There are few CNC people that even know what parametric programming is --
and fewer still that know how to use it! Given the enhancements that this kind
of programming brings, it is surprising that more machine tool builders,
control manufacturers, and technical schools don't say more about it. In this
short discussion, we'll explain what parametric programming is and show its
main applications.
What it is
Parametric programming can be compared to any computer programming language
like BASIC, C Language, and PASCAL. However, this programming language resides
right in the CNC control and can be accessed at G code level, meaning you can
combine manual programming techniques with parametric programming techniques.
Computer-related features like variables, arithmetic, logic statements, and
looping are available. Like computer programming languages, parametric
programming comes in several versions. The most popular is Custom Macro B (used
by Fanuc and Fanuc-compatible controls). Others include User Task (from Okuma),
Q Routine (from Sodick), and Advanced Programming Language [APL] (from G&
L)
In addition to having many computer-related features, most versions of
parametric programming have extensive CNC-related features. Custom macro, for
example, allows the CNC user to access many things about the CNC control (tool
offsets, axis position, alarms, generate G codes, and program protection) right
from within a CNC program. These things are impossible with only normal G code
programming techniques.
Applications:
Many companies have excellent applications for custom macro and don't even know
it. Of course, if you don't even know you have an application for something,
it's impossible to even consider using it. While these applications are covered
in much greater detail during our video
course and CD-rom course,
applications for custom macro fall into five basic categories. Do any of these
sound familiar?
Families of parts
Almost all companies have at least some applications for custom macro that
fit into this category. Possibly you have prints dimensioned with variables
right on the print. The programmer must reference a chart on the drawing to
come up with values needed in the program. Or perhaps you consistently find
yourself editing one CNC program to make another one. If you do, you have a
perfect application for custom macro!
User-created canned cycles
Even if you don't have a perfect family of parts application for custom
macro, surely you have at least some workpieces that require similar machining
operations. Or maybe you find yourself wishing your CNC control had more (or
better) canned cycles. With custom macro, you can develop general purpose
routines for operations like thread milling, bolt hole patterns, grooving, and
pocket milling. In essence, you can develop your own canned cycles!
Complex motions
There may be times when your CNC control is incapable of easily generating
a needed motion. To perform accurate taper thread milling (taper threads), for
example, your control must have the ability to form a spiraling motion in XY
while forming a linear motion in Z (helical motion will not suffice in this
case). Unfortunately, most CNC controls do not have spiral interpolation. But,
believe it or not, with custom macro you can generate this desired motion. In
essence, custom macro allow you to can create your own forms of interpolation.
Driving accessory devices
Probes, post process gauging systems, and many other sophisticated devices
require a higher level of programming than can be found in standard G code
level programming. Custom macro is the most popular parametric programming
language used to drive these devices. In fact, if you have a probe on one or
more of your machines, you probably have custom macro!
Utilities
There is a world of things you can do with custom macro that you would
never consider doing without it. Custom macro can help reduce setup time, cycle
time, program transfer time, and in general, facilitate the use of your
equipment. A few example applications that fit into this category include part
counters, tool life managers, jaw boring for turning centers, using standard
edge finders as probing devices, and facilitating the assignment of program
zero
Example:
To stress what can be done with parametric programming, we show a simple
example written in custom macro B for a machining center application. It will
machine a mill a hole of any size at any location. Notice how similar this
program is to a program written in BASIC.
