Class A Carbon Fibre Reinforced Plastic (CFRP) Body Panels on

The MG Rover SV

SPE 2003

Class A CFRP on a OEM Supercar

Customer requirements

Manufacturing solution for 250 units per year

Design freedom to develop a visually striking car

Low body weight to aid performance

Class A finish for vehicle life

Short lead time from concept to production

Design flexibility / niche production volumes

Design factors lead to a carbon fibre reinforced plastic (CFRP) solution Allows for a faster prototyping cycle while maintaining realistic development costs

The car consists of 32 composite components that vary in both size and complexity

Design flexibility / niche production volumes

Prototype phase was to last 5 months and produce a full set of male masters, a full set of female production tools and the first 5 prototype car sets

Nov 2002 – Car Unveiled at the British motor show

Dec 2002 – Orders placed to machine male masters

Jan 2002 – Tooling manufactured

Feb 2002 – Composite layup designs generated

March 2002 – First car set delivered

April 2002 – Cars sets delivered 2-5

The budget assigned to complete this phase was approximately $1.5m

History of lightweight CFRP in automotive (light, stiff, strong)

CFRP prepreg application

Tool Face

Carbon Prepreg (280g 4x4 Twill)Glue Film

Honeycomb Core

Advantages Extremely light weight High Stiffness High Strength Short Lead Time Cost effective tooling for limited No. parts

Disadvantages Limited cycle time due to labour intensive process

Premium material costs Expensive autoclave curing Surface needs significant work to achieve Class A

Attributes of CFRP prepreg

Material developments

Breathable Prepregs

Dry fibres extract air from laminate prior to curing

Eliminates the need for debulks, autoclave and allows for multiple plies to be laid up at once

Faster lay-up due to heavier more frequent plies

A single ply material capable of a CPT from 0.04” > 0.1” Designed to have a Tg1 > 260oF for stability in high

ambient temps Process can be adapted for different fibre architecture Syntactic core is currently manufactured at 0.04” and 0.03” Minimise weight/ maximise stiffness by increasing

thickness remove fibre from neutral axis,replace with low density resin

Car Body Sheet (CBS)

Woven Carbon

& Epoxy Skins

Low density

syntactic core

SPRINT CBS micrograph

0.011”

0.011”

0.04”

Advantages Combination of fibre and syntactic resin provides a

laminate that weighs 20% of steel (0.04”) for equivalent stiffness

Or weighs 35% (0.06”) of aluminium for equivalent stiffness

Dry fabrics aids air evacuation, typically void content 0 – 0.5 %

Zero bleed process therefore possible to accurately control component tolerances +/- 0.005”

Attributes

Issues effecting Class A

Pin holes caused by entrapped air, leads to surface defect

Surface Void Primer LayerColour Coat

Will require rework before repainting

Issues effecting Class A

Fibre read through caused by different CTE of resin system and fibre

Hard to conceal with a paint process Typically remerges with time/temperature/humidity

Issues effecting Class A

Mould Quality – Components ultimately reflect the tools from which they were removed

Air entrapment is eliminated by fine fibre structure sandwiching a catalysed resin film, on curing this forms a homogeneous surface layer

Class A surface films

The resin system is engineered with a Tg in excess of 260oF and additives to reduce the CTE

(Carbon 3 x 10–6/oC , Epoxy 70 x 10 –6/oC, SF 30 x 10 –6/oC )

The fabric used is a specially selected thermoplastic to ensure its mechanical properties does not distort the surface resin layer in service. (Low Modulus)

Finely woven thermoplastic

Resin Matrix has Tg > 260oF

Resin is formulated with

easy sand fillers to aid prep.

Woven Carbon

& Epoxy Skins

Low density

syntactic core

Class A surface film

Class A surface film

BlisteringPanel Primer Initial 240h hum. Initial 240h hum. Initial 240h hum. 240h hum.

SP CBS 830R 88,9 88,3 Gt 0 Gt 0 10 9 fewhigh build 87,2 86,2 Gt 0 Gt 0 10 10 microhigh build+flex 86,4 85,3 Gt 0 Gt 0 10 10 none

Competitor Y

830R 88,6 88,5 Gt 0 Gt 0 10 10 few high build 86,9 85,9 Gt 0 Gt 0 10 10 nonehigh build+flex 87,3 85,8 Gt 0 Gt 0 10 10 none

Competitor Z

830R 87,5 87,8 Gt 0 Gt 0 9 9 fewhigh build 87,1 85,1 Gt 0 Gt 0 9 9 nonehigh build+flex 86,6 85,2 Gt 0 Gt 0 9 10 none

Gloss Adhesion (#) Adhesion (X)

Class A surface film

ChipPanel Primer Initial 240h hum. Temp. cycle - 4°F

Fibre read through

SP CBS 830R slight slight slight Gr 2high build slight slight slight Gr 1high build+flex OK OK OK Gr 1

Competitor Y

830R moderate moderate severe Gr 2high build moderate moderate severe Gr 1high build+flex moderate severe severe Gr 2

Competitor Z

830R moderate severe moderate Gr 3high build moderate severe moderate Gr 2high build+flex moderate severe moderate Gr 2

Class A panels under Defracto analysis

Typical Component

Thin aerofoil requires increased stiffness through addition of syntactic cores

Indicator cut out, syntactic core must be removed

Mounting point on perimeter of part requires reinforcement

Meeting productivity

Still a manual process dependent of operators with some composite experience Productivity is a function of the number of components fabricated in tool over a period of time Minimise manual operations both in and out of the tool, decrease cost and increase productivity

Pre kit materials to form just one structural ply

Meeting productivity

Kits are delivered to the customer with surface film and CBS ready for application.

The prototyping phase was completed on time with the first 5 test vehicles produced within the 5 month cycle within budget

With in the next 2 months a further 10 production prototypes were produced

Currently from 1 tool set and a single shift production stands at 5 car sets a week (250 units per annum)

Paint lines are reporting a 80% increase on productivity over previous composite vehicle

Current programs are based around manufacturing 3000 parts per annum

Summary