Improved removal of dross when cutting or drilling with lasers

Abstract

An apparatus is described which, compared with the prior art, may improve the removal of dross during processing of a workpiece with a laser. One part of the apparatus is comprised of an unpressurised processing head which movably carries the laser beam lens. A second part is comprised of a tubular arrangement for directing a gas flow to remove dross. The two parts can be connected in order to mount the tubular arrangement accurately with respect to the laser beam.

Description

[0001] IMPROVED REMOVAL OF DROSS WHEN CUTTING OR DRILLING WITH LASERS

[0002] TECHNICAL FIELD

[0003] The present invention relates to a laser processing assembly and a method of use of the same.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of high-power lasers for materials processing is well established. During such processing, dross is often created. In the current context, dross may be defined as waste solid particles and / or molten droplets (often together called “spatter”) and / or vaporised material.

[0006] When such processing involves welding or heat treating of the workpiece material, little or no dross is created. However, when processing involves cutting or drilling of the workpiece material by focusing the beam to intensities sufficient to melt and / or vaporise the material quickly, dross is inevitably created. Dross creation is often a major problem for achieving efficient high-quality cutting or drilling. This is true regardless as to whether or not the focussed beam is arranged to fully penetrate the workpiece.

[0007] A major problem with dross is that it will usually be created with sufficient kinetic energy to be ejected towards the glass lens or curved mirror or other element that focusses the beam onto the workpiece. Basic physics dictates that a highly focussed beam requires for its creation a focussing element to have a short focal length and consequently to have a short working distance between it and the workpiece surface, typically about 70 mm. For such a short distance, ejected dross can irreversibly damage the focussing element, typically within seconds, unless it is somehow protected. A sacrificial protective item such as a flat glass slide can be used as a disposable spatter shield for the focussing element, but this is rarely sufficient. Instead, the usual main protective approach is to provide a fast-flowing jet of gas directed at the working area, which is the small area on the surface of the workpiece that is exposed at any relevant instant to the focussed beam. The gas is often provided by a source of compressed air. If appropriately arranged, the concentrated fast flow of gas deflects dross away from the focussing element. A second major problem with dross is the requirement that, after processing of the workpiece, resolidified dross should be absent from the edges and inner walls of cut lengths and holes. In most cases, the beam is arranged to fully penetrate through the workpiece rather than just provide a blind groove or blind hole. The width of the penetration usually is required to be less than the thickness of the workpiece because the ability of lasers to produce fine (narrow) perforations is a key reason for their use in preference to alternatives such as plasma jets or oxy-acetylene torches. Removing dross from such fine perforations is often difficult. Further, the molten dross from any working area should not be removed in a manner that allows it to stick and build up onto parts of the workpiece surface that are later to be similarly processed. In order to remove dross cleanly from all the cuts, holes and potential working areas on a workpiece, a common approach is to use the same fast-flowing jet of gas that is used to protect the beam focussing element.

[0008] Another major problem with dross is that it quickly can contaminate a working environment such as a factory building unless it can be collected and disposed appropriately. This problem affects process efficiency and it is also an occupational health and safety issue. The workpiece and at least the moving mechanical parts for the materials processing equipment (such as an X-Y table or rotary motion device) can be arranged to fit inside a semi-sealed housing to restrict the dispersal of dross, although such housings often need to be huge. The housing may be arranged to draw in fresh air and exhaust contaminated air, as described, for example, in patent application publication number WO 2022 / 250051. However, the heavier dross particles will remain inside the housing and accumulate, requiring frequent cleaning. In addition, difficulties arise in accessing the contents of the housing, including loading / unloading workpieces and inspecting them.

[0009] Thus it can be appreciated that, for the reasons given above, arranging a suitably concentrated and appropriately directed fast flow of gas is usually essential for cutting and drilling applications using lasers. Various gas flow arrangements exist but, as will be explained below, an improved novel approach is desirable, particularly in cases where the rate of creation of dross is high, as occurs for example during multi-hole drilling.

[0010] A traditional arrangement for dross removal is exemplified in US patent 5,374,803 which considers laser cutting. As illustrated in Figure 1, a beam focussing lens disk is fixed horizontally inside a vertical hollow cylinder such that the disk seals the upper end of the cylinder. The laser beam is incident on the lens from above the cylinder and coaxial with it. A screw-on conical piece, projecting downwards, seals the bottom of the cylinder except for a small central hole at the apex of the cone at the bottom. The hole is just sufficiently large to allow the beam, partially focussed there, to exit downwards without obstruction. The beam is incident on a working area of a workpiece placed closely below, but not touching, the apex of the cone. The almost-sealed cylinder is pressurised with compressed gas via an inlet below the lens and exits through the bottom hole as a jet collinear with the beam. Thus in principle at least, the gas jet in this particular arrangement prevents dross from damaging the lens and also removes dross from both the upper and the lower surface of the workpiece near the working area.

[0011] This traditional arrangement is not always satisfactory. By itself, it does little to prevent the abovementioned problem in which the dross contaminates the working environment. During the pre-penetration phase of cutting, which effectively is a drilling action to initiate the cut, most of the dross is ejected vertically upwards in this arrangement, directly towards the hole in the bottom of the conical nozzle. That hole is typically only a few mm above the surface of the workpiece owing partly to the usual requirement to have a short working distance between the lens and the workpiece, as previously discussed. Therefore, the gas jet, being only a few mm long, must have a high dynamic pressure if it is to prevent dross from entering the hole in the conical nozzle and prevent dross from adhering to the lips of the hole and gradually occluding it. During the pre-penetration phase with this arrangement, virtually all of the dross is scattered in all horizontal directions above the workpiece, making disposal of it very difficult. In addition, much of the dross may adhere and partially clog cuts that were made earlier, initially cleanly, in the same workpiece. Further, the dross may adhere to, and accumulate on, working areas yet to be processed, thereby compromising subsequent cut quality.

[0012] These deficiencies in this traditional arrangement are worse when the pre-penetration phase of processing is significant in comparison to the post-penetration phase. A common example of this situation occurs when many cuts of short length are required, including when small holes are cut in sheet metal by trepanning the laser beam. Although the US patent 5,374,803 refers to cutting, that same traditional arrangement is used for drilling holes except that the laser must be pulsed. For drilled holes, the pre-penetration phase is usually dominant over the post-penetration phase, and the amount of dross then scattered uncontrollably over the top surface of the workpiece can be a huge problem. An example of this situation is described in Australian patent number 626075 which refers to the production of fine filter screens by laser drilling large surface areas of shim steel with huge numbers of very closely-spaced tiny holes. In this application, experience shows that shims 0.7 mm thick typically have about 35% of their total volume converted to dross at a dross creation rate of about 200 cubic cm / hour (1.5 kg / hour).

[0013] Various alternatives to the traditional arrangement exemplified in US patent 5,374,803 exist or have been proposed, but all exhibit deficiencies for general applicability similar to those just described. Some are impractically complex. Others are limited to a specific and limited set of processing circumstances.

