83 1183 1198 Influence of Non Metallic Inclusions in Super Finish Wire Cutting

INFLUENCE OF NON-METALLIC INCLUSIONS
IN SUPER-FINISH WIRE CUTTING

F. Klocke, T. N¨othe and M. Klotz

Laboratory for Machine Tools and Production Engineering

Department of Manufacturing Technology

Aachen University of Technology

RWTH Aachen

Abstract

Today wire-EDM (wire-Electro-Discharge-Machining) is a mostly autonomous
process due to the developments in the fields of generator technology, pro-
cess knowledge, wire electrodes and control techniques. Until now almost
no attention has been paid to the question to what extent the quality and
the production method of the workpiece material have an influnce on the
surface quality and outline accuracy of the machined workpiece. In the re-
search project presented here was examined systematically to what extent
the degree of purity, homogeneity, carbide size and distribution (and with
it concomitantly the manufacture method) of tool steels influence the result
of super-finish wire cutting (WEDM). These investigations serve the aim to
define concrete requests to the characteristics of the workpiece material in
dependency of a given quality target.

Keywords:

Tool and Die Manufacturing, Wire-EDM, Non-Metallic Inclusions

INTRODUCTION

In the modern production of tools (especially for pressing, cutting, fine

blanking or extruding) wire-EDM is an integral and not replaceable part of
the process chain. As the machining principle is based on thermal erosion
of the workpiece this technology works completely independent from the
workpiece hardness. Since the introduction of this machining process into
industrial practice in the nineteenseventies the cutting rates for steel of ini-
tially approx. 30 mm

/min rose up to 300 mm

/min. Surface qualities up

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6TH INTERNATIONAL TOOLING CONFERENCE

to R

= 0.06 µm can be obtained by application of the super-finish cut-

ting technology. Accuracies went down to 1 µm. Regarding the workpiece
quality preliminary research work showed that non-metallic inclusions and
different dispersion of carbides might have an influence on the machining
result [1, 2]. Here systematic examinations should clarify to what extent the
degree of purity, homogeneity, carbide size and distribution (all influenced
by the manufacture method of tool steels) influence the result of wire-EDM
trim cuts. Based on the results of this project the user should be enabled to
define concrete requests to the characteristics of the material in dependency
of a given quality target. Furthermore it should be examined whether by vari-
ation of the technological parameters of the wire-EDM machine influence
on the incidence and the development of the outline errors can be exerted
(Fig. 1).

E D M - P r o c e s s

T o o l s t e e l

- P u r i t y

- H o m o g e n e i t y

- M a n u f a c t . m e t h o d

M e a s u r e s

D e t e r m i n a t i o n o f s u i t a b l e

p r o c e s s i n g c o n d i t i o n s f o r

t h e a v o i d a n c e o f

s u r f a c e d e f e c t s

D e f i n i t i o n o f r e q u e s t s

c o n c e r n i n g t h e

m a t e r i a l q u a l i t y

- S t r a t e g y

- P a r a m e t e r s

T e c h n o l o g y

J o b r e s u l t

f a i l u r e s : - C a v i t i e s

- G r o o v e s

- C o n v e x i t i e s

Figure 1.

Methodology of the project presented here.

This report first describes the different influences of the tool steel on the

wire-EDM process. In the next paragraph the examined materials and the
investigation procedure are presented. The following sections deal with the
influence of the degree of purity, of segregations and of the manufacture
method on the surface formation.

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1185

MATERIAL CHARACTERISTICS INFLUENCING THE
WIRE-EDM PROCESS

As mentioned above the mechanical material properties play a subordi-

nated role in spark erosion. Impurities in the form of non-metallic inclusions
are of special importance, since they can entail process disturbances and out-
line errors. The electrically non-conductive inclusions can be removed only
indirectly or not at all by means of trim cuts with subsequently reduced
discharge energy. The following mechanisms are possible:

The wire electrode will be deflected at the inclusion, so that a bump on
the component surface develops. This requires an accordingly small
working gap.

The inclusion is extracted of the surrounding matrix and leaves a cavity
in the component.

The inclusion is molten or evaporated by thermal conduction [3, 4].
The precipitation of these different effects depends on the height of
the discharge energy and on the melting point as well as on the kind
of inclusion and on the gap width.

