Method and apparatus for laser cutting of very high strength metal materials

Abstract

A laser cutting method for producing n trimmed sub-blanks from a master blank made of metallic material, where n is an integer strictly greater than 1, the laser cutting method comprising the following steps: - Op1 / Positioning the master blank on a cutting table, the cutting table comprising n strips arranged to move relative to each other in a transverse direction; - Op2 / Clamping at least a portion of the master blank to the cutting table; - Op3 / Cutting n undragged sub-blanks from the master blank in a longitudinal cutting direction using a laser source; - Op4 / Separating the n strips of the cutting table from each other in a transverse direction; - Op5 / Releasing the clamps; - Op6 / Clamping the n undragged sub-blanks to the n strips; - Op7 / Laser trimming the n undragged sub-blanks to form n trimmed sub-blanks; - Op8 / Releasing the clamps; - Op9 / Unloading the n trimmed sub-blanks from the cutting table.

Description

Technical Field

[0001] This invention relates to a method and apparatus for laser cutting of very high-strength steel. Background Technology

[0002] The increasing demand from vehicle manufacturers to improve vehicle safety and reduce their environmental footprint is driving the use of high-strength metallic materials, particularly high-strength steel. These materials possess, for example, an ultimate tensile strength exceeding 980 MPa.

[0003] When this metal is cut to form blanks for stamping motor vehicle parts, manufacturers face the challenge of mitigating residual stress, which can lead to poor geometric accuracy in the cut blanks. This is particularly critical when cutting long and narrow blanks.

[0004] These thin and narrow blanks made of high-strength materials can be used in a variety of applications. In particular, these blanks can be used in welded blanks, in which case the geometry of the blank and the quality of the cut edges are especially critical for subsequent welding operations.

[0005] For example, such thin and narrow blanks can be used in welded blanks to produce floor panels or rocker reinforcements, both of which are very long because they span the entire length of the vehicle’s passenger compartment and may be very narrow relative to their width. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned technical challenges by providing a method and an apparatus that allow for laser cutting of very high-strength metallic materials to achieve excellent blank geometry, excellent edge quality, excellent productivity, and less process waste.

[0007] Therefore, the present invention relates to a laser cutting method for producing n trimmed sub-blanks from a master blank made of metallic material, where n is an integer strictly greater than 1, the laser cutting method comprising the following steps:

[0008] -Op1 / Position the blank on a cutting table, the cutting table comprising n strips arranged to move relative to each other in a lateral direction.

[0009] -Op2 / Clamp at least a portion of the blank to the cutting table.

[0010] -Op3 / Use a laser source to cut n untrimmed sub-blanks from the master blank along the longitudinal cutting direction.

[0011] -Op4 / Separate the n slats of the cutting table from each other in the transverse direction.

[0012] -Op5 / Release clamping,

[0013] -Op6 / Clamp n untrimmed sub-blanks into n strips.

[0014] -Op7 / Performs laser trimming on n untrimmed sub-blanks to form n trimmed sub-blanks.

[0015] -Op8 / Release clamping,

[0016] -Op9 / Remove n trimmed sub-blanks from the cutting table.

[0017] For a given master blank, a given untrimmed sub-blank, or a given trimmed sub-blank, each operation Opi is executed before operation Opi+1, where i is an integer between 1 and 9.

[0018] Other optional features, either individually considered or based on any possible combination of techniques, according to the laser cutting method according to the invention:

[0019] - Clamping operations Op2 and Op6 are performed using magnetic clamping.

[0020] - The first clamping operation Op2 is performed only on a portion of the surface of the mother blank, which corresponds to the last m untrimmed sub-blanks to be cut in the first cutting operation Op3, where m is an integer between 1 and n-1.

[0021] - The laser trimming operation Op7 is performed on each untrimmed sub-blank by simultaneously laser-cutting both untrimmed cutting edges of each untrimmed sub-blank.

[0022] - The length of the trimmed sub-blank measured in the longitudinal direction is at least twelve times the width of the trimmed sub-blank measured in the transverse direction.

[0023] - The ultimate tensile strength of the master blank is at least 980 MPa.

