that said third tool slide can be operated first to complete a roughing cut on said workpiece and said first tool slide can be operated next to complete a finishing cut on the same portion of said workpiece.

6. A machine tool according to any of the preceding claims including a fourth toolholder mounted on said first toolhead and clamping means for clamping said fourth toolholder in position on said first toolhead so that it rotates with said toolhead in an orbit of predetermined diameter for turning a circle of fixed diameter on said workpiece.

7. A method of operating the machine tool of claim 2, characterized by the steps of: (A) simultaneously engaging said first and second tools with said first and second portions of said workpiece, respectively, and simultaneously rotating said first and second toolheads to simultaneously perform machining operations on said first and second portions of said workpiece; (B) disengaging said first and second tools from said first and second portions of said workpiece after said machining operations are completed; (C) rotating said fixture support table through 1800 to interchange said first and second portions of said workpiece; and (D) simultaneously engaging said first tool with said second portion of said workpiece and said second tool with said first portion of said workpiece and simultaneously rotating said first and second toolheads to simultaneously perform additional machining operations on said first and second portions of said workpiece.

8. A method of operating the machine tool of claim 5, characterized by the steps of: (A) engaging said first tool with said workpiece while said third tool is disengaged from said workpiece and moving said first tool slide to move said first tool over a portion of said workpiece to make a rough cut therein; (B) disengaging said first tool from said workpiece; and (C) engaging said third tool with said workpiece while said first tool is disengaged from said workpiece and moving said third tool slide to move said third tool over the rough cut portion of said workpiece to make a finish cut therein.

9. A machine tool substantially as herein described with reference tithe accompanying drawings.