Keynote Papers

Advanced Techniques for Die and Mold Manufacturing

T. Altan (1) and 6. W. Lilly, ERC/NSM, Ohio State University, USA - J. P. Kruth (I), KU Leuven, Belgium -
W. Konig (I), WZL, RWTH Aachen, Germany - H. K. Tonshoff (I), IFW, TU Hannover, Germany -
C. A. van Luttervelt (I), TU Delft, Netherlands - A. 6. Khairy, University of Edinburgh, UK.

Summary

Die and mold manufacturing represents a significant area of production technology since it influences the feasibility and
economics of producing a very large number of discrete components. M.odern die manufacturing includes just about all aspects of
manufacturing: part design, geometry handling and transfer, die design, process modeling, prototype production, control of
dimensional and surface quality as well as advanced mechanical, electrical. and electrochemical machining methods. This paper,
prepared with input from various CIRP colleagues, attempts to review the latest advances and practical applications in the field.

1. Introduction

A large percentage of discrete parts are manufactured by using a "Near Net Machining. vii) surface conditions and polishing, and viii) dimensional
Shape" (NNS) process-such as forging, die casting, stamping or injection control of electrodes, dies, and the NNS formed product.
molding-prior to machining and grinding to assembly ready tolerances.
These processes utilize dies and molds to impart the NNS geometry on an
incoming shapeless material or a previously preformed workpiece. Thus the
cost effective manufacturing of dies and molds, with specified geometry, 2. Part and Process Design
tolerances, surface finish and stren-th requirements, is a most significant
manufacturing activity. Often the intkate geometry with sculptured surfaces In manufacturing discrete parts by a NNS process using dies or molds, the
and relatively high material hardness make die and mold design and part design must be compatible with the process in order to assure the
manufacturing a most demanding and difficult engineering task [Konig. M.. production of high quality parts at low'cost. and with short Isad times. Thus.
921. In addition, each specific process imposes its own special requirements part, process and die design are best considered simultaneously,as illustrated
on the die or mold characteristics [Boes and van Luttervelt. 901. For example, in Figure 2 [Grubb 931 The die design should assure that the dies actually
hot forging and die casting dies are subject to thermal fatigue and erosive produce the product directly according to specifications without any "fine
wear. while cold forging dies must sustain very high stresses, and must be tuning" or "trial and error". This objective can only be achieved through
resistant to mechanical low cycle fatigue; injection molds must have excellent good communication between the product and tool designer, who are usually
surface finish, and be resistant to corrosion. in separate companies and locations. The use of different CAD systems by
each party further complicates the communication.
In most countries the die and mold industry consists mainly of small
companies. typically with fewer than 100 employees. In the U.S., for example, It is well known that the design activity represents only a small portion. 5 to
approximately 15.000 die shops represent an annual sales volume of about 15 percent, of the total production costs of a part. However, decisions made at
$20 billion [Destefani, 931. The users of dies and molds increasingly expect the design stage have a profound effect upon manufacturing and life cycle
that: a) manufacturing costs and lead times are reduced, b) dimensional costs of a product. In addition to satisfying functional requirements, for the
accuracy and overall quality are increased, c) dies and molds allow the selected NNS process, the part design must consider a) geometric complexities
production of short prototype series quickly for testing and evaluation that affect producibility. b) equipment and tooling requirements, c) process
purposes, and d) design changes can be easily accommodated. As a result of capabilities such as size, geometry and production rate, and d) properties of
these requirements. die makers are forced to increase communication with the incoming material.
their customers. improve the training level of their employees, and utilize
modern manufacturing technologies such as process modeling, high speed
and unmanned machining. automated polishing and CAD/CAM [Kruth and
Kesteloot. 891. 2.1. Part Design for NNS Manufacturing. As seen in Figure I . the
assembly-ready part geometry, part file or drawing. is first transferred
electronically to the dielmold maker using a "standard" format such as ICES
or VDA-FS. This activity is far from routine and still requires considerable
attention and quality control. Sometimes the part geometry is in the form of a
1.1 Classification and Terminology. A review of the steps used i n physical model that is digitized on a coordinate measuring machine to
manufacturing forging and stamping dies is given in the Handbook of Meral generate a CAD model [Ma et al, 931. The second significant step is to
Forming [Lange, 851. This review covers: a) the classification of dies for transform the assembly-ready geometry into a NNS (forging. casting,
various forming processes and by geometric features, and b) various die molding, stamping) geometry by using experience-based design guidelines
manufacturing processes used for different applications. Methods for making or by using a "computer assisted" design system. This initial NNS part design
injection molds are also summarized in various handbooks [Stoeckert. 831, may later be modified, based on information developed by process modeling,
[Dubois and Pribble, 871. [Menges and Mohren. 861. using CAE techniques.
Dies and molds are composed of functional and support components. The As an example, the structure of a computer aided design system for cold
former are emphasized in this review paper. In injection molding and die forging is seen in Figure 3 [Altan and Miller, 901. For a given assembly-
casting. the functional components are called cavity and core plates or inserts; ready part, the output from this system is the "initial" part and process
in forging these are die cavities and in stamping they are usually called punch. sequence design. In generating the geometry that can be hot forged from a
and die. The cavity and core plates or inserts are usually machined out of given material and in a selected machine. for example, it is necessary to use
solid blocks of die steel. However, large stamping dies and punches are often design rules such as machining allowance. minimum draft. parting line, and
cast to near-final geometry with a machining allowance added. In some cases minimum rib and web thickness, Figure 4 [Doege and Mathieu, 841. Similar
forging and injection molding dies are also manufactured by cold and hot design rules, some already computerized, are available for "initial" NNS part
hobbing. Support components are usually standard parts and assure the design for sheet metal forming [Pool, 901, injection molding [Ishii er al. 891
overall functionality of the die assembly in such areas as alignment, part and die casting [Liou ef al. 901.
ejection. and mold heating or cooling. By using standard die and mold
components, the time necessary for manufacturing a die is reduced, and 2.2. DielMold and Process Design. In solid state NNS processes, such as
machining is mainly devoted to producing the core and cavity. or the punch forging and stamping, several forming steps are necessary to manufacture the
and the die. final part. Thus, in these processes it is necessary first to use empirical
guidelines to establish an initial process sequence that is then refined by
1.2 Process Planning in Die Manufacturing. The information flow and process modeling. An example is seen for cold forging round parts in Figure
processing steps used in die manufacturing may be divided into: die design 5 [Kim er al. 921. Liquid state processes, e.g. injection molding and die
(including geometry transfer and modification). toolpath generation. rough casting. require only one die or mold set.
machining (of die block and/or EDM electrode) finish machining (including
prefinishing where necessary), finishing (including manual and automated The functional components of dies and molds, e.g. cores and cavities as well
polishing) and die tryout (Figure I). In a recent survey conducted of the U.S. as other auxiliary features such as flash lands in forging, runners and gates in
injection molding industry [Shanahan. 931, the total mold manufacturing time injection molding and die casting. and trim and binder surfaces in stamping.
varied between 1,200 to 3.800 hours, depending on mold size, geometry and are initially designed on CAD systems, using empirical guidelines or simple
complexity. The time spent for each manufacturing step. as a percent of the equations. By using process modeling, however, the initial designs are
total. was in the range o f 15-248 for design, 14-178 for tool path modified and further refined, as shown in Figure I . Major efforts are devotgd
generation. 8-168 for rough machining. 27-396 for finish machining, 13- to the development of prototype expert systems in cold forging, sheet metal
2 3 8 for finishing, and 4-68 for try-out. The results of a similar survey, forming, die casting. and injection molding [Lecluse et al. 921. The
conducted in 1986 for stamping dies, are given in Table I . [Becker, 921. application of expert systems in injection molding appears to find larger
industrial acceptance. In this case, a commercial CAD system is used for
The information summarized above and in Figure I illustrates that die and designing standard as well as non-standard mold components. This system
mold manufacturing must be considered ils a total system that includes: i) part can prepare quotations. and has routines to compensate for anisotropic
design for NNS manufacturing. ii) production of prototypes for visualization, shrinkage. a library of standard components, a generalized postprocessor,
testing and evaluation, iii) process modeling for optimum mold design, iv) (suitable for milling and EDM). a DNC link. and a process planning module
CNC machining, v) manufacturing of EDM electrodes, vi) Electro-Discharge for EDM [Kruth, 861.

