Abstract:
An air handling system for a laser-equipped machine tool. The machine base is specially configured to include and form part of the duct work which extracts fumes produced during the cutting operation. An elongated collection duct is provided in portions of the machine base bracketing a slag collection surface, and the port pattern in the collection ducts is graduated so as to achieve relatively even flow across the entire machine. The collection duct communicates with a main duct in the machine base which has outlet connections at three sides of the base, affording flexibility in selecting a particular outlet for connection to an external vacuum source. Cooperating with the air extraction components, the machine is enclosed and air vents are provided at strategic locations in the enclosure to control both the volume and direction of air into the enclosure to provide for efficient extraction of fumes produced as a by-product of the cutting operation.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to machine tools, and more particularly relates to machine tools using lasers for cutting metal and other materials. 
     BACKGROUND OF THE INVENTION 
     Laser-equipped machine tools are often used to cut parts from sheet metal and relatively thin plate. In such machine tools a laser beam, concentrated by a focusing lens or mirror to a small diameter spot, is directed to position the focal point above, on or below the surface of the material to be cut. The laser beam is directed from the focusing optic through a nozzle disposed immediately above the material workpiece with a pressurized gas being directed through the nozzle, typically coaxially with the laser beam, to assist making the cut. The pressurized gas interacts with the laser beam and material facilitating the cutting process, and creates a gas stream which carries the removed material away from the cut. The removed material consists of fumes, various size particles and drops of molten material some of which are small enough to remain airborne for some time. The amount of fumes created during metal cutting is usually small. More fumes are generated cutting non-metallic materials. Depending upon concentration of fumes in breathed air and the type of material cut, fumes can be a health hazard. Some fumes are poisonous. 
     Laser-equipped machine tools are Computer Numerically Controlled and are manufactured in many configurations and sizes and with lasers of various types and power. In one configuration, “flying optics”, the cutting head is adapted for movement along one axis, such as the Y-axis which is mounted on a bridge adapted for movement in an orthogonal, X-axis. The work is supported on a stationary pallet or table below the bridge. Movement of the cutting head is coordinated with movement of the bridge to define a precise path on the part. The cutting head and laser are controlled to pierce and cut the metal to form holes and shapes in the material, and then to cut the part from the material. In this configuration the laser is mounted on the stationary machine base or on a separate floor mounted stand. 
     Many same or different parts of common thickness and material type may be cut from a sheet or plate. Such groups of parts are commonly referred to as a nest. Left over material, after the parts have been removed, is referred to as a remnant or a skeleton. A small remnant which falls from a hole cut in a part is called a slug. Remains of material from the cut is called slag. Resolidified material clinging to the part is called dross. The mixture of slugs and slag residue from cutting sheet material is generally called scrap. 
     When using laser-equipped cutting machine tools it is advantageous to utilize optics with different focal lengths to cut various thicknesses of material. The focal length of the optic contributes to the diameter of the focal spot and thus the energy density, Watts per unit area, at the focal spot. Shorter focal length optics create smaller focal spots having higher energy densities. The focal length of the optic also contributes to depth of focus of the focal spot with longer focal lengths having greater depth of focus. Shorter focal length optics are advantageous for cutting thinner materials while longer focal length optics are advantageous for cutting thicker material. 
     Various means for dealing with fumes have been utilized and in some cases the problem is ignored. Laser equipped machine tools are available which have no provisions for removing fumes generated by the cutting process. Usually these machines are utilized to cut low carbon steel. In these cases it is assumed that plant ventilation is adequate to prevent fume concentrations reaching hazardous levels. 
