Note: Descriptions are shown in the official language in which they were submitted.
20~869~
AN APPARATUS FOR CLAMPING WORKPIECES WHICH HAVE
TO BE MACHINED BY A MACHINE TOOL
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention refers to an apparatus for clamping work-
pieces which have to be machined by a machine tool, the clamp-
ing apparatus compris;ng a rectangular frame means including
two longitudinal frame members and two transverse frame mem-
bers, and clamping means adapted to fix the workpieces to be
machined to the rectangular frame.
Further, the invention refers to a clamping bar adapted to be
used in an apparatus for clamping workpieces which have to be
machined by a machine tool.
Prior Art
If a workpiece is to be machined by means of a machine tool,
the workpiece has to be fixed or clamped in a suitable manner
to the worktable of the machine tool or within the working area
of the machine tool. It is well known in the prior art to pro-
vide the worktable of the machine tool with undercut grooves
which are adapted to receive displaceable clamping bolts. By
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means of such clamping bolts and additionally by means of hoop-
shaped fasteners a workpiece to be machined can be fixed to thc
worktable of the machine tool. Such a clamping method is cum-
bersome and time-consuming and often not suitable for small
workpieces.
Furthermore, a clamping apparatus is known which comprises a
frame provided with clamping members. Usually, according to a
well known embodiment, one side of the frame is in the form of
a stationary clamping jaw, and a further, displaceable jaw is
provided which is under the influence of one or several clamp-
ing screws, spindles or the like. Thus, the workpiece to be
clamped can be fixed between the stationary and the displace-
able jaw.
A main drawback of such a known clamping apparatus is that only
one single or several workpieces having exactly identical size
can be clamped. Another drawback is that such a clamping frame
comprising a fixed and a displaceable jaw, if it is to be used
for the clamping of big workpieces or a plurality of identical-
ly sized small workpieces, is either tooflexible since it resi-
liently deforms during clamping of the workpiece and workpie-
ces, respectively, or is extraordinarily bulky and heavy if it
is to be designed with the required rigidity.
,
In many applications, particularly if a workpiece has to be
machined by wire erosion, it is of paramount importance that
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the clamping frame be designed to be open such that the erosion
wire can pass through the clamping frame. This request renders
it even more difficult to design such a clamping frarne such
that it posses the required rigidity without being too bulky
and heavy.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a clamping appara-
tus for clamping workpieces which have to be machined by a ma-
chine tool which is light and manageable, but simultaneously
presents an extraordinary high resistance against resilient
deformation during the clamping of one or more workpieces.
It is a further object of the invention to provide a clamping
apparatus for clamping workpieces which have to be machined by
a machine tool by means of which, at will, either single big
workpieces can be reliably and accurately clamped, even if they
have irregular shape, or a plurality of small workpieces, even
if they have different size.
It is a still further object of the invention to provide a
clamping apparatus for clamping workpieces which have to be
machined by an electro erosive process using a wire as erosion
electrode by means of which, at will, either single big work-
pieces can be reliably and accurately clamped, even if they
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have irregular shape, or a plurality of small workpieces, even
if they have different size.
SUMMARY OF THE INVENTION
In order to meet these and other objects, according to a first
aspect, the invention provides an apparatus for clamping work-
pieces which have to be machined by a machine tool. The appara-
tus of the invention comprises, in a first general embodiment,
a rectangular frame including two longitudinal frame members
and two transverse frame members, and clamping means adapted to
fix the workpieces to be machined to said rectangular frame.
The clamping means comprise at least one auxiliary frame which
is removably inserted in said rectangular frame. Each of said
auxiliary frames includes two clamping bars which can be ad-
justably connected to each other. The ends thereof are adapted
to be connected to the longitudinal frame members of said rec-
tangular frame such that they are adjustable in the longitudi-
nal direction of said longitudinal frame members.
The clamping bars comprise a plurality of first bores running
essentially parallel to the longitudinal frame members when the
clamping bars are connected to the longitudinal frame members,
and said bores are adapted to selectively receive a clamping
screw.
