ISABE-2009-1169 Blisk Production of the Future

ISABE-2009-1169
Blisk Production of the Future
Technological and Logistical Aspects of Future-Oriented Construction and Manufacturing
Processes of Integrally Bladed Rotors
Martin Bußmann, Dr. Erwin Bayer
MTU Aero Engines
Abstract
This paper describes the state-of-the-art in the
manufacturing technology for integrally bladed
compressor and turbine rotors (blisks) in today’s engine construction and addresses the
technological and logistical challenges to be
resolved to ensure flexible and future-oriented
blisk manufacture.
Abbreviations
ECM
PECM
HPC
Blisk
IBR
LFW
IHFP
LPC
AM
CMM
Electrochemical Machining
Precise Electrochem. Machining
High Performance Cutting
Bladed integrated Disk
Integrated Bladed Rotor
Linear Friction Welding
Inductive High Frequency Pressure-Welding
Low pressure compressor
Adaptive Milling
Coordinate measuring
machine
Figure 1: Blisk drum.
2. Introduction
Integrally bladed rotors (blisks) are increasingly
being used in modern engine construction.
Meanwhile, advanced compressors for both
commercial and military engines frequently
come as all-blisk designs. Essential benefits
over conventional rotor designs where the
blades are fitted in slots in the disk rim include
weight reductions up to 20 percent and significant efficiency improvements.
The next step of integration which promises
further weight savings — welding of individual
blisks to form multi-stage blisk drums — has
already been put to practice and is being further developed (see figure1: blisk drum). The
same applies to the hollow fan blade technology which is used to achieve further weight
reductions. Furthermore, investigations are
presently being carried out into the feasibility of
manufacturing dual-material blisks and into the
use of blisks in highly stressed turbine stages.
With respect to manufacturing technology this
means that a wide range of materials, sizes
and geometries has to be investigated.
A company that intends to manufacture the
entire spectrum of blisks in a cost-effective
manner, must focus on some core manufacturing techniques for airfoils and be able to combine these techniques to best effect. In the
process, additional requirements in terms of
manufacturing logistics and facility planning
strategy must be met.
And last but not least, the blisk design poses
new challenges for repair technology. The
established shop repair process chains which
base on the repair of the detail parts, blades
and disk, must be modified or newly developed
from scratch.
Figure 2 below is an overview of the various
blisk designs which differ in size and configuration.
1.2 Range
EJ 200
LPC
Ti64
LFW + AM
TP400 Drum
IPC
Ti64
EBW / IFW
HPM
PW6000
HPC
Ti6242
HPM + IFW
EJ 200 Drum
HPC
Ti6242
HPM + IFW
NGPF
HPC
U720;IN718
(PECM)
Figure 2: Overview of the blisk types manufactured by MTU Aero Engines.
3. From the strategic approach to the present-day situation at MTU Aero Engines
A strategic approach towards market-driven
blisk manufacture was defined by MTU Aero
Engines back in 2004.
Machining resistance (material)
To be able to manufacture various blisk types
to satisfy the demand on the commercial and
military markets long-term, several core manufacturing technologies for the production of the
flow duct profile must be developed that can be
used in any combination, depending on the
type of blisk involved.
ECM / PECM
HPC
LFW / IHFP
current
Current
Blisk spectrum
spectrum
blisk
HPC
Blade surface area / airfoil length (geometry)
Exc. : Applications of airfoiling processes
as referred to two parameters
Figure 3: Core airfoiling processes for blisk
Focusing on these core technologies makes
sense because the production of the flow duct
accounts for the major part of the manufacturing costs. In addition, the use of suitable core
technologies may help reduce raw material
consumption and hence costs.
These core technologies are then supplemented by hub machining and surface treatment processes to obtain an optimum process
chain tailored to suit the respective type of
blisk.
If these manufacturing technologies are then
used in conjunction with advanced design and
construction methods a component can be
manufactured that is optimized in terms of
function, quality and costs.
Based on this approach, a number of development projects were launched which focused
on:
-
design to cost
new or further developed joining, milling and ECM/PECM techniques
shot peening techniques
new quality assurance methods
new repair strategies
The Tool Box Approach in Process Chain Generation
Peripheral
processes
Peripheral
processes
Airfoiling
-
Niblisk
Tiblisk
ECM
HPC
LFW /
IHFP
Finishing
ECM /
PECM
X
X
X
X
:
:
X
X
:
:
HPC
LFW /
IHFP +
AM
CG
Post-airfoiling processes / QM
Pre-airfoiling processes
Rough-machining
Surfacetreatment
Grinding,
etc.
X
X
:
:
:
:
X
X
X
:
:
X
X
X
X
X
:
:
:
:
:
:
Figure 4: Tool box approach
For the annulus surfaces, proof could be furnished that milling marks that extend in the
direction of the flow have no adverse effects
whatsoever, as long as their depth does not
exceed a certain threshold value. This significantly reduces the finish-machining effort.
3.1 Design to cost
The primary objective of design-to-cost measures in blisk production is to reduce the manufacturing costs by bringing the requirements for
airfoil and annulus surfaces as well as leading
/ trailing edge geometries as closely as possible in line with the fluid mechanical requirements. In the process, the friction losses of
processed surfaces (milled, shot peened,
ground) and/or the geometry variations of the
edges must be accounted for in the aerodynamic design as accurately as possible.
The results of investigations into possible leading edge geometries on compressor blades
have also revealed technical potential for expanding the acceptance standards.
T
basic profile 1/4 T stub
1/3 T stub 1/8 T concave 1/8 T convex 1/6 T concave
∆ω
mittel
∆ω
Figure 4: Edge geometries investigated.
0,00%
1/4
1/4stumpf
stub
1/3
1/3stumpf
stub
1/8
1/8concave
konkav
1/8 convex
konvex
1/6
1/6concave
konkav
1-2 Grafiken
3.2 Manufacturing technologies
Edge
Kantenform
geometries
3.2.1 Joining
Figure 5: Losses ∆ω of the deviating edge profiles investigated as compared with a basic profile
with constant edge radius.
Linear friction welding (LFW) has proven to be
a suitable method to produce the highly
stressed joint between the blades and the disk
and is now used in production. Further development efforts in this field are mainly targeted
at the machine technology to achieve higher
flexibility with respect to the various component
geometries to be joined.
Since the LFW technique calls for highly engineered machinery and presupposes certain
geometric conditions regarding the components to be produced, the next generation of
blisk joining techniques is presently being developed: the inductive high-frequency pressure
(IHFP) welding process.
Figure 6:
Figure 8: section through a IHFP welded joint.
Detail parts and
blisk joined by LFW
Here, the energy required to heat the materials
to be joined is produced by high-frequency
alternating electromagnetic fields so that the
complicated machinery needed in the LFW
process to produce the mechanical vibrations
and high joining forces is no longer required.
Another benefit of the technique is that the
component proper is subjected to lower
stresses during welding.
Figure 9: Simulation of the heating process
during IHFP welding
Presently, the technology is being matured for
common joints on titanium materials and crosssections from the fan area to the low-pressure
compressor. In the process, a capable simulation of coil / alternating field is used which is
particularly suited for the component geometry
and significantly reduces parameter testing.
1
3.2.2 Milling
1
3
2
4
1= HF generator
2= Welding equipment
3= Hydraulic system
4= CNC control unit
Figures 7 IHFP welding machine
At MTU Aero Engines, milling is the most
commonly used technique to produce blisk
airfoils. In this field, a holistic approach to the
milling process—machine, setup, milling strategy, tooling, tool holders, coolant-lubricant,
etc.—helped achieve considerable savings. A
significant contribution came from the MTUpatented circular stagger milling process.
While with conventional milling the angle of
contact may be up to 180°, this angle is limited
to 30° to 60° with circular milling. This reduces
the cutting forces and increases the material
removal rate by means larger cutting depths
and higher cutting speeds.
angle of contact
angle of contact
These highly dynamic milling processes are
performed using special 5-axis milling machines. The necessary acceleration can be
achieved by means of direct axis drives.
3.2.3 ECM / PECM
Rounding of the cutting edge markedly reduces the risk of micro-chipping, and the cutting edge normally exhibits a uniform rubbing
wear.
(-)
Continuous
feed
Electrolyte
(+)
Essential prerequisites for high-performance
machining using the circular milling approach
are the selection of the most suitable cutter
material and the definition of an optimum cutter
geometry. Also, the life of the rough-milling
tools can be more than doubled with an appropriate edge preparation.
´Tool
Figure 11: Milling on a 5-axis machine
Part
Figure 10: Angle of contact with circular
and conventional milling
So far, the advantage of electrochemical machining processes used in the production of
airfoil geometries, i.e. minimum tool wear, has
been offset by the drawback of inaccurate
contours particularly in the edge and radius
areas and a relatively long iteration process.
