Information
-
Patent Grant
-
6644637
-
Patent Number
6,644,637
-
Date Filed
Friday, September 13, 200221 years ago
-
Date Issued
Tuesday, November 11, 200320 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 269 152
- 269 8
- 269 16
- 269 289 R
- 269 27
- 269 24
- 269 32
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International Classifications
-
Abstract
A reconfigurable fixture for workpieces is disclosed. It utilizes a flat surface magnetic chuck with modular workpiece supporting, locating and clamping elements that are carefully located on it and held by magnetic attraction to it. These elements are precisely located to hold the workpiece in spaced relation to the chuck surface. Some locating elements are mechanically fixed to the chuck for securing the workpiece from transverse movement on the chuck surface. Preferably, each of the supporting, locating and clamping members are fixed to separate steel bases for magnetic attraction to the chuck. Each base may also carry its own hydraulic actuator for height adjustment of a support element or for height adjustment and closure of a clamping element. These modular elements can be selected from a storage magazine and located on a chuck by numerically controlled mechanisms.
Description
TECHNICAL FIELD
This invention pertains to reconfigurable magnetic workholding fixtures. More specifically, this invention relates to robust and easily re-configured fixtures comprising a flat magnetic chuck surface with magnetically attached modular supporting, locating and clamping elements that are useful for locating and securing workpieces, especially non-magnetic workpieces.
BACKGROUND OF THE INVENTION
There is a need in manufacturing operations for durable and reconfigurable workholding fixtures especially for flexible manufacturing operations. The fixtures must be readily and accurately adaptable to hold different workpiece shapes for machining applications or the like. Sometimes the workpieces are similar or related part shapes such as cast aluminum cylinder heads for different engines. In other manufacturing situations the parts may be of unrelated design but requiring similar manufacturing operations. In these varied applications, the fixture reconfiguration or changeover from one part design to another has to be fast enough to meet the productivity requirements of current manufacturing systems.
Magnetic chucks have been available for holding some magnetic workpieces. For example, magnetic chucks providing flat holding surfaces are commercially available under the trade designation “Quadsystem” by Technomagnete S.P.A. These chucks are provided with a plurality of magnetic pole pieces often arranged in a rectangular grid on a base plate within peripheral walls. Apart from the coils that energize or de-energize the steel pole pieces, the chuck also includes high energy permanent magnets (neodymium-iron-boron magnets) interspersed among the poles. U.S. Pat. Nos. 4,847,582 and 4,956,625 appear to describe such flat surface chucks. Suitably placed and oriented electrical coils permit the chuck to be magnetized to different levels and demagnetized for locating, securing and removing a magnetizable work piece as is described in the specifications and drawing figures of these patents which are incorporated herein by reference. However, this chuck has not proven useful for securing and machining non-magnetic workpieces such as, e.g., cast aluminum alloys.
It is an object of this invention to provide a fixture utilizing a magnetic chuck for workpieces, especially non-magnetic workpieces. It is a more specific object of this invention to provide an easily reconfigured workpiece holding fixture comprising a magnetic base and modular workpiece supporting, locating and clamping elements.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of this invention a workholding fixture basically comprises an electromagnetic chuck and several modular fixture elements for locating, clamping, and supporting a non-magnetic workpiece. Such a fixture is also useful for iron or steel workpieces.
A suitable magnetic chuck is one that can be energized and de-energized with an electric pulse from a stationary electric power source. Thus, the magnetic chuck provides a fast attach/release capability and a flat surface on which modular workpiece supporting, locating and clamping elements can be securely held by the magnetic force. Preferably, the strength of the field can be varied from a first level for sensitive and accurate modular element placement to a second, higher level for strongly securing the elements. In addition, the energized magnetic chuck,can maintain its magnetic attractive force even when the chuck is disconnected from the power source. This is important because it provides the required mobility of the workholding fixture to be transferred from one machining station to another machining station.
The autonomous integrated modular clamping or supporting elements are designed and constructed to be precisely located on the flat surface of the magnetic chuck and to then receive and securely hold a non-magnetic workpiece for a machining or other manufacturing operation. The work piece may be a nonferrous alloy such as an aluminum or magnesium alloy or the like. The workpiece is held spaced apart from the magnetic chuck by suitably located and cooperating supporting, locating and clamping members.
