This document discusses collaborative machining and the need for quick NC data verification and re-processing. It begins with an abstract that introduces collaborative machining and identifies verification and re-processing as critical issues. It then reviews traditional NC simulation methods like B-rep, section, and Z-map representations. The document proposes a dynamic in-process stock model using a new geometry representation and describes a system developed for quick NC verification and re-processing using OpenGL. Test results showed the system can effectively optimize machining processes in collaborative environments.

1. DRAFT
Proceedings of IMECE2005
2005 ASME International Mechanical Engineering Congress and Exposition
November 5-11, 2005, Orlando, Florida USA
NC VERIFICATION AND RE-PROCESSING FOR COLLABORATIVE MACHINING
PeiLing Liu**, YiQiang Lu*, XiaoMing Ding*, QinRong. Fu*, ChyeBeng Lim+
*Institute of High Performance Computing
1 Science Park Road, #01-01 The Capricorn
Singapore Science Park II, Singapore 117528
**Singapore Institute of Manufacturing Technology
71 NanYang Dr, Singapore 638075
+ AMG Technologies (M) Sdn. Bhd
Abstract:
Collaborative machining is becoming a
common practice worldwide. In mold
manufacturing industry, as the specialized
workshops often do machining much faster
and cheaper than big mold firms, the mold
makers are sub-contracting the machining jobs
to other workshops especially the specialized
workshops for higher efficiency and profit.
This practice causes the separation of NC data
generation, verification, and re-processing
which requests new ways to manage NC data.
This paper investigates the collaborative
machining process and identifies quick NC
data verification and re-processing as critical
issues. The functionalities and limitations of
the commercial systems are studied and the
related NC model, simulation, verification,
and optimization technology are scrutinzed. A
dynamic in-process stock model based on a
new geometry representation is proposed, then
a system for quick NC verification and re-
processing is developed using OpenGL. The
system has been implemented in many mold
manufacturing companies and the results show
that the pervasive machining modeling,
simulation, verification, and re-processing can
effectively optimize machining processes in
collaborative machining environments.
Keywords:
NC verification, NC simulation, NC post-
processing, Collaborative machining
NOMENCLATURE
IPM In-process model
LM layered manufacturing
M&S modeling & simulation
1. INTRODUCTION
Outsource manufacturing is a worldwide
trend. In Asia mold manufacturing industry, as
the specialized workshops often do machining
much faster and cheaper than big mold firms,
the mold makers are sub-contracting the
machining jobs to other workshops especially
the specialized workshops for higher
efficiency and profit. This practice causes the
separation of NC data generation, verification,
and re-processing which requests new ways to
manage NC data. Collaborative NC
programming and machining create new
challenges for CAM programmers and
machinist.
For example, a NC programmer may not
know for certain a machine tool to post-
processing NC toolpath to machine control
data, such as M/G code, since the contract
machine shop could use different machine
tools to cut same the part, pending on the
availability of the machine tool. Contract
machine shop may have to switch to an
available machine tool, which needs to re-post
NC data through another post-processor.
When received a set of NC data files plus
setup drawing, a machinist has to verify and
check data integrity before start cutting. Raw
material is increasingly expensive nowadays
and a new order may take days to complete.
Even through it is common now that original
NC toolpath are verified inside CAM software,
there are still many chances of NC data errors

2. during post-processing and NC file
management, as human fatigue is the main
cause. Since machinists only have a few hours
to cut the part to a certain stage, there is no
time to run traditional NC simulation software,
which typically needs more time than cutting
itself, especially for high speed machining,
where blocks of M/G code can easily reach
one million.
Shop floor NC programming could be one
solution for this complication, where a part
model and machining process plan are sending
to contract machining shop. However, this will
burden contract machining shop with
expensive CAM software and experienced NC
programmer. Separation of CAD and CAM is
less effective and create some problem for
process planning. Most contract machining
shops are majoring only a certain process of
machining, such as roughing mold base, EDM
of cavity, and profile grinding of inserts. 3D
in-process models (IPMs) are very essential
for the integration of various activities related
to manufacturing process planning, toolpath
generation, and machine inspection. By
sharing accurate IPMs among the related
activities, engineering change could be
managed in an efficient way.
