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Solid Modeling, CAM and CNC: Recommended Practices  Don
LaCourse, 3DCADTips.com
Robert Byrnes, VX Corporation
December 13, 2004
reprinted by permission from
NC (Numerical Control Tool Paths) is primarily a
downstream application with regard to solid modeling, so the primary
concern should be the flow of information from solid modeling to NC.
Whether or not the solid modeling and NC software are provided by the
same vendor the following tips should be considered.
-
Primitive
Preference
Use solid modeling primitives whenever possible and appropriate to
the design. This may significantly reduce computation for everything
from display to tool path generation and will reduce database size.
Also, most NC machine controllers have built-in capabilities for
machining specific shapes. Being able to take advantage of these
capabilities can result in much shorter NC output and often better
parts.
The most common of these
special capabilities are known as cycles. Examples of cycles are
making holes and cutting smooth arcs. A few NC controllers are
capable of smoothly driving advanced shapes, such as conics,
splines, and bi-cubic patches. Your NC site will likely be
sufficiently pleased if you use axially-symmetric primitives such as
arcs, circles, cylinders, and spheres instead of similarly shaped
splines or ruled, lofted, or meshed surfaces.
-
Information
Availability
The effectiveness of product development is largely based on the
quality and quantity of information that can be conveyed among the
participants. Successful and cost efficient product development
provides NC operators with the information they need to machine good
parts. Whenever possible, data should be contained within the solid
modeling database so that all applications have access to it.
-
Site Specific
There are many variables which are necessarily different from site
to site. This compels the participants to investigate the best
mechanisms for optimal efficiency at their location and application.
-
Determine &
Identify
-
Identify which
geometry types can be communicated and utilized by the NC
software. (2D, 3D, wireframe, surfaces, B-Rep solids)
-
Identify limitations
on geometry positioning, curvature, and other shape limitations
that will pose barriers for the NC software.
-
Identify what
information other than geometry can be communicated and utilized
by the NC software. For example: tolerances, dimensions, and
other product specifications.
-
If design features
are supported, determine if any can be communicated to and
utilized by the NC software.
-
If you have policies
against the conversion of geometry from one mathematical form to
another, determine if a single mathematical form can be
maintained throughout.
-
If NC operators add
or modify geometry, determine if and how those changes should be
communicated back to design for approval and incorporation into
the design database.
-
Determine how part
releases and revisions will be managed.
-
If change management
is built into your solid modeling system, determine if the NC
software can manage changes and if special steps should be taken
to support this. This capability can greatly reduce costs,
especially if simultaneous design and manufacturing planning is
desired or multiple prototypes are needed.
-
If more than one NC
group is involved, determine if and how they should communicate
data between each other.
-
In order to support
Design for Manufacturing (DFM) procedures, investigate how
manufacturing constraints can be communicated from the NC
Department to the Design Department.
-
If a tool must be
machined in order to manufacture the part, determine if the
design group or the manufacturing group is responsible for the
design of the tool. Corporations often form committees using
members of both groups for this purpose.
-
Conventions to make
communication clearer should be determined, for example, the use
of layers/levels, colors, rules for naming, attributes, etc.
-
If individual
components of the part are to be machined by different groups,
NC operators will need to coordinate how fit and tolerance
requirements will be met.
About the Authors Robert Byrnes is Vice President of
VX Corporation and a pioneer in the
integration of CAM and CNC with solid modeling applications. He
currently heads the VX CAM development group at VX Corporation.
Don LaCourse is Editor and Founder of
3DCADTips.com, Principal Partner of eDocHelp,
and Contributing Editor for Cadalyst Magazine. Don has over 25 years of
experience in design, documentation and writing about CAD/CAM/CAE issues.
3DCADTips.com is a free, independent and objective information resource for
3D CAD users, administrators, and managers developed exclusively by eDocHelp
and in partnership with Cadalyst Magazine, TenLinks.com and many other 3D
CAD sites.
Its goal is simple but challenging - to continuously provide a wide range of
valuable tips on 3D CAD, CAM and CAE and to bring all application tips on
the web under one roof where they can be contents, indexed, searched and
browsed by you.
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