CNC Programming and Computer-Aided
Manufacturing/Design
CNC programming,
computer-aided manufacturing, and large-scale control systems such as SCADA —
the hardware side of industrial programming is at least as important to
industry as its more glamorous sibling, computer-aided design. CNC programming
is what makes machine tools actually perform the complex tasks that are
required of them; without it, much of today’s technology would not be possible.
Software and Web design trends may come and go, but CNC and CAM skills are always in demand.
CNC: What Is It?
CNC stands for Computer Numeric Control.
CNC, CAD (Computer-Aided Design), and CAM (Computer-Aided Manufacturing),
together form the basis of modern-day software-controlled industrial
manufacturing systems. CNC machines are software-controlled machine tools, such
as lathes, mills, and cutters. They are used to perform the same tasks as
traditional machine tools and mechanically-automated tools; CNC machines,
however, are controlled entirely by software. CNC machines include extremely
precise multi-axis milling tools and high-powered, high-precision laser and
electron-beam devices which could not be operated accurately using strictly
mechanical controls.
What About 3D Printing?
“Lathes and mills? I thought that 3D
printers were going to replace them!”
3D printing is a rapidly-growing field,
and 3D printers are already among the most important CNC tools. But they do
have some built-in limitations. 3D printers are excellent with plastics and
other materials which can harden by thermal or chemical processes after being
formed. 3D printing with metals generally requires the metal to be sintered or
melted at some point in the process, resulting in mechanical properties which
may be very different from those of a piece machined from a rolled or
heat-tempered alloy. And at this point, the 3D printing process simply can not
match the precise tolerances of high-precision machining. For the time being,
at least, the fully-automated factory floor is likely to have 3D printers
working side-by-side with more traditional CNC machines, rather than replacing
them entirely.
Trace It Back
Most descriptions of computer-controlled
manufacturing systems focus on CAD and CAM — design and high-level programming
— and treat factory-floor machine-tool control almost as an afterthought. But
since we’ve been talking about CNC, let’s start with the CNC machine tools
themselves, then trace the process backward to computer-aided manufacturing and
design systems. After all, without the CNC machines on the factory floor, there
wouldn’t be any computer-aided manufacturing. And as we’ll see, there are
likely to continue to be significant opportunities for skilled machinists with
a good working knowledge of low-level CNC programming, as well as high-end
CAD/CAM software.
How They Work
Mechanically, many CNC machines work
like traditional machine tools, with the workpiece, the cutting tool, or both
rotating rapidly, and with the overall motion of the workpiece or the cutting
tool precisely controlled by mechanical means. In a CNC machine, however, these
mechanical actions are controlled by stepper motors or other servo-type
mechanisms, which are themselves controlled by software. Besides mechanical
cutting, milling, grinding, or drilling action, CNC machines can use flame,
plasma, laser, electric discharge, or water-jet cutting, punches, knives, or
even such specialized tools as embroidery needles.
For all of these systems, however, the
actions of the tool and the workpiece are controlled by means of commands
written in a CNC programming language.
CNC Programming Languages
While there is no single programming
language for all CNC tools (many of which have strictly proprietary languages),
G-code (or the G programming language) is the most widely used CNC programming
languages, available in a variety of largely proprietary implementations. Of
these, the FANUC implementation became at least a partial standard in the CNC
industry in the 1990s. Initially, G-code resembled a low-level programming
language, such as assembly language; later versions, however, include control
structures and other features more typical of a high-level language. Current CAD/CAM softwaremakes it possible to
create machine instructions at the design level, then automatically convert
them into G-code for the individual tools.
G and M
G-code largely consists of two types of
command: G codes and M codes. G codes consist of the letter G (designating the
memory address where the command will be stored) followed by a control number
(from 0 through 99). G codes are traditionally called preparatory codes,
because they tell the machine how it should move. G01 is a typical G code; it
tells the machine to move the cutting tool (or workpiece) in a line at a
specific feed rate or distance. It will be followed by codes indicating the
axis of motion and increment.
M codes are called often miscellaneous
codes; they control more general machine operations (motor on/motor off,
coolant on/coolant off, spindle motion, etc.), and like G codes, consist of the
M prefix followed by a one to three digit numeric code. Other codes (represented
by letters of the alphabet followed by integer or decimal numbers) control such
things as the axis, speed, or geometry of the cut. While other, strictly
proprietary CNC languages may have different commands, they generally operate
on similar principles.
Higher-Level Control
As you can imagine, writing G-code
directly can be a time-consuming task, and the chances of introducing serious
errors into the code are fairly high. Manual G-code programming is a bit like
the days of MS-DOS, when programmers had to write their own printer drivers,
sending low-level escape codes directly to the printer. And just as
contemporary operating systems supply their own printer drivers, relieving the
programmer of the need to send commands directly to the printer, contemporary
CAD/CAM systems allow manufacturing designers and programmers to create control
programs in a higher-level language (or wizard-style development environment)
which the CAM software then converts to G-code. (Note, however, that in many
situations, programmers still need to write their own low-level G code, since
CNC programming is not yet as fully standardized as desktop or mobile OS
programming.)