Annals of the CIRP Vol. 42/2/7993 707

Operation
Percent Of
Total Time Major Operation -
1. 2. 3. 4.
Purchasing Hold
Machining 58 Release Design

BoringIHobbing 36
Milling 19
Copy Milling 28

Hand Finishing 42
- .
Surface Modification 39 9. 8. 6.
Grinding of Scallops 53
Hand Fitting 8
--.--
- v
Table 1:Time Used for Various Operations in Manufacturing of OEM Sign-Off
Stamping Dies [Becker, 921 Only Time All patties Get Together

a) Conventional "linear" procedure

b) Advancedlfuture "radial" procedure

Figure 2: Conventional and advanced methods for

production of near net shape parts [after Grubb, 921:

-
1) initial part design and quality plan; 2) moldability review of (1);
3) revise part design & tolerances; 4) repeat (2) & (3) as necessary;
5) final part design; 6) quote project; 7 ) select capable molder.

USER INTERFACE

DESiGN (IPFSD)

Knowledge-based system
for evaluating forming mrchme
sequences

FORMEX

I I
I m
fGES Cold Forging Rules
and Guidelines
I
CAD SYSTEM DEFORM

CADsystem for usewith FEM Program for the

the FEM program and simulation of selected
for diedesign and operations in the
manufacture

Figure 3 Computer aided design system for design of

I
I - I
I
' I cold forged products and forming sequences [Altan and Miller, 901
T
I Polishin
(Maiual. Mechanical. E%ctm-Chemical) I Schmiedestijtk
1
CaviWesICorns

-I,-

Bearbeitungszugabe fijr Zerspanen

Figure 1: Information flow and processing steps @ Mindestschriigen @ Wanddirken
in die and mold manufacturing 0 Lage der Gesenkteilung 0Flansthdicken
Figure 4 Design considerations for die and workpieces
in hot forging [Doege and Matthieu, 841

708
 r:
il frec-formed plastic model, and by backing up the sprayed shell with epoxy
in an aluminum die block. A proprietary process, developed by 3M as
"Tartan" tooling, is now marketed by a licensee company [Burns, 931. It is

a' reported that another proprietary method is being developed ,at Carnegie
Mellon University for producing steel dies by means of arc spray deposition
I '
d r; [Ashley, 911. Powder metal technology is also used for manufacturing molds
from stellite. It is claimed that with this process, permanent cavities can be
produced, with P hardness of Rc 41-60 and with a surface finish of 20-15
rms [Vawter. 931.
Rapid prototyping of molds is an attractive application in some instances.
Figure 5: Example forging sequence for cold forged parts [Kim et al, 921 However, often it is desirable to prototype the product as well as the process
because once production starts. the "real" process and the associated lead
times and costs must be accounted for. Thus, some highly advanced die and
mold manufacturing companies seem to prefer to produce their dies with
advanced CNC and EDM techniques within a very short time. e.g. in a matter
of days. The time penalty is not very large and the prototype production is
used to make parts with "actual" tolerances and properties. Consequently, the
parts can be tested for functionality and at the same time, the details and costs
of the "real" production process are better estimated [Beard. 93bl.
4. Cavity and Core Manufacturing by Machining

Cores and punches consist predominantly of convex surfaces: thus they can
be easily machined by 3-axis or S-axis milling. Cavities. on the other hand,
may have deep pockets andlor surfaces that may be difficult to reach and
-- rework generate by end mills. For this reason sinker EDM is often selected to finish
.-g 70 2% machine cavities. Most die and mold manufacturers use 3-axis machining.
-- although 5-axis machining offers distinct advantages in machining large
!
a punches with convex surfaces [Konig and Zander. 911. By using flat end mills
2 50 -- roughing roughing while keeping the cutter axis orthogonal to the punch surface, an improved
surface finish is obtained. In addition. set-up requirements and machining
time may be reduced up to 50% of that obtainable with 3-axis milling
[Tonshoff and Hernandez-Camacho, 891. Some of these results from the
company Droop and Rein are seen in Figure 6, as reported in the literature
[Becker. 921. The metal working industry uses 5-axis milling routinely in
producing components with complex geometries. However, this technology is
being accepted only gradually i n die manufacturing because 5-axis
programming is somewhat more difficult and error-prone [Gehring er 01. 901.
As pointed out earlier by other researchers in Figure 7 [Konig, M.. 921, in
copy-milling Baxis NC-milling %&xis NC-milling CNC milling of cores, punches, and cavities the following major process steps
source: Dmop k Rein and variables are considered: a) NC path generation, b) advanced machining
techniques such as high speed milling and machining of heat-treated die
Figure 6: Process comparison-copy milling vs. NC milling steels, c) tool materials and monitoring, and d) machine tool characteristics
Source: Droop & Rein, from [Becker, 921 and controls. In addition to these technological considerations, modern cost
effective die manufacturin- techniques require integrated planning of the
roughing. finishing. and polyshing steps [Tonshoff er al, 921.