[0014] As one representative example, US patent 7,022,94 Idescribes a simple alternative arrangement in which a gas jet is directed at the working area substantially tangential to the surface of the workpiece instead of perpendicular to it. An embodiment of this arrangement uses one or more tubes to direct and manage the gas flow, the gas exiting the open end of the tube(s) just a few mm upstream of the working area. The resulting spray of dross is difficult to control, the removal of dross from the inner walls of the cut or hole in the workpiece is often unsatisfactory, and the gas jet is very noisy. This tube-directed gas flow arrangement can be used in combination with the traditional arrangement, as exemplified in US patents 6,492,617 and 6,204,475. Another variation of the tube-directed gas flow approach is to add one or more suction tubes facing substantially into the gas flow in an attempt to collect the dross spray, as exemplified in WIPO patent application publication WO 2021 / 004641. In practice, these variations generally do little to correct the deficiencies just described herein. Some other alternative arrangements require a nozzle-shaped device similar in some respects to that in the traditional arrangement but with the nozzle involving suction rather than positive gas pressure, and requiring for its operation a sliding seal onto the workpiece surface (for example, US patents 4,027,137 and 10,799,982 ). This sort of arrangement is complex, its seal is problematic if it has to travel over parts of the workpiece that have already been processed, and its ability to suck dross from the working area is limited.

[0015] An objective of the present invention is to make available an apparatus which is simple to construct and operate and which substantially ameliorates or at least partially overcomes the deficiencies and limitations described above in the prior art. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0016] SUMMARY OF THE INVENTION

[0017] A first major embodiment of the present invention comprises:

[0018] An apparatus which provides a directed flow of a gas that provides a suction force to remove molten matter and / or solid particles and / or vapourised matter from a working area on a surface of a workpiece, the working area being created by an interaction of a laser beam with the workpiece, the working area being located within an ambient atmosphere, wherein:

[0019] (a) the directed flow is directed by, and substantially confined within, an arrangement of tubular components connected serially which constitute a tube that is continuous between a source of the gas and a discharge end of the tube,

[0020] (b) the longitudinal centreline of the laser beam incident onto the workpiece passes once through the tube,

[0021] (c) the tube at the longitudinal centreline of the laser beam is substantially perpendicular to the longitudinal centreline,

[0022] (d) the laser beam passes through the tube via two apertures in a wall, or walls, of the tube, and each of the two apertures is dimensioned and positioned such that the laser beam passes substantially unobstructed,

[0023] (e) an internal cross-sectional area of the tube at the longitudinal centreline of the laser beam is greater than, and preferably at least two times greater than, an internal cross-sectional area at a flow aperture located upstream in the directed flow from the longitudinal centreline of the laser beam, and

[0024] (f) an outer wall of the tube immediately adjacent to one of the two apertures, specifically an aperture closest to the working area, is preferably 10 mm or less, and more preferably 5 mm or less, from the working area as measured along the longitudinal centreline of the laser beam. In another embodiment of the present invention, the apparatus has the following additional features:

[0025] (a) one of the two apertures, specifically an aperture closest to the working area, has an area of clear passage measured in a plane perpendicular to the centreline of the laser beam that is less than nine times an area of the laser beam measured in the same plane, and

[0026] (b) the flow aperture is at a distance from the centreline of the laser beam that is less than ten times an average internal width of the tube, wherein the average is calculated over all crossflow directions and over the length of the tube between the longitudinal centreline of the laser beam and the flow aperture.

[0027] In another embodiment of the present invention, one of the two apertures, specifically the aperture most distant from the working area, has an area of clear passage measured in a plane perpendicular to the centreline of the laser beam that preferably is less than nine times an area of the laser beam measured in the same plane.

[0028] In some embodiments of the present invention, the apparatus has the following features:

[0029] (a) between a laser source of the laser beam and the tube is positioned a beam focussing device for the laser beam which typically is a glass lens, and

[0030] (b) at all points along the longitudinal centreline of the laser beam between the beam focussing device and the outer periphery of the tube, a gas is present which is the gas of the ambient atmosphere at its ambient pressure. Typically, the ambient gas is air at normal atmospheric pressure and it is stagnant.

[0031] In another embodiment, the apparatus has the following features:

[0032] (a) one of the two apertures, specifically the aperture most distant from the working area, has a seal, complete or partial, separating the inside of the tube from the ambient atmosphere,

[0033] (b) a part of the seal includes a window which is substantially transparent to the laser beam, and

[0034] (c) the window is dimensioned and positioned such that the laser beam passes substantially unobstructed through it.

[0035] Preferably, the window resides in an alcove of the tube projecting towards the direction of incidence of the laser beam, an auxiliary flow of gas is injected into the alcove immediately adjacent to the window and a flow rate of the auxiliary flow preferably is less than one-tenth of the flow rate of the directed flow.

[0036] In a further embodiment, when the directed flow is present, the window is attached, at least in part, to the tube by the differential pressure between the pressure of the ambient atmosphere and the pressure within the tube immediately adjacent to the window.

[0037] In a further embodiment, where the laser beam is incident on the workpiece, a process gas that is not air is injected into the space between the tube and the working area with a flow rate and a pressure sufficient to displace substantially the ambient atmosphere.

[0038] In some embodiments, an adjustable clamp enables fixedly positioning and / or orienting the tube with respect to the working area in order to align the two apertures with the laser beam and to permit the outer wall of the tube immediately adjacent to the aperture closest to the working area to be a variable fixed distance from the working area as measured parallel to the longitudinal centreline of the laser beam.

[0039] Preferably, the adjustable clamp is attached to a machine part which movably carries one or more beam focussing devices for the laser beam and the machine part is able to move parallel to the longitudinal centreline of the laser beam.

[0040] In some embodiments, the workpiece is movable relative to the position of incidence of the laser beam on the workpiece, either by movement of the workpiece or by movement of the laser beam or by a combination of such movements, such that a plurality of working areas can be created sequentially on the workpiece.

[0041] In some embodiments, for a surface area encompassing the plurality of working areas, the surface area is substantially flat.

[0042] In some embodiments, the laser beam produces in the workpiece a plurality of blind holes or a plurality of through holes at the plurality of working areas.

[0043] In some embodiments, the laser beam produces in the workpiece a plurality of blind cuts or a plurality of through cuts along the plurality of working areas. Preferably, the direction of incidence of the laser beam on the workpiece is oriented substantially vertically downwards.

[0044] Preferably, the tube has a nozzle-shaped section immediately upstream of the flow aperture and the nozzle-shaped section is shaped so that its cross-sectional area progressively decreases in the direction of the directed flow.

[0045] Preferably, the tube at any distance downstream of the longitudinal centreline of the laser beam has an internal cross-sectional area that is substantially equal to, or greater than, the cross-sectional area of the tube at the longitudinal centreline.

[0046] In a further embodiment, the aperture closest to the working area has a minimum width parallel to the direction of the directed flow and a minimum width perpendicular to the direction of the directed flow that each exceed the corresponding widths of the laser beam at the aperture by a ratio preferably less than 3:1.

