Efficient Titanium Machining

Efficient Titanium Machining 

Update STC-Serie 

Sept. 2011

Challenges in Titanium machining 

Titanium and its varying grades of alloys are attractive materials for structural applications 

in the aerospace industries. 

conventional future 

Starrag 

Alu 

70% 

Steel 

7% 

Titanium 

6% Composites 

10% 

Dörries Heckert Scharmann SIP Droop + Rein TTL Berthiez WMW Ecospeed 

Alu 

20% 

Other 

9% 

Steel 

7% 

Titanium 

14% 

Composites 

50% 

Machining titanium parts efficiently requires a delicate balance between productivity and 

profitability. The cutting process poses a big challenge to the machine and tool system. 

In the past experiments to use standard machines failured. In Titanium machining solid and 

accurate machine tools with high performance in drives and spindle become accepted in the 

market. 

Other 

7% 

Source : Airbus 

1


We at StarragHeckert are aware of the necessity to optimise our machine tools for titanium cutting. We 

have taken significant steps in the development, design and optimisation of even the larger machine 

tools to provide high stability and rigidity, temperature control and effective compensation. 

We have carried out all the necessary calculations and practical measurements to detect temperature 

sources. 

Calculation and experimental 

verification of machine 

characteristics 

Starrag 


2


The fundamental criteria for the machining of complex titanium components are a high rigidity/ low 

resonance of the Machining Centers from the base to the milling head, combined with a high-drive 

rating and main spindle torque. 

What can we do to be precisely productive ? 

- Machine design 

- Heavy duty gear spindle 

- Axis drive concept 

- Advanced thermal management 

- Energy efficiency 

- Power cuts and extensive optimisations 

- Process Knowledge 

- Intelligent Service Solutions 

Starrag 


3

Expertise in machine tool building 

Examples for process stability oriented machine design 

Welded column and machine bed 

use of massive roller guideways and bearings for linear and 

rotary axes 

Large dimensioned drives and guideways 

use of additional releasable thrust bearing in ball screw drives 

(stiffness higher than two conventional ball screw drives) 

Hardened steel worm wheel 

Extensive experimental verification of the design quality 

static and dynamic stiffness measurements (experimental 

modal analysis) 

Starrag 

Deformation at point E 


E 

D 

100 

80 

60 

40 

20 

0 

D 

D 

Percentage E E 

Form A Form B Form C 

4


Based on the milling of a typical component roughing time is usually 

calculated at > 70% (even for forged parts). 

It has quickly become apparent that an increase in productivity is 

directly related with the dissipation and removal of swarf away from 

the component. The ideal machine must be so designed and built 

that it can attain high volumes of swarf removal in actual/real cutting 

conditions. 

Spindle torque diagrams and cutting force 'data' only tell half the story. 

The most important element is to use a machine that enables deep 

and stable chatter-free cuts. A well designed and balanced concept 

(weakness-free) as well as high stiffness, low resonance and high 

dampening qualities are imperative. 

A prime example of high stiffness and high dampening is the use of 

a gear spindle instead of a motor spindle. Apart of the extreme 

robustness, a gear spindle has the advantage of high dampening 

properties when dealing with rotor bending moment forces. 

The spindle rotor stiffness is much higher due to the rugged spindle 

shaft and short distance from the spindle nose to the rear spindle bearings. 

Starrag 

Nodding head with two 

supports and a heavy 

duty gear spindle 

Spindle options : 

8000 rpm/ 940 Nm 

5600 rpm/ 1300 Nm 


5


Gear spindle shows best behavior in class: 

highest rigidity and process stability due to 

– rugged spindle bearings 

– rugged spindle shaft 

– short axial distance of bearings 

Spindle rotor much more rigid than competition 

compact design allows shortest distance between spindle 

nose and A-axis 

– 220mm in comparison to > 400mm 

– shorter lever arm leads to better flow of forces and to 

ultimately higher rigidity 

– smaller evasive motions are required 

compact and rigid design leads to 

– highest crash resilience 

– easy maintenance and repair 

Starrag 

220 

mm 


6


The drives for linear and rotary axes for titanium cutting must comply with the following 

requirements: 

High stiffnesses and high thrust forces 

Smooth run and close following of control setpoints 

Acceleration and velocity levels to comply with lasted tool technology 

All of this is accomplished for the Starrag drive concept the following way: 

Linear axes 

– Ball screws are used (no excitation of the drive due to the use of gear wheels) 

– Due to hydraulically releasable thrust bearing the stiffness of the drive chain is doubled 

(in comparison to conventional bearings) 

Rotary axes 

– Worm wheels are used (no excitation of the drive due to the use of gear wheels) 

– Contact zone provides extraordinary damping 

Belt transmissions 

– Between drive motors and ball screws/ worm wheels a belt transmission is used 

– Belt transmissions provide extra damping 

– Transmission ration allows for layout simultaneous for good control behavior, 

high thrust forces and high acceleration levels 

Starrag 


7


The BTP and STC series are not universal use machine tools, but made 

specifically for simultaneous 5-axis machining of hard to cut materials: 

A unique damping disk in the A axis is used allowing unmatched depths of cut 

for 5 axis simultaneous machining and therefore the implementation of 

advanced roughing strategies 

The optional 100 bar internal coolant pressure supply is top in class. Its 

optimized installation reduces internal pressure losses and leads to longer 

tool life 

Extensive optimization of the machine frame, drives, guideways has taken 

place for improving the machining capabilities – hands on experiences are 

made in our “Center of Production Excellence” every day 

Starrag 


8


The StarragHeckert Machining Centers provide a number of further benefits: 

Advanced thermal management 

– optimized, homogeneous and stable machine 

and coolant system design 

– state-of-the-art thermal compensation for spindle, 

swiveling head and structure (patent pending) 