[0024] - The longitudinal direction of the n trimmed sub-blanks is approximately the same as the rolling direction of the coil from which the master blank has been cut.

[0025] The present invention also relates to: a trimmed sub-blank obtained by applying the above-described laser cutting method; a laser-welded blank comprising at least one trimmed sub-blank obtained by applying the above-described laser cutting method; and a shaped part for a motor vehicle obtained by forming a laser-welded blank comprising at least one trimmed sub-blank obtained by applying the above-described laser cutting method.

[0026] The present invention also relates to a cutting stage for a laser cutting method, the cutting stage comprising a plurality of slats arranged to be movable relative to each other in a lateral direction. The slats may be mounted on at least one linear guide support, and each slat may include a clamping device, preferably a magnetic clamping device.

[0027] The present invention also relates to a cutting production line comprising at least one cutting head and at least one cutting table corresponding to the above description. The production line may include, for example, at least two cutting tables corresponding to the above description. The production line may also include, for example, at least two laser cutting heads. Attached Figure Description

[0028] Other aspects and advantages of the invention will become apparent upon reading the following description, which is given by way of example and made with reference to the accompanying drawings, in which:

[0029] - Figure 1 This is a flowchart of the laser cutting method according to the present invention.

[0030] Figures 2a and 2b are top views of two different configurations of cutting tables that can be used during the laser cutting process according to the present invention.

[0031] Figures 3a and 3b are top views of two untrimmed sub-blanks after process stages Op4 and Op5, respectively, according to the present invention.

[0032] - Figures 4a and 4b are top views of the sub-blanks during method steps Op7 and Op8 according to the present invention.

[0033] Figure 5 This is a top view of a laser cutting production line according to a specific embodiment of the present invention. Detailed Implementation

[0034] A steel billet refers to a flat steel sheet that has been cut into any shape suitable for its application. The billet has a top surface and a bottom surface, also referred to as a top side and a bottom side, or a top surface and a bottom surface. The distance between these surfaces is specified as the thickness of the billet. This thickness can be measured using, for example, a micrometer, with its spindle and anvil positioned on the top and bottom surfaces. Similarly, this thickness can also be measured on shaped parts.

[0035] As for "roughly parallel" or "roughly perpendicular", it means that the direction can deviate from the parallel or perpendicular direction by no more than 15°.

[0036] Welded blanks are manufactured by assembling, for example, several steel blanks called sub-blanks together, to optimize the performance of the part in different areas, thereby reducing the overall weight and cost of the part. The sub-blanks forming the welded blank can be assembled with or without overlap; for example, these sub-blanks can be laser butt welded (without overlap) or they can be spot welded to each other (with overlap).

[0037] In the following description and in the accompanying drawings, for simplicity, the blanks and sub-blanks described and depicted have a generally rectangular shape. However, it should be understood that the invention is not limited to rectangular blanks and can be applied to blanks with different shapes.

[0038] Yield strength, ultimate tensile strength, uniform elongation and total elongation were measured according to ISO 6892-1, published in October 2009.

[0039] Reference Figure 1 Figure 4 shows a method for laser-cutting n trimmed sub-blanks 12 from a master blank 10 made of metallic material. The longitudinal direction is depicted by the arrow marked "L" in Figure 2, and the transverse direction is depicted by the arrow marked "T" in Figure 2. In this specification, the length of the uncriminated sub-blank 11 or the trimmed sub-blank 12 refers to the dimension of the sub-blank measured in the longitudinal direction, and the width of the uncriminated sub-blank 11 or the trimmed sub-blank 12 refers to the dimension of the sub-blank measured in the transverse direction. In this specification, the length of the uncriminated sub-blank 11 or the trimmed sub-blank 12 is greater than the width of the uncriminated sub-blank 11 or the trimmed sub-blank 12.

[0040] In the following description, the terms “top” and “bottom” will be defined according to the vertical direction—for example, referring to Figure 2a, “top” corresponds to the top of the figure, while “bottom” refers to the bottom of the figure.

[0041] In the following description, the terms "left" and "right" will be defined according to the horizontal direction—for example, referring to Figure 2a, left corresponds to the left side of the figure, while right refers to the right side of the figure.

