通過立式六軸控制并應用超聲振動加工銳角轉角

1、Manufacture of Overhanging Sharp Corner by Means of 6-Axis Control Machining with the Application of Ultrasonic Vibrationsfeliciano H.JAPITANA*,koichi MORISHIGE*,shugo YASUDA* and yoshimi TAKEUCHI The study proposes a new machine method to creat an create an overhanging sharp corner. Sharp corners o

2、n overhanging surfaces are difficult to machine in conventional way or even in 3 to 5-aixs EDM especially if the surfaces have different angles. This is due to the limitation of the feed direction and the structure of the electrode wherein it must be symmetrical with the target shape. In present res

3、earch, we try to machine the sharp corner with overhanging surfaces using the new machining method. The 6-axis control machining is applied to set a non-rotational tool at an arbitrary position with arbitrary position with arbitrary attitude against the workpiece. During cutting, the ultrasonic vibr

4、ation is applied on the cutting edge of the tool, while the tool travels along the feed direction. As the cutting is performed, the 6-axis (X,Y,Z,A,B and C) move simultaneously, depending on the tool attitude at a certain cutting point. Form the experimental results, it is shown that the 6-axis cont

5、rol ultrasonic vibration cutting is capable of producing a sharp overhanging surface. Key Words: 6-axis Controlled Cutting, CAD/CAM System, Bore Byte Tool, Overhanging Sharp Corner, Ultrasonic Vibration Cutting Tool 1. introductionThe flexibility of products may be extended greatly if the restrictio

6、n in manufacturing process can be minimized or eliminated. If rotational tools such as ball end mills or square end mills are used in the production of a mould with an overhanging sharp corner (OHSC), it seems difficult to clearly obtain the target shape with sharp edge lines. This is due to the res

7、ult of processing with the rotational tools, Which are symmetrical with the rotation. The arc-like radius remains are produced on adjoining surfaces, as shown in Fig.1Conventionally, most of overhanging or inclined surface can be machined by setting the workpiece at a certain angle in the vise, swiv

8、elling the universal vise, or by setting the tool head to a certain angle and feeding the cutting tool head, as shown in Fig.2(a). In this process, the overhanging surfaces and the sharp edges at the bottom are produced. However, if the target is an OHSC consisting of two overhanging side surfaces,

9、and the inclination angle of surface is not uniform, the processing of the target shape is difficult to achieve since the cutting direction in the process is fixed and limited only to linear cutting. Thus ,it needs a lot of jigs and fixtures to hold a workpiece ,to position correctly with respect to

10、 a machine tool and to support it during machining. Fig.1 5-axis control machining using rotational toolFig.2 method of producing sharp corner with overhanging surfacesThe other possible method to produce such a shape is multi-axis Electric Discharge Machining (EDM), as shown in Fig.2(b).However, ev

11、en using this method ,it is difficult or impossible to produce an OHSC with different angle .It needs 6 degrees of freedom to fully execute the machining of the required shape.In the previous researches, ultrasonic vibration (USV) was applied in turning of ductile material and milling of glassfiber-

12、reinforced plastic. The cutting force with USV is considerably reduced. However , in the former process ,the workpiece is rotated or moves to towards the cutting tool, and in the latter, machining is limited only to 2 or 3 axis control one. In the other field of research, multi-axis control machine

13、tool is used to complete a machining in one setup, which leads to the production of workpiece with high accuracy and quality and to the reduction in machining time.In this study, 6-axis control cutting using a non-rotational cutting tool with the application of ultrasonic vibration (USV) is used, as

14、 shown in Fig.2(c).It is applied to scrutinize the validity of the method in the fabrication of OHSC, The C-axis rotates the non-rotational tool simultaneously together with X,Y,Z,A or B axis during machining .The movement of the axes is based on the tool attitude and the cutting point generated by

15、a developed CAM software. The CAM program generates a collision free tool path to assure the safety of the process. The 6-axis control machine tool provides easily the machining capability of OHSC, since 6degrees of freedom make the machining execute fully the required product shape. Also, with the

16、application of USV, a bore byte tool is utilizded, considering its size and stiffness during machining operation since the cutting force is greatly reduced.2. Experimental procedureThe experiment steup is shown in Fig.3, wherein the workpiece is mounted on the table of the 6-axis control machining c

17、enter. The bore byte tool is mounted in the USV tool using an adaptor. The USV tool is turn mounted on the main spindle of the 6-axis control machining center.2.1 Multi-axis control machine tool and bore byte toolThe 6-axis control machining center used in the study is shown in Fig.4. The machining

18、center provides multi-axis CNC machine tools.The 6-axis control machine tool has 3 rotational axes A,B and C. It is constructed by adding the rotational function C on the main spindle of a 5-axis control machining center which has 2 rotational axes,namely;A, which is a rotary tilting table and B, wh

19、ich is the rotary index table. The minimum unit for translation movement X,Y and Z is 1, and that of rotational one A,B and C is 0.36 arc second. In the case of cutting of OHSC, A axis is used for determination of side surface and the inclination angle of sharp corner ,B axis for workpiece rotation