[0047] In a further embodiment, the discharge end of the tube discharges the directed flow into an inlet of an exhaust chute or waste receptacle.

[0048] During operation, the source of the gas for the directed flow is at a pressure sufficient to cause the pressure within the tube at the longitudinal centreline of the laser beam to be less than the pressure of the ambient atmosphere.

[0049] A second major embodiment of the present invention is a laser processing assembly comprising:

[0050] (a) a processing head extending between a first end and a second end with a lens supported therebetween, the second end of the processing head being located adjacent a workpiece in use and the lens being configured to align a laser beam through the second end onto the workpiece; and

[0051] (b) a gas flow arrangement having an elongate conduit that extends laterally across the second end of the processing head between the second end and the workpiece, the gas flow arrangement being configured such that a gas flows through the conduit, a pair of apertures through the conduit each aligning with the laser beam such that at least a portion of the laser beam extends therethrough onto the workpiece in use; wherein a pressure differential between the gas within the conduit proximal the pair of apertures and the ambient atmosphere outside the conduit creates a suction force that draws at least a portion of dross created during processing of the workpiece into the conduit.

[0052] The present invention also includes methods for processing a workpiece using a laser processing assembly, one example of which is the laser processing assembly comprising:

[0053] (a) a processing head that extends between a first end and a second end with a lens supported therebetween, the lens being configurable so as to align a laser beam of the laser processing assembly through the second end onto the workpiece in use, and

[0054] (b) a gas flow arrangement having an elongate conduit that extends laterally across the second end of the processing head between the second end and the workpiece, a pair of apertures through the conduit each aligning with the laser beam such that at least a portion of the laser beam extends therethrough onto the workpiece in use, and a constrictive portion of the conduit existing upstream of the pair of apertures; and the method comprising:

[0055] (a) locating a working area of the workpiece adjacent a first aperture of the pair of apertures through the conduit,

[0056] (b) initiating a gas flow through the conduit of the gas flow arrangement at a supplied pressure of the gas sufficient to create a pressure differential between the gas within the conduit proximal the pair of apertures and the ambient atmosphere outside the conduit, thereby creating a suction force in a region proximal the pair of apertures,

[0057] (c) initiating operation of a laser whereby the laser beam processes the workpiece, and

[0058] (d) drawing at least a portion of dross created during the processing of the workpiece into the conduit via the first aperture.

[0059] Advantageously, the current invention provides a suction action at the working area that causes dross to become entrained in the directed gas flow and thereby enables the dross to be discharged cleanly from the working area and for it to be collected readily. Further advantageously, the laser beam focussing device, typically an expensive and fragile glass lens, is readily protected from impact of dross and is also not exposed to pressurised or flowing gas that may contain oil vapour and other impurities. Also advantageously, the apparatus in this invention is simpler than many of the prior art alternatives. Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of inventions disclosed.

[0060] BRIEF DESCRIPTION OF THE FIGURES

[0061] The accompanying drawings facilitate an understanding of the various embodiments. The invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0062] Figure 1 is a cross-section side view schematic of a prior art laser processing machine.

[0063] Figure 2 is a cross-section close-up side view schematic of a first embodiment of the laser processing machine according to the present invention.

[0064] Figure 3 is a cross-section close-up side view schematic of a second embodiment of the laser processing machine according to the present invention.

[0065] Figure 4.1 is a cross-section close-up side view schematic of a third embodiment of the laser processing machine according to the present invention.

[0066] Figure 4.2 is a cross-section close-up top view of the gas flow arrangement and mounting arrangement of the embodiment of Figure 4.1.

[0067] DETAILED DESCRIPTION OF EMBODIMENTS

[0068] The present invention relates to an apparatus for removing dross from a workpiece during the processing of the workpiece by a laser beam, and a method of use of the same. In particular, the present invention relates to the production of a directed flow of gas to remove dross.

[0069] Referring to Figure 1, a traditional prior art laser processing machine 1 is shown. A workpiece 3 is positioned on top of a movable X-Y worktable 4. Although shown as a flat object, a person skilled in the art would appreciate that the workpiece 3 may have a more complex shape. A laser 5 emits a laser beam 6. The laser 5 may be of various types such as a fibre laser, a Nd-YAG laser, a carbon-dioxide laser, and an excimer laser, and it may emit a continuous-wave beam 6 or a pulsed beam 6. For example, when drilling the workpiece 3, the laser beam 6 may be pulsed. When cutting, the laser beam 6 may be either continuous-wave or pulsed. For convenience, the laser beam 6 initially emits horizontally and is subsequently directed vertically downwards by a mirror 8 so as to enter the processing head 2 as laser beam LB. The path of the laser beam 6 and laser beam LB between laser 5 and the processing head 2 is flexibly enclosed (not shown) in order to exclude room dust. The laser beam LB then is focussed by a lens 7, often made of glass, onto working area 3.1 on the surface of workpiece 3 at, or very close to, the focal point of the laser beam LB.

[0070] Referring again to Figure 1, during operation, gas G is fed into the processing head 2 below the lens 7 via an inlet port 10 at a pressure that is in excess of atmospheric (ambient) pressure. A high-pressure source (not shown) of the gas G may, for example, be a mechanical air compressor or commercially-available compressed gas cylinders. Importantly, the source must be arranged to provide gas G that is substantially free of oil and moisture and other impurities which might deposit onto lens 7. In use, the gas G exits the processing head 2 through a small hole 2.1.1 situated at the bottom apex of a conical nozzle 2.1 which is part of the processing head 2. The hole 2.1.1 is just sufficiently large enough to allow unobstructed passage of the partially-focussed laser beam LB. The gas G exiting from hole 2.1.1 forms a jet-like stream having sufficient force so as to repel the dross created at the working area 3.1 from entering the processing head 2 via the hole 2.1.1 and damaging the lens 7. The gas G also propels at least a portion of the dross away from the working area 3.1, effectively removing the dross from the immediate vicinity of the working area 3.1. In practice, the hole 2.1.1 must typically be within a few mm of the surface of the workpiece 3 in order to enable laser processing and dross removal. A laser machine controller 9 controls the operations of the X-Y table 4, the laser 5, the gas flow valve 11, and a positioning device (not shown) for adjusting the height of the processing head 2 in the Z (vertical) direction.

[0071] It is convenient now to use Figure 1, the traditional laser materials processing arrangement, as an illustration of two fundamental issues that apply to it and virtually all alternative commercial laser processing arrangements, including an arrangement incorporating the apparatus of the present invention, soon to be discussed here.

