CADCAM2005_APT.pdf

APT Language (Automatically Programmed Tools) Prototype APT MIT 1956 AIA & MIT APT II (Aerospace Industries Association) & (Massachusetts Institute of Technology) APT III 1961 Present APT has approximately 300 words Today still used extensively Here in AIT we use PCAPT (3D APT processor – Freeware) InterCIM APT (Full Commercial APT – 5-axis)

Geometric Expressions (16) POINT LINE PLANE CIRCLE CYLNDER ELLIPS HYPERB CONE SPHERE...

APT Point Definitions (10 ways) 1. By Coordinates POINT/x, y, z,

PT1 = POINT/10.1, 5

2. Intersection of two lines PT2 = POINT/INT of LIN 1, LIN 2 3. By a center of a circle PT3 = POINT / CENTER, C 1

APT Line Definition (13 ways) 1. Through two points LT 1 = LINE / PT 1, PT 2 2. By a point and a tangent circle L1=LINE/P1, LEFT, TANTO, CIR 1 L2=LINE/P1, RIGHT, TANTO, CIR 1 3.

Through a point and an angle with another line

L1 = LINE / P1, ATANGL, 40.00, 1.2

APT Plane Definitions (8 ways) 1. There points are not on the same straight line PL 1 = PLANE / P1, P2, P3 2. By a parallel plane and the perpen dicular distance between the two planes XLARGE XSMALL PLANE/PARLLEL, symbol for a plane, YLARGE, offset YSMALL ZLARGE ZSMALL

PL 2 = PLANE / PARLLEL, PL 1, ZSMALL, 5.1

APT Circle Definitions (10 ways) 1.

By three points through which the circle is passing

C1 = CIRCLE / PN2, (POINT / 5.5, 7, 4.1), PNT 1 2.

By the center and a point on the circum ference

C2 = CIRCLE / CENTER, (POINT / 9, 7, 3), PT 1 3.

By the center and the radius

C3 = CIRCLE / CENTER, PT1, RADIUS 3

Motion Expressions The tool motion is specified using motion statements groups of motion statements are available: Point - to - point & contouring operations

APT Point-to-point motion statements FROM / symbol for a defined point - indicates the initial position of the cutter center GOTO / symbol for a defined point - positions the tool center at a specified point GODLTA / ∆X, ∆Y, ∆Z - positions the cutter center in the specified increment from its current location

APT Contouring Motion Statements In APT it is assumed that the part remains stationary and the tool moves . Three surfaces control the tool motion in contouring: •The tool end moves on the PART SURFACE •The tool slides along the DRIVE SURFACE •Until the tool encounters the CHECK SURFACE

Before the tool can move along the contouring surfaces it must be brought to them, this is done by the initial motion statements : GO / cutter specifier, drive surface, cutter specifier, partsurface, cutter specifier, check surface Four variations of cutter specifiers: TO ; ON ; PAST ; TANTO

ex.

GO / TO, CIR 1, ON, PL1, TO, LIN1

The drive surface of a GO/statement will be the surface cut along in the next motion statements, the part surface is established for all the subsequent motion statements. The initial motion statement appears only once in a part program (from set point to work piece). The actual cutting is controlled by another type of statement the intermediate motion statement. Four VARIANTS of intermediate contouring motion statements may be used in APT. The most useful has following format: Motion word/drive surface, cutter specifier, check surface ex. GOLFT / DRS, TO, CKS

There are six different motion words: GOLFT GORGT GOFWD GOBACK GOUP GODOWN

1. Motion words are programmed from the tools view point 2. Each motion statement is dependent upon the preceding statement for the direction of motion 3. The check surface for the current motion is usually the drive surface of the next motion.