[0042] The master blank 10 is cut from a steel coil, for example, a high-strength steel coil with an ultimate tensile strength higher than 980 MPa. The steel coil is a long steel plate that has been processed into a coil form for packaging, handling, transportation, and subsequent processing. The steel coil has a rolling direction corresponding to the direction in which the steel is processed during the hot rolling and / or cold rolling steps of the steel production process. Steel coils typically have very long lengths (hundreds of meters, sometimes even thousands of meters) when uncoiled along the rolling direction, while having a limited maximum width due to limitations of the production equipment (limitations in the dimensions of the equipment in the width direction, and limitations in the strength of the manufacturing equipment, such as hot rolling or cold rolling equipment). Therefore, when producing very long sub-blanks with a length greater than the maximum width of the steel coil, the longitudinal direction of the sub-blank will be the same as the rolling direction of the steel coil from which the sub-blank was produced.

[0043] The blank 10 is cut from the steel coil as described above, for example. The blank 10 is cut off from the steel coil using a mechanical shear on a cutting production line, a cutting die on a punching production line, or a laser cutter on a laser punching production line to produce the blank from the steel coil. For example, the blank 10 is cut such that its length is oriented along the rolling direction of the coil and is greater than its width, the width of which approximately corresponds to the width of the steel coil. As previously stated, this cutting direction is the only possible way to produce a blank 10 having a longitudinal direction greater than the maximum achievable width of the steel coil.

[0044] Referring to Figures 3 and 4, the untrimmed sub-blank 11 refers to a sub-blank that has been directly cut from the mother blank 10 without any subsequent processing steps. The untrimmed sub-blank 11 has two untrimmed cutting edges 111, which correspond to the edges of the untrimmed sub-blank 11 that have been produced from the mother blank 10 through the aforementioned cutting operation.

[0045] Referring to Figures 4a and 4b, the trimmed sub-blank 12 refers to a sub-blank that has been produced from an untrimmed sub-blank 11 by further performing a cutting step called a trimming step on the cut edge 111 of the untrimmed sub-blank 11 to form two trimmed cut edges 112.

[0046] For productivity reasons, it is of interest to use the maximum possible number n trimmed sub-blanks 12 cut from a single master blank 10. In fact, the cutting method involves positioning the master blank 10 on the cutting production line, which takes time. The larger the number n, the faster the total cutting process time for each blank. For example, the total number n of trimmed sub-blanks for each master blank 10 is 8. Or, for example, the total number n of trimmed sub-blanks for each master blank 10 is 16.

[0047] The method of the present invention is particularly suitable for cases where the ratio of the length to the width of the trimmed sub-blank 12 is high. In this type of configuration, when the sub-blank is cut from the parent blank, there may be geometric problems with the shape of the unetended sub-blank 11. In particular, there is a risk that the unetended sub-blank 11 will exhibit a bent shape—also known as a “banana shape”—after being cut from the parent blank 10. Without being bound by theory, this type of deformation is due to the fact that the material has internal stresses derived from the steelmaking process. For example, these internal stresses may partly originate from the hot rolling and / or cold rolling steps. For example, these internal stresses may partly originate from the annealing step after cold rolling and / or the quenching step after annealing and / or the skin-passing step after annealing. In the case of laser cutting, another reason that can be explained by the geometric problems on the unetended sub-blank 11 is the heat input of the laser cutting operation, which may cause additional mechanical stresses and problems, for example, related to thermal shrinkage.

[0048] Figure 3b illustrates the curved shape of the untrimmed sub-blank 11. Similar to the general shape of a banana, the top and bottom portions of the untrimmed sub-blank 11 are oriented to one side (in this case, the right side, although this could be reversed depending on the distribution of internal stress within the parent roll 10), while the middle portion of the untrimmed sub-blank 11 in the longitudinal direction is oriented to the opposite side (in this case, the left side). In other words, even if the cutting operation used to produce the untrimmed sub-blank 11 from the parent blank 10 follows a straight line, the resulting cut edge 111 is not straight but follows a curved path. This shape defect can be significant; for example, the top and bottom of the untrimmed sub-blank 11 may be offset by up to several millimeters compared to the middle of the sub-blank 11. It should be understood that the aforementioned curved shape or "banana shape" is a highly illustrative description, and the direction and magnitude of such deformation can be highly variable from one parent blank 10 to another, and within a given parent blank 10, from one untrimmed sub-blank 11 to another. In fact, the deformation stems from the manufacturing history of the parent blank 10, and each blank potentially has a different history due to many possible variations arising from the industrial processes involved.