Most important, for some practical
consideration especially in Asia, original
designers do not want to share part model with
contract machining shop.
Comparing with the sharp decline of the
computing cost, worldwide material and
machine tool prices are upsurge significantly.
Saving material and manufacturing cost
through pervasive application of modeling and
simulation (M&S) is not only technically
possible, but also makes business sense in
today’s highly increasing competitive
environment. How to quick verify and re-
processing NC data are becoming a critical
issue in modern contracting machining.
For the last two decades, we have
developed NC simulation using different
cutting simulation method, IPMs evolved from
B-rep, section method, Z map, and patented
extended Z map. The novel hybrid multiple
contract machining and layered manufacturing
processes posed a new challenge to process
planning and verification.
2. NC PROGRAM ERRORS
ANALYSIS
The average scrape rate for local mould
maker is 15%. There are different kinds of
NC program errors.
The low quality of solid model will cause
low quality NC program:
• The surface deformation is too big
during to data exchange problem.
• The surface tolerance maybe as
low as 0.1mm.
• There are data defects, for
example the gaps between
surfaces
The NC toolpath generation algorithms are
unstable:
• The toolpath planning is a very
difficulty task.
• The toolpath sampling method
varies quite differently.
• There is no exact offset solution
for curves and curved surfaces.
The lack of in-process stock IPMs causes a
lot of air cut and gouging.
• The cutter may move through
remaining stock too fast.
• There maybe too many
conservative air cuts in semi
finishing cut and finishing cut.
• Near touch condition may cause
cutter wear off.

3. The post-processor generates arcs with several
meters radius, which will cause errors in some
CNC controllers.
The human errors occur depending on NC
programmer’s experience. The possible cases
include:
• The patching up of surfaces.
• Plan machining process.
• Wrong part face, check face and
boundary choice.
• Wrong machining set-up.
• Wrong cutting parameters.
3. GENERL METHODOLOGY
A. NC SIMULATOR
INTRODUCTION
NC Simulation features full 3D, solid
model, shaded simulation of entire NC
machine tools and material removal. This
visualisation tool enables programmers and
machinists alike to preview exactly what will
happen on the shop floor and check for
collisions. Many use NC SIMULATION for
electronic shop floor documentation.
NC Verification detects problems in the
NC tool path program. It is a powerful visual
inspection tool, which highlights fast feed
errors, gouges, and potential crashes/collisions.
Programmers can detect and correct problems
before prove-out. With NC Verification you
can virtually eliminate NC program mistakes,
greatly reduce the time spent on prove-outs,
and make the move to "lights-out" machining.
NC Analysis identifies the tool path record
responsible for an error. Users can quickly
verify the dimensional accuracy of the entire
part with a full array of 3D measurement tools.
NC Analysis compares the simulated part to
the design model so to ensure the machined
part match the design intent.
NC Optimisation automatically determines
the best feed rate for each segment of the tool
path based on the machining conditions and
amount of material removed. Optimizing NC
feed rates greatly reduces the time it takes to
machine parts and improves the quality of
surface finish.
The functions of NC simulation can be
summarized as follows:
• NC simulation saves time and reduces
or eliminates prove-outs and save
machine tool, operator, and part
programming time – all of which
decrease time-to-market.
• NC simulation increases quality and
verifies dimensional accuracy and
optimises tool paths for better finishes
on surfaces and edges.
• NC simulation Save money and
reduce or eliminate the cost of
machine tool crashes, rework,
scrapped parts, and damaged tooling,
fixtures, and clamps.
• NC simulation Increase productivity
by reducing machining times and
interrupts production less frequently.
• NC simulation gives confidence.
Through testing part programs on a
computer so they run right the first
time and operators don’t need to keep
one hand on the "emergency stop"
button.
