Laser cutting method and machine, and automatic programing apparatus

According to a laser cutting method, a processed part is laser-cut so that the processed part doesn't drop off from a sheet-shaped workpiece. In the laser cutting method, a cut slit of a pressing protrusion, which is curved due to a laser cutting process along an outline of the processed part and then presses a peripheral surface of the processed part, is preliminarily formed around the processed part to be cut out from the workpiece. Then, the laser cutting process is carried out along the outline of the processed part. The pressing protrusion curves toward the processed part due to the laser cutting process of the processed part, and then the processed part is retained by the pressing protrusion.

TECHNICAL FIELD

The present invention relates to a laser cutting method and machine, and to an automatic programing apparatus.

BACKGROUND ART

While cutting out a processed part from a sheet-shaped workpiece by a laser processing, the processed part may be stuck on plural pin-supports on which the workpiece is laid or be placed on the workpiece and thereby may inhibit motions of a laser processing head, or the processed part may be stuck under the workpiece. In order to prevent these events, a processed part is jointed with a workpiece by a minute jointing portion(s) called as a micro-joint(s) and thereby the processed part is not entirely separated from the workpiece. A minute protrusion may be formed on the processed part due to the micro-joint in this case when the processed part is separated from the workpiece, and thereby a process for removing the minute protrusion is needed. Therefore, joining of a processed part with a workpiece without using a micro-joint is proposed (see Patent Documents 1 and 2 listed below).

Note that, in general, a “micro-joint” is a jointing work for making a processed part retained by a workpiece in order to prevent the processed part from dropping off from the workpiece during a laser processing, and is also called as a “wire-joint”. According to the “micro-joint”, the processed part is made retained by the workpiece by forming a jointing portion having a width from several micrometers and several hundreds micrometers while cutting an outline of the processed part.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Patent Application Publication No. H5-245671

Patent Document 2: Japanese Patent Application Publication No. H6-238475

SUMMARY OF INVENTION

The Patent Document 1 discloses a laser processing method for restricting a cut piece (processed part) from being separated from a workpiece by supplying adhesives on a cut line(s) (slit(s)) of laser processing while cutting out the cut piece from the sheet-shaped workpiece by a laser processing. Therefore, removal of the adhesives is needed when separating the cut piece from the workpiece.

The Patent Document 2 discloses a laser processing method for restricting a cut piece from being separated from a workpiece by utilizing melted residues of the workpiece generated through a laser processing while cutting out a product from the workpiece. Depending on a laser processing condition, it may occur that the product is melted by the melted residues and thereby the melted residues adhere firmly on the product. In this case, removal of the melted residues is needed.

In addition, a focused beam diameter of fiber laser having a 1 μm-band wavelength is smaller than that of carbon dioxide laser having a 10 μm-band wavelength, and thereby a cutting slit by the fiber laser is narrow. Since a cutting slit gets wide when cutting by the carbon dioxide laser, a cut piece drops off through plural pin supports without being stuck with them. However, the cut piece will be more likely to be stuck with the workpiece due to the narrow cutting slit made through cutting by the fiber laser, and thereby there is concern that motions of a laser processing head is prohibited.

A first aspect of the present invention provides a laser cutting method for cutting out a processed part from a sheet-shaped workpiece, the method comprising: (a) preliminarily laser-cutting a cut slit of a pressing protrusion around the processed part to be cut out from the workpiece, the pressing protrusion being curved due to a laser cutting process along an outline of the processed part and then pressing a peripheral surface of the processed part; and (b) carrying out the laser cutting process along the outline of the processed part.

A second aspect of the present invention provides a laser cutting machine for cutting out a processed part from a sheet-shaped workpiece, the machine comprising: a laser processing head movable relative to the workpiece W in X, Y and Z-axis directions; and a control device for controlling motions of the laser processing head, wherein the control device comprises: a processing program memory that stores a processing program for laser-cutting the processed part; a program analyzer that analyzes a shape and dimensions of the processed part by analyzing the processing program; a weight arithmetic section that calculates a weight of the processed part based on the analyzed shape and the analyzed dimensions of the processed part and a thickness of the workpiece; a number arithmetic section that calculates the number of pressing protrusions based on a calculation result of the weight arithmetic section, each of the pressing protrusions being curved due to a laser cutting process along an outline of the processed part and then pressing a peripheral surface of the processed part; a pressing protrusion arranger that arranges the pressing protrusions around the processed part based on a calculation result of the number arithmetic section; a processing program generator that generates a laser cutting program for forming the pressing protrusions at positions arranged by the pressing protrusion arranger; the processing program memory that stores the laser cutting program generated by the processing program generator; and an axial motion controller that controls axial motions of the laser processing head according to the laser cutting program stored in the processing program memory.

