METHOD AND SYSTEM FOR HEATING USING AN ENERGY BEAM

Abstract

A method of heating a selected portion of an object includes the steps of projecting an energy beam onto a surface of the object and repetitively scanning the beam in accordance with a scanning pattern so as to establish an effective spot on the surface, and displacing the effective spot along a track to progressively heat a selected portion of the object. The selected portion has a first width at a first position along the track and a second width at a second position along the track. The second width is less than 75% of the first width.

The scanning pattern is repeated with a first frequency in correspondence with the first position and with a second frequency in correspondence with the second position, the second frequency being more than 60% and less than 140% of the first frequency.

Claims

1. A method of heating at least one selected portion of an object, the method including the following steps: projecting an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the energy beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, and displacing the effective spot along a track on the surface of the object to progressively heat a selected portion of the object; wherein the selected portion has a first width at a first position along the track, and a second width at a second position along the track; wherein the energy beam is scanned in accordance with the scanning pattern so that the scanning pattern is repeated by the energy beam with a first frequency in correspondence with the first position along the track, and with a second frequency in correspondence with the second position along the track, and wherein both of the first frequency and the second frequency are larger than 10 Hz, wherein the second width is less than 75% of the first width, and wherein the second frequency is more than 60% of the first frequency and less than 140% of the first frequency.

2. The method according to claim 1, wherein the second width is less than 60% of the first width.

3. The method according to claim 1, wherein the second frequency is more than 70% of the first frequency.

4. The method according to claim 1, wherein the second frequency is less than 130% of the first frequency.

5. The method according to claim 1, wherein the average velocity of the primary spot along the scanning pattern is substantially higher when the effective spot is at the first position along the track than when the effective spot is at the second position along the track.

6. The method according to claim 5, wherein the average velocity of the primary spot along the scanning pattern is at least 10% higher when the effective spot is at the first position along the track than when the effective spot is at the second position along the track.

7. The method according to claim 6, wherein the average velocity of the primary spot along the scanning pattern is at least 20% higher, when the effective spot is at the first position along the track than when the effective spot is at the second position along the track.

8. The method according to claim 1, wherein the effective spot features a first radiation energy flow onto the surface of the object in correspondence with the first position along the track, and a second radiation energy flow onto the surface of the object in correspondence with the second position along the track, the second radiation energy flow being not more than 110% of the first radiation energy flow, and not less than 90% of the first radiation energy flow.

9. The method according to claim 1, wherein both of the first frequency and the second frequency are larger than 25 Hz and smaller than 150 Hz.

10. The method according to claim 1, wherein adaptation of the two-dimensional energy distribution of the effective spot includes adapting the two-dimensional energy distribution by modifying the width of the effective spot by adapting the scanning pattern, and adapting the average velocity with which the primary spot moves along the scanning pattern.

11. The method according to claim 1, wherein the energy beam has a first average power in correspondence with the first position along the track, and a second average power in correspondence with the second position along the track, the second average power being at least 10% smaller than the first average power.

12. The method according to claim 1, wherein the effective spot is displaced along the track with a first velocity in correspondence with the first position along the track, and with a second velocity in correspondence with the second position along the track, the second velocity being different from the first velocity.

13. The method according to claim 1, wherein the effective spot has a length in the direction parallel with the track that is smaller in correspondence with the first position than in correspondence with the second position.

14. The method according to claim 8, wherein the effective spot is displaced along the track with a first velocity in correspondence with the first position along the track, and with a second velocity in correspondence with the second position along the track, the second velocity being different from the first velocity.

15. The method according to claim 14, wherein the second velocity is higher than the first velocity, and wherein the energy beam has a first average power in correspondence with the first position along the track, and a second average power in correspondence with the second position along the track, the second average power being substantially identical to the first average bean power.

16. The method according to claim 14, wherein the second velocity is lower than the first velocity, and wherein the energy beam has a first average power in correspondence with the first position along the track, and a second average power in correspondence with the second position along the track, the second average power being at least 10% smaller than the first average power.

17. The method according to claim 8, wherein the effective spot has a length in the direction parallel with the track that is smaller in correspondence with the first position along the track than in correspondence with the second position along the track.

18. The method according to claim 17, wherein the effective spot is displaced along the track with a first velocity in correspondence with the first position along the track, and with a second velocity in correspondence with the second position along the track, wherein the second velocity is higher than the first velocity.

19. A method of heating at least one selected portion of an object, the method including the following steps: projecting an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, and displacing the effective spot along a track on the surface of the object to progressively heat a selected portion of the object; wherein the selected portion has a first width at a first position along the track, and a second width at a second position along the track, the first width being larger than the second width; wherein the energy beam is scanned in accordance with the scanning pattern so that the scanning pattern is repeated by the energy beam with a first frequency in correspondence with the first position along the track, and with a second frequency in correspondence with the second position along the track, and wherein both of the first frequency and the second frequency are larger than 10 Hz, wherein the energy beam has a first average power in correspondence with the first position along the track, and a second average power in correspondence with the second position along the track, the second average power being smaller than the first average power.

20. A method of heating at least one selected portion of an object, the method including the following steps: projecting an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the energy beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, and displacing the effective spot along a track on the surface of the object to progressively heat a selected portion of the object; wherein the selected portion has a first width at a first position along the track, and a second width at a second position along the track, the first width being larger than the second width; wherein the energy beam is scanned in accordance with the scanning pattern so that the scanning pattern is repeated by the energy beam with a first frequency in correspondence with the first position along the track, and with a second frequency in correspondence with the second position along the track, and wherein both of the first frequency and the second frequency are larger than 10 Hz, wherein the effective spot is displaced along the track with a first velocity in correspondence with the first position along the track, and with a second velocity in correspondence with the second position along the track, the second velocity being different from the first velocity.

21. A method of heating at least one selected portion of an object, the method including the following steps: projecting an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the energy beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, and displacing the effective spot along a track on the surface of the object to progressively heat a selected portion of the object; wherein the selected portion has a first width at a first position along the track, and a second width at a second position along the track, the first width being larger than the second width; wherein the energy beam is scanned in accordance with the scanning pattern so that the scanning pattern is repeated by the energy beam with a first frequency in correspondence with the first position along the track, and with a second frequency in correspondence with the second position along the track, and wherein both of the first frequency and the second frequency are larger than 10 Hz, wherein the effective spot has a length in the direction parallel with the track that is smaller in correspondence with the first position than in correspondence with the second position.

22. The method according to claim 19, wherein the effective spot features a first radiation energy flow onto the surface of the object in correspondence with the first position along the track, and a second radiation energy flow onto the surface of the object in correspondence with the second position along the track, the second radiation energy flow being not more than 140% of the first radiation energy flow, and not less than 60% of the first radiation energy flow.

23. The method according to claim 22, wherein the first scanning pattern represents a third radiation energy flow defined as the energy supplied by the energy beam during one sweep along the first scanning pattern divided by the surface area swept by the primary spot during that one sweep along the first scanning pattern, and wherein the second scanning pattern represents a fourth radiation energy flow defined as the energy supplied by the energy beam during one sweep along the second scanning pattern divided by the surface area swept by the primary spot during that one sweep along the second scanning pattern, wherein the third radiation energy flow is substantially identical to the fourth radiation energy flow.

24. A method of heating at least one selected portion of an object, the method including the following steps: projecting an energy beam onto a surface of the object so as to produce a primary spot on the surface, and repetitively scanning the energy beam in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the surface, the effective spot having a two-dimensional energy distribution, and displacing the effective spot along a track on the surface of the object to progressively heat a selected portion of the object; wherein the selected portion has a first width throughout a first sub-portion and a second width throughout a second sub-portion of the selected portion, the first width being larger than the second width, wherein the energy beam is scanned in accordance with a first scanning pattern in the first sub-portion and in accordance with the second scanning pattern in the second sub-portion, wherein the first scanning pattern is repeated by the energy beam with a first frequency and wherein the second scanning pattern is repeated by the energy beam with a second frequency, and wherein both of the first frequency and the second frequency are larger than 10 Hz, wherein the first sub-portion is subjected to a first radiation energy flow and wherein the second sub-portion is subjected to a second radiation energy flow, and wherein the first scanning pattern represents a third radiation energy flow defined as the energy supplied by the energy beam during one sweep along first the scanning pattern divided by the surface area swept by the primary spot, and whereas the second scanning pattern represents a fourth radiation energy flow defined as the energy supplied by the energy beam during one sweep along the second scanning pattern divided by the surface area swept by the primary spot, wherein the first radiation energy flow is substantially identical to the second radiation energy flow, and wherein the third radiation energy flow is substantially identical to the fourth radiation energy flow.