• NC simulation conserves resources. It
can reduce machine tool wear and
reduce cutting tool wear so cutting
tools can be used longer before
needing to be reground or replaced.
• NC simulation improves safety &
training. It can train programmers,
operators, and students without using
machine tool time or risking a
dangerous, costly collision.
• NC simulation improves
documentation. Enable operators and
managers to preview all machining
operations.
B. TRADITIONAL NC
SIMULATION METHODS
ALL of the current NC verification
systems are based on view dependent extended
Z-buffer pixel. The pixel model could not be
zoomed from different viewpoint. It is only
good for animation. Also it does not provide
dynamic information about the manufacturing
process.
The recent development of high speed
machining (HSM) requires huge tool path to
realise the constant load. The milling tool path
can easily exceed a half million blocks of
machine code. As the feed rate is already very
high, it is almost impossible to run test cutting
by increasing the feed rate. Visual tool path
check is difficult as the tool path overlapping
with each other. It takes a long time to run
traditional simulation software. The constant
load is a very important factor in HSM as the
cutter will break under uneven cutting force.

4. Currently there is no way to check this before
the operation. There are strong requirements
from industry for a real dynamic simulation to
optimize feed/speed.
NC simulation could be classified by their
geometrical models, which are sometimes
called in-process model (IPM) since it is
deformable. The in-process model represents
the state of the product at each step in the
machining process. It is represented as a 3D
geometry that reflects the results of the
machining operations. This model allows the
user to visually verify that the machining
operations which have been defined accurately
and ensure their sequence is correct. This 3D
model can be automatically re-generated when
there are changes in the product design,
machining parameters or sequence of the
machining operations [1]. In following
sections, the geometric representation
techniques of IPMs for the traditional
manufacturing simulation are presented.
B-rep
The first choice of IPM should be
naturally B-rep, which is the typical
geometrical model of commercial CAD
system. The benefits of using the same
geometrical model of CAD as the IPM are
obvious. The CAD geometrical model is
matured and available through CAD
development kit, so there is little need to
develop a new geometrical model kernel.
Sharing common geometrical model with
CAD, the IPM facilitates seamless integration
of CAD-CAPP-CAM.
The author of this paper developed an
automatic forging design and manufacture
system in 1986, in which pre-form forging
IPMs were same as the CAD system
CV/MUDUSA running on VAX-11/750
computer [5-6]. The creation of pre-form
forging IPMs took days of calculation and
often failed due to Boolean operation failure.
It is very difficulty to deform a B-rep model
other than traditional Boolean operation,
where the topologies of B-rep model are
altered and more faces are added. Boolean
operations have to loop through all the faces to
trim blank body with tool body. Localization
of Boolean has been tried with limited success.
With great research efforts in the last two
decades, the B-rep geometrical model has been
improved a lot in term of Boolean operation
stability, but the B-rep based IPMs are still
limited to 2.5 axis milling (Figure 1). S. C.
Park reported a prismatic IPM generation
method that employed a polygon extrusion
algorithm, which could be used to sweep a
ball-nose cutter [1].
Section Method
Since the integrated B-rep IPMs can not be
created inside a CAD geometrical model, the
ad-hoc cross-section-wire-frame based
approach is proposed in a new concept forging
die CAD/CAM system [5]. The idea is to use a
series of paralleled cross section drawing as
representation of 3D shapes (Figure 1).
The cross section IPM is widely used in
many commercial CAD/CAM systems. I-
DEAS from SDRC uses water level cross
section as IPM for generative machining. In a
traditional NC programming environment, a
significant amount of time is spent trying to
visualize the in-process stock as it goes
through various process stages. With I-DEAS,
the IPM - in-process stock model can be
created for downstream applications such as
toolpath generation, process planning, fixture
designing, and clamp positioning.
A part can be sectioned along XYZ axis.
The Z-axis section is usually called water level
section. For 3-axis milling, the water level
section could have many loops, which will
make the set operation between sections
complicated. X and Y sections are single half
loops and the Z value is unique for every
points.