[0072] The first of these two fundamental issues is that the lens 7 is both critically important and delicate. The lens 7 may be a multi-element lens 7, particularly if a non-circular working area 3.1 is desired, although even a circular working area 3.1 typically benefits from use of a multi-element lens 7. The lens 7 must be designed to manage the high beam intensities typical in the art of laser materials processing. Lens 7 must also be of very high optical quality if it is to enable the typically high levels of efficiency and quality expected in commercial laser processing. In this context, cuts or holes made by the laser beam LB in the workpiece 3 are considered in simple terms to be made efficiently if, subject to practical limitations, they are made at a commercially- acceptable rate with a minimal and consistent kerf width if cut, or made with a well-defined and consistent hole width if drilled. Consequently, the lens 7 is an expensive and critical component that must be maintained in good condition. Unacceptable damage to the lens 7 can be caused by even a very small amount of (say) molten dross, such as a single piece that is about 0.5 mm in width resolidifying onto the lower surface of lens 7 near the centreline CL of the laser beam LB. Non-adhering impacts of solid particles can cause pitting of that surface. An optional sacrificial glass disk (not shown) can be positioned in a replaceable manner just below the lens 7 as disposable protection, but replacing the sacrificial disk is not trivial given that the processing head 2 is pressurised. Thus this use of a sacrificial protective disk in the traditional processing arrangement of Figure 1 negatively affects process efficiency and it does not alter the requirement to prevent dross from entering the processing head 2 in the first instance.

[0073] The second of the two fundamental issues is that space for machine components above the workpiece 3, at least vertically, is limited. As previously discussed, basic physics dictates that the distance between the lens 7 and the workpiece 3, known in the art as the working distance, must typically be about 70 mm for fine cutting and hole drilling. Simplistically expressed, the shorter the focal length of lens 7, the smaller can be the cut kerf width or drilled hole width. This generally implies higher quality and higher efficiency, essentially because the beam is then more tightly focussed. This requirement limits the vertical space above the workpiece 3 that is available to fit components to manage dross removal. Dross removal devices below the workpiece are useless during the often-dominant pre-penetration phase of the processing, as previously discussed.

[0074] Referring now to Figure 2, a schematic diagram of one embodiment of the present invention is shown as a cross-section in a vertical plane that includes the centreline CL of the laser beam LB. As would be appreciated by a person skilled in the art, some components shown in Figure 1 are omitted for clarity in Figure 2 but still exist as accompaniments to embodiments of the present invention and the features are considered to be the same unless specified as being otherwise.

[0075] The processing head 20 of a laser processing machine of the present invention can be a tube of cylindrical or other hollow cross-sectional shape within which the lens 7 is mounted. For example, the lens 7 can be mounted to an interior surface wall of the tubular processing head 20 via an annular lens mounting plate 7.1. As is well known in the prior art of laser processing machines, the processing head 20 can be adjustably supported above the workpiece 3, and the vertical height of the processing head 20 above the workpiece 3 can be varied and accurately controlled continuously during processing of the workpiece 3. The upper surface of the lens 7 can be protected from dust, or other contaminants, by a flexible enclosure (not shown) that can locate between the laser 5 and the processing head 20. as is also well known in the prior art.

[0076] In some forms, the vertical position of the lens mounting plate 7.1 within the processing head 20 can be adjusted whilst the laser processing machine is not in operation. Variation of the vertical position of the lens mounting plate 7.1 enables the processing head 20 to accommodate for lenses 7 of various focal lengths. For example, in some forms, at least a portion of the interior surface wall of the tubular processing head 20 can comprise threaded ridges therearound that correspond to, and are adapted to mate with, a threaded outer rim of the lens mounting plate 7.1.

[0077] The processing head 20 can be configured to include an optional sacrificial slide 20.2 that is transparent to the laser beam LB. This sacrificial slide 20.2 assists in protecting the lower surface of the lens 7 from damage caused by the dross generated by the laser processing machine during operation whilst processing the workpiece 3. For example, a pair of slots 20.1.1, 20.1.2 can be provided through the walls of the processing head 20 on opposing sides of the processing head 20. The slots 20.1.1, 20.1.2 can be formed to have a slightly greater height and width than the height thickness and lateral width, respectively, of the sacrificial slide 20.2. As the interior of the processing head 20 is not pressurised, it is not necessary for the sacrificial slide 20.2 to be sealed within the pair of slots 20.1.1 and 20.1.2. The sacrificial slide 20.2 may therefore be easily removed and replaced when required. In some forms, the sacrificial slide 20.2 can have a longitudinal length that is greater in distance than the outer diameter of the tubular processing head 20. This may advantageously enable a manual or automated repositioning of the sacrificial slide 20.2 by a slidable movement of the sacrificial slide 20.2 longitudinally along its length until a fresh, undamaged portion of the sacrificial slide 20.2 is exposed to the laser beam LB. In some forms the sacrificial slide 20.2 can be repositioned during a processing operation, if required. The sacrificial slide 20.2 can be fabricated and selected depending on the type of laser 5 used. For example, in some forms where the laser 5 is of a type that emits visible light or near-infrared light, the sacrificial slide 20.2 can be manufactured from strips of relatively inexpensive B270 glass which is available commercially in sheet-form and has sufficient optical quality for use as a sacrificial slide 20.2 in such instances. The slide 20.2 can be anti-reflection coated on both faces in order to minimise reflective losses of the laser beam LB.

[0078] Referring again to Figure 2, a tubular gas flow arrangement 30 can be used to remove the dross generated by the processing of the working area 3.1 of the workpiece 3 by the laser beam LB. Compressed gas can be provided to the gas flow arrangement 30 by an air compressor or compressed gas cylinders (not shown) or other sources. Preferably, the gas G used in the gas flow arrangement 30 is free of oil and moisture. In use, when a valve 38 of the gas flow arrangement 30 is opened, the gas G is allowed to flow through an upstream tube 31, and then subsequently to flow through a middle tube 33 and then through one or more discharge tubes 34. The discharge tubes 34 can range in length from a few centimetres to several metres long. Consequently, to reduce wall friction losses as the gas G flows along the discharge tubes 34, the tube, or plurality of tubes 34, can progressively increase in cross- sectional area. For example, where a plurality of tubes 34 are used, the downstream end of each segment of tube 34 can be located within the upstream end of the adjacent successive segment of tube 34, with the upstream end of the successive segment of tube 34 having an inner diameter, or cross-section, that closely corresponds to the outer diameter, or perimeter shape, of the downstream end of the prior adjacent segment of tube 34. The discharge tubes 34 direct the flow of gas G, and where applicable any dross 35 that enters the discharge tubes 34, into any one or more waste receptacle devices (not shown). For example, in some forms the waste receptacle device can be a large plenum or other container that is integrated with a centrifugal exhaust fan that is configured to exhaust the relatively clean gas G to the atmosphere. For purposes of description, the tubular components 31, 33 and 34 are described as having a circular cross-section that extends perpendicularly to the direction of the gas G flow. As would be appreciated by a person skilled in the art, the cross-sectional shape of the tubular components 31, 33 and 34 of the gas flow arrangement 30 can also be ovular, rectangular, or other shapes, and the shape can vary along each tubular component.

[0079] The upstream tube 31 and middle tube 33 can be aligned such that their respective longitudinal axes are collinear to one another. In some variations, the longitudinal axes of the upstream tube 31 and middle tube 33 can be offset vertically at the junction 32 between the two tubular components 31, 33. In some variations, a horizontal offset of the longitudinal axes can also exist at the junction 32. In some further variations, the upstream tube 31 can be coupled with middle tube 33 with the respective longitudinal axes being at an angle to one other in the vertical plane and / or horizontal plane about junction 32. It may be preferable in some embodiments for the longitudinal axes to be horizontally coplanar with one another.