[0049] If the intended shape of the sub-blank is not rectangular, the same type of problem will occur: the cutting edge 111 will not follow the contour on which the cutting operation is based.

[0050] The above-mentioned geometric problems are particularly critical under the following conditions:

[0051] - The length of the undressed sub-blank 11 is significantly greater than its width. In fact, when this is not the case, the bending shape of the undressed sub-blank 11 will be insignificant and will not cause significant problems. For example, the inventors have found that the bending problem begins to become very noticeable when the length of the undressed sub-blank 11 is at least twelve times the width of the undressed sub-blank 11.

[0052] - The material used to make the master blank 10 has very high strength. In fact, when this is not the case, the aforementioned residual stresses within the blank are insufficient to cause any significant shape deformation. For example, when the material has an ultimate tensile strength higher than 980 MPa, shape becomes critical.

[0053] Another factor is the subsequent use of the sub-blank. In fact, when the sub-blank is used in applications where the final shape requirements are not stringent, the aforementioned geometric issues may not be critical industrial problems. However, in many applications, the shape of the sub-blank needs to be very precise. For example, this is a case of butt-to-butt laser welding using the aforementioned sub-blank, where the cut edge 112 of the trimmed sub-blank 12 is welded to another blank. Butt laser welding requires very precise positioning of the blanks to be welded so that a constant distance is maintained between the edges to be welded. This is impossible when the blanks are significantly bent. In practice, in industrial operations, the trimmed sub-blank 12 will undergo quality control, and this does not mean that sub-blanks with fixed standards such as geometric standards will be rejected. If a large amount of material does not meet quality standards, there will be a large amount of rejected material; in other words, there will be a large amount of process waste. This will increase production costs and reduce productivity.

[0054] In addition to the aforementioned geometric issues, the quality of the finished sub-blank 12 is also related to the quality of its cut edges. When viewed in cross-section along a plane perpendicular to the cut edge 112, it is desirable to have straight cut edges 112 that form right angles with the top and bottom surfaces of the sub-blank. This is referred to as the cut edge quality. For example, in the case of butt laser welding, the cut edge quality is also crucial for maintaining a fixed distance between the edges to be welded and for the subsequent quality of the welded parts. One of the best industrially achievable cut edge qualities is known to be provided by laser cutting. Unlike mechanical shearing, there is no problem of mechanical burrs, and the edge profile is very uniform. Furthermore, the edge quality is independent of the state of the cutting tool, as in mechanical shearing, where the edge quality gradually decreases between two maintenance operations of the cutting tool. In the case of laser cutting, the fact that there is no direct contact between the tool and the material to be cut means that tool operation does not deteriorate through the cutting operation itself, and there are downtime periods for cutting tool maintenance. This, in turn, reduces process waste and increases productivity.

[0055] In a particular embodiment, the blank 10 is made of steel having a chemical composition comprising, by weight percent, the following: 0.13% < C < 0.25%, 2.0% < Mn < 3.0%, 1.2% < Si < 2.5%, 0.02% < Al < 1.0%, wherein 1.22% < Si+Al < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05%, with the remainder being Fe and unavoidable impurities, and having a microstructure comprising: 8% to 15% retained austenite; the remainder being ferrite, martensite, and bainite, wherein the sum of the martensite and bainite fractions is between 70% and 92%. Using this composition, the steel sheet has a yield strength between 600 MPa and 750 MPa and an ultimate tensile strength between 980 MPa and 1300 MPa when measured along the rolling direction, while maintaining a total elongation of more than 19%.