< Machining Task ]

workpiece.gromctry
2.3 Process Modeling. As indicated in Figures 1 and 2, process modeling as * work m a l e r i a l
part of Computer Aided Engineering, helps to (i) finalize part design, (ii)
establish the process conditions and sequences. where applicable. and (iii)
design the dielmold components such as flash in forging, binder surface and
draw beads in stamping. and gates and runners in die casting and injection
molding. Process modeling is now being applied with increasing success in
cold and hot forging [Altan and Knoerr, 921, sheet metal forming
[Makinouchi el al. 911, injection molding [Glozer. er al, 92 1. and die casting
[Cassidy, 921. Initially. process modeling in forging was largely driven by
aerospace applications where isothermal forging of jet engine disks requires
very expensive dies. In this application, process modeling reduces the risk of
die breakage and improves process reliability. In sheet forming, the
application of process modeling is predominantly in automotive applications * influencing
where the part geometry is truly 3D and rather complex. Therefore, the parameters on
practical application of modeling for predicting and avoiding failure in sheet quality and
metal forming has only recently become a practical reality. In injection 1001 l i f e
molding and die casting, however, the developments have been going on for
many years. As a result, there are several commercial programs that are
routinely used, even by small companies, in die casting, injection molding. Figure 7 General aspects in prdcess layout of NC milling
and gas injection molding. The process simulation software available today
not only allows the prediction of material flow, temperature, and solidification. of dies and molds [M. Konig, 921 .
but it also estimates the elastic recovery as well as residual stresses.
microstmcture. and in some instances even properties in NNS parts.
Pick
3. Production of Prototype Parts and Molds
During the last decade, various processes have been developed for rapid
production of plastic and ceramic models directly from a CAD model. These
processes, generally considered to be "rapid prototyping" techniques, are
I1
classified under various names such as direct CAD manufacturing, 3D
printing [Sachs er al. 931. desk top manufacturing, instant manufacturing,
solid free-form fabrication, layer manufacturing, material deposit
manufacturing, or material accretion manufacturing. All these techniques
apply some sort of selective solidification or binding of liquid or solid
particles by gluing, melting and resolidification, polymerization or a chemical
reaction. Excellent reviews of this technology for manufacturing prototype CASE 1 CASE 2
parts and molds were prepared by our CIRP colleagues [Kruth. 911 and
[Bjlrke. 911. Various additional summaries are available in a very large I Tolerance 1 ,0002" I .0oO040" I
number of publications, conference proceedings, and recent books [Ashley,
911, [Burns, 931. [Bj~rke.921. An interesting application of stereolithography (Feed Value I .040"- .om" 1 .012" I
for 3D plotting has been demonstrated by our CIRP colleagues [Nakagawa el
al. 921. Cusp Height .0005'* - .om'' .00009(Y'

Some of these techniques are suitable for manufacturing tooling for molding Mean Line Segment Length .050" .026"
prototype parts. In cases where tolerances are not very critical (larger than
0.10 mm). it is possible to use a stereolithography (SLA) model to Minimum NC Command Value .0004" .00004(Y'
manufacture molds from silicon, epoxy, ceramics, or high strength chemically ~

bonded ceramics. These molds can be used for injection molding parts in
small quantities [Kmth. 911. Plastic injection molds that last for several
Data Volume 3.3 - 6.6 M byte 57.1
thousand shots can be fabricated by arc spraying Kirksite or a zinc alloy upon
Figure 8: Requirements for high definition finish
milling [Shanahan,931

709
 4.1. Tool Path Generation. There arc basically three methods for generating
tool paths i n dielmold machining, namely: copymilling (duplicating and P L A C I N G OF C O A T I N G WITH
tracing). digitizing. and CAD/CAM or NC programming.topymilling. while PAR T IC LES PARTICLES
still in use. IS being gradually phased out because feeds and speeds in this
process are limited by the cutting conditions. As a result. a good surface finish
requires very long cutting times.

g. Digitizing is a very valuable method because: a) there are still very

mold shapes that cannot be produced cost effectively by CADICAM.
odifications made during die tryout must be captured and read into
carburizing
bath nitriding
gas nitriding
II hard plating
CVD
PVD
the data base. c) in some cases the physical model (old part or die, hand-made plasma nitriding
model) may be available. while the CAD model would be costly to develop. d) plasma spraying
digitizing can be done unattended. and e) digitized data can be transferred. boronizing
modified. converted (from core to cavity. mirrored or scaled). and can be used flame spraying
for accurate and high speed NC machining. as well as for geometric quality ion implanting hard facing

1
control on a C M M [Shanahan. 931. [Haller and Steger. 921.
The most accurate and widely used method of digitizing today i s contact laser beam alloying laser beam cladding
tracing, in which the probe operates with constant pressure against the model.
This process is slow, but can be conducted unattended. with typical feed rates laser beam dispersing ...
of 1000 to 5000 m d m i n . Laser digitizing. with a multi-axis laser head. is a
relatively new technique that can obtain geometric data more quickly and with ... I
sufficient accuracy for most applications.
Figure 9 Thennochemical surface treatment technologies
NC Programming is the most widely used and mature technology for cutter [Konig et al, 92bI
path generation. Aspects of this technology that need most attention are:
a) Geometry transfer: there are still problems with data transfer via
standard formats such as ICES (US)and VDA-FS (Europe). However, often
‘ these problems are related to communication and management issues within
and between organizations: they can often be handled by training and
improved communication protocols.
b) NC program verification saves cost and time because it eliminates
the need for machining models and “dry running” the programs. Advanced
die and mold shops are increasingly using visualization software. such as
Vericirr or N-See. in order to identify programming errors off-line [Esterling.
931.
c) Simulation of the mechanics of milling i s gaining increasing
attention. The objective is to examine the detailed mechanics of milling with
multiple edged cutters in order to predict milling forces as a function of the
cutting geometry and process conditions [Smith and Tlusty, 911. [Tsai e r n / .
901. Thus the feed rate is continuously adjusted to meet a given parameter, for
example to maintain the milling force below a maximum value [Yazar er nl.
931. [Fussell and Ersoy. 921. This results in reduced milling time. chatter. tool
deflection. and tool wear [Bouwkis et nl. 921. [Yainazaki er a / ,911.

4.2. H i g h Speed Machining-Controls and Machine Tools. An extensive

review of high speed machining was conducted by our ClRP colleagues
[Schulz and Moriwaki. 921. A l l die and mold milling operations-rough.
semi-finish and finish machining-can benefit from high speed machining
technology, with high feed rates in the range of 15dmin. high spindle speeds
(20.000 rpm or higher) and surface cutting speeds of 700mlmin. I n die
manufacturing the objectives of high speed machining are to: reduce
benching (hand finishing) time. improve accuracy and surface quality, reduce Figure 1 0 Operating principles and advantages of laser-assisted
lead time and ultimately. reduce labor by unattended machining. By using milling [Konig, 92bl
smaller pick feed values. (Figure 8) [Shanahan. 931, a high RPM spindle, and
higher feed rates. a cavity or core can be machined to very high definition In industrial practice. tool monitoring (monitoring of spindle drive current)
with excellent surface finish. For high speed machining i t is necessary to have on a real time basis allows: a) the control of feed rate based on spindle
special CNC controls. a rigid and dynamically balanced spindle and machine loading, and b) automatic changing of worn out mols without operator
tool structure. and specialized milling cutters. intervention. Thus, totally unattended milling becomes a practical reality.

