Development methods for
high performance machine tools
Petr Kolar, Matej Sulitka, Jaroslav Šindler
8.5.2014
CZECH TECHNICAL UNIVERSITY IN PRAGUE | FACULTY OF MECHANICAL ENGINEERING
Department of Production Machines and Equipment | PME
Research Center of Manufacturing Technology | RCMT
www.rcmt.cvut.cz
2
Presentation overview
1. challenges in the design of large machine tools
2. point of success in machine tool design
3. description of the development methodology
4. case study 1: kinematics of a milling machine
5. case study 2: cross beam optimization of a portal milling machine
6. conclusions
3
Challenging requests of machine tool user
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competition in the segment of large machine tools (working space > 1 m3) has
increased over the last years
customers are asking for:
– lower price  machine tool total cost reduction through the cost reduction of all
all components (mainly structural parts = structural mass reduction)
– shorter delivery times  modular design
– higher productivity and efficiency  multifunctionality (milling, drilling, turning,
grinding…)
– higher accuracy  better static and dynamic stiffness, thermal stability
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Challenging requests of machining technologies
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typical 3+2 operation (with indexed rotary axes)
– typical operation: face milling, pocketing, drilling
– new cutting strategies: circular milling, plunging
increasing volume of high performance structural
materials
– high alloyed steels, Ti alloys, Ni alloys
– composites (CFK, GFK)
all these factors increase requests for:
– higher movement speeds
– higher spindle power
– higher accuracy
Courtesy: Walter
5
Relations between machine tool user and producer
machine tool user
machine tool producer
workpiece
cutting tool and
machine tool
size, material,
technological operations
surface quality,
accuracy, productivity
stiffness, accuracy,
performance
price of the workpiece
machine tool price,
running costs
acceptable market price
point of success of the
whole production chain
6
Complexity of development of a new machine tool
inputs:
workpiece spectrum
machine tool concept
modern optimization methods
can support the decision-making
process within the beginning
development phase of a new
machine tool, where there is a
low level of information on the
machine tool
machine tool design
variables:
machine structure and size
technology requirements
(power, speed, force)
structural material
modular structural parts
other customer requirements
(max. feed, energy
consump.)
concept/proposal of drives
price limit of the machine
proposal of linear
and rotary joints
machine tool development process
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Integrated development approach
Design input data:
machine kinematics, axis strokes, max. dimensions, material information
Task
definition
Conceptual
topology
optimization
Topology
optimization
First design
proposal
Parametric
optimization
Final design
check
Functional demands:
static stiffness, modal properties, dynamic stiffness, feed drive pass bands
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Case study 1: The machine tool optimal kinematics
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case study: decision making in case of the machine tool optimal kinematics
task requirements:
– five axis milling machine tool with a table diameter of 1,600 mm
– solution for low mass and high stiffness
two different kinematic structures:
– type A: a bridge-type machine with a vertical movable ram and movable table
– type B: a one-column-type machine with a horizontal ram and movable table
Type A
Type B
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The conceptual topologic optimization
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a simplified variation of a topologic optimization
all structural parts have a virtual density of ρ∈<0,1>
the real density and Young’s modulus are proportional to the virtual density
the goal is to predict the influence of every structural part on the final static stiffness
the main result is information about the mass of the material needed for reaching the
specific stiffness
the results are presented in the correlation matrices and the paretofront of output
dependence
Stiffness [N/mm]
optimal solutions
non-optimal
solutions
Structural mass [ton]
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Boundary conditions
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fixation of the columns to the ground
input forces in x, y, z directions in tool center point
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Parametric FE model
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five geometrical parameters were defined for dimensional variation of the structure
one parameter of virtual density and Young’s modulus
Increased column
width in the X
direction – p1x
D = <0, 1500> mm
Increased column
width in the Y
direction – p3y
D = <0, 1500> mm
Increased cross
beam width in the X
direction – p2x
D = <0, 1000> mm
Increased cross
beam width in the Y
direction – p4y
D = <0, 1000> mm
Increased cross
beam width in the
Z direction – p5z
D = <0, 500> mm
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Results for variant A
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Stiffness [N/mm]
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the paretofront consists of all optimal variants
effective mass range <8 t, 20 t> for maximizing of
stiffness in the X and Y direction
effective mass range <8 t, 30 t> for maximizing of
stiffness in the Z direction
increasing of total structural mass over 25 tons
does not increase the static stiffness significantly
Z
Structural mass [ton]
Y
X
Stiffness [N/mm]
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Structural mass [ton]
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Results for variant B
