CNC-RP: A Rapid Prototyping Method Using Computer
Numerical Controlled Machining
Matthew C. Frank
Industrial and Manufacturing Engineering
Iowa State University
Richard A. Wysk
Industrial and Systems Engineering
North Carolina State University
1
Agenda
•
•
•
•
•
What is RP?
Limitations of RP
Economics of RP
New directions in RP
Observations and conclusions
2
Introduction
•
Prototyping is critically important during product/process design
– Reduce time to market
– Early detection of errors
– Assist concurrent manufacturing engineering
•
Prototypes are used to convey a products’:
– Form
– Fit
Need for model
– Function
accuracy increases
•
Prototype building can be a time-consuming process requiring a highly skilled
craftsperson
– Time spent testing prototypes is valuable
– Time spent constructing them is not…
•
“Rapid Prototyping” (RP) methods have emerged
– (Solid Freeform Fabrication, Additive Manufacturing, Layered Manufacturing)
3
Stereolithography (SLA)
Stereolithography is a common rapid
manufacturing and rapid prototyping
technology for producing parts with high
accuracy and good surface finish. A device
that performs stereolithography is called an
SLA or Stereolithography Apparatus.
Stereolithography is an additive fabrication
process utilizing a vat of liquid UV-curable
photopolymer "resin" and a UV laser to build
parts a layer at a time. On each layer, the laser
beam traces a part cross-section pattern on the
surface of the liquid resin.
4
Selective Laser Sintering (SLS)
SLS can produce parts from a relatively wide range
of commercially available powder materials,
including polymers (nylon, also glass-filled or
with other fillers, and polystyrene), metals (steel,
titanium, alloy mixtures, and composites) and
green sand. The physical process can be full
melting, partial melting, or liquid-phase sintering.
And, depending on the material, up to 100%
density can be achieved with material properties
comparable to those from conventional
manufacturing methods. In many cases large
numbers of parts can be packed within the
powder bed, allowing very high productivity.
5
Fused Deposition Modeling (FDM)
•
•
•
Fused deposition modeling, which is often referred to by its initials FDM,
is a type of rapid prototyping or rapid manufacturing (RP) technology
commonly used within engineering design. The technology was developed
by S. Scott Crump in the late 1980s and was commercialized in 1990. The
FDM technology is marketed commercially by Stratasys Inc.
Like most other RP processes (such as 3D Printing and stereolithography)
FDM works on an "additive" principle by laying down material in layers. A
plastic filament or metal wire is unwound from a coil and supplies material
to an extrusion nozzle which can turn on and off the flow. The nozzle is
heated to melt the material and can be moved in both horizontal and vertical
directions by a numerically controlled mechanism, directly controlled by a
Computer Aided Design software package. In a similar manner to
stereolithography, the model is built up from layers as the material hardens
immediately after extrusion from the nozzle.
Several materials are available with different trade-offs between strength
and temperature. As well as Acrylonitrile butadiene styrene (ABS)
polymer, the FDM technology can also be used with polycarbonates,
polycaprolactone, and waxes. A "water-soluble" material can be used for
making temporary supports while manufacturing is in progress. Marketed
under the name WaterWorks by Stratasys this soluble support material is
actually dissolved in a heated sodium hydroxide solution with the
assistance of ultrasonic agitation.
6
Laminated Object Manufacturing
(LOM)
Laminated Object
Manufacturing (LOM) is a
rapid prototyping system
developed by Helisys Inc. (Cubic
Technologies is now the
successor organization of
Helisys) In it, layers of adhesivecoated paper, plastic, or metal
laminates are successively glued
together and cut to shape with a
knife or laser cutter.
7
Electron Beam Melting (EBM)
•
•
Electron Beam Melting (EBM) is a type of rapid
prototyping for metal parts. It is often classified as a
rapid manufacturing method. The technology
manufactures parts by melting metal powder layer
per layer with an electron beam in a high vacuum.