The CNC control must have high speed data processing capability. Often. in
addition to a standard 32 bit CPU. additional computing capability. (e.g.. a
.
4.4 M i l l i n g vs. EDM. As seen in Figure I. rough machining and
prefinishing are usually done by milling. Finish machining. however, may be
RISC CPU). may be used to facilitate rapid processing of part program data. done with either milling or EDM, depending on pan geometry. availability of
For a line segment (movement per block) of 0.3 mm, and feed rates of 4000- machine tools and scheduling. At the Technical University of Hannover,
5800 m d m i n . block processing times required are in the range of 4 to 5 ms. research on 3- and 5-axis milling of sculptured surfaces for die and mold
I n order to feed a control that processes NC data (a block) in 4 ms, it i s manufacturing led to the establishment of optimum cutting conditions for die
necessary to have DNC transmission speeds of 76,800 baud. As movement steels and graphite electrodes [Hernandez-Camacho, 911. As a continuation
per block becomes smaller. the need for high speed data transmission of this work, software is being developed for selecting the most cost effective
becomes even more critical. Today, block processing times of 0.05 ms are alternative (milling or EDM) for a given material. geometry and production
possible [Roders. 921. High speed milling machines are available for conditions. Optimization criteria are reduction of lead time, reduction of cost.
machining hardened steel (e.g.. H I 3 at Rc 50) using a surface cutting speed andlor increase in flexibility [Hernandez-Camacho er nl, 891. As a rule, EDM
o f 300dmin. coolant delivery at 1,OOO psi through the spindle, a 10 mm is used to machine deep and narrow cavities that are difficult to reach with a
diameter tool at 12,000 RPM and a feed rate of 2000 mmlmin [Shanahan. milling cutter. However, under certain circumstances. e.g.. when a new set up
931. Further, special milling machines are available with up to 15dmin feed must be avoided. it may be more cost effective to mill deep cavities as well
rate. 95.000 RPM spindle speed. and a maximum positioning accuracy of using the process and tool technology discussed earlier [Konig. ef nl, 92al.
5pm [Roders. 921.
The technology of cavity and core manufacturing i s influenced by customer
For high speed machining. high level servo control features must be provided demands. which can be summarized as: reduction in lead time. reduction in
to enhance performance under dynamic conditions. I t i s necessary to have a cost, increase in flexibility. and improvement in quality. As h result. the need
special processor that calculates optimal speed and acceleration with respect to for unattended machining will continue to increase [Beard. 93al. Thus, both
tool path geometry and machine dynamics as well. advanced milling (high speed machining of hardened die materials) as well as
E D M techniques (palletized systems. orbital adaptjvely-controlled EDM) will
4.3. High Speed Machining-Procw and Tool Technology. For high speed continue to compete and be utilized in machining cores and cavities. In
cutting tools four criteria are critical: tool material and coating. cutting edge addition. laser machining technology will also be applied to machining of
geometry. tool design, and interface between tool and spindle [Schulz and small cavities to precise dimensions [MAHO. 921.
Moriwaki. 921. Initial investigations conducted at the WZL Aachen illustrated
that i t is practical to CNC mill forging dies, after heat treatment to operational 4.5 Abrasive Processes
hardness levels [Konig and Bieker, 891. Advanced tool materials are able to
machine hard steels (with strength beyond 1400Nlmm2 )[Konig er a / , 926) at Many components of dies and molds are produced from hardened materials
high metal removal rates. The best performance of carbide in finish milling of to high accuracy and with good surface finish. Therefore, abrasive processes
hardened hot work die steel. for example. is achieved by increasing the cutting such as grinding. honing, lapping and polishing are significant processes in
speed from the conventional Vc=140mlmin up to 500mlmin. At this high tool and die shops. Trends are to automate hand work, especially in the case
speed. the tool life decreases only slightly but the machining time is reduced of polishing, where the use of specific purpose robots are becoming widely
and the surface finish is improved. Milling cutters with CBN inserts can cut accepted. CNC grinding machines are widely used. Some progressive tool
tool steels economically at speeds up to 900 m/min. Coating of carbides with makers are introducing automatic tool and workpiece changing systems for
titanium nitride. titanium aluminum nitride and titanium carbon nitride unmanned grinding of even small batches. This requires a very systematic
further increases tool life in hard machining at high speeds. Using ball end process planning. These trends are discussed in two other keynote papers [El
mills from Cermet or with CBN inserts and spindle speeds of 100.OOO rpm. Maraghy. ef nl. 93 and Inasaki. el 0193)
very high feed rates of 1000 mlmin with excellent surface finish can be
achieved in machining hardened die materials [Ikeda et el. 92). 5. Surface Treatment Techniques
Die wear is the single most important factor that affects the economics of NNS
manufacturing processes. Conventional surface treatment techniques, such as
nitriding. PVD and CVD coatings. and others are summarized in Figure 9
[Konig er nl. 92bl. Most of these techniques are successful for extending die
life in most cold forming operations. In hot forming processes. however. such

