Method and machining tool for cutting workpieces and associated computer program product

A method cuts a, in particular flat, workpiece by a cutting beam and a cutting fluid. A workpiece part to be cut away is consecutively cut into at least two smaller portions which fall or are lowered downwards from a surrounding remaining workpiece after they have each been cut away. The division into smaller portions and the execution of the cut for separating the first smaller portion occur such that the point at which the first-cut, first smaller portion is cut away lies within the outer contour of the workpiece part to be cut away.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a method and a machining tool for cutting an in particular plate-like workpiece by means of a cutting beam and a cutting fluid, wherein a workpiece part to be cut away is successively cut into at least two smaller part portions which fall or are lowered downwards from a surrounding remaining workpiece after they have each been cut away, and also to an associated computer program product. The part portions are cut away at a cutaway point at which the respective separating cut of the part portion is completed into a closed contour. The cutting beam and the cutting fluid, for example in water jet cutting, may be identical i.e. formed by the same medium.

When cutting in particular plate-like and metallic workpieces by means of a cutting beam, e.g. by means of a plasma jet, laser beam and/or water jet, small waste parts (offcuts) occur which are usually discharged from the machining region of the cutting tool by free fall. Depending on the thickness of the workpiece and the geometry of the waste part, such a part may however tilt or seize or catch in the remaining workpiece while it is being cut away. These parts can cause collisions with the cutting head and hinder later automated removal of the remaining workpiece from the machine.

It is known from the prior art, for example JPH 10244394 A or WO 2015/080179 A1, in order to improve the process reliability in cutting and discharging workpiece parts, to divide the workpiece part into smaller part portions which can drop safely down after being cut away. JPH 10244394 A discloses, in a U-shaped workpiece part, firstly cutting away the two side legs and then the connecting piece. US 2013/0200051 A discloses chopping up offcuts into a spiral form.

SUMMARY OF THE INVENTION

In comparison, the object of the present invention is to further improve the process reliability when cutting, by means of a cutting beam, workpiece parts which are discharged from the cutting region by free fall after being cut away.

This object is achieved according to the invention in that the division into the part portions and the execution of the cut for separating the first part portion take place such that the cutaway point of the first-cut, first part portion lies inside the outer contour of the workpiece part to be cut away.

According to the invention therefore, the cutaway point of the first part portion does not lie on the outer contour of the workpiece part to be cut away, and is therefore closer to the center of gravity of the first workpiece part. At the moment of cutting away, the tilt moment acting on the first part portion because of the pressure of the cutting fluid (gas pressure, water pressure) is reduced in comparison with a cutaway point on the outer contour of the workpiece part. This leads to a reduced, or in the best case no tilt movement of the first part portion which can thus fall out of the remaining workpiece significantly more reliably. In a second step then, the second part portion is cut away from the remaining workpiece and, since it is largely no longer surrounded by material but lies freely inside the opening in the remaining workpiece which was formed in the first step, falls safely down out of the remaining workpiece. The division of the part portions and the execution of the cut allow the first part portion to be cut away at an optimal cutaway point and thus drop from the remaining workpiece without tilting.

Preferably, the workpiece part to be cut away is divided by area into a larger first part portion and a smaller second part portion. The larger the first part portion, the closer the center of gravity of the first part portion lies to the overall center of gravity of the workpiece part, which increases the process reliability. For example, the workpiece part to be cut away can be divided into a first part portion and a second part portion which is surrounded on three sides by the first part portion. In this case, the second part portion extends as a web into the first part portion.

The second part portion must be selected sufficiently large that the heat introduced into the second part portion during cutting the first part portion can be dissipated to the remaining workpiece. If the width of the second part portion transversely to the heat flow direction is selected too small, the heat cannot be dissipated sufficiently quickly, and a thermal distortion of the second part portion and a seizing of the first to the second part portion may occur. Advantageously therefore, the division into part portions and the execution of the cut for separating the first part portion take place such that the width of the second part portion is at least as large as the thickness of the workpiece.

In order to ensure that only a minimal tilt moment acts on the first part portion because of the cutting fluid pressure at the time of cutting away, the division into the part portions and the execution of the cut for separating the first part portion take place particularly preferably such that the cutaway point of the first part portion lies in a radius about the center of gravity of the first part portion, wherein the circle area delimited by the radius takes up less than ⅓ of the area of the first part portion. Preferably, the cutaway point of the first part portion lies in the center of gravity of the workpiece part to be cut away, in the center of gravity of the first part portion or in the region between these two centers of gravity.

The geometry of the second part portion is established such that it constitutes as small as possible a risk of tilting of the first part portion after it has been cut away. For this, the geometry of the second part portion may be selected such that its cross-section or the distance of the mutually opposing side edges from the cutaway point of the first part portion to the cutaway point of the second part portion is increased. Thus the second part portion has side edges running inward towards one another from the outer contour of the workpiece part, giving a conical shape of the second part portion. Further preferably, the shape of the second part region is symmetrical, and in particular the outer contour of the second part region does not have any right angles at the corners but is chamfered or rounded at the corners.

