GB2387560A

GB2387560A - Machine tool

Info

Publication number: GB2387560A
Application number: GB0207915A
Authority: GB
Inventors: Steve Sale
Original assignee: Mmic Eod Ltd
Current assignee: Mmic Eod Ltd
Priority date: 2002-04-05
Filing date: 2002-04-05
Publication date: 2003-10-22
Also published as: GB0207915D0

Abstract

The drilling machine 1 has a chassis 2 of aluminium plate, with two side plates 3, a top plate 4 and a bottom plate 5. Two evacuatable feet 6,7 are connected to the chassis by respective lower links 8 pivoted to the side plates 3 close to the bottom plate 5 and by upper links 10 lockable at slots 11 in the side plates 3 at their mid-height by hand-wheels 12. The feet each have three aluminium sandwich plates, 14,15,16, with a membrane 17 captivated between upper and lower individual sandwich plates. The lower plates are less extensive at their peripheries, allowing a margin of the membrane to have an peripheral seal 18 of foam elastomer material to be secured to the membrane, with the upper sandwich plates extending over the seal. The sandwich plates are secured to each other by bolts 19. Strips 20,21 of membrane exposed between the sandwiches 14,15,16 allow feet to adapt to a cylindrical contour. Extending between the bottom plate 5 and brackets 22 inside the side plates 3 are carriage bars 23 for journals 24 carrying a drill mounting plate 25. The position of this longitudinally along the bars is under control of two pneumatic actuators 26. The mounting plate carries an air motor 29 having a chuck 30, in the form of a stud 31 having a drive lug 32. A drill bit has a hollow shank 41 having a front portion 42, tapering down 43 to a reduced diameter 44 with a thread 45 along most of its tail. The bore 46 of the shank matches the diameter of the stud 31 and has a bayonet slot 46 for driving connection with the lug 32. The front of the portion 42 carries cutting teeth 47. Mounted on the reduced diameter portion 44 is a sealing sleeve 48. This is a plain sleeve of nylon, with a hexagonal head 49 at its end nearest to the chuck, when mounted. The diameters of the front portion and the outside of the sleeve 48 are the same, as is the across-the-flats dimension of the head 49.

Description

MACHINE TOOL

The present invention relates to a machine tool particularly, though not exclusively, for machining apertures in closed vessels.

Machining apertures in a vessel or a pipeline, hereinafter referred to as a container, containing a substance which may be noxious or otherwise and/or pressurised or otherwise is complex, where it is important that the substance should not be allowed to escape.

It is known to clamp a saddle to the container in a pressure tight manner and to introduce a drill bit through a sealable bore in the saddle. However, such solutions involve complexity in attaching the saddle and indeed of being able to remove the saddle after forming the aperture with the latter remaining sealed.

The object of the present invention is to provide an improved aperture forming machine and an improved drill bit adapted to seal a drilled aperture.

According to the invention there is provided a machine tool for machining an 20 aperture in a workpiece with a drill bit, the tool comprising: À a chassis, À at least one evacuatable foot for securing the chassis to the workpiece, À a drilling head mounted on the chassis for rotatably driving the drill bit to form the aperture and 25 À means for advancing the drilling head to feed the drill bit into the workpiece.

In use, the chassis is positioned with the drilling axis of the drilling head aligned with a desired aperture position. The or each evacuatable foot is evacuated to secure the foot, the chassis and the machine as a whole to the workpiece. The drilling 30 head is actuated to rotate the drill bit and it is advanced towards the workpiece to drill the aperture.

- Whilst a single annular foot encircling the drilling axis can be envisaged for flat container surfaces; preferably two or more feet able to adapt to the contour of a curved workpiece are provided. Conveniently, these are pivotably and adjustably attached to the chassis.

s Where the aperture is to be of a size such that a twist drill bit may not drill true, the drill bit can be of the type having a plurality of hard cutting elements mounted on a shank and the chassis can be provided with three or more bearing races arranged to bear on the shank to guide the drill bit.

Where the aperture being formed is intended to be sealed immediately on formation, the drill bit can carry a seal.

