This technical paper summarizes recent breakthroughs in rough machining of titanium. It discusses three main improvements: 1) using powdered metal cutters which have increased speeds to 70 SFM from 60 SFM for cobalt cutters; 2) plunge roughing with carbide inserts which reduces roughing time by nearly 2/3; and 3) spiral or trochoidal side cutting with solid carbide cutters which allows rough cutting of titanium surfaces with carbide. These new techniques for rough machining titanium have resulted in nearly a two-thirds reduction in machining time. The paper also discusses some recent improvements to finish milling of titanium.

1. TECHNICALPAPER
2005
Society of Manufacturing Engineers ■ One SME Drive ■ P.O. Box 930
Dearborn, MI 48121 ■ Phone (313) 271-1500 ■ www.sme.org
TP05PUB73
Breakthroughs in Rough
Machining of Titanium
author(s)
EDWARD F. ROSSMAN, PHD
The Boeing Company
Seattle, Washington
abstract
The purpose of this report is to present the latest techniques for high-efficiency rough
machining of titanium. Improvements as high as 8X in milling speed of finish cuts on
titanium have been made and reported in the last eight years, but little progress has
been made in rough cutting of titanium until now. For the past 40 years, nearly all
rough milling of titanium has been with cobalt cutters at speeds up to 60 surface feet
per minute (SFM). With 0.005 in. (0.013 cm) chip loads, and cutter life increased by
approximately 1½ hours.
terms
Carbide
Machining
Titanium
Coatings
Milling
Trochoidal

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3. BREAKTHROUGHS IN ROUGH MACHINING OF TITANIUM
Author
________________________________________________________________
Edward F. Rossman, Ph.D.
Associate Technical Fellow, MR&D
Integrated Defense Systems
The Boeing Company
Abstract
________________________________________________________________
The purpose of this report is to present the latest techniques for high efficiency
rough machining of titanium. Improvements as high as 8X in milling speed of
finish cuts on titanium have been made and reported in the last eight years, but
little progress has been made in rough cutting of titanium until now. For the past
40 years nearly all rough milling of titanium has been with cobalt cutters at
speeds up to 60 surface feet per minute (SFM). With 0.005” chip loads this gave
about 1-½ hours of cutter life.
Three areas of improvement in rough milling of titanium are discussed:
1. Use of powdered metal cutters.
2. Plunge roughing with carbide insert cutters.
3. Spiral (trochoidal) side cutting with solid carbide cutters.
These techniques for rough milling of titanium have resulted in time reductions of
nearly two-thirds.
Some fresh findings on finish milling of titanium are also discussed.
Principle Terms
_______________________________________________________________
Carbide Coatings Cobalt
Machining Milling Spiral Milling
Titanium Trochoidal
________________________________________________________________
© 2005. The Boeing Company. All Rights Reserved

4. 2
BREAKTHROUGHS IN ROUGH MACHINING OF TITANIUM
INTRODUCTION
Background
Since publication of the writer’s technical paper on finish machining of
titanium, “Collected Thoughts on High Speed Machining of Titanium,” in 2003 by
The Society of Manufacturing Engineers, there have been improvements in the
rough machining of titanium, and some additional progress has been achieved in
finish milling. For the past 40 years nearly all rough milling of titanium has been
with cobalt cutters at speeds up to 60 surface feet per minute (SFM). With
0.005” chip loads this gave about 1-½ hours of cutter life with few improvements
until now.
Purpose of Report
The purpose of this report is to present the latest techniques for high
efficiency rough machining of titanium. Three areas of improvement in rough
milling of titanium are discussed:
1. Use of powdered metal cutters.
2. Plunge roughing with carbide insert cutters.
3. Spiral (trochoidal) side cutting with solid carbide cutters.
Some fresh findings on finish milling of titanium are also presented. The
writer offers the following notes as an attempt to stay abreast of changes.
Order of Reporting
Where deemed important, the contrast in areas between finish and rough
milling are presented. Major sections are discussed in the following order in the
body of this report.
• Cutter materials
• Cutter types

