Abstract:
The invention relates to a method for allocation of a pipe or several pipes with several pipe parts to be cut for a laser cutting installation, wherein the pipe parts to be cut are selected from an order table. Methods include measuring a length of each of the one or more pipes, calculating, before measuring, a nesting of a pipe part relative to the same pipe part or a different pipe part of the order table, calculating a plurality of pipe allocation variants for a particular pipe of the one or more pipes with the pipe parts to be cut based on the nesting and the measured pipe length of the particular pipe, selecting one of the plurality of calculated pipe allocation variants as a desired pipe allocation, and initiating cutting of the particular pipe based on the desired pipe allocation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims priority under 35 U.S.C. §120 to PCT/DE2009/000412, filed on Mar. 31, 2009, and designating the U.S., which claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2008 016 734.7, filed on Mar. 31, 2008. The contents of the prior applications are hereby incorporated by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a method for the allocation of a pipe or several pipes with several pipe parts to be cut for a processing machine, in particular for a laser cutting machine, wherein the pipe parts to be cut are selected from an order table, and also to a computer program product that is adjusted for performing the method. 
       BACKGROUND 
       [0003]    Within the scope of the present application, a tube is defined as an elongated element the length of which is generally substantially larger than its cross-section and which is produced from a substantially inflexible material. Pipes can have any open or closed cross-sectional shape, wherein round and rectangular pipes are the most common pipes. Pipe-shaped elements that are produced from pipes by laser cutting are designated as pipe parts within the scope of the present application. 
         [0004]      FIG. 1  shows a processing machine  1  for laser cutting of pipes  2  known as “TruLaser Tube,” which is designated as a laser cutting machine and is designed for processing pipes having any cross-sectional shape. The illustrated laser cutting machine  1  comprises a supply device  3  for lateral supply of a pipe  2  to be cut to the laser cutting machine  1 , a processing device  4  for laser cutting of pipe parts from the pipe  2  and a discharge device  5  for discharging the cut pipe parts out of the laser cutting machine  1 . All essential functions of the laser cutting machine  1  are controlled by means of a numerical control device  6 . 
         [0005]    The supply device  3  comprises a rotating and feeding means  7  that serves as workpiece moving means, and a machine bed  8  with guiding rails  9  and a push-through means  10 . The rotating and feeding means  7  is driven by a motor and can be moved in the feed direction  11  on the guiding rails  9 . On the side facing a pipe  2  to be fed, the rotating and feeding means  7  has a clamping means  12  that is controlled to be rotatable in the direction of an axis of rotation  13  and surrounds the supplied pipe  2  from the outside to stationarily clamp it. The supplied pipe  2  is supported by a workpiece support  14  integrated in the machine bed  8 . The pipe  2  is guided through the push-through means  10  in the area of the processing device  4 . The push-through means  10  is designed in such a fashion that the clamped pipe  2  is guided in the feed direction  11  and is not stationarily clamped. The pipe  2  can be rotated about the axis of rotation  13  in the push-through means  10 . 
         [0006]    The processing device  4  comprises a laser beam source  15  for generating a laser beam  16 , a processing head  17  and a beam guidance  18  that guides the laser beam  16  from the laser beam source  15  to the processing head  17 . The laser beam  16  exits the processing head  17  and is focused on the outer peripheral surface of the clamped pipe  2 . The discharge device  5  is provided on the side of the push-through means  10  facing away from the machine bed  8 , and discharges the pipe parts cut from the pipe  2  and the residual pipe out of the laser cutting machine  1 . 
         [0007]    In order to increase the productivity of the laser cutting machine  1 , the laser cutting machine  1  of  FIG. 1  has a loading device  19  as automation component with which a pipe  2  is automatically transported into a transfer position  86  ( FIG. 3 ) and transferred to the supply device  3  of the laser cutting machine  1 . The machine arrangement of laser cutting machine  1  and loading device  19  is called flexible manufacturing cell  20  (abbreviated as FMC). 
         [0008]    When the pipe  2  supplied via the loading device  19  is located in the transfer position  86 , the rotating and feeding means  7  is initially in an initial position remote from the processing head. For processing a pipe, the rotating and feeding means  7  moves out of its position with opened clamping means  12  towards the supplied pipe  2  until the end of the pipe  2  facing away from the processing head  17  comes to rest within the clamping means  12 . The clamping means  12  is closed and the pipe  2  is thereby stationarily clamped on the rotating and feeding means  7 . The rotating and feeding means  7  and the pipe  2  move together towards the processing head  17 . The end of the pipe  2  facing the processing head  17  thereby initially enters the push-through means  10  and is moved in the feed direction  11  through the push-through means  10 , wherein the pipe  2  can be rotated about the axis of rotation  13  in the push-through means  10 . The pipe  2  is delivered to the desired processing position  92  relative to the processing head  17  through movement of the rotating and feeding means  7  in the feed direction  11 . 