According to another aspect of the invention there is provided a drill bit for is cutting and sealing an aperture of a nominal diameter, the drill bit comprising: À a shank; À a front portion of the shank having a front diameter not greater than the nominal diameter; cutting elements at the front of the front portion of the shank, the cutting 20 elements being arranged to cut the nominal diameter; À a reduced diameter portion behind the front portion and having an outside diameter reduced from that of the front portion; À a threaded section of the reduced diameter portion of the shank, the thread extending at least at the rear end of the reduced diameter portion; 25. a sealing sleeve carried on the reduced diameter portion of the shank; and À a sealing sleeve captivator threadedly engaged with the thread for sealing captivation of the sealing sleeve on the shank and in the aperture.

Whilst it is envisaged that the cutting elements can be ground in the front 30 portion, the shank being of a suitable steel, preferably the elements are welded on inserts such as of tungsten carbide.

It is envisaged that the sealing sleeve may have sealing formations, such as external, annular lips directed away from the front portion. However, it is preferably plain and adapted to seal by axial compression inducing radial expansion, the arrangement being such that on penetration of the cutting elements through a 5 workpiece to an extent such that the sealing sleeve occupies the cut aperture, winding of the captivator towards the front portion longitudinally compresses and radially expands the sealing sleeve, which seals against the workpiece and the shank.

Conveniently the shank has a plain length between the threaded section and lo the front portion, for captivating the sealing sleeve between the bored diameter in the workpiece and the plain length.

The shank can be provided with an abrupt step between plain length and the front portion. However, in the preferred embodiment, the step is tapered, whereby 5 threading of the captivator towards the front portion of the shank expands the sealing sleeve over the step, with the step being drawn into the inner orifice of the aperture, with the inter- position of the sealing sleeve.

Again in the preferred embodiment, the sleeve has an outer step for abutting 20 against the outer orifice of the aperture. The sleeve has an increased diameter rear portion, which itself forms the sealing sleeve captivator, there being no separate component comprising the captivator. Nevertheless, it is envisaged that there could be such a separate component.

25 The captivator will usually have a non-circular outside for engagement with engagement means for its threading action in compressing the sleeve.

Where the drill bit is adapted to be guided by bearing races arranged to act on its shank, the sleeve conveniently has the same diameter and the threaded member has 30 an outside contour to engage irrotationally with the bearing races.

Again it is envisaged that the thread could be a left-hand thread, whereby continued clockwise rotation of the drill bit after penetration and formation of the aperture draws the shank back outwards in a single operation until the seal has been

effected. However, it is preferred that the thread be right-hand, whereby the seal is effected on reverse of the drive to the shank.

To help understanding of the invention, a specific embodiment thereof will s now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a front view of a machin e tool according to the invention; Figure 2 is an underneath view of the machine tool; Figure 3 is a side view of the machine tool; l o Figure 4 is a half sectional side vie w of sealing sleeve prior to fitting to a drill bit for the machine; Figure 5 is a similar view of the dri 11 bit; and Figure 6 is a similar view of the sea ling sleeve expanded to seal an aperture cut in a workpiece.

Referring to the drawings, the drilling machine 1 there shown has a chassis 2 of aluminium plate, with two side plates 3, a top plate 4 and a bottom plate 5. Two evacuatable feet 6,7 are connected to the chassis by respective lower links 8 pivoted to the side plates 3 close to the bottom plate 5 and by upper links 10 lockable at slots 20 11 in the side plates 3 at their mid-height by hand-wheels 12. The geometry of the linkage allows the height of the chassis above a workpiece W to be substantially the same whether the workplace is flat or curved regardless of radius of curvature within reason. The linkage also allows the feet to pivot to adapt themselves to the shape of the workpiece. To provide additional flexibility to workplace shape, the feet each 2s have three aluminium sandwich plates, 14,15,16, with a membrane 17 captivated between upper and lower individual sandwich plates. The lower plates are less extensive at their peripheries, allowing a margin of the membrane to have an peripheral seal 18 of foam elastomer material to be secured to the membrane, with the upper sandwich plates extending over the seal. The sandwich plates are secured to 30 each other by bolts 19. Strips 2O,21 of membrane exposed between the sandwiches 14,15,16 allow feet to adapt to a cylindrical contour.