[0080] As would be appreciated by a person skilled in the art, each of the tubular components 31, 33 and 34 of the gas flow arrangement 30 can extend substantially linearly along their length, or alternatively can comprise one or more gradual curves along their length. For example, in some forms it may be preferable for the upstream tube 31 to comprise a curve such that the tube 31 bends upwards at a location 5 cm or more upstream of the junction 32. The middle tube 33 and the portion of the upstream tube 31 that locates proximal to the junction 32 are preferably formed using a rigid material, for example copper, brass, steel, ceramic. The remaining portion of the upstream tube 31 and parts, or all, of the discharge tubes 34 can be formed from either a rigid material or from a flexible material. In some forms, it may be preferable that the discharge tubes 34 are formed from a light flexible tubing.

[0081] The area of the aperture for the gas G to flow through the junction 32 is smaller than the internal cross-sectional area of the middle tube 33 at the centreline CL of the laser beam LB. In some forms it may be preferable that the area of the aperture through the junction 32 is half or less of the cross-sectional area of the middle tube 33 at the centreline CL of the laser beam LB. In some forms, such as those shown in Figures 2 to 4, the portion of the upstream tube 31 that locates proximal to the junction 32 can gradually decrease in cross-sectional area in the direction of flow of gas G so as to define a gradually-constricting segment 31.1 immediately upstream of the junction 32. Alternatively, in some variations, not shown, the aperture at junction 32 does not have a gradually-constricting section 31.1 upstream of it; instead, the upstream tube 31 has a constant internal cross-sectional area immediately upstream of the junction 32 in which case the upstream tube 31 can have a constant inner diameter or cross-sectional area that is less than the inner diameter or cross-sectional area of the middle tube 33 at the centreline CL of the laser beam LB. In some forms of these variations it may be preferable that the area of the aperture through the junction 32 is half or less of the cross-sectional area of the middle tube 33 at the centreline CL of the laser beam LB. It may also be preferable in some forms having a constant internal cross-sectional area immediately upstream of the junction 32 that the length of the section of upstream tube 31 having that constant cross-sectional area is at least three times the average internal width of that section of the upstream tube 31.

[0082] The middle tube 33 comprises an upper hole (or aperture) 36 that locates substantially concentrically with the centreline CL of the laser beam LB. The middle tube 33 further comprises a lower hole (or aperture) 37 that locates substantially concentrically with upper hole 36, the lower hole 37 being directly below the upper hole 36 on an opposing side of the middle tube 33. In this description, the terms “upper” and “lower” are used for descriptive convenience only. The “upper” hole 36 may be defined more generally as the hole most distant from the working area 3.1 of the workpiece 3 and the lower hole 37 may be defined more generally as the hole closest to the working area 3.1 of the workpiece 3, regardless of the orientation of the centreline CL of the laser beam LB with respect to gravity. As would be appreciated by a person skilled in the art, the upper and lower holes 36, 37 can have the same or different circular or non-circular shapes, provided that both holes 36, 37 allow for unobstructed passage of the laser beam LB through the middle tube 33 and onto the working area 3.1 of the workpiece 3. Each of these holes 36, 37 are formed to be as small as possible without obstructing any significant part of the laser beam LB while nevertheless allowing for some tolerance and uncertainty in the alignment of the centre of the holes 36, 37 with the centreline CL of the laser beam LB. In addition, it may be preferable that the lower hole 37 is smaller than the upper hole 36.

[0083] Alignment of the laser beam LB with the holes 36,37 can be facilitated by the use of a low- power visible laser alignment beam, not shown, that is arranged to be coincident with the centreline CL of the high-power laser beam LB. The alignment beam preferably has a diameter equal to, or less than, the smallest width of the lower hole 37. In addition, the horizontal and vertical positioning of the tubular gas flow arrangement 30 can be adjusted and then rigidly fixed relative to the processing head 20. Preferably, the tubular gas flow arrangement 30 is fixed to a support that is isolated from the one or more potential sources of vibration within the laser processing machine such as the worktable 4. For example, the tubular gas flow arrangement 30 can be rigidly fixed to the processing head 20. It is also preferable that the gas G flow be controlled so as to minimise, or prevent, the gas G from generating vibrations that may negatively affect the alignment of the holes 36, 37 with the laser beam LB. As would be appreciated by a person skilled in the art, a number of techniques exist in the art that address for minimising, or preventing, the gas G from generating vibrations. For example, such techniques include the use of a non-pulsating gas source such as a screw air compressor, or the use of flexible tubing for parts of upstream tube 31 and downstream tubes 34, or the use of a soft-action gas valve 38.

[0084] In stable operation, when the gas flow G passes through the aperture at the junction 32, the pressure within the middle tube 33 near the centreline CL of the laser beam LB is reduced below atmospheric (ambient) pressure provided the pressure of the supply of gas G is sufficiently high. Since the ambient atmosphere external to the middle tube 33 and adjacent to holes 36 and 37 in the middle tube 33 is at atmospheric (ambient) pressure, the pressure differential at the holes 36, 37 causes ambient gas (usually air) to be sucked into the middle tube 33. At least a portion of the dross 35 created at the working area 3.1 is sucked through the lower hole 37 and attains a trajectory T in the gas flow G. This desirable situation can be arranged readily by ensuring the pressure provided by the gas source is appropriately adjusted (typically 690 kPa, or 6.8 atmospheres, in the case where the ambient atmosphere is air at normal atmospheric pressure) and the junction 32 is sufficiently close to the laser beam centreline CL. Typically, junction 32 can be located between 0.5 to 3 cm away from the centreline CL of the laser beam LB.

[0085] The suction force through the lower hole 37 can be sufficient such that molten dross does not collect on the downstream lip of lower hole 37. For example, the suction force can be sufficiently great that the trajectory T of the dross 35 initially can be nearly vertical so as to enable the dross 35 to pass unobstructed through the lower hole 37. Additionally, the distance between the lower hole 37 and the working area 3.1 can be adjusted to be sufficiently small, typically between 1 to 5 mm, such that the trajectory T of the dross 35 at the location where it is pulled through the lower hole 37 by the suction force is nearly vertical. In some forms, it may be preferable for the lower hole 37 to comprise a bevelled edge around the lip, or at least on the downstream side of the lip of the lower hole 37.

[0086] The process gas that envelops the working area 3.1 and which may assist in processing the working area 3.1 is typically ambient air at normal atmospheric pressure, even if the gas G is not air. As would be appreciated by a person skilled in the art, in some applications a process gas other than air may be desirable. For example, it may be desirable for the ambient air in the immediate vicinity of the working area 3.1 to be displaced by supplying a flow of the desired non-air process gas to the working area. The flow rate of process gas can be considerably less than the flow rate of the gas G in the gas flow arrangement 30. In some forms, not shown, a small tube can supply the process gas close to the working area 3.1, so as to efficiently displace the ambient air otherwise enveloping the working area 3.1.