Unlike some metal sintering techniques, the parts
are fully solid, void-free, and extremely strong.
Electron Beam Melting is also referred to as
Electron Beam Machining.
High speed electrons .5-.8 times the speed of light
are bombarded on the surface of the work material
generating enough heat to melt the surface of the
part and cause the material to locally vaporize.
EBM does require a vacuum, meaning that the
workpiece is limited in size to the vacuum used.
The surface finish on the part is much better than
that of other manufacturing processes. EBM can be
used on metals, non-metals, ceramics, and
composites.
8
Types of RP Systems
Prototyping Technologies
Base Materials
Selective laser sintering (SLS)
Thermoplastics, metals powders
Fused Deposition Modeling (FDM)
Thermoplastics, Eutectic metals.
Stereolithography (SLA)
photopolymer
Laminated Object Manufacturing
(LOM)
Paper
Electron Beam Melting (EBM)
Titanium alloys
3D Printing (3DP)
Various materials
9
Time and Cost to machine
10
Material cost
• In most cases this is independent of the
number of parts
11
Production time per piece
tP =
t
j
setup
j
t L/UL
j
/n
setupbt
j
j
(t + tL/UL + t m + t i + tc )
the time required for setup for an operation (load
fixture, retrieve tooling , etc.)
the time required to load and unload a product
for feature operation j (chuck, fixture, etc..)
j
tm
the machining/processing time for feature j
tc
tool change time/part
ti
idle time due to scheduling control
nbt
number of parts per batch
12
• The product cost can be expressed
as:
C p = t p Cmo + C t / n p/t + C setup / n p/t
Production cost per piece, Cp
13
where
Cmo
is the cost of machine and operator/hour
Ct
is the perishable tooling cost
np/t
is the number of pieces that can be produced per tool
Csetup
is the setup resource cost for the part
(fixture, jig, steady-rest, etc)
14
Problem Introduction
• Rapid Prototyping?
physical models
– Technology for producing accurate parts directly from CAD
models in a few hours with little need for human intervention.
– Pham, et al, 1997
• Prototype?
– A first full-scale and usually functional form of a new type or
design of a construction (as an airplane)
– Webster’s, 1998
• Model?
– A representation in relief or 3 dimensions in plaster, papier-mache,
wood, plastic, or other material of a surface or solid
– Webster’s, 1986
How can we automatically create toolpath and fixture plans
for CNC?
15
Engineering cost
CE = Ced / nt + Cpc / nt + Cpd / nb
total parts
total parts parts in a batch
16
Manufacturing cost
• One time costs
– Process planning and design
– Fixture engineering and fabrication
• Set up cost (Cset)
– Cost to set up a process
• Processing cost (Cpsc)
– Cost of processing a part
• Production cost (Cpdc)
– Cost of tooling and perishables
17
Manufacturing cost
CM = Cone / nt + Cset / nb + Cpsc +
Total parts
parts in a batch
each part
Cpdc // ntool
tool cost by parts/tool
18
So how can engineering costs be
reduced for CNC machining?
Machine cost
Fixture cost
Process planning cost
19
• CNC-RP Method: A part is machined on a 3-Axis mill with a
rotary indexer and tailstock using layer-based toolpaths from
numerous orientations about an axis of rotation.
