Automated Preforming of Carbon-Fibre Reinforcements for Automotive Composite Components

Automated Preforming of Carbon-Fibre Reinforcements with Active
Forming Manipulation for the Manufacturing of Complex Shaped
Composite Components
Dr. Farbod Nezami, CIKONI

Source: Airbus, Boeing, ETZ, Daimler
Automotive Composite Forming:
Reliable, fast, effective, but…
Geometry
Process
• Complex shaped geometries
• Small sectioned parts
• Packaging- & design demands
What to do about
quality?
• High lot size
• Cost sensible
Fast forming
processes
How can we improve the quality of preforms with an holistic quality approach?
1. Parts free of wrinkles and reduction of fiber distortions (“waviness”)
2. Influencing of fiber orientation and shear angles

Resin Transfer Moulding (RTM):
High Volume Manufacturing in the Automotive Industry
Forming
Mechanisms
Fibre Movement
Shearing
Bending
Layers Gliding
Reinforcement
Cutting &
Stacking
Preforming Infiltration Cutting
Handling • Draping
Handling Handling
• Bonding of
Layers
Source: Daimler AG, Krauss Maffei

Sources: www.mercedes-benz.de
Quality Issues and Defects in Forming of Complex Geometries:
Wrinkles and Fiber Waviness
Fiber
Waviness
Complex double curved areas
Wrinkles
Fiber Waviness and wrinkles are the most occurring defects in composite forming and cause high rejection rates

State of the Art (Selection) und Shortcomings:
Forming Manipulation Systems during Draping
Principle
BMW AG, 2000 BMW AG, 2011 Daimler AG, 2001
Segmented
blank holders
Spötzl, 2003
Draw bead Vacuum fixation Pressure tube
Ply specific?
Method?
Initiation of
tensile forces
Initiation of
tensile forces
Initiation of
tensile forces
Initiation of
tensile forces
• Use of clamping / tensile forces / membrane tensions
• No consideration of layered character of preforms yet
Development Goals:
1. Development of methods of application for forming manipulation systems
2. Implementation of methods in active, ply specific and localized forming manipulation systems

Studies
Fundamentals
Approach: Increase of Forming Complexity
From Fundamentals to an Automotive Application
Forming behavior of single
ply under tension
Full scale automated preforming of automotive components
Optimization of process
parameters
Characterization of
interactions
T, t, F
Which causal loops will lead to defects? Which measures are necessary?
Preforming with increasing complexity
Isolation of complex shape
Transformation of methods
Transformation of methods

Material characterization with process induced factors:
Shear-Tension Coupling
A
B
Membrane tension
No wrinkles at 55°
Tension free
Wrinkles at 55°

Forming manipulation of woven fabrics:
Possibilities and Limits
1 2 3 4
• Homogeneous membrane tensions will lead to symmetric draw-in of fabrics
• Wrinkles can be suppressed efficiently
• Asymmetric membrane tensions allow control of material draw in and influence of fiber orientation
• Limited possible discretization due to fabric‘s architecture
• Further possibilities are given by process controlled tensioning

Draping of Multilayer Preforms:
Influence of ply orientation
Multilayer without blank holders
Single ply with blank holders
• Relative displacements due to superposition of divergent local forming mechanisms of fabrics will increase the risk of in-plane forming
defects
• Despite same ply-orientation small radii increase friction and lead to interaction based forming failures
• Blank holders won‘t allow ply specific manipulation
• Contrary demand for suppression of wrinkles and fiber distortions

Definition of a Forming Limit Diagram for Interaction Defects
Acting forces
Integrity against damage
• Damage is a complex interplay of structural integrity of reinforcement and acting forces
• A constellation-dependant damage diagram was derived for discription of in-plane damaging inition
• Normal pressure is dominant driver of in-plane damage
→ Reduction of normal forces necessary

Recent developments in prediction of fiber waviness
The first chapter of the approach showed us that:
– There is an interlink between tension (process) and wrinkling (textile)
– There is an interaction of layers towards each other which can cause fiber waviness
– Both factors can be described by physical characterization experiments
Fine, but what can we do in process development?

Decoupling of fabrics' interaction under blank holders:
Passive interlayers to reduce friction between layers
Decoupling of interaction under blank holders
Opening
Fabric
Metallic interlayer
Stacking
Opening for male
tools
Geometry matched forming manipulation (here for 0°)
Direct interplay of
fiber orientation and
damage initiation

Integration of piezo actuators for quality improvements:
From passive to active manipulation "Tailored Drape"
Blank holder utilization with metallic interlayer
Material draw-in only controllable globally
No discrete manipulation of single ply possible
Limited manipulation of fiber orientation possible
Demanding draping simulation due to variable friction coefficients
Prevention of interaction based defects under blank holders
Interaction based defects inside the cavity
Taken measure: Integration of piezo bending actuators
Piezo bending actuators
Oscillations to reduce friction
Tension initiation to eliminate wrinkles

Transfer of principle to active interlayers for friction reduction
and ply specific tensioning
Mechanical actuators
Reduction of interaction force and fiber
waviness by oscillations
Reduction of wrinkling due to local application
of tensile forces

Active interlayers:
Selection of effects on forming quality
Clamping with
mechanical
actuators
Prevents wrinkles
Manipulation of fiber orientation
possible
Ply-specific clamping achieved
Higher clamping force
necessary
Draw-in
Reference
without interlayer
„Tailored Drape“
result
Reduction of friction
between plies
by oscillations
Damaged
Improved Quality

Application: Mercedes-Benz AMG Backlid
Transfer to
active interlayers
Multilayer draping with active
interlayers
Cut-out optimization and ply
Orientation clamping0°
Cut / Dart
Clamping
Clamping
Piezo actuators
for oscillations
0/90° top layer
•
Homogenous
Reduction
Blank
of
Holder
the size
Force
of
wrinkles by 81,5%
• Complete suppression
of interaction based
defects
Orientation 45°
Different material
draw-in and
clamping
necessary!
Ply-specific clamping

Process integration, challenges and benefits:
Easy Automation and Fast Cycle Times
Shown here: passive system
without oscillations

Conclusions
• To increase quality of parts being produced by composite forming an holistic approach is necessary
as interlinks of domains drive overall quality
• Early stage material characterization can help to identify dominant quality drivers
• In preforming it was found that wrinkles can be suppressed by local tensioning, but risk of
interaction defects like fiber waviness can increase hereby. Therefore reduction of normal contact
forces is necessary.
• This was realized by the utilization of active interlayers which can actively control tensioning and
reduce interlayer friction by oscillations
• The approach can be easily automated and it can be integrated into existing hydraulic presses
• Automation for smaller lot sizes of up to 5000 parts/year shown as feasible