FIELD OF THE INVENTION
[0001] This invention relates to an improved workpiece positioning assembly and to a punch
press incorporating such an assembly.
, BACKGROUND OF THE INVENTION
[0002] Existing punch presses usually include a frame having an upper and lower limb defining
a throat therebetween. The punch assembly for punching a hole in a sheet of metal
is carried by the upper limb and an aligned die assembly is carried by the lower limb.
In order to move a sheet of metal relative to the punch assembly so that more than
one hole may be punched without lifting the sheet from the press the sheet of metal
is clamped to a movable traverse in the form of a beam which extends at right angles
to the axis of the throat of the press. The beam is movable in the axial direction
of the throat and is supported at each of its ends by a bearing bar which extends
parallel to the axis of the throat. Such an arrangement allows movement in the one
direction; movement in a right-angled direction being provided by a movable carriage
supported on horizontally or vertically spaced bearing bars and to which the sheet
is clamped: for example such an arrangement is disclosed in British Patent Specifications
1096284, and 1378487.
[0003] As an improvement over the disclosures in 1096284 and 1378487 there is disclosed
in our prior British Patent No. 1563921 a workpiece positioning assembly for a machine
tool comprising a first traverse, a second elongate traverse unsupported at its ends
and mounted intermediate its ends upon the first traverse for horizontal movement
in a direction perpendicular to the axis of the second traverse, each traverse including
two parallel vertically spaced tracks, and a workpiece support movable in a direction
parallel to the axis of the second traverse. Whilst this arrangement enabled the punch
press to be much more compact since no lateral horizontal support was required at
the ends of the beam and the beam required a minimum throat depth we have now found
that, although the vertically-spaced tracks of the first traverse made the punch press
more compact, the second traverse had to have a large bearing area in order to counter
any unbalance created by mounting the first traverse one side of the lower limb only.
[0004] Therefore, since the development of the arrangement disclosed in our British Patent
No. 1563921 we have been concentrating on trying to devise an arrangement which will
be both compact and reduce the size of the second traverse.
[0005] In the past it has always been accepted that, in order to achieve the required stability
for support and movement of a workpiece carriage along the X axis and to prevent twisting
two parallel spaced tracks are required. In some instances this has meant two separate
horizontally spaced rails, e.g.: as in British Patent 1378487, where space at the
back of the throat has been sacrificed so that the point of support can be positioned
down low in line with the sheet. In other cases, such as in British Patent 1096284
and in U.S. Patent No. 3058380,the tracks have been positioned vertically to save
space at the back of the throat, but this arrangement necessarily means that some
form of bearing has to be provided below the lower track. In Figure 3 of 3058380 for
example it will,be seen that the vertically-spaced tracks are provided by rollers
on V-shaped members cooperating with the opposed faces of a dove-tail strip carriage.
However, although the workpiece sheet has been positioned in line with the strip carriage,
it will be seen that the sheet has to be positioned some distance above the lower
limb of the frame in order to accommodate transverse movement of the lower rollers.
[0006] Thus prior arrangements for the X-axis have been a compromise between saving space
at the rear of the throat and positioning the point of support down low in line with
the sheet and as close to the lower limb as possible. Also, in punch presses incorporating
turrets, such as in our British Patent No. 1420594, it has always been the practice
for the lower turret forming a die holder for the dies to be formed with a plurality
of holes of different size which receive the dies. This arrangement means that the
turret is not able to accept different types of die.
SUMMARY OF THE PRESENT INVENTION
[0007] Surprisingly, we have now found that by providing a bearing which is capable of accepting
a greater load and which resists rotational load about the axis, there is no longer
a need for two rails on the X-axis. Consequently, the X-axis traverse can be made
compact and. lightweight with the advantages of both the vertically and horizontally
spaced arrangement of the prior art.
[0008] Moreover in a preferred arrangement we may include a lower turret which is more versatile
in its acceptance of dies of different types.
[0009] Therefore, according to the present invention a workpiece positioning assembly for
a machine tool comprises a first traverse, a second traverse mounted upon the first
traverse for horizontal movement in a direction perpendicular to the axis of the second
traverse, and a workpiece support movable in a direction perpendicular to the axis
of the first traverse, the second traverse comprising a single rail.