Fig. 1 section representation and regulated
section
A working system of using IPM for pre-
forging design was described in [5]. A section
drawing sheet of part section was created first
using BACIS command language of
CV/MEDUSA CAD system. Since there were
many sections in a drawing sheet, the section
wire frame was assigned to different layers
according to their Y distance, and a certain
number of sections could be looped through
layers. Then the cutter sections were moved to

5. the cutter location and compared with the part
sections. The overlap between the cutter
section and the part section was removed from
the part section and a real milling IPM was
obtained from the collection of the result
sections.
The display of sections was line segment
and could be confusing when there were too
many lines. There was a need to render IPM
as a realistic 3D image. In order to calculate
the surface normal, which was needed for
rendering, we divided the section wire frame
along X direction by the same step over of Y
direction. A so-called regulated section was
formed to facilitate the calculation of surface
normal and interpolation of points between the
sections. A certain node in one section was
linked to a certain node in the next section. A
node’s normal could be calculated by the four
neighboring nodes.
The regulated section can also be used to
accelerate set operation between cutter section
and part section. The calculation of
intersection, trimming between two sections
and the re-ordering of the line segments are
very time consuming. This can be improved
with the regulated sections, where the line
segments were indexed in both cutter section
and part section. Only the line segments with
the same index were compared and trimmed.
There is no need to loop through every
segments of the section. If all the line
segments fall on the regulated nodes, there is
no need to trim two line segments. The set
operation could be simplified to the
comparison of two Z values. The comparison
of two values could be very fast and stable.
The so called Z map representation of IPM
was born [6].
Z Map Representation
If all the section line segments fall on the
nodes, the object surface can be represented by
the Z values of the nodes. A map of Z values
represents the object geometry. (A Z map can
also be seen as a forest of uniformed planted
trees, where the heights of trees represent the
geometry of the forest.) Mathematically, Z
map could expressed as a two-dimension array
Z[i, j], where i represents the index in X
direction and j represents the index in Y
direction. The XY position of the Z map can
be calculated by i or j times grid size.
The best way to describe a Z map is using
a needle bed sample, where needles are
uniformly distributed over XY plane. The
height of every needle touches the object
surface that it represents. The milling
simulation can be seen as the tool cutting
through needle bed. These needles can be
described in math term as z axis aligned
vectors, passing through the grid points on the
XY plane. Z map representation can be
effectively used for the surface that is always
visible from above in the direction parallel to
the Z axis. Since 3-axis milling parts are
composed of surfaces visible in the z direction,
they can be effectively expressed by the Z map
representation. With the Z map representation,
the machining process can be simulated
through cutting the Z map vectors by the cutter.
Fig. 2 classic Z Map and display
The vector in Z map has direction and
length. The vector in Z map is infinitely thin
without volume. The top of the vector is just a
point and has no shape at all. Only at this point
the Z map and the object meet with each other.
Z map mode could not give accurate object
geometry besides these points. There are many
ways of interpolating the geometry between
grid points. For example, triangle needs to be
formed by tri neighboring Z values to render a
Z map model.
Fig. 3 NS simulation based on Z Map
The extended Z map representation
method comprises the steps of providing
geometric data of an object having a surface,

6. the object constituting one of a physical object
and a virtual object, and the geometric data
being indicative of the surface of the object.
As shown in Fig 4, firstly it generates a
reference plane with z-axis being
perpendicular to the reference plane, then
constructs a z-map grid, the z-map grid being
planar and coincident with the reference plane,
after that constructs a first z-map of a first
portion of the surface of the object which is
generated with reference to the z-map grid,
finally constructs a second z-map of a second
portion of the surface of the object which is
generated with reference to the z-map grid. Z
map could be expended with another Z value
to represent an object with top and bottom
surface.
Fig. 4 Extend Z map to top and bottom faces
This Z map has many alias or hybrid
cousins such as ray casting, Z buffer etc.
