CNC Swiss machinery:
Computer numerical
control (CNC) is a computer "controller" that reads G-code and
M-code commands and drives a machine tool, a powered mechanical
device typically used to fabricate components by the selective
removal of material. CNC numerically interpolates the points
along a cutting tool's tool path and directs the servomechanisms
that translate the data into movement. The operating parameters
of the CNC can be altered via the Master Control Unit (MCU) of
the machine.
Types of
instruction:
G-codes are known as
preparatory and movement codes. Depending on the number directly
following the G, they can
perform an extremely wide range of commands. The G00 code for
example, stands for Rapid Traverse, which moves the machine to a
given point at top speed. In the industry it is known as the WFO
command. The G01 command is the most common command, in which it
tells the machine to move in linear interpolation to a given
point. The G02/G03 (clockwise/counter clockwise) command is
circular interpolation allowing the machine to make near perfect
circles with one move.
The M-codes are the Misc. functions of the machine. They do
things like turning the coolant on and off, activating drill
cycles and starting chip conveyors. They complement the G-codes,
for example the M03/M04 commands turns the spindle on/off. The
command M30 marks the end of a program.
Movements
Lately, some controllers have implemented the ability to follow
an arbitrary curve (NURBS), but these efforts have been met with
skepticism since, unlike circular arcs, their definitions are
not natural and are too complicated to set up by hand, and CAM
software can already generate any motion using many short linear
segments.
Drilling
A tool can be used to drill holes by pecking to let the swarf
out. Using an internal thread cutting tool and the ability to
control the exact rotational position of the tool with the depth
of cut, it can be used to cut screw threads.
A drilling cycle is used to repeat drilling or tapping
operations on a workpiece. The drilling cycle accepts a list of
parameters about the operation, such as depth and feed rate. To
begin drilling any number of holes to the specifications
configured in the cycle, the only input required is a set of
coordinates for hole location. The cycle takes care of depth,
feed rate, retraction, and other parameters that appear in more
complex cycles. After the holes are completed, the machine is
given another command to cancel the cycle, and resumes
operation.
Parametric programming
A more recent advancement in CNC interpreters is support of
logical commands, known as parametric programming. Parametric
programs incorporate both G-code and these logical constructs to
create a programming language and syntax similar to BASIC.
Various manufacturers refer to parametric programming in
brand-specific ways. For instance, Haas Automation refers to
parametric programs as macros. GE Fanuc refers to it as Custom
Macro A & B, while Okuma refers to it as User Task 2. The
programmer can make if/then/else statements, loops, subprogram
calls, perform various arithmetic, and manipulate variables to
create a large degree of freedom within one program. An entire
product line of different sizes can be programmed using logic
and simple math to create and scale an entire range of parts, or
create a stock part that can be scaled to any size a customer
demands.
Parametric programming also enables custom machining cycles,
such as fixture creation and bolt circles. If a user wishes to
create additional fixture locations on a work holding device,
the machine can be manually guided to the new location and the
fixture subroutine called. The machine will then drill and form
the patterns required to mount additional vises or clamps at
that location. Parametric programs are also used to shorten long
programs with incremental or stepped passes. A loop can be
created with variables for step values and other parameters, and
in doing so remove a large amount of repetition in the program
body.
Because of these features, a parametric program is more
efficient than using CAD/CAM software for large part runs. The
brevity of the program allows the CNC programmer to rapidly make
performance adjustments to looped commands, and tailor the
program to the machine it is running on. Tool wear, breakage,
and other system parameters can be accessed and changed directly
in the program, allowing extensions and modifications to the
functionality of a machine beyond what a manufacturer
envisioned.
SM Series:
SQX Series:
