I-PDF Artifex_WB110909_WB 2014 01_GB_FIN

SPECIAL
> Grinding, Hard-fine Machining
With Drill Polishing
the ease of implementation and
operation are particularly advantageous, there are no
additional investment costs necessary because the
existing grinding
machine will be
used.
Drill Polishing - a new method of edge preparation
Radiussing drills with
elastic-bonded abrasives
The process of drill polishing facilitates the edge preparation of cutting and drilling
tools after the grinding cycle using the same machine. This is where elastic-bonded
abrasives are making their mark in a new mechanical process.
BY JENS BRODBECK, STEFAN ROTHENAICHER, DIRK BIERMANN,
TOBIAS HEYMANN AND MARK WOLF
> In cutting tool manufacture, edge
preparation or radiussing is an established
procedure for increasing life. The cutting
edge preparation follows the grinding
process and is designed to remove the resulting micro defects from the grinding
wheel to produce the required edge profile
of the cutting tool. The established processes of plunge grinding, brushing and drag
finishing are often exclusively performed
on separate machines necessitating
rechucking of the tool [1,2,3,4]. However,
in order to reduce down-time, carrying out
such operations on the same machine is an
advantage.The innovative approach to the
production of cutting tools with the aid of
elastic-bonded grinding wheels on the
same machine is therefore becoming the focus of research. This well known approach
is based on the kinematics for a polished
chamfered cutting edge, that is, the rotating grinding wheel is moved definitively
along the cutting edge of the flute. The relatively high flexibility of the elastic bonding produces a rounded edge shape [5,6].
A fundamentally different approach is being developed by Rothenaicher Cutting
Tools and Artifex Dr. Lohmann GmbH &
Co. KG using elastic-bonded abrasive polishing wheels [7].
Thr Drill Polishing process
In the process, best described as drill polishing, a spindle-mounted cutting tool
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Bilder: ISF
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drills into a non-rotating elastic-bonded
polishing wheel. As this wheel is static
and not used in the normal way, it is referred to as the ›grinding body‹ in what
follows.
Material removal along the cutting
edge results from the interaction of the
motion of the cutting tool and the abrasive grain suspended in the elastic matrix
of the wheel. From this kinetic process,
the parameters shown in Figure 1 result.
Critical above all for this material removal are the rotational speed ›n‹ of the
workpiece, the drill depth ›Lt,‹ the feed
rate ›vf‹ and the drilling angle ›αA‹ at which
the tool enters the grinding body.
1 Schematic of the process parameters of the edge preparationprocess Drill Polishing
i
INSTITUTION / MANUFACTURER
Institut für Spanende Fertigung (ISF)
der TU Dortmund
44227 Dortmund
Tel. +49 231 7552784
www.isf.de
GrindTec Augsburg Halle 6-606
Artifex Dr. Lohmann GmbH & Co KG
24568 Kaltenkirchen
Tel. +49 4191 9350
www.artifex-abrasives.de
GrindTec Augsburg Halle 3-3002
Rothenaicher Schneidwerkzeuge
87746 Erkheim
2 Optical micrographs of a ground and a polished solid carbide twist drill Abrasive Tool:
SC-HDR, Type 1A1, Silicon Carbide in a rubber bonding, made by Artifex Dr. Lohmann
GmbH & Co. KG, Process parameters: Speed = 1,650 rpm, feed rate vf = 6 mm/min,
drill depth Lt = 1,5 mm, Drill angle αA = 30 °
Influence of the process on the
cutting edge Produced
Figure 2 shows the effects of this new
process on the shape of the cutting edge
of a solid carbide twist drill, diameter
8,5 mm, with all process parameters remaining constant. A rubber-bonded elastic silicon carbide grinding wheel from the
renowned German manufacturer Artifex
was used as the grinding body. The semifinished drill shown in Figure 2 displays
along the cutting edges the micro-defects
resulting from the first grinding operation. Based on the process parameters,
these defects are easily removed. The conWB 1-2/2014
tact time of t = 15 secs between the grinding body and the cutting tool is sufficient
to achieve this. The main cutting edges of
the flutes are not in contact, thanks to the
cutting angle αA = 30° and the minimal
drill depth of Lt = 1,5 mm. From the selected process parameters, the desired
moderate radius on the tip edges of s̄ =
24,3 µm and form factor of κ = 0,88 is very
consistent. The minimal bore depth ›Lt‹
means that once the complete periphery
of the wheel has been used, it can be
dressed back to present a completely new
working surface.With only one wheel, numerous tools can be processed using this
Tel. +49 8336 80876
www.rothenaicher-tools.de
system. Figure 3 compares scanned images
for detailed analysis using an electron microscope. These results show the very consistent size of the radius over the whole
tool radius on the workpiece which in the
area of the main secondary cutting edge
decreases only slightly during transition
to cross-cutting. This slight decrease is
classified as positive for the cutting process
due to the high mechanical stress in the
drill center [8].