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the paretofront consists of all optimal variants
effective mass range <10 t, 30 t> for maximizing of
stiffness in the Y and Z direction
effective mass range <8 t, 30 t> for maximizing of
stiffness in the X direction
Z
Y
Stiffness [N/mm]
Stiffness [N/mm]
X
Structural mass [ton]
Structural mass [ton]
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Summary: comparison of variants
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comparison of machines with total
weight of 15 tons: type B has higher
stiffness and lower movement mass
the conceptual topology
optimization can support the key
decision about the machine concept
before the development process of
the machine tool starts
Z
Y
X
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Case study 2: top structure of a milling machine
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case study: design modification of top structure (cross beam, cross slide, ram) of
a portal milling machine
existing machine:
– cast structure of the cross beam, cross slide and ram
– the maximal clearance between columns is 5600 mm
task requirements:
– structural design for increased column clearance up to 9100 mm
– minimizing of the mass, similar static stiffness also for higher clearance
– design for modular casting technology
– interfaces with the column should not be modified
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Design space and boundary conditions
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design space defined by the cross section of an existing cross beam
loading with own weight and with forces in X and Y direction
observed results: movement in the X and Y direction, rotation in the Y direction
deformation
due to own weight
Dx
Fy
Dy
rotY
Fx
static deformation in X
direction
Dx
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Topological optimization
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finding of optimal material distribution inside the narrowest version (with the smallest
clearance) of the cross beam in order to find the most important structural features
main results: solid peripheral walls + latticework structure inside the cross beam and
also cross slide
solid peripheral walls
internal lattice work
structure
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Parametric model of the design proposal
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parametric optimization computes properties of various parametric models
the result is a paretofront of the optimal dimensional shape (including wall and rib
thicknesses) of the model variant (cross beam, cross slide and ram)
parametric optimization of the narrowest version in order to find the optimal
structure dimensions
X deformation [um]
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various optimal results
mass [kg]
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Modular design & thickness optimization
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modular design using the modular
casting technology (mould model
consists of specific segments)
a new parametric model has been
prepared with respect to additional
segments for the cross beam
prolongation
the length and the structure of the
model changes with the addition of
specific segments
+2,5 m
+2 m
+1,5 m
+1 m
+0,5 m
basic version
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Thickness optimization
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thickness optimization is a specific parametric optimization method
optimization of wall thickness over all the size variants
technological limits: wall thickness from 12 mm up to 55 mm
criteria: mass under 12 tons, maximized stiffness and eigenfrequencies
– the narrowest version is used as a reference version
min max
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𝑢𝑥
𝑢𝑦 𝑓𝑟𝑟𝑒𝑓
,
,
𝑢𝑥𝑟𝑒𝑓 𝑢𝑦𝑟𝑒𝑓 𝑓𝑟
the optimal results are on the border of the group of all solutions
selection of the final version depends on priorities of the machine tool builder
Z
Y
X
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Summary and conclusion of the case study
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a combination of topologic and parametric optimization is a strong tool for finding
of the optimal machine tool design with minimized structural material volume
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the method is applicable for modular design of parts for a combined optimization
through structural parts shape and a through the size variants
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mass reduction potential on typical machine tool structures is 10-40%
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Conclusions
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the machine tool development process is a complex task
– many inputs and requirements should be taken into account and evaluated in
relation with each other
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modern optimization methods can support decision making during the whole machine
tool development process
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an integral approach should be used – a proper combination of topologic and
parametric optimization shows big potential for structural mass reduction
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design & optimization chain can be configured for every specific task
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application of the mentioned methodology shows big potential for the design of new
high performance machine tools with respect to the technological and market
challenges
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Thank you for your attention
Dr. Petr Kolar
Dr. Matej Sulitka
Jaroslav Šindler
collaborative projects
head of simulation group
advanced FEM specialist
E: [email protected]
E: [email protected]
E: [email protected]
www.rcmt.cvut.cz