When a group of virtually light rays pass
through an object from Z direction, there will
be intersections between the light ray and the
object. These top and bottom Z values are
stored in the depth buffers of the graphics card
and used for hidden surface removal algorithm.
This process was called ray casting or tracing
technology and is used for many graphics
application such as volume rendering. The
detailed description of the extended Z map
method can be found in two patents [12].
Dexel or extended Z buffer extends Z map to
multi segments and positions it along screen
normal, so a faster cutting animation could be
achieved but it is view dependent.
Fig. 5 extended Z buffer Dexel model
Z map can not approximate vertical wall
very well since it always has a slope as
showed in Fig 7. This is not a big problem for
forging die design since there always are draft
angles in forging parts. This is a big problem
for milling parts since profiling always creates
vertical walls.
Fig. 6 classic Z Map cannot model vertical
walls precisely
It is obvious that the XY resolution of the
Z map grid is the precision of Z map model.
The smaller grid has the better precision but
needs greater memory. For a part of
1000mm*1000mm, the size of the Z map is
1000*1000 if the precision is 1mm, but it
increases to 2000*2000 if the precision is
0.5mm. Reducing the model size and
achieving suitable precision appears to be a
critical issue on Z map.
Because of its simplicity in the data
structure and fast computation time, Z map
model is used by most commercial CAM
software [7-9]. One of the solutions is to
balance Z precision and XY precision. One
invention in [12] is to use integer array to
replace the float array of Z map, which
reduces the Z map size by half, and at the
same time improves the boolean operation
speed because the comparison of integers is
much faster than the comparison of floats. The
memory of Z map is further reduced it by half
through compressing Z map file section by
section.
4. QUICK NC SIMULATION
METHODS
4.1 Sub-cell
Since the precision of Z map is decided
mainly by the XY resolution along the vertical
walls, how to increase the resolution along
these walls and reduce memory becomes a
critical issue. Viewing from top, the vertical
walls only cover a small percentage of Z
direction projection, how can we use finer
resolution along the vertical walls while

7. maintain a rough resolution in the planar area?
This was the initial idea of extended Z map.
In this study, at least one grid on a z-map
is segregated into sub-cells. Only grids
corresponding to intricate features on the
surface of an object are assigned sub-cells to
improve representation of object features.
Figure 7a shows the front sectional view,
while Figure 7b illustrates the plan view of
the z-map grid with sub-cells 52.
Fig. 7 extend Z Map with sub-cells along
vertical walls
The size of the grid can be reduced
through using sub-cells. But the precision of
XY dimension is still limited by the size of
sub-cells. For a sub-cell of 0.1mm, the best
precision is 0.1mm in XY plane. There is a
need to represent XY dimension precisely.
Instead of using vectors in the sub-cells, we
use sticks in the sub-cells that have volumes
and surface geometry. A B-rep surface model
can be represented precisely using a map of B-
rep sticks.
Fig. 8 stick method and a sample display
Milling simulation in stick method
involves Boolean operation of cutter and stick.
Figure 10 shows different stick shape after
cutting. The experiments with B-rep stick
model are very slow and create a huge B-rep
model. To simplify stick and Boolean
operation, polygon instead of real surface is
used in a stick cell. This can greatly increase
simulation speed. The data structure of
polygon is much simpler than that of B-rep
which needs a group of complicated pointers
to maintain a double wing data structure.
Fig. 9 different shapes of stick elements
The real world objects are not always
uniform in XY dimension and can be any
shape. Nodes are used to enhance sub-cell’s
precisions in representation of object face. For
example, one edge of the sub-cell may have
two overlapping nodes to represent a vertical
face. The nodes of a sub-cell may not be
uniformly distributed over XY plane. Figure
11 shows an exploded plan view of a portion
of the z-map grid with nodes 54. Figure 12
shows how stick method represents a circular
hole and vertical walls.