25. The method according to claim 24, wherein the effective spot is displaced along the track with a first velocity in correspondence with the first position along the track, and with a second velocity in correspondence with the second position along the track, the second velocity being different from the first velocity.

26. The method according to claim 25, wherein the second velocity is higher than the first velocity, and wherein the energy beam has a first average power in correspondence with the first position along the track, and a second average power in correspondence with the second position along the track, the second average power being substantially identical to the first average bean power.

27. The method according to claim 25, wherein the second velocity is lower than the first velocity, and wherein the energy beam has a first average power in correspondence with the first position along the track, and a second average power in correspondence with the second position along the track, the second average power being at least 10% smaller than the first average power.

28. The method according to claim 24, wherein the effective spot has a length in the direction parallel with the track that is smaller in correspondence with the first position along the track than in correspondence with the second position along the track.

29. The method according to claim 28, wherein the effective spot is displaced along the track with a first velocity in correspondence with the first position along the track, and with a second velocity in correspondence with the second position along the track, wherein the second velocity is higher than the first velocity.

30. The method according to claim 24, wherein the energy beam has a first average power in correspondence with the first sub-portion and a second average power in correspondence with the second sub-portion, the second average power being smaller than the first average power.

31. The method according to claim 19, wherein the second width is less than 90% of the first width.

32. The method according to claim 19, wherein the second frequency is more than 60% of the first frequency and less than 140% of the first frequency.

33. The method according to claim 1, wherein the energy beam is a laser beam.

34. A system for heating at least one selected portion of an object, the system comprising: means for producing an energy beam and for projecting the energy beam onto a surface of the object, and a scanner for scanning the energy beam in at least two dimensions; wherein the system is programmed for carrying out the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0090] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:

[0091] FIGS. 1A and 1B are perspective views schematically illustrating a system and method in accordance with one possible embodiment of the disclosure, for heat treatment of an object such as a vehicle pillar.

[0092] FIGS. 2A and 2B are top views schematically illustrating an embodiment of the disclosure.

[0093] FIGS. 3A-3C schematically illustrate additional or alternative options for adapting the process to changes in the width of the portion to be heat treated, which can be used in accordance with different embodiments of the disclosure.

[0094] FIGS. 4A and 4B schematically illustrate an embodiment of the disclosure using scanning patterns having different lengths and different widths in the direction parallel with and perpendicular to the track, respectively.

[0095] FIGS. 5A and 5B are photographs of tracks that have been laser hardened on circular steel rods, using different scanning frequencies.

DETAILED DESCRIPTION OF THE DRAWINGS

[0096] FIGS. 1A and 1B illustrate a system in accordance with one possible embodiment of the disclosure, in this case for heat treatment of a sheet metal object such as a vehicle pillar. The system comprises a laser head including a scanner 2 for directing a laser beam 1 onto a workpiece 100. The laser beam can be originated by a laser source remote from the laser head or within the laser head.

[0097] The laser beam 1 is projected onto the workpiece 100 to produce an effective spot 12A, 12B by repetitively scanning the laser beam (and thus the primary spot that the laser beam projects on the workpiece) in two dimensions, according to a scanning pattern. For this purpose, the laser head includes a scanner 2, such as a galvanometric scanner with two scanning mirrors 21 and 22, as schematically illustrated in FIGS. 1A and 1B. The scanning pattern followed by the primary spot projected by the laser beam 1 on the surface of the workpiece 100 at each specific moment is schematically illustrated as a set of parallel lines in FIGS. 1A and 1B. However, any other suitable scanning pattern can be used, including scanning patterns as known from WO-2015/135715-A1 referred to above, scanning patterns with curved segments, etc.

[0098] Thus, as known from for example WO-2016/146646-A1, the two-dimensional energy distribution within the effective spot 12A, 12B can be tailored by the choice of scanning pattern, velocity of the primary spot along the scanning pattern and along the different portions or segments thereof, beam power at each specific portion of the scanning pattern, size of the primary spot, etc. This allows for dynamic adaptation of the two-dimensional energy distribution so as to optimize the heat treatment. Thus, the two-dimensional energy distribution and the total power of the effective spot can be dynamically adapted as the effective spot travels along the track 101 to progressively heat a selected portion 102 of the workpiece 100, as schematically illustrated in FIGS. 1A and 1B.