A third aspect of the present invention provides an automatic programming apparatus of a laser cutting machine, the apparatus comprising: a weight arithmetic section that calculates a weight of the processed part based on a shape and dimensions of a processed pat that are input though a CAD and a thickness of a workpiece; a number arithmetic section that calculates the number of pressing protrusions based on a calculation result of the weight arithmetic section, each of the pressing protrusions being curved due to a laser cutting process along an outline of the processed part and then pressing a peripheral surface of the processed part; a pressing protrusion arranger that arranges the pressing protrusions around the processed part based on a calculation result of the number arithmetic section; a processing program generator that generates a laser cutting program for forming the pressing protrusions at positions arranged by the pressing protrusion arranger and laser-cutting the processed part; a processing program memory that stores the laser cutting program generated by the processing program generator; and a program transferrer that transfers the laser cutting program stored in the processing program memory to a control device of the laser cutting machine.

DESCRIPTION OF EMBODIMENTS

As shown inFIG. 1, a rectangular-shaped processed part1is to be cut out from a sheet-shaped workpiece W by a laser cutting process. Here, while cutting out the processed part1by the laser cutting process, a cut slit11having an appropriate length is preliminarily formed by a laser processing at at least one position of a scrap3to be discarded after cutting out the processed part1. Each cut slit (cutting slit)11is formed along an outline5of the processed part1and formed by a long slit9and a short slit7, and a short side opposite to the short slit7is remained without being cut. Each cut slit11has a slit-shape continuously formed by the long slit9and the short slit7. After the cut slit11is formed, the laser cutting process is carried out along the outline5of the processed part1. Note that the short slit7has a length not larger than a thickness of the workpiece W.

When forming the cut slit11, a portion of the cut slit11is melted by heats of the laser cutting process. Then, a portion around the cut slit11is quickly cooled due to heat conduction after the laser cutting process of the cut slit11. Further, when the processed part1has been cut out from the workpiece W by carrying out the laser cutting process along the outline5, a pressing protrusion15having a rectangular shape longwise in a direction along the outline5is formed between the cut slit11and the outline5. A width H of a short side of the pressing protrusion15is not larger than the thickness of the workpiece W, and a length L of a long side thereof is three to eight times larger than the thickness.

Relations between dimensions (the width H and the length L [mm]) of the pressing protrusion15and its retention force [N] are actually measured by using the workpiece W made of an iron-based material and an aluminum-based material. Note that the retention force is a retention force exerted by a single pressing protrusion15. A size of the cut-out processed part1is a 65 mm square, and one of two pairs of opposite two sides of the square is parallel to a roll-expanding direction of the workpiece (the roll-expanding direction will be explained later). The pressing protrusion15is formed for each side one by one, and an end of the pressing protrusion15is positioned at the center of said each side. In addition, an extending direction of the pressing protrusion15coincides with a cutting direction of the outline5(the extending direction and the cutting direction will be explained later).

The iron-based material of the workpiece used for the measurements is SECC (electro galvanized zinc plated steel sheet) and SUS (stainless steel sheet). A thickness of SECC is 2.3 mm, and a thickness of SUS is 2.0 mm (an after-explained base-end hole13is a mere pierced hole). The measurement results (the relations between the dimensions of the retention protrusion15and its retention force) of SECC are shown by a graph inFIG. 2, and the measurement results of SUS are shown by a graph inFIG. 3. In addition, the aluminum-based material of the workpiece used for the measurements is a sheet member made of aluminum alloy A5052, and its thickness is 2.0 mm (an after-explained base-end hole13is a mere pierced hole). The measurement results of the aluminum-based material are shown by a graph inFIG. 4.