drive surf part surf check surf Ò Ò Ò GO / TO, L1, ON, PLN, PAST, LL GORGT / L1, TO, L2 GORGT / L2, TANTO, C1 GOFWD / C1, TANTO, C3 GOFWD / L3, PAST, L4 GOLFT / L4, PAST, L5 GOLFT / L5, PAST, L6 GOLFT / L6, PAST, LL GOLFT / LL, PAST, L1 GOTO / SP

Additional APT Statements 2/3 of an average program are Geometric & motion statements others are : - Postprocessor statements defines post processor to be used MACHIN / postprocessor name some postprocessor control statements are: COOLNT / ON → ref. m08 SPINDL / ON → ref. m03 FEDRAT / 25 → ref. 25 mm/min SPINDL / 1250, CCLW → ref. 1250 RPM / min ToolNO / 3572, 6 → Tool number 3572, 6 units length END → ref. m02

Tolerance and cutter specifications all contouring motion commands are reduced to sequences of straight-line motions required to approximate a given curve, the precission is specified by a tolerance word. OUTTOL / 0.0005 INTOL / 0.0001 TOLER / 0.005 CUTTER / 10.0

-Initial and Termination statememts The first statement in the APT Program is PARTNO... The last statement in the APT Program is FINI

APT STATEMENTS FOR 5-AXIS MODE MILLING The program has to start with the statement: 0. MULTAX/ON Tool axis specification statements: 1.TLAXIS/vector TLAXIS/a,b,c 2.TLAXIS/NORMPS TLAXIS/NORMDS 3.TLAXIS/1 Current cutter axis orientation is to be maintained; stays in effect upto another TLAXIS statement 4.TLAXIS/PARLEL,1 (or 2) 1 for tool axis parallel to ruling of PS 2 for tool axis parallel to ruling of DS

1 vector 5.TLAXIS/ATANGL,or,H,or 2 CUTANGL,I The vector or CUTANGL statements are optional. The angle I is called the cutangle or also the lead (I +) or lag (I -) angle. If a vector is specified the plane is perpendicular to that vector Instead of to the forward motion. This can be useful to force the Tool axis orientation in a fixed plane (used for 4-axis machining with 3 linear and 1 rotary axis. 6.CUTTER/d,r,e,f,A,B,h When CUTTER/d or CUTTER/d,r are used the other parameters take the following default values: A=0; B=0; f=r; e=d/2-r; h = 5 units or r if r > 5 units.

RLDSRF Definitions A ruled surface is the surface generated by a space line moving in contact with two space curves. Each space curve is defined as the intersection of a surface and a plane. The second curve can degenerate to a point. The two RLDSRF definition formats are: 1. RLDSRF/ subsurface, curve point, curve point, direction point or vector, $ subsurface, curve point, curve point, direction point or vector 2.RLDSRF/ subsurface, curve point, curve point, direction point or vector, $ vertex point In format 1, the RLDSRF is defined by two space curves, each of which is defined by a subsurface, two curve points, and a direction point or vector. In format 2, the second curve has degenerated to a point which is a vertex of the surface. The subsurfaces can be any type of APT surface except another RLDSRF.

RI=RLDSRF/CY1, P1A, P1B, P1C, CY2, P2A, P2B, P2C In this example, the three points P1A, P1B, and P1C define a plane whose intersection with the cylinder CY1 defines a circle. The arc of the circle from P1A to P1B is used as one of the two curves that define the ruled surface. Similarly, P2A, P2B, and P2C define a plane whose intersection with the cylinder CY2 defines a circle. The arc of this circle from P2A to P2B is used as the second curve to define the ruled surface. The ruled surface itself is formed by connecting the two arcs with straight lines.

Complex Surfaces The following illustrates a ruled surface defined by a curve and a vertex point. R2=RLDSRF/CYl, P1A, PlB, P1C, P2

In this example, the first curve is defined in the same manner as in the previous example. The point P2 is specified instead of a second curve. This point acts as a vertex of the ruled surface - all rulings pass through it.