Extending between the bottom plate 5 and brackets 22 inside the side plates 3 are carriage bars 23 for journals 24 carrying a drill mounting plate 25. The position of

this longitudinally along the bars is under control of two pneumatic actuators 26, whose rods 27 are attached to the plate 25 and cylinders are attached to the top plate 4. A displacement transducer 28 is mounted between the plate 25 and one of the side plates. s The mounting plate carries an air motor 29 having a chuck 30, in the form of a stud 31 having a drive lug 32. In the drawings, much of the pneumatic pipe-work, including control valves, for the machine is omitted. However, the exhaust from the motor is lead to a swarfblower 33 mounted on the bottom plate 5 at a central aperture lo 34 through which a drill bit 40 extends from the chuck in use. Beneath the plate 5 spaced around the aperture 34 are three ball bearings 35. The inner races are bolted to the plate, whilst the outer races are free and arranged for support within them of the drill bit.

5 The latter comprises a hollow shank 41 having a front portion 42, tapering down 43 to a reduced diameter 44 with a thread 45 along most of its tail. The bore 46 of the shank matches the diameter of the stud 31 and has a bayonet slot 46 for driving connection with the lug 32. The front of the portion 42 carries cutting teeth 47.

Mounted on the reduced diameter portion 44 is a sealing sleeve 48. This is a plain 20 sleeve of nylon, with a hexagonal head 49 at its end nearest to the chuck, when mounted. The diameters of the front portion and the outside of the sleeve 48 are the same, as is the across-the-flats dimension of the head 49.

In use, the machine is placed on the workpiece W. The hand-wheels are 25 released to allow the feet to contact the workpiece and bend at exposed membrane strips 20,21 and adapt to the curvature of the workpiece. Air pressure is applied to a venturi evacuator 50, to draw a vacuum (via non-shown pipework) between the feet 6,7 and the workpiece. This firmly attaches the machine to the workpiece. Prior to this, a drill bit was inserted into the chuck from below, with the drill mounting plate 30 25 and air motor 29 withdrawn upwards. The drill is thus positioned to drill the workpiece. The air motor is activated to spin the drill bit and the pneumatic actuators 26 have pressure applied to them sufficient to cause the bit to cut into the workpiece.

This pressure is pulsed, to break the swarf from the cutting operation. The swarf is blown clear by the blower 33. The drill bit is guided by the three bearings 35.

As soon as the drill breaks through the wall of the workpiece, the displacement transducer detects sudden forwards movement of the drill. This initiates stopping of the motor and its reversal. On forwards movement, the hexagonal head of the seal 5 engages the bearings, stopping its rotation. This contributes to stopping of the motor and the drill bit, which have low inertia. Once the transducer detects that the drill mounting plate is so positioned that the hexagonal head is fully engaged, the motor is reversed. This draws the shank back by screwing of the thread 45 into the hexagonal head. This occurs against the action of the actuators 26, which keep the head engaged 0 at the corners between its flats with the outside of the workpiece. As the shank is drawn back, the forward end of the seal is expanded by the taper 43 to extend outside the forward end of the shank. This action continues until the taper seats against the portion of the sealing sleeve expanded against the inside orifice of the aperture cut in the workpiece.

The motor stalls, the drill mounting plate has been withdrawn to a predetermined position and the bayonet connection disconnects. The actuators are then powered to withdraw the motor and chuck from the drill bit. The vacuum can be allowed to dissipate in the evacuation feet. The machine can then be removed. The 20 shank is firmly sealed in the aperture that has been cut. Its hollow central bore 46 carries an O-ring S1. In case there is pressure inside the workpiece, a central plug 52 is engaged in the bore at the O-ring and engages at a step 53 in the internal diameter of the bore. The step is conveniently provided at a junction between the front portion of the shank and the rear portion, which can be threadedly connected together.

For access to the inside of the workpiece after removal of the machine, a fitting 61 can be screwed onto the tail of the shank and sealed on. A probe 62 can then be inserted through the fitting and the shank, displacing the plug 52.

30 The invention is not intended to be restricted to the details of the above described embodiment. For instance, the sealing of the drilled aperture can be effected via the drill - or possibly with another member replacing the drill - by means of a member sealing in the aperture such as an O-ring. In such case, the drill can be locked by pivoted fingers expanding radially from the drill once within the workpiece.

Claims

CLAIMS:

1. A machine tool for machining an aperture in a workpiece with a drill bit, the tool compnsmg: À a chassis, 5 À at least one evacuatable foot for securing the chassis to the workpiece, À a drilling head mounted on the chassis for rotatably driving the drill bit to form the aperture and À means for advancing the drilling head to feed the drill bit into the workpiece.