The supporting, locating and clamping elements may be individually carried on a suitable base plate. The base plate is preferably made of steel or other magnetizable alloy and sized so that the support or clamp is tightly held on the magnetized chuck plate. Support or clamp posts stand upright from the base plate. In one embodiment, the support is simply a post of predetermined length fixed at one end to the base plate with the other end configured to engage and support a surface of a workpiece. The length of the support post is determined by the shape of the work piece and its intended distance from the chuck surface. The clamp is typically a rotatable horizontal arm attached to the upper end of a post carried by a base plate. Clamp arms of varying shapes may be used to accommodate different workpieces.
In addition to the magnetically attached locating, supporting and clamping elements, the fixture preferably comprises a rigid guide rail and at least one locator element (which is also a support element) that are precisely located and mechanically fixed to the surface of the magnetic chuck. These mechanically fixed elements constrain the workpiece from transverse movement on the chuck surface. Movable locator elements used in combination with these fixed elements assure that the fixture is suitably reconfigured for different cylinder heads or other workpieces.
In its simplest terms the fixture comprises a magnetic chuck with a mechanically fixed guide rail and locator element, and at least one support element and one clamp arm element each secured to the surface of the chuck by magnetic force. Generally, a plurality of the magnetically attached elements will be located on the chuck surface to cooperate in holding the workpiece for a machining operation or the like. However, in a preferred embodiment of the invention, the height of the movable support elements and clamping elements are not fixed, they are adjustable to accommodate different workpieces.
In support elements or clamping elements of adjustable height, the posts can, for example, be fitted into a cylinder or other housing and threaded for screw height adjustment, or adjusted hydraulically. Such support and clamping elements are commercially available. Hydraulic height adjustment of post height may require that the base plate be modified to accommodate suitable hydraulic pressure supplying components.
The magnetic chuck and modular support and clamp elements allow a fixture to be easily assembled or modified. For example, support and clamp elements can be individually selected from a suitable inventory or storage magazine by a numerically controlled robot and precisely located on a magnetic chuck surface. The element-placing robot arm will have a suitable gripping adapter to grip the support or clamp element and place it base down on the chuck surface. Similarly, support and clamp elements are removed from the chuck when the need for the present fixture assembly is finished. The chuck is partially magnetized for element placement and removal and fully magnetized to secure the elements to the chuck in the working fixture.
The fixed guide rail and locator post(s) are located for general fixture applications. The magnetically attached locator, support and clamp elements are positioned for each workpiece configuration. They are positioned so that the clamp arms can press against a surface of the workpiece and force it against a suitable surface piece on the top of each support post. The workpiece is hoisted and placed against the support posts and the arms of the clamps rotated into position engaging the workpiece.
The assembled fixture can be situated horizontally or vertically, or in any desired attitude with the workpiece securely held by the clamping elements against the locator and support elements in a position spaced from the surface of the chuck. The combination of the mechanically fixed and magnetically fixed supporting, locating and clamping elements holds the workpiece for machining or the like, even with heavy stock removal.
In another embodiment of the invention the roles or positions of the large magnetic chuck plate surface and the support plates for the support or clamp elements are reversed. In this embodiment, the fixture system essentially consists of a large conventional, magnetizable steel fixture plate and a collection of modular fixture elements for locating, clamping, and supporting a workpiece. The modular elements are all mounted on magnetic holding bases of some common dimensions. These magnetic holding bases are smaller versions of the magnetic chuck plates described above. The magnetic holding base for the support or clamp elements can be an electropermanent magnet construction so that it can be activated or de-activated with an electric switch. Alternatively, it can be a simple lift magnet design activated by a mechanical lever. The magnetic holding base will carry a support and/or clamp element and optionally a hydraulic pressure supplying component. The role of the magnetic holding base is to provide a fast attach/release capability to the flat steel fixture plate and also a platform on which a modular fixture element can be affixed mechanically. In addition, the activated magnetic support or clamp base will maintain its magnetic attractive force when the base is disconnected from the electric source or as long as the mechanical lever stays in the same position. This portability provides the required mobility of the smart workholding fixture plate to be transferred from one machining station to another machining station.
