LASER CUTTING METHOD

Abstract

The present invention concerns a laser cutting method, the method comprising the steps of providing a workpiece of a metallic workpiece material, directing a laser beam onto a surface of the workpiece and moving the laser beam relative to the metal workpiece to create a laser cut. According to an aspect of the invention, a supplemental material is provided at the position of incidence. In this, the supplemental material is capable of reducing the melting temperature of the workpiece material when combined with the workpiece material. For example, the workpiece material and the supplemental material may together form a eutectic system.

Claims

1-16. (canceled)

17. A laser cutting method, the method comprising the steps of: Providing a workpiece of a metallic workpiece material, and Directing a laser beam onto a surface of the workpiece to locally make the workpiece material flowable at a position of incidence, and moving the laser beam relative to the metal workpiece to create a laser cut, the method comprising the further step of Providing a supplemental material at the position of incidence, the supplemental material capable of reducing a melting temperature of the workpiece material when combined with the workpiece material; Determining a required laser energy input per surface area to be made flowable or per cut length for the given workpiece without the supplemental material, Calculating a reduced required laser energy input using information on the supplemental material as a input and applying the reduced required laser energy input, characterized in that the step of providing the supplemental material comprises providing at least a portion of the supplemental material as a gas supplied to the position of incidence.

18. The method according to claim 1, further comprising directing a gas jet onto the position of incidence.

19. The method according to claim 1, wherein the step of providing the supplemental material further comprises providing a portion of the supplemental material as a coating of the workpiece material, the coating being applied prior to the step of directing the laser beam onto the surface.

20. The method according to claim 3, wherein the coating has a higher absorptivity for the laser radiation than a surface of the workpiece material.

21. The method according to claim 3, wherein the coating covers a surface of the workpiece material facing a direction from which the laser beam is incident.

22. The method according to claim 3, wherein applying the coating comprises applying the coating selectively only at positions where subsequently the laser cut is created.

23. The method according to claim 1, wherein the supplemental material contains elemental carbon.

24. The method according to claim 1, wherein the workpiece material and the supplemental material together form part in a eutectic system.

25. The method according to claim 1, wherein the workpiece material is steel.

26. The method according to claim 1, wherein the workpiece is plate-shaped, and the laser beam perpendicular is perpendicular to a plate surface of the workpiece.

27. The method according to claim 1, wherein at the position of incidence, a heterogeneous mixture of molten material that includes the workpiece material and the supplemental material, and of solid particles is created removed to create the cut.

28. A laser cutting machine system, the laser cutting machine comprising a laser cutting head for emitting the laser beam (A) and for emitting a gas jet comprising a cutting gas and a supplemental material, a moving mechanism for moving the laser cutting head relative to the workpiece for creating the laser cut, a cutting gas container for storing the cutting gas, and a supplemental gas container for storing the supplemental material, the machine being programmed for a property of the supplemental material being input as supplemental material parameter and for adapting the laser energy input on the workpiece based on the supplemental material parameter, the laser cutting machine system being comprising a laser cutting machine controlling software or laser cutting preparation software, which software is configured to calculate a required laser energy input per surface area to be made flowable or per cut length for the given workpiece without the supplemental material, and to calculate a reduced required laser energy input using information on the supplemental material as a input, the laser cutting machine system being configured to apply the reduced required laser energy input, the laser cutting machine being quipped to carry out the method according to any one of the previous claims.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Hereinafter, embodiments of the present invention are described in more detail referring to drawings. The drawings are schematic and not to scale. In the drawings, same reference numbers refer to same or similar components. They show:

[0031] FIG. 1: A generic phase diagram of a eutectic system;

[0032] FIG. 2 A laser cutting machine;

[0033] FIG. 3: A laser cutting head and a workpiece in an embodiment of the first group;

[0034] FIG. 4: A laser cutting head and a workpiece in an embodiment of the second group; and

[0035] FIG. 5 A phase diagram of the iron-carbon system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] FIG. 1 depicts a schematic phase diagram of a metallic binary eutectic system of the components A and B of which both or one may be metallic. The eutectic point 101 defines a eutectic composition (defined ratio between A and B) and a melting point of the eutectic composition, and defines a solidus line 102 corresponding to the melting point of the eutectic composition. At temperatures below this solidus line temperature, the system will form solid mixtures of A and the eutectic (A+e) or of B and the eutectic (B+e) if the composition deviates from the eutectic composition. Above the solidus line, but below the respective liquidus line 103, 104, the system if deviating from the eutectic composition will form supersaturated solutions, namely a melt plus solid A (m+A), or a melt plus solid B (m+B), respectively, whereas above the respective liquidus line 103, 104 the system will just form a melt (unsaturated solution).