These disadvantages have now been overcome by a further development of the process,
the so-called precise electrochemical machining (PECM) technique. A reliable and precise
control of this process, which involves very
small gaps between component and vibrating
electrode, has now been made possible by
further developments in semiconductor technology and control systems (precise pulsing
and response times in the microsecond range
at high machining currents).
The results of trials have shown that, in the
case of materials which are difficult to machine
(nickel-base alloys, nickel PM material), PECM
is distinctly superior to milling in terms of machining speed, tool wear, surface finish, and
process stability of the geometric features. The
technology has been matured for production
use by MTU Aero Engines and first development hardware is being machined on prototype
facilities.
ECM for rough-machining
(electrochemical machining)
• gap > 1 mm
• lower accuracy
• high removal rates
(+)
(-)
Part
Tool
Pulsed
feed
PECM for finishing
(precise electrochemical machining)
•extremely narrow, controlled gap
< 0.1 mm
• pulsed current
• increased accuracy of forming
• lower removal rates
Figure 12: Sharp-edged and rounded edge of
a rough-milling cutter for blisk machining
Figure 13: ECM / PECM operating principle
Part
Peening Chamber
Sonotrode
Piezo Shaker
ECM premachining
Controller
+ Amplifier
SONATS
Figure 16: Principe of US shot peening
PECM finishing
Conventional shot peening
Intensity: 0.2 A, coverage: 125 %
Figure 14: Blisk manufacture by a combination
of ECM premachining and PECM finishing –
airfoil geometries and surfaces.
3.2.4 Shot peening
Most of Blisk blades are subject to controlled
shot peening to increase their fatigue strength.
Alongside conventional shot peening MTU
Aero Engines uses ultra-sound assisted shot
peening which offers the advantage of minimum component distortion, since both airfoil
sides are normally compacted simultaneously.
US shot peening
Intensity: 0.2 A, coverage 150 %
250µm
Figure 17: Comparison of the surface texture
achieved by a) conventional and b) US shot
peening
schematic
Figure 15: Test setup for US shot peening
Since US shot peening does not increase the
roughness of the airfoil surfaces, in particular
in the leading and trailing edge areas, postpeening finishing processes that had to be
performed after conventional shot peening are
no longer required.
3.2.5 Quality assurance
In this area, optical measuring techniques hold
promise of time savings and more reliable
quality statements as compared with conventional measurements using coordinate measuring machines (CMM).
In contrast to conventional assembly of rotors,
the manufacture of blisks is subject to particularly stringent requirements in terms of airfoil
location, radius and airfoil profile tolerances.
Depending on the stability of the manufacturing process used, therefore, extensive dimensional inspections must be performed in the
course of in-process and final inspection.
Compared with the tactile systems used on
CMMs today’s advanced optical systems offer
great potential of reducing the inspection effort.
They need far less time to provide complete
models of the components which can then be
verified by means of computation routines, for
example to assess manufacturing deviations in
boundary cases.
In cooperation with the measuring system
manufacturers, MTU Aero Engines has succeeded in improving the accuracy of the systems also for dimensional inspection of leading
and trailing edges, for example.
method also for individual blades, involve
processes, such as buildup welding or patching that call for perfectly matched process
steps, particularly when recoating or subsequent heat treatments are required.
Repair processes
Figure 20 : Repair categories A, B, C, D
Of the repair categories illustrated above, the
replacement of complete airfoils poses the
most exacting requirements, as this repair
involves the use of cutting and joining processes in the vicinity of critical component
zones. Category A to C repairs are already
used at MTU AERO ENGINES, category D is
being developed.
4. Future developments
4.1 New designs
Figure 18: Dimensional inspection of a blisk
The blisk design having become state-of-theart in the entire compressor area, including the
high-temperature-resistant high-pressure compressor stages, MTU Aero Engines is now
working on the development of fabricated,
high-stressed low-pressure turbine blisks.
Unlike with the smaller, integrally cast variants
used, for example, in auxiliary power units
(APUs), the special challenge to be overcome
here in manufacturing is the material mix of
forged disks and high-temperature cast blades
and even single-crystal materials.