[0056] In a particular embodiment, the blank 10 is made of steel having a chemical composition comprising, by weight percent: 0.15% < C < 0.25%, 1.4% < Mn < 2.6%, 0.6% < Si < 1.5%, 0.02% < Al < 1.0%, wherein 1.0% < Si+Al < 2.4%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, with the remainder being Fe and unavoidable impurities, and having a microstructure comprising: 10% to 20% retained austenite; the remainder being ferrite, martensite, and bainite. Using this composition, the steel sheet, when measured along the rolling direction, has a yield strength comprising between 850 MPa and 1060 MPa and an ultimate tensile strength comprising between 1180 MPa and 1330 MPa, while maintaining a total elongation of over 13%.

[0057] MS1500:

[0058] In a particular embodiment, the blank 10 is made of steel having a chemical composition comprising, by weight percent, the following: 0.15% ≤ C ≤ 0.5%, for example, the steel having a fully martensitic microstructure and an ultimate tensile strength of over 1500 MPa.

[0059] According to the present invention and as Figure 1 The flowchart depicts a cutting method for producing n trimmed sub-blanks 12 from a master blank 10 made of metal material, including the following steps labeled as operations Op1, Op2, etc.:

[0060] -Op1 / Position the blank 10 on the cutting table 1, which includes n strips 2 arranged to move relative to each other in the lateral direction.

[0061] -Op2 / Clamp at least a portion of the blank 10 to the cutting table 1

[0062] -Op3 / Using a laser source, n untrimmed sub-blanks 11 are cut from the master blank 10 along the longitudinal cutting direction.

[0063] -Op4 / Separate the n strips 2 of the cutting table 1 from each other in the transverse direction.

[0064] -Op5 / Release clamping

[0065] -Op6 / Clamp n untrimmed sub-blanks 11 to n strips 2

[0066] -Op7 / Perform laser trimming on n untrimmed sub-blanks 11 to form n trimmed sub-blanks 12.

[0067] -Op8 / Release clamp

[0068] -Op9 / Remove n trimmed sub-blanks 12 from the cutting table.

[0069] For a given master blank 10, a given untrimmed sub-blank 11, or a given trimmed sub-blank 12, each operation Opi is performed before operation Opi+1, where i is an integer between 1 and 9.

[0070] Each operation will be explained in more detail later.

[0071] Op1 simply involves positioning the mother blank 10 on the cutting table 1, and is not worth further explanation as it is a standard operation specific to each cutting production line. It is sufficient to say that this operation typically occupies a portion of the process time entering the productivity calculation of the process. To minimize the productivity loss associated with Op1, it is of interest to provide a mother blank 10 from which a maximum possible number n sub-blanks can be produced. Furthermore, as will be explained later, it is of interest to design cutting production lines with at least two cutting tables 1 such that Op1 can be performed simultaneously on another cutting table 1 while another blank is being cut.

[0072] Op2, which includes clamping the blank 10 to the cutting table 1, is also a standard operation on the cutting production line. In fact, for accurate cutting, it is important that the blank is precisely positioned and does not move during the cutting process or due to any other reason, such as movement of the cutting table 1 itself or vibrations on the production line. Clamping itself can be performed using any available clamping technology. For example, mechanical clamping can be considered. Advantageously, magnetic clamping allows for the effective clamping of magnetic blanks, such as steel blanks, and allows this to be done without any contact between the clamping device and the blank to be clamped. This is particularly important in the case of laser cutting because the magnetic clamping system does not come into direct contact with the blank, and therefore there is no risk of damage to the clamping device from the laser beam during the cutting operation.

[0073] Op3 involves producing n unequal sub-blanks 11 from a master blank 10 using a laser source. This first cut is also referred to as a "free cut" because the unequal sub-blanks 11 detach from the master blank 10. Laser cutting technology is well known in itself. In certain embodiments, laser cutting can be performed using more than one laser source to perform multiple laser cuts simultaneously and thus increase productivity. The sequence of cutting the unequal sub-blanks 11 from the master blank 10 can be programmed in different ways to best suit industrial constraints and facilities. For example, when using two laser sources, the cutting can be performed such that each laser head begins on opposite sides of the master blank 10 and meets in the middle. For example, when using two laser sources, the cutting can be performed such that each laser head begins side-by-side in the middle and gradually moves in opposite transverse directions to complete on opposite sides of the master blank 10.