[0037] From this diagram it becomes clear that for compositions deviating from pure or nearly pure A or B, it is sufficient to heat to the solidus temperature (temperature defined by the solidus line 102 corresponding to the melting point of the eutectic) to melt or partially melt the composition and thereby make the composition capable of flowing (flowable).

[0038] FIG. 2 shows an example of a laser cutting machine 1. The machine comprise a laser radiation source 2, a radiation guide 3, a laser cutting head 4, and a laser head 4 moving mechanism comprising a frame 5 relative to which the laser cutting head 4 is movable, relative to a working table (not shown) supporting the workpiece 7, in x direction and which itself is movable, for example on a pair or rails 6, in y direction. Other configurations with movable laser heads (“flying optics” configurations) and/or with a movable workpiece are possible and known in the art.

[0039] A common cutting gas such as N.sub.2 is stocked in a gas container 12 and is fed via a gas line 13 to the cutting head 4. The cutting head 4 directs a focused laser beam A onto the workpiece 7 to generate, when the laser head is moved relative to the workpiece 7 a cut therein. In addition to the laser beam, the cutting head will also direct a gas jet (not shown in FIG. 2) onto the workpiece. The gas jet in a laser cutting process may have several functions. Firstly, it blows away any molten material in the cut. Secondly, by the gas composition being well-known it ensures reproducible conditions. The most commonly used gas jet is a gas jet of N.sub.2. Alternatively, gas jets containing molecular oxygen for a burning process in the workpiece are also common.

[0040] FIG. 3 illustrates the method according to the first group of embodiments. The workpiece 7 in addition to the workpiece material 20 is provided with a coating 21 of a coating material. The coating material contains, and for example even consists of, a supplemental material. The material of the workpiece 7 and the supplemental material together form part of a two or more component eutectic system, such as of the iron-carbon system the Cu—Sn system, the Cu—Zn system or any other suitable system. The laser head emits, in addition to the laser beam 10, a gas jet 11 of for example a common cutting gas such as N.sub.2. The laser beam will initiate a melting and mixing process, initially at the interface between the workpiece material 20 and the coating 21, whereby the temperature at which the material becomes flowable (by at least a portion thereof being molten) is reduced to the melting temperature of the eutectic or near eutectic. This will result in a cut through the material at an energy input that is reduced compared to the prior art.

[0041] In this, the coating material may be applied to the workpiece only locally at the cutting line, e.g. by printing. The coating material may alternatively be applied to the whole surface of a workpiece by plotting or in form of a foil, e.g. from a coil 15 (FIG. 2), covering the surface of the workpiece.

[0042] For example if the coating material is a foil, for example containing carbon, it may be applied to the workpieces (especially metal sheets) when they are being moved into the cutting machine or even before e.g. after production of the workpiece and before the workpiece is fed into the laser cutting machine.

[0043] FIG. 4 illustrates the method according to the second group of embodiments. The workpiece 7 does not necessarily comprise a coating but instead the gas jet comprises a supplemental material capable of forming a eutectic system together with the workpiece material 20. For example if the workpiece material is steel, the gas jet may comprise carbon dioxide as the supplemental material which may be delivered from a gas container 14 (FIG. 2).

[0044] In both groups of embodiments, the sequence of method steps may be summarized as follows: A metallic workpiece and a supplemental material are provided. Also, the laser cutting machine may be appropriately programmed. In embodiments in which the supplemental material is provided as a coating, the coating is applied to the workpiece material. The laser beam is then, in presence of the supplemental material, directed onto a surface of the workpiece to locally make the workpiece material flowable where the laser beam impinges on the workpiece. A gas jet—which in embodiments of the second group may contain the supplemental material or a portion thereof—is used to blow away flowable material. During these steps of using the laser beam to locally make material flowable and blowing flowable material away, the laser beam is moved relative to the workpiece to generate a laser cut.

[0045] FIG. 5 is an excerpt of the online encyclopedia Wikipedia (https://en.wikipedia.org/wiki/File:Iron_carbon_phase_diagram.svg, retrieved on 11 Mar. 2019) and reproduces the phase diagram of the iron-carbon-system. It becomes clear that at a carbon content of 4.3% a eutectic is formed, having a melting point of 1147° C., compared to 1536° C. of iron. Hence, adding a sufficient amount of carbon—by way of a coating or stemming from a gas—will lead to a substantial reduction of the temperature required for making the iron-based. Steel-based workpiece materials will generally already include some elemental carbon (and may for example comprise other alloy components). Thus, the amount of carbon needed for the flowable phase at a temperature above 1147° C. and a carbon content above 2.06% to exist may depend on the circumstances.

[0046] In FIG. 5, the dashed line shows the stable Fe/Carbon phase.