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According to a second aspect of the invention, an apparatus for
clamping workpieces which have to be machined by a machine tool
is provided. In a second general embodiment, the apparatus com-
prises a rectangular frame including two longitudinal frame
members and two transverse frame members, and clamping means
adapted to fix said workpieces to be machined to the rectangu-
lar frame.
The clamping means comprise at least one auxiliary frame which
is removably inserted in the rectangular frame. Each of said
auxiliary frames includes two clamping bars which can be ad-
justably connected to each other. The ends thereof can be con-
nected to said longitudinal frame members of said rectangular
frame such that they are adjustable in the longitudinal direc-
tion of the longitudinal frame members.
The clamping bars comprise a plurality of continuous threaded
bores running essentially perpendicular to the clamping bars,
said bores being enlarged to a predetermined nominal diameter
and said bores being adapted to selectively receive a clamping
screw.
Such a design, either according to the first or the second as-
pect of the invention, provides for the clamping of workpieces
between two clamping bars which are roughly adjusted to the
desired distance, i.e. to the width or length of the workpiece
to be clamped. Thereafter, the clamping bars are provisionally
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fixed at their both ends to the two longitudinal frame mernbers
of the rectangular frame. The real clamping of the workpiece or
of the plurality of workpieces thereby is effected by means of
the auxiliary frame or frames in a place which is optimally
suited therefore such that the rectangular main frame is not
subjected to any clamping forces.
The invention further provides a clamping bar adapted to be
used in an apparatus according to the invention for clamping
workpieces which have to be machined by a machine tool, in
which said clamping bar comprises a plurality of continuous
threaded bores running essentially perpendicular to said clamp-
ing bar, said bores being enlarged to a predetermined nominal
diameter.
The continuous threaded bores are in a position to perform
three different functions:
1. In order to avoid a bending of the clamping bars, two ad-
jacent bores of two cooperating clamping bars located im-
mediately besides the workpiece to be clamped can be pro-
vided with a continuous threaded bolt which is loosely
inserted into the aligned bores and which is locked by
means of a threaded nut.
2. Some of the threaded bores can be provided with stud
screws to be clamped against the workpiece or workpieces
~ ~ 7 ~ 2~869~
received between the two clamping bars. In this way, it is
possible to clamp irregularly formed workpieces or work-
pieces with different dimensions.
3. Some of the threaded bores can be provided with cylindri-
cally shaped stop bars on which or against which the work-
piece or the workpieces rests and rest, respectively. This
measure is especially favourable if a plurality of identi-
cal workpieces has to be clamped in the clamping apparatus
of the invention in the same position one after the other
one.
Further embodiments of the apparatus of the invention are cha-
racterized in the claims 2 to 19.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, two preferred embodiments of the apparatus of
the invention will be further described, with reference to the
accompanying drawings, in which:
Fig. 1 shows a top view of a first embodiment of
the clamping apparatus of the invention with
several workpieces clamped therein;
Fig. 2 shows a lateral view of a clamping bar ac-
20~8~9~
cording to a first embodiment;
Fig. 3 shows a bottom view of the clamping bar oF
Fig. 2;
Fig. 4 shows a partial sectional view of the clamp-
ing bar of Fig. 2, seen along the line IV-IV
in Fig. 2;
Fig. 5 shows a top view of a second embodiment of
the clamping apparatus of the invention with
several workpieces clamped therein;
Fig. 6 shows a lateral view of a clamping bar ac-
cording to a second embodiment;
Fig. 7 shows a bottom view of the clamping bar of
Fig. 6; and
Fig. 8 shows a partial sectional view of the clamp-
ing bar of Fig. 6, seen along the line
VIII-VIII in Fig. 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the schematic view shown in Fig. 1, a rectangular
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frame is provided whicl- is generally designated with reference
numeral 1. The rectangular frame 1 is fastened to the (not
shown) work table of a machining tool by (not shown) Eixing
means. The rectangular frame 1 comprises two transverse frame
members 2 and 3 as well as two longitudinal frame members 4 and
5; the frame members 2 and 3 and the frame members 4 and 5 to-
gether form a rigid rectangular frame structure. The two longi-
tudinal frame members 4 and 5 are provided with threaded bores
6 equidistantly arranged in a row extending along the length of
the frame members 4 and 5; said threaded bores 6 run in a di-
rection perpendicular to the plane of the rectangular frame 1.