End mill
Round stock
Axis of rotation
Table
Rotary indexer
Opposing
3-jaw chucks
20
STEPS TO CREATE A PART
( MT. Bike Suspension Component)
2. Second orientation is machined
(Side View)
1. First orientation of part section is machined 3. Third orientation is machined
Rotate Stock
2. Second orientation is machined
4. Fourth orientation is machined
21
STEPS TO CREATE A PART
( MT. Bike Suspension Component)
5. Left support section is machined
7. Temporary supports are removed
6. Right support section is machined
8. Part is severed from stock at supports
22
Process/fixture planning time: Minutes
Processing time ~20 hours
Part fixtured with final 2 sacrificial supports
Part fixtured with final 2 sacrificial supports
4”
Material: Steel
4”
Layer depth: 0.001” (0.025mm)
Finished Steel Part
Finished Steel Part
23
PROCESSING STEPS
(Side View) Machine the visible surfaces
from each of a set of orientations using
layer-based toolpaths
ROTATE to next orientation
MACHINE
ROTATE
MACHINE
The number of rotations
required to machine a
model is dependent on its
geometric complexity
ROTATE
MACHINE
REMOVE model at sacrificial supports
24
Methodology
•
Creation of complex parts using a series of thin layers (slices) of 3-axis
toolpaths generated at numerous orientations rotated about an axis of the part
•
Toolpath planning based on “layering” methods used by other RP systems
•
“Slice” represents visible cross-sectional area to be machined about
(subtractive) rather than actual cross section to be deposited (additive)
•
Slice thickness is the depth of cut for the 2½-D toolpaths
•
Tool used is a flat end mill cutter with equal flute and shank diameter (or
shank diameter < flute diameter)
•
Stock material will be cylindrical, therefore toolpath z-zero location will be
same for all orientations
25
Methodology (cont.)
Flat end mill cutter
“Staircase” effect
Region not visible from
current orientation
Set of visible slices from
current orientation
Toolpath planning using this approach is done with ease in current CAM
software (MasterCAM rough surface pocketing)
26
Methodology (cont.)
• Fixturing accomplished through temporary feature(s) (cylinders)
appended to the solid model prior to toolpath planning
• Cylinders attached to solid model along the axis of rotation
• Incrementally created during machining operation as the model is
rotated
• Model remains secured to stock material then removed (similar to
support structures in current RP methods)
27
Rapid Prototyping
•
Basics:
–
–
Solid model (CAD) is converted to STL format
•
Facetted representation where surface is approximated by triangles
•
Intersect the STL model with parallel planes to create cross sections
Create each cross section, adding on top of preceding one
z
y
x
CAD (ProE)
STL
“slicing”
operation
2-D cross
section
28
Rapid Prototyping
•
•
Fixtures are created in-process (Sacrificial Supports)
– Secure model to the build platform
– Support overhanging features
Remove fixture materials in post-process step
Model material
Support material
Build Platform
FDM Model with/without supports
29
RP versus CNC Machining
•
•
RP processes are very flexible and very capable
However:
– RP processes rely on specialized materials
– Limited accuracy in some cases
Functional prototypes?
•
CNC Machining is:
– Subtractive process
– Accurate
– Capable of using many common manufacturing materials
•
CNC Machining is NOT:
– Automated
– Easily usable except by highly skilled technicians
•
CNC machining cannot create all parts
• No hollow parts
• No severely undercut features
The time consuming tasks of process and fixture planning are major factors which
prohibit CNC machining from being used as a Rapid Prototyping Process
– Wang et al, 1999
•
30
Previous Work
•
Chen and Song, 1991
– Layer based machining for prototyping
– Machined layers using robotic arm/machine tool
– Layers laminated in a stack
•
Merz, et al, 1994
– Shape Deposition Manufacturing
– Additive/Subtractive Process
•
Walczyk and Hardt, 1998; Vouezelaud et al, 1992
– Rapid tooling
– Laminated machining for dies
•
Lennings, 2000
– Deskproto software
– CNC machining planner
– Processes similar to a mill/turn operation
31
Motivation
•
RP processes are almost completely automated “turnkey” operations
– User does not have to be skilled technician
– Process planning is simplified by layer-based approach
– Fixtures are created in process
•
The approach to CNC-RP will have to relax many of the traditional constraints
– Efficient machining is not a major driver (Traditional feeds/speeds not used)
– Not feature-based (Not necessary to machine entire feature in one setup orientation)
– Surface finish not as critical (Allow staircase effect)
•
Goal of this research is to develop a method for CNC rapid prototyping such that:
– Toolpath planning, sequencing, tool sizing is automated
– Fixture design is created in-process, flexible, and allows access to almost all
surfaces
– Setups/orientation automatically calculated, executed
– No collision problems
32
•
•
Methodology
Overview:
– Visible surfaces of the part are machined from each orientation about an axis of
rotation
– Long, small diameter flat end tool with equal flute and shank diameter used.