     Providing for efficient fume collection is not a simple problem. The material to be cut is supported on a worktable or pallet which has been sized for the maximum size part to be cut and designed to provide as much open area through the table as possible while providing adequate support for the workpiece and parts cut from it. Normally, a border remains around the workpiece on the worktable or pallet. This border provides space for work locators, clamps and sheet tolerances. Often the workpiece cut is smaller than the maximum size the table is designed to handle. As a result there is a lot of variation in the space around the workpiece through which fumes can escape. Also cutting the workpiece creates holes and open spaces through which fumes can escape. These conditions make it difficult to provide an efficient and reasonably sized and priced blower and filter system. 
     In some machines the cutting area has been enclosed from the sides by the design of the machine creating a trough. A large duct and blower is placed at the end of the trough creating an air flow under the part to collect the fumes. Because of factors described earlier, these systems are not very efficient fume collectors. 
     In other cases multiple ducts have been provided under the cutting area providing multiple fume collection points. Efficiency depends upon the number of collection points and the distance between the collection points and where the cut is made. 
     In other cases the cutting area, under the work support, is partitioned into several zones by sheetmetal and duct work, the duct work provided with valves which open the zone in which cutting is taking place. The other zones are left closed. This reduces the size of the collection area and allows use of a smaller blower and dust collector. 
     As lasers, with beam qualities suitable for cutting, are developed and become available in higher powered versions, machines are developed having the ability to cut greater thicknesses of material. Adapting high power lasers to cut thicker materials leads to using focusing lenses with longer focal lengths. Below the focal point, a laser beam expands at approximately the same rate that it was focused. For example, if a 35 mm diameter laser beam is focused by a lens with a 10″ focal length, then, 10″ below the focal point, unless absorbed by the material cut, the beam would be about 35 mm diameter again. Twenty inches below the focal point the beam would be about 70 mm diameter. This remnant, expanding beam from high power lasers has considerable capability to cause damage. For example, in an experiment a 0.125″ thick aluminum plate was scuffed with steel slag, then a 38 mm diameter 5500 Watt beam was directed at the surface. The aluminum was cut through in 40 seconds. Similar tests were done with 0.25″ thick stainless steel and carbon steel. Both were cut through in well under a minute. These tests indicated that a dust collection system, underlying the cutting area of a high power laser system, with long focal length optics in use, would be at considerable risk of being damaged by the remnant laser beam. 
     It would be advantageous to provide a dust collection system for a high power laser-equipped machine tool which can remove fumes produced by the cutting process and which is not at risk of being damaged by the high power laser beam. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is a general aim of the present invention to provide an air handling system for a laser-equipped machine tool which is built directly into the machine base, and which cooperates with a machine enclosure to provide controlled air flow through the cutting zone to effectively and efficiently withdraw the fumes resulting from the laser cut. 
     In that regard, it is an object of the present invention to utilize the machine base structure itself as an element of the air handling system. An even more detailed object, in that regard, is to configure the machine base to provide a plurality of connection points for a dust collector and extractor, to allow the user to select a particular one of those connection points to suit a particular installation. 
     It is also an object of the invention to provide an air handling system which is not at risk of damage by a high power laser beam. 
     It is another object of the invention to provide an air handling system which avoids the complexity of shutting off ducts in zones of the system when cutting is being done in another zone, yet provides for effective withdrawal of the gases and dust without dependence on the position in the system where the cutting is taking place. 
     It is another objective of the present invention to provide an air handling system with an improved ability to draw gases and fumes from the entire cutting area below the worktable of the machine tool. 
     It is another objective of the invention to control air flow into and through the enclosure such that dead spaces where fumes could accumulate are eliminated. 
     A specific object of the present invention is to build the main collection duct into the machine base such that it requires no additional room, has no duct work exposed to the laser beam, does not extend the internal size of the machine, and concurrently provides for multiple connection points selectable to the user. 