In the embodiment shown in Fig. 1, the rectangular frame 1 is
provided with four identical clamping bars 7, 8, 9 and 10. The
design of these clamping bars is shown in detail in Figs. 2 to
4 whereby, as an example, the clamping bar 7 is shown in a la-
teral view in Fig. 2, in a bottom view in Fig. 3 and in a par-
tial sectional view in Fig. 4.
The following description of the clamping bars particularly
refers to the clamping bar 7. However it is understood that the
following description also refers to the design of the clamping
bars 8, 9 and 10.
The clamping bar 7 is constituted by a longitudinal bar member
made of steel and having essentially rectangular cross section.
Both ends of the clamping bar 7 are provided with a flattened
2018695
extension ll having less height dimension than the clamping bar
itself. The length of the clamping bar 7 without the extensions
11 corresponds to the inner width of the rectangular frarne l,
measured between the inner faces of the longitudinal frame mem-
bers 4 and 5. The size of the extensions 11 is such that they
at least partially cover the top faces of the longitudinal fra-
me members 4 and 5 which are provided with the threaded bores
6. The clamping bar 7 being positioned in the rectangular frame
1, the extensions 11 rest on the top surfaces of the longitudi-
nal frame members 4 and 5.
The extensions 11 are provided with longitudinal slits 12
running transversely with respect to the clamping bar 7. The
design and position of said slits 12 is such that they lay over
the threaded bores 6 in the longitudinal frame members 4 and 5
when the clamping bar 7 is positioned in the rectangular frame
1. The length of the slits 12 is somewhat greater than the
distance between two adjacent threaded bores 6 such that each
clamping bar 7, 8, 9 or 10 can be inserted into and fixed to
the rectangular frame 1 at any voluntary position; thereby, the
clamping bars run parallely to the transverse frame members 2
and 3. As can be furthér seen from Fig. 1, screws 13 are pro-
vided which penetrate the slits 12 and which are screwed into
the threaded bores 6 in order to fix the clamping bars 7, 8, 9
and 10 in a desired position.
One of the longitudinal head faces of the clamping bar 7 is
ll- 201~69~
provided with a plurality of equidistantly positioned prismatic
recesses 14. Between said recesses 14 a small p~ain portion o~
the longitudinal head face of the clamping bar 7 is provided.
Furthermore, the clamping bar 7 comprises a plurality of bores
15 running parallel to the plane of the rectangular ~rame 1 and
extending transversely the the length of the clamping bar 7.
These bores 15 are located in said small plain portions of the
longitudinal head face of the clamping bar 7, between the
aforementioned prismatic recesses 14. Finally, additional bores
15a can be provided near to the two end portions of the clamp-
ing bar 7 and close to the extensions 11.
The design of the bores 15 and 15a, respectively, can be seen
from Fig. 4. Basically, the bores 15 and 15a are standard
threaded bores; however, these standard threaded bores are en-
larged to a predetermined nominal value n. Preferably, this
nominal value n has a size which is essentially the mean value
between the core bore diameter k and the nominal thread dia-
meter g. In the example shown in Fig. 4, the threaded bores 15
and 15a, respectively, are provided with a metric M-10-thread,
the nominal thread diameter thereof being lOmm. The core bore
diameter of a M-10-thread is approximately 8.2mm. Thus, the
nominal value to which the threaded bores 15 and 15a, respecti-
vely, are enlarged, amounts to approximately 9mm.
Such a design allows to use the threaded bores 15 and 15a, re-
spectively, for three different purposes:
20~8695
1. It is possible to screw M-10-screws or M-10-bolts into the
bores 15 and 15a, respectively, whereby these screws or
bolts are fixed against axial displacement.