[0010] Preferably, in order to reduce the load on the single rail the second traverse is
mounted on a first traverse consisting of two horizontally spaced tracks symmetrically
disposed with relation to the centre point of the second traverse thereby balancing
the second traverse on the first traverse.
[0011] Suitably, the single track constituting the second traverse may be a bearing capable
of accepting load from all directions for example a bearing as disclosed in U.S. patent
specification 3,897,982.
[0012] The invention also includes a punch press comprising a frame having an upper member
and a lower member defining a throat therebetween, a first traverse on the frame and
extending in a direction parallel to the throat, a second traverse mounted upon the
first traverse for horizontal movement in a direction perpendicular to the axis of
the second traverse, and a workpiece support movable along the second traverse, the
second traverse comprising a single rail.
[0013] Preferably the punch press is a turret punch press having an upper turret for punches
and a lower turret for dies, the lower turret having its circumference rebated to
provide a plurality of datum surfaces against which a die assembly may be received.
[0014] The lower turret suitably has a scalloped configuration so as to receive a die assembly
against an arcuate datum surface.
[0015] The die assembly may comprise a die holder, means for releasably securing the die
holder on the lower turret, and a die releasably received within the die holder.
[0016] Preferably the means for releasably securing the die holder on a punch press comprises
a groove on the die holder which is cooperable with an angularly movable, eccentric
locking head of a retainer on the turret.
[0017] The die holder may include an 0-ring for engaging the die and retaining it by a friction
fit.
[0018] Suitably the die holder has two protruding location pins set at 90° to one another
and four equally-spaced location slots offset by 45° from said pins, and the die has
one location pin for cooperation with the location slots in the holder, adjustment
of the location pins enabling the die to be set angularly at intervals of 45°.
[0019] Preferably the movement of the second traverse and the workpiece support is numerically
controlled the movement being transmitted by means of orthogonally arranged driven
lead-screws. However, if desired, rack and pinion drive may be used as an alternative.
[0020] The arrangement of the present invention enables the rail supporting the workpiece
carriage to be positioned down low in line with the sheet that is being moved and
just above the lower limb.
[0021] In our British Patent No. 1563921 the construction of the beam forming the second
traverse was a closed box section for strength. However, we have now found that a
beam of U-shaped cross-section open to the top and having 45° angular cross-ties is
lighter in weight and more suitable. Such a beam structure makes assembly much easier,
and resists angular movement about a vertical axis.
[0022] According to another aspect of the invention there is provided a punch press comprising
a C-shaped frame having an upper limb and a lower limb defining a throat therebetween,
a first traverse on the frame and extending in a direction parallel to the throat,
said first traverse including two parallel spaced rails one secured to each side of
the lower limb of the frame, said rails extending forwardly and rearwardly from the
back of the throat to enable a maximum throat depth to be employed during punching,
a second elongate traverse including a single bearing rail and supported on the first
traverse intermediate the ends of the second elongate traverse for movement in a direction
perpendicular to the axis of the second traverse, support means extending rearwardly
of the second elongate traverse so as to engage with the rearwardly extending portions
of the rails of the first traverse to enable the second elongate traverse to be withdrawn
to the back of the throat, a workpiece support mounted on the single rail of the second'
elongate traverse, a first driven means in driving connection with the second traverse
for moving the second traverse along the two horizontally-spaced rails of the first
traverse in a direction perpendicular to the axis of the second traverse, and a second
driven means in driving connection with the workpiece support for moving the workpiece
support along the second traverse.
[0023] Preferably the first driven means is a leadscrew positioned alongside one of the
two rails of the first traverse. The second driven means may be a leadscrew suitably
positioned above the single track of the second traverse.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The invention will now be described by way of example with reference to the accompanying
drawings in which:
Figure 1 is a side elevation of a punch press having a C-shaped frame;
Figure 2 is a plan view of the lower limb of the punch press shown in Figure 1 with
the lower turret shown diagrammatically and partially broken away;
Figure 3 is a section through the second traverse (X-axis);
Figure 4 is a section through that half of the first traverse shown to the left in
Figure 2;
Figure 5 is a side elevation of a preferred die assembly,
Figure 6 is a plan view of a preferred lower turret; and
Figure 7 is a section on A-A of figure 6.