Other objects and advantages of the invention will be understood from a description of preferred embodiments. Reference will be made to drawing figures that are described in the following section.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is an exploded, generally plan view of an assembled workpiece fixture in accordance with the invention with an overlying aluminum cylinder head.
FIG. 2
is an oblique view of a modular, self contained hydraulic clamping element, comprising a hydraulically actuated clamp arm and a screw actuated hydraulic pump both contained in a steel base member, suitable for use in a workpiece fixture of this invention.
FIG. 3
is a side view, partially in cross-section of a modular clamp assembly similar to that of FIG.
2
.
FIG. 4
is a side view, partly in cross-section, of a modular, self contained hydraulic support element and screw actuated hydraulic pump both contained in a steel base member, suitable for use in workpiece fixture of this invention.
FIG. 5
is an oblique, fragmentary view of a locator element, clamped to a guide rail for use in a workpiece fixture of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The practice of the invention will be illustrated by describing a fixture for machining of an aluminum alloy cylinder head for an automotive vehicle engine. Such a part is typically cast of a silicon containing, aluminum alloy as close to final shape as possible. However an automobile engine cylinder head casting is a very complex structure. The cylinder head shown schematically in
FIG. 1
at
10
is for a three cylinder engine. The cylinder head contains openings for four valves in each cylinder, openings for spark plugs, intake passages for air and exhaust passages for exhaust gas. The head also contains oil passages and passages for coolant. It is a complex structure that requires a considerable amount of machining following the casting operation.
In order to facilitate such machining the cylinder head must be securely held in a fixture so that numerically controlled machine tools can properly remove metal from the casting to arrive at its specified finish dimensions. A reconfigurable, magnetic fixture to support and hold cylinder head
10
is shown generally at
12
in FIG.
1
. Fixture
12
includes a magnetic chuck
14
that, in this example, has a complex flat rectangular working surface (indicated, generally at
16
) of many magnetic pole elements
18
. Applied to the surface
16
of chuck
14
are a number of fixture elements that are movable to accommodate varying workpiece shapes or machining positions.
Fixture
12
also includes a rigid guide rail
20
that is bolted, or otherwise suitably fixed, to surface
18
of the magnetic chuck
14
. Guide rail
20
is illustrated as straight but it may be of any desired length or configuration. Also, clamped to guide rail
20
are two locator post elements
22
that are thus mechanically fixed to the surface
18
of chuck
14
(see
FIG. 5
for a suitable clamping arrangement). On the top of each locator posts
22
are pins
23
that are shaped and located for fitting into locator holes (sometimes termed B-C holes not seen in
FIG. 1
) formed in the bottom of cast cylinder head
10
. The B-C holes serve to facilitate precise location of the workpiece for machining operations. Guide rail
20
and locator posts
22
are important in precisely locating and rigidly supporting a massive work piece such as cylinder head
10
. Furthermore, they assist the magnetic chuck
12
in keeping workpiece
10
from sliding transversely on surface
18
under dynamic or impact machining forces.
Also attached by magnetic attraction to flat surface
16
of magnetic chuck
14
are several self-contained modular hydraulically adjustable and actuated clamping elements
24
and several modular support elements
26
of fixed height. Both the clamping elements
24
and support elements
26
are shown schematically in FIG.
1
. In
FIG. 1
the hydraulic clamping elements
24
are identical to each other and the fixed height support elements
26
are identical to each other. It may be preferred to use identical modular clamping and support elements for simplicity of inventory and reconfiguration of the fixture. But these elements don't have to be of common design. Similarly, the support elements in
FIG. 1
are illustrated as simply having a base
29
with a post
27
of fixed length. However, the support elements
26
may also be provided with hydraulic height adjustments like the clamping elements
24
. A representative clamping element is shown in more detail in
FIGS. 2 and 3
, and an adjustable support element is shown in FIG.
4
.
The support elements
26
are located so as to space cylinder head
10
from chuck surface
16
and to support it from deflection during machining operations. The clamping elements have clamp arms
28
(best seen in
FIGS. 2 and 3
) that are rotatable from an open position when cylinder head
10
is being placed on the fixture, or removed from it, to a closed position. In the closed position the clamp arms engage a flange or other portion of the cylinder head. Clamps
24
press the cylinder head against the tops of the support members
26
.
