Abstract:
A method for performing piercing preferentially on a laser beam machine by taking advantage of a capability to change laser machining tools automatically. A laser beam machine is equipped with a device for changing a torch and nozzle automatically. The laser beam machine is equipped with a means of selecting preferential treatment of piercing after nesting data is prepared by a CAM or NC system and performs piercing alone in favor of cutting by changing to a special-purpose piercing tool.

Description:
The present application is based on and claims priority of Japanese patent application No. 2004-155934 filed on May 26, 2004, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a piercing method which makes it possible to enable unskilled operators to operate a laser beam machine, maximize machining quality and productivity for each material and workpiece thickness, accomplish long, unattended operation, and perform piecing preferentially with a special-purpose piecing torch. 
   2. Description of the Related Art 
   According to conventional machining methods, machining programs are created by adding machining conditions such as laser intensity, feed rates, piecing conditions to predetermined machining geometries and then machining is performed by specifying one or more created machining programs for material. 
   When machining predetermined geometries from the middle of material rather than end of the material, holes are pierced at machining start points in the material in order for a laser beam and assist gas to pass the material (hereinafter this process is referred to as “piercing”) before starting machining, and then the predetermined machining operations are performed according to the machining programs (hereinafter this process is referred to as “cutting”). 
   When laying out multiple machining geometries with the best yield rate (hereinafter this process is referred to as “nesting”) and machining individual geometries, piercing and cutting are performed alternately. Besides, if workpiece thickness is large, piercing takes a long time, building up heat and resulting in machining defects. 
   Also, when small machining geometries are involved, heat builds up during piercing and cutting, resulting in machining defects. 
   On the other hand, a method is known in which piercing and cutting are performed by adjusting focal distance according to machining programs (Japanese Patent Laid-Open No. 7-223084 or Patent Document 1). 
   Generally, optimum machining conditions for piercing and cutting do not coincide. If piercing is optimized, cutting is not optimized. If cutting is optimized, piercing is not optimized. Since a compromise is sought between piercing and cutting, it is impossible to perform both piercing and cutting using optimum values and thus it is impossible to optimize machining quality and productivity. 
   Also, if piercing is not optimized, piercing takes a long time. This not only reduces productivity, but also causes heat build-up in the workpiece, which in turn will cause machining defects such as degradation of machining quality or even disable machining. 
   SUMMARY OF THE INVENTION 
   The present invention provides a piercing method on a laser beam machine which solves the above problems. 
   A laser beam machine according to the present invention comprises, as basic means, a bed, a pallet which is disposed on the bed and holds a workpiece, a column which moves along an X axis, that is, a longitudinal axis of the bed, a saddle which is supported by the column and moves along a Y axis orthogonal to the X axis, and a machining head which is supported by the saddle and moves along a Z axis perpendicular to the plane formed by the X axis and Y axis. 
   Besides, it comprises means for performing piecing alone preferentially before performing laser machining. 
   The preferential treatment of piercing can be selected after nesting data is created. 
   Since machining conditions can be specified separately for piercing and cutting, the present invention makes it possible to perform piercing and cutting under optimum machining conditions, thereby improving productivity greatly. 
   Since piercing is optimized, piercing takes a shorter time. This not only increases productivity, but also reduces heat build-up in the workpiece, which in turn will improve machining quality and enable continued stable machining. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing an entire laser beam machine according to the present invention; 
       FIG. 2  is a plan view of the laser beam machine according to the present invention; 
       FIG. 3  is a front view of essential part of the laser beam machine according to the present invention; 
       FIG. 4  is a perspective view of the essential part of the laser beam machine according to the present invention; 
       FIG. 5  is a side view of the essential part of the laser beam machine according to the present invention; 
       FIG. 6  is a front view of a setup station for laser machining tools; 
       FIG. 7  is a plan view of the setup station for laser machining tools; 
       FIG. 8  is an explanatory diagram of a piercing method; and 
       FIG. 9  is a process flowchart of the piercing method. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a perspective view showing an overall configuration of a laser beam machine according to the present invention,  FIG. 2  is a plan view,  FIG. 3  is a front view,  FIG. 4  is a perspective view of the relevant portion, and  FIG. 5  is a side view. 