20、,C axis for determination of cutting tool direction, X and Y axis for the determination of feed direction of feed direction while the depth of cut is determined by Z axis. Fig 5 shows the non-rotational cutting tool (bore byte tool) used in the study. It is made of tungsten carbide usually used here

21、 in 6-axis control cutting. The total length and diameter of the tool are 70mm and 6mm respectively.2.2 Ultrasonic vibration toolFif.6 is a commercially available USV tool (SB-150:Taga Electric Co). used in the study. The USV is applied on the cutting edge of the tool.In order to perform an efficien

22、t and effective vibration cutting, the vibration direction must be set parallel to the cutting direction. Since the vibration direction is not always parallel with the feed direction, the tool attitude of the bore byte tool is subjected to arrangement. As illustrated in fig.7(a), the tool axis vexto

23、r T and the tool direction vector D and modified by arranging the rolling and the inclination angle respectively. These are converted into modified tool axis vector T and modified tool direction vector D, as shown in fig.7(b). The transformation of the tool axis vector and the tool direction vector

24、are carried out in cutter location (CL) conversion.2.3 CAD/CAM systemThe configuration of 6-axis CAD/CAM system is shown in fig.8, where 3D-CAD data of the target shape is generated . The type of bore byte tool must be selected, based on the target shape. The main processor generates the collision f

25、ree CL data on the bases of tool information and tool orientation as well as 3D-CAD data of the target shape.The post processor converts CL data generated by the main processor into 6-axis control NC data suitable for the coordinate system of the machining center with reference to the structure info

26、rmation of the machining center, setting information, cutting condition and vibration condition. In addition, so-called linearization operation is dine in order to keep the feed rate to the machining center structure constant and to minimize the tool path deviation. It leads to assure the smoothness

27、 of the product surface especially in dealing with curve surfaces.Before converting CL data into NC data, CL data must be firstly checked for collision to assure the safety of the machining process .If the collision is detected in this stage, the modification of CL data is carried out, using the mai

28、n processor.3. Manufacture of Sharp Corner with Overhanging Surface3.1Determination of tool attitude In order to expresshe entire tool attitude for 9-axis control ultrasonic vibration cutting, the tool attitude of the bore byte tool, as shown in Fig.9, is appointed by the coordinates P for cutting p

29、oint, the tool axis vector T and the tool direction vector D. These PTD coordinates are converted to NC data, and are in turn used in machining operation. In 6-axis control cutting with application of ultrasonic vibration, the movement and the attitude of the tool must be determined in consideration

30、 of the vibration direction. Since the cutting direction changes rapidly, the tool attitude changes a lot to keep the tool angle constant to the surface shape.3.2Generation of tool path The tool path generating method for OHSC can be described as follows; the OHSC is composed with two ridgelines, as

31、 illustrated in Fig.10. The intersecting line is called as a bottom ridgeline and the cross section line is called as a side ridgeline .Finishing the side ridgeline as well as the bottom ridgeline is required to make a sharp corner.3.2.1Generation of tool path for side surface The surface that makes

32、 a side ridgeline is composed with left and right surfaces respectively. In producing a side ridgeline of the sharp corner, machining of left and right surfaces is necessary. The outline of the tool path generation method for side surfaces of the OHSC is described in Fig.11.The side to be machined a

33、nd the tool feed direction must be selected at first, based on the type of bore byte tool and the target shape. The adjoining surfaces that make a side ridgeline, is expressed with parameters u and v. The fix curve , which is equal to parameter v, is generated on the side from the upper part of the

34、surface to the bottom. The division number of surface is input to sequentially generate the number of cutting points. Each cutting point on a reference line are generated, using the value of parameter u, so that the distance between the cutting points may settle below in the specified value.Changing

35、 the tool attitude at every point of the cutter location ,the tool moves sequentially on each cutting point from the start point until the side ridgeline is formed. Although the cutting point is connected each other in order to acquire the tool path, it is difficult to process both adjoining sides b

36、y one direction due to the tool structure and the target product shape. In addition , the collision may take place between the tool and the workpiece. In this situation, the tool starts from the start point of the tool path to process the left side surface, and ends at the corner where the ridgeline

37、 is to be formed. Thus is repeated until it reaches to the bottom surface. The depth of cut is based in the division number of the total length of curve for curve surface. The same thing is done on the right side surface since there is still an arc-like remain at the corner part of the side surface.