5. 3
• Cutter coatings
• Plunge roughing
• Spiral or trochoidal milling
• Recent thoughts on finish milling
Acknowledgements
The writer wishes to note that this report is a collection of ideas toward
more efficient machining of titanium. I can not remember exactly where each bit
of information came from, but the following persons come to mind: Garry Booker
(Programmer) of Boeing Commercial for initial descriptions of plunge and spiral
milling breakthroughs, Paul Schaffner of GKN ST. Louis for fresh efforts with
powdered metal cutters, Kieth A. Young of Boeing Phantom Works, Mike Watts
and collaborators of Boeing MR&D who in 1997 launched an enterprise wide
“High performance titanium research” effort, Hector Davis of Aerospace
Dynamics International, Kevin Van Dyke of Summit Design & Manufacturing, and
David West of MR&D here at Boeing. I also give my thanks and appreciation to
those not remembered and acknowledged by this aging mind.
Definitions
Carbide cutters– solid carbide cutters or carbide inserted cutters.
Climb milling – refers to the direction of cutter rotation where the teeth
enter into the top surface of the material rather than entering under the chip and
lifting as in conventional milling which is the opposite rotation.
Cutter rotation
Direction of
Feed
Part

6. 4
Cobalt cutters – cutters made of a good grade of high-speed steel with 8-
10% of cobalt.
Conventional milling – cutter rotates in the opposite direction of climb
milling. Here the cutter teeth enter under the chip and lift the chip. Conventional
milling was the norm until about 40 years ago, but unfortunately is seldom used
today.
High-Speed Machining of titanium – Moving beyond the conventional
speeds of 60 SFM for cobalt cutters and 120 SFM for carbide cutters.
Spiral or Trochoidal milling – a cutter path that is similar to the path
made by a mark on the side of a wheel as it rolls along a surface. The center of
the cutter spirals along such a path.
Taln – Cutter coating – Titanium Aluminum Nitrate.
Cutter rotation,
Lifts the chip
Direction of
Feed
Part

7. 5
Body of Report
Cutter Materials
Materials for Rough Cutting
The traditional cutter material for roughing of titanium is cobalt, but recent
developments in powdered metal cutters, spiral milling with solid carbide, and
plunge roughing with carbide inserts result in much faster roughing. Cobalt
cutters were used because carbide does not hold up well on uneven surfaces,
but the plunge and spiral milling techniques described below get around this
problem.
Powdered Metal Cutters: The writer had some bad experiences with
powdered metal cutters about ten years ago. Rex 20 of that era did not hold up
above Rockwell C40, and heat-treated (beta-annealed) titanium averages about
C41. Recent progress in powdered metal technology has caused the writer to re-
look at these materials. Recent applications of powdered metal have reduced
roughing costs (70 SFM is being used for powdered metal v. 60 SFM for cobalt
with about 1.5 hours of cutter life). One of our machining suppliers is having
good success working with powdered metal cutters, - the materials are Rex 15,
20 & 75 from Brubaker Materials for rough or finish Cutting.
Solid Carbide Cutters: Spiral Milling (Trochoidal Milling): Spiral milling,
reported by Garry Booker (Boeing programmer) while assigned to assist one of
our machining suppliers, used solid carbide cutters for rough milling. We
generally only used cobalt cutters for roughing until now – see details in Spiral
Milling below.
Carbide Inserts: Plunge roughing brings carbide inserts into the rough
milling picture. This is not new, but is mentioned as a still important practice.

8. 6
Cutter Types:
Cutters for Rough cutting:
Use of cobalt wave cutters or similar functioning cutters for roughing
produces good results.
Plunge roughing – brought to my attention by Garry Booker (Boeing NC
Programmer – 787 program), - suggests 4” diameter Plunge cutters for this with
as many inserts as possible, - inserts are on their side for end cutting & through
the spindle coolant is important to get chips out of the way.
Per Jonathan Saada of Hanita, use a 4” dia. cutter with normal coolant.
Paul Schaffner of GKN Saint Louis and Boeing Phantom works have
independently worked on new cutter geometry.
Garry Booker has also done some spiral side milling during roughing
operations (also known as Trochoidal Machining) – best done with cutters that
are under 1” dia. (Carbide).
___________________________________________________________
Cutter Coatings:
Coatings for Rough Cutting
Some tests performed by the writer about ten years ago showed about
35% greater cutter life with coated cobalt cutters, but the cutters cost more if
coated and you need to re-coat after re-sharpening, - so there is little payback for
coating of cobalt cutters used for roughing.
Coatings for Finish Cutting
Solid carbide cutters, - several machining suppliers are experimenting with
coatings, - “x.ceed” from Balsars and a new formulation from Hanita. Early
reports show 3 hours of tool life at 600-800 SFM in side cutting. (Note: tool life is