What is striking is that the effect of this
is localized in the process parameters to
the area of the main and cross cutting
zones. Additionally no material removal
can be seen directly adjacent to the cutting edge areas of the flank and rake faces
which extends beyond the actual ra-
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SPECIAL
> Grinding, Hard-fine Machining
3 Influence of
process parameters on
the cutting edge shape
and topography
Process parameters:
Rotation speed
n = 1650 min-1, Feed
rate vf = 6 mm/min,
Drill depth Lt =
1,5 mm, Cutting angle
αA = 30°
4 Comparison of profile sections of cutting
edges produced by
Drill Polishing and wet
blasting process;
Process parameters
(Drill Polishing):
Rotation speed
n = 1650 min-1,
Feed rate vf =
6 mm/min, Drill depth
Lt = 1,5 mm,
Cutting angle
αA = 30 °
diussing. Similarly, the removal of material at the secondary cutting edge is very
small. Here only a slight radiussing is evident in the area around the cutting corner. The desired topography of the cut is
determined critically by the surface profile of the grinding body. Evident is a
groove-like structure with a preferred direction orthogonal to the edge. In a similar way to a conventional grinding
process with rotating wheels the individual abrasive grit is reflected in the surface
of the cutting tool. The chipping of the
cutting edge thereby produced was very
low with a value of Rs = 1,2 microns, so
that a relatively smooth cutting edge is
created. The analysis of the profile shape
generated is based on a profile section of
the main cutting edge. For comparison
with an established process, the profile
produced by Drill Polishing can be compared to the cutting edge produced by a
wet method. These profile sections shown
in Figure 4 were determined with a transmission electron microscope. The wetproduced tool exhibits a circular radiussing of the cutting edge, whereas the edge
resulting from finishing with an elasticbonded abrasive wheel displays a much
flatter profile with a pronounced plateau.
The transitions from the rake and flank
surfaces in this plateau are clearly rounded. Although this tool displays a chamferlike profile, it is inadvisable to describe it
as a cutting edge with recognisable sizes
of chamfer, as this can lead to significant
measurement errors caused by the radius
feed.
Influence of process parameters
on the cutting edge shape
In qualitative sampling tests using a drill
angle of αA = 30°, the effect of the variable parameters of spindle speed, drilling
depth and feed rate on the size of the radius was investigated. It could be seen that
by increasing both the contact length and
contact time between the cutting tool and
grinding wheel by the specified adjustment scales, a reducing material-removal
rate is achieved. A noticeable rounding of
the edges can thus already be produced at
low levels for the adjustment variables.
High radius sizes require significantly larger contact times and lengths. A reason for
this lies in the shape of the radius generated. The surrounding carbide substrate
exerts a high level of support on the exposed area of the cutting through the flat
cutting edge profile and so complicates the
extraction of individual carbide grains.