As understood from the graphs inFIG. 2toFIG. 4, the widths H 1.00 mm to 1.75 mm are good, and 1.25 mm is better. In addition, the lengths L 7.5 mm to 15 mm are good, and 15 mm is better. Note that, with respect to the length L, larger one than 15 mm is not measured. In consideration of practical aspects such as the dimensions of the processed part1(the product to be cut out) and a plastic deformation amount of the pressing protrusion15, it is determined that the pressing protrusion15longer than 15 mm is not needed.

Residual stress exists in the pressing protrusion15due to affection by heats of the laser cutting process of the cut slit11. Then, the residual stress is released when the outline5of the processed part1has been laser-cut after the laser cutting process of the cut slit11. As the result, a free end of the pressing protrusion15curves toward the processed part1(in a direction indicated by an arrow A) due to the residual stress (seeFIG. 10), and thereby the free end presses a peripheral surface (cut face) of the processed part1. Therefore, by carrying out the laser cutting process along the outline5of the processed part1after preliminarily forming at least one cut slit11around the processed part1, the processed part1can be retained by the curvature of the pressing protrusion15due to the residual stress so as not to drop off from the workpiece W.

Note that, in the first example shown inFIG. 1, the pressing protrusion15is formed at each of four corners of the processed part1. Namely, the four pressing protrusions15are formed in the first example. In the second example shown inFIG. 5, a pair of the pressing protrusions15is arranged oppositely to each other with the processed part1interposed therebetween. Then, the pressing forces of the two pressing protrusions15are applied toward the processed part1, and opposed to each other. Therefore, the processed part1is clamped by the pressing forces of the two pressing protrusions15, and the processed part1can be retained efficiently by the less pressing protrusions15. Note that the pressing protrusions15are formed longwise in the roll-expanding direction of the workpiece W. Advantages brought by forming the pressing protrusions15longwise in the roll-expanding direction of the workpiece W will be explained later.

For the laser cutting process of the cut slit11, a base-end hole13is laser-processed at a start end of the long slit9(a base end of the pressing protrusion15) at first. The base-end hole13is a through hole. In addition, a radius of the base-end hole13is made larger than a radius of a pierced hole merely penetrated by piercing. Namely, the retention force can be improved by making a curvature support point (a portion from a closest position to the outline5on an inner circumferential edge of the base-end hole13to a cutting slit of the outline5) of the pressing protrusion15close to the processed part1to enhance the inward curvature of the pressing protrusion15. Note that the radius of the base-end hole13is determined so that the curvature support point of the pressing protrusion15doesn't get broken (ensures sufficient stiffness to keep the retention force) with its width got by subtracting the cutting slit width of the outline5and the radius of the base-end hole13from the above-mentioned width H. For example, in a case where a thickness of a workpiece is 2.0 mm or so, a radius of the base-end hole13may be 0.75 mm and the width H may be 1.25 mm.

After forming the base-end hole13, the long slit9and the short slit7are sequentially formed without deactivating a laser light and stopping the motions of the processing head. Just after forming the base-end hole13, a portion around the base-end hole13is quickly cooled due to heat conduction outward from the position of the base-end hole13that is an initial position of the leaser processing. Therefore, the residual stress on a side of the free end of the pressing protrusion15becomes larger than the residual stress on a side of the base end thereof (near the base-end hole13). Then, in a case of where the cutting direction of the outline5of the processed part1is made coincident with the extending direction of the pressing protrusion15to be formed (the cutting direction of the long slit9), the pressing protrusion15can be effectively curved in the direction indicated by the arrow A with the above-mentioned curvature support point serving as a base end. Note that, if the cutting direction of the outline5and the extending direction of the pressing protrusion15are opposite to each other, the pressing protrusion15can be curved in the direction indicated by the arrow A but its retention force becomes slightly smaller.

The relations between the diameter (radius×2) of the base-end hole13and the retention force [N] are actually measured by using the workpieces made of the iron-based material and the aluminum-based material. Note that the retention force is a retention force exerted by a single pressing protrusion15. A size of the cut-out processed part1is a square whose each side is 65 mm, and one of two pairs of opposite two sides of the square is parallel to the roll-expanding direction of the workpiece. The pressing protrusion15is formed for each side one by one, and the end of the pressing protrusion15is positioned at the center of said each side. In addition, the extending direction of the pressing protrusion15coincides with the cutting direction of the outline5.