         [0009]    Processing machines are controlled by means of numerical controls that are also called NC controls, wherein NC is the abbreviation of the English term “Numerical Control.” Since the early 1970s, permanently wired NC controls have been replaced by computer-controlled NC controls that are called CNC controls (Computerized Numerical Control). Modern NC controls are exclusively based on microprocessor technology, for which reason the terms NC control and CNC control are practically used synonymously. One advantage of NC controls on the basis of microprocessor technology is that uniform hardware components that are available in large quantities can be adjusted to special processing machines and production tasks by implementing different software components. The current state of modern NC controls is provided e.g. in the textbook by Manfred Weck, Werkzeugmaschinen Fertigungssysteme, volume 4 “Automatisierung von Maschinen and Anlagen” (automation of machines and systems), Springer-Verlag. 
         [0010]    NC controls are generally divided into three control units:
       MMC control unit (Man Machine Communication) as data input and visualization unit,   adjustment control unit as central control unit that is also referred to as SPS or PLC, wherein SPS is the abbreviation of the term “memory programmable control,” in English Programmable Logic Controller, abbreviated as PLC,   NC control unit.       
 
         [0014]    Data or control commands input via the MMC control unit are decoded in the NC control unit, separated and further processed in accordance with geometrical data, technological data and switching functions. Geometrical data contains e.g. path information about the paths on which the tools and workpieces must be moved (processing head and pipe movement), whereas technological data contains e.g. processing parameters such as feed speed and laser beam power. Switching commands control e.g. tool change, feeding of parts (load pipe) and removing parts (unload pipe part). Switching commands are passed on to the SPS control unit where they are linked with responses from the processing machine and are transformed into control commands for the units to be switched in accordance with the gradually processed control program. The geometrical and technological data generates corresponding commands of axis movement for the processing machine upon request by the NC control unit. The NC and SPS control units transmit the current status of the machine to the MMC control unit for visualization. 
         [0015]    The three control units, MMC, SPS and NC control unit were realized in the form of separate processors (multi-processor technology) in the past due to limited processor power. Modern processors are so efficient that even one single processor (so-called single-processor technology) can provide the required power. With NC controls with single-processor technology, the MMC, SPS and NC control units are only separated at the software level today. 
         [0016]    For controlling a processing machine, the NC control requires a suitable control program that is also called NC program. Each command to a processing machine is expressed in the form of so-called functions encoded in a DIN code. Basic functions that are used for each processing method are stated in international guidelines, in particular in the DIN standard 66025. The basic functions include movement information to a defined position, geometrical information describing the contour profile of a part (sheet metal part, pipe part) and technological information for the production of the contour (e.g. laser cutting). In addition to the basic functions that are defined in the DIN code, the machine manufacturers develop special NC functions for their processing machines and the associated processing methods. For laser cutting of pipes, the different wall thicknesses require e.g. different piercing methods that can each be accessed via their own NC functions. 
         [0017]    For automatic generation of NC programs, machine manufacturers and software companies developed so-called programming systems. Programming systems know the basic and special NC functions and know which technology data is required and which processing rules are applied. 
         [0018]    In this way, they can automatically define the processing and generate an NC program. Special NC functions are stored and documented in the programming system such that a programmer can use an NC function without knowing its DIN code. Nowadays, a programmer does not need any classical programming knowledge, his/her expert knowledge rather includes finding the optimum processing parameters and processing strategies. 
         [0019]      FIG. 2  shows the numerical control device  6  of the laser cutting machine  1  of  FIG. 1  that comprises all hardware and software components that are used to control the laser cutting machine  1  and the manufacturing cell  20 . 
         [0020]    On the hardware side, the control device  6  comprises an MMC control unit  30  with a control computer  31  that is e.g. designed as an industrial PC, and an operating means  32  having a screen  33  as display unit, and a keyboard  34  as input unit, as well as a machine control panel  35  for manual operation of the laser cutting machine  1  and of the manufacturing cell  20 , and an NCU assembly  36  (Numerical Control Unit) with integrated NC control unit  37  and SPS control unit  38 . All hardware components of the control device  6  are networked via a bus system (not shown) to which further control components can be connected. The MMC control unit  30  and the NCU assembly  36  with NC and SPS control units  37 ,  38  are designed in the form of two separate components in this embodiment. In an alternative fashion, the MMC, NC and SPS control units  30 ,  37 ,  38  can be designed in the form of three separate components or as one common processor for single-processor technology. The control computer  31  and the NCU assembly  36  can be disposed in a switch cabinet (not shown) associated with the laser cutting machine  1 . 
