What is RS274D (also known as ISO 6983)?
RS274D is the data standard currently used to tell CNC
systems how to make a part. An RS274D file contains a list of
instructions called G-codes. Each code tells the CNC machine where to
move the cutting tool next. If the CNC executes all of the
instructions correctly, then the part is made. Each code is very
primitive and an RS27D file needs to contain hundreds of thousands of
codes to make a part. The CNC is not given any information about what
it is making or why the instructions have to be executed in the given
order. Therefore, no optimizations can be made on the control.
The RS274D standard is also limited in functionality, and CNC vendors have invariably extended it to include newer features in their controls such as spline interpolation. These "dialects" are not standardized, so programs written for one vendor's CNC are unlikely run on another vendor's CNC.
What is a Post Processor?
To handle the wide variety of RS274D dialects (over 5,000), post
processors are used to automatically convert tool path data generated
by CAM to G-codes specific to a CNC's RS274D dialect. In some cases
this is done by the CAM system internally, in others the CAM system
generates APT "cutter location" data that is converted to G-codes by a
third party post processor. Post processing is not a value-added step,
and no new capabilities are added. STEP-NC eliminates the requirements
for post processors, because STEP-NC has no dialects.
What is IGES?
IGES is a standard for transferring drawing information between CAD
systems and between customers and suppliers. When a customer wants a
job shop to make a part, it sends a description of the part as a
drawing in an IGES file. The job shop then reads that IGES file into a
Computer Aided Manufacturing (CAM) system and an operator uses it to
generate the RS274D code necessary to make the part on a specific
machine tool. It can take quite a long time for the operator to
convert the drawing into RS274D codes and if anything changes the
whole process has to start again. The people who developed IGES used
the lessons learned to develop an international standard for the
complete life cycle of a product and called it STEP. There will be no
more versions of IGES after the current one.
What is AP-238?
AP-238 is the official ISO STEP number for the STEP-NC standard. In
AP-238 the information required to control a machine is linked to the
information created by CAD and CAM systems to create a truly
independent, fully documented CNC control file for the first time.
What is ISO 14649?
ISO 14649 is the machining data model underlying AP-238. The authors
of ISO 14649 assessed the state of the art in CNC, and developed an
object-oriented data model based on the concepts of features and
working steps that reflected today's high-performance machining
needs. AP-238 takes this data model and brings it into the suite of
STEP standards, so that CNCs can be fully integrated with CAD, CAM,
CAPP and other CA- applications.
What is AP-203 edition 2?
AP-203 Edition 2 is a recently released new version of the AP-203
standard for exchanging 3D geometry between CAD systems. The new
edition extends the old version to include Geometric Dimensions &
Tolerances (GD&T) data. The new data has been designed to meet the
requirements of design and manufacturing so the same model has also
been incorporated into AP-238 (and the other STEP Manufacturing AP's).
When this model is fully implemented, smart algorithms in the CAM and
CNC systems will be able to compute the best speeds and feeds for some
operations automatically.
What are the other STEP Manufacturing standards?
There are several. The most well known is AP-224. This was the first
standard to describe machining features for milling and turning. The
same features have been adopted by the other STEP manufacturing
standards including AP-238. Other standards in the STEP Manufacturing
suite include AP-219 for CMM inspection data, AP-240 for process
planning data and AP-223 for casting and forging data.
Why is AP-238 special?
AP-238 defines a new interface for existing systems. With the
exception of conformance class 4, it does not require new capabilities
to be added to existing systems. Instead it defines a new standard for
existing information that is already in CAM systems so that the
information can be passed into the CNC systems to make them easier to
program and operate.