JEC COMPOSITES MAGAZINE - Issue #92 - October/November 2014 - 61

geometries were developed and tested.
The conclusions of this work are as follows:

Fig. 3: Diamonds for CFRP drilling

The results indicate that the proposed
new drill point design is capable of creating holes in the H10 tolerance. Using
optimized machining conditions, even H8
hole tolerance levels are achievable with
good process reliability. No dependency of
hole quality on the cutting edge material
could be seen. PCD and carbide tools
with the same drill point geometry create
similar hole quality results.
Burr height
A clear dependency on the drill cutting
edge material can be shown when discussing the drilling results in regard to burr
height control and wear mechanisms.
Figure 2 shows the burr height progression
versus hole count for a carbide tool and
two PCD tools (grades KD1415 and G4).

It can be seen that a carbide drill creates
excessive titanium exit burrs after only 14
holes, whereas the first holes out of specification for the two PCD drills are at 57 and
117 holes, respectively.
In theory, burr height progression should
be a function of corner wear of the cutting
tool. This can be shown between carbide
and PCD due to the significant difference
in material hardness and therefore the
slower progressing corner wear on PCD
tools. The PCD drill shows much less
corner wear than the carbide drill. The
difference in wear progression among the
three PCD grades seems to be minor. The
dominating wear pattern of PCD grades is
cutting edge/corner chipping.

KD1415

KD1425

Drill 1

Drill 2

123

Drill 3

Table 1 gives an overview of the tool life
results for the three tested PCD grades. As
can be seen, G4 and KD1415 are very similar in regard to average tool life. KD1415
shows a more consistent tool life as well as
the best machinability to reduce manufacturing cost, therefore it was chosen as the
most suitable grade for this application.

Average

Conclusions

Deviation
(+/-)

(46/49)

(12/8)

(17/29)

Tab. 1: Tool life results of the three tested PCD
grades

Brazed PCD solid carbide drills with three
different PCD grades and optimum tool

- 3D brazing technology allows the
manufacture of PCD tools with flexible
helix angles and therefore large rake angles.
Compared with capped PCD solutions,
3D brazing enhances machinability by
removing less PCD from functional faces.
- With the optimum tool geometry
(double point angle, helical flutes, internal
spiral coolant channels, large rake angles),
the developed PCD drills were able to generate good hole quality (hole size diameter
and burr height control).
- Compared with uncoated solid carbide
drills, PCD drills show significant improvements in terms of tool life.
- All the tested PCD drills have the same
wear pattern, which starts off from micro
fractures in the rake face and finally ends
with catastrophic corner chipping.
- KD1415 outperformed G4 and KD1425
with a more consistent tool life and better
machinability. Therefore, KD1415 was the
most suitable grade for this application. n
More information:
ww.kennametal.com

About Kennametal
Celebrating more than 75 years as an
industrial technology leader, Kennametal Inc. delivers productivity to
customers seeking peak performance
in demanding environments. The
company provides innovative wear-resistant products, application engineering and services backed by advanced
material science, serving customers
in 60 countries across diverse sectors
of aerospace, earthworks, energy,
industrial production, transportation
and infrastructure. With approximately 14,000 employees and nearly $3
billion in sales, the company realizes
half of its revenue from outside North
America, and 40% globally from
innovations introduced in the past five
years.

No92 October - November 2014 /

jec composites magazine 61

http://www.kennametal.com

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

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