Cybercut is a rapid manufacturing
process containing three main steps; design - CAD, planning - CAPP, and
fabrication - CAM. The user enters the Cybercut Web Site, and downloads
a Java applet that connects to the design agent in the MAC. The design
agent then allows the designer to choose a process planning agent. The
user can now select a fabrication agent from those available to the planning
agent. The fabrication agent then sends its capabilities (workspace, size,
tolerances, turn-around times, and cost-estimates) to the planning agent.
The planning agent can then create a set of design options, based upon
its own abilities, and the information from the fabrication agent. These
design options are sent to the design agent. Based upon the information
provided by the planning agent, the design agent can now present a set
of rules for the designer.
CAD (Computer Aided Design) is the first step. It uses a program called
DSG (Destructive Solid Geometry). Cybercut is the only rapid manufacturing
process that uses DSG instead of CSG (Constructive Solid Geometry). CSG
builds a design in layers adding on to nothing. DSG means that the user
starts out with a solid piece and removes chunks of material. The user
is constrained to removing certain shapes of material referred to as "features".
These features take the form of pockets, blind holes, through holes, arcs,
and face-off operations. This is to make the next step easier. Each of
these features can be readily mapped to a standard CNC milling process.
The next step is CAPP (Computer Aided Process Planner). The planner can
be broken down into two parts; the macro planner and the micro planner.
The macro planner is used to determine the best tool to be used for the
user-entered features, decide which fixturing steps will be needed, and
then it sends the individual features to the micro planner. The micro planner
has access to a tooling database for the open architecture machine that
cuts the final part and uses this knowledge to break down features into
a series of cutting operations. Each operation is assigned a tool, cutting
path, feed, and speed. There are two types of planners that the designer
can choose from. The first is an incremental CAPP. Incremental refers to
the fact that the manufacturing plan is updated after each feature is added.
The planner examines the interactions between the new feature and the pre-existing
ones. The planner will either accept this new feature or notify the designer
of a design rule violation. There are two types of violations; hard and
soft. A hard violation means the feature the designer requested can not
be fabricated. A soft violation is that the feature can be fabricated but
not at the tolerance requested. The design process is an ongoing negotiation
between the designer and the planner, with the planner making suggestions
to the designer on how to improve the manufacturability of the part. The
resulting design can be fabricated at any step of it’s development. The
second type of planner is a Batch-Mode CAPP. To start a set of design rules
and capabilities; such as workspace, size, tolerances, turn-around times,
and cost estimates are uploaded from the fabrication site. The user creates
features based on these rules. When the design is finished, the resulting
geometry is sent to the process planner, which converts the geometry into
machining script. There are problems with using this type of planner, however.
The user can create an infeasible design, such as generating a thin wall
between two features that can break during maching. The responsibility
for taking care of local feature interactions now shifts to the designer.
The design is now in maching script and sent to the CAM.
The last step in the process is CAM (Computer Aided Maching). A machining
script is sent to Berkeley’s Machine tool Open System Advanced Intelligent
Controller for Precision Machining (MOSAIC-PM). MOSAIC-PM is the computer
system that controls a Hass 3-axis vertical machine center with a 16 tool-bit
position changer. MOSAIC-PM system’s structure allows a programmer to control
all aspects of the machining process, from high-level programming that
accomplishes complicated machining tasks automatically, to mid-level point
to point moves, to the lowest level, real-time control of the voltage outputs.
High level machining helps overcome errors due to tool wear, material deformation,
and tool deflection. The ability to manipulate the low level aspects of
machine control enables the programmer to adjust the values of acceleration
used for the standard trapezoidal velocity profile. When the part is being
machined it uses a hardware fixturing method, called Reference Free Part
Encapsulation (RFPE). RFPE frees up the design space and also greatly expands
the possible range of the parts that can be designed and then machined.
RFPE also allows the machining of parts with thin spaces and narrow cross-sections.
RFPE uses a bi-phase material, Rigidax, to encapsulate a workpiece and
provide support during the machining process. Once one side of a component
has been machined, Rigidax is poured around the features, returning the
stock to the encapsulated brick-like appearance which can be easily re-clamped.
A grad student is used for this part.