While the guide rail
20
and locator posts
22
are mechanically attached to the magnetic chuck
12
, the modular support elements
26
and clamp elements
24
are held to the chuck surface
16
by its magnetic field.
As stated above, magnetic chucks are commercially available in a variety of sizes and shapes. Chuck
12
is larger than the footprint of cylinder head
10
. In a representative commercial embodiment, chuck
12
has a steel base, not seen in
FIG. 1
, with opposing rectangular side walls
30
,
32
. Supported on the base and confined within side walls
30
,
32
are many steel cubes that serve to concentrate magnetic flux and as magnetic poles. Only the upper flat surfaces
18
of the cubes are seen in FIG.
1
and there are
126
such pole surfaces in this embodiment. Each polar square (typically 50 mm by 50 mm) is an independent magnet body presenting a magnetic pole at surface
16
. And each such square
18
is surrounded on the other four cube sides by smaller magnets of opposite polarity. Embedded electric coils serve to magnify and de-magnify the magnetic pieces as illustrated, for example, in
FIGS. 1-3
of the above referenced U.S. Pat. No. 4,956,625. The construction and assembly of the magnets assures that the magnetic flux produced by the chuck runs flat and horizontally at the surface
16
of chuck
12
. The coils around the reversible permanent magnets can be energized to generate a strong momentary electromagnetic field and they are capable of reversing the polarity of the chuck. Thus a relatively low magnetic field may be initially applied to assist in holding and locating the modular clamping
26
and support
24
members without jerking them to the surface
16
of the chuck. But the magnetic field can be substantially increased to strongly hold the modular pieces to the surface of the chuck. When it is time to reconfigure the workpiece fixture the magnetic field is partially turned off and the pieces removed.
The external frame of the chuck has the mechanical function of containing the magnetic components. It also serves to convey the magnetic flux lines so as to insulate the active surface of the chuck from other machine or processing elements.
An illustrative modular clamping element
24
for use in the workholding fixture of this invention is shown in
FIGS. 2 and 3
. Clamping element
24
comprises a hydraulically actuated and lockable clamping cylinder and arm
40
of a known type. The clamping element
24
also contains a hydraulic screw pump
42
of a known type. However, in the practice of this invention, screw pump
42
and the hydraulic clamping arm
40
are fixed in a specially designed base
44
. Base
44
preferably made of a ferrous metal alloy such as steel. The steel base
44
is large enough to receive a suitable screw pump
42
and hydraulic clamping arm
40
. But it is also sized and constructed so as to concentrate magnetic flux lines from the magnetic chuck
14
to be strongly attracted to surface
16
. One suitable clamp base is rectangular as seen in
FIG. 2
with dimensions of 100 mm×125 mm. Base
44
also provides a channel
46
(
FIG. 3
) for hydraulic fluid between screw pump
42
and clamp
40
.
Hydraulic clamping arm devices suitable for use in the practice of this invention are commercially available. Such a device comprises a clamp arm
28
attached to the end of a rod
48
, such as by a bolt
50
. Rod
48
extends into one end of a hydraulic cylinder
52
(FIG.
3
). The other end of cylinder
52
admits hydraulic fluid that applies force to the rod
48
, or a piston affixed to it. Upon the application of fluid pressure (such as from screw pump
42
through channel
46
), the mechanism within cylinder rotates rod
48
and arm
28
to a clamping position. When fluid is withdrawn from cylinder
52
, rod
48
is retracted and arm
28
rotated to a clamp release position. Depending upon the specifications of the commercial device, arm
28
may be rotated, e.g., ninety degrees and the stroke of rod
48
may be 11 to 25 mm.
Various commercial clamps are available depending upon the height required for clamp arm
28
and different clamp arm shapes are available. In
FIGS. 2 and 3
, arm
28
is illustrated as being straight. However, clamp arms with intermediate bent sections provide higher or lower height adjustments.
The hydraulic clamp mechanism
40
is fixed within tube
54
and attached upright to base
44
. As illustrated in
FIG. 2
, a spacer
56
may also be used to alter the height of clamp arm
28
.
In modular clamp unit
24
, hydraulic clamp
40
is used in combination with a hydraulic screw pump
42
. Such pumps are commercially available. However, in the practice of this invention, the screw pump is inserted upright into a bore
66
in elevated portion
68
of magnetic base
44
(see FIG.