– Sacrificial supports (temporary features) added to the solid model and created inprocess
– Begin with round stock material, clamped between two opposing chucks
Example:
z
z
y
x
y
Toolpath layers at 0º orientation
z
y
Toolpath layers at 180º orientation
z
y
x
33
Research Problems
•
Setup/Orientation
– How many rotations (setup orientations) about the axis of rotation are required?
– Where are they?
•
Toolpath planning
– For each orientation, how can we automatically generate toolpaths?
– What diameter and length tools should be used?
– In what order should the toolpaths be executed?
•
Fixture planning
– How can we automatically generate sacrificial supports?
– What diameter and length should they be?
34
Determining the number of rotations
•
A problem of tool accessibility
•
Approximated as a problem of visibility (line of sight)
•
A Visibility map is generated via a layer-based approach
•
Tool access is restricted to directions in the slice plane (2D problem)
•
Goal is to generate the data necessary to determine a minimum set of rotations required to
machine the entire surface
Set of segments on a slice visible
from one tool access direction
35
Approaches to 2D visibility mapping
• Shortest Euclidean paths - Lee and Preparata, 1984
• Convex ropes - Peshkin and Sanderson, 1986
• 2D visibility cones - Stewart, 1999
Issues:
• Computing S.E.P.s/VCs for
polygons with holes
• Granularity of STL files, may
need to add collinear points to
polygon segments
• Would need to retriangulate
36
Solution approach
• Visibility for each polygonal chain is determined by calculating
the polar angle range that each segment of the chain can be seen.
• Since there can be multiple chains on each slice, we must consider
the visibility blocked by all other chains.
Θb
Θc
Θb
Θa
Θa
(a) Visibility for the segment=
[Θa,Θb,]
Θd
(b) Visibility for the segment=
[Θa,Θb,], [Θc,Θd,]
37
Step one: Visibility with respect to own chain
•
We have a polygon P and its convex hull S
•
For any point Pi not on S, the visible range can be found by investigating points from the
adjacent CCW convex hull point to the adjacent CW convex hull point
•
These points will be denoted the “left” and “right” convex hull points of Pi, LCHP(Pi) and
RCHP(Pi), respectively.
•
It is only necessary to calculate the polar angles from Pi to the points in the set [LCHP,
RCHP], excluding Pi.
S1 : [ LCHP, Pi 1 ]
The set is divided into, S1 and S2 where:
S 2 : [ Pi 1 , RCHP ]
•
LCHP
RCHP
Pi+1
Pi
P:
S:
,
not
visible
RCHP
LCHP
Pi-1
Pi+1
Pi
38
•The visible range for a point is bounded by the minimum polar angle from Pi
to points in S1 and the maximum polar angle from Pi to points in S2.
•This is the visible range for the point Pi with respect to the boundary of its
own chain, and is denoted V(Pi).
Where:
V ( Pi)  [ Max( Pi X ), Min ( Pi Y ]
X S 2
Y S 1
V(Pi): [43.82 ,121.31]
V(Pi)
S1
Pi
S2
39
• Consider the segment defined by points in P, u and v, where:
u: Pi and v: Pi+1
• The intersection of visibility ranges for the points u and v and the 180º range
above the segment define a feasible range of polar angles in which the segment
could be reached.