         [0021]    On the software side, the control device  6  comprises operating software for controlling the automation components (loading device  19 ) as well as software modules for job management, tool management and pallet management that are combined as operating software  39  for the manufacturing cell (manufacturing cell operating software, FMC software). Operating software  40  for the laser cutting machine (machine operating software, MMC software), program management  41  for managing the NC programs and, if necessary, further applications such as e.g. a programming system  42  are installed on the control computer  31  in addition to the FMC software  39  for the manufacturing cell. 
         [0022]    In order to be able to create an NC program that is called NC parts program in a programming system for a pipe part to be cut, the programmer requires a design drawing of the pipe part that is loaded into the programming system. A pipe part is constructed by means of a construction system  43  (CAD system) or a combined construction and programming system  44  (CAD/CAM system), wherein the abbreviations CAD and CAM stand for Computer Aided Design and Computer Aided Manufacturing. The finished design drawings are stored in a common CAD data storage  46  provided for this purpose in a network  45 , which the programmers can access when required. 
         [0023]    An NC parts program for laser cutting of a pipe part can be created in two different ways. In the first case, the NC parts program is created during work preparation by means of a programming system and transferred to the control device  6 . Previously read-in NC parts programs can be subsequently changed or corrected via the operating means  32 . In the second case, the machine operator manually creates the NC parts program on the operating means  32  of the MMC control unit  30 . In the embodiment shown in  FIG. 2 , in addition to the programming system  42 , further programming systems are installed in the network  45  on the control computer  31  in the form of a combined construction and programming system  44  (CAD-/CAM system) and a pure programming system  47  (CAM system). The control computer  31  and the programming systems  42 ,  44 ,  47  are connected to a CAM data storage  48  that the programmers and machine operators can access. The programmer stores the finished NC parts programs in the CAM data storage  48 . The machine operator can access the CAM data storage  48  and import the NC parts programs from the CAM data storage  48  into the program management  41  of the control computer  31 . The data transfer of the NC parts programs into the program management  41  can also be realized via a storage medium such as a CD ROM or a USB stick such that it is also possible to import NC parts programs that are not stored in the CAM data storage  48  into the program management  41 . 
         [0024]    For producing a pipe part on the laser cutting machine  1 , the machine operator generates an order table  49 , schematically indicated in  FIG. 1 , in the FMC software  39 , in which table a parts order  49   a ,  49   b  is created for each pipe part stating the quantity of pipe parts in addition to the program name of the associated NC parts program. During creation, the parts orders  49   a ,  49   b  are associated with a status “blocked” or “approved.” Only approved parts orders, i.e. parts orders that have the status “approved” are processed on the laser cutting machine  1 . Blocked parts orders, i.e. parts orders that have the status “blocked” cannot be processed and are therefore not taken into consideration in automatic pipe allocation. The FMC software  39  shows the status “active” in the order table  49  when an approved parts order is being processed on the laser cutting machine  1 . A parts order that was duly processed shows the status “finished” in the order table  49 . 
         [0025]      FIG. 3  shows the loading device  19  of the laser cutting machine  1  of  FIG. 1 . The loading device  19  comprises a bundling recess  80  for receiving pipes  2 , a separating means  81  for separating the pipes  2  from the bundle recess  80 , a lifting means  82  for lifting a separated pipe and a transfer means  83  with grippers  84  for transferring the pipe  2  to the supply device  3  of the laser cutting machine  1 . Since the pipes can differ in length by up to a few centimetres, the loading device  19  moreover includes a measuring means  85  for measuring the length of the pipes. The length must be measured to determine the X position (position in the feed direction  11 ) of the transfer position  86  of the pipe to the rotating and feeding means  7 . 
         [0026]    During processing of a pipe on the laser cutting machine  1  or during unloading of the residual pipe, the loading process of the next pipe is prepared. The process “prepare loading” includes the method steps to move a pipe  2  out of the bundle recess  80  via a measuring position  87  into a waiting position  88 . The pipes are fed and measured during machining until the waiting position  88  is reached. 
         [0027]    Several pipes  2  that are provided for processing on the laser cutting machine  1  are located in the bundle recess  80 . The pipes  2  are automatically transferred from the bundle recess  80  to the separating means  81 . The separating means  81  of the present embodiment has a first transport section as an accumulation section  89  and a second transport section as a separation section  90 . The accumulation section  89  and the separation section  90  consist of motor-driven conveyor chains that extend parallel to each other and cross each other. The pipes  2  disposed on the accumulation section  89  are transferred to the separation section  90 . The pipes  2  are pulled apart and thereby separated by increasing the transport speed of the separation section  90  with respect to the accumulation section  89 . 