Optimized swarf flow 

– swarf, coolant evacuation, flushing system and 

covers are optimized for highest productivity 

– high quality Knoll components are used 

Starrag 


9

Other interesting 

Options 

Starrag Dörries Heckert Scharmann SIP Droop + Rein TTL Berthiez WMW Ecospeed 10 

10

Option STC1000/130 

Basic Machine Variant 130 / Y1900, Support STC1250 

Starrag Dörries Heckert Scharmann SIP Droop + Rein TTL Berthiez WMW Ecospeed 11

Pallets 

Pallets are available with taped holes or T-slots 

STC800/130 

800 x 800 mm 

800 x 1000 mm 

790 x 800 mm with rounded pallet interface 

STC1000/130 

800 x 800 mm 

800 x 1000 mm 

1000 x 1000 mm 

STC1250/130 & 150 

1000 x 1000 mm 

1000 x 1250 mm 

1250 x1250 mm (/130) 

STC1600/130 

1250 x 1250 mm 

1250 x 1600 mm 

1600 x 1600 mm 

1600 x 1800 mm 


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Mill-Turn-Machining, STC800/160 

MT … multi tasking 

Maximum productivity through process integration 

STC800/160 

X / Y / Z travel 1,350 / 1200 / 1,450 mm 

Milling / turning table 500 min -1 

Pallet sizes 790 x 800 mm 

Ø 1,000 mm 

Load weight 2,000 kg (at n = 60 min -1 ) 

1,000 kg (at n = 500 min -1 ) 

Workpiece dimensions Ø 1,400 x 1,400 mm 


Mill-Turn-Machining, STC800/160 

Rotary Option Highlights 

Powerful rotary table with direct drive (torque motor) 

55 kW / 2,380 Nm 

Use of type HSK-T100 holders ensures exact radial 

positioning accuracy 

Allows use of circular and rectangular pallets 

Simple electronic balancing 

Gear spindle clamping with Hirth coupling 

ensures exact radial positioning accuracy 

2380Nm (S1) 


10000 

MS [Nm] 

PM [kW] 

1000 

100 

10 

1 

55kW (S1) 

0 

250 500 

1 10 100 

n [min 

1000 

-1 ]

STC 800 - 1600 

Coolant Supply System with 100 bar 

High pressure through spindle coolant 

Pressure 100 bar 

Flow rate 70 l/min 

Pressure range 7 pressures 

Frequency converter 

(Standard: 70 bar / 20 l/min) 

High pressure through spindle coolant 

with frequency converter 

Vakuum band filter 

35 ym; lost filter material 

Option Turbofilter 

50 ym; self cleaning 


Automatic Machine Adjustment 

Alignment of A-axis 

The offset between B-axis an machine 

zero offset is determined and 

automatically compensated. 

The measurement is taken on the pallet 

carrier or at a position which is defined by 

the user. 

The offset between the main spindle axis 

and the A-Axis as well as the measure 

220 mm is determined an automatically 

compensated. 

Measurement of A-axis alignment. 

Increased machining accuracy thru 

machine adjustment at operating 

temperatur 

Easy inspection of machine accuracy 

after a machine collision 

The measurements are carried out with a 

tactile probe. 

Position of rotary axis 

B-axis 


16 

Z 

X 

220 mm 

Position of Tool Center Point

New spindle option for titanium machining 

Torque [Nm] 

Face milling 

2000 Full cut, DoC = 6 mm, Vc = 80, feed/tooth= 0.14 mm 

1800 

1600 

1400 

1300 

1200 

1000 

800 

600 

400 

5‘600 rpm / 1300 Nm (Option) 

8‘000 rpm / 940 Nm 

a) 

Contouring 

DoC = 1 x Dia., WoC = ½ x Dia., Vc = 80, 

feed/tooth= 0.13 mm 

b) 

200 

c) 

d) Finishing, Vc = 150 m/min 

0 

Dia 6 mm: 7960 rpm 

10 100 375 1000 10000 8000 


Spindle Speed [rpm] 



5600 

a) Face mill 45° Dia 160 mm 

b) Porcupine Dia. 80 mm 

c) End mill Dia. 20 mm 

d) Conical Ball end mill Dia. 6 mm

Comparision : 

Milling head STC 

against the competition 


18

Compact Milling Head 

Standard milling head 

Milling head STC-Machine 

A 

B 

Allows the use of short stable tools 

Good accessibility to the workpiece: 

Easier programming 


a 

b 

x 

x

Process stability 

Milling head STC- 

Machine 

M A1 

M 1 

a 

b 

Standard milling 

head 

F 

Unique short distance between tool tip and A-axis with this class of machine 

Minimal compensation movements of linear axis during 5-axis simultaneous machining 

Minimal load during roughing operations 

With a tool length of 180 mm there is up to a 50 % reduction in effect torque acting on 

the A-axis! 

High stiffness on the tool tip resulting in the highest machining quality and tool life. 


M 2 

M A2

Process stability 

Short milling head overhang: 

Up to 35% less torque acting on the mill head and 

column 

Minimal torsion and bending stress acting on 

machine structure 

The short distribution of forces combined with the 

stiff machine structure results in an extremely high 

process stability 

Economical machining with the metal removal 

rates and workpiece quality 

Up to 1.35 x a 


Standard milling head 

Milling head STC-Machine 

a

References 

HEC/ STC-Serie 


22

Keeping Aerospace leaders at the cutting edge 

FMS with each 8 STC1250 

FMS with HEC1250; BTP 5000/2 

Titanium machining / F35 - long spars and longerons 

Starrag 

FMS with 3HEC1250 and 3 STC1250 

Titanium machining / Pylons 


23

Efficient Titanium Machining

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