As the preceding examples have illustrated, the two points and the third point or vector define a plane whose intersection with a surface defines a space curve. The first two points in a curve definition also act as end points in order to define the part of the curve actually used to define the ruled surface. The straight line segment between the two end points of a curve is called the base line of the curve. Its length is considered to be 100% with the first specified point being at 0% and the second at 100%. It is important that the points in the two curve definitions be specified in the same relative order since the 0 % ruling of the surface is generated by connecting the first point of the first curve to the first point of the second curve and, similarly, the 100% ruling connects the second points of the two curves.

The RLDSRF processor uses the direction point or vector to generate intermediate rulings. If a direction vector was specified in the curve definition, it is used directly. If a direction point was specified, the direction vector is generated perpendicular to the base line and pointing to the side of the base line on which the direction point lies. A point on the base line of the first curve at a particular percentage can be projected along the first direction vector onto the first curve and, hence, onto the ruled surface itself. Similarly, a point on the second base line at the same percentage can be projected along the second direction vector onto the second curve and onto the surface. The line between these two points is a ruling of the surface. Rulings, then, connect curve points corresponding to equal base line percentages. Note that the RLDSRF processor looks from the base line in the direction of the specified or generated vector only, not in the opposite direction as well, so it is essential for the...direction vector to point in the proper direction.

For example, consider the following curve defined by two points and a vector:

In this case, the intersection of the surface with the plane defined by P1, P2, and V1 is a closed curve, but only the part of the curve below the base line is used since this is the part pointed to by the direction vector V1. If a vector pointing in the opposite direction, V2, were specified, the part of the curve above the base line would be used. The figure illustrates how a curve point for defining a ruling at 25 % is generated. The point BP is on the base line at a distance from P1 equal to 25% of the total base line length (.5/2 = .25). This point is projected along V1 onto the curve to produce the point CP. The line passing through CP and a point generated in a similar manner on the second curve is the desired 25 % ruling.

The following example is similar to the previous one except that a direction point is specified instead of a vector

In this case, the direction vector is generated perpendicular to the base line and pointing toward the direction point P3. Obviously, the direction point must lie on the proper side of the base line. If P4 were specified instead of P3, the curve above the base line would be used instead of the curve below. Note that when you specify three points in a curve definition, the three points must not lie in a straight line since this would not define a unique plane. The first two points specified in a curve definition ordinarily lie on the curve and can, therefore, be used directly as the end points of the curve. However, it is not essential that the specified points lie on the curve. When a point does not lie on the curve, it is projected onto the curve in a direction parallel to the direction vector.

Complex Surfaces Example:

R1=RLDSRF/SI, PI, P2, VI, - -The RLDSRF processor does not generate a fixed number of rulings and store them as the canonical form for the ruled surface. Instead, the canonical form is composed of the canonical forms of the two subsurfaces, the two curve points used to define each curve, and the given or generated direction vector. Rulings are-generated dynamically as close together as necessary as the cutter is positioned relative to the ruled surface. When you specify a direction point in a curve definition, you are assured that a direction vector normal to the base line will be generated. When you specify a direction vector, you have the option of specifying a vector not normal to the base line. Usually, however, the type of surface that is desired is the type generated by vectors normal to the base lines.

When the angle between the direction vectors becomes large, the resulting surface can have undesirable curvature properties. Such a surface is illustrated by the following figure, in which the angle between VI and V2 is relatively large.

RSI=RLDSRF/SI, PI, P2, VI, S2, P3, P4, V2 The angle between the direct,ion vector and the base line cannot be less than six degrees.

Complex Surfaces A RLDSRF is limited laterally; it does not extend beyond the 0% and 100% rulings. On the other hand,longitudinally, the rulings of the surface extend infinitely in both directions. However, the mathematical techniques used by the RLDSRF processor become less reliable as the distance from the defining curves increases. Generally, you should not try to position the cutter relative to a. RLDSRF at a distance from a defining curve that is greater than the distance between curves. . Examples: RI=RLDSRF/SI, PI, P2, VI - -GO/RI GORGT/RI, PAST, LI The GORGT statement cannot be executed because the RLDSRF does not exist beyond the 100% ruling at P2.

