Autobody panels by using PU-Compositeswairco.org/IJCMCE/December2013Paper229.pdfLF I moulding has just two process steps. The first step takes place in the mixing head. Glass- fibre

International Journal of Conceptions on Mechanical and Civil Engineering Vol. 1, Issue. 1, Dec’ 2013; ISSN: 2357 – 2760

121 | 1 3 3

Autobody panels by using PU-Composites C Sivakandhan

Dept. of Mechanical Engineering, Karpagam University,

Coimbatore, India. [email protected]

P Deepak Sharma Dept. of Mechanical Engineering,

P M C Tech. Engg. College, Hosur, India.

[email protected]

P Sureshprabhu Dean, Dept. of Mechanical Engineering,

United Institute of Technology, Coimbatore, India.

J Dinesh Dept. of Industrial Engineering & Management,

Bangalore Institute of Technology, Bangalore, India.

[email protected]

Abstract— Steel plays a vital role in making most of the auto components like auto-body panels, doors, etc.,. But the invention of composites had created a revolution in the field of engineering especially in the application of making components with composites instead of using metals like steel. The present work is the idea of making auto-body panels with PU-composites These composites are lighter in weight but have good mechanical properties. Hence these composites will increase the “Power to Weight ratio” and also increase the fuel efficiency of the vehicle.

Keywords- PU- Composites, increased strength to weight ratio,low mould cost, increased PTW ratio, High strength and stiffness ratio.

I. INTRODUCTION “Composite Materials”, are a new emerging class of

materials to overcome the current limits of monolithic conventional materials. Here we are having another innovation (i.e) making the body panel of automobile with PU-Composite instead of using steel. This will gradually reduces the weight of the body frame but have better mechanical properties in comparison with steel.

Composites

Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct within the finished structure.

A common example of a composite would be disc brake pad which consists of Hard ceramic materials embedded in soft metal matrix. Another example is found in shower stalls, bath tubs, which are made of fibre galss. Imitation granites, cultured marble sinks and countertops are widely used. The most advanced example peform routinely on spacecraft in demanding environments.

PUR-COMPOSITES

PUR (PolyUrethane) composites are produced with rigid thermoset resins, as opposed to elastomeric or thermoplastic polyurethane (TPU). “Composites manufactured from these PU resins have superior tensile strength, impact resistance, and abrasion resistance compared with composites based on unsaturated polyester and vinyl ester resins. These composites cites typical values for tensile modulus around 430,000 psi, tensile strength of about 12,500 psi, and elongation to failure of over 7.5%. These PUR-composites can give weight reduction of about 20% than steel.

The polyurethane composites are reinforced with glass flakes. These glass flakes are held together by binder which are commonly plastic resins.

FIBRES

Fiberglass properties vary somewhat according to the type of glass used. However, glass in general has several well–known properties that contribute to its great usefulness as a reinforcing agent. The advantages of the glass fibres are that they are available at low cost, they are corrosion-resistant..

Fig 1.1. Honey comb Structure

Preparation

The composites for the autobody panels are prepared by LFI-process (Long Fibre Injection).The process is followed

International Journal of Conceptions on Mechanical and Civil Engineering Vol. 1, Issue. 1, Dec’ 2013; ISSN: 2357 – 2760

122 | 1 3 3

by injects glass fibres and polyurethanes into a open mould in a single working process.

These composites are also termed as high density composites which contains more glass fibres than in the traditional matrix materials. These composites will have glass content of about 38% and are having tensile strength and impact resistance.

LFI-Process LF I moulding has just two process steps. The first step takes place in the mixing head. Glass- fibre from a roving is chopped, the PU R compo- nents are mixed, the fibres are wetted and the mix is poured into the open mould. The second process is post-mould processing. Table 1.1.Composition & Characteristics

Process LFI-FIBERIM Glass-Length (mm) 12.5/25

Specific Gravity 1.3 Percent Glass 38

Tensile Strength(MPa) 298 The special characteristics of these composites is that they are having good finished and gloss surface. A paint layer is sprayed directly on to the mould. A spray mixing head then sprays a barrier coat on top of the paint. The LFI is poured into the mould, the mould is closed and clamped. The pressing step is final stage in producing high strength, fibre-reinforced part with high glossed surface.

Processing Materials processed in LFI moulding are polyure- thanes

(PUR) and glass, carbon, sisal or flax fibres. Fibre length can be 12 – 100 mm. A typical applica- tion is