Furthermore, the contact area between
cutting edge and grinding wheel increases with the removal of material. Through
this observed reduction in material-removal rate, a secure and robust process
arises in relation to the size of radius to be
produced when the drill angle of αA = 30°
is considered. In addition to speed, depth
and feed rate, the drill angle is also crucial
for the removal rate. With smaller values,
there is a trend of increasing material removal. This is caused by the fact that with
identical depth, a higher volume of the
disc-shaped grinding tool is machined. At
a drill angle of αA = 0 ° for example, the
largest material removal is achieved, since
all the end cutting edges of the drill are
symmetrically engaged. However, this effect is relative to the total depth of immersion of the cutting corners into the
disc-shaped grinding tool. As a result of a
variation of the drill angle, significant interactions with the other process parameters arise and additional studies are needed to build up a detailed understanding
of the process.
CONCLUSION
Above all the process of Drill Polishing is
notable for its innovative kinematic
process together with the potential for finishing the cutting tool without switching
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to another grinding machine. In particular, this simple implementation and operation is of benefit to the user. Furthermore,
no additional investment costs are required because the same grinding machine
can be used. The cutting edges produced
have a uniform, ultra-thin rounded profile over the radius with low edge chipping.
The process is limited almost exclusively
to the area around the end cutting edges.
The previously mentioned regressive material removal rate at the cutting edge facilitates a reproductable result. ❚
> WB110909
L I T E R AT U R E
1 B. Denkena, L. de León, E. Bassett, E., M. Rehe:
Cutting Edge Preparation by Means of Abrasive
Brushing. Key Engineering Materials, 438 (2010),
S. 1-7
2 I. Terwey: Steigerung der Leistungsfähigkeit von
Vollhartmetallwendelbohrern durch Strahlspanen.
Dissertation, Technische Universität Dortmund,
Vulkan Verlag, Essen 2011
3 H. Gegenheimer: Verbesserte Finishbearbeitung
von Werkzeugen und Werkstücken. MM – Maschinenmarkt, (2012) 8, S. 78-81
4 C.-F. Wyen: Rounded cutting edges and their influence in machining titanium. Dissertation, ETH
Translated by ARTIFEX DR. LOHMANN GMBH &
CO. KG
Zürich, 2011
5 D. Biermann, R. Aßmuth, M. Wolf, M. Kipp: Der
letzte Schliff formt die Mikrogestalt – Neue Poten-
Jens Brodbeck is R&D Manager at Artifex
Dr. Lohmann in Kaltenkirchen
[email protected]
Stefan Rothenaicher is Managing Director
of Rothenaicher in Erkheim
[email protected]
ziale in der Schneidkantenpräparation mittels
elastisch gebundener Diamantschleifscheiben. Forum Schneidwerkzeug- und Schleiftechnik, 26
(2013) 2, S. 76-83
6 C. Effgen, B. Kirsch: A new method for the preparation of cutting edges via grinding. Advanced Materials Research, 769 (2013), S. 85-92
Prof. Dr.-Ing. Dirk Biermann is Director
of the ISF at the TU Dortmund
[email protected]
Dipl.-Wirt.-Ing. Tobias Heymann is Research
accociate at the ISF
[email protected]
7
Dipl.-Wirt.-Ing. Mark Wolf is Research accociate at the ISF
[email protected]
Beschaffenheit der Schneide bestimmt das Bohr-
N.N.: Der Trick mit der Scheibe –
Werkzeugschleifen: Kontrollierte Schneidkantenverrundung von Rothenaicher zusammen mit Artifex. Fertigung, (2012) März, S. 34
8 D. Biermann, I. Terwey, M. Wolf: Einfluss der
Mikrogestalt auf die mechanische Belastung –
moment und die Zerspankräfte beim Bohren. WB
Werkstatt und Betrieb, 144 (2011) 10/11, S. 57-59
© Carl Hanser Verlag, München 2014. All rights including reprinting,
photographic reproduction and translation reserved by the publishers.
WB 1-2/2014
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