METHOD OF INVESTIGATIONS

The flow of investigations was as follows (Fig. 2): The materials in this

project were chosen according to the needs of tool and die manufacturers,
especially those making tools for injection moulding [5, 6]. The raw mate-
rial of the plastic moulding steel had the hardness as supplied by the steel
manufacturer, while the hot-work tool steel and the two high-speed steels
were hardened. This corresponds to practice. After hardening samples were
cut out by wire-EDM. These samples were prepared by grinding and pol-
ishing and were afterwards submitted to a structural examination using an
optical microscope in order to determine the initial state of the material.
Additionally EDX (Energy-Dispersive X-Ray Spectroscopy) analyses were
executed to identify certain elements and compounds. In the next step of
the examination sequence flat samples were cut out using a standard super-
finish technology with three to five trim cuts. The surfaces of these samples
were submitted to a detailed analysis for evaluation of the test results. This
contained the measurement of surface roughness in feed direction with a

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6TH INTERNATIONAL TOOLING CONFERENCE

brush analyser, the detection of surface failures using an optical microscope
as well as the analysis of the surfaces by means of scanning electron micro-
scope (SEM) and EDX.

T a k i n g o f s a m p l e s

E x a m i n a t i o n o f t h e m a c h i n e d s u r f a c e w i t h r e s p e c t t o

s u r f a c e , t o p o g r a p h y a n d f a i l u r e s

( l i g h t m i c r o s c o p e , R E M , E D X , b r u s h a n a l y z e r )

S a m p l e s

4 0 C r M n M o 7 , 4 0 C r M n M o S 8 - 6 ,

4 0 C r M n M o 8 - 6 ( r o l l e d s c r a p o f i n g o t b o t t o m ) ,

X 3 8 C r M o V 5 - 1

H S 6 - 5 - 3 , H S 6 - 5 - 3 ( P M )

C u t t i n g o u t a n d p r e p a r a t i o n o f s a m p l e s

E x a m i n a t i o n u s i n g l i g h t - m i c r o s c o p e ,

R E M a n d E D X

M a c h i n i n g o f w i r e - e r o s i v e t r i m c u t s

u s i n g a s t a n d a r d s u p e r - f i n i s h t e c h n o l o g y

G e o m e t r y :

F l a t m a t e r i a l , w o r k p i e c e h e i g h t : 4 0 m m

M a t e r i a l s :

E v a l u a t i o n o f t h e t e s t r e s u l t s :

- C l a s s i f i c a t i o n o f t h e s u r f a c e e r r o r s

d e p e n d i n g o n t h e m a t e r i a l p r o p e r t i e s

- D e d u c t i o n o f d e m a n d s c o n c e r n i n g t h e

m a t e r i a l c h a r a c t e r i s t i c s

Figure 2.

Diagram of the flow of investigations.

INFLUENCE OF THE DEGREE OF PURITY ON THE
SURFACE FORMATION

The materials examined here are the plastic moulding steel types 40CrM-

nMo7 and 40CrMnMoS8-6 in usual delivery quality as well as rolled ingot
bottom scrap iron from 40CrMnMo8-6. These materials were used in the
given hardness of 280-325 HB. The determination of the degree of purity
was executed in accordance with DIN 50602 [7]. This procedure yields
the so-called K-value whereby a high K-value indicates a high degree of
impurity.

INVESTIGATIONS ON INGOT BOTTOM SCRAP OF
THE PLASTIC MOULDING STEEL 40CRMNMO8-6

For this investigation four loads of different degree of purity were chosen.

The main inclusion type detected was sulfidic-oxidic. The wire-erosive
machining was performed on two workpieces per load with four tests on
each workpiece. The obtained surface quality of the samples is represented
in Fig. 3. The analysis of the surface quality shows that the degree of purity

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1187

exerts a clear influence on the job result only starting from the fourth trim
cut, i.e. starting from a desired surface quality of approx. R

= 0.2 µm. The

discharge energy is obviously still sufficient in the third trim cut to extract
the inclusions from the matrix without wire deflection. Furthermore the
shrinking gap width depending on sinking discharge energy (only approx.
6 µm in the fifth trim cut) influences the risk of contact. Herein a further
cause for the number of outline errors rising with the machining level is
to be seen. Furthermore it becomes clear that only in the fourth and fifth
trim cut a K4-value (explained in [7]) starting from 15–20 results in outline
errors. Furthermore the job result depends on the machining direction. With
cutting in rolling direction, the inclusions represents a higher portion of the
machined surface than with cutting transversely to the direction of rolling.
This is reflected in the obtained surface roughnesses and in the frequency of
the outline errors.