[0074] Op4 involves separating n undressed sub-blanks 11 laterally from each other using specific features of a cutting table 1. The cutting table 1 comprises n slats 2, which are spaced apart from each other laterally. Each slat 2 corresponds to its corresponding undressed sub-blank 11 in a subsequent position after being cut from the parent blank 10. Each slat 2 includes a clamping mechanism for clamping its corresponding undressed sub-blank 11, as will be seen during other operations of the method. For example, the slats 2 can be mounted on a linear support 3 for lateral movement, as depicted in Figures 2a and 2b, which show the positions of the slats 2 before and after Op4, respectively. For example, the slats may move laterally by 10 mm to 12 mm relative to each other.

[0075] Op5 involves releasing the clamps after free cutting has been performed. The "banana-shaped" deformation of the undressed sub-blank 11 only occurs after the clamps are released, i.e., after Op5. In fact, before the release operation, the undressed sub-blank 11 is held in place by the clamping mechanism and therefore cannot deform into its natural resting shape. This is depicted in Figures 3a and 3b, which are schematic representations of the shape of the undressed sub-blank 11 before and after Op5, respectively. Since the undressed sub-blank 11 has effectively acquired its natural shape, subsequent trimming operations can be applied to set it to its correct final shape.

[0076] Op6 involves re-clamping the undressed sub-blank 11 to prepare it for the laser finishing step. In fact, to properly hold it in place for the laser finishing operation, the undressed sub-blank 11 needs to be firmly held in place by clamping. Each strip 2 on which the undressed sub-blank 11 rests is equipped with a clamping mechanism, such as magnetic clamping.

[0077] Op7 involves laser trimming of n untrimmed sub-blanks 11 to form n trimmed sub-blanks 12. This is accomplished by using a laser to cut the untrimmed cutting edges 111 to form two trimmed cutting edges 112. For example, the trimming operation sequentially removes a 2 mm to 3 mm width of material from either side of the untrimmed sub-blank 11 to form the trimmed sub-blank 12. Figure 4a is a schematic reproduction of the trimming step Op7, which is performed along the dashed line 5 to obtain the trimmed sub-blank 12 of Figure 4b. Op7 allows the production of trimmed sub-blanks 12 that have the desired final sub-blank shape and do not release the internal stress present in the untrimmed sub-blanks 11 prior to clamping at Op5. In fact, after Op5, the untrimmed sub-blanks 11 have no internal stress, which releases itself to deform the overall shape of the untrimmed sub-blanks 11 into a curved "banana shape." Since the individual untrimmed sub-blanks 11 have already been laterally separated from each other during Op4, there is no risk that parts of two adjacent sub-blanks 11 might overlap due to the "banana shape" effect. This means that the laser trimming operation Op7 can be performed without the risk of incorrectly cutting a portion of an adjacent blank, a risk that would inevitably lead to shape problems in the trimmed sub-blanks 12, requiring scrapping. It also means that adjacent untrimmed sub-blanks 11 do not need to be moved in any way if overlap is detected, which would involve additional detection equipment and time to move the untrimmed sub-blanks 11, resulting in reduced productivity and potentially quality problems due to lower repeatability of the position of the untrimmed sub-blanks 11.

[0078] Op8 involves releasing the clamping of the trimmed sub-blank 12. At this point, contrary to what happens after Op5, there is little or no deformation due to internal stress, because the untrimmed sub-blank 11, which has already produced the trimmed sub-blank 12, has no internal stress.

[0079] Op9 involves removing n untrimmed sub-blanks 12 from the cutting table 1 by known means in order to free up the cutting table for processing the next mother blank 10.