[0025] In Figures 1 to 4 of the drawings a workpiece positioning assembly is shown in position
on a punch press frame 1 of C-shape, having upper and lower limbs 2 and 3 defining
a throat 4. The workpiece positioning assembly comprises a first traverse 5 forming
the Y-axis fixed to the frame 1 and a second traverse 6 forming the X-axis supported
for movement along the'Y-axis traverse 5.
[0026] The Y-axis traverse 5 (see Figures 2 and 4 particularly) comprises two horizontally-spaced
rails 7, one secured to each side of the lower limb 3 of the punch press frame 1.
Extending parallel to the rails 7, and secured on one side only of the lower limb,
is a leadscrew 8 driven, via a belt connection 9, by a DC servo motor 10. The rails
7 are not secured directly to the frame 1 but, as shown, are disposed on an intermediate
mounting member 11 and these extend forwardly and rearwardly from the back of the
throat 4 as clearly seen from Figure 1.
[0027] The X-axis traverse 6 comprises an elongate beam 12 of U-shaped cross-section and
having a lattice of cross-ties 13 for strength. Secured along the lower front edge
of the beam 12 (see Figure 3), as low as possible, is a single bearing rail 14 for
supporting a workpiece carriage 15. The workpiece carriage 15 includes two workpiece
clamps (not shown) and is movable along the second traverse by means of a driving
connection with a driven leadscrew 16.
[0028] As seen from Figure 2 the driven leadscrew 16 is also driven by a DC servo motor
17 via a belt connection 18. The belt connections 9 and 18 enable the respective motors
10 and 17 to be positioned alongside the respective leadscrews rather than at one
end thereby producing a more compact arrangement.
[0029] Extending rearwardly from the main beam 12 of the X-axis traverse are two support
extensions 19 which engage with the rearward extensions of rails 7 and enable the
traverse to be withdrawn right to the back of the throat whilst maintaining rigidity.
[0030] As explained above the single bearing rail 14 is arranged to take load in all directions
and preferably is a bearing as disclosed in the above-mentioned U.S. Patent Specification.
Also, in view of the superior stiffness and load capacity of these bearings, it is
preferable that the bearing rails 7 are also of this type.
[0031] Referring once again to Figure 1 it will be seen that the free end of the upper limb
2 supports a hydraulic ram assembly 20 and an upper turret 2i. Around its peripheral
edge the turret 21 is provided with roller chain drive 22 for rotating the turret
into a desired angular position to bring a desired punch below the operative position
of the hydraulic ram assembly 20. The workpiece may be locked in position for clamp
repositioning by means of retractable clampingmechanism 23.
[0032] Disposed below the upper turret 21, on the lower limb 3, is the lower turret 24 shown
in detail in Figures 6 and 7. The lower turret 24 also has a roller chain drive 25
around its periphery and the two chains are driven by a single drive motor-(not shown)
so that the movement of the two turrets are synchronised. The lower limb 3 also carries
at the front of the machine a datum arm 26 including a datum plunger 27 for ensuring
accurate positioning. Table surfaces 28 with protruding ball bearings 29 are also
shown for support of a workpiece during punching.
[0033] The construction of the preferred die assembly is show in Figure 5. The assembly
30 comprises a die holder 31 having two laterally projecting location pins 32 set
at 90° (only one shown) and a locking groove 33. The holder 31 receives a die 34 having
a location pin 35 locating in one of four location slots 36 and retained in position
by frictional engagement with an 0-ring 37 in the die holder 31. The location pins
32 are offset from the location slots 36 by 45° so that adjustment at 45° intervals
is possible with only four slots.
