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 Tg 1 > 260 o F 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” 0.04”

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 +/ ” Attributes

Issues effecting Class A Pin holes caused by entrapped air, leads to surface defect Surface Void Primer Layer Colour 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 260 o F and additives to reduce the CTE (Carbon 3 x 10 –6 / o C, Epoxy 70 x 10 –6 / o C, SF 30 x 10 –6 / o C ) 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 > 260 o F 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 Chip PanelPrimerInitial240h hum.Temp. cycle - 4°F Fibre read through SP CBS830Rslight Gr 2 high buildslight Gr 1 high build+flexOK Gr 1 Competitor Y 830Rmoderate severeGr 2 high buildmoderate severeGr 1 high build+flexmoderatesevere Gr 2 Competitor Z 830RmoderateseveremoderateGr 3 high buildmoderateseveremoderateGr 2 high build+flexmoderateseveremoderateGr 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