Fig. 10 extended sub-cells to approximate
vertical wall
4.2 Color index
In addition, a color index is assigned to
each grid point on the z-map grid and stored in
a reference list containing cells corresponding
to each grid point on the z-map. A computer
model of the object is pre-rendered using the
reference list onto a plurality of display lists
corresponding to different portions of the
computer model of the object. By recalling the
required display list for display when the
computer model is virtually displaced, the time
lag for displaying the computer model to a
user is substantially reduced.
The system starts with a solid model of the
machined part and quickly simulates and
optimizes machining processes. NC code
could be selectively reverse post processed
into 3D tool path graphics display and
interactively viewed, edited, and optimized.
44
52 5252

8. The user can highlight or hide operation, tool
path, or layer. The user also can display and
edit a certain layer of toolpath. Tool paths and
cutting results can be viewed from any
viewpoint and checked automatically. The
machined part and the design part are
compared for the remaining stock and over cut.
Error-free tool paths are created, eliminating
the need for a time-consuming test cut. Quick
and simple post processors export the
optimized toolpath to NC code.
4.3 Applications
We developed several practical
applications for mould manufacturers. These
include QuickSeeNC and PartingAdviser,
which provide “What You See is What You
Cut” functionality for shop floor machine
operators and designers. It could be integrated
with other CAM software such as UG through
a native APT adapter.
The actual application example of a steel
insert of discman mould comes from last
author’s company. The steps to do simulation
is described below: Step 1 was to setup stock
size as 3300*220*100mm; Step 2 was to open
APT toolpath discman.cls. There were 16
operations in this CLS file that contains almost
half million of NC blocks. QuickSeeNC
loaded in half million lines in seconds and
displayed toolpath in different colours
according to operation. User could control the
display by layers or operation, depending on
the editing needs.
Fig. 11 almost half million of NC block
The system abstract toolpath and cutter
info from cls file and created NC data file that
could be sent to shop floor:
NC Program Data Sheet core_insert_nc
No. Program Name Cutter SOL Time
1 V64C61CA D20.00 R0.000 L75 96m
2 V61CA1 D20.00 R0.000 L75 11m
3 V64C61CB D12.00 R6.000 L75 31m
4 V64C61CC D6.000 R3.000 L75 45m
5 V64C61CD D6.000 R3.000 L75 153m
6 V64C61CE D4.000 R2.000 L75 33m
7 V61CE1 D4.000 R2.000 L75 11m
8 V64C61CF D20.00 R0.000 L75 2m
9 V61CF1 D20.00 R0.000 L75 1m
10 V64C61CG D8.000 R0.000 L75 6m
11 V61CG1 D8.000 R0.000 L75 7m
12 V61CG2 D8.000 R0.000 L75 7m
13 V61CG3 D8.000 R0.000 L75 7m
14 V61CG4 D8.000 R0.000 L75 7m
15 V64C61CH D16.00 R0.000 L75 13m
16 V61CH1 D16.00 R0.000 L75 14m
Total NC Program = 16
Machine time = 7 hours 23 minutes
In step 3 a user studied the operation using
toolpath manager. The red colour shows the
current toolpath. cutting simulation from start
to finish could be completed in less than one
minute. After scrutiny the IPM, 16 operations
was scheduled to different machine tools and
quick post out to NC code, with all the cutter
and process info inserted on the top of the NC
data file.
Fig. 12 Extended Z map IPM
5. TOWARDS A UNIFIED MODEL FOR
MULTIPLE MACHINING AND LM
SIMULATION
The term voxel represents a volume
element in space decomposition geometrical
model schema, just like the term pixel denotes
a picture element in raster graphics.
Voxelization is the process of converting a 3D
object into a voxel model. After analyzing the
voxel model, the authors of this paper believe
the voxel-based volume modeling is a very
promising approach to the unified IPM for
multiple machining and layered manufacturing

9. simulation. As a natural clone of the LM
technology, the voxel model of an object and
the object fabricated using an LM closely
resemble each other since both are made of
layers of small cells. It eliminates the STL
format and eases accomplishments of tasks
such as estimation of errors in the physical
parameters of the fabricated objects, tolerance
and interference detection. Furthermore, voxel
based models permit the designer to analyze
the LM object and modify it at the voxel level
leading to the design of custom composites of
arbitrary topology.
