Lapping and polishing fixture having flexible sides

Details Lapping and polishing fixture having flexible sides Lapping and polishing fixture having flexible sides

1999-12-10

2002-09-03

Hughes, S. Thomas (Department: 3726)

Metal working

Method of mechanical manufacture

Shaping one-piece blank by removing material

C029S559000, C451S286000

Reexamination Certificate

active

06442825

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to fixtures for holding workpieces during lapping and polishing operations and more specifically to an improved fixture which accommodates different sized workpieces.
2. Description of the Related Art
Ceramic substrates routinely go through a process of lapping and/or polishing, after they have been fired, to achieve desired flatness, roughness and thickness specifications. These processes involve the fixturing of the substrate in a dressing wheel or polishing head which is then turned on a spinning table upon which abrasive slurries are applied.
FIG. 1
illustrates a conventional double-sided lapping machine. Motor
1
turns gearbox
2
to drive an upper dressing/working wheel
3
. Similarly, motor
8
turns gear box
9
to drive a lower dressing/working wheel
7
, via a belt
10
. A workpiece to be lapped (not illustrated) is placed in a fixture (not illustrated), between two working wheels
3
and
7
. Motor
4
and belt
6
turn gear box
5
to drive a workpiece drive
11
.
A large wheel
20
(shown in FIG.
2
), typically made of spring-steel that contains round openings
21
, is mounted on the workpiece drive
11
. The workpiece drive
11
turns the large wheel
20
. Plastic fixtures
22
(e.g., disks) are inserted into these round openings
21
. It is these fixtures
22
that are the subject of this invention.
FIG. 3
shows a conventional fixture
30
that holds two ceramic substrates
40
(
FIG. 4
) for lapping or polishing in separate openings
31
. The fixture
30
holds the substrate
40
in place and must be fabricated to fit the individual substrates
40
. The fixture
30
can be made of any machinable material, such as polyvinyl chloride (PVC), plastic or metal.
The fixture
30
must be thinner than the workpiece or substrate
40
and thin enough to allow for sufficient removal of material from the workpiece
40
. Openings
31
are typically fabricated to a tolerance of −0.000″/+0.005″ of the overall length
41
and width
42
of the workpiece
40
to be lapped or polished. This tolerance is required to minimize the amount of movement within the opening
31
. Too much movement results in chipping of the workpiece edges during lapping and polishing.
If the opening
31
in the fixture
30
is too small, the substrate
40
will not fit inside the fixture
30
. If the opening
31
in the fixture
30
is too big, the substrate
40
will move around too much and will result in “chipping” on the substrate.
This invention solves the problem that occurs when the length
41
and width
42
of the substrate
40
varies more than the tolerance of the fixtures
30
. This usually occurs when the workpiece
40
is to be lapped and/or polished after sintering. In other words, the length
41
and/or the width
42
of the workpiece
40
commonly varies by more than 0.005″.
Conventional solutions to this problem include a sizing operation between sintering and lapping or polishing. In this manner, all parts (e.g., substrates
40
) would be accurately cut to fit the opening
31
. However, this is an expensive solution. Another conventional solution is making multiple sized openings
31
and “best fitting” the parts
40
to the openings
31
. However, this process is time consuming and difficult.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a structure and method for the fabrication of curved flexures built into the fixture that maintain contact with the workpiece at all times. Any movement within the fixture will be dampened by the flexure.
The flexures can be adjusted for different dampening strengths. The flexures can also provide a single contact point with the workpiece sides or multiple contact points. The flexures can be fabricated using typical machining or punching methods.
More specifically, the invention includes a fixture for holding a workpiece in a polishing/lapping apparatus. The fixture comprises at least one opening having at least one curved flexible side for elastically holding the workpiece and a slot adjacent each curved flexible side for allowing the side to flex.
The slot has a length approximately equal to that of the side and a shape approximately equal to that of the side. An amount of travel of the side is controlled by a width of the slot.
The invention also includes a web positioned between the side and the slot, wherein a tension of the side against the workpiece is controlled by a width of the web.
The side is curved toward a center of the opening such that the workpiece contacts the side only at a distinct point. The side can also be a multiple-curve side having at least two curves, such that one distinct point on each curve of the at least two curves touches a same side of the workpiece. The opening can be a four-sided opening having a first number of the curved flexible sides and a remaining number of straight sides. The fixture can comprise one of a plastic, polyvinyl chloride, metal or other suitable material.
The invention similarly includes an apparatus for machining a workpiece, the apparatus comprising a motor, a wheel turned by the motor, a fixture attached to the wheel and for holding a workpiece in the machining apparatus. The fixture comprises at least one opening having at least one curved flexible side for elastically holding the workpiece.
The invention also includes a method for producing a fixture for holding a workpiece in a machining apparatus, comprising steps of supplying a disk of material, forming at least one opening in the disk of material having at least one curved flexible side for elastically holding the workpiece. The invention similarly includes a method of machining a workpiece comprising forming a fixture for holding the workpiece in a machining apparatus, forming at least one opening in the fixture having at least one curved flexible side for elastically holding the workpiece, mounting the workpiece in the opening, elastically holding the workpiece, using the curved flexible side, in the opening and machining the workpiece while being held by the fixture.


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