3
). Screw pump
42
contains a rod
58
with helical threads
59
along the central portion of its length. One end
60
of rod
58
is inserted in threaded
59
engagement into hydraulic cylinder
62
. The upper end
64
of rod
58
is a hexagonal nut for manual or robotic actuation of the pump
42
. The lower end
60
of rod
58
is attached to piston
70
. The space
72
within cylinder
62
above piston
70
is vented
74
to the atmosphere. Space
76
below piston
70
contains hydraulic fluid which also fills channel
46
and the fluid space of hydraulic clamp
40
. Seal
78
provides a fluid barrier between piston
70
and cylinder
62
.
The structure of screw pump
42
in
FIGS. 2 and 3
is the same. In
FIG. 3
the pump
42
is simply shown as inserted into elevated portion
68
of base
44
. In
FIG. 2
, screw pump
42
in enclosed in a cover piece
71
with slots
73
. This cover piece
71
with slots
73
is to facilitate robotic grasping of the modular clamping element
24
for placing on, and removal from, magnetic chuck
14
When the screw pump rod
58
is rotated so as to drive hydraulic fluid into the hydraulic clamp, the clamp is initially rotated from a non-clamping position to its clamping position. At the same time the clamp is lowered by a half inch or so until it comes into engagement with a work piece such as a flange surface or other suitable surface on the aluminum cylinder head. So long as the hydraulic pressure is then maintained by the screw pump, the clamp arm remains locked in position. When it is time to release a work piece, the screw pump rod
58
is reversed, piston
70
is lifted and hydraulic fluid flows back from the modular clamp body. Clamp arm
28
is raised and turned from its clamping position.
FIG. 4
illustrates a three component, hydraulically adjustable, modular support element
80
suitable for use in an embodiment of this invention. Different support posts have been used in the practice of this invention. Some have been of fixed height and some were adjustable. These supports are the workpiece locators in the direction perpendicular to the base
16
of the fixture
12
. In principle, three support elements could be sufficient to define a locating plane for the workpiece. However, extra supports can be added to bear loads more evenly and to reduce workpiece deflection during machining. In one embodiment a simple flat top post of suitable length was mounted on a 75 mm by 75 mm magnetic steel base. These support posts are illustrated at
26
in FIG.
1
. These structures are useful where the support height is fairly constant in different fixture requirements. However, hydraulically adjustable modular units can also be used.
A three component modular support unit
80
is illustrated in cross section in FIG.
4
. Again, hydraulic support units are commercially available in different sizes and capacities. A representative hydraulic support unit
82
is obtained and adapted for support in an upright pedestal portion
86
in steel base
84
. The steel base
84
also receives an upright hydraulic screw pump
42
in pedestal portion
88
. Screw pump
42
in this support module may be the same as the screw pump used in the clamping module
24
. The screw pump was illustrated in cross-section and described in connection with FIG.
3
. It is similarly illustrated in
FIG. 4
but the identical description will not be repeated. Base
84
also contains a hydraulic fluid channel
90
connecting screw pump
42
and hydraulic support
82
.
Hydraulic support unit
82
includes a rod
92
inserted within hydraulic cylinder
94
. Cylinder
94
is fixed in base pedestal
86
. Screwed into the upper end of rod
92
is a workpiece support surface body
96
. Support surface
96
is shown to be generally flat but may be shaped as desired for contact with a workpiece. In a suitable commercial support element like
82
the other end of rod
92
engages a compression spring (not shown) carried on the base of the support element. The lower end of cylinder
94
contains an opening (not shown) for hydraulic fluid which is admitted into cylinder
94
from screw pump
42
through channel
90
to lock the desired position of rod
92
. Rod
92
also preferably contains a V-groove
98
for engagement with an adapter used for placing modular support
80
at a predetermined x-y coordinate position on surface
16
of magnetic chuck
12
.
The height of support surface
96
is adjusted with the module
80
on the surface
16
of chuck
14
. Surface
96
and rod
92
is pushed down against such compression spring to a precise predetermined height. In general, the height of support surface
96
above chuck surface
16
can be controlled to a part of a millimeter. This adjustment may be made manually or with mechanical robotic assistance. Hydraulic fluid pressure is then applied by screw pump
42
in cylinder
94
to hydraulically lock the hydraulic support
82
in position.