         [0028]    The lifting means  82  is provided at the end of the separation section  90  for lifting one single pipe  2  into the measuring position  87  in which the length of the pipe  2  is measured using the measuring means  85 . The measurement of the length is performed automatically through movement of a toothed belt drive, provided with a pressure sensor, against an electrically detected switch. The measured value of the pipe length is transferred by the measuring means  85  to the control device  6  of the laser cutting machine  1 . The grippers  84  of the transfer means  83  move from a basic position  91  to the measuring position  87 , take over the pipe  2  after its length has been measured and move together with the pipe  2  to the waiting position  88  in which they remain until the loading process is approved. As soon as the grippers  84  with the pipe  2  are arranged in the waiting position  88 , the process “prepare loading” is terminated. 
         [0029]    After approval of the loading process, the grippers  84  move into the transfer position  86  in which the measured pipe is transferred by the grippers  84  to the rotating and feeding means  7 . When the pipe  2  is in the transfer position  86 , it is clamped by the clamping means  12  of the approaching rotating and feeding means  7 . The grippers  84  return to their basic position  91 . The loading process is terminated and the message “pipe loading terminated” appears on the screen  33  of the MMC control unit  30 . 
         [0030]    In the conventional laser cutting machine  1  of  FIG. 1 , the pipe allocation with several pipe parts to be cut is either created in the associated programming system  42 ,  44 ,  47  or in the FMC software  39  of the control computer  31 . 
         [0031]    The programming system “TruToPs Tube” used by the conventional laser cutting machine “TruLaser Tube”  1  optionally comprises a nesting module “TubeLink” for optimizing the allocation of a pipe with several pipe parts to be cut.  FIG. 4  shows a flow chart of the individual method steps of the method known from TubeLink for optimizing the pipe allocation. In a first step S 1 , the programmer determines the nesting options, wherein he/she specifies the minimum pipe length of the pipes to be cut, the distance between the pipe parts and the length of the pipe piece that cannot be processed in the dead area of the clamping means  12  as “minimum residual length.” In a second step S 2 , the programmer creates a new production package or opens an existing one and includes the NC parts programs of the pipe parts to be nested in the opened production package in a third step S 3 . In a fourth step S 4 , it is checked whether the production package contains all desired NC parts programs. When the result of the test of step S 4  is negative (N), the method is continued with step S 3  and a further NC parts program is included in the production package. When the result of the test of step S 4  is positive (J), it is examined in a fifth step S 5  whether the NC parts programs and therefore the pipe parts are arranged in the desired order. The pipe parts to be nested are disposed on the pipe in the same sequence as recorded in the production package. When the result of the test of step S 5  is negative (N), the programmer changes in a sixth step S 6  the order of the pipe parts in the production package through re-sorting of the NC parts programs. When the result of the test of  FIG. 5  is positive (J) or after step S 6 , nesting of the pipe part with respect to the previous pipe part is calculated in a seventh step S 7 . Nesting is defined by displacement of the pipe part in the feed direction  11  (X-offset) and rotation about the axis of rotation  13  (A-offset). In an eighth step S 8 , it is checked whether the pipe part shall be produced in a quantity larger than 1. When the result of the test of step S 8  is positive (J), nesting of the pipe part with respect to the same pipe part is calculated in a ninth step S 9 . When the result of the test of step S 8  is negative (N) or subsequent to step S 9 , all nesting results from step S 7  and, if necessary, of step S 9  are stored in a tenth step S 10 . In an eleventh step S 11 , it is checked whether a further pipe part is arranged behind the present pipe part. When the result of the test of step S 11  is positive (J), the method is continued with step S 7  and nesting of the further pipe part with respect to the previous pipe part is calculated. When the result of the test of step S 11  is negative (N), the production package is stored as complete pipe allocation in a twelfth step S 12 . After step S 12 , the conventional method for optimizing the pipe allocation is terminated. 
         [0032]    In an alternative fashion, the pipe allocation of the conventional laser cutting machine “TruLaser Tube”  1  is performed after creating an order table  49  by means of the FMC software  39 . The order in which the pipe parts to be cut are arranged on the pipe is determined by one of four allocation types: “fixed allocation,” “endless processing,” “endless processing with filler part” and “longest pipe part at first,” wherein pipe orders for the allocation type “fixed allocation” are manually created by the machine operator and for the other allocation types they are automatically created by the FMC software  39 . For the allocation type “fixed allocation,” NC parts programs or pipe parts are manually moved from the program management  41  to the pipe and created as a pipe order and stored. The pipe order is successively processed until the stated quantity of pipe parts has been reached. This type of allocation is mainly suited to produce pipe parts in assemblies. For the allocation type “endless processing,” all parts orders with the status “approved” are used in accordance with their sequence numbers for automatic pipe allocation, and are disposed one after the other on the pipe. Parts orders with the status “blocked” are blocked for pipe allocation and are not taken into consideration in automatic pipe allocation. As soon as the overall length of the pipe has been exceeded, the last pipe part is removed and the sequence of the pipe parts is stored in the form of a pipe order. The number of pipe orders that are created corresponds to the number that is required in order to process all parts orders with the status “approved.” For the allocation type “endless processing with filler part,” the pipe allocation is initially performed analogously to “endless processing.” In order to improve the utilization of the pipe, the parts orders are searched for short pipe parts. These short pipe parts are moved as filler parts into the still usable areas on the pipe that are generated as residual pipes in the allocation type “endless processing” when the parts orders are moved to the pipe exclusively in accordance with their sequence numbers. For the allocation type “longest pipe part at first,” all parts orders with the status “approved” that are sorted according to the pipe part length are used for automatic pipe allocation. The pipe allocation starts with the longest pipe part arranged next to one another until the required quantity has been achieved or the overall length of the pipe has been exceeded. When the quantity of longest pipe parts has been reached, the next shorter pipe part is disposed on the pipe until the required quantity has been achieved or the overall length of the pipe has been exceeded. 