38、 The procedure is almost the same as with the processing of the left side surface, however the cutting end point is the same with the end point of the left side processing, to form the clear ridgeline .Processing of the right side surfaces is also done using the left hand tool. The tool direction ve

39、ctor D during the tool path generation for side surfaces is rotated by 10degrees to make the vibration direction parallel to the feed direction vector F. The tool path is generated by connecting the cutting points in order from the starting point to the end point. The tool attitude during cutting is

40、 determined from the normal vector N and the tool feed direction vector F at the cutting point. The tool feed direction vector D and the tool axis vector T can be expressed as D=F*N and T=N respectively.3.2.2Generation of tool path for bottom surfaceFigure 12 describes that tool path generating meth

41、od for bottom surface that makes the bottom surface that makes the bottom ridgeline of the OHSC. After generating the tool path for side surfaces, the tool path for bottom ridgeline is successively generated, where the tool is inclined to the bottom surfaces. There are two methods of generating a to

42、ol path for bottom surfaces; one is one-path method shown on the upper left part, and the other multi-path method shown in the upper right part of the figure. In one path method ,the cutting tip of the tool directly makes contact with the location of the bottom ridgeline. In this operation, the tool

43、 inclination angle is necessary to fully remove the arc-like remains on the bottom surface and to form a clear ridgeline. During the tool path generation, the tool axis vector T is inclined, based on the calculated inclination angle against the bottom surface and the clearance angle of the cutting t

44、ool, which is 5 degrees.The method of determining the cutting start point as well as the cutting end point is the same as that of generating a tool path for side ridgeline.In multi-path method, the pitch from the bottom surface is expressed by use of parameters u and v. The generation range of a cut

45、ting reference line is determined from the shortest distance between the arc-like remains after rouging and the reference line of the bottom ridgeline. Cutting points is generated on the basis of parameter v in each reference line. The systems determines the tool attitude during cutting from the too

46、l axis vector N at the bottom surface and the tool feed vector F at cutting point along a cutting reference line. The tool axis vector T and the tool direction vector D can be express as T=N and D=N*F respectively. The cutting start point is assumed near the arc-like radius remains and it ends at th

47、e last point of the generated cutting point in the reference line. Moving the tool along each neighboring cutting point can make the tool path.4. Experimental Results4.1 Effect on cutting forceThe cutting force was measured by use of piezoelectric dynamometer (9257B,Kistler Co,Ltd), thus averaging t

48、he measured cutting force and processing it in the root mean square(rms) manner. table1 measured cutting forceMachining was conducted both with USV and without USV. The cutting conditions used are as follows: feed speed of 400mm/min and different depth of cut of 0.1,0.2,and 0.3mm respectively. The v

49、ibration conditions are in the following; frequency of 19kHz, amplitude of 36 and rolling angle of 10 degrees. The acquired result is shown in Table1. It can be seen that the cutting force in cutting with USV is much smaller as compared to cutting without USV. Since the cutting force was greatly red

50、uced, the stiffness of the tool can be maintained all throughout the process.4.2 Machining of OHSC The cutting experiment was also made in order to scrutinize the validity of the new machining method. The workpiece size used for the experiment is 10010020 mm and the material is an aluminimu alloy(JI

51、S A5052), which is also commonly used for low cost mould with low molding pressurre such as blow moulding, vacuum forming, rubber moulding,etc. Two types of OHSC model were tired in the experiment, one is OHSC with plane surface and the other is OHSC with curve surface. The side surfaces consist of

52、different inclination angle. The inclination angle o the surface at the cutting start point is not the same as the inclination angle at the cutting end point. In this condition, the inclination angle is not uniform all thoughout. Shown in Fig.13(a) is the machining model for OHSC with plane surfaces

53、, rugh cutting must be at firdt done in order to perform an effcient cutting by 5-axis control machining, using the rotational ball end mill with a radius of 3mm and 1.5mm respectively. Machining is carried out until the target product shape is almost obtained. Since the target sharp corner is not c

54、learly obtained due to the arc-like remains, as shown in Fig .13(b), finishing will be performed, using the 6-axis control cutting with the application of theUSV. with plane surface. In this process ,the left side or right side surface is firstly machined, depending on the choice. Let us assume that

55、 the left side surface is machined. The cutting and vibration conditions listed in Table 2 were used in machining on the basis of NC instructions generated by the developed CAM program. After machining the side surface, the bottom surfaces is machined in the next step, using the one path method. The

56、 cutting conditions listed in Table 2 were also used except for the inclinations angle of 9 degrees and the depth of cut of about 1.5mm. The depths of cut were based on the arc-like remains of the ball end mill used during roughing. Machining of the left side surfaces is done, using the right hang t

57、ool.After finishing the machining of the left side surface, the right side is processed in the next step under almost the same conditions as the processing of the left side except that the tool used is a left hand too. Shown in Fig.13(d) is the result of machining experiment. The machining model for

58、 OHSC with curve surfaces is shown in Fig.14(a). In machining OHSC with curve surface, roughing must also be performed, as shown in Fig.14(b). The sequence of operation from roughing to finishing is almost the same as described previously. However, so-called linearization operation is required to ma

59、ke the product surface smooth. To process the bottom surface that makes the ridgeline, the multi-path method was emplyed since the method is suitable in curved surfaces. Table 2 lists the cutting and vibration conditions used in the process. Also, shown in Fig.14(c) and Fig.14(d) are the actual machining and the product after finishing process respectively. The total machining time with this experiment is 112 minutes includi