Turning – Lathe – Multiple
Reexamination Certificate
1994-08-26
2002-05-21
Tsai, Henry (Department: 3722)
Turning
Lathe
Multiple
C082S147000, C082S173000
Reexamination Certificate
active
06389939
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multiple spindle bar machine and, more particularly, to an improved spindle carrier and spindle carrier bearing design.
BACKGROUND ART
Multiple spindle bar machines are well known in the prior art. A multiple spindle bar machine includes a spaced apart array of four, six or eight rotatable workpiece holding spindles mounted in a spindle carrier. The spindle carrier is supported in a headstock and is intermittently rotated or indexed a fraction of a full turn. Each spindle includes a collet at one end of the spindle adjacent a machining work zone for releasably securing a piece of bar stock. A predetermined length of the bar stock extends from an end of each spindle, defining a workpiece. At each spindle carrier indexing position, cutting tools, mounted on tool slides, engage workpieces at the machining work zone to perform machining operations. Each spindle is rotated at the same angular velocity by a spindle drive shaft which extends from a gearbox housing through an aperture in the spindle carrier coincident with the spindle carrier's axis of rotation or central axis. The gearbox housing is spaced apart from the headstock and supports a motor and associated sets of gears for rotating the spindle drive shaft at a desired angular velocity and rotating a main drum shaft. The main drum shaft, drives an indexing mechanism which rotates or indexes the spindle carrier. The main drum shaft also drives sets of cams which move the tool slides and other cams which advance bar stock through its corresponding spindle to define a new workpiece.
Each spindle, and therefore each workpiece, moves in steps about the central axis of the spindle carrier as the spindle carrier indexes. For example, in a six spindle machine, a spindle completes one orbit or a 360 degree rotation every six steps or indexes of the spindle carrier, that is, each index rotates the spindle carrier 60°. As the spindle carrier indexes, a spindle moves in an arcuate path about the spindle drive shaft and the workpiece held by that spindle moves through successive spindle indexing positions within the machining work zone.
The tool slides include a hexagonal end slide, having a tool mounting surface corresponding to each spindle carrier indexing position and a plurality of cross slides, one cross slide per spindle carrier indexing position. For example, a six spindle machine has six indexing positions and six cross slides. After the spindle carrier indexes, the end slide and six cross slides, whose movement is controlled by the main drum shaft in conjunction with sets of cams, move from starting locations removed from the machining work zones toward the workpieces. Tools mounted on the end and cross slides engage the workpieces at their current spindle indexing positions to perform the machining operations. After the longest cycle machining operation is complete, the end and cross slides retract to their starting locations and the spindle carrier is indexed to the next spindle carrier indexing position. Sufficient clearance is provided between the tool slide starting locations and the workpieces so that the workpieces do not impact the tools when the spindle carrier indexes to its next position. Tools mounted on the end slide engage the workpiece in a direction parallel to the central axis, that is, parallel to the spindle drive shaft, of the spindle carrier while tools mounted on the cross slides engage the workpieces in a direction perpendicular to the spindle carrier central axis.
A bar stock pusher moves the bar stock along an axial dimension at a first spindle carrier indexing position. The spindle collet at that position opens and the predetermined length of bar stock is fed through the spindle to move a section of new unfinished bar to the machining work zone thereby defining a new workpiece. The spindle collet then closes to secure the new workpiece in position for subsequent machining operations. At successive spindle carrier indexing positions various machining operations are performed on the rotating workpiece. When the spindle carrier indexes to the final indexing position, a cut-off tool mounted on a cross slide engages and severs the completed workpiece from the remaining bar stock. Upon the next index of the spindle carrier, the spindle returns to the first indexing position and the bar feeding, machining and cut-off sequence is repeated. Performing simultaneous machining operations on four, six or eight spaced apart rotating workpieces provides significant economies of scale in the high volume manufacture of parts as compared to single spindle machines wherein only one workpiece at a time is machined.
A prior art publication entitled
Handbook for Operators—Acme Gridley Multiple Spindle Bar Machines
, copyright 1980, by National Acme Division, Acme-Cleveland Corporation, depicts the design and operation of a multiple spindle bar machine. The foregoing publication is incorporated herein in its entirety by reference.
In spite of the production efficiency of multiple spindle bar machines, problems remain relating to machining accuracy, tool chatter and dimensional stability of pieces produced over time. Many of these problems can be traced to the effects of heat on a multiple spindle bar machine. In addition to the actual metal cutting operations, operation of the machine involves a complex set of rotating drive shafts and gears, sprockets and spindles, sprocket chains and clutches, rotating cams and engaging cam followers, all of which generate a significant amount of thermal energy. As various components of the bar machine are heated, they expand at differing rates depending on their heat absorption and dissipation properties and machining precision suffers. Cooling the entire machine is not a feasible alternative. Especially critical to machining precision is the position of the spindle carrier.
The spindle carrier is rotatably supported in a bore in the headstock by two spaced apart roller bearing assemblies. Conventionally, the two spindle carrier roller bearings provided radial support to the spindle carrier, but did not provide axial support. That is, the spindle carrier was permitted to move axially within the headstock bore. Axial support for the spindle carrier was provided by a bearing coupled to the gearbox housing and a tubular spindle carrier stem overlying a portion of the spindle drive shaft, the carrier stem was coupled to the spindle carrier near one end of the carrier stem and rotatably journaled in the gearbox housing bearing at an opposite end of the carrier stem. The gearbox housing bearing provided both thrust and axial support to the carrier stem, that is, the bearing prevented both lateral and axial movement of the carrier stem. Since the spindle carrier was pinned to the carrier stem, axial movement of the spindle carrier was also constrained by the gearbox housing bearing.
Experience has taught the aforementioned structure for axially constraining the spindle carrier resulted in a loss of machining accuracy due to thermal expansion of the spindle carrier stem during operation of the bar machine. The expansion of a tube in the axial direction when heated is proportional to the tube's length. As the bar machine heated up during operation, the tubular carrier stem would expand axially. The axial expansion of the carrier stem over the distance between the gearbox bearing, which constrained the carrier stem, and the pinned spindle carrier resulted in a significant axial displacement of the spindle carrier within the headstock bore. The axial displacement of the spindle carrier as the bar machine heated up and cooled down unacceptably degraded machining accuracy.
DISCLOSURE OF THE INVENTION
A multiple spindle bar machine constructed in accordance with the present invention includes a new and improved bearing structure for rotatably supporting a spindle carrier for indexed movement through multiple work orientations. A bar machine headstock includes first and second spaced apart uprights having a throughbore dimensioned to
Babuder Kirt M.
Bender Thomas M.
Joseph Douglas A.
Stupica L. Joseph
DeVlieg Bullard II, Inc.
Jenner & Block LLC
Tsai Henry
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