The iron-based material of the workpiece used for the measurements is SECC (electro galvanized zinc plated steel sheet) and SUS (stainless steel sheet). A thickness of SECC is 2.3 mm, and a thickness of SUS is 2.0 mm. The measurement results (relations between dimensions of the retention protrusion15and its retention force) of SECC are shown by a graph inFIG. 6, and the measurement results of SUS are shown by a graph inFIG. 7. In addition, the aluminum-based material of the workpiece used for the measurements is a sheet member made of aluminum alloy A5052, and its thickness is 2.0 mm. The measurement results of the aluminum-based material are shown by a graph inFIG. 8. In cases where the hole diameter of the base-end hole13is “N/A” in the graphs, the base-end hole13is a mere pierced hole and its hole diameter is not enlarged intentionally (the diameter of the pierced hole is 0.5 mm).

As understood from the graphs, with respect to the ion-based material, a larger retention force can be obtained when forming the base-end hole13having a diameter larger than that of a mere pierced hole. However, when the base-end hole13is too large, the stiffness of the above-mentioned curvature support point becomes insufficient and thereby the retention force reduces. With respect to SECC, the retention force increases by about 20% when the diameter of the base-end hole13is set to 1.5 mm. With respect to SUS, the retention force increases by about 15% when the diameter of the base-end hole13is set to 1.0 mm. However, with respect to the aluminum-based material, cases where the base-end hole13having a diameter larger than that of a mere pierced hole is not formed are better.

Note that it is sufficient that the width H and the length L of the pressing protrusion15are a width and a length by which the pressing protrusion15curves during the laser cutting process of the outline5of the processed part1and thereby presses the processed part1to retain the processed part1by a friction resistant force due to the pressing force. Therefore, the width H and the length L of the pressing protrusion15may be set to a width and a length that are desired according to a size of the processed part1, the number of the cut slits11to be formed around the processed part1and so on.

Note that the residual stress generated in the pressing protrusion15during the formation of the cut slit11is reduced in some degree when the pressing protrusion15is heated during the laser cutting process of the outline5. In addition, the residual stress of the pressing protrusion15reduces in some degree as time goes on. However, necessary residual stress never gets dissipated while cutting the processed part1and while separating the processed part1from the workpiece W, and thereby the retention for the processed part1is unaffected.

Further, the pressing protrusion15curves more remarkably in the direction indicated by the arrow A when being formed longwise in the roll-expanding direction of the workpiece W than when being formed longwise in a direction perpendicular to the roll-expanding direction. Therefore, it is desired that the number of the pressing protrusions15longwise in the roll-expanding direction is increased in order to retain the processed part1separably. However, the residual stress due to (heats of) the laser cutting process is more predominant than the residual stress due to the roll-expansion, so that there may be a case where the residual stress due to the roll-expansion can be ignored when the thickness of the workpiece W increases.

According to the present embodiment, the cut slit11(e.g. having an L-shaped in the present embodiment) is preliminarily formed along the outline5of the processed part1by carrying out the laser cutting process in a desired area around the pressing protrusion15while cutting out the processed part1from the workpiece W. The pressing protrusion15presses the peripheral surface of the processed part1due to the residual stress while laser-cutting the outline5of the processed part1and thereby retains it so that the processed part1is not separated from the workpiece W (not separated from the scrap3). The pressing protrusion15is formed longwise along the outline5.

In a case of forming a hole1H inside the processed part1(the outline5) as shown inFIG. 9(the third example), an inside portion17of the hole1H becomes a scrap at last. In this case, the cut slit(s)11is preliminarily formed in the inside portion17and a laser cutting process is carried out in a desired area around the pressing protrusion15while laser-cutting an outline of the hole1H. By laser-cutting the outline of the hole1H in this manner, the pressing protrusion15presses an inner peripheral surface of the hole1H and thereby the inside portion17is retained (the inside portion17is restricted from being separated from the processed part1).