FIG. 5
is a fragmentary view of the clamping mechanism for securing the locator elements
22
to the guide rail
20
. Each locator element
22
is fixed to a steel base
110
. A pair of clamp arms
112
on base
110
fix the locator element
22
to rail
20
. After the locator element
22
with its workpiece engaging tip
23
has been precisely positioned against rail
20
, clamp arms
112
are locked by screws
114
. As stated above locator tips
23
engages the workpiece in a locator hole such as the B-C holes formed in cylinder heads and like engine castings.
A principle feature of this workholding fixture system is to reconfigure a part holding fixture quickly and automatically at a suitable fixture setup station using the modular supporting, locating and clamping components described above in this specification. The fixture setup station may, for example, be organized like a state-of-the-art multi-axis machining center in which a numerically controlled robot (CNC) is programmed to select a cutting tool and perform a machining operation on a precisely fixtured workpiece. A state-of-the-art pick and place robotic station may be selected if its accuracy and repeatability lies within the tolerance requirements of the intended machining and fixturing applications. In any case, the special fixture setup station needs CNC servo drives to control its X-, Y-, and Z- motions accurately. For this fixture setup application, the programmable cutting tool storage magazine and the automatic cutting tool changer is redesigned into a fixture element storage magazine and a fixture element changer. The end of the machine spindle nose will have a special adapter so that a modular fixture element can be swiftly attached to or released from it. The adapter is configured, for example, to engage cover
71
with slots
73
on a screw pump
42
of a clamping element as shown in
FIG. 2
or to engage V-groove
98
on modular support element
80
(
FIG. 4
) or V-groove
116
, or the like on a locating element
22
as shown in FIG.
5
. Thus, the machine spindle nose selects and places the locating, supporting and clamping elements on a suitably positioned magnetic chuck
14
to configure a workpiece fixture
12
as seen in FIG.
1
.
In the first fixture setup station, the magnetic chuck is brought to the station table, hooked up to a power source, and energized at a reduced magnetization level (for a horizontal spindle machining center, the magnetic chuck will be located on the pallet). A modular fixture element (locating
22
in
FIG. 1
, clamping
24
, or supporting
26
) as dictated by the specific part fixture design is gripped by the fixture element changer from the storage magazine and attached to the spindle nose adapter. The XY drives of the fixture setup station will move simultaneously so that a precise X-Y coordinate position on the magnetic chuck
14
is aligned with the spindle nose adapter centerline, i.e., the centerline of the fixture element base plate. The fixture element is then brought very close to the surface
16
of the magnetic chuck
14
by the motion of the Z axis. Once the fixture element base plate (for example, clamp base plate
44
or support base plate
84
) is in solid contact with the magnetic chuck
14
, the fixture element is released by the spindle nose adapter. The fixture element automatically attaches itself gently to the X-Y coordinate location on the magnetic chuck surface
16
by the magnetic attractive force. The reduced pre-selected magnetization level is to ensure the fixture element will not be slamming violently onto the chuck. If a hydraulic work support cylinder element is to be used as a locating element, then a command is given to the machine to push in and lock up the support cylinder plunger at the desired height. The fixture setup program then initiates the next round of commands to setup the second fixture element, the third element, and so on. After all the modular fixture elements are set up accurately in their respective positions, the magnetic chuck
14
is energized so as to hold the modular elements (
24
,
26
,
80
) with the designed maximum holding power.
Then, the part
10
will be laid on the fixture
12
(
FIG. 1
) by an overhead gantry loader or other material handling equipment. The spindle nose adapter will pick up a wrench type of device (a nut-runner with a torque limiter) from the storage magazine and actuate the screw pumps
42
in the various supporting
80
and clamping elements
24
in a prescribed sequence. Finally, the magnetic chuck
14
together with its fixture elements and the clamped part is transferred to a designated machining station for processing.