(Vu  Vv )  [ RV u , LVu ]  [ RV v , LVv ]  [ RV v , LVu ]
RVv
LVv LVu
RVu
u-1
vu
v+1
u
uv
v
•The sets S1 and S2 are redefined:
S1 : [ LCHP (u ), (u  1)]
S 2 : [(v  1), RCHP (v)]
•The ends of the visibility range are: RV (uv)  [ Max(vx)]
xS 2
LV (uv)  [Min (uy)]
yS1
40
Problem Surfaces
LV
I1
u v I2
u v I2
RV
(a)
RV
I1
LV
(b)
RV
LV
RV
LV
I2
I1
u
(c)
I2
I1
v
u
v
(d)
(a) RV is outside of the 180º range, (b) Both RV and LV are out of the 180º range, (c)
No visibility due to overlapping, (d) Visibility to the entire segment is not possible
since RV > LV.
41
Step two: Visibility blocked by all other chains on the slice
•
V( uv)j* is the visibility with respect to the chain j on which
denoted j*.
•
For all obstacle chains
denoted VB( uv )j.
•
The set of visible ranges for the segment is defined:
j  J \  j *
uv
resides,
, the polar range blocked by the chain is
VIS (uv)  V (uv) j*  VB(uv) j
•
Visibility blocked to the segment uv is the union of the visibility blocked by
chain j to point u and the visibility blocked by chain j to point v, intersected
with the 180º range above segment uv
•
The set of angles blocked to the segment where:
VB(uv) j  {[[VB(u ) j ]  [VB(v) j ]]  [uv, vu]}
•
The set of angles blocked to points u and v where:
VB(u ) j  [ RB u , LBu ]
VB(v) j  [ RB v , LBv ]
42
• Considering the condition that
blocked visibility is only for blockage
in the 180º range above the segment,
it can easily be seen that the set:
(VBu  VBv )  [ RB u , LBu ]  [ RB v , LBv ]  [ RB u , LBv ]
LBu
RBv
LBv
RBu
• RBu is simply the minimum polar
angle from u to all points on the
blocker chain
• LBv is the maximum polar angle from
v to all points on Pj, where Pj is the
set of points for the blocker chain.
RBu  [ Min (ux)] LBv  [ Max(vy)]
xP
j
uv
yPj
43
Recall: VIS (uv)  V (uv) j* 
VB(uv)
j
•For each segment the collection of visible ranges given in polar angle about the
axis of rotation:
VIS tjk : [ a ,  b , ]1 , [ a ,  b , ] 2 ,...[ a ,  b , ]r
where: rMAX = n
•From the data in [VIS] we can formulate a set corresponding to the segments visible
from a given angle.
 s  {( SEGtjk ) ( a   s   b ) for some range, [ a ,  b ] r  VIS tjk }
VIS1,1,1 (Θa,Θb)1, (Θa,Θb)2, …(Θa,Θb)n
VIS2,1,1 (Θa,Θb)1, (Θa,Θb)2, …(Θa,Θb)n
Θ1
Θ2
SEG1,1,1, SEG2,1,1, SEG1,5,3…
(Θa,Θb)1, (Θa,Θb)2, …(Θa,Θb)n
Θs
SEG
tjk. . . .
.
.
.
.
VIStjk
.
.
.
.
.
.
.
.
.
VISqnp (Θa,Θb)1, (Θa,Θb)2, …(Θa,Θb)n
.
.
.
.
.
.
Θ359
SEG13,1,2, SEG14,1,2, …
.
.
.
.
.
SEGtjk. . . .
The Minimum Set Cover problem:
Given: A collection of subsets Θs of a finite set SEG (the set of all segments)
Solution: A set cover for SEG, i.e., a subset S’  S such that every element in SEG belongs to at
least one member of Θs for s  S ' .
44
Implementation/Results
•
•
Algorithm implemented in C
Computation times on a 2.0GHz Pentium 4
C.H.
A.C.