Figure 19 : Leading and trailing edges inspected using optical systems
3.2.6 Repair
Due to the integral construction of blisks a
variety of repair processes needs to be modified or newly developed. Repairs that go beyond the scope of blending, a standard repair
Figure 21: Design example of a fabricated
turbine blisk
4.2 Materials
4.4 Quality assurance
New engine concepts with enhanced efficiencies call for the use of high-strength and hightemperature alloys. In the low-pressure compressor, the simple titanium alloy Ti6V4 is increasingly being replaced by the alloys Ti6242
or Ti6246, and in the high-pressure compressor, the modified alloy DA718 with approx. 7 %
more strength is being used instead of the
standard alloy IN718. The last compressor
stages upstream of the combustion chamber
which are subject to higher thermal stresses
will be made from PM nickel alloys. With these
materials, electrochemical machining processes are particularly cost-effective.
Blisks are inspected using the standard inspection methods developed for conventional
disks, such as fluorescent penetrant inspection, ultrasonic inspection and segregation
etching. For the inspection of blanks, phased
array technologies are presently being further
developed and adapted to suit the particular
requirements. Such technologies with their
high resolution permit production inspection to
be performed quickly and effectively.
4.3 Surfaces
To protect blisk blades from erosion by sand
and dust, MTU Aero Engines has developed
new protective coatings which have meanwhile
become the standard coatings for airlines operating in erosive environments. In the coating
area, too, poor accessibility of the blisk calls for
special processes.
4.5 Design
Highly advanced 3D design tools are used in
the design of the blisk blades. Present-day
airfoils are highly twisted, the edges frequently
having the form of an “S”. The blade tips are
hard-faced to protect them against rubbing
wear. These features result in new challenges
for manufacturing technology.
Figure 23 : 3D CAD model of a high-pressure
compressor blade
4.6 Industrial production concepts
The manufacturing concept presented here
bases on the following prerequisites:
Figure 22: Blisk airfoils with anti-erosion coating
With aerodynamically optimized compressors,
highest surface finish requirements have to be
satisfied especially in the high-pressure compressor area. To achieve the surface finishes
needed blisks with their special geometrical
constraints have to be processed using other
and, above all, more cost-effective techniques
than those used on individual blades. In this
field, automated electrochemical process sequences and other processes are being tested
at present.
- Tool box concept
The cost-effective and high-quality manufacture of a wide spectrum of different blisk types
is possible only by the combination of various
core manufacturing techniques for airfoiling.
- High investments into the special machinery
required are necessary to put the tool box concept in place. Therefore, the manufacturing
concept must ensure optimum utilization of the
special machines.
- Owing to the integral construction and the
criticality of the component and the associated
interdependence of important quality characteristics maximum control over an essential
part of the manufacturing process chain must
be ensured.
5. Summary
- Long response times regarding the current
quality situation of individual manufacturing
processes must be avoided. A prompt quality
control of the processes with effective possibilities to interfere with the processes is a must.
Against this background two basic manufacturing approaches are conceivable:
In advanced engine concepts, blisk construction makes an important contribution towards
optimizing efficiencies and reducing weight.
Therefore, blisks will find increasing use, also
in the turbine area.
To be able to manufacture these critical and
highly stressed engine components in a costeffective manner, a variety of sophisticated
manufacturing and quality techniques is
needed. These have then to be combined into
process chains optimally designed to suit the
various types of blisks to ensure best results in
terms of costs and quality.
I) Central concept
Processes that do not form part of the core
manufacturing techniques are used for the
entire parts spectrum and are designed to
ensure adequate flexibility of machines and
fixtures. Whether and when a new core manufacturing technique is included in the tool box
depends on the parts volume to be processed.
As long as this volume is below a cost-effective
threshold value the parts must be processed
using other methods.
II) Decentral concept
The parts volume for an optimum combination
of core manufacturing techniques must be
such that a complete autonomous process
chain is justifiable from the economic point of
view.
pre-stage
parts
pre-airfoiling
processes
rough airfoiling
finish airfoiling
milling
welding
PECM
X
X
milling
X
X
ECM
X
X
post-airfoiling
processes
quality
inspection
Figure 24: Central Concept
p re -s ta g e
p a rts
p re -a irfo ilin g
p ro c e s s e s I
a irfo ilin g
p ro c e s s I
p o s t-airfo ilin g
p ro c e s s e s I
q u ality
in sp e c tio n
p re -s ta g e
p a rts
p re -a irfo ilin g
p ro c e s s e s II
a irfo ilin g
p ro c e s s II
p o s t-airfo ilin g
p ro c e s s e s II
q u ality
in sp e c tio n
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Figure 25: Decentral concept