[0099] As schematically illustrated in FIGS. 1A and 1B, the selected portion 102 to be heat treated has a width that varies along the track, and therefore the width of the effective spot is varied; it can be observed how the effective spot is wider in FIG. 1A than in FIG. 1B.

[0100] This concept is schematically illustrated in FIGS. 2A and 2B, showing another embodiment in which the effective spot 12A, 12B is likewise created by repetitively scanning the primary spot 10 along respective scanning patterns 11A, 11B, in correspondence with two different segments or sub-portions 102a, 102b of a strip or portion 102 of the workpiece to be heat treated. The effective spot is swept along a track 101 to progressively heat the two sub-portions 102a, 102b. The first sub-portion 102a has a first width W1 (in the direction perpendicular to the track), and the second sub-portion 102b has a second width W2 (in the direction perpendicular to the track). In the illustrated embodiment, the second width W2 of the second sub-portion is less than 50% of the first width W1 of the first sub-portion. Obviously, other embodiments feature other relations in width between the two sub-portions, sometimes including transition portions where the width increases or decreases progressively (rather than stepwise as in FIGS. 2A and 2B), etc.

[0101] In the case of the embodiment shown in FIGS. 2A and 2B, the scanning pattern is a simple scanning pattern with a rectangular shape. In practice, any suitable scanning pattern can be used, including complex scanning patterns including multiple lines and segments, including straight and/or curved segments. In the schematically illustrated embodiment, the primary spot 10 repetitively follows the scanning pattern 11A in correspondence with the sub-portion 102a having the first width W1, and the narrower scanning pattern 11B in correspondence with the sub-portion 102b having the second width W2, thereby determining the (varying) width of the portion of the object subjected to heat treatment in one sweep of the effective spot 12A, 12B along the track 101. In the illustrated embodiment, the effective spots 12A and 12B both feature an energy distribution with a leading portion featuring a higher energy density than the trailing portion. As explained in for example WO-2014/037281-A2 referred to above, this approach is sometimes preferred to allow for a rapid heating to a desired temperature by the leading edge or portion of the effective spot, whereafter the trailing portion serves to substantially maintain the temperature at the required level for a certain amount of time. In other embodiments, other energy distributions are used.

[0102] The higher energy density at the leading portion may for example be established by keeping the beam power constant while scanning the laser beam with a slower velocity along a leading segment 11A′, 11B′ of the respective scanning pattern, and with a higher velocity along trailing segments 11A″, 11B″. In other embodiments, the beam power can be adapted to achieve the same effect. In other embodiments, combinations of these approaches can be used, and/or other parameters can be changed. For example, and whereas FIGS. 2A and 2B schematically illustrate the use of one single basic scanning pattern layout (namely, a rectangular one), in other embodiments different scanning patterns may be used for the two sub-portions 102a and 102b of different width. For example, the scanning pattern used in the second and narrower sub-portion 102b may have a larger length in the direction parallel with the track, and the corresponding effective spot may move more rapidly along the track, than what is the case with the scanning pattern used in the first and wider sub-portion 102a.

[0103] In some embodiments the repetition rate of the narrower scanning pattern 11B is substantially the same as the repetition rate of wider scanning pattern 11A: for example, in some embodiments, the frequency of repetition of the narrower scanning pattern 11B in the sub-portion 102b having the narrower width W2 is more than 80% but less than 120% of the frequency of repetition of the scanning pattern 11A in the sub-portion 102a having the larger width W1. This also implies that the average velocity of the primary spot 10 along the scanning pattern 11A used in the sub-portion 102a having the larger width W1 (more than twice the width W2 of the second sub-portion) may be substantially higher than the average velocity of the primary spot 10 along the scanning pattern 11B used in the second sub-portion 102b. The average beam power may in many embodiments be higher in the sub-portion 102a having a larger width W1 than in the sub-portion 102b having a smaller width W2.