2. A machine tool as claimed in claim 1, wherein the evacuatable foot is a single 0 annular foot encircling the drilling axis.

3. A machine tool as claimed in claim 1, wherein two or more evacuatable feet are provided, pivotably and adjustably attached to the chassis.

4. A machine tool as claimed in claim 1, claim 2 or claim 3, wherein the drill bit is of the type having a plurality of hard cutting elements mounted on a shank and the is chassis is provided with three or more bearing races arranged to bear on the shank to guide the drill bit.

5. A machine tool as claimed in any preceding claim, in combination with a drill bit carrying a seal.

6. A drill bit for cutting and sealing an aperture of a nominal diameter, the drill bit 20 comprising: À a shank; À a front portion of the shank having a front diameter not greater than the nominal diameter; À cutting elements at the front of the front portion of the shank, the cutting 25 elements being arranged to cut the nominal diameter; À a reduced diameter portion behind the front portion and having an outside diameter reduced from that of the front portion; À a threaded section of the reduced diameter portion of the shank, the thread extending at least at the rear end of the reduced diameter portion; 30 À a sealing sleeve carried on the reduced diameter portion of the shank; and À a sealing sleeve captivator threadedly engaged with the thread for sealing, captivation of the sealing sleeve on the shank and in the aperture. It l r l

7. A drill bit as claimed in claim 6, wherein the cutting elements are ground in the front portion, the shank being of a suitable steel.

8. A drill bit as claimed in claim 6, wherein the cutting elements are welded on inserts, preferably of tungsten carbide.

5 9. A drill bit as claimed in claim 6, claim 7 or claim 8, wherein the sealing sleeve has sealing formations.

10. A drill bit as claimed in claim 9, wherein the sealing formations are external, annular lips directed away from the front portion.

11. A drill bit as claimed in claim 6, claim 7 or claim 8, wherein the sealing sleeve is lo plain and adapted to seal by axial compression inducing radial expansion, the arrangement being such that on penetration of the cutting elements through a workpiece to an extent such that the sealing sleeve occupies the cut aperture, winding of the captivator towards the front portion longitudinally compresses and radially expands the sealing sleeve, which seals against the workplace and the shank.

12. A drill bit as claimed in any one of claims 6 to 1 1, wherein the shank has a plain length between the threaded section and the front portion, for captivating the sealing sleeve between the bored diameter in the workplace and the plain length.

13. A drill bit as claimed in any one of claims 6 to 12, wherein the shank has an abrupt step between plain length and the front portion.

20 14. A drill bit as claimed in any one of claims 6 to 12, wherein the shank has with a step between plain length and the front portion, the step being tapered, whereby threading of the captivator towards the front portion of the shank expands the sealing sleeve over the step, with the step being drawn into the inner orifice of the aperture, with the interposition of the sealing sleeve.

25 15. A drill bit as claimed in any one of claims 6 to 14, wherein the sleeve has an outer step for abutting against the outer orifice of the aperture.

16. A drill bit as claimed in claim 15, wherein the sleeve having an increased diameter rear portion, which itself forms the sealing sleeve captivator, there being no separate component comprising the captivator.

30 17. A drill bit as claimed in claim 15, including a captivator as a separate component..

18. A drill bit as claimed in any one of claims 6 to 14, wherein the captivator has a non-circular outside for engagement with engagement means for its threading action in compressing the sleeve.,, l l

19. A drill bit as claimed in any one of claims 6 to 18, wherein the sleeve has the same diameter as the shank and the threaded member has an outside contour to engage irrotationally with the bearing races, the drill bit being adapted to be guided by bearing races arranged to act on its shank, 5 20. A drill bit as claimed in any one of claims 6 to 19, wherein the thread is a left hand thread, whereby continued clockwise rotation of the drill bit after penetration and formation of the aperture draws the shank back outwards in a single operation until the seal has been effected.

21. A drill bit as claimed in any one of claims 6 to 19, wherein the thread is a right o hand thread, whereby the seal is effected on reverse of the drive to the shank.

22. A machine tool substantially as hereinbefore described, with reference to Figures 1 to 3 of the accompanying drawings.

23. A drill bit substantially as hereinbefore described, with reference to Figures 4 to 6 of the accompanying drawings.