   A laser beam machine, generally denoted by reference number  1 , has a pallet (table)  20  which is disposed on a bed  10  to carry a plate-shaped workpiece W 1 . A pallet changer  12  is placed on the longitudinal extension of the bed  10 , and a pallet  20   a  carrying a workpiece W 2  to be machined next is awaiting its turn. 
   A pair of guide rails  34  are installed on both sides of the bed  10  along its length and a column  30  is mounted on the guide rails  34  in such a way as to be movable along an X axis. 
   Means for driving the column  30  along the X axis is provided by, for example, a linear motor, which is formed by a stator installed on the guide rails  34  and a moving member installed on a linear-motion guide  32 . 
   A guide rail  44  is installed on the column  30  along a Y axis orthogonal to the X axis and a saddle  40  is mounted in such a way as to be movable along the Y axis. The saddle  40  is equipped with a linear-motion guide  42  which is engaged with the guide rail  44 . A linear motor is formed by the guide rail  44  and linear-motion guide  42 . 
   The saddle  40  has a guide rail installed along a Z axis perpendicular to the plane formed by the X axis and Y axis and has a machining head  50  mounted in such a way as to be movable along the Z axis. The machining head  50  has an optical system which admits a laser beam from a laser oscillator  72 . 
   The machining head  50  is equipped replaceably with a laser machining tool  60 . A machining area is fitted with a cover  90  to ensure safety. A power panel  70  and the laser oscillator  72  are disposed adjacent to the bed  10 . A control panel  80  for use by the operator to give various commands is disposed on a longitudinal end of the bed  10 . A setup station  100  for laser machining tools is installed on that end of the bed  10  which is closer to the control panel  80 . 
     FIG. 6  is a front view of the setup station  100  for laser machining tools as viewed from the table and  FIG. 7  is a plan view. 
   The setup station  100  for laser machining tools includes a tool station  200  and nozzle station  300 , where the tool station  200  is equipped with a tool change magazine for laser machining tools which in turn are equipped with a torch and nozzle while the nozzle station  300  is equipped with a nozzle change magazine for nozzles of laser machining tools. 
     FIG. 8  shows products W 10 , W 11 , etc. laid out (nested) for laser machining on workpiece W 1  material mounted on a pallet  20 . 
   Before machining the products W 10 , W 11 , etc., locations of pilot holes Ph to be pierced at machining start points outside of cutting lines CL of the products are determined automatically. 
   During regular machining, a laser machining tool performs piercing to produce pilot holes Ph and then moves from the pilot holes Ph to cutting lines CL. 
   The laser beam machine according to the present invention can perform machining by automatically changing laser machining tools among those stored in a plurality of tool magazines. 
   This makes it possible to prepare special-purpose tools most suitable for piercing and concentrate on piercing. 
     FIG. 9  is a process flowchart of a preferential piercing method. 
   In Step S 10 , processing is started. In Step S 11 , a CAM or NC system (numerical control system) is selected. In Step S 12 , nesting data is prepared. In Step S 13 , preferential piercing is selected. If preferential piercing is not selected, the flow goes to Step S 20 , where regular machining processes are repeated as follows: piercing→cutting→piercing→cutting. 
   If preferential piercing is selected, the CAM or NC system rearranges a machining sequence in Step S 14  based on the nesting data by giving priority to piercing. 
   In Step S 15 , a machining head selects a special-purpose piercing tool. The laser beam machine according to the present invention allows a torch and nozzle of the laser machining tool to be replaced separately. This makes it possible to replace only the nozzle with one suitable for piercing while using a torch intended for cutting. 
   Piercing is performed in Step S 16  and the machining tool is replaced with a torch or machining tool intended for cutting in Step S 17 . 
   Cutting is performed according to a cutting program in Step S 18  and the processing is finished in Step S 19 . 
   Incidentally, although a linear motor has been cited in the above example as a driving means along the X and Y axes, the present invention can also employ a ball screw. 
   Also, although the preferential treatment of piercing is selected after preparation of nesting data, it may be selected when a CAM or NC system is selected before preparation of the nesting data.