CAD
Now let’s look at the higher end.
Computer-aided design (CAD) software is used to design items to be manufactured,
ranging from a fairly simple stand-alone object to a complex, high-precision
system made of a large number of individual parts. Design in CAD is primarily
engineering design, rather than simple graphic design, and CAD output typically
includes precise dimensions, tolerances, and even material requirements; CAD is
frequently integrated with computer-aided engineering (CAE). The
best CAD software is extremely sophisticated (and often very
expensive), and skilled CAD designers are in high demand. There are very
definitely good opportunities for anyone with a good knowledge of CAD software and the ability
to produce technically complex designs that meet the precise engineering
requirements of today’s technology.
CAM
CAD systems may be integrated with an
entire suite of software, including project management and scheduling systems,
product lifecycle management software, and computer-aided manufacturing (CAM)
systems. When integrated with a CAD system, CAM software can take CAD output
(essentially the design and specifications for a manufactured piece) and
convert it directly or indirectly into CNC programming code.
In an ideal world, this
design-to-manufacturing cycle would be seamless and easy: the designer would
create the design in a CAD module and send it to a fully integrated CAM module,
which would then automatically convert it perfect CNC code and send it to the
appropriate factory-floor machines. In the actual world of here-and-now, of
course, it isn’t that easy.
Human Skills Are in Demand
In practice, the G codes generated by
CAM software are still, like most machine-generated code, often not as
efficient or as well-tailored to the specific situation as the hands-on product
of a first-rate programmer. Generated code may be much less prone to errors,
but its design is based on generalized assumptions, rather than the specific
requirements of the situation. In the case of CAM-generated codes, this may
mean that the output must be checked and edited by hand before it can be run,
in order to take into account the particular requirements of the machinery, or
of the production run.
Seeing With a Machinist’s Eyes
A CAM program can’t see the factory
floor through the eyes of an experienced machinist. Actual manufacturing
conditions may require some tasks to be done by hand, even if they could
theoretically be done as part of the CNC manufacturing process. And it isn’t
unusual at all for workplaces to include improvised processes and steps, often
in order to compensate for problems that were not anticipated in the original
design phase. it’s not really surprising, since manufacturing processes go on
in the physical world, where things are rarely as simple as they are in the
idealized world of computer design.
Some Adjustment Required
What does this mean to anyone interested
in pursuing a career in machine control or operation? Basically, it means
that there will probably continue to be a need for skilled, knowledgeable
machinists who understands both low-level CNC programming and practical factory-floor
problems. Designers may be able to produce complete, sophisticated designs in high-end
CAD software, then convert them into machine control codes with the click of a mouse,
but they will still need skilled machinists at the factory-floor level to make
that code work (and make it work efficiently) under real-world conditions.
CAM: Computer Aided Manufacturing
Definition: Computer-Aided Manufacturing (CAM) is the use of
computer software and hardware in the translation of computer-aided design
models into manufacturing instructions for numerical controlled machine tools.
Applications of
Computer-Aided Manufacturing
The field of computer-aided design has steadily advanced
over the past four decades to the stage at which conceptual designs for new
products can be made entirely within the framework of CAD software. From the
development of the basic design to the Bill of Materials necessary to
manufacture the product there is no requirement at any stage of the process to
build physical prototypes.
Computer-Aided Manufacturing takes this one step further by
bridging the gap between the conceptual design and the manufacturing of the
finished product. Whereas in the past it would be necessary for a design
developed using CAD software to be manually converted into a drafted paper
drawing detailing instructions for its manufacture, Computer-Aided
Manufacturing software allows data from CAD software to be converted directly
into a set of manufacturing instructions.
C
AM
software converts 3D models generated in CAD into a set of basic operating
instructions written in G-Code. G-code is a programming language that can be understood
by numerical controlled machine tools – essentially industrial robots – and the
G-code can instruct the machine tool to manufacture a large number of items
with perfect precision and faith to the CAD design.
AM
software converts 3D models generated in CAD into a set of basic operating
instructions written in G-Code. G-code is a programming language that can be understood
by numerical controlled machine tools – essentially industrial robots – and the
G-code can instruct the machine tool to manufacture a large number of items
with perfect precision and faith to the CAD design.
Modern numerical controlled machine tools can be linked into
a ‘cell’, a collection of tools that each performs a specified task in the
manufacture of a product. The product is passed along the cell in the manner of
a production line, with each machine tool (i.e. welding and milling machines,
drills, lathes etc.) performing a single step of the process.
For the sake of convenience, a single computer ‘controller’
can drive all of the tools in a single cell. G-code instructions can be fed to
this controller and then left to run the cell with minimal input from human
supervisors.
Benefits of Computer-Aided Manufacturing
While undesirable for factory workers, the ideal state of
affairs for manufacturers is an entirely automated manufacturing process. In
conjunction with computer-aided design, computer-aided manufacturing enables
manufacturers to reduce the costs of producing goods by minimising the
involvement of human operators.