It is a necessary and common practice to orient and fixture the part differently several times in a complex machining line so that various part surfaces and design features can be accessed for machining. Hence, it is envisioned that there will be similar number of fixture setup stations interspersed among the machining stations for the purpose of re-fixturing. When a part locked up by the modular fixture elements and its magnetic chuck is brought to one of these fixture setup stations, the part is unclamped and released from the fixture. It will then be located and clamped onto a different fixture and transferred down the production line. The previous fixture is recycled to its originating setup station upstream to be used again. It is estimated that the total time for unclamping, transferring, and clamping the part at the fixture setup station will be well within the typical cycle time for the machining line and so there will be no loss in the overall line throughput.
An alternative way of setting up the fixture is to use the machine tool for both machining and fixturing. Most of the modern CNC machine tools or machining centers are accurate enough to carry out precise fixturing. This practice would save capital investment in a dedicated setup station but the production tool would-lose a few productive cycles during changeover.
During the transition phase of a changeover to machine a new part design (in-family or cross-family), the magnetic chuck has to be demagnetized and the modular fixture elements need to be re-arranged to form new fixturing configurations at all the fixture setup stations. Depending on the cycle time of the machining line, there may or may not be a lower throughput of the line during the transition. For example, if the fixture rearrangement takes 5 to 6 minutes and the machining cycle time is longer than that, then the changeover for a new part design will be transparent to the production system.
It is to be understood that the function of the large magnetic chuck plate
14
could be incorporated into the support bases for the support or clamp elements. The large magnetic chuck could be replaced with a steel plate of suitable size and shape, for example, like that of the chuck
14
illustrated in FIG.
1
. Smaller versions of the chuck plate would then be adapted as, for example, base
44
for clamp
40
in
FIGS. 2 and 3
or base
84
for support
82
as depicted in FIG.
4
. The chuck plate bases would be adapted to carry, a hydraulic pressure supplying component like screw pump
42
shown in
FIGS. 2-4
and hydraulic fluid channels like channel
46
in FIG.
3
and channel
90
in FIG.
4
.
Thus, in this embodiment, the fixture system essentially consists of a large conventional, magnetizable steel fixture plate and a collection of modular fixture elements for locating, clamping, and supporting a workpiece. The modular elements are all mounted on magnetic holding bases of some common dimensions. These magnetic holding bases are smaller versions of the magnetic chuck plates described above. The magnetic holding base for the support or clamp elements can be an electro-permanent magnet construction so that it can be activated or de-activated with an electric switch. Alternatively, it can be a simple lift magnet design activated by a mechanical lever. The magnetic holding base will carry a support and/or clamp element and optionally a hydraulic, pressure supplying component. The role of the magnetic holding base is to provide a fast attach/release capability to the flat steel fixture plate and also a platform on which a modular fixture element can be affixed mechanically. In addition, the activated magnetic support or clamp base will maintain its magnetic attractive force when the base is disconnected from the electric source or as long as the mechanical lever stays in the same position. This portability provides the required mobility of the smart workholding fixture plate to be transferred from one machining station to another machining station.
While the invention has been described in terms of certain preferred embodiments it is apparent that other embodiments could readily be devised by one skilled in the art. The scope of the invention is to be considered limited only by the following claims.
Claims
- 1. A workpiece holding fixture comprising:a chuck plate of ferromagnetic material, said chuck plate having a flat surface, a guide rail fixed to said chuck plate and at least one workpiece locating post with a workpiece locating surface, said post being attached to said guide rail, at least one workpiece support member, said support member comprising a post with a workpiece engaging post surface, said post being carried upright on a base of ferromagnetic material, said base being adapted for magnetic attachment to said chuck plate surface at a predetermined location, and at least one workpiece clamp member comprising a clamp arm carried on an upright post that is carried on a base of ferromagnetic material, said clamp post base being adapted for magnetic attachment to said chuck plate surface at a predetermined location, and one of (i) said chuck plate and (ii) said clamp base and said support base being magnetizable and de-magnetizable on command, whereby each said support member and each said clamp member is located on said chuck plate surface so that a workpiece can be held by said clamp(s) against said post surface(s) in spaced relation to said chuck plate surface for work on said workpiece.
- 2. A The workpiece holding fixture as recited in claim 1 in which said workpiece locating surface of said locating post comprises a workpiece locating pin.