[0104] FIGS. 3A-3C schematically illustrate how adaptation of the process to different widths of the scanning pattern may involve the change in operation parameters such as the velocity V1/V2 with which the effective spot moves along the track (that is, the process velocity), the average beam power P1/P2, and/or the length L1/L2 of the effective spot. In different embodiments, these parameters may remain substantially constant, and in other embodiments some or more of them may change. For example, the average beam power may be chosen to be lower (P2) when applying heat treatment to a narrower sub-portion 102b, and higher (P1) when applying heat treatment to a wider sub-portion 102a. One reason for this is that when attempting to keep the radiation energy flow in terms of J/m.sup.2 constant, if using the same average beam power in a narrower sub-portion as in a wider sub-portion, such as in the widest sub-portion, overheating may take place. For example, in the case of laser hardening, undesired melting may take place. Of course, one possibility of avoiding overheating could involve displacing the effective spot along the track using a higher velocity V2 along the narrower sub-portion 102b than along the wider sub-portion 102a, but that may have a negative impact in terms of quality, for example, in terms of hardening depth. In some embodiments, a higher velocity may be compensated by using an effective spot featuring a length L2 in the narrower sub-portion 102b that is larger than the length L1 of the effective spot in the wider sub-portion, the length being the extension of the effective spot in the direction parallel with the track. For example, additional segments of the scanning pattern can be added to make the scanning pattern longer and thereby distributing the energy over a larger surface, fully or partially compensating the reduced width of the portion being heated and/or the higher velocity with which the effective spot moves along the track. Thereby, a balance can be established between the desire the provide a substantially constant radiation energy flow in correspondence with the different sub-portions that are subjected to heat treatment, the desire to make efficient use of the available laser power (preferably operating at a relatively high power level, such as at or close to the maximum power level allowed by the chosen equipment), the need to achieve an appropriate product quality in terms of, for example, surface hardness or softness, depth affected by the treatment, etc., and the desire to operate at a high speed in terms heat treated product quantity (such as in units/hour, meters/minute, etc.).

[0105] Although it is considered that it is generally preferable to keep the frequency (that is, the repetition rate of the scanning pattern) substantially constant, in some embodiments also the frequency may vary substantially between a wider and a narrower sub-portion subjected to heating, although it may often be preferred that the frequency remains within a range of 80%-120% of a reference frequency.

[0106] Just as an example of the kind of calculations that may be involved when selecting the parameters for heat treatment of a sub-portion having a second width on the basis of the parameters chosen for a sub-portion having a first width (a “reference sub-portion”), the following example is given, assuming a rectangular scanning pattern and a constant beam power and scanning velocity (that is, not involving a leading portion with higher energy density):

[0107] Length of the first sup-portion (in the direction parallel with the track): LSP1=50 mm

[0108] Width of the first sub-portion: W1=30 mm

[0109] Length of the second sub-portion: LSP2=70 mm

[0110] Width of the second sub-portion: W2=15 mm

[0111] Beam power applied at the first sub-portion: P1=5000 W

[0112] Beam power applied at the second sub-portion: P1=4000 W

[0113] Diameter of the primary spot: d=5 mm

[0114] Width of the scanning pattern at the first sub-portion: WS1=W1−d=25 mm

[0115] Length of the scanning pattern (in the direction parallel with the track) at the first sub-portion: LS1=8 mm

[0116] The first scanning patterns is repeated with a frequency (repetition rate) of F1=100 Hz

[0117] Process velocity (the velocity of the effective spot in the direction parallel with the track) at the first sub-portion: PV1=600 mm/minute=10 mm/s

[0118] The parameters applied to the first sub-portion can be considered to be reference parameters which have been found to provide for a desired product in terms of, just to give an example, hardening depth.

[0119] Now, the radiation energy flow EF1 at the first sub-portion can be calculated as follows:

EF1=(P1*LSP1/PV1)/((LSP1−d)*W1+(W1−D)*d+PI*(d/2){circumflex over ( )}2)≈16727 kJ/m.sup.2

[0120] Now, the radiation energy flow at the second sub-portion EF2 shall be substantially the same as the radiation energy flow at the first sub-portion: EF2=EF1≈16727 kJ/m.sup.2

[0121] As the power P2 and the dimensions LSP2 and W2 are known, the process velocity PV2 at the second sub-portion can be calculated: PV2=(LSP2*P2)/[(((LSP2−d)*W2)+((W2−d)*d)+(PI*(d/2){circumflex over ( )}2)))*EF2)]≈961 mm/minute≈16 mm/s

[0122] However, as explained above, it is also preferred that also the radiation energy flow (in terms of J/m.sup.2) of the scanning patterns be the same at the first and the second sub-portion: EFS1=EFS2.