In the case of forming the hole1H inside the processed part1, it is preferable to laser-cut the outline of the hole1H (the inside portion17) in a state where the processed part1is being unified with the workpiece W (before carrying out the laser cutting process of the outline5of the processed part1) and then laser-cut the outline5. Since the length of the outline of the hole1H is overwhelmingly shorter than the length of the outline5of the processed part1(in other words, an area of the hole1H is overwhelmingly smaller than an area within the outline5of the processed part1/a weight of a cut piece inside the hole1H is overwhelmingly smaller than a total weight of the cut piece inside the hole1H and the processed part1), the retention force by the pressing protrusion15is more effective for an object having a smaller weight. Note that, if the difference of the weights is small or if there is restriction in carrying out the process, the outline of the hole1H may be laser-cut after the laser cutting process of the outline5of the processed part1.

Although general configuration of a laser cutting machine for carrying out a laser cutting process of a workpiece W is commonly known, configuration of a laser cutting machine21according to the present embodiment will be explained hereinafter. As schematically shown inFIG. 11, the laser cutting machine21includes a support frame (work table)23that supports a workpiece W. A gate-shaped movable frame (carriage)25is provided on the support frame23so as to be movable in an X-axis direction. A slider27is provided on the carriage25so as to be movable in a Y-axis direction. A laser processing head29is provided on the slider27so as to be movable vertically (in a Z-axis direction).

The laser processing head29is provided so as to be movable relative to the workpiece W in the X, Y and Z-axis directions. Setting of the relative position of the laser processing head29in the X, Y and Z-axis directions is controlled by driving an X-axis servo motor, a Y-axis servo motor and a Z-axis servo motor (not shown in the drawings). A fiber laser oscillator31is provided as one example of a laser oscillator in order to laser-cut the workpiece W by the laser processing head29. The fiber laser oscillator31and the laser processing head29are connected with each other by an optical fiber33.

The laser cutting machine21configured as explained above is controlled by its control device35(seeFIG. 12). Operations of the laser processing head29and operations of the laser oscillator31are also controlled by the control device35, and thereby the processed part1is cut out from the workpiece W as explained above.

The control device35is configured of a computer, and includes a CPU, a RAM, a ROM, an input device37and a display device39. An automatic programming apparatus41that supplies (transmits) a processing program to the control device is connected with the input device37. Note that the processing program (NC data) generated by the automatic programming apparatus41can be supplied to the control device35by an appropriate memory media.

The control device35includes a processing program memory43that stores the processing program. In addition, the control device35also includes a program analyzer45. The program analyzer45preliminarily reads out the processing program stored in the processing program memory43and then analyzes it, and then calculates an arrangement position on the workpiece W, a shape and dimensions of the processed part1.

Further, the control device35also includes an arithmetic section47that executes various arithmetic calculations. In the arithmetic section47, included is a weight arithmetic section47A that calculates a weight of the processed part1and also calculates a barycentric position and/or a center position of the processed part1with referring to a shape and dimensions of the processed part1obtained by analyzing the processing program, a material and a thickness of the workpiece W and so on. In addition, in the arithmetic section47, also included is a press-force arithmetic section47B that calculates a pressing force of the pressing protrusion(s)15to be arranged around the processed part1.

The press-force arithmetic section47B refers to the width H and the length L of the pressing protrusion15and a laser cutting condition and then calculates the pressing force P=F(H, L, laser cutting condition) [f(a, b, c) is a function with variables a, b and c]. In the laser cutting condition, a laser output power, a processing speed, a focal position, a duty ratio of a pulse output, a pressure of assist gas, a diameter of a head nozzle and so on are included. Therefore, it is hard to determine the laser cutting condition inclusively. Then, in order to determine the laser cutting condition inclusively, the control device35also includes a cutting condition parameter memory57.

Various parameters are stored in the cutting condition parameter memory57. Namely, residual stresses are preliminarily measured at the laser cutting processes by varying a processing speed, a focal position, a duty ratio of a pulse output, a pressure of assist gas, a diameter of a head nozzle and so on for each set of a material and a thickness of the workpiece W, and these various laser processing conditions are stored in the cutting condition parameter memory57as parameters. Therefore, an appropriate parameter(s) can be selected from the cutting condition parameter memory57according to the laser cutting condition. The pressing force P is calculated based on the selected parameters.