2. It is possible to insert cylindrical bars having a dia-
meter of 9mm into the bores 15 and 15a, respectively,
which can be axially displaced, but which are received in
said bores reliably and essentially without axial clearan-
ce.
3. Screws or threaded bolts having a M-8-thread can be in-
serted into the bores 15 and 15a, respectively, without
being fixed against axial displacement.
Coming back to Fig. 1, the advantages of the aforementioned
design will be explained further. As a first example, six cy-
lindrical workpieces have to be clamped in the rectangular fra-
me 1 such that their axes extend perpendicularly to the plane
of the rectangular frame 1. For this purpose, the two clamping
bars 7 and 8 are used in an orientation as shown in Fig. 1. The
workpieces 16 align with the prismatic recesses 14 of the
clamping bar 7 and, thus, are equidistantly positioned. The
clamping bar 7 can be fixed to the rectangular frame 1 in any
desired position by means of the screws 13. Then, the second
clamping bar 8 is inserted into the rectangular frame 1, is
displaced until it rests on the workpieces 16 and is slightly
fixed to the longitudinal frame members 4 and 5 in such a man-
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2als6ss
ner that it can be further displaced in the direction of the
extension of the longitudinal frame members 4 and 5.
Now, all aligned pairs of threaded bores 15 of the two clamping
bars 7 and 8 are provided with threaded bolts 17 and secured
each with a nut 18. The nuts 18 are successively tightened in
turn with the result that the clamping bar 8 which is but loo-
sely fixed to the longitudinal frame members 4 and S is dis-
placed towards the clamping bar 7 so as to clamp the workpieces
16 between the prismatic recesses 14 of the clamping bar 7 and
the plain longitudinal head face of the clamping bar 8 directed
towards the clamping bar 7. As soon as the workpieces 16 are
securely clamped between the two clamping bars 7 and 8, the two
fixing screws 13 of the clamping bar 8 can also be tightened.
Dùe to the fact that a threaded bolt 17 is provided directly
besides each of the workpieces 16, any elastic deformation of
the clamping bars 7 and 8 is avoided during the clamping there-
of and all workpieces 16 are reliably clamped in the desired
position.
As a second example, a hexaedral workpiece 19 shall be posi-
tioned and clamped between the two clamping bars 9 and 10. One
surface 20 of the hexaedral workpiece 19 is not plain and has
an undefined shape. For this purpose, the clamping bar 9 is
inserted into the rectangular frame 1 in a suitable position
and fixed to the two longitudinal frame members 4 and 5 by
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means of the screws 13. Thereafter, the second clamping bar lO
is loosely inserted into the rectangular frame l with a certain
distance to the clamping bar 9, such distance being somewhat
more than the greatest size of the workpiece 19 in transverse
direction. Now, two stop bars 2l having a diameter of 9mm are
inserted into two aligned bore pairs 15 of the clamping bars 9
and lO in a certain distance from each other which is less than
the length of the workpiece l9; in this way, each of the two
stop bars 21 projects into the space between the two clamping
bars 9 and 10.
In a next step, the workpiece l9 is put on the two stop bars 21
and between the two clamping bars 9 and lO; thereby, the height
position and the parallel orientation with reference to the
plane of the rectangular frame is fixed. Thereafter, the clamp-
ing bar 10 is displaced towards the surface 20 of the workpiece
19 such that a small clearance between said surface 20 and the
facing surface of the clamping bar lO is maintained. Now, the
clamping bar 10 is loosely fixed to the two longitudinal frame
members 4 and 5 of the rectangular frame 1 by means of two
screws 13. As a next step, two M-8-threaded bolts 17 are in-
serted into those pairs of bores lS and 15a, respectively,
which are next to the ends of the workpiece l9, and each
threaded bolt 17 is provided with a nut 18 which is tightened
by hand such that it just rests on the lateral surface of the
clamping bar 9.