[0080] As described above, for a given master blank 10, a given untrimmed sub-blank 11, or a given trimmed sub-blank 12, the above processing steps are performed sequentially. However, when observing the entire process, for different sub-blanks, some operations may occur simultaneously or in different orders. This will be of particular interest in improving the overall productivity of the process. For example, once the first untrimmed sub-blank 11 has been cut from the master blank 10 (Op3), its corresponding strip 2 can be moved laterally to separate the first untrimmed sub-blank 11 from the remaining material (Op4), and the clamping of the first untrimmed sub-blank 11 can be released (Op5)—while other untrimmed sub-blanks 11 can still be cut from the same master blank 10 (Op3). Therefore, Op3 for a given sub-blank can be performed simultaneously with Op4 and / or Op5 for another sub-blank. The key point is that for any given sub-blank, the above method steps are performed in the above order.

[0081] The inventors have discovered that the present invention can be successfully applied to produce very good results in terms of blank shape and cut edge quality even when the entire surface of the mother blank 10 is not clamped to the cutting table 1 during Op2. This may be of concern for productivity reasons, as the release step of Op5 can be time-consuming if applied to each of the n sub-blanks. For example, when magnetic clamping is applied, the release operation may take on the order of 1 to 2 seconds. In a particular embodiment, the clamping operation Op2 is performed only on the following portion of the surface of the mother blank 10: this portion corresponds to the last m untrimmed sub-blanks to be cut in the first cutting operation Op3, where m is an integer between 1 and n-1. Thus, Op5 need not be performed on the first nm untrimmed sub-blanks 11, which are located on the area of ​​the cutting table 1 where the magnetic clamping of Op2 is not applied. This allows for some release time and thus improves productivity.

[0082] Regarding the laser trimming step Op7, it may be of interest to simultaneously perform laser trimming on the two untrimmed cut edges 111 of a given untrimmed sub-blank 11 to further optimize the final quality and shape of the corresponding trimmed sub-blank 12. In fact, laser trimming generates heat on the sides of the sub-blank—if laser trimming is performed on one untrimmed cut edge 111 at a time, the heat input during laser trimming is asymmetrical, and this can lead to some internal stress due to differences in thermal expansion and contraction, which may cause some deformation of the trimmed sub-blank 12 after the clamping is released during step Op8. In a particular embodiment, the laser trimming operation Op7 is performed on each untrimmed sub-blank 11 by simultaneously laser cutting the two untrimmed cut edges 111 of each untrimmed sub-blank 11. For the purpose of simultaneous laser cutting, this means that the two laser beams used for trimming begin to move at the same speed at a position where they are approximately aligned with each other in the lateral direction.

[0083] The present invention also relates to a trimmed blank 12 obtained by applying the above-described laser cutting method.

[0084] The present invention also relates to a laser-welded blank comprising at least one trimmed sub-blank 12 obtained by applying the laser cutting method described above.

[0085] The present invention also relates to a shaped part for a motor vehicle obtained by forming a laser-welded blank, the laser-welded blank comprising at least one trimmed sub-blank 12 obtained by applying the laser cutting method described above.

[0086] The present invention also relates to a specific cutting table 1 equipped with at least n slats for applying the above-described cutting method. The cutting table 1 comprises n slats 2, which may be spaced apart from each other in the transverse direction. Each slat 2 includes a clamping mechanism, such as a magnetic clamping mechanism or a mechanical clamping mechanism. For example, the slats 2 may be mounted on a linear support 3 for movement in the transverse direction.

[0087] Reference Figure 5 The present invention also relates to a cutting production line 6 equipped with at least one cutting table 1, the cutting production line 6 having the aforementioned features for implementing the above-described cutting method and having at least one laser cutting head 7. For example, as Figure 5As depicted above, production line 6 has two cutting tables 1 and two laser cutting heads 7. Advantageously, this allows, for example, Op1 and Op2 to be performed on the first worktable, i.e., positioning and clamping the mother blank 10, while the laser head 7 is busy performing cutting and / or trimming operations on the second worktable. Additionally, this allows the final operations Op8 and Op9 to be performed while the laser head 7 is busy performing cutting and / or trimming operations on the second worktable, i.e., releasing the clamp on the trimmed sub-blank 12 and removing the trimmed sub-blank 12 from the first cutting table. This type of sequencing and production organization is particularly advantageous because it means that the laser head 7 is continuously operational during material handling and clamping operations rather than being idle. This, in turn, ensures efficient use and maximum productivity of the laser head 7, an expensive and highly productive component of the equipment that should be kept as busy as possible.