D e g r e e o f P u r i t y K 4

, 1

0 . 5

1 . 5

2 . 5

µ m

3 . 5

1 7 . 5

2 0

2 7 . 5

f o

lin

ilu

r 1

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

0 . 5

1 . 5

2 . 5

3 . 5

Figure 3.

Surface quality after the 5th trimcut in rolling direction.

Using a scanning electron microscope, errors in the form of cavities could

be determined which go back to the extraction of non-metallic inclusions.
There were no inclusions remaining in the workpiece surface so that a direct
allocation of the inclusions to wire deflection-caused crests was not possible.

1188

6TH INTERNATIONAL TOOLING CONFERENCE

It is assumed that the inclusions possess a weak bond to the matrix after
machining so that they are extracted almost completely when cleaning the
samples afterwards.

0 . 2 m m

v a l u e o f p u r i t y K 4 : 2 7 . 5

o p e n e d i n c l u s i o n ,

o x i d i c - s u l f i d i c

s l i g h t l y m o l t e n a t t h e e d g e s

o p e n e d i n c l u s i o n ,

o x i d i c - s u l f i d i c

s l i g h t l y m o l t e n a t t h e s u r f a c e

T e s t m a t e r i a l

M a t e r i a l :

S i z e :

H a r d n e s s :

4 0 C r M n M o 8 - 6

( i n g o t b o t t o m s c r a p )

K 4 - v a l u e : 2 7 . 5

F l a t m a t e r i a l

c r o s s s e c t i o n 2 0 0 x 4 0 m m

2 8 0 - 3 2 5 H B

0 . 0 2 m m

Figure 4.

Transverse cross sections after wire-erosive trim cuts.

In order to prove that outline errors are not to be attributed primarily to

carbide inclusions a series of transverse cross sections of the eroded surfaces
was made. First an inclusion was localised with the optical microscope and
afterwards marked. Thereupon a transverse cross section of this inclusion
was made. As it can be seen in Fig. 4 the opened inclusions show the typical
stretched structure of an oxidic-sulfidic inclusion.

INVESTIGATION OF THE PLASTIC MOULDING
STEELS 40CRMNMO7 AND 40CRMNMOS8-6

In 40CrMnMo7 the inclusions appear in a strongly stretched form (max.

length approx. 100 µm). They consist either of manganese sulfide or of a
type of mixture with a core of aluminum and magnesium oxide and a narrow
seam of manganese sulfide. In 40CrMnMoS8-6 the inclusions consist of
manganese sulfide or of a mixture (small core: oxides and sulfides of alu-
minium and manganese; edge: manganese sulfide/oxide). The inclusions

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1189

have coagulated structures with a max. length of approx. 100 µm. Alto-
gether the K-values are substantially higher with 40CrMnMoS8-6 due to the
higher sulfur content (approx. 0.07 %) in comparison with 40CrMnMo7
(approx. 0.003 %).

The analysis of the surface quality after wire-erosive trim cuts supplies

generally the same tendencies as it was the case with the rolled ingot bottom
scrap from 40CrMnMo8-6. With 40CrMnMo7 after the fourth trim cut
and with 40CrMnMoS8-6 after the fifth trim cut outline errors (crests) and
cavities occur. The height of the crests is almost exclusively below 5 µm.
The dimensions of the cavities amount to less than 10 µm. The number
of outline errors per 10 mm of machining distance is almost equal to the
number of outline errors of the steel 40CrMnMo8-6 with the lowest K-value
below 0.5. Furthermore also here surface roughnesses are slightly higher
when machining in direction of rolling. Since the obtained surface quality is
practically the same for both materials it can be concluded that the sulfidic
inclusions do not influence the surface quality whereas oxidic inclusions
represent a disturbing factor due to the poor electrical conditions.

µ m

3 . T C

4 . T C

5 . T C

m a c h i n i n g s t e p

4 0 C r M n M o 7

i n d i r e c t i o n o f r o l l i n g

r o

f o

lin

ilu

r 1

µ m

3 . T C

4 . T C

5 . T C

* 1 0

m a x

o u t l i n e f a i l u r e s / 1 0 m m

r o

f o

lin

ilu

r 1

4 0 C r M n M o S 8 - 6

i n d i r e c t i o n o f r o l l i n g

m a c h i n i n g s t e p

Figure 5.

Surface quality in dependence of the machining step.

