Low Carbon Vehicle Technology Project
(LCVTP)
WS 7 Lightweight Structures - Technology Review
November 17th 2011
Geraint Williams
WMG
Materials and process development for
structural applications.
M W Pharaoh
Contents
 Introduction
 Concept process outline
 Stacking of UD layers
 Tool design considerations
 Carriers and surface finish
 Part quality
 Costing
 Future processing developments
 Conclusions
Introduction
 Requirements
> Fit into presently existing supply chain and manufacturing route as this
will need less investment.
> This means:
 Stamping of shapes – “black metal, not black art”
 Adhesives and fixings.
 Engineering polymers – PBT/PET, PA6:6, PA6 – focus PA6
> The glass dominates the properties.
 Primary reinforcement – UD Glass as stacked UD layers
 Ribbed structure support – random glass.
Introduction - Scope
• Multiple seats and beams made to compare the performance.
> approx200 beams
> Steel DP600
> Al 5754
> Hybrid Comp/Al
> All Comp
> Carbon Comp
> Hybrid Comp:
Aligned / random
> approx 50 seats
Engineering
Polymers
Focus has been on PA6. All the tooling, testing and modelling is
applicable to any of the engineering polymers. This will allow
tailoring for environmental / temperature effects.
Material
Melting Point / C
Use temp/C
PolyPropylene / glass
165
90
1.48
PolyAmide 6/ glass
220
120
1.6
/ 225
110
1.54
PPS Poly(p-Phenylene Sulfide) /
glass
280
220
30
1.55
PEEK / carbon
390
250
50
1.57
PBT(PolyButylene terephthalate)
glass
Approx Cost. £/kg Density
.
g/cm3
Stacked UD layers
 Fine tailoring of
properties
to specific directions
gives
best efficiency: tension,
flexure and crush.
 Balanced and
Symmetric
lay-ups.
Layers shown neither balanced or
Symmetric!
Concept Process
Outline
1. UDtapesupply
a) → → cut each piece to basic shape
2. Stack tapes
a. → layers spot tacked using a soldering iron.
b. → Trim as stacked blank or preconsolidate and trim.
3. Melt matrix → Melt matrix → just above melting point
a) → stack wrapped in carrier to ease handling and create surface → stack wrapped in
carrier to ease handling and create surface
4. Transfer → Transfer → manually in about 15s
5. Press and Cool → Press and Cool → rapid cooling in tool, about 45s
6. Remove
7. Trim to shape → mechanical, water-jet or laser Trim to shape → mechanical, waterjet or laser
Stacking of UD layers
 Presently the layers are stacked and tacked manually.
 Cut to different lengths depending on ply angle
 “spot welded” together using a soldering iron.
 This is the slowest of the processes used; 1 person can
S&T about 5-8kg per hour.
> But there are concepts to automate.
Fibre Angles
0° - glass direction.
45°
90°
3 layer laminate.
Glass directions,
0/90/0
UD lay-ups
1
1
2
1
3
1
4
1
5
1
6
1
7
1
8
Seat lay-up for initial prototype pieces.
This lay-up was the product of multiple
runs in DYNA.
1
9
1
10
1
11
1
12
1
13
1
14
1
15
1
16
1
17
1
18
1
0deg
90deg
67.5
-67.5
The top-hat used a 0/90 balanced symmetric 11 layer structure:
0/90/90/0/0/90/0/0/90/90/0
Tool Design
 Relatively simple design to test tooling concepts
 Using design pointers from metal press
tooling
> Sprung edges / centres
> Draw beads
 Metaltools
 Oil heating capability, can heat up to 180°C
 Twotools made
> Top hat section: 450mm x 110mm
> Seat back: 850mm x 650mm
Top-hat section parts
Metals, composite laminate: with
closure plate.
Composite hybrid: integral flowformed ribs
Top-hat Finishing
 Closure plate, vacuum bagged – due to availability of flat press tool.
 Top-hat and plate water jet cut to shape
 Adhesive + self pierce riveted to hold box together
 Adhesive cured at 150°C
 More detail in joining section.
Seat back parts
 Centre sprung effectively
creating a 2 stage process.
 Also holds the part in place.
 Finished composite weight
approx 3.5kg.
Carriers and Surface
Finish
 These have been used to aid manual handling of the molten laminate.
 They need a melting point above matrix of composite.
 Also have the effect of changing the surface finish of the parts.
 2 types used. Both are borrowed from thermoset processes:
> PVF bleed fabric. Creates a glossy surface with long wave ripples.
> PA6:6 peel ply. Creates a fine textured matt surface. Produces a very
good surface for adhesive bonding.
 In a more automated process with robotic handling a carrier maybe
unnecessary.
Molten Laminate with Carrier
Large flatbed heater,
2m x 1m allows
multiple stacks to be
heated concurrently.
Simple trials have
given a cycle time of
3 mins with minimal
effort with top-hat
tool.
Metallic Parts
 Dedicated press tools for both:
> Aluminium 5754
> Steel DP600
 Press formed at Premier Sheet Metal
> Crash formed
 For consistency these parts were also adhesively bonded and self pierced
together.
 The same rivets were used in all parts.
Part Quality
 There are several aspects to part quality that need to be considered:
> Spring back / Spring-in
> Porosity
 Studied this using both ultrasound and CT. Both have been effective in
showing the presence of internal flaws.
> “Earing” in metal terminology.
 This is due to the part shape, double curvature, and is similar to that
expected in metalics.
 Drape has not been closely examine, but the stacked UD layers or able to
move over each other easily when molten.
Flaws:
Springin
 Parts show good
stability after moulding
above the melt temperature.
 Typically varies with tool
temperature, higher tool
temperature creates more
springing.
 Typically 1°to 3°
depending on tool
temperature.
Tool shape
Moulded Part
Springback
Springin
Flaws:
Ripples?
 Due to double
curvature.
 Reduced /
removed
by reducing transfer
time and increasing
pressure, up to
4MPa.
Costing
Approximation
 Factors affecting cost:
> Tooling cost.
 Simple tooling and low wear reduces cost
> Material cost
 Greater than steel and aluminium
> Cycle time
 Short cycle times 60– 90s key to keep cost down
> Trimming and finishing
 Conclusion
> Cost competitive up to 50k – 70k units
Future Developments Processing
• The processing work has highlighted several key areas what will take the
concepts to full volume production runs. These are:
> Automation of the stacking and tacking
> Improved understanding of the forming limits
> Automation of transfer – although manual transfer is very quick!
Conclusion
 Stamp forming of stacked UD aligned fibre (glass and carbon) composites
with an engineering polymer (PA6, PBT, PA66) matrix.
 Rapid in-tool cycle time - <60s
 Good part complexity and quality
 Large part size – up to 4kg and 1m x 0.80m dimension. Larger parts
capable,
up to 6kg and 1.5m x 1m.
 Costing results suggest that potential cost competiveness if cycle time can
be kept low.
END