JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 59

edge sharpness is limited by the coating
thickness. Moreover, due to the significant
difference in hardness between the carbide
substrate and the diamond coating, this
solution has a low impact energy absorption capacity. Chipping resistance is also
limited.
- Capped PCD drills: A cone-shaped PCD
is sintered onto a small carbide substrate
to specific point geometries. The semifinished component is then brazed onto a
solid carbide drill body. This PCD solution
offers limited PCD grade optimization
potential due to the necessity of managing high carbide/PCD interface stresses.
Post-sintering processing can also be costly
due to the extra effort needed to remove
diamonds from non-functional areas and
add internal coolant holes.
- Veined PCD drills: A solid carbide rod
with a pre-machined slot is filled with
PCD precursor powder and then subjected
to extremely high pressure and temperature to synthesize the PCD structure.
Then, the rod is cut, brazed onto a drill
body and finally ground to the designed
tool geometry. This veined PCD technology can generate a complex geometry with
high positive rake angles and shape, and
requires less grinding than capped PCD.
It is limited in size due to the application
of high pressure and temperature onto a
complex 3D geometry. In addition, a high
cobalt content is usually needed, thus
reducing the PCD's hardness and wear
resistance.
- Brazed PCD drills: 2D brazing is the
most common technology for PCD drills
(e.g. spade-type PCD drills). For smaller
sizes, a special carbide sandwiched PCD is
used, whereas individual PCD tips can be
used for larger sizes. This solution has serious geometrical limitations as it is difficult
to add the positive rake angles needed for
composite machining.
The 3D brazing technology involves cutting a bulk of PCD block of the desired
grade and microstructure in a helical shape
as designed. A corresponding helicalshaped slot is ground in a solid carbide
drill to host the PCD blade. Compared
with the capped PCD solution, 3D brazing
only applies PCD on functional areas, substantially enhancing machinability. This

3D brazing technology was selected to develop the test PCD drills in this research.
Another important factor for the choice of
a suitable PCD grade is the machinability
of the diamond material. As part of this
research, machinability was rated by measuring manufacturing times for identical
tools made from different PCD raw materials, focusing on the manufacturing steps
involving PCD disk erosion and PCD
grinding. The results of this machinability
test are displayed in Table 1. The better
the machinability, the higher the rating, as
faster manufacturing times relate to lower
manufacturing cost, which is just as important as tool performance when developing
a competitive tooling solution.

PCD brazing
As the tool introduced in this paper
requires a braze joint of a helically cut
slice of PCD raw material into a tungsten
carbide body, the selected brazing technology needs to prevent graphitization of the
metastable polycrystalline diamond, but
also bond the PCD to tungsten carbide.
This requires an active brazing technology.
An active braze material usually includes
higher melting compounds like titanium.
Brazing temperatures are therefore higher,
which negatively affects the stability of
the diamond phase. In order to prevent
graphitization, an oxidizing atmosphere
needs to be shut out during brazing. Stateof-the-art technologies include induction
brazing using argon atmosphere and
vacuum brazing.

Optimum tool geometry
Choosing the optimum tool geometry for
drilling composite/titanium stacks is difficult, as the two cutting materials require
different drill features. CFRP drilling
normally involves high helix angles and
long cutting edges, as carbon fibres should
be sheared along the cutting edge. Long
cutting edges are realized by low point angles. Additionally, drills for CFRP should
induce low axial forces in order to avoid
exit delamination. All this translates to
rather sharp cutting geometries with small
wedge angles. Clearance angles go as high
as 20 degrees with helix angles around 30

degrees.
Titanium cutting can, in principle, also
utilize a sharp cutting edge; however
compared to CFRP drilling, a more stable
wedge angle is needed. Typical clearance
angles for titanium applications range
from 8 to 14 degrees. Compared to steel
machining, these clearance angles are
typically higher (around 12 degrees in the
presented case) as heat development on
the clearance face should be minimized
in order to decrease flank wear. As high
clearance angles in combination with
typical helix angles of around 30 degrees
would weaken the cutting edge too much,
the helix angle has been lowered to a 15-20
degree range in order to counterbalance
the use of high clearance angles. The presented manufacturing technology allows
for variable helix angles depending on the
tool geometry needed. This is one of its
main advantages, as typical corner-tipped
PCD tools only allow for helix angles up to
8 degrees.
In order to achieve tight hole diameter tolerances, it is absolutely necessary that the
drill point have an excellent self-centering
capability. From another perspective, the
point angle also plays a significant role in
burr formation. It is known that either below 90 or above 150 degrees, point angles
help minimize hole exit burr height. A drill
with a point angle of 155 degrees would
therefore be suitable for titanium exit
needs, but does not have good centering
capability. Therefore, a double point angle
design is proposed with an inner point angle at 130 degrees and an outer point angle
at 155 degrees. The overall point height
of such a drill is rather short compared to
commonly used drills with long cutting
edges. This brings the 3rd and 4th margins
in contact with the material very quickly,
helping to keep tight hole tolerances.
Another advantage of the proposed drill
design is its internal coolant capability.
When drilling pure CFRP plates, internal
coolant holes help quickly transport CFRP
dust out of the drill flutes via compressed
air. When cutting CFRP/titanium stacks,
minimum quantity lubrication (MQL)
can be applied using these sealed internal

No92 October - November 2014 /

jec composites magazine 59



JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014

Cover
Edito
Point of view: oil & gas
Contents
COMPANY & BUSINESS In Brief
Recycling
Biocomposites
Spin-off
Agenda of Events
APPLICATIONS
Sustainability
Defense
Automotive
MARKET
Biocomposites
Inside the factory
SPECIAL JEC AMERICAS - FALL EDITION
Gain insight into the JEC 2014 I.C.S. Americas Program
JEC Americas Innovation Awards Program
Maintenance - Certified composite repair system for pipelines
Carbon fabrics - Successful first flight test for the VX-1 KittyHawk C-PlyTM aircraft model
Design - Composite aerostructure development in high-performance enterprises
RESEARCH & DEVELOPMENT
Reinforcement
Process
TECHNOLOGY & INNOVATIONS
NDT
Tooling
Infusion
Index
In the world
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Cover
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 2
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Edito
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Point of view: oil & gas
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 5
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Contents
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 7
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - COMPANY & BUSINESS In Brief
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Biocomposites
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Recycling
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Spin-off
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 12
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 13
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Agenda of Events
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Ad1
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Ad2
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 15
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Sustainability
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 17
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 18
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 19
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Defense
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 21
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Automotive
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Biocomposites
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 24
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 25
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 26
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 27
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Inside the factory
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 29
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 30
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - SPECIAL JEC AMERICAS - FALL EDITION
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Gain insight into the JEC 2014 I.C.S. Americas Program
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 33
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 34
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 35
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 36
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - JEC Americas Innovation Awards Program
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 38
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 39
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 40
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 41
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Maintenance - Certified composite repair system for pipelines
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Carbon fabrics - Successful first flight test for the VX-1 KittyHawk C-PlyTM aircraft model
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Design - Composite aerostructure development in high-performance enterprises
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 45
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 46
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Reinforcement
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 48
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 49
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 50
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Process
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 52
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 53
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 54
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - NDT
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 56
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 57
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Tooling
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 59
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 60
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 61
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Infusion
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 63
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 64
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - Index
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - In the world
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 67
JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 68
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