[0087] Referring now to Figure 3, a further embodiment of the present invention is illustrated in which the upper hole 36 in the middle tube 33 is sealed, or at least partially sealed, or preferably mostly sealed, by a transparent window 40 which is transparent to the laser beam LB. In such embodiments, little or none of the ambient atmosphere is sucked into the middle tube 33 via the upper hole 36 when gas G is flowing through the gas flow arrangement 30. By effectively sealing the upper hole 36, the suction force drawing part of the ambient atmosphere and dross through the lower hole 37 may be increased. This may advantageously improve the removal of dross 35 from the working area 3.1 and reduce the likelihood of dross building up around the lip of lower hole 37. The use of a transparent window 40 also enables the width of the upper hole 36 to be increased, which may make it easier to align the centreline CL of the laser beam LB through the holes 36, 37 in middle tube 33. The transparent window 40 may also act as a substitute for, or an addition to, the sacrificial slide 20.2 in that it may offer protection for the lens 7. The transparent window 40 can be formed from the same materials that would be suitable for use as the sacrificial slide 20.2, or from other suitable transparent materials. In some embodiments, the optional sacrificial slide 20.2 can act as a backup protection mechanism to the transparent window 40. For example, if an error is made in the processing operating procedure and the flow rate of the gas G is set too low, the dross may gradually damage, and even destroy, the window 40. The sacrificial slide 20.2 thus may be used as a secondary protection mechanism for the lens 7.

[0088] The transparent window 40 can be used as a permanent component, or in some variations it can be regarded as sacrificial and preferably readily replaceable. For example, the transparent window 40 can be replaced during pauses in the processing operation. Conveniently, the suction force that is present at the upper hole 36 during operation of the laser processing machine 1 means that the window 40 can be easily mounted in a replaceable manner. For example, the suction force during operation can effectively seal the window 40 in-use against an ungreased soft O-ring 41 that is arranged within a window mount 42.

[0089] The window mount 42 can be fixed and sealed to the middle tube 33 about the upper hole 36, for example by a weld 42.1 or by brazing. The vertical distance H between the upper surface of the middle tube 33 and the lower surface of the transparent window 40 can be set by the height of the window mount 42. Minimising the vertical distance H enables shorter working distances (between the lens 7 and the workpiece 3) to be accommodated but may increase the risk that dross will impact the lower surface of the transparent window 40. As would be understood by a person skilled in the art, the transparent window 40 and the O-ring 41 can each be circular in shape or non-circular, and can be the same or a different shape to one another. In some embodiments, it may be preferable that the transparent window 40 is mounted substantially horizontally such that it is not inclined to move under gravity, even when no suction force is applied at the upper hole 36. The transparent window 40 can be fixed in position against vertical or horizontal movement. For example, the transparent window 40 can be fixed to the window mount 42 by a plurality of retaining lugs 42.2 that are each free to swivel about a respective axis through approximately 180 degrees between an open and closed position, with the bottom edge of the arm of each lug 42.2 closely corresponding to the upper surface of the transparent window 40 so as to only just clear it when being rotated. The pivot base 42.3 of each retaining lug 42.2 can be arranged sufficiently close to the side edge along the perimeter of the transparent window 40 so as to prevent excessive horizontal movement. As would be understood by a person skilled in the art, other mounting arrangements can be used to restrict or prevent vertical or horizontal movement of the transparent window 40.

[0090] In some variations, an auxiliary flow of gas 43 can be injected into the space immediately below the transparent window 40 via one or more auxiliary gas tubes 44. The flow rate of the auxiliary gas 43 can be adjusted so that it prevents, or significantly reduces, the risk that dross reaches and impacts against the lower surface of the window 40, whilst nevertheless retaining a sub-atmospheric pressure at the upper hole 36. Typically, the flow rate of auxiliary gas 43 can be approximately 1% or less of the flow rate of the gas G in the tubular arrangement 30. The auxiliary gas 43 is preferably free of oil, moisture and other impurities.

[0091] Referring now to Figures 4.1 and 4.2, yet a further embodiment of the present invention is illustrated in which the tubular flow arrangement 30 is fixed in position using a suitable mounting arrangement. Figure 4.1 is a schematic cross section of the embodiment in the vertical plane that includes the laser beam centreline CL. Figure 4.2 is a schematic cross section in a horizontal plane of a small part of the arrangement. As would be appreciated by a person skilled in the art, other suitable mounting arrangements can be used in the context of the present invention provided relevant requirements are accommodated, as described immediately below.

[0092] During processing operation, it is required that the middle tube 33 is arranged to remain rigidly fixed and free of excessive vibrations. Consequently, the part of the upstream tube 31 adjacent to the middle tube 33 must also be rigidly fixed because it is rigidly attached to the middle tube 33. Preferably, the holes 36 and 37 in the middle tube 33 are positioned precisely with respect to the centreline CL of the laser beam LB. Typically, the holes 36 and 37 are centrally located with respect to the centreline CL. To obtain the best quality focus of the laser beam, the beam centreline CL passes precisely through the centre of the lens 7 ; therefore it is preferable that the alignment of the beam through holes 36 and 37 is not reliant excessively on adjusting the direction of the laser beam away from the ideal centreline CL which passes through the precise centre of the lens 7 and which is perpendicular to its horizontal plane. Consequently, it is required that although the mounting arrangement is to provide rigid fixation of middle tube 33 at least, it is also required that the mounting arrangement provides scope for adjusting the position of the middle tube 33 at least. In addition, the mounting method is required to allow the tubular arrangement 30 to be moved away easily from the workpiece 3 during pauses in the processing operation so that the workpiece 3 can be inspected or replaced. The embodiment shown in Figures 4.1 and 4.2 successfully accommodates all these requirements.

[0093] Referring to Figure 4.1, the upstream tube 31 is bent so as to be substantially vertical at a clamped position because this vertical orientation facilitates decluttering components, including for example a flexible segment, not shown, of upstream tube 31, from the vicinity of the workpiece 3. However, the upstream tube 31 can be instead substantially horizontal at a suitable clamp, not shown, or at any angle between the horizontal and the vertical orientations at a suitable clamp. These various choices can be achieved by means of simple variations to the arrangement shown in Figures 4.1 and 4.2.