9. 7
45 minutes with no coating and 1.5 hours with TALN coating). Another supplier
is working on a new coating from Germany – no details on this one yet.
________________________________________________________________
Plunge Roughing
Plunge roughing was first brought to the writers attention by Garry Booker
(Boeing NC Programmer – 7E7 program –He reports plunge cutting at 20-40
inches per minute (feed in the Z axis) – this leads to reducing roughing time by
nearly 2/3 over conventional roughing with cobalt cutters. Garry suggests a 4”
diameter cutter for plunging with as many inserts as possible, - inserts on their
side for end cutting & through the spindle coolant to get chips out of the way.
Garry uses a rule of thumb of .5 gallons per minute per horsepower of
coolant flow through the spindle. He suggests about 0.5-inch step into work for
next plunge and 1.25-inch step sideways. A slight move out (radially) before
retraction will reduce cutter wear, or reposition plunge for next lower step on
waterfall types of cuts. Garry also suggests 400-600 SFM. With 6 inserts this
yields about 18 cu in per minute. Note: horsepower comes into play here – allow
at least 1.4 HP per cubic inch of removal per minute. The writer has seen
machines stall on two occasions.

10. 8
Per Jonathan Saada of Hanita, use a 4” dia. cutter, step 1” into work and
2.5” sideways, 6 inserts at .008” chip load and 180 SFM. Normal coolant. This
yields about 9 cu in per minute.
Spiral or Trochoidal Milling
Garry Booker has also done some spiral side milling (also known as
Trochoidal Machining) – best done with cutters that are under 1” dia. (Carbide).
Here he uses about a ¼ inch spiral motion and 600 SFM (3600 RPM for a
.625” dia. cutter). Chip load is 0.004-0.005” per tooth. Usually limits Axial Depth
of Cut (ADC) to one diameter. Care is taken to have no more than 30 degrees of
cutter engagement maximum. This allows two great things to happen:
1. Allows cutting of rough – as forged – surfaces with carbide
2. Keeps the cutter cool
In pocketing he comes back with a smaller cutter and spirals the corners
to finish them. All is with climb milling.
Recent Thoughts on finish Milling
One of our machining suppliers is getting high-speed success with cobalt
cutters. The writer asked Dave West of Boeing commercial to test cobalt at high

11. 9
speeds on finish cuts where 0.024 to 0.030” was left for clean up. Dave had
some test success with cobalt at about 400 SFM to confirm the supplier results.
To the writer this result is very ironic -- the supplier heard about high-
speed finish milling of titanium, but did not know that one had to switch to solid
carbide for high-speed results. We experts that developed high-speed cutting
with solid carbide cutters presumed that cobalt would not work at high speeds
and never bothered to test cobalt at high speeds until now. Sometimes we are
not as smart as we think we are. Traditionally, cobalt cutters on heavier cuts will
only give reasonable tool life of one hour or more when driven at 50 – 60 SFM.
Solid carbide and carbide inserts are the primary cutting materials for high
efficiency finish cuts at 600 to 800 SFM, but we now find that cobalt and
powdered metal cutters can be used for finish speeds as high as 400 SFM v. the
traditional 60 SFM.
________________________________________________________________
The Author
DR. ED ROSSMAN IS AN ASSOCIATE TECHNICAL FELLOW IN
MANUFACTURING R&D WITH BOEING INTEGRATED DEFENSE SYSTEMS.
ROSSMAN IS CONSIDERED AN EXPERT IN MACHINING AND THERMAL
PROCESSING. HE HOLDS A PHD IN ENGINEERING MANAGEMENT. ROSSMAN IS
CURRENTLY A CONSULTANT AND TROUBLESHOOTER WITH MACHINING
SUPPLIERS TO BOEING AND HAS PUBLISHED AND PRESENTED RESEARCH
PAPERS ON MACHINING AND THERMAL PROCESSING OF TITANIUM.
DR. ROSSMAN IS THE PAST CHAIRMAN OF THE MACHINING
TECHNOLOGY ASSOCIATION OF THE SOCIETY OF MANUFACTURING
ENGINEERS, AND, WAS AWARDED AN “INDUSTRY OUTSTANDING
CONTRIBUTION AWARD” BY HANITA CUTTING TOOLS AT THE COMPLEX
MACHINING SYMPOSIUM IN VALENCIA, CA, ON JAN. 22, 2004, FOR HIS LONG-
TIME PROMOTION AND EDUCATION OF HIGH SPEED TITANIUM MACHINING TO
THE MACHINING INDUSTRY.
HE IS A CURRENT STEERING COMMITTEE MEMBER OF THE MACHINING &
MATERIAL REMOVAL COMMUNITY OF SME.
________________________________________________________________