- 3. A workpiece holding fixture comprising:a chuck plate of ferromagnetic material, said chuck plate having a flat surface and being magnetizable and de-magnetizable on command, a guide rail fixed to said chuck plate and at least one workpiece locating post with a workpiece locating surface, said post being attached to said guide rail, at least one workpiece support member, said support member comprising a post with a workpiece engaging post surface, said post being carried upright on a base of ferromagnetic material, said base being adapted for magnetic attachment to said chuck plate surface at a predetermined location, and at least one workpiece clamp member comprising a clamp arm carried on an upright post that is carried on a base of ferromagnetic material, said clamp post base being adapted for magnetic attachment to said chuck plate surface at a predetermined location, whereby each said support member and each said clamp member is located on said chuck plate surface so that a workpiece can be held by said clamp(s) against said post surface(s) in spaced relation to said chuck plate surface for work on said workpiece.
- 4. The workpiece holding fixture as recited in claim 3 which said workpiece locating surface of said locating post comprises a workpiece locating pin.
- 5. The workpiece holding fixture as recited in claim 4 in which a workpiece support member is a modular hydraulic support member comprising a said base; a support post of adjustable height, said post comprising a rod slidable in a support member cylinder, said cylinder being fixed at one end to said base and adapted to receive hydraulic fluid for adjusting or maintaining the height of said support post; a pump for delivery of hydraulic fluid to and from said support member cylinder, said pump being carried by said base; and said base comprising a fluid channel for transport of said fluid between said pump and said support member cylinder.
- 6. A The workpiece holding fixture as recited in claim 4 in which a workpiece clamp member is a modular hydraulic clamp member comprising said base; a clamp arm, said clamp arm being carried on a rod slidable and rotatable in a clamp member cylinder, said cylinder being fixed at one end to said base and adapted to receive hydraulic fluid for rotating and adjusting the position of said rod; a pump for delivery of hydraulic fluid to and from said clamp member cylinder, said pump being carried by said base; and said base comprising a fluid channel for transport of said fluid between said pump and said clamp member cylinder.
- 7. The workpiece holding fixture as recited in claim 3 in which a workpiece support member is a modular hydraulic support member comprising a said base; a support post of adjustable height, said post comprising a rod slidable in a support member cylinder, said cylinder being fixed at one end to said base and adapted to receive hydraulic fluid for adjusting or maintaining the height of said support post; a pump for delivery of hydraulic fluid to and from said support member cylinder, said pump being carried by said base; and said base comprising a fluid channel for transport of said fluid between said pump and said support member cylinder.
- 8. The workpiece holding fixture as recited in claim 3 in which a workpiece clamp member is a modular hydraulic clamp member comprising said base; a clamp arm, said clamp arm being carried on a rod slidable and rotatable in a clamp member cylinder, said cylinder being fixed at one end to said base and adapted to receive hydraulic fluid for rotating and adjusting the position of said rod; a pump for delivery of hydraulic fluid to and from said clamp member cylinder, said pump being carried by said base; and said base comprising a fluid channel for transport of said fluid between said pump and said clamp member cylinder.
- 9. A workpiece holding fixture comprising;a selectively magnetizable and de-magnetizable chuck plate of ferromagnetic material, said chuck plate having a flat surface with x-y coordinates for the magnetic attachment of workpiece supporting, locating and clamping elements; a guide rail attached to said chuck plate and at least one workpiece locating post with a workpiece locating surface, said post being attached to said guide rail; at least one workpiece support member, said support member comprising a base of ferromagnetic material, said base being adapted for magnetic attachment to said chuck plate surface at a predetermined x-y coordinate location; and at least one workpiece clamping member, said clamping member comprising a base of ferromagnetic material, said base being adapted for magnetic attachment to said chuck plate surface at a predetermined x-y coordinate location, a hydraulic pump carried on said base, and a hydraulically actuatable clamping member carried on said base, said base comprising a hydraulic fluid channel between said pump and said clamping member.
- 10. The workpiece holding fixture as recited in claim 9 in which a workpiece support member comprises a said base, a hydraulic pump carried on said base, and a hydraulically actuatable support member carried on said base, said base comprising a hydraulic fluid channel between said pump and said support member.
- 11. The workpiece holding fixture as recited in claim 9 in which said workpiece locating surface of said locating post comprises a workpiece locating pin.
US Referenced Citations (7)