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2018fi95
In the region of the workpiece 19 three bores 15 are left un-
occupied. In these three left bores 15 of the clamping bar 10
M-10-stud screws 22 are screwed to such an extent that their
free surface rests against the irregular surface 20 o~ the
workpiece 19. In this way the workpiece 19 is securely clamped
between the stud screws 22 and clamping bar 9. Finally, the
fastening screws 13 of the clamping bar 10 can be tightened as
well.
Also in this case there is the advantage that the threaded
bolts 17 are positioned very close to the ends of the workpiece
l9 such that an eventually occuring elastic defor~ation of the
clamping bar 9 and lO during the clamping operations will be
well within very low limits.
A second embodiment of the apparatus of the invention is shown
in Fig. 5. The rectangular frame of the clamping apparatus is
generally designated with reference numeral 101. Again, the
rectangular frame lO1 is fixed to the (not shown) worktable of
a machining tool by means of suitable fixing elements (not
shown). The rectangular frame lOl comprises two transverse
frame members 102 and 103 as well as two longitudinal frame
members 104 and 105 which together form a rigid rectangular
frame structure. The two longitudinal frame members 104 and 105
are provided with threaded bores 106 equidistantly arranged in
a row along the longitudinal extension of the frame members 104
and 105 and running perpendicularly to the plane of the rectan-
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201869~
gular frame 101.
According to the embodiment shown in Fig. 5, the rectangular
frame 101 is equipped with two identically designed clamping
bars 107 and 108. The particular design of these two clamping
bars 107 and 108 is shown in detail in Figs. 6 to 8, whereby,
as an example, the clamping bar 107 is shown in a lateral view
in Fig. 6, in a bottom view in Fig. 7 and in a sectional view
in Fig. 8. The clamping bar 107 is constituted by a longitudi-
nal bar member made of steel and having essentially rectangular
cross section. Both ends of the clamping bar 107 are provided
with a flattened extension 111 having less height dimension
than the clamping bar itself. The length of the clamping bar
107 without the extensions 111 corresponds to the inner width
of the rectangular frame 101, measured between the inner faces
of the longitudinal frame members 104 and 105. The size of the
extensions 111 is such that they at least partially cover the
top faces of the longitudinal frame members 104 and 105 which
are provided with the threaded bores 106. The clamping bar 107
being positioned in the rectangular frame 101, the extensions
211 rest on the top surfaces of the longitudinal frame members
104 and 105.
Extensions 111 are provided with longitudinal slits 112 running
transversely with respect to the clamping bar 107. The design
and position of said slits 112 is such that they lay over the
threaded bores 106 in the longitudinal frame members 104 and
... . .. .
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20~869~
105 whell the clamping bar 107 is positioned in the rectangular
frame 101. The length oE the slits 112 is somewhat greater than
the distance between two adjacent threaded bores 106 such that
each clamping bar 107 and 108 can be inserted into and fixed to
the rectangular frame 101 at any voluntary position; thereby,
the clamping bars run parallely to the transverse frame members
102 and 103. As can be further seen from Fig. 5, screws 113 are
provided which penetrate the slits 112 and which are screwed
into the threaded bores 106 in order to fix the clamping bars
107 and 108 in a desired position.
The clamping bar 107 is provided with a plurality of bores 115
running in the plane of the rectangular frame 101 and extending
transversely to the longitudinal extension of the clamping bar
107. These bores 115 are located in the narrow plain portion of
the longitudinal surface of the clamping bar 107 and are equi-
distantly arranged. In addition, further bores 123 are provided
which run transversely to the bores 115 in a plane perpendicu-
lar to the plane of the rectangular frame 101; the bores 123
are located between two adjacent bores 115. The bores 123, the
exact design thereof being evident from Fig. 8, comprise a nor-
mal thread and serve to receive (not shown) clamping means.
Finally, the clamping bar 107 is provided with support protru-
sions running along to adjacent edges of the clamping bar 107
which extend parallel to the plane of the rectangular frame 101.