710
 as hot forging and die casting. conventional surface treatment methods are not (permitting safe unmanned operation). reduction of pollution problems, and
very effective. In such applications. surface welding or plasma deposition with increase in EDM efficiency. The disadvantages are: posslble corrosion of
high temperature alloys offer considerable improvements. machine elements. low material removal rate, high electrode wear rate. possible
adverse effects on process stability. and relatively inferior surface finish
Recently developed laser surface treatment methods offer very promising (about 15pm RZ).
alternatives. Various alloying techniques with an overview of processes and
applications are summarized in a recent CIRP paper [Heuvelman er al, 921. In Significant improvements in machining time have been achieved. however. by
laser alloying of round die inserts with WC-Co, used in a horizontal high using graphite as electrode material and glycerine as an additive to water
speed forging machine. die life could be increased up to 500% [Konig er al, [Konig and Jorres. 871 (Figure I I ) or by using dielectrics specifically
911. However, similar experiments on screw and eccentric presses and on developed for this purpose [Dunnebacke, 911. In selected cases, cavity sinking
hammers did not show such dramatic improvements. Thus, the economic costs per die set can be reduced 25 to 50%.
advantage of laser alloying for increasing die life cannot yet be generalized.
Additional research and development is needed for expanding the cost 6.3. EDM Milling. CNC control of the EDM process allows “EDM Milling” or
effective application of this technology in hot forging [Konig et al, 911. Bahnerosion” using electrodes of simple shapes, used as end mills and rotated
Results obtained to date, however, are promising and indicate that this at high speeds. The maximum benefit of this technology is realized by
technology can be used not only for surface treatment of new dies but even integrating it into a system where electrode design and manufacture are
more economically for repair of worn forging and die casting dies [Konig er highly simplified and electrode handling is automated [Konig and
al. 9261. WaOenhoven. 9 1 ~ 1 .Development of specific software for NC programming.
based on feature-based part description and using different types of electrode
An entirely new concept for die manufacturing integrates NC milling and shapes. has the potential of further improving the efficiency of EDM milling
laser surface heat treatment [Konig er al. 92bl. The economic advantage of [Lauwers and Kruth. 921.
such an integration is expected to be in the shared use of a single handling or
process unit and i n the reduction of set-up, transport and idle time. The In EDM milling and pocketing three different gaps (frontal. side and bottom)
integration of the laser with a milling machine also permits laser-assisted must be simultaneously accounted for. To avoid inaccuracies. the exposure
cutting. This process, which is currently under development, involves using time must be as constant as possible in each point of the programmed path.
the laser beam to heat the material to be removed directly at the point of The finishing tool radius should be at least two times smaller than the fillet
removal. Figure 10 [Konig er al, 92bl. radius of the corners of the workpiece [Kruth er al, 931. The relative velocity
between the rotating electrode and the workpiece influences the surface finish.
6. Electro Discharge Machining (EDM). the material removal rate, and the electrode wear. It was found that in
prefinishing as well as finishing the higher viscosity dielectrics offer better
In manufacturing of dies and molds with sculptured surfaces, sinker or results [Konig and WaOenhoven, 91bl. In EDM milling the tool shape is
,plunge-type EDM plays a major role. Wire EDM, however, is equally simple and can be easily duplicated. Thus it is more economical to erode at
lmportant in manufacturing progressive dies, as well as dies for blanking. high power settings, even though this results in high electrode wear. and then
extrusion and drawing. For a given part and blank geometry, modern 4-axis replace the worn tool using an automatic tool changer.
wire EDM machines allow machining of ruled surfaces with up to 30° taper
and can automatically calculate the optimum prefinishing and finishing EDM milling offers the capability to perform difficult and specialized tasks,
parameters, including the required wire diameter. Modern fixturing systems, as shown in Figure 12. For example, in part (a) of this figure, the electrode
coupled with automatic wire feeders, drastically reduce the set-up time and has the shape of a hollow rectangle and removes an entire curved section from
allow unattended operation, one of the major advantages of both wire and the die block. In part (b) a small rotating cylinder is used to make minor
sinker EDM. modifications on an existing cavity [Schumacher, 9061.
The sinker EDM is best suited for machining deep and thin cavities in hard 6.4. Electrode Wear. Unattended EDM requires that electrode wear either be
materials, and lends itself to integration in a CIM environment [DeVries er al. eliminated or compensated for. The so-called “no-wear” parameter settings
19901. The process, however, is relatively slow compared to milling, In on EDM machines have been in use for some time. [Guitrau. 931 In cases
addition, the use of conventional dielectric fluids causes environmental where the “no-wear” setting cannot be used, it is possible to program the
concerns, in addition to posing a potential fire hazard. Much work in recent machine to measure the electrode wear by touching off against a reference
years has been devoted to orbital EDM. EDM milling, unattended and high block mounted in the dielectric tank, and checking against the stored part
speed EDM. use of non-flammable dielectric fluids, increasing machining dimensions. If electrode needs changing, then the automatic tool changer can
accuracy, and the reduction and control of electrode wear. take a new electrode from the magazine. Redressing is more suitable for
copper electrodes than for graphite, and for relatively simple shapes [Guitrau.
6.1. Orbital EDM In modern CNC machines, the EDM electrode can be 931. For this purpose a dressing block can be used with the machine set for a
rotated and a relative motion between the electrode and the workpiece can be
obtained along very complex paths. As a result it is often possible to use the
same electrode geometry for roughing and finishing, and achieve adequate
flushing without the commonly used flushing holes in the electrodes. Thus,
unmanned EDM for long periods of time is now a rule rather than the
exception, especially in Japan and Europe, by using automatic electrode
changers and palletized workpiece setups. Sales data on sinker EDM machines
illustrate that a large majority of the EDM machines sold in Japan and
Germany are equipped with CNC, while more than 70% of the machines sold
in the U S . market are manually operated [Shanahan, 931.
In orbital EDM electrode wear is reduced, leading to improved control of
cavity tolerances. Nevertheless, in planning the orbiting EDM tool path, it is
necessary to consider electrode erosion because the electrode is constantly
changing its orientation with respect to the workpiece and as a result the
contact area changes as well [Levy er al, 771. Although orbiting aids i n
flushing, removal of debris from the gap still remains a primary concern
because gap contamination through eroded debris influences ignition as well
as discharge location and gap width [Schumacher, 90aI. It is suggested to
measure the concentration of debris particles suspended in the dielectric in the F-J-
working gap so that the timing of the discharge and thus its efficiency can be
better controlled [Frei er al. 871.
Motion-induced flushing, where the electrode moves along the sinking
direction. is significant for avoiding the use of external flushing and for
facilitating unmanned operations. Studies conducted at WZL have
demonstrated that the relationship between electrode motion and flushing can
be optimized to reduce electrode wear, increase material removal rate and Prduction
prevent qcing [Weck and Dehmer, 911.
of a
It is also reported that high speed EDM with adaptive control can reduce
machining time by 50% [Sasagawa and Ema. 901. Such a control has a dual steering knuckle
power supply, shortens the total pulse cycle, makes adjustments for the
increased debris, and adds power as the “contact” surface increases. The with different
material removal rate is further increased by using pre-assembled graphite
electrodes and a suction mechanism to remove the gases and the debris working media
created by the process. Thus, the quality of the dielectric fluid is maintained
and the need for motion-induced flushing is eliminated. resulting in reduced
machining time.
Another method for reducing the contamination of the dielectric in the gap is
to change the orientation of the sinking axis, from vertical to horizontal.
While this method looks promising, it is reported that the buoyancy of the
bubbles created during erosion opposes the force of gravity, causing debris to
Em
TH mcnm
remain trapped in the gap. resulting in uneven wear. One proposed solution to -w-
this problem is to rotate both tool and workpiece together, thus allowing the
trapped debris particles to dissipate. [Kunieda and Masuzawa, 881
6.2. Water-Based EDM Dielectrics High speed EDM using water-based Figure 11: Comparison of h y d r o c a r b o n a n d water/glycerine
dielectrics offers several advantages, such as elimination of fire hazards EDM dielectrics [Konig, 921