[0088] Figure 5 An example of a cutting production line 6 with a top worktable 1 and a bottom worktable 1 is shown, wherein two laser heads 7 are mounted on guide rails 8, which are movable laterally along the guide rails 8, and the guide rails themselves are movable longitudinally within the production line 6. Figure 5 In the process, the cutting method is being performed on the top worktable. The laser head 7 moves from the opposite edge of the mother blank 10 toward the center to perform free cut Op3. Two first untrimmed sub-blanks 11 have been cut off (Op3), and their corresponding strips 2 have been separated from their adjacent strips (Op4). The laser head is completing the free cut of another set of two untrimmed sub-blanks 11 (Op3). While this is happening, the robot arm 9 is positioning a new mother blank 10 on the bottom worktable 1 to prepare it for the cutting method.

Claims

1. A laser cutting method for producing n trimmed sub-blanks (12) from a master blank (10) made of metallic material, wherein n is an integer strictly greater than 1, the laser cutting method comprising the following steps: - Op1 / Position the mother blank (10) on a cutting table (1), the cutting table (1) comprising n strips (2) arranged to move relative to each other in a lateral direction. - Op2 / Clamp at least a portion of the mother blank (10) to the cutting table (1). - Op3 / Using a laser source, n untrimmed sub-blanks (11) are cut from the mother blank (10) along the longitudinal cutting direction. - Op4 / Separate the n strips (2) of the cutting table (1) from each other in the transverse direction. - Op5 / Release clamping, - Op6 / Clamp the n untrimmed sub-blanks (11) to the n strips (2). - Op7 / Laser trimming is performed on the n untrimmed sub-blanks (11) to form n trimmed sub-blanks (12). - Op8 / Release clamping, - Op9 / Remove the n trimmed sub-blanks (12) from the cutting table (1), For a given mother blank (10), a given untrimmed sub-blank (11), or a given trimmed sub-blank (12), each operation Opi is performed before operation Opi+1, where i is an integer between 1 and 9.

2. The laser cutting method according to claim 1, wherein, The clamping operations Op2 and Op6 are performed using magnetic clamping.

3. The laser cutting method according to claim 1 or 2, wherein, The first clamping operation Op2 is performed only on a portion of the surface of the mother blank (10), which corresponds to the last m untrimmed sub-blanks (11) to be cut in the first cutting operation Op3, where m is an integer between 1 and n-1.

4. The laser cutting method according to claim 1 or 2, wherein, The laser cutting operation Op7 is performed on each untrimmed sub-blank (11) by simultaneously laser cutting the two untrimmed cutting edges (111) of each untrimmed sub-blank (11).

5. The laser cutting method according to claim 1 or 2, wherein, The length of the trimmed sub-blank (12) measured in the longitudinal direction is at least twelve times the width of the trimmed sub-blank (12) measured in the transverse direction.

6. The laser cutting method according to claim 1 or 2, wherein, The ultimate tensile strength of the mother blank (10) is at least 980 MPa.

7. The laser cutting method according to claim 1 or 2, wherein, The longitudinal direction of the n trimmed sub-blanks (12) is approximately the same as the rolling direction of the coil from which the mother blank (10) has been cut.

8. A cutting table (1) for applying the laser cutting method according to any one of claims 1 to 7, the cutting table (1) comprising a plurality of slats (2) arranged to be movable relative to each other in a transverse direction.

9. The cutting table (1) according to claim 8, wherein, The slats (2) are mounted on at least one linear guide rail support (3).

10. The cutting table (1) according to claim 8 or 9, wherein, Each slat (2) includes a clamping device.

11. The cutting table (1) according to claim 10, wherein, Each of the slats (2) includes a magnetic clamping device.

12. A cutting production line (6) comprising at least one laser cutting head (7) and a cutting table (1) according to any one of claims 8 to 11.

13. The cutting production line (6) according to claim 12, comprising two cutting tables (1) according to any one of claims 8 to 11.

14. The cutting production line (6) according to claim 12 or 13, comprising two laser cutting heads (7).

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