         [0033]    The conventional nesting module “TubeLink” optimizes nesting of two pipe parts disposed next to one another on the pipe. With each of the four types of allocation, the pipe parts are arranged in accordance with the so-called rectangular allocation, wherein the pipe parts are shown as rectangles in the unrolling state, wherein the sides of the rectangle are determined by the outer points of the initial and final geometries. 
       SUMMARY 
       [0034]    In contrast thereto, the present invention provides an improved method for the allocation of a pipe or several pipes with several pipe parts to be cut, thereby taking into consideration the actual pipe length. 
         [0035]    In accordance with one aspect of the invention, the pipe or the pipes are measured, nesting of the pipe part with respect to the same pipe part and/or to one or more different pipe parts of the order table is calculated for one or more pipe parts of the order table prior to measuring the length of the pipe or pipes, and after measurement of the length of the pipe or pipes, different pipe allocation variants with the pipe parts to be cut are calculated taking into consideration the previously calculated nestings and measured pipe length, and one of the calculated pipe allocation variants is selected as the desired, or “best pipe allocation.” The pipe allocation variant that has the largest sum of pipe parts (number of pipe parts) is preferably selected as the “best pipe allocation” from all calculated pipe allocation variants. The pipe allocation variant having the smallest occupied pipe length is preferably selected as the desired, or “best pipe allocation” from several calculated pipe allocation variants having the same largest sum of pipe parts, so that the residual pipe length is preferably maximum for further processing. The pipe is cut based on the desired pipe allocation. 
         [0036]    When two pipe parts are nested, the possible rotation and/or displacement of one pipe part relative to the other pipe part are calculated. Whether and to which extent a pipe part can be rotated and/or displaced is determined by the programmer via the properties “rotatable about A-offset” and “displaceable about X-offset” when the NC parts program is created. The property “tiltable or mirrorable” states whether a pipe part can be horizontally tilted. For a tilted pipe part, the initial and final geometries are interchanged compared to the non-tilted pipe part and rotated through 180° about the axis of rotation  13 . For calculating nesting with respect to a tiltable pipe part, the possible rotation and displacement is calculated both with respect to the non-tilted and to the tilted pipe part. 
         [0037]    In accordance with the invention, the actual pipe length of a pipe or several pipes is taken into consideration for optimizing the pipe allocation and for determining the sequence of the pipe parts. 
         [0038]    Nesting is preferably calculated for each pipe part of the order table with an approved parts order. Nesting is calculated, in particular, with respect to the same pipe part and to all different pipe parts of the order table with an approved parts order and, if necessary, with respect to all different pipe parts of the order table with a blocked parts order. 
         [0039]    The calculation of the pipe allocation variants is advantageously started as soon as the measured pipe length has been transferred to a control device of the laser cutting machine. 
         [0040]    The calculation of different pipe allocation variants is advantageously terminated as soon as the pipe has been disposed in a transfer position and has been transferred to a supply device of the laser cutting machine or as soon as a preset time has elapsed or as soon as the pipe has been disposed in a processing position. 
         [0041]    The invention also relates to a computer program product including code means that are adjusted to perform all steps of the above-described optimization method when the program is run on a data processing system. 
         [0042]    Further advantages of the invention can be extracted from the claims, the description and the drawing. The features mentioned above and below can be used individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0043]      FIG. 1  shows a conventional laser cutting machine for cutting pipes; 
           [0044]      FIG. 2  shows the numerical control device of the conventional laser cutting machine shown in  FIG. 1 ; 
           [0045]      FIG. 3  shows the loading device of the conventional laser cutting machine shown in  FIG. 1 ; 
           [0046]      FIG. 4  shows a flow chart of the individual steps of the conventional method for optimizing the allocation of a pipe with several pipe parts to be cut; 
           [0047]      FIG. 5  shows a flow chart of the individual steps of the inventive method for optimizing the allocation of a pipe with several pipe parts to be cut; and 
           [0048]      FIGS. 6   a - d  show the performance of the preparatory calculation ( FIG. 6   b ) in accordance with the invention with the example of two pipe parts of different length ( FIG. 6   a ) and the determination of the “best allocation” of a pipe ( FIGS. 6   c, d ). 