711
 Measuring

1 2 3 4 5 6

Figure 1 3 The EDEM concept [Haas, 911:

1) unmachined electrode; 2) machined electrode; 3) electrode
measurement 4) workpiece erosion; 5) workpiece measurement;
6) finished workpiece.
c

Figure 12: Possible uses of EDM milling technologies [Schumacher,921

high wear erosion cycle, with the polarity reversed. By moving the electrode
across the dressing block several times, electrodes with simple shapes can be
redressed, remeasured, and reused several times before they are replaced.
The economics of EDM is greatly influenced by electrode manufacturing and
wear. Following this observation, a novel EDEM (Electric Discharge and
Electrode Machining) machine has been developed, (Figure 13) [Haas, 911. In
this machine concept the following modules are integrated: an interactive
programming system for process planning, storage for electrodes and
measurement sensors. a high speed milling machine. an electrode
measurement station, an EDM machine, a workpiece measurement station, and
a tool changer/transporter. In a typical unattended operation. and using the
same electrode holders. the EDEM system is capable of a) milling graphite

n
electrodes. b) measuring them, c) EDMing. d) determining electrode wear and
refinishing. and e) measuring the finished workpiece. This system illustrates
the future direction of unattended and fully automated EDM technology. electrodeconference

7. Manufacturing of EDM electrodes

The design and manufacturing of electrodes are critical for integrating EDM
into a CIM environment. Figure 14 shows the complexity of the entire process u
1
design

for making dies, even for a relatively simple product such as a push button on
a telephone receiver. As discussed earlier, and illustrated in Figure 2, it is
desirable that at the planning stage, cooperation is established between the
people involved in various aspects of die and mold production: mold
I TOOL ASSEMBLY
h l i n g m d RmI
iNppcaiOn I NC programming
I
designers, NC programmers, process planners, and the EDM operators
[Perchewski et al, 901. .
In EDMing a given mold. separate electrodes, requiring individual CNC
1-1 I electrode planning

fabrication of electmdes
programs, may be used to sink various parts of the mold cavity. The surface
generated by these electrodes must be “seamless”. requiring precise location
of each electrode with respect to the workpiece surface. In other cases, EDM
may be used for some parts of the cavity while other cavity surfaces may be
produced by CNC milling. Today such strategies are easily achieved by using
standard high precision fixtures for locating the electrodes and the workpiece
Imeasuring and recording
I
on the various machines used for manufacturing dies and molds, i.e. the CNC
mill. the CMM. and the EDM, as well as the machines for surface finishing via
ECM or mechanical polishing.
PRODUCTDESIGN
(mmpueraidd daign)
7
1 die sinking program
L I
7.1. Milling of Electrodes. Nearly all sinker EDM electrodes are
manufactured from graphite or copper. Currently about 85% of the
electrodes made in USA are from graphite [Guitrau, 931. Copper is used
predominantly for EDMing small and precision dies, used in cold forging and
coining. Compared to copper, high quality graphite with small particle size,
available today, offers several advantages such as light weight, high material
PRODUCT PUNNING
lcmnputccaided m@mminS,
n EDM dieainking

removal rate, and lower wear rate during roughing. In addition, graphite can Part Production Mold Production
be machined at very high speeds although it is brittle and generates fine
abrasive dust during machining. Thus graphite electrodes are best machined
on special milling machines, with automatic vacuum dust collection systems
and high speed spindles (up to 50,000rpm) [Haas, 911, [EMAG, 931. These Figure 14: Steps in the design and production of a part and mold
machines have the appropriate high speed CNC controls and servo drives to (after Perchewski, 90)

712
 operate with cutting speeds up to 3.000nl/min and feed ratec up to IOm/inin.
as discussed earlier. To avoid chatter and chipping. graphite i s best machined
using carbide tools or tools with diamond or CBN inserts with a chip load
(feed rate) o f 0.05-0.1 mm per tooth [Shanahan. 931. For example. using a
spindle speed o f 15.000 rpm and a ball end inill o f 6 mm diameter with two
flutes, the recommended feed rate is I500 mmlmin. Compared with carbide
and cermets the polycyrstalline diamond (PKD) offers the best tool l i f e Cutting tool
because of its high hardness IHernandez. 901 ravolutlon equlpmenc

7.2. Other Cutting Processes. Electrodes with simple geometries that can be
generated by ruled surfaces can be manufactured by wire EDM. This method
IS more suited for copper than for graphite because the latter has a low
conductivity and high sublimation temperature [Guitrau. 931. Graphite
electrodes o f suitable geometries can be machined faster. using a diamond
wire saw. at speeds o f about 4 0 m d m i n [Vogel. 901.

7.3. Casting a n d Forming of Electrodes. Abrading of graphite electrodes.

with an orbiting negative abrasive master for subsequent use in orbital EDM.
is a well known method used in the forging industry for more than a decade.
Recently. efforts have been made to apply Rapid Prototyping or Layer
Manufacturing Techniques (LMT) to rapid production o f electrodes (lensen
and Hovtun. 19911. [Bjorke. 921. Initial efforts to form an electrode directly
by adding copper or graphite powder to the Stereolithography (SLA) resin Figure 1 5 Configuration of compound manufacturing system
were not successful. Partial success was achieved in plating an SLA model with
a conductive surface or spraying it with several layers o f metal. The possibility
combined with an EDM machine [Sakai et al, 921
o f compressing graphite directly to make an electrode is also being
investigated. I t seems that the LMT methods will have some future application
in electrode manufacturing. However, it is still too early to predict which
specific alternatives will be economically viable for which applications.

8. Automation in Die and M o l d Polishing

I t is estimated that from 3 5 8 [Shanahan. 931 to 50% [Lilly el a/. 881,

[Tonshoff er a / . 931 o f the total dielmold manufacturing time is devoted to
surface finishing or polishing. Considering the potential time and cost savings
involved, it is surprising that. with the exception o f Japanese companies, the
mold industry has so far paid relatively little attention to this operation.
Recent advances in hioh speed machining o f hardened die surfaces w i l l
reduce the need for auxziary finishing operations. Nevertheless. improvement
o f the surface finish o f dies and molds, using mechanical. electrical or electro-
chemical methods. will continue to be a major concern in die manufacturing.