In addition to lower running costs there are several
additional benefits to using CAM software. By removing the need to translate
CAD models into manufacturing instructions through paper drafts it enables
manufactures to make quick alterations to the product design, feeding updated
instructions to the machine tools and seeing instant results.
In addition, many CAM software packages have the ability to
manage simple tasks such as the re-ordering of parts, further minimising human
involvement. Though all numerical controlled machine tools have the ability to
sense errors and automatically shut down, many can actually send a message to
their human operators via mobile phones or e-mail, informing them of the
problem and awaiting further instructions.
All in all, CAM software represents a continuation of the
trend to make manufacturing entirely automated. While CAD removed the need to
retain a team of drafters to design new products, CAM removes the need for
skilled and unskilled factory workers. All of these developments result in
lower operational costs, lower end product prices and increased profits for
manufacturers.
Problems with
Computer-Aided Manufacturing
Unfortunately, there are several limitations of
computer-aided manufacturing. Obviously, setting up the infrastructure to begin
with can be extremely expensive. Computer-aided manufacturing requires not only
the numerical controlled machine tools themselves but also an extensive suite
of CAD/CAM software and hardware to develop the design models and convert them
into manufacturing instructions – as well as trained operatives to run them.
Additionally, the field of computer-aided management is
fraught with inconsistency. While all numerical controlled machine tools
operate using G-code, there is no universally used standard for the code
itself. Since there is such a wide variety of machine tools that use the code
it tends to be the case that manufacturers create their own bespoke codes to
operate their machinery.
While this lack of standardisation may not be a problem in
itself, it can become a problem when the time comes to convert 3D CAD designs
into G-code. CAD systems tend to store data in their own proprietary format (in
the same way that word processor applications do), so it can often be a
challenge to transfer data from CAD to CAM software and then into whatever form
of G-code the manufacturer employs.
Further information regarding computer-aided manufacturing
can be found at the Berkeley CAM Research site, UC Irvine’s CAM resource site
and the National Institute of Standards and Technology (NIST) (PDF).
Article Details
·
Written By: Sandi Johnson
·
Edited By: John Allen
·
Last Modified Date: 19 September 2014
·
Copyright Protected:
2003-2014 Conjecture Corporation
2003-2014 Conjecture Corporation
·
Computer-aided manufacturing has come to be used as a general term to
describe a variety of industrial automation technologies. Some common types of
computer-aided manufacturing, also known as CAM, include numerical control (NC)
machines; industrial robots; flexible manufacturing systems (FMS); and complete
facility systems that incorporate CAM with computer-aided design (CAD) software, product life cycle software,
and overall facilities management. Modern manufacturing facilities use CAM
technologies to machine products, convert two-dimensional plans into
three-dimensional schematics, monitor equipment, and even track and order raw
material inventory.
In the early years of computer-aided manufacturing, CAM simply implied
automation throughcomputer software. Software helped design
and tool aircraft and automotive parts or helped operate robotic arms during
assembly. Machinists were still needed in most CAM facilities to reset machines
and reason through problems associated with tool misalignment and machine
maintenance. Modern computer-aided manufacturing, however, is much more
advanced that early CAM technology.
Numeric control (NC) machines, one of the oldest and most common types of
computer-aided manufacturing, applies specific formulas to processing raw
materials. For example, if a circle must be cut from a sheet of metal, an NC
machine can determine, using mathematical calculations and numeric input,
exactly where and how to cut to get a perfect circle. Additionally, using the
same algorithms, the computer can determine the exact placement of cuts to
produce the largest number of circles per sheet, as well as exactly how to
position the metal for optimal cutting.
Industrial robots are another example of computer-aided manufacturing.
Robots perform many of the repetitive tasks once performed by human hands.
Computers control the robots, sending and receiving data such as the number of
pieces to produce per minute, placement of robotic arms, and timing between
task stations. Programmers and other computer experts thus replace human
workers, who now run the computer system rather than performing the
manufacturing tasks.
Flexible manufacturing systems, CAM/CAD integrated systems, and setups that
integrate with various data exchange systems provide unlimited possibilities
for computer-aided manufacturing. As technology continues to evolve and
broaden, flexible systems can easily produce several similar products with the
same equipment, assisted by CAM software. Specific changes needed for various
products can be performed within the CAM software, allowing the entire
production process to become automated.
Nearly every aspect of the manufacturing process, with the exception of
skilled computer programmers and operators, could be controlled by CAM
technologies. Rather than simply controlling the manufacturing or fabrication
process, computer-aided manufacturing software can monitor supplies, track
performance, order replacement parts for machines, and even notify maintenance
personnel of needed upkeep or repairs. Customization of various systems and
available technologies makes the different types of CAM software virtually
unlimited.
Sumber: http://www.wisegeek.com/what-are-the-different-types-of-computer-aided-manufacturing.htm
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