Further, in the arithmetic section47, also included is a number arithmetic section47C that calculates the number of the pressing protrusions15to be provided based on the calculation result of the weight arithmetic section47A and the calculation result of the press-force arithmetic section47B. If a calculation result includes a digit(s) after the decimal point, the number arithmetic section47C carries up the calculation result into an integer.

Furthermore, the control device35also includes a pressing protrusion arranger49. The pressing protrusion arranger49arranges the pressing protrusions15around the processed part1based on data analyzed by the program analyzer45and then stored in an analyzed data memory45A, such as the arrangement position, the shape and the dimensions of the processed part1and the calculation result of the number arithmetic section47C.

For example, in a case of providing one pressing protrusion15, the pressing protrusion arranger49arranges the pressing protrusion15at a position where a distance from the barycentric position or the center position of the processed part1to the outline5is made minimum so that the pressing force of the pressing protrusion15is directed in a direction toward the barycentric position or the center position. In a case of providing two or more pressing protrusions15, it arranges the pressing protrusions15around the processed part1at even intervals along its peripheral direction.

There may be another way in which the processed part1is displayed on a display screen39A of the display device39after the calculation of the number of the pressing protrusions15by the number arithmetic section47C, and then the pressing protrusions15are arranged around the processed part1by operating the input device such as a mouse. In this case, it is possible to increase the number of the pressing protrusions15more than the number calculated by the number arithmetic section47C. In addition, in this case, the display device39, the mouse and so on function also as the pressing protrusion arranger49.

The shape and the dimensions of the pressing protrusion15, i.e. the lengths of the long side and the short side of the rectangular shape are preliminarily determined through experiments as parameters in association with the material and the thickness of the workpiece W and the shape and the dimensions of the processed part1. In addition, the parameters for determining the shape and the dimensions of the pressing protrusion15are stored in a workpiece parameter memory51. Therefore, an appropriate shape and appropriate dimensions of the pressing protrusion15are selected from the workpiece parameter memory51according to the material and the thickness of the workpiece W.

When the shape and the dimensions of the pressing protrusion(s)15have been selected, a processing program for the laser cutting process of the pressing protrusion15is generated according to the shape and the dimensions of the pressing protrusion15that have been selected. Namely, the control device35includes a laser cutting program memory53that preliminarily stores various laser cutting programs for various sets of the shape and the dimensions of the pressing protrusion15. When the shape and the dimensions of the pressing protrusion(s)15have been selected by the parameters, a processing program generator55selects an appropriate laser cutting program from the laser cutting program memory53according to the determined parameters, and then stores it in the processing program memory43.

Further, the control device35includes an axial motion controller59. The axial motion controller59controls axial motions of the laser processing head29in the X, Y and Z-axis directions according to the processing program stored in the processing program memory43.

For example, in a case of cutting out the processed part1from the workpiece W as shown inFIG. 1, the processing program is analyzed by the program analyzer45when the processing program generated by the automatic programming apparatus41has been stored in the processing program memory43. Then, the material and the thickness of the workpiece W and the shape and the dimensions of the processed part1are stored in an analyzed data memory45A as analyzed data.

When the processing program has been analyzed, the weight arithmetic section47A calculates a weight of the processed part1based on the analyzed data (the material and the thickness of the workpiece W and the shape and the dimensions of the processed part1). In addition, the appropriate shape and the appropriate dimensions of the pressing protrusion15are selected from the workpiece parameter memory51based on the analyzed data.

When the appropriate shape and the appropriate dimensions of the pressing protrusion15have been selected from the workpiece parameter memory51, an appropriate laser cutting condition for the laser cutting process of the pressing protrusion15is selected from the cutting condition parameter memory57. Then, the processing program generator55generates the laser cutting program of the pressing protrusion15based on the selected laser cutting condition and the shape and the dimensions of the pressing protrusion15, and stores it in the processing program memory43. In addition, the press-force arithmetic section47B calculates the pressing force of the pressing protrusion15based on the selected laser cutting condition and the width H and the length L of the pressing protrusion15.