Volume graphics, voxelization and
volume rendering have attracted considerable
research in recent years. However, all of this
works are directed at the display of volume
data, mainly for medical applications. In this
paper we propose a simplified voxel-based
IPM to unite the new LM and traditional
machining processes simulation.
The memory requirements of traditional
voxel models are enormous. There is a need to
store the voxel array in compressed form and
use algorithms that will operate directly on the
compressed data, specially when the material
is homogenous, where internal voxel could
represented by boundary voxel extension. It is
possible to convert the voxel array into some
other more compact representation and
reconvert into voxels when required. However,
this could be mainly used for storage purpose.
We keep the original geometric representation
and use voxelization algorithms when
necessary. This is especially valuable since
design data are mainly generated from
conventional CAD system.
A voxel-based system should be able to
update the display at interactive rates. Current
graphics rendering systems cannot provide a
level of rendering performance on voxel
models that is comparable to their polygon-
rendering performance. Parallel algorithms
and hardware support for volume rendering are
the focus of current research efforts. Only
boundary voxel needs to be rendered by a
patented color list, which effectively avoid
expensive ray-casting of huge internal voxels.
The rendering of voxel model is easily
achieved by rendering a points cloud.
However, internal voxel display is not possible
with this method and needs more study.
Voxel based LM simulation could be
achieved by the voxelization of the road
shapes, which are similar to a pipe along the
LM toolpath. Boolean addition between the
road shape voxel and the base voxel is fast and
stable, independent of the model shape, which
is a critical issue with B-rep. One layer of road
shapes would make B-rep based solid modeler
very slow, since B-rep Boolean operation is
dependent on model shape.
During a combined LM and machining
manufacturing, such as shape deposition
manufacturing, a LM part needs to be inserted
with a electronic device and milled to a certain
shape. The unified LM-machining simulation
displays the machining process in which the
initial LM generated workpiece is
incrementally converted into the finished part.
The voxel representation is used to model
efficiently the state of IPM, which is generated
by successively subtracting tool swept
volumes from the workpiece. The voxel
representation also simplifies the computation
of regularized Boolean set operations and of
material removal volumes. By using the
material removal rate measured by the number
of removed voxels, the feedrate can be
adjusted adaptively to increase the machining
productivity.
6. CONCLUSIONS
Numerical Control Machining is the
cutting edge of modern manufacturing
technology. NC errors could destroy work
pieces, even damage machine tool. One NC
error could make the workpiece a waste and
take days to rework a new workpiece. The
machining errors eat into profit. In the age of
small batch production, there is no time for
trial and errors. Verifying and optimizing
precision NC machining make profits.
In the age of high speed (HSM) precision
machining, the fast moving and expensive
cutter is very easy to be broken. However,
traditional NC simulation only checks
geometry errors which is not good enough.
The dynamic machining load will greatly
affect cutter life, geometry accuracy and
surface finishing.
The challenges also come from huge tool
path of HSM. Million lines of NC code are
common practice in today’s shop floor. The
traditional NC verification is so slow that even
HSM itself is faster than verification. The size
of the program combined with a high feed rate
makes it almost impossible to run test
simulations prior to cutting metal.

10. 3D IPMs is very essential for collaborative
machining and the integration of various
activities related to manufacturing process
planning, toolpath generation, and machine
inspection. By sharing accurate IPMs among
the related activities, engineering change could
be managed in an efficient way. We generated
the machining IPMs through different cutting
simulation method, evolved from B-rep,
section method, Z map, and patented extended
Z map. The novel hybrid multiple machining
and layered manufacturing processes posed a
new challenge to process planning and
verification. Towards the vision of pervasive
modeling & simulation, we proposed a unified
voxel-based in-process geometrical model for
multiple machining and layered manufacturing
simulations.
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