RI=RLDSRF/SI, PI, P2, VI - -GO/RI GORGT/RI, PAST, LI This illustrates the cutter being positioned relative to the RLDSRF RI at a position not between the two curves but within a distance d of the top curve. This is proper since the distance from the top curve is not greater than d.

One of the most common applications of the RLDSRF feature is for defining a ruled surface in terms of two T ABCYLs. A typical method of defining a curve for such a surface is to specify two of the points used to define the T ABCYL as end points of the curve and to specify a third point on the T ABCYL between the other two as the direction point. Complex Surfaces Example:

TCI=TABCYL/NOZ, SPLINE, PI, P2, P3, P4, P5, P6 TC2=TABCYL/NOZ, SPLINE, PH, P12, P13, P14, P15 RSI=RLDSRF/TCI, PI, P6, P4, TC2, PH, PI5, PI3

Restrictions The methods used by the RLDSRF processor impose certain restrictions that you should observe when defming ruled surfaces. 1.It is not permissible for the line tangent to a RLDSRF space curve at any point to be perpendicular to the base line for the curve. This problem could arise, for example, when the surface forming the curve is a cylinder and the base line is a diameter of the cylinder. Example:

Rl = RLDSRF /CY1, P1, P2, V1, - - -

In this example, if it was not necessary that the curve be an entire semi-circle, the problem could be eliminated by moving the base line so it is no longer a diameter:

R1=RLDSRF/CYI, P3, P4, VI, -- ---

Another solution is to define the surface as two or more ruled surfaces:

2.A curve should not intersect its base line nor should the direction vector intersect the curve more than once on the curve side of the base line.

RI=RLDSRF/TAB1, PI, P2, VI, -- --Here, a curve generated by a TABCYL intersects the base line. APT could drive the cutter along this surface until it encountered the area between the intersection points I1 and I2. A failure would then occur since the surface does not exist in this area.

Multi-axis Programming The APT System can determine not only the tool center locations for controlling the linear axes of machine tools but also the orientation of the tool axis for controlling the rotary axes of multi-axis machine tools.The orientation of the tool axis is defined by the unit tool axis vector,which originates at the tool end point and points toward the top of the tool. Unless otherwise specified, the tool axis is assumed to be parallel to the z-axis; that is, it is defined by the vector (0, 0, 1). MULTAX Tool axis vectors are passed on to postprocessors via the cutter location (CL) fIle. The postprocessor uses the components of the tool axis vectors to determine the positions of the rotary axes. The output of tool axis vectors to the CL fIle is controlled by the MULTAX (multiple axis) statement, which can have the following formats: MULTAX MULTAX/ON MULTAX/OFF

The first two formats are equivalent. Either causes the components of the tool axis vector to be output with each succeeding cutter location point that is output to the CL file. MULTAX/OFF overrides a previous MULTAX or MULTAX/ON statement with the result that tool axis vectors are no longer output to the CL file. This is the assumed mode if no MULTAX statement is programmed. You should not program MULTAX if you are using a postprocessor not designed to accept tool axis vectors, as is the case with many postprocessors for non-multiple axis machine tools. Note that MULTAX merely controls the output of tool axis vectors but has no effect on the values of the vectors that are output. APT can operate in two modes as far as tool axis orientation is concerned - with the tool axis fixed at a constant orientation or with it varying according to a specified set of conditions.