       
    
    
     DETAILED DESCRIPTION 
       [0049]      FIG. 5  shows the individual method steps S 21  to S 33  of a method for optimizing the allocation of a pipe with several pipe parts to be cut in the form of a flow chart. The method includes a first process stage with steps S 21  to S 25 , measurement of the length of the pipe (steps S 26  and S 27 ) and a second process stage with steps S 28  to S 33 . The first process stage is performed prior to measurement of the length and the second process stage is performed after the measurement of the length of the pipe. 
         [0050]    In a first step S 21 , a parts order for a pipe part to be cut is created and approved in the order table  49  of the FMC software  39 , wherein the parts order also states the quantity of the pipe parts to be cut in addition to the program name of the associated NC parts program. When the NC parts programs of the pipe part that are required for creating a parts order are not contained in the program management  41  of the control computer  31 , the NC parts programs are imported into the program management  41  when the parts order is created. In a second step S 22 , it is checked whether nesting of this pipe part with respect to the other pipe parts of the order table with the status “approved” and with respect to the same pipe part was performed and whether the nesting results are already present. When two pipe parts are nested, any possible rotation (A-offset) and/or displacement (X-offset) of one pipe part relative to the other pipe part is calculated. Whether and to what extent a pipe part can be rotated and/or displaced is determined by the programmer via the properties “rotatable about A-offset” and “displaceable about X-offset” while creating the NC parts program. The rotatability is important e.g. for pipes having a weld seam in the longitudinal direction. When the longitudinal seam of all cut pipe parts shall have the same orientation, the pipe parts must not be rotated relative to one another during pipe allocation and the pipe parts are non-rotatable. The displaceability is e.g. important for pipe parts that make high demands on the surface quality in the area of the initial and final geometries. When the laser beam pierces the initial and final geometry, part of the laser beam hits the pipe, mainly on the opposite pipe inner side and can cause discoloration of the pipe part at that location. If discoloration of the pipe part in the area of the initial and final geometries is not desired, the pipe part must not be displaced at all or only within a limited range. Nesting is based on unrolling of the three-dimensional pipe parts with the initial and final geometries into the two-dimensional plane. When the result of the test of step S 22  is negative (N) and the pipe part is not or only incompletely nested, nesting of the pipe part with respect to the same pipe part and to all approved pipe parts of the order table is calculated in a third step S 23 , and the nesting results (X and A-offsets) are stored in a fourth step S 24 . The steps S 23  and S 24  are called preparatory calculation. Either after step S 24  or when the result of the test of step S 22  is positive (J), it is checked in a fifth step S 25  whether a parts order has been created and approved in the order table for all pipe parts to be cut. When the result of the test of step S 25  is negative (N), the first method stage is continued with step S 21  and a further parts order for a pipe part is created and approved in the order table. When the result of the test of step S 25  is positive (J) and a parts order for all pipe parts to be cut has been created and approved in the order table, the first process stage of the inventive method for optimizing the pipe allocation is terminated. 
         [0051]    In a sixth step S 26 , the length of the pipe is measured and the measured value of the pipe length is transferred from the measuring means  85  to the control device  6  of the laser cutting machine  1  in a seventh step S 27 . 