Facets
Slice ( in )
0.0025
0.0050
0.0100
0.0200
0.0400
•
STL Resolution
xcoarse
coarse
medium
fine
xfine
0.0075"
0.005"
0.0025"
0.00125"
0.000625"
0.5
0.5
0.5
0.5
0.5
865
1286
1990
3686
6578
#sgmts time( s ) #sgmts time( s ) #sgmts time( s ) #sgmts time( s ) #sgmts time( s )
19,566
22.750 27,285
25.812 36,199
29.390 49,975
36.623 69,212
47.122
9,772
11.230 13,553
12.875 18,178
14.671 25,044
18.640 34,458
23.389
4,850
5.687 6,781
6.515 9,054
7.405 12,476
9.297 17,306
11.843
2,375
2.875 3,409
3.312 4,597
3.907 6,269
4.859 8,683
6.281
1,182
1.453 1,655
1.718 2,159
2.032 2,974
2.453 4,123
3.141
Set cover problem solved as integer linear program using LINDO:
140º
49º
228º
320º
The “Jack”…
45
Results (cont)
z
Cell phone face plate…
y
x
x
z
y
x
z
z
Turbine…
y
x
y
46
Toolpath Planning
•
•
•
Layer based toolpaths
– Machine visible surfaces from approach direction
– 2½-D pocketing, easily generated using current CAM software (MasterCAM,
rough surface pocketing)
– A gouge-free approach, given flute and shank diameter are same (or shank < flute)
– Investigated as a rough machining approach - Balasubramanium, 1999
Can approach finish machining using very small depths of cut
We assume that tool length, not diameter will be active constraint
– To avoid collision, tool length > maximum swept diameter of part (Same as stock
diameter)
– Tool diameter chosen as smallest available for required length (not conventional
tools)
47
Toolpath Planning
•
Stock diameter/Tool length can be found from slice data used in VISI algorithm
– For each slice, find diameter of the set of points
– Set stock diameter to MAX
– Ds = MAXDIAM(CHP(slice points)) for all slices k
– Set tool length to diameter of the stock Lt = Ds
•
Toolpath sequencing is a significant problem
– Need to avoid “thin web” conditions
– Can occur during one toolpath or from successive toolpaths
d
n  
Depth of cut(max) = -Ds
 n1   n  180
Where Ds= Stock Diameter
Ds = Ds + 2d
(1)
Lt = Ds + d
(2)
48
Toolpath Planning
• Thin material conditions resulting from thru-pocket part geometry:
 n1
n  
n  
 n1   n  90
 n1   n  90
o

 n  (90   d )

(3)
o



(
180


)
d
 n
where: d  10o
n
• For each successive toolpath
planned in sequence, undesirable
orientations to be avoided:
49
Toolpath Planning
• Preparatory toolpath sequence to avoid thin material conditions
• Removes bulk of stock material prior to processing remainder of toolpaths
• Choose from orientations in the solution set, or add new
Model
Remaining stock
material
*Preparatory passes adhere to condition: (3)
50
Fixture Planning
•
•
•
•
•
Approach uses “sacrificial supports” to retain the prototype within the stock material
Round stock clamped between opposing chucks
As prototype is rotated b/w toolpaths sacrificial supports are incrementally created
Supports cut away to remove finished part
Current approach assumes model surfaces exist along axis of rotation
– Only one fixture support cylinder used on each end
– No change to visibility calculations
Problems:
Where do cylinders begin/end?
What diameter?
51
Fixture Planning
•
•
Start/end of cylinder
– Need to have room for tool diameter to pass b/w end of part and stock
– Cylinder end protruding into the part must be fully “embedded”
Use slice geometry to calculate depth of penetration where cylinder is fully attached
Part length
Lf
Lf
Pd ?
Free fixture length: Lf > Dt
Where Dt = diameter of tool
52
Fixture Planning
•
Determine first slice where fixture cylinder diameter is contained within the boundary
chain of the part ( Circle with center at axis of rotation )
*
Slice k=1 (0.005”)
Slice k=1 (0.010”)
Slice k=1 (0.015”)
Part slice boundary
Fixture cylinder diameter
Pd = 0.015”
53
Fixture Planning
•
What is the diameter of the fixture cylinder?