The investigations on the influence of the degree of purity using the two

plastic moulding steel types 40CrMnMo7 and 40CrMnMoS8-6 showed that
with the standard qualities the desired values of R

are achieved. However

crests to a height of approx. 5 µm as well as cavities with dimensions within
the micrometer area occur using these steels and the assigned technology.

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6TH INTERNATIONAL TOOLING CONFERENCE

INFLUENCE OF SEGREGATIONS ON THE SURFACE
FORMATION

The microscopic check of the samples of the hot-working tool steel

X38CrMoV5-1 (1.2343) was made in the annealed state. In order to exam-
ine the influence of segregations over the entire workpiece width, samples
of the center as well as of the edge of the workpieces were cut out. The
cross section surface which was examined is thereby in rolling direction.
Analyses and evaluation of the cross sections were carried out in accordance
with Stahl-Eisen test sheet 1614 [8]. Figure 6 shows the comparison of the
optical microscope photos with the equivalent reference pictures taken from
[8]. The pictures are representative for all sample positions. No segregation
lines are present.

o p t i c a l m i c r o s c o p i c e x a m i n a t i o n

X 3 8 C r M o V 5 - 1

c o m p a r i s o n t a k e n f r o m

t h e V D E h - s t a n d a r d s

fic

G A 3

S A 1

0 . 5 m m

0 . 0 5 m m

0 . 5 m m

0 . 0 5 m m

Figure 6.

Structure of X38CrMoV5-1 used here compared with the VDEh standards.

The wire-erosive cuts were executed in direct proximity of the points

where the cross section samples were taken. In this point of the project
machining transverse to the direction of rolling was not examined. The

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1191

s u r f a c e q u a l i t y o f a c e n t e r p i e c e

3 . T C

4 . T C

5 . T C

* 1 0

m a x

n u m b e r o f o u t l i n e

f a i l u r e s / 1 0 m m

r o

f o

lin

r 1

s u r f a c e q u a l i t y o f a p i e c e c l o s e t o t h e e d g e

3 . T C

4 . T C

5 . T C

* 1 0

m a x

n u m b e r o f o u t l i n e

f a i l u r e s / 1 0 m m

r o

f o

lin

r 1

Figure 7.

Surface qualities with X38CrMoV5-1 in center and edge piece.

results of the surface analysis of the eroded samples are shown in Fig. 7. As
the cross section investigations suggest, first of all no significant difference
results from the cut position, and secondly the desired R

-values are achieved

as far as possible. However outline errors with a dimension up to 3 µm also
occur in the fifth trim cut when using this steel. This indicates that this steel
is not free of impurities either.

INFLUENCE OF THE MANUFACTURE METHOD OF
HIGH-SPEED STEEL ON THE SURFACE FORMATION

Within this topic the high-speed steel HS6-5-3 (1.3344) in the pyromet-

allurgical as well as in the powder metallurgical version were examined.
Position, geometry and dimensions of the cross section samples and cuts
were selected similarly to the tests on the plastic moulding steel types. Be-
fore the microscopic analysis the workpieces were recompensed on 62 HRC.
The analysis covered six samples per version. Figure 8 shows first the results
of this analysis for HS6-5-3 (molten). This steel indicates obvious oxidic
inclusions, segregations as well as clear carbide lines.

The analysis of the powder metallurgical steel shows a homogeneous and

segregation-free structure with a small number of sulfidic inclusions (Fig.
9). These differences are based on the sinter-technical manufacture method,
with which segregations in the usual sense cannot occur. Furthermore the
carbides possess substantially smaller dimensions.

At each steel eight tests consisting of one main cut and five trim cuts were

executed. The test results are represented in the Fig. 10 and Fig. 11. Con-
cerning HS6-5-3 (sintered) a separation of the results regarding the direction
of rolling was omitted because of the missing significant anisotropy.

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6TH INTERNATIONAL TOOLING CONFERENCE

1 7 5 3

1 7 5 0

1 8 0 9

0 . 1 m m

0 . 0 2 m m

N o n - e t c h e d p r e p a r a t i o n

E t c h e d w i t h H N O

M a g n i f i c a t i o n : 2 0 0 x

fic

A l

M g

E D X - S p e c t r u m

0 . 0 5 m m

Figure 8.

Metallurgical investigations of HS6-5-3 (molten).