In order to effectively prevent a tilting of the first part portion on the second, preferably the separating cut between the first and second part portions is made without angular corners, but with chamfered or rounded corners.

In a refinement of the invention, the separating cut between the first and second part portions is made obliquely such that the lower edge of the first part portion protrudes further outward than the upper edge, i.e. for example mutually facing side edges of the second part portion have a downwardly tapering conical form. This facilitates the downward fall of the first part portion and is possible if the machining tool allows an oblique setting of the machining head so that cut edges can be produced which slope relative to the workpiece surface.

To improve the edge quality on cutting the second part portion, when the first part portion is cut away, a partial separating can already be made between the second part portion and the remaining workpiece, so the connecting contour between the second part portion and the remaining workpiece is already started.

In particular if the center of gravity of the workpiece part to be cut away lies outside the workpiece part, the workpiece part may be subdivided into several segments to be cut successively, wherein at least one segment is divided into at least two part portions as described above, which are cut successively. The segments here are selected such that their center of gravity lies inside the contour of the respective segment. It is also possible to divide all segments into at least two part portions.

The invention also relates to a machining tool suitable for performing the method according to the invention, with a cutting beam (jet-like tool) and a cutting fluid, with a machining head which can be moved relative to the workpiece and from which the cutting beam and cutting fluid emerge, and with a machine controller which is programmed to control the relative movement between the machining head and the workpiece according to the method described above. In a water jet cutting machine, the cutting fluid simultaneously forms the cutting jet, i.e. the cutting jet and cutting fluid are identical.

The invention finally relates to a computer program product having coding means which are adapted for performing all steps of the method described above when the program runs on a machine controller of a machining tool.

Further advantages and advantageous embodiments of the subject of the invention arise from the description, the claims and the drawing. Also, the features mentioned above and those presented below may be used alone or grouped in arbitrary combinations. The embodiments shown and described should not be regarded as a comprehensive list, but rather have an exemplary character for the illustration of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG.1shows in perspective a machining tool with a beam-shaped tool, using the example of a laser machining tool1. Further exemplary embodiments of such machining tools are a combined punching/laser cutting machine, a plasma cutting machine or a water jet cutting machine. The laser machining tool1for example comprises a CO2laser, a diode laser or a solid state laser as a laser beam generator2, a movable machining head3and a workpiece support4. The laser beam generator2generates a laser beam5which is guided from the laser beam generator2to the machining head3by means of an optical fiber cable (not shown) or deflecting mirrors (not shown). A workpiece6in the form of a plate is arranged on the workpiece support4. The laser beam5is directed onto the workpiece6by means of a focusing optic arranged in the machining head3.

The laser machining tool1is furthermore supplied with cutting gases7, for example oxygen and nitrogen. Alternatively or additionally, compressed air or application-specific gases, such as e.g. inert gases, may be provided. The cutting gas7is conducted to a cutting gas nozzle8of the machining head3, from which it emerges together with the laser beam5in the direction of the workpiece6. The laser machining tool1furthermore comprises a machine controller9which is programmed to move the machining head3and its cutting gas nozzle8relative to the workpiece6following a cutting contour.

Instead of moving the machining head3relative to the stationary workpiece6, the workpiece6may also be moved relative to a stationary machining head3. It is also possible to superpose a movement of the machining head3and a movement of the workpiece6.

A laser cutting process for cutting a workpiece part10away from the workpiece6is described below with reference toFIG.2, wherein the workpiece part10to be cut away constitutes a waste part (an offcut) and is cut successively along a separating cut23(FIG.3) into two smaller part portions11,12which, after being cut away, drop downward from the surrounding remaining workpiece13. The part portions11,12are each cut away at a cutaway point at which the cutting contour of the part portion, i.e. the respective separating cut23, is completed into a closed contour. The cutaway point of the first part portion11is marked14inFIG.2.

The division into the part portions11,12and the execution of the cut for separating the first part portion11are selected such that the cutaway point14of the first-cut, first part portion11lies inside the outer contour15of the workpiece part10to be cut away, i.e. not on the outer contour15. Preferably, the first part portion11is larger in area than the second part portion12and surrounds the second part portion12on three sides. As shown as an example inFIG.2, the first part portion11may be approximately U-shaped, and the second part portion12approximately rectangular.