– Cylinders must limit deflection (torsion) caused by machining forces
•
Approach
– Assume part is significantly stiff
– Negligible bending
L1
– Active constraint will be deflection caused by twisting
– Model as a statically indeterminate torsional shaft
L2
L = L1 = L2 = 2*Dt+
T = Ft(r)
d
Deflection =
r sin t
16 LT
t 
 d 4G
r = part radius
r sin t
Ft
Thrust force
54
Fixture Planning
•
Fixture setup:
– Straightforward to determine work offset location, length of stock
– Ensures collision avoidance
D
h
b a
c
a = clamping depth
b = .5Dh - .5(Dt)
work offset from jaw face
c = Lp + 2a + 2b + 2Lf
Where: Dh = tool holder diameter, Dt = tool diameter, Lf = free fixture length, Lp = Part length
55
Example- The “Jack”
Material: 6061 Aluminum
Tool: 1/8” Flat end mill
Machine: Haas VF-O, 3-Axis mill
Layer thickness: 0.005”
Speed: 7500rpm, Feed: 350 ipm
Machining time: 3 hours
Prototype after
2 of 4 rotations
1”
Toolpath and Fixture planning time: < 15 minutes!
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57
58
59
60
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Wire EDM Rapid Prototyping
• Medical RP, one of the major territories for RP application
– Manufacturing of dimensionally accurate physical models of
the human anatomy derived from medical image data using a
variety of rapid prototyping (RP) technologies
– CNC-RP?
• Typical bio/medical Material
– Titanium
– Stainless steel
– Cobalt alloy
• Advantage of Wire Electric
Discharge Machining(WEDM)
– Cut any electrical conductive material regardless hardness
– Ignorable cutting force
– Capable to produce complex part
Satisfy material requirement
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• WEDM is different from traditional
machining process
Point contact
Linear
Surface
• Wire EDM
• Laser
• Waterjet
63
• Visibility problems are different
Can we see it?
Can we access it?
Tool orientation
wire orientation
– “Can we see it” vs. “Can we access it using a
straight line”
64
Wire EDM RP
Can we make it?
How to make it?
(setup)
How to make it?
(Toolpath, NC code)
65
Wire EDM RP
• Investigate the manufacturability
– Part Geometry
– 6-axis Wire EDM
– Rigid machining part
– No internal through features
Can we make
it?
How to make it?
(setup)
• Find the B-axis orientation
– Try to minimize number of B-axis orientation
66
Wire EDM RP
• Toolpath generation
– Discrete Toolpath for B-axis and
– STEP-NC
How to make it?
other
5-axis
(Toolpath,
NC code)
• Fixture Design
– Ignorable cutting force : Clamp part
67
Sample Prototype
•
Prototype: The “Jack”
– 6061 Aluminum
– 1/8” Flat end mill
– 3-Axis HAAS mill
– Speed 7500 rpm, Feed 350 ipm
– Layer thickness 0.005”
– Process time ~3hours
– Process Planning time ~15 minutes
140º
49º
228º
320º
…after 2 rotations
Finished prototype
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Conclusions
• For prototyping, the process is dominated by engineering
cost
– Product engineering, Process engineering, production engineering
• RP has come a long way
– Usable products
– Process and production engineering coasts are minimal
• Conventional methods are on their way back
– CNC RP
– Wire EDM RP
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Conclusions -- continued
•
The methods developed (CNC-RP and Wire EDM –RP) represent a deliberate
approach at making CNC machining usable by engineers and designers, not
just machinists
•
Capable of producing fully functional prototypes in the appropriate material
•
Wide spread availability of CNC machines provides fast, low-cost integration
to current product design processes
•
Quick changeover from RP to Production setup will enable higher utilization
of machines
•
The concept of sacrificial supports for CNC machining represents a significant
area of basic research that may yield even greater contributions outside of RP
70
References:
•
•
•
•
•
•
•
•
•
•
•
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September 1992