8.1. Electrical Polishing Methods. One o f the principal reasons for die
’ polishing is the elimination o f the E D M recast layer. This is achieved by
means o f sophisticated CNC controllers. available on today‘s modern E D M
machines. By using progressively smaller power levels. as the eroded surface
approaches the desired die surface. the amount o f recast layer i s gradually
reduced. In effect. the last few steps in the E D M process cycle are designed to
remove only the recast layer left from previous steps [AGIE, 911. Extremely
fine surface finishes can be achieved by shortening the puke times and by
reversing the polarity of the electrodes, making the tool the cathode and the
workpiece the anode. Thus, the craters left on the workpiece tend to be Relatively little R&D is being devoted to mechanical polishing processes.
smaller, resulting in an improved surface finish. With this technique. using Researchers at the University o f Karlsruhe developed polishing heads that can
reverse polarity. a current o f I Amp. an open gap voltage o f 180 Volt and a be mounted on a 6-axis robot [Weule dnd Timmermann. 89,901. Two o f the
pulse time o f 5 psec. surface finishes o f Ra=0.18pm could be obtained heads mimic the reciprocal motions o f human hand. with short and long
strokes. The third head is rotary with a higher cutting speed. Basic studies
[Jorres. 891. have been conducted to develop a theoretical model and to determine metal
removal rate as a function o f feed velocity and specific normal force.
This process, often called Electro-Chemical Arc Machining (ECAM). utilizes Research at the University o f Hannover uses polishing heads with roller
pulsed power across the cathodic tool and anodic workpiece. separated by a guided abrasive belts rather than reciprocating or rotating motions
gap filled with electrolyte. in order to achieve combined Electro-Chemical [Hernandez-Camacho er a / , 901. [Tonshoff and Gehring. 931. The polishing
Dissolution (ECD) and Electro Discharge Erosion (EDE) o f the workpiece. heads are incorporated into 3-or 5-axis CNC machines and move over the die
E C A M is a very important process for die and mold manufacturing industry. surface under CNC control. Equations that predict a so called “projected
I n this process, however, any theoretical prediction o f the metal removal rate is contact length” have been developed [Gehring, 911. Thus, it is possible to
extremely difficult. Nevertheless, E C A M has been investigated with a estimate in real time the necessary polishing force. Using compliant rollers, it
stochastic modelling, thus accounting for the random nature o f the process. is possible to LLcontroI*’the polishing surface to some extent. Additional
[Khairy and McGeough , 871. work seems to be necessary. possibly by developing different types o f roller
guided polishing heads. so that complex sculptured surfaces can also be
E D M polishing requires long times. A much faster technique uses an ECM- handled with thisapproach.
based process without any high electrolyte pressures [Sakai ef n/. 891. The
current is pulsed between the electrode and the workpiece in bursts o f about 9. Advances in Die and M o l d Quality Control
10 msec. The tool is moved away from the workpiece periodically. allowing
fresh electrolyte (NaCI or NaNO3) into the gap. Thus, current densities of The final stage in any manufacturing process i s very often quality control. I n
IOOAlcm2 can be maintained. without the large gap pressures o f the E C M die and mold manufacturing. however, the end product. i.e.. the mold or die, is
process. Studies indicate that with appropriate machine settings. an EDMed so expensive and so complex that the diemaker cannot afford to wait until
surface o f 40pm Rmax can be improved to 3.5pm Rmax in 12 minutes and a final assembly to check for quality. Rather. quality control is an essential part
recast layer can be removed in just a few minutes. o f every step i n the process, beginning with the C A D geometry and
continuing on until final tryout.
Recently, an integrated system has been developed which performs electrode
machinmg. EDM sinking, and ECM finishing. all with the same electrode on The multi-axis. computerxontrolled coordinate measuring machine ( C M M )
the same machine (Figure 15). The electrode material. graphite in this case, is is an indispensable part o f the modern mold and die making operation. The
mounted in the spindle o f the EDM machine and milled by a high speed C M M is very often involved in the diemaking process from the very first. as i t
spindle with tungsten carbide tooling operating under NC control. After the . is frequently used to digitize a three dimensional part model [Haller and
cavity is formed by the E D M machine. the dielectric fluid is drained from the Steger. 921. The numerical data is then transferred to a C A D system. where
machine. and replaced by an electrolyte. NnNO3. The power supply is also smooth surfaces are fitted to the data. and machining paths are generated. As
changed at this time. and the E C M process commences, using the same discussed earlier. digitizing by C M M s will tontinue to be used in practice.
electrode. By this method. it is reported that the heat affected layer left from
the EDM process was completely removed, and a mirror-like surface C M M s are often used to check a machined surface against the perfect surface
obtained. Performing all o f these operations on a single machine is obviously embodied in the C A D model. By checking the electrode for errors before the
extremely efficient [Sakai rr 111, 921. expensive die block is machined. much time and expense can be spared. Once
machining is complete. electrodes are again measured for’ we3r. and often
8.2. Mechanical Polishing Methods. Mechan&l polishing machines, capable reused as roughing electrodes.
o f finishing 3-D sculptured surfaces. are usually built in gantry design or as a
special purpose robot. They have been on the market for almost a decade I n manufacturing large automotive stamping dies. i t is useful to allow the die
[Lilly er 111, 881. The economic use of these machines. however, still requires designer to establish the inspection procedure. For example. such an approach
considerable skill and experience because the fundamentals of mechanical has been used to integrate the inspection routines into the CATIA CAD/CAM
polishing are far from being entirely understood. The design of the polishing system [Menq ef al. 921. [Sahoo and Menq. 911. This allows the designer not
tools and selection o f the polishing stones require improvements. A rotary only to plan an inspection path for the part after it is produced, but also to
head. developed at the University o f Tokyo. uses sintered diamond and iron include other inspection attributes in the C A D database for future use by the
with a magnet that helps to hold the polishing tool on the sculptured die inspection team. Another experimental surface finishing system is developed
surface [Kunisda F I a / , 851. This tool has found wide acceptance in the , for an integrated process planning and in-process control for finishing o f
industry [Komatsu. 851. sculptured surfaces [Philpott rr a / , 911. Others also integrated the C M M into