4 4 5 1

4 4 4 7

4 4 7 3

0 . 1 m m

0 . 0 2 m m

0 . 0 5 m m

N o n - e t c h e d p r e p a r a t i o n

E t c h e d w i t h H N O

M a g n i f i c a t i o n : 2 0 0 x

fic

I n c l u s i o n i n d i r e c t i o n o f r o l l i n g

Figure 9.

Metallurgical investigations of HS6-5-3 (sintered).

The moderate structure quality of HS6-5-3 (molten) becomes obvious

by the comparatively high number of outline errors per distance (Fig. 10),
which are due to the large oxidic inclusions (Fig. 12). The roughness values

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1193

M a c h i n i n g i n d i r e c t i o n o f r o l l i n g

3 . T C

4 . T C

5 . T C

µ m

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

r o

f o

lin

r 1

M a c h i n i n g t r a n s v e r s e t o d i r e c t i o n o f r o l l i n g

3 . T C

4 . T C

5 . T C

µ m

r o

f o

lin

r 1

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

Figure 10.

Surface characteristics of HS6-5-3 (molten) depending on the machining step.

r o

f o

lin

r 1

µ m

3 . T C

4 . T C

5 . T C

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

Figure 11.

Surface characteristics of HS6-5-3 (sintered) depending on the machining step.

of the two steels deviate hardly from each other. Machining of the molten
steel version leads to more outline errors in direction of rolling as it was the
case with the steel types 40CrMnMo8-6 and 40CrMnMo7. No outline errors
were registered when machining the sintered steel. So this steel ensures the
best prerequisites for the machining of super-finish surfaces as compared to
all other steel types examined here due to the manufacture method.

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6TH INTERNATIONAL TOOLING CONFERENCE

A l

S i

F e

S i

F e

E D X - A n a l y s e s

S E M - p h o t o a f t e r t h e f i f t h t r i m c u t

Figure 12.

Surface failure due to an oxidic inclusion in HS6-5-3 (molten).

INFLUENCE OF THE TECHNOLOGICAL
PARAMETERS

To make clear whether there are process parameters where non-metallic

inclusions, carbides and segregations have little or no influence on the job
result two machining strategies deviating from the standard were examined.
Using a standard technology the lateral feed is 5 µm in the fifth trim cut. The
feed rate in cutting direction is constant – not as in trim cut 1 to 3, where the
feed rate is adapted to the respective discharge current. The first non-standard
machining strategy operates with a fixed feed rate and without lateral feed.
Target here was it to reduce the probability of a wire deflection by a non-
metallic inclusion. It was guaranteed in preliminary tests that also without
lateral feed a constant erosion takes place. In the second strategy the machine
control operates with a fixed feed speed, here likewise with short-circuit
retreat, i.e. on detecting a short-circuit the machine draws back the wire
against the machining direction and tries to process this place again. With
this machining strategy it was intended to remove sufficiently electrically
conductive inclusions or to process the crests which developed before. The
examined material was again the plastic moulding steel 40CrMnMo8-6, here
especially a load from rolled ingot bottom scrap with a K4-value of 27.5.
This material indicated a comparatively high number of outline errors (Fig.

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1195

3) at earlier points of investigation and is thus especially suitable in order to
test the potential of the different machining strategies.

3 . T C

4 . T C

5 . T C

µ m

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

r o

f o

lin

r 1

Figure 13.

Surface characteristics in rolling direction in trim cuts without lateral feed.

If one regards those in Fig. 13 and Fig. 14 explained results of working

with the first machining strategy (without lateral feed, fixed cutting speed),
then it can be stated that the number of outline errors in the fifth trim cut
remained the same.

Likewise the test series executed with the second machining strategy

(short-circuit retreat) show that this technology variation has no positive
influence on the surface formation after the fifth trim cut. Taking into ac-
count these surface characteristics which were measured after machining
transverse to the direction of rolling it is shown that after the fifth trim cut
a significant degradation of the outline accuracy in the comparison to the
machining with standard parameters occurs (Fig. 15 and Fig. 16).

SUMMARY

This article describes the influence of tool steel properties on the surface

formation after super-finish wire cutting. The investigations were arranged
according to the aspects degree of purity (non-metallic inclusions), homo-
geneity, carbide size and distribution as well as technology variation. As
test materials three plastic moulding steel types, one hot-work tool steel and
two high-speed steels were used.

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6TH INTERNATIONAL TOOLING CONFERENCE

µ m

3 . T C

4 . T C

5 . T C

r o

f o

lin

r 1

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

Figure 14.