[0094] As shown in Figure 4.1, the processing head 20 can be mounted by being screwed into a large horizontal mounting plate 50. As will be known by a person skilled in the prior art, such a large mounting plate 50 and the components it bears usually are moveable vertically on a motorised slider, not shown. Preferably, the large mounting plate 50 is square or rectangular in the horizontal plane and the large threaded hole that accommodates the processing head 20 is centred, at least approximately, in it. A vertical mounting bracket 51.1 can be attached to a side of the large mounting plate 50 by two or more sturdy threaded bolts 53 (only one is shown). Alternatively, less preferably, only one bolt 53 can be used. The diameter of the clearance holes for these bolts 53 in the vertical mounting bracket 51.1 can be chosen so as to provide a desirable amount of minor adjustment, if required, for the position of the tubular arrangement 30 in a horizontal plane that contains the longitudinal axis of the middle tube 33. Some minor adjustment in the position of the tubular arrangement 30 horizontally left - right in Figure 4.1 can be achieved by inserting one or more annular spacers (washers) 54 on the bolts 53 between the vertical mounting bracket 51.1 and the large mounting plate 50. A horizontal mounting bracket 51.2 can be firmly attached to the vertical mounting bracket 51.1 by means of a weld 51.3, for example. The horizontal mounting bracket 51.2 preferably projects away from the processing head 20 because space in the opposite projection is limited.

[0095] As shown in Figure 4.2, the horizontal mounting bracket 51.2 can have a semi-circular cutout on its outer edge that is sized to partially accommodate snugly and adjustably a vertical part of upstream tube 31. (For simplicity, a circular cross section is shown for upstream tube 31, but a tube with a different cross section can be used by altering the cut-out to suit.) This part of tube 31 can be firmly clamped in position using a matching clamp piece 52 with two or more threaded bolts 55 that screw into the horizontal mounting bracket 51.2. A cut-out in the clamp piece 52 can be machined so that it is semi-circular in shape but less than semicircular in extent so that a small gap 52.1 exists even when the bolts 55 are fully tightened. Preferably, the upstream tube 31 is sufficiently robust at the position of the clamp piece 52 that it does not distort when clamped, thereby ensuring that a firm clamping action can be achieved. Also preferably, the part of the tubular gas flow arrangement 30 between the clamp piece 52 and the downstream end of middle tube 33 is of a material that is sufficiently strong and with a sufficient wall thickness to maintain that part rigidly in position to the desired precision at holes 36 and 37 in the middle tube 33. Preferably, that part of the tubular gas flow arrangement 30 can be formed from one or more materials including brass, copper, steel and ceramic, but other materials may also be suitable. For this part, a wall thickness between 2 and 5 mm can be suitable. Upstream of clamp piece 52, all or part of the upstream tube 31 can be flexible for convenience in operation.

[0096] In some embodiments, not shown, a similar mounting arrangement to that shown in Figures 4.1 and 4.2 can be used to clamp discharge tube 34 in position. However, the clamping action at the clamp piece 52 on upstream tube 31 preferably is dominant over any clamping action on discharge tube 34, otherwise adjustments to the position and / or alignment of the tubular arrangement 30 can be difficult. In some variations, the mounting arrangement for discharge tube 34 can be a simpler and less physically restrictive version of the mounting arrangement shown in Figures 4.1 and 4.2, or it can even be omitted. A light and flexible discharge tube 34 can be attached directly to the middle tube 33 with only a non-restrictive support under the discharge tube 34 to prevent its weight from acting on the middle tube 33. In some variations, the discharge tube 34 can be omitted entirely if the flow of gas G discharged from middle tube 33 can be disposed of satisfactorily via a nearby collection chute or similar arrangement.

[0097] In some forms, an example method of installation and use of the disclosed apparatus as part of a laser processing machine comprises:

[0098] 1. Setting up the laser processing machine in a manner essentially the same as that in the prior art, as illustrated in Figure 1, but with the processing head 20 of the present invention (as described above) instead of the processing head 2 of the prior art. This includes precisely aligning a low-power alignment laser with the centreline CL of the high-power laser beam LB. The components of the tubular gas flow arrangement 30 of the present invention (as described above) are to be available for subsequent installation and use. The upstream tube 31 can be connected to the compressed gas source and the discharge tube 34 can be connected to a waste receptacle. 2. Moving the processing head 20 to a convenient height, and attaching the combination of mounting brackets 51.1 and 51.2 to the large mounting plate 50.

[0099] 3. Holding the rigid part of the tubular gas flow arrangement 30 consisting of at least the combination of the upstream tube 31 and the middle tube 33 in position against the horizontal mounting bracket 51.2 and then attaching clamp piece 52 slightly loosely so that the upstream tube 31 can be moved rotationally and vertically but not slip down under gravity.

[0100] 4. Moving the large mounting plate 50 (with all that it now carries) down to its operating position with care that the middle tube 33 and the upstream tube 31 are sufficiently high at this stage that they do not contact the workpiece 3.

[0101] 5. Using the low-power alignment laser as a guide, adjusting the position of the combined rigid upstream tube 31 and middle tube 33 so that the alignment beam passes precisely through the desired positions within the holes 36 and 37 in the middle tube 33. At this time, also adjusted is the vertical clearance distance between the bottom of the middle tube 33 and the surface of the workpiece 3. Assuming that the combination of rigid tubes 31 and 33 have been accurately dimensioned in advance, only small adjustments can be required. Final small horizontal adjustments to accommodate the position of the combination of rigid tubes 31 and 33, such as 1 mm at the position of lower hole 37, can be made by redirecting the beam centreline CL of laser beam LB; however, such adjustments are not preferable because they slightly misdirect CL away from the precise centre of the lens 7, possibly distorting the laser beam.

[0102] 6. Attaching any flexible part of upstream tube 31 to the rigid part of upstream tube 31, and (if required) attaching the discharge tube 34 to the downstream end of middle tube 33. If required, in some embodiments the auxiliary gas flow tube(s) 44 is attached and the flow of gas 43 through this is initiated at the desired rate. Also, the flow of gas G is initiated at the required rate by adjusting the pressure of the supply of gas G to a setting that has been predetermined as suitable by earlier trial use of the laser processing machine. The alignment attained in the previous step is rechecked and readjusted if necessary.

[0103] 7. Proceed to operate the laser processing machine as would be understood by a person skilled in the art. The satisfactory removal of dross is checked during operation by observing the behaviour of the suction action pulling dross into the tubular gas flow arrangement through the lower hole 37 in middle tube 33. If this behaviour is not satisfactory, operation of the laser processing machine is paused and the alignment attained in step 5 is checked and readjusted, if required, before proceeding with the operation.

[0104] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[0105] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

[0106] Wherever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of". A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[0107] In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "front" and "rear", "inner" and "outer", "above", "below", "upper" and "lower" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

Claims

CLAIMS1. An apparatus which provides a directed flow of a gas that provides a suction force to remove molten matter and / or solid particles and / or vaporised matter from a working area on a surface of a workpiece, the working area being created by an interaction of a laser beam with the workpiece, the working area being located within an ambient atmosphere, wherein:(a) the directed flow is directed by, and substantially confined within, an arrangement of tubular components connected serially which constitute a tube that is continuous between a source of the gas and a discharge end of the tube,(b) a longitudinal centreline of the laser beam incident onto the workpiece passes once through the tube,(c) the tube at the longitudinal centreline of the laser beam is substantially perpendicular to the longitudinal centreline,(d) the laser beam passes through the tube via two apertures in a wall, or walls, of the tube, and each of the two apertures is dimensioned and positioned such that the laser beam passes substantially unobstructed,(e) an internal cross-sectional area of the tube at the longitudinal centreline of the laser beam is greater than an internal cross-sectional area at a flow aperture located upstream in the directed flow from the longitudinal centreline of the laser beam, and(f) an outer wall of the tube immediately adjacent to one of the two apertures, specifically an aperture closest to the working area, is 10 mm or less from the working area as measured along the longitudinal centreline of the laser beam.