[0034] In order to prevent upward lifting of the die holder 31 a retainer 38 is provided
which has an eccentric locking head 39 for engagement with locking groove 33. The
die holder 31 is designed to be received in the scalloped lower turret 24 (see Figure
6), the die holder being located by one of pins 32 being positioned in a slot 40 in
the turret station datum face 41. In use the slot 40 is closed vertically by means
of a permanently set grub screw (not shown). The retainer 38 is loosely received in
an aperture 42 in the turret and has a vertical slot (not shown) joining peripheral
groove 43. The vertical slot and groove 43 cooperate with a locking screw 44 in the
aperture 42 to allow removal of the retainer only when the locking head is released
i.e. angular movement of the retainer 38 to release the locking head 39 from the groove
33 enables the locking screw for the retainer 38 to be aligned with the vertical slot.
_
[0035] As seen from figures 6 and 7 the lower turret, in addition, includes holes 45 for
pinched slugs to drop through and holes 46 for pin locators (not shown) to accurately
orientate the turret - equivalent pin locators being provided on the upper turret
also. The locking screws 44 pass through holes 47.
[0036] Although the invention has been particularly described with reference to a punch
press (single hole or multiple hole) it will be understood that it may be used with
other machine tools.
1. A workpiece positioning assembly for a machine tool comprising a first traverse
(5), a second traverse (6) mounted upon the first traverse for horizontal movement
in a direction perpendicular to the axis of the second traverse, and a workpiece support
(15) movable in a direction perpendicular to the axis of the first traverse, characterised
in that the second traverse comprises a single rail (14).
2. A workpiece positioning assembly according to Claim 1 characterised in that the
first traverse (5) comprises two horizontally spaced tracks (7) symetrically disposed
with relation to the centre point of the second traverse.
3. A punch press comprising a frame (1) having an upper member (2) and a lower member
(3) defining a throat (4) therebetween, a first traverse (5) on the frame and extending
in a direction parallel to the throat, a second traverse (6) mounted upon the first
traverse for horizontal movement in a direction perpendicular to the axis of the second
traverse, and a workpiece support (15) movable along the second traverse, characterised
in that the second traverse comprises a single rail (14).
4. A punch press according to Claim 3 including an upper turret (21) for punches and
a lower turret (24) for dies, characterised in that the lower turret has its circumference
rebated to provide a plurality of datum surfaces (41) against which a die assembly
(30) may be received.
5. A punch press according to Claim 4 characterised in that the circumference of the
lower turret (24) has a scalloped configuration so as to receive a die assembly against
an arcuate datum surface.
6. A punch press according to Claim 4 or 5 characterised in that the die assembly
(30) comprises a die holder (31), means (33, 38) for releasably securing the die holder
on the lower turret, and a die (34) releasably received within the die holder.
7. A punch press according to Claim 6 characterised in that the means for releasably
securing the die holder on the lower turret comprises a groove (33) on the die holder
which is cooperable with an angularly movable, eccentric locking. head (39) of a retainer
(38) on the turret.
8. A punch press according to Claim 6 or 7 wherein the die holder (31) is circular
has two protruding location pins (32) set at 900 to one another for cooperation with a datum face of the lower turret, and four equally-spaced
location slots (36) offset by 45° from said pins, and the die (34) has one location
pin (35) for cooperation with the location slots in the holder, adjustment of the
location pins enabling the die to be set angularly at intervals of 450.
9. A punch press comprising a C-shaped frame (1) having an upper limb (2) and a lower
limb (3) defining a throat (4) therebetween, a first traverse (5) on the frame and
extending in a direction parallel to the throat, said first traverse (5) including
two parallel spaced rails (7) one secured to each side of the lower limb of the frame,
and a second traverse (6) supported on the first traverse intermediate the ends of
the second traverse for movement in a direction perpendicular to the axis of the second
traverse, a workpiece support (15) mounted on the second traverse, and drive means
for effecting two dimensional coplanar movement of the workpiece support, characterised
in that the rails (7) of the first traverse extend forwardly and rearwardly from the
back of the throat to enable maximum throat depth to be used during punching, the
second traverse includes a singel rail (14), and the second traverse includes support
means (19) extending rearwardly therefrom so as to engage with the rearwardly extending
portions of the rails of the first traverse to enable the second elongate traverse
to be withdrawn to the back of the throat.
10. A punch press according to Claim 9 wherein the structural frame of the second
traverse is U-shaped in cross-section open to the top and has 45° angular cross-ties.