         [0052]    The second process stage of the method starts after the control device  6  has received the measured value of the pipe length in step S 27 . In an eighth step S 28 , a first pipe allocation variant is determined for which the sum of the lengths of the pipe parts (sum of pipe parts) and also the occupied pipe length are calculated by means of the nesting results from the preparatory calculation (steps S 23  and S 24 ) of the first process stage. The first pipe allocation variant is stored together with the sum of pipe parts and the occupied pipe length in a ninth step S 29  as the desired, or “best pipe allocation.” In a tenth step S 30 , it is checked whether the calculation of the pipe allocation variants was interrupted or terminated. When the result of the test of step S 30  is positive (J) and the calculation of the pipe allocation variants is terminated, the method for optimizing the pipe allocation is terminated and the pipe allocation variant stored in step S 29  as the desired, or “best pipe allocation” represents the result of the optimization method. When the result of the test of step S 30  is negative (N) and the calculation of further pipe allocation variants is continued, in an eleventh step S 31   a  further pipe allocation variant is determined for which the sum of pipe parts and the occupied pipe length are calculated by means of the nesting results of step S 23 . In a twelfth step S 32 , the sum of pipe parts of the further pipe allocation variant is compared with the sum of pipe parts of the “best pipe allocation” stored in step S 29 . When the result of the comparison of step S 32  is smaller (N), i.e. the sum of pipe parts of the further pipe allocation variant is smaller than the sum of pipe parts of the “best pipe allocation,” the further pipe allocation variant is dismissed and the inventive method is continued with step S 30 . When the result of the comparison of step S 32  is, however, larger (J), i.e. the sum of pipe parts of the further pipe allocation variant is larger than the sum of pipe parts of the desired, or “best pipe allocation,” the method is continued with step S 29  and the further pipe allocation variant with the sum of pipe parts and the occupied pipe length is then stored as the “best pipe allocation.” When the result of the comparison of step S 32  is equal (G), i.e. the sum of pipe parts of the further pipe allocation variant corresponds to the sum of pipe parts of the “best pipe allocation,” the occupied pipe length calculated in step S 31  is compared in a thirteenth step S 33  with the occupied pipe length of the “best pipe allocation.” When the result of the comparison of step S 33  is larger or equal (N), the pipe allocation variant determined in step S 31  is dismissed and the method is continued with step S 30 . When the result of the comparison of step S 33  is smaller (J), the method is continued with step S 29  and the further pipe allocation variant with the sum of pipe parts and the occupied pipe length is then stored as the “best pipe allocation.” In comparison with all other calculated pipe allocation variants, the “best pipe allocation” is e.g. characterized in that the sum of pipe parts is maximum and with identical sum of pipe parts, the occupied pipe length is minimum. When the pipe occupancies for several pipes are optimized (cross-pipe optimization method) it is also feasible not to use the maximum sum of pipe parts as a criterion for the “best pipe allocation” for a pipe when it is better to dispose a pipe part on another pipe. 
         [0053]    In order to limit the time for preparatory calculation, the method for optimizing pipe allocation shown in  FIG. 5  only uses approved parts orders of the order table, i.e. parts orders that have the status “approved.” When there is sufficient time for preparatory calculation, nesting of a pipe part with respect to the blocked parts orders, i.e. parts orders with the status “blocked,” can also be calculated in addition to the approved parts orders. It is also possible to calculate nesting of a pipe part with respect to the same pipe part and to other pipe parts already during importing the associated NC parts program into the program management  41 . In this case, the required time and storage space can dramatically increase. 
         [0054]    One parts order normally refers to one single pipe part that is unambiguously characterized by the associated NC parts program name. When pipe parts are to be produced in assemblies, the different pipe parts of the assembly can be combined into one order. In this case, the order comprises all NC parts programs of the individual pipe parts. 
         [0055]    Parts orders for pipe parts need not be created in FMC software  39  but can be created outside of the FMC software  39  in a programming system. The order table is subsequently imported together with the NC parts programs into the FMC software  39 . Nestings of the pipe parts with respect to each other can also be calculated in the programming system. The nesting results are then imported together with the order table into the FMC software  39 . 
         [0056]      FIGS. 6   a - d  show how step S 23  of the preparatory calculation of the first process stage ( FIG. 6   b ) and the steps S 28  to S 33  of the second process stage ( FIGS. 6   c, d ) of the optimization method for pipe allocation are performed by means of example of a longer first pipe part  100  of a length L A =55 cm and a shorter second pipe part  101  of the length L B =45 cm. The pipe parts  100 ,  101  can each be produced in a quantity of 4, for example. For purposes of illustration, the measured pipe length is provided as 185 cm and the dead area of the clamping means  12  is provided as 10 cm. 
         [0057]      FIG. 6   a  shows the pipe parts  100 ,  101  with their initial and final geometries. The first pipe part  100  has a 90° separating cut at the initial geometry  102  and a 45° separating cut at the final geometry  103 . The second pipe part  101  has a 45° separating cut at the initial geometry  104  and a 63° separating cut at the final geometry  105 . Since the final geometries  103 ,  105  of the two pipe parts  100 ,  101  represent an inclined section other than 90°, both pipe parts  100 ,  101  are not “cuttable.” A pipe part is defined as cuttable when there is no contour cut in the dead area of the clamping means  12  and the final geometry of the pipe part represents a 90° separating cut and coincides with the pipe end. 
         [0058]      FIG. 6   b  shows the four different arrangements  106  to  109  of the two pipe parts  110 ,  101  below one another: Arrangement  106  shows two longer pipe parts  100 , arrangement  107  shows a longer  100  and a shorter pipe part  101 , arrangement  108  shows a shorter  101  and a longer pipe part  100  and arrangement  109  shows two shorter pipe parts  101 . The feasible displacements and/or rotations between the pipe parts  100 ,  101  are calculated within the scope of the preparatory calculation (steps S 23  and S 24 ). With a pipe diameter of 10 cm, the following example displacements are obtained: X AA =0 cm, X AB =10 cm, X BA =0 cm and X BB =5 cm. When a first pipe part  100  is disposed behind a first or second pipe part  100 ,  101  (arrangements  106 ,  108 ), displacement is not possible due to the 90° separating cut as initial geometry  102  (X AA =X BA =0 cm) and the occupied pipe part length of the pipe part  100  cannot be reduced. When a second pipe part  101  is disposed behind a first pipe part  100  (arrangement  107 ), the occupied pipe part length of the second pipe part  101  is reduced by X AB =10 cm to 35 cm. When two shorter pipe parts  101  are disposed one behind the other (arrangement  109 ), the occupied pipe part length of the second pipe part  101  is reduced by X BB =5 cm, i.e. to 40 cm. 