2. The apparatus as claimed in claim 1 wherein:(a) one of the two apertures, specifically an aperture closest to the working area, has an area of clear passage measured in a plane perpendicular to the centreline of the laser beam that is less than nine times an area of the laser beam measured in the same plane, and(b) the flow aperture is at a distance from the centreline of the laser beam that is less than ten times an average internal width of the tube, wherein the average is calculatedover all cross-flow directions and over the length of the tube between the longitudinal centreline of the laser beam and the flow aperture.

3. The apparatus as claimed in claim 1 or claim 2 wherein one of the two apertures, specifically an aperture most distant from the working area, has an area of clear passage measured in a plane perpendicular to the centreline of the laser beam that is less than nine times an area of the laser beam measured in the same plane.

4. The apparatus as claimed in any one of claims 1 to 3 wherein:(a) between a laser source of the laser beam and the tube is positioned a beam focussing device for the laser beam, and(b) at all points along the longitudinal centreline of the laser beam between the beam focussing device and an outer periphery of the tube, the ambient atmosphere is present.

5. The apparatus as claimed in any one of claims 1 to 4 wherein:(a) one of the two apertures, specifically an aperture most distant from the working area, has a seal, complete or partial, separating an inside of the tube from the ambient atmosphere,(b) a part of the seal includes a window which is substantially transparent to the laser beam, and(c) the window is dimensioned and positioned such that the laser beam passes substantially unobstructed through it.

6. The apparatus as claimed in claim 5 wherein the window resides in an alcove of the tube projecting towards the direction of incidence of the laser beam, an auxiliary flow of a gas is injected into the alcove immediately adjacent to the window and a flow rate of the auxiliary flow is less than one-tenth of a flow rate of the directed flow.

7. The apparatus as claimed in any one of claims 1 to 6 wherein, where the laser beam is incident on the workpiece, a process gas that is not air is injected into a space between the tube and the working area with a flow rate and a pressure sufficient to displace substantially the ambient atmosphere.

8. The apparatus as claimed in any one of claims 1 to 6 wherein an adjustable clamp enables fixedly positioning and / or orienting the tube with respect to the working area in order to align the two apertures with the laser beam and to permit an outer wall of the tube immediately adjacent to the aperture closest to the working area to be a variable fixed distance from the working area as measured parallel to the longitudinal centreline of the laser beam.

9. The apparatus as claimed in claim 8 wherein the adjustable clamp is attached to a machine part which movably carries one or more beam focussing devices for the laser beam and the machine part is able to move parallel to the longitudinal centreline of the laser beam.

10. The apparatus as claimed in any one of the previous claims wherein the workpiece is movable relative to a position of incidence of the laser beam on the workpiece, either by movement of the workpiece or by movement of the laser beam or by a combination of such movements, such that a plurality of working areas can be created sequentially on the workpiece.

11. The apparatus as claimed in claim 10 wherein, for a surface area encompassing the plurality of working areas, the surface area is substantially flat.

12. The apparatus as claimed in claim 10 or claim 1 Iwherein the laser beam produces in the workpiece a plurality of blind holes or a plurality of through holes at the plurality of working areas.

13. The apparatus as claimed in claim 10 or claim 11 wherein the laser beam produces in the workpiece a plurality of blind cuts or a plurality of through cuts along the plurality of working areas.

14. The apparatus as claimed in any one of the previous claims wherein the gas in the directed flow is air.

15. The apparatus as claimed in any one of the previous claims wherein the tube has a nozzle-shaped section immediately upstream of the flow aperture and the nozzle -shaped section is shaped so that its cross-sectional area progressively decreases in the direction of the directed flow.

16. The apparatus as claimed in claim 5 or 6 wherein, when the directed flow is present, the window is attached, at least in part, to the tube by the differential pressure between the pressure of the ambient atmosphere and the pressure within the tube immediately adjacent to the window.

17. The apparatus as claimed in any one of the previous claims wherein the tube at any distance downstream of the longitudinal centreline of the laser beam has an internal cross-sectional area that is substantially equal to, or greater than, the cross-sectional area of the tube at the longitudinal centreline.

18. The apparatus as claimed in any one of the previous claims wherein the aperture closest to the working area has a minimum width parallel to the direction of the directed flow and a minimum width perpendicular to the direction of the directed flow that each exceed the corresponding widths of the laser beam at the aperture by a ratio less than 3:1.

19. The apparatus as claimed in any one of the previous claims wherein the outer wall of the tube immediately adjacent to the aperture closest to the working area is 5 mm or less from the working area.

20. The apparatus as claimed in any one of the preceding claims wherein the discharge end of the tube discharges the directed flow into an inlet of an exhaust chute or waste receptacle.

21. The apparatus as claimed in any one of the previous claims wherein the source of the gas is at a pressure sufficient to cause the pressure within the tube at the longitudinal centreline of the laser beam to be less than the pressure of the ambient atmosphere.

22. A laser processing assembly comprising a processing head extending between a first end and a second end with a lens supported therebetween, the second end of the processing head being located adjacent aworkpiece in use and the lens being configured to align a laser beam through the second end onto the workpiece; and a gas flow arrangement having an elongate conduit that extends laterally across the second end of the processing head between the second end and the workpiece, the gas flow arrangement being configured such that a gas flows through the conduit, a pair of apertures through the conduit each aligning with the laser beam such that at least a portion of the laser beam extends therethrough onto the workpiece in use; wherein a pressure differential between the gas within the conduit proximal the pair of apertures and an ambient atmosphere outside the conduit creates a suction force that draws at least a portion of dross created during processing of the workpiece into the conduit.

23. A method of processing a workpiece using a laser processing assembly, the laser processing assembly comprising: a processing head that extends between a first end and a second end with a lens supported therebetween, the lens being configurable so as to align a laser beam of the laser processing assembly through the second end onto the workpiece in use, and a gas flow arrangement having an elongate conduit that extends laterally across the second end of the processing head between the second end and the workpiece, a pair of apertures through the conduit each aligning with the laser beam such that at least a portion of the laser beam extends therethrough onto the workpiece in use, and a constrictive portion of the conduit existing upstream of the pair of apertures; the method comprising: locating a working area of the workpiece adjacent a first aperture of the pair of apertures through the conduit; initiating a gas flow through the conduit of the gas flow arrangement at a supplied pressure of the gas sufficient to create a pressure differential between the gas within the conduit proximal the pair of apertures and an ambient atmosphere outside the conduit, thereby creating a suction force in a region proximal the pair of apertures;initiating operation of a laser whereby the laser beam processes the workpiece; drawing at least a portion of dross created during the processing of the workpiece into the conduit via the first aperture.

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