In the first method step, the first part portion11is cut away and drops out of the surrounding remaining workpiece12,13. At the moment of cutting away, i.e. at the cutaway point14, the tilt moment acting on the first part portion11because of the pressure of the cutting gas7is reduced in comparison with a cutaway point which lies on the outer contour15. This leads to a reduced, or in the best case no tilt movement of the first part portion11, which can therefore fall away from the surrounding remaining part portion12,13more reliably or without tilting. The second part portion (“macro joint”)12initially remains connected to the surrounding remaining workpiece13. In a second method step, the second part portion12is then cut away from the remaining workpiece13and, since it is largely no longer surrounded by material but lies freely inside the opening formed in the remaining workpiece13in the first method step, falls down from the remaining workpiece13reliably and without tilting.

To ensure that at the time of cutting away, as far as possible no tilt moment or only a negligible tilt moment acts on the first part portion11because of the effect of the cutting gas pressure, the cutaway point14of the first part portion11lies as far as possible in a radius R around the center of gravity16of the first part portion11, wherein the circle area17delimited by the radius R amounts to less than ⅓, preferably less than ⅕ of the total area of the first part portion11. Preferably, the cutaway point14of the first part portion11lies in the center of gravity18of the workpiece part10to be cut away, in the center of gravity16of the first part portion11, or in the region between these two centers of gravity16,18.

As shown further inFIG.2, the second part portion11is preferably symmetrical to a line19running through the centers of gravity16,18of the workpiece part10to be cut away and the first part portion11.

The second part portion12must be selected sufficiently large that the heat introduced into the second part portion12on cutting of the first part portion11can be dissipated to the remaining workpiece13. Also, the second part portion12must be selected so wide that, until the first part portion11is completely cut away, it can absorb the weight of the workpiece part10and the cutting gas pressure without any significant bending of the second part portion12. Therefore the width B of the second part portion12should be at least as large as the thickness D (FIG.4) of the workpiece6.

InFIG.2, a cutting gas nozzle8is used from which the cutting gas7emerges coaxially to the laser beam5in the direction of the workpiece6, i.e. at the time of cutting away the first part portion4, the contact point20at which the cutting gas7meets the first part portion11lies in the cutaway point14.

If however the cutting gas7meets the workpiece6eccentrically to the laser beam5, at the time of cutting away the first part portion11, either the cutting gas7meets the workpiece6outside the first part portion11or, if this is not possible, the cutaway point14of the first part portion11lies if possible in the region between the center of gravity16of the first part portion11and the contact point20.

FIG.3shows an advantageous execution of the cut for cutting away the first part portion11from the second part portion12and from the remaining workpiece13. The piercing point occurs at21, close to the cutaway point14for the first part portion11, and the cutting line (starting cut)22then runs to the cutaway point14at the tip of the second part portion12before then the closed separating cut23of the first part portion11is executed and again ends at the cutaway point14. If a part is produced without starting cut, the piercing point lies on the closed separating cut23of the first part portion11. To improve the edge quality when cutting away the second part portion12, during cutting of the first part portion11, a partial separating cut24may be made between the second part portion12and the remaining workpiece13. The laser beam5, starting at 25, moves slightly along the connecting contour between the second part portion12and the remaining workpiece13, is switched off at the turning point26and switched on again at the point25in order to cut the contour of the first part portion11to the end. The later separation of the second part portion12can take place with improved quality at the cut edge.

The geometry of the second part portion12is established such that this constitutes a small as possible a risk of tilting of the cutaway first part portion11. As shown inFIG.4, the separating cut27between the first and the second part portions11,12is ideally executed obliquely such that the lower edge28aof the first part portion11protrudes further into the second part portion12than the upper edge28b. In this way, the first part portion11has edges29which slope with respect to the second part portion12and do not hinder the dropping of the first part portion11.

As also shown inFIGS.2and3, the separating cut23between the first and the second part portions11,12may be executed not with angular corners but with chamfered or rounded corners30, in order thus to effectively prevent tilting of the first part portion on the second.

As shown inFIG.5, alternatively or additionally to the oblique edges29, the division into the part portions11,12may take place such that the second part portion12has two side edges29a,29brunning towards one another from the outer contour15of the workpiece part10to the cutaway point14of the first part portion11. The side edges29a,29b, which do not run parallel to one another, also counter any tilting of the first part portion on the second.

In particular for the case in which, as inFIG.6, the center of gravity18of the workpiece part10to be cut away lies outside the workpiece part10, the workpiece part10is subdivided into several segments31a-31cto be cut successively, which in turn—as described above—may each be divided into two part portions11a,12b,11b,12band11c,12c, which—as described above—are then cut successively. The workpiece part10must be subdivided into smaller segments until the cutaway point14of the first part portion11a,11b,11cin each segment lies inside the outer contour of the respective segment. InFIG.5, firstly segment31aand then segment31band finally segment31care cut.

If the second part portion12aof a first segment31a(as shown inFIG.7) is attached to an adjacent second segment31bwhich should also drop down, there is no need for distinct separation of the second part portion12a. The second part portion12aof the first segment31athus becomes part of the first part portion11bof the second segment31b. Thus the productivity of the cutting process may be increased.