713
 the design process. but have concentrated primarily on updating the C AD Beard. T.. 1993a. “ A Sense of Balance”. Moderti ,Wdiitic Sltop. Feb. 93, pp.
model as alterations are made in the actual part surface. through tryout and 66-74.
engineering changes [Haller and Steger. 921.
Beard. T.. 1993b “Prototyping the Process”. M o d e r n Mwhittr Shop. Fcb.
In using CMMs. often it i s necessary to accurately locate the part with respect 93. pp. 83-91
to the machine’s coordinate system. This problem can be handled with
software. by adjusting the inspection path for misalignment. By inputting six Becker. M.. 1992. “Efficient Planning in Die Manufacturing and Limitations
points o f a sculptured surface and by means of the software. developed for o f Technological Processes”, (in German)Derrtsches Itidrisrriclfoririii
this purpose, it is possible to compare the mold surface with the CAD data. fiir Teclinologie, 21113101. 1992
Thus, the machine can determine the orientation of the part on the C M M
worktable very quickly before it begins the inspection routine [Menq er a / . Bjerke. 0.. 1991. “How to make Stereolithography into a practical tool for
921. tool production”. Annals of rhe CIRP. Vol 4011. 1991, pp. 17.5-177 .
Another solution to the misalignment problem i s to prevent it from occurring Bjerke. 0.. ed.. 1992. k r w r Maiirrfncrrrring-A Cliolletrgr for rhr Fiirure.
in the first place. This idea has resulted in very sophisticated. extremely Tapir Publishers, Trondheim. 1992. ISBN 82-519-1 125-7.
precise tooling systems for EDM machines and machining centers [Erowa.
19921. [Mecatool, 19921 [System 3R. 19911. A l l of these systems rely on Boes. P.J.M.. & C.A. van Luttervelt. 1990. “Reduction of Throughput Time
mechanical precision to ensure that punches, cavities, and electrodes are in Tooling Industry” (in Dutch), MB Proditcrirrechtiik. No. 9. pp.
located within very close tolerances on the machining centers and ED M 308-3 17.
machines. By installing pallets and chucks on these machines and on the
C M M machines, rapid production and inspection of tools and cavities can be Bouzakis. K.D.. K. Efstathiou. R. Paraskevopoulou. 1992. “NC-Code
achieved. Preparation with Optimuin Cutting Conditions in 3-Axis Milling”.
Annals of rlie CIRP, Vol 4111 pp. 513-516.
10. Summary and Future Developments
Burns, M.. 1993. Automated F~ibricurioii-lniproi~irrg Protlircrii,itv i n
Die and mold manufacturing will continue to represent a very significant Matir~facruring.Prentice Hall, Englewood Cliffs. ISBN 0-1 3-1 19462-
aspect o f production technology. I t is interesting to observe the development 3. 1993.
o f competing technologies for dielmold manufacturing. e.g. high speed
machining vs. adaptive EDM. Several technological trends are quite apparent: Cassidy. V.M.. 1992. “From Craft to Science-The future of near net parts
manufacturing”. Modern Mernls. December. 1992.
a. Dies and molds must be manufactured with shorter lead times to
offer flexibility and for rapid introduction of products to market. Thus, the Destefani. J.D.. 1993. ”Mold and ‘Die Making in Transition”. T~io/iti,qwid
role of simultaneous or concurrent engineering will be even more important Producrion. April 93. pp.69-7 I
in the future. CAE or process modeling, already practiced extensively in
injection molding of polymers, will be increasingly used in forming and DeVries. M.F.. N.A. Duffie. J.P. Kruth. D.F. Dauw. B. Schumacher. 1990.
casting. Thus, product. process and dielmold design wil l be done “Integration of ED M within a C IM Environment”. Aiinols of rhe
concurrently. CIRP. VOI. 3912. 1990. pp. 665-672.
b. Today. electronic data transfer does not present any major technical Doege. E.. and H. Matthieu, 1984. “Computer Aided Shaping of Interstages
problems. However, in die and mold manufacturing. the geometries are at Die Forging Conditions for Laying-out Forging Tools by Means of
usually complex and data files are very large. Therefore, in this industry CAD Systems”. Atiiials of rhe CIRP, Vol. 3311. pp. 141-145.
human error, communication. and training of personnel are still issues to be
addressed for practical and routine application of available technology. DuBois, J.H.. & Pribble, W.I.. 1987. Plrsrics Mold Etigiiieerin,qH a n h ~ o l4th
.
Edition. Van Nostrand Reinhold. New York. 1987.
c. High speed machining for die manufacturing i s well established.
Present software allows automatic feed rate control to account for cutter path Diinnebacke. G..1991. “High Efficiency EDM with Water-Based Dielectric”.
geometry. Possibilities exist to augment this capability by predicting or (in German) Der Sr~ililfortirenbaiier319 I , pp.33-43.
monitoring the milling force as a function of tool path geometry. Thus. feed
rate may be adjusted not only based on geometry but also based on cutter EMAG. 1992. HBZ-Fortnula I niiioitg rlie Mocliiiiing Cells. (in German)
force. EMAG Maschinenfabrik GMBH. Salach, Germany.
d. The use of high speed machining of hardened die surfaces allows El Maraghy. el a1 1993. “Evolution and Future Perspectives of C A P P
the production o f excellent surface finishes with relatively little increase in Keynote Paper, Annals of CIRP. vol. 4212
required milling time. Thus, this method of obtaining acceptable surface
finish may reduce the need for and the amount of mechanical polishing. Erowa Inter AG. 1991. Robot Swrenis for rlie airrotnorion of NC rirrrchine
However, research may still be needed to establish the optimum combination rools, F. Troxler. Erowa Inter AG. Buron, Switzerland, 1991.
of milling and polishing sculptured surfaces.
Esterling. D., 1993. “Reduce Machining Costs with NC Verification“ Modern
e. The trend for unattended machining i s very strong. Thus, ED M Muchitie Slidp. July 1993. pp. 76-85.
integrated with electrode manufacturing and C M M can be expected to
“compete” successfully with high speed machining, especially with the Frei. C.. C. Hirt. R. Giardin, D.F. Dauw. 1987. “A New Approach for
further development of water-based EDM. optimized flushing techniques, and Contamination Measurements for EDM Dielectrics” Annuls of rhe
adaptive EDM. CIRP Vol. 3611. pp. I 1 1 - 1 14. 1987.
f. Modern special purpose milling machines for graphite electrode Fussel. B. K. & C. Ersoy. 1992. “Computer Generated CNC Machining
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that the basic technology of machining graphite , especially for producing Aurosiorioti. ASME. pp. 377-384.
thin and long geometries. could be further improved.
Gehring. V., M. Becker, & J . Hernandez-Camacho. 1990. “Development
11. Acknowledgments Trends in Tool and Die Manufacturing” (in German). VDI Zeirsclirif,
Vol. 132, No. 8. August. 1990. pp. 12-16.
The authors would like to thank all the colleagues who responded to the
request for information in preparing this review paper. Special thanks are due Gehring. V.. 1991. “NC-Belt Grinding as a Polishing Process for Die & Mold
to our colleagues. Prof. R. lppolito of Politecnico D i Torino. D;. V. Gehring Manufacturing” (in German). VDI Zeirschrifr, Vo1.133. Nov.. 1991.
and Mr. M. Becker of the IFW Hannover. Dr. D. Allen of Cranfield Institute pp. 32-41.
. o f Technology. Dr. G. Levy of Soudronic. Prof. J. McGeough o f the
University o f Edinburgh. U.K.. and Prof. F. 0. Rasch of Technical University Gehring, V.. 1993. Nunieriscli gesrerrrrrrs Fornischlrifen voti gekriiiiisiren
of Trondheim. Werksriickoherflachen (Nurnerical1.v Conrrolled Form Grinding of
Curved Die Surfaces) Ph. D. Dissertation. Universitat Hannover. 1993.

Glozer. G. K. Ishii. and T. Altan, 1992. Verificarion of Wurpage Siinulurion

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