         [0059]      FIGS. 6   c, d  show how the pipe allocation variants for steps S 28  and S 31  are determined by means of tree structures  110 ,  111 , wherein  FIG. 6   c  shows the pipe allocation variants on the basis of the longer first pipe part  100  and  FIG. 6   d  shows the pipe allocation variants on the basis of the shorter second pipe part  101 . Pipe allocation variants, in which the occupied pipe length exceeds the measured overall length of the pipe are highlighted in grey, all pipe allocation variants highlighted in white represent one possible pipe allocation variant. The dead area of the clamping means  12  must be taken into consideration when checking whether a pipe allocation variant is possible. At first, it is checked whether the occupied pipe length of a pipe allocation variant is smaller or equal to the measured pipe length reduced by the dead area (reduced pipe length). When the result of the test is negative, and the last pipe part is a cuttable pipe part, it is checked whether the occupied pipe length is smaller or equal to the measured pipe length. A pipe part is cuttable when there is no contour cut in the dead area of the clamping means  12  and the final geometry of the pipe part represents a 90° separating cut and coincides with the pipe end. The property “cuttable” is determined by the programmer during creation of the NC parts program. 
         [0060]    For determining a first pipe allocation variant for step S 28 , the longer pipe part  100  is arranged next to one another until the desired quantity of the pipe part  100  has been arranged on the pipe or the reduced pipe length of the pipe has been exceeded. With a reduced pipe length of 175 cm, it is possible to arrange three longer pipe parts  100  one after another, for the fourth pipe part  100  one obtains an occupied pipe length of 220 cm such that the reduced pipe length is exceeded. The fourth longer pipe part  100  is removed and replaced by a shorter pipe part  101 . Since this pipe allocation variant also exceeds the reduced pipe length of the pipe and the pipe part  101  is not cuttable, the pipe allocation variant  112  with three longer pipe parts  100  is the first pipe allocation variant that is used in step S 28 . In order to determine further pipe allocation variants for step S 31 , the third longer pipe part  100  in the pipe allocation variant  113  is replaced by a shorter pipe part  101  which results in an occupied pipe length of 145 cm. When a first pipe part  100  or a second pipe part  101  is arranged therebehind, the occupied pipe lengths are 200 cm or 185 cm, i.e. more than the reduced pipe length of 175 cm. When all possible pipe allocation variants  112 ,  113  with two pipe parts  100  have been determined, the second longer pipe part  100  is replaced by a shorter pipe part  101 . The tree structure  110  is subsequently supplemented by adding the pipe parts  100 ,  101  and one obtains further pipe allocation variants  114 ,  115 . When all possible pipe allocation variants  112  to  115  that are based on the longer first pipe part  100  have been calculated in  FIG. 6   c , all pipe allocation variants  116  to  119  in  FIG. 6   d  are determined on the basis of the shorter second pipe part  101 . The tree structures  110 ,  111  enable that only the last possible pipe allocation variant of one branch is used as further pipe allocation variant in step S 31  and must be compared with the best pipe allocation in step S 32  (sum of pipe parts) and in step S 33  (occupied pipe length), since the pipe allocation variants of the branch disposed above have a smaller sum of pipe parts. 
         [0061]    The best pipe allocation for the example of  FIGS. 6   a - d  is the pipe allocation variant  115  consisting of a longer first pipe part  100  and three shorter second pipe parts  101  with a sum of pipe parts of 190 cm and an occupied pipe length of 170 cm. The further pipe allocation variants consisting of a longer pipe part  100  and three shorter pipe parts  101 , wherein the longer pipe part  100  is disposed at the second, third or fourth position, have the same sum of pipe parts of 190 cm. The pipe allocation variants in which the longer first pipe part  100  is disposed at a second position (pipe allocation variant  117 ) or third position (pipe allocation variant  118 ), have an occupied pipe length of 175 cm each and are therefore larger than the occupied pipe length of the best pipe allocation. The “best pipe allocation” is characterized in that the sum of pipe parts is maximum and, with the same sum of pipe parts, the occupied pipe length is minimum. The pipe allocation variant in which the longer first pipe part  100  is disposed at a fourth position does not represent a feasible pipe allocation variant, since the occupied pipe length of 180 cm is larger than the reduced pipe length of 175 cm and the last pipe part  100  is not cuttable. 
         [0062]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.