[0123] EFS1 corresponds to the amount of energy applied during one sweep of the primary spot along the scanning pattern, divided by the surface area swept by the primary spot:

[0124] The amount of energy applied during one sweep of the primary spot along the scanning pattern is P1/F1=50 J. The area swept is (((LS1*2)+(WS1*2))*d)+(PI*(d/2){circumflex over ( )}2)≈350 mm.sup.2. Thus, the radiation energy flow of the first scanning pattern EFS1≈143 kJ/m.sup.2. Thus, the parameters for the scanning in correspondence with the second sub-portion are to be selected so that EFS2=EFS1≈143 kJ/m.sup.2.

[0125] With the beam power, spot diameter, frequency (repetition rate) and width of the sub-portion known, the remaining parameter to be adjusted is the length of the second scanning pattern, LS2. The amount of energy applied during one sweep of the primary spot along the scanning pattern is P2/F2=P2/F1=40 J. If the area that is swept by the primary spot during one scanning cycle is A m.sup.2, 40/A=143006, that is, A≈40/143006≈0.000280 m.sup.2, that is, 280 mm.sup.2.

[0126] The area swept is (((LS2*2)+(WS2*2))*d)+(PI*(d/2){circumflex over ( )}2)=((2*10+2*LS2)*5)+(PI*(5/2){circumflex over ( )}2)=100+10LS2+(PI*(5/2){circumflex over ( )}2) (mm.sup.2). Thus, LS2=((280−(PI*(d/2){circumflex over ( )}2))/d)−(100))/10) mm≈16 mm. That is, the length of the second scanning pattern in the direction parallel with the track will be longer than the length of the first scanning pattern in the direction parallel with the track, and the same applies to the extension of the effective spot along the track. This concept is schematically illustrated in FIGS. 4A and 4B, showing a layout similar to the one of FIGS. 2A and 2B but with the second scanning pattern 12B having a length or extension LS2 substantially larger than the length or extension LS1 of the first scanning pattern 12A (in the direction parallel with the track 101). There is a corresponding difference in the lengths of the corresponding effective spots (that is, L2>L1).

[0127] This is just an example of how, on the basis of the parameters selected for the heat treatment of the first sub-portion having the width W1, and based on the condition that the radiation energy flows (in terms of J/m.sup.2) are to be kept constant both in what regards the radiation energy flow applied to the heated sub-portion and in what regards the radiation energy flow of the scanning pattern (that is, the energy applied during one sweep of the primary spot along the scanning pattern divided by the area actually swept by the primary spot), the length of the second scanning pattern can be determined for a given power level.

[0128] These calculations are based on a simple rectangular scanning pattern with constant beam power and scanning velocity and thus with an even distribution of the energy along the scanning pattern. If a more complex pattern/energy distribution is used, such as one with a higher energy density in correspondence with a leading portion than in correspondence with a trailing portion, the calculations can be carried out separately for the leading and the trailing portions, and the condition that the radiation energy flow is to be constant has to be complied with both for the leading portions and for the trailing portions.

[0129] FIGS. 5A and 5B are photographs of tracks that have been hardened on a circular steel rod. In both cases, the heat treatment took place using a rectangular scanning pattern with a size of 10 mm×8 mm, a beam power of 2000 W, and a process velocity of 200 mm/min. The difference between the heat treatments corresponding to FIGS. 5A and 5B is that in the heat treatment corresponding to FIG. 5A, the frequency (repetition rate) of the scanning pattern was 100 Hz, whereas in the heat treatment corresponding to FIG. 5B, the frequency (repetition rate) of the scanning pattern was 250 Hz. It was observed that when the higher frequency (250 Hz) was used, re-melting took place (FIG. 5B), whereas no re-melting to place when the lower frequency (100 Hz) was used.

[0130] It should be observed that the different specific scanning patterns discussed above and illustrated in the respective drawings are in no way intended to represent scanning patterns that are adequate or optimized for the described purposes. They are merely intended to schematically illustrate the concept of using scanning patterns in accordance with the disclosure and adapting them in accordance with the specific two-dimensional energy distribution that is selected at each specific moment, so as to produce the heating in the desired manner. The person skilled in the art will typically choose suitable scanning patterns using simulation software and trial-and-error approaches.

[0131] In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0132] On the other hand, the disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the disclosure as defined in the claims.