As far as the bores 115 are concerned, the same is true as ex-
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2018695
plained in connection w;tll the bores lS in the clamping bar 7;
reference is made to the explanations in connection with Fig. 4
which analogously apply to the design of the bores 115.
Coming back to the embodiment ShOWTI in Pig. 5, in the ~ollow-
ing, the advantage of this embodiment will be described. As an
example, four hexaedral workpieces 116 shall be fixed to and
clamped in the rectangular frame 101. For this purpose, the
clamping bar 107 is inserted into the rectangular frame 101 in
a suitable position and fixed to the two longitudinal frame
members 104 and lQ5 by means of the two fixing screws 113.
Thereafter, a second clamping bar 108 is loosely inserted into
the rectangular frame 101 in a certain distance to the clamping
bar 107; the distance between the clamping bars 107 and 108
approximately corresponds to the relevant size of the work-
pieces 116. Now, stop bars 121 having a diameter of 9mm are
inserted in suitably located bores 115 of the clamping bar 107
to such an extent that they protrude somewhat into the space
between the clamping bars 107 and 108.
As a next step, the workpieces 116 can be inserted into the
rectangular frame 101 between the two clamping bars 107 and 108
and between the stop bars 121; thereby the workpieces 116 rest
on the support protrusions with the result that the height po-
sition and the mutual distance between the workpieces is fixed.
Thereafter, the clamping bar 108 is displaced towards the work-
pieces 116 until there is a small clearance between the front
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face of the workpiece 116 and the opposite front ~ace of the
clamping bar 108. The clamping bar 108 now can be loosely fixed
to the longitudinal frame members 104 and 105 of the rectangu-
lar frame 101 by means of the two fixing screws 113.
Thereafter, the pairs of bores 115 in the clamping bars 107 and
108 which are next to the lateral surfaces of the workpieces
116 are equipped each with a threaded bolt 117 of M-8-size, and
on each bolt 117 a nut 118 is screwed on and tightened by hand
to such an extent that it just rests again the lateral face of
the clamping bar 108. Now, four suitably located bores 115 of
the clamping bar 108, i.e. bores llS which open to the front
faces of the workpieces 116, are equipped with M-10-stud screws
122 which are tightened such that each workpiece 116 is clamped
between the stud screws 122 and the clamping bar 107. Finally,
also the fixing screws 113 of the clamping bar 108 can be
tightened.
Also with this embodiment, the advantage can be observed that
the threaded screw bolts 117 can be placed very close to the
side faces of the workpieces 116 with the result that an even-
tually occurring elastic deformation of the clamping bars 107
and 108 is within very low limits.
It is understood that, in a corresponding manner, a plurality
of small workpieces can be clamped one next to the other one
which have different width. The difference in width may easily
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be compensated by screwlng the stud screws 122 more or less
into the corresponding threaded bore 115.
The rectangular frame 1 and 101, respectively, o~ the inven-
tion, finally equipped with the workpieces to be machined, is
extraordinarily rigid and has comparatively low weight, due to
the fact that the clamping means (threaded screw bolts 17 and
117, respectively; stud screws 22 and 122, respectively) can
always be located directly besides or very close to the work-
pieces to be clamped. The result is that the clamping bars can
be designed relatively narrow and, therefore, light in weight.
The same is true for the transverse and longitudinal frame mem-
bers of the rectangular frame 1 and 101, respectively, since
they are not loaded with clamping forces at all, but only have
the function to hold the clamping bars 7 to 10 and 107, 108,
respectively, and thereby the workpieces 16, 19, 116, in the
desired position. With other words, the real clamping function
is fulfilled by an auxiliary frame, constituted by, e.g., a
pair of clamping bars and two or more threaded screw bolts,
said auxiliary frame being fixed by the screws 13 and 113, re-
spectively, to the main frame.
The clamping apparatus of the invention is very versatile for
the clamping of small or big workpieces, of a single workpiece
or of several workpieces, of a plurality of different workpie-
ces with irregular shape etc., because only a few basic ele-
ments (clamping bars, threaded screw bolts, stud screws, stop
bars) are to be used.
