CHAPTER 13

ISOPARAMETRIC PLOTTING AND MACHINING


A facility for plotting and machining by using the isoparametric lines of a sculptured surface has been provided as an alternative to regional milling. This provides the cheapest method of plotting and machining, but lacks the flexibility of the more general regional milling facility. Provision is also made for defining regions on a surface that are to be machined or avoided (pockets or islands). Besides the full set if APT4-SS geometry all kinds of non-native geometry can be used.

13.1 The PLOTFT statement

13.1.1 Single Curve Plotting

To plot a curve or a parametric line on a sculptured surface the following statement can be used: scurv › FLOW ! › INCR,incr! PLOTFT/ ›,START,t1!›,THRU,t2! ›,PARAM! ›,CHORD,tol! ssurf,UCONST,u VCONST,v o The scurv or the u-const or v-const parametric curve on a parametric surface between the start value t1 and the end value t2 is generated and written onto the EXFILE to be used by a plot porocessor. o If the START and THRU definitions, together with the associated values are omitted, the natural ends of the curve are used. A negative value t1 and a value t2 which is larger than the end parameter of the curve generates points on the line o FLOW and PARAM are only applicable for scurv and signal that the START and THRU values are flow or natural parameters of the scurv (if not given, PARAM is assumed). o The point spacing is organised with INCR,incr or CHORD,tol. With INCR, an increment for the running parameter t between t1 and t2 can be introduced (default: incr=.05). With CHORD,tol a chord height tolerance can be specified. o If a part surface thickness is given via THICK/ , offset curve data are generated.

13.1.2 Output of a Surface GRID

To plot a set of curves on a sculptured surfaces the PLOTFT-GRID feature can be used: › INCR,incr! PLOTFT/ssurf,GRID›,UCONST,u!›VCONST,v!º, º › CHORD,tol! o Primarily all grid lines in u- and v-direction of a mesh surface are polygonized and written onto the EXFILE. o The point spacing is organized as described in 13.1.1. o The part surface thickness is used if THICK/ has been issued. o For plotting via a plot postprocessor PENUP and PENDWN records are inserted to prevent unintended draws. o With UCONST and VCONST a selection of only u-lines or only v-lines can be organized. With the associated u- and v-values the number of parameter lines between the grid lines can be defined. Note: If UCONST and VCONST are omitted. ...UCONST,0,VCONST,0... is assumed.

13.2 The GOLOFT Statement

To move an APT cutter along a parametric line of a ssurf the following GOLOFT statement can be used: › t1 ! º º UCONST,u º TO º GOLOFT/ssurf, º,START , ON ,eb1 º $ VCONST,v › PAST ! › t2 ! º º º TO º º,THRU , ON ,eb2 º $ › PAST ! ›,INVERS! ›,MIRROR! $ ›,INCR,incr! ›,LENGTH,! ›,CHORD,tol! To position an APT cutter at a parametric line on a ssurf the following GOLOFT statement can be used: › t ! º º UCONST,u º TO º GOLOFT/ssurf, º,AT , ON ,eb1 º VCONST,v › PAST ! With GOLOFT a set of cutter path positions is generated and output on the EXFILE. The cutter is contacted on the side where the surface normal is pointing to. o A position on a parametric line for the AT, START and THRU can be given by a single parametric value (t, t1 or t2) or with planar check surfaces which are contacted by the cutter in TO, ON or PAST condition (INVERS does not effect this sense). - The sense of direction is always taken from the ascending parameter direction. - THICK/, TOLER/, INTOL/, and OUTTOL/ -values of the 1st check surface are taken for the AT and START plane and values of the 2nd surface for the THRU plane. - The full seven segment APT cutter is involved in this check surface calculation process. o The point spacing with INCR,incr and CHORD,tol is described in 13.1.1. o With LENGTH,l a maximum cut length can be defined. If not given, the MAXDP value is taken as default. o With INVERS the output order of the points is reversed. o With MIRROR the cutter is positioned on that side of the surface to which the surface normal does not point. Interface with the APT-ARELEM: o The full APT seven segment cutter is used. o All 3-, 4- and 5-axis TLAXIS definitions are integrated (see Section 12.6 of this Volume). Because of the absence of a drive surface in 4- and 5-axis calculations the tool axis which is closer to the previous tool axis is selected. o The part surface thickness given in a THICK/ statement is given. o TLONPS/TLOFPS is not yet used because GOLOFT always produces TLOFPS points. TLONPS can be generated with PLOTFT. o The linearization of the cutter path does not follow the ARELEM algorithm with part surface tolerances. INCR,incr and CHORD,tol are used instead. o GOLOFT produces all extended EXFILE data for part surface if necessary (see Section 12.5). o Cutter location data (EXFILE) are transformed into an actual REFSYS coordinate system if PROPTN/REFMOT,ON has been issued earlier in the part program. o The REGION definition (13.3) causes limited cutter path calculation. o With GCLEAR (13.4) the approach to and the retract from a GOLOFT cut sequence can be organized.

13.3 The Region Statement

To limit the movement over a sculptured surface to a given boundary the following REGION statement can be used: IN REGION/id, OUT REGION/OFF The region refers to an EXFILE data segment 'id' (12.5.2) which has to describe the parametric contour on the intended surface by by means of UVPPS output. o The REGION function assumes a closed 2-dimensional (u,v) polygon. The first and last polygon points can be identical. o The (u,v)-polygon can be created by all kinds of motion statements GO/, GOLFT/, GORGT/, ..., and GOLOFT/. o The sense of the curve direction does not affect the IN or OUT specification. o IN means that the region consists of all inside polygon points. OUT means that the region consists of all points which are not inside the polygon. o The REGIONinspects the given (u,v)-polygon for self intersection. o OFF cancels the REGION use.

13.4 The GCLEAR Statement

To manage all data necessary to start to or retract from a cut sequence (GOLOFT see 13.2) the following GCLEAR statements can be used: 4 › START ON ! GCLEAR/ º AWAY , OFF º º BACK 'a' º › THRU ! 1 ON GCLEAR/ OFF Clearance surfaces, increment motions and local feedrates can be defined to 4 different situations: o at start of a cut sequence : START o at end of a cut sequence because of an island situation : AWAY o at start of a cut sequence after an island situation : BACK o at end of a cut sequence : THRU This assignment is valid whether or not the cut sequence is reversed (INVERS in the GOLOFT statement). The complete GCLEAR definition or components of it can be switched ON or OFF without loss of definitions. The individual data 'a' for the four situations can be described as follows: Retract data: ›,MOTDIR,x! ›,NORMAL,y! ›,FEED,f! ›,CLEARS,surface! ›PARLEL,vector ! o The MOTDIR value x and the NORMAL value y are multiplied, if coded, with the unified motion and surface normal vector. The combination of these two vectors results in the incremental motion. Note that for a plunge-in motion the NORMAL value y has to be negative. o Alternatively to MOTDIR/NORMAL the incremental motion can be coded directly with PARLEL,vector. o With CLEARS,surface a clearance surface can be introduced. The position calculated on the clearance surface is a projection of the cut sequence end point plus the increment motion onto the clearance surface. Surface types accepted by the translator are line, plane, sphere, cylinder, circle, cone, ssurf. Note: GOLOFT services only line and plane. o With FEED,F the feedrate of the increment motion can be specified. When FEED is specified the global feedrate given with a FEDRAT/ statement is re-established. For the move to clearance points and to plunge-in start points a RAPID record is issued.