Fixed Tool Axis Control The following formats of the TLAXIS statement establish the fixed axis mode: 1. TLAXIS/i, j, k (vector components) 2. TLAXIS/vector (vector symbol) 3. TLAXIS/l (switch from variable to fixed) Formats 1 and 2 establish the specified vector as the constant tool axis. It is not essential that the specified vector be a unit vector since it is converted to a unit vector by APT. The specified vector remains in effect until overridden by another TLAXIS statement. Tool axis vectors are not output to the CL file by themselves but only with cutter location points. Therefore, a TLAXIS statement has no effect on postprocessing until a following motion statement causes a cutter location point to be output.

(0, 0, 1 axis assumed) FROM/Pl TLAXIS/l, 0, 0 (axis parallel to x-axis) GOTO/P2 GOTO/P3

FROM/Pl (0, 0, 1 axis assumed) TLAXIS/l, 0, 1 (45 degrees to x and z axes) GO/Sl, S2

It is also permissible to specify a constant tool axis in a FROM or GOTO statement, which also establishes the fixed axis mode. The formats are as follows: FROM/x, y, z, i, j, k (point coordinates, vector components)

Multi-Axis Programming FROM/point, vector GOTO/x, y, z, i, j, k GOTO/point, vector

(point, vector symbols) (point coordinates, vector components) (point, vector symbols)

Specifying a vector in a FROM or GOTO statement is equivalent to specifying the vector in a TLAXIS statement preceding the FROM or GOTO statement. For example, GOTO/l, 7, 5,1,0,0 is equivalent to TLAXIS/l, 0, 0 GOTO/l, 7, 5 The following format of the GODLTA statement is very useful for multiaxis programming: GODLTA/d A positive d causes a withdrawal move of length d along the tool axis; a negative d causes a plunge move in the direction opposite the tool axis. This statement allows you to program a move along the tool axis even when you don't know what the tool axis orientation is. The statement TLAXIS/l causes APT to switch from the variable axis mode to the fIxed axis mode with the last tool axis vector computed in the variable axis mode being retained as the constant tool axis for the fIxed axis mode.

The Variable TLAXIS Statement The variable TLAXIS statement establishes a mode of operation in which the tool axis is varied as necessary in order to conform to specified conditions. Its general format is: TLAXIS/surf, type, ra, hi, alpha, i, j, k, beta surf= 2 part surface control surf= 3 drive surface control type= 0 4-axis control type = 1 5-axis control type = 2 RLDSRF control ra = radius of disk cutter hi = height of disk cutter alpha = angle between tool axis and control surface normal i, j, k = 4-axis control vector beta = lead, lag angle This is the general format but all entries are not always required. When type equals 2, no entries beyond hi are used.Beta is optional for types 0 and 1 and is assumed to be zero when not specified.

Multi-Axis Programming The 4-axis vector i, j, k is used only when type equals 0. However, if beta is specified when type equals 1, values must be included (zeros will suffice) for i, j, k since beta, when specified, must be the ninth entry to the right of the slash. The variable tool axis statement applies to those statements that involve a part surface and a drive surface -GO, GOLFT, GORGT, GOFWD, GOBACK, GOUP, GODOWN. One of these surfaces - the part surface if surf equals 2, the drive surface if surf equals 3 - is used to control the orientation of the tool axis. The other surface is treated in the normal manner and does not directly influence the tool axis orientation. The entries ra and hi define a point on the tool that becomes a disk as the tool revolves. Ra is the radial dimension, measured from the tool end perpendicular to the tool axis. Hi is the height dimension, measured from the tool end along the tool axis.

Following are examples of ra and hi:

Note that both ra and hi can be zero, in which case the disk degenerates to the tool end point. The purpose of the disk is to define the point of contact between the cutter and the control surface. The normal cutter defined by the cutter statement is not used to compute offset positions from the control surface but the disk is used instead. The angle alpha specifies the tilt of the tool axis relative to the control surface. When beta is zero, alpha is measured in the plane normal to the direction of forward motion; that is, in the plane containing the normals to the part surface and the drive surface. Alpha is positive when measured from the normal to the control surface toward the normal to the non-