Surface characteristics transverse to rolling direction in trim cuts without lateral

feed.

r o

f o

lin

r 1

µ m

3 . T C

4 . T C

5 . T C

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

Figure 15.

Surface characteristics in rolling direction in trim cuts with short-circuit retreat.

The investigations for the influence of non-metallic inclusions in a tool

steel for injection moulds provided the following results: Surface defects
in the form of crests and cavities which go back to non-metallic inclusions
appear in a considerable way only starting from a quality target of R

= 0.2

µm (here: fourth trim cut). Using steel grades in normal delivery quality
outline errors rise up to 5 µm and the dimensions of the cavities up to approx.

Influence of Non-Metallic Inclusions in Super-Finish Wire Cutting

1197

r o

f o

lin

r 1

µ m

3 . T C

4 . T C

5 . T C

m a x

n u m b e r o f o u t l i n e e r r o r s / 1 0 m m

Figure 16.

Surface characteristics transverse to rolling direction in trim cuts with short

circuit retreat.

10 µm. With increasing values of the oxidic degree of purity (which means
lower quality) the number and the extent of surface defects rise. The error
rate when machining in direction of rolling is on the average higher than with
machining transverse to the direction of rolling. Starting from a K4-value
of approx. 15-20 the roughnesses desired cannot be achieved any longer.
High K-values due to sulfidic inclusions lead however to no impairment of
the surface quality.

The influence of segregations was examined on the basis of a hot-work

tool steel. In the structure analyses no considerable inhomogeneities could
be determined, so that the results of machining were accordingly positive.
Occurring outline errors in the fifth trim cut could however not be completely
prevented with this steel either. This is probably also caused by non-metallic
inclusions.

The influence of carbide size and distribution was analyzed by the ex-

ample of a high-speed steel made in the conventional (molten, liquid phase)
and in the non-conventional (sintered using a powder, semi-liquid) way. The
unusually poor structure quality of the molten steel type did not permit a di-
rect investigation. So it is to be assumed that the high number of outline
errors essentially go back to the oxidic inclusions in this steel. Using the sin-
tered steel no outline errors were determined. Concerning the characteristic
roughness values no difference between both versions is visible. Regarding

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6TH INTERNATIONAL TOOLING CONFERENCE

super-finish wire cutting with highest requests concerning surface quality
therefore preference is to be given to the sintered version. A variation of the
technological parameters when cutting a load of rolled ingot bottom scrap
iron of the material 40CrMnMoS8-6 (40CrMnMo8-6) showed that by mod-
ification of the machining strategy no improvement of the outline accuracy
could be achieved. The strategy "short-circuit retreat" even showed a degra-
dation of the outline accuracy with machining transverse to the direction of
rolling.

Altogether the investigations showed that material-dependent impairments

of the surface quality within the extreme finishing area cannot be excluded.
The extent of the outline deviations is limited with today’s delivery quali-
ties usually to the µm-area. Tool construction materials manufactured by
sintering prove as favourable.

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Oberflächen- und Randzonenausbildung. Dissertation RWTH Aachen 1994

[2] W. K ¨

ONIG and R. SIEGEL, : Funkenerosives Feinstschneiden – Randzonenausbildung

und Dauerfestigkeit. dima, 10/93, S. 29-34

[3] T. IKAI and K. HASHIGUCHI , K.: Heat Input for Crater Formation in EDM. Inter-

national Symposium for Electromachining (ISEM XI), Lausanne, 17.-21.04.1995 (mit
Vortragshandbuch)

[4] K. ALBINSKI, K. MUSIOL, A. MIERNIKIEWICZ and S. LABUZ, : Plasma Temper-

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[5] J. STEINER, : Stahlauswahl für Werkzeuge und die Polierbarkeit der Stähle. Vortrag

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[6] F. RAKOSKI,: Nichtmetallische Einschlüsse in Stählen. Stahl und Eisen, 144 (1994) 7,

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[7] DIN 50 602: „Mikroskopische Prüfung von Edelstählen auf nichtmetallische Ein-

schlüsse mit Bildreihen". Sept. 1985, Beuth Verlag GmbH, Berlin

[8] Stahl-Eisen-Prüfblatt 1614 des Vereins Deutscher Eisenhüttenleute: „Mikroskopische

Prüfung von Warmarbeitsstählen". 1. Ausgabe, Sept. 1996, Verlag Stahleisen GmbH,
Düsseldorf

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