Based on the calculation result of the weight arithmetic section47A and the calculation result of the press-force arithmetic section47B, the number arithmetic section47C calculates the required number of the pressing protrusions15for pressing and retaining the processed part1so as to restrict the processed part1from dropping off from the workpiece W. Note that, without using the press-force arithmetic section47B, the required number of canonically-shaped pressing protrusions with respect to a weight of a retention object may be preliminarily determined and then the required number of the pressing protrusions15may be calculated based on the weight of the retention object.

When the number of the pressing protrusions15has been calculated by the number arithmetic section47C, the pressing protrusions15are arranged around the processed part1by the pressing protrusion arranger49. Note that the number arithmetic section47C calculates the required minimum number. Therefore, for example, the pressing protrusion(s)15can be additionally arranged around the processed part1displayed on the display screen39A of the display device39by the input device such as a mouse.

When the arrangement positions of the pressing protrusions15have been set, the cut slits11are laser-cut according to the arrangement positions of the pressing protrusions15. Then, after the laser cutting of the cut slits11, the outline5of the processed part1is laser-cut according to the processing program stored in the processing program memory43. When the outline5has been laser-cut in this manner, the processed part1is pressed and retained by the plural pressing protrusions15arranged around the processed part1as explained above so as not to drop off from the workpiece W.

In the above explanations, the processing program generated by the automatic programming apparatus41is stored in the processing program memory43of the control device35, and the program analyzer45of the control device35analyzes this stored processing program. However, there may be another way in which the automatic programming apparatus41analyzes a laser cutting program generated by itself, and then a program transferrer63(seeFIG. 13) of the automatic programming apparatus41transfers this analyzed laser cutting program to the control device35.

The automatic programming apparatus41in this case will be explained. Note that components identical or equivalent to the already-explained components of the control device35of the laser cutting machine21are labelled with the identical reference signs and their redundant explanations are omitted.

As shown inFIG. 13, the automatic programming apparatus41includes an arithmetic section47equivalent to the arithmetic section47of the control device35. Therefore, when an operator inputs a shape and dimensions of the processed part through a CAD61, the automatic programming apparatus41calculates a weight of the processed part1, and a pressing force and the number of the pressing protrusions15to be arranged around the processed part1(a weight arithmetic section47A, a press-force arithmetic section47B and a number arithmetic section47C). Then, the automatic programming apparatus41calculates the number of the pressing protrusions15, and a pressing protrusion arranger49arranges the pressing protrusions15around the processed part1.

When the arrangement positions of the pressing protrusions15have been set around the processed part1, a processing program generator55generates a laser cutting program for carrying out a laser cutting processing of the pressing protrusions15and the processed part1. The processing program generator55stores a laser cutting program generated by itself in a processing program memory43. The program transferrer63transfers the laser cutting program stored in the processing program memory43to the control device35.

Therefore, the control device35laser-cuts the workpiece W by controlling operations of the laser processing head29according to the laser cutting program generated by the automatic programming apparatus41.

Note that, in the above embodiments, the length L of the pressing protrusion15is made three to eight times larger than the thickness of the workpiece W. If it is smaller than three times large value, the inward curvature of the pressing protrusion15decreases and thereby an sufficient pressing force cannot be got. On the other hand, if it exceeds over eight times large value, a curvature of the pressing protrusion15other than inward is subject to be generated. For example, the pressing protrusion15becomes subject to be twisted due to the weight of the processed part, and thereby the inward pressing force cannot be got effectively.

In addition, the measurements of the retention force are done by using the workpieces W whose thickness is 2.0 mm and 2.3 mm in the above embodiments, but it is still preferable, even if its thickness is larger, that the width H of the pressing protrusion15is made smaller than the thickness of the workpiece W and the length L of the pressing protrusion15is made three to eight times larger than the thickness of the workpiece W.

According to the above embodiments, the control device35or the automatic programming apparatus41arranges one or plural pressing protrusions15around the processed part1to be cut out from the sheet-shaped workpiece W. The curving pressing protrusion(s)15retains the processed part1so as not to drop it off from the workpiece W.

The entire contents of a Japanese Patent Application No. 2017-55555 (filed on Mar. 22, 2017) are incorporated herein by reference. Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Scope of the present invention is determined in the context of the claims.