     It is a feature of the present invention that the machine base is provided with a welded box structure, with the box structure altered to provide a duct internal to the base which can be accessed at several locations around the machine, any one of which can provide a connection point for a vacuum source or dust collector. These comparatively larger main ducts, serving as exit ducts, are built directly into the machine base and are interconnected with smaller collection ducts, also built into the machine base, but in an area above the slag collection surface. Ports into the collection duct are sized with respect to their distance from the junction with the main duct, so as to render the air flow into the air handling system comparatively uniform, or to allow tailoring of the air flow to the particular needs of a particular installation. The elements of the air handling system are positioned outside of the cutting zone, except for the main duct which is protected from laser damage by the slag collection plate. 
     As a further feature of the invention, the entire cutting machine is enclosed by a cover which can be opened and manipulated for ready access to the machine, but which can be closed during cutting. When the enclosure is closed, air flows through intended inlets, which are positioned in cooperation with the collection ducts in order to provide controlled air flow through the cutting zone adapted to maximize extraction of fumes. 
     Other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation of a laser-equipped machine tool having a base structure incorporating an air handling system exemplifying the present invention; 
     FIG. 2 is a plan view of the machine tool of FIG. 1; 
     FIG. 3 is an end elevation sectional view of the machine tool of FIG. 1; 
     FIG. 4 is a sectional view taken along the line  4 — 4  of FIG. 2, and better illustrating the machine base structure; 
     FIG. 5 is a simplified plan view showing the machine base and the air handling ducts of the machine tool of FIG. 1; 
     FIG. 6 is a simplified schematic plan view of the machine base emphasizing the collection ducts and main duct of the air handling system; 
     FIG. 7 is a sectional view taken along the line  7 — 7  of FIG. 6; 
     FIG. 8 is a partial view, like FIG. 7 but enlarged to better show the graduated ports; and 
     FIG. 9 is a partial sectional view of the area denoted by oval  9  in FIG. 6, showing the preferred form of connection between an inlet port aperture plate and the collection duct; and 
     FIG. 10 is an end elevation of the machine tool of FIG.  1 . 
     While the invention is susceptible of various modifications and alternative constructions, and certain illustrative embodiments thereof have been shown in the drawings which will be described below in detail, it should be understood that there is no intention to limit the invention to the specific forms disclosed. On the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention as defined by the appended claims. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and with specific reference to FIG. 1, a preferred embodiment of the present invention is generally depicted as embodied in machine tool  20 . By way of background machine tool  20  includes a laser source  22  which delivers a high power laser beam to a collimator  24 , which in turn directs a collimated laser beam  26  to first bending mirror  27  (see FIG.  2 ). The laser beam  26  is then directed to a second bending mirror  28  and then to cutting head  30  which includes a focusing optic  32  (See FIG. 1) which focuses the laser beam onto workpiece  34 . The laser beam  26  is projected through a nozzle  29  at the base of the cutting head along with a flow of assist gas, such as nitrogen or oxygen. The laser beam and assist gas interact with each other and with the metal to cut through the workpiece  34 . While an important use of laser cutting machines is the cutting of metal, it will be noted that other materials can be cut, and the invention is not limited to lasers for cutting metal. 
     Workpiece  34  in the preferred embodiment, is mounted on table or pallet  36  which is constructed for minimum interference with the laser beam, and to allow slag and scrap to readily fall through the table. The table or pallet  36  is preferably made up of a plurality of bars spanning the width of the table, and turned on edge so that their narrow cross-section is presented to the laser. The upper edge of each bar is serrated in large tooth-like fashion to support the workpiece at a plurality of points in bed-of-nails fashion. Such worktables are known in the laser cutting art, and will not be further described, except to note the feature that the scrap material generated during the cut will readily fall through the worktable. 
     The machine base  50  supports the operative elements discussed thus far, including the table  36  and the cutting head  30 , along with additional elements such as the slag collection bed, and a slag removal system. The machine base, as will be described in greater detail below, also provides the main duct work for the air handling system. Those familiar with machine tools will appreciate that the base must be strong, rigid and stable in order for a high performance machine as illustrated to perform within its close machining tolerance capabilities. 
     In providing for a strong and rigid base, the present invention uses a welded structure comprising interlocked box structures, joined by a plurality of rigid cross-members. FIG. 5 shows the base in plan view and FIG. 4 in elevation. As shown in end elevation in FIG. 3 the base is of U-shaped configuration, with a trough  51  underlying the worktable and cutting area, interposed between a pair of upstanding legs  53  at either side, which provide support, for example, for the ways  53   a  on which the bridge carrying the cutting head rides. 
     Thus, referring again to FIGS. 4 and 5, vertical plates  52  run in the lateral direction and are L-shaped with the foot  52   a  of the L underlying the trough  51 , and the ascender  52   b  of the L underlying the legs. These parts may, for convenience be referred to herein as the short lateral plates  52   a  and the taller lateral plates  52   b . Running longitudinally of the machine and intersecting the lateral plates  52  are longitudinal plates. Short longitudinal plates  57  are about the same height as the short lateral plates  52   a and attached to those plates, to form a supporting structure within the trough  53 . Taller longitudinally directed plates  58  are about the same height as the longer lateral plates  52   b  and define the sides of the legs  53 . 
     FIG. 4 shows the structure in elevation, and also shows top and bottom members for the box structure. More particularly, a top is formed by a longitudinally extending horizontal plate  60 , which establishes the level of the slag collection trough. The plate  60  establishes a cavity for receiving sheets of insulation  69 , preferably gypsum board, which in turn are covered by a slag collection plate  69   a , preferably comprised of a plurality of individual side-by-side sections spanning the bed from left to right, and affixed to the base and supported by the insulation  69 . A bottom plate  61  is attached to the foot of each of the upstanding plates. The legs  53  are closed at their tops by plate  53   b . Mounting pads  63  are rigidly affixed to the bottoms of certain of the box structure plates, as illustrated in FIG. 5, in order to provide a supporting structure for leveling feet  64  (FIG. 1) which engage the pads  63  and are adjusted for leveling of the machine. The base structure is a welded tab and slot construction. Thus, the vertical longitudinal plates  57 ,  58 , the vertical lateral plates  52 ,  54  and the horizontal plates  60 ,  61  have appropriate tabs  66  and slots  67  welded, for example at  68  (see FIG. 4 for an exemplary tab/slot/weld location) to provide the rigidified box structure. This strength and rigidity is provided without the weight penalty of a cast base. 
     In practicing the invention, the base structure just described is specially configured to provide the duct arrangement for the air handling system which removes fumes (sometimes referred to herein as contaminated air) from the cutting zone. Referring again to FIG. 5, it will be seen that the box structure of the machine base is arranged to provide a main duct  70  formed directly by the welded plates which make up the base. The main duct  70  is highlighted in FIG. 5 by symbols intended to represent fumes. The duct  70  connects collection ducts, to be described below, to a vacuum source or extraction system (not shown in FIG.  5 ). The duct  70  is T-shaped in configuration with arm sections  71 ,  72  and a stem section  73 . In cross-section the duct is a four-sided rectangular tube, with the bottom plate  61  (FIG. 4) making up the bottom of the duct, the top plate  60 , making up the top of the duct and vertical plates  52 ,  54  or  57  making up the duct sides. The box structure of the base is designed with selected boxes open in end-to-end fashion to create a continuous duct through the machine base. Thus there is no need for additional duct work within the machine, the passages for connection to the exhaust equipment are directly built into the base. The T-shaped configuration provides three connection points  74 ,  75  and  76  for air and dust extraction equipment. Other locations could be provided, if desired. It would not be useful, however, to provide one at the right hand end of the machine (as seen in FIG. 5) because that end is facing the loading station and must be kept clear for machine operator access, for bringing new work into the machine, old work out of the machine and for clearing slag and scrap. A cover for one of the duct sections,  74  is illustrated in FIG. 1, comprising a gasketed plate  78  which can be affixed in place over the unused duct outlets. Cover  79  encloses electrical connection points which are provided at each duct location for connection of dust collector blower electricals. Electrical conduits internal to the base for dust collector electricals are not shown. FIG. 1 shows a duct fitting  80  connected to the end duct  76  leading to remotely positioned dust collector  80   a  equipped with blower  80   b  and blower motor  80   c . These remotely positioned elements are sometimes referred to herein as the vacuum source. Electrical connections would be made through the corresponding electrical outlet. In the FIG. 1 configuration, covers would be in place over the duct work at outlets  74  and  75 . However, the three outlets are provided so that when the laser-equipped machine tool is installed in a particular plant, the user can select the location most convenient for that particular installation. It is also noted that FIG. 2 shows duct fittings connected at all three locations  74 ,  75  and  76 , simply to show all possibilities. It would not be necessary to use more than one for any given installation. 
     Referring to FIGS. 3 and 5, it will be seen that in addition to the main duct  70  built into the lower base section, the leg sections  53  also house a portion of the duct work. In this case collection ducts  82 ,  83  are built into the respective legs and have a plurality of apertures denoted by center lines  84 ,  85  which serve to connect the collection duct with the trough area  51  of the machine tool from which the fumes are to be collected. It will be appreciated that the fumes will be generated at and below the cutting nozzle  21  as the cutting head  30  traverses the workpiece from side to side and front to back. Most of the dust and gases will be concentrated below the workpiece, in the volume referred to as cutting zone  89  (FIG.  6 ). The horizontal plane of the cutting zone is best seen in FIG. 6, where  89   Y  identifies the approximate extent of the plane along the Y-axis, and 89 X  the approximate extent of the zone in the X-axis direction. FIG. 3 shows the third coordinate  89   Z  as existing between the slag collection base  75  and approximately the workpiece  34 . The volume  89  approximately identified by the three coordinates, is the area in which the highest concentration of fumes is expected to exist, and which must be removed during cutting. Some fumes, will rise above the workpiece, and the air flow paths to be described below will tend to carry them to the duct system. 
     FIG. 6 also illustrates the multiple levels of the air handling system according to the invention. The T-shaped duct  70  in the lower base is illustrated in double dash lines, and the collection ducts  82 ,  83  are illustrated in dashed lines. The center lines  84 ,  85  are shown spaced across the length of the collection ducts  82 ,  83 . Each center line represents a port through which air will be withdrawn from the cutting zone  89 , and it will be seen that they are spaced along the entire length of the cutting zone, on both sides thereof. 
     Referring in greater detail to the duct  82  in FIG. 3, it will be seen that the wall  82   a in which the ports are formed is one of the upstanding walls of the frame structure. The remaining walls  82   b ,  82   c ,  82   d  represent three sides of a fabricated duct welded or fixed in place. As shown in FIG. 6 the duct extends along the entire length of the cutting zone  89  but is positioned just outside the cutting zone in an area protected from the laser. In the region where the ducts  82  and  83  cross the main duct legs  72 ,  73 , the collection ducts are apertured as shown at  90 ,  91  so that the material drawn into the collection duct is then passed to the main duct  70  and to the exhaust and dust collection system. This system will be equally effective whether the exhaust system is connected to any of the selected ports  74 ,  75  or  76 , since the vacuum drawn by the extraction system, wherever connected, will be communicated through the openings  90 ,  91  into the collection ducts  82 ,  83  and thereby draw air through each of the ports connected to the collection duct. 
     In practicing one aspect of the invention, the ports through which the contaminated air is drawn into the collection ducts  82 ,  83  are configured to balance the flow across the entire length of the cutting zone. Alternatively, if a particular installation tends to do more or heavier cutting on one end of the machine than on the other, the machine could be configured to increase the air flows in that zone. 
     The manner in which that is accomplished is best illustrated in FIGS. 7 and 8 which show a longitudinal array of ports  95  of varying diameter and cross-sectional area configured to achieve substantially constant flow of air across the entire length of the machine. Apertures  91  show the connection of the duct section  71  with the collection duct  83 . It is seen that each port in the array of ports  95  is made up of two concentric apertures. In the preferred practice of the invention, the wall  58  which comprises a vertical member of the side wall has a plurality of apertures  94  formed therein, preferably all of the same size, and preferably larger than the largest port. The ports are then sized by means of removable port plates, two of which are shown in FIG. 7 at  98 , and  99 . Each of the port plates has a pattern of holes formed therein to fit over the larger apertures  94  to define a smaller port by means of its smaller aperture size. The apertures in the plates  98  &amp;  99  are configured so that the apertures nearest the main duct entrance, i.e. apertures  97  have the smallest diameter, and the apertures at the greatest distance therefrom, i.e. apertures  96  have the largest diameter. The vacuum pressure within duct  83  will vary due to the distance from connection  91  and due to increasing volume of air flow along the length of duct  83 , with the minimum volume flow near the ends and the maximum volume flow at the center. The larger port size at increasing distance from the main duct maintains a substantially equal flow from port to port across the length of the duct, thereby to achieve substantially constant withdrawal flow across the length of the cutting zone. As noted above, however, if something other than an even withdrawal flow were required, it would be a simple matter to configure the ports with an array of port sizes needed to achieve that end. For the configuration requiring even flow across the machine, one example of the machine has been configured with the nearest ports  97  being approximately 20 mm in diameter whereas the farthest ports  96  have a diameter of about 50 mm, and intermediate ports are graduated in size therebetween. 
     FIGS. 8 and 9 illustrate the manner in which a ported plate is fitted to the side wall of the machine to tailor the port size to that desired for a particular installation. FIG. 9 shows the upstanding base member  58  and the duct  83  formed by sides  83   a - 83   d . The larger apertures  94  formed in the wall  58 , preferably of equal size, are illustrated, as well as a port plate  98  having smaller port sizes  96 ,  96   a , to restrict the size of the opening through which air is drawn. The plate  98  is fixed in place with the ports overlying the apertures  94 . Conveniently a plurality of clips  100  (only one is shown in FIG. 9) is utilized which allow the plate  98  to be roughly positioned with the clips  100  inside associated apertures  96 , then slid to the right until the clips seat as shown in FIG. 9, automatically aligning all of the ports with all of the apertures. Other means of affixation can be utilized, but suffer from the complexities of requiring threaded openings or other fasteners. The simple solution provided by the clipped in place adjustable ports will now be apparent. 
     In further practice of the invention, cooperating with the duct and port arrangement described thus far, means are also associated with the machine tool for controlling the entrance of air into the machine, so as to render controllable the collection and exhaust of contaminated air and to provide a more effective and efficient system. In accordance with the invention, means are provided for both controlling the amount of air which enters the machine and also the direction from which it enters, so as to maximize flow of fumes to the exhaust and filter system. From an examination of FIGS. 1,  2  and  10 , it will be apparent that the entire cutting zone of the machine is enclosed. Upstanding walls  110 ,  111  close the front and back sides of the machine. Upstanding walls  112  with access doors close the end near laser  22 . A roof  113  encloses the top. Upstanding walls  114  with an access door enclose the end near the load station. The trough  51  (FIG. 3) area near the load station is also closed by a metallic gate  115  (FIG. 10) except for a rectangular opening  116  providing for entrance and removal of the work support pallet. For convenience of operation, doors  118  which make up the walls  110 ,  111  can be arranged on sliding tracks in bypass fashion so that some or all of the doors can be opened for access to the machine, such as during maintenance. However, during the cutting operation, it is expected that all of the doors will be closed. A flow of make up air into the enclosure is necessary to replace that removed to remove fumes. The primary path for make up air is through pallet passageway opening  116 . The opening is at the level of the pallet, and therefore the flow will be directly to the pallet. Due to the suction created in the cutting zone below the workpiece, the primary flow will be beneath the workpiece, where the gases, dust and fumes are projected during the cut. The opening spans the width of the workpiece, but is limited in height, so that the curtain of air, which is the primary volume of makeup air into the system, flows right into the cutting zone and through the graduated ports into the collection duct of the exhaust system, carrying with it the fumes created during the cut. 
     Formed in the roof  113  are a plurality of air inlets  120  which allow air flow into the cutting area from the top of the enclosure. The air inlets  120  are located at about the periphery of the cutting zone  89 , so that the air flow will be through the vents, downwardly onto or past the workpiece and to the collection ducts  82 ,  83 . The vents  120  provide for a continuous but limited amount of air flow through the air space at the top of the enclosure above the workpiece, and into the cutting zone for exhaust. Providing these air flow paths in the upper part of the housing avoids the creation of air pockets in the housing which might otherwise collect fumes. The provision of vents spaced along the roof with some air stirring obtained when the bridge traverses back and forth prevents the collection of pockets of fumes in the upper portion of the housing, while the main flow through the large inlet vent  116  supplies the primary flow through the collection zone for pickup of contaminants created during the cut. It will be noted that when “vents” is used herein, unless the context indicates otherwise, its is intended to be generic to include all inlets of controlled size, in the illustrated embodiment primarily the inlets  120  and the opening  116 . 
     Positioning the air inlets  120  where shown, and the air flow through pallet passageway  116  at the loading end of the machine creates a very even air flow through the system capable of efficiently withdrawing fumes from the cutting operation. The air inlets  120  are provided with air flow paths such that there is no direct escape path for reflected laser beam energy. 
     The pattern of air flow will be best appreciated with reference to FIGS. 3,  7  and  10 . The main air flow enters from the slot  116  at the loading end of the machine. Thus the main air flow enters at about the level of the workpiece and is drawn below the workpiece by the suction through the ports leading to the collection ducts  82 ,  83 . In order to prevent the accumulation of fumes in the upper portion of the enclosure above the workpiece, the circulating air flow through the vents  120  flows down past the edges of the workpiece, and in some cases through cutouts in the middle of the workpiece, to also enter the exhaust system. A certain amount of mixing is also achieved by virtue of the traverse of the bridge and the cutting head across the machine as parts are cut. The blower in the dust collection system is set so that the air velocity in the collection zone is high enough to remove the fumes but low enough so that the particulates settle out onto the slag bed rather than being pulled into the vacuum system. This tends to reduce the demands on air handling volume, and also importantly prevents the duct work from clogging with particles which might fall out of the air stream in particular locations. The dust is intended to be left for clean up with the slag, with the air handling system primarily withdrawing the fumes and the smaller particles carried along with them. 
     Air flow into the collection ducts  82 ,  83  is substantially uniform, and continues in the ducts  82 ,  83 , thereof to the central portion of the duct where it descends through the apertures  90 ,  91  into the main duct  70  in the sub-base. Depending on the location of the exhaust equipment, the air flow will then be through the main duct to the external blower and extraction equipment. 
     In view of the foregoing, it will now be appreciated that what has been provided is an improved air handling system for a laser-equipped machine tool. The system has the main duct work elements built into the base such that it is not at risk of being damaged by a high power laser beam. The main duct, positioned in the sub-base, has plural exits for connection of the extraction equipment. Any of the plural connection points can be selected. The collection ducts span the length of the cutting area and have a plurality of ports facing the cutting zone. The ports are of graduated size so that the air flow into the collection duct is tailored. Cooperating with the extraction portion of the air handling equipment, the machine is enclosed and air inlets through associated vents are provided to control both the direction and quantity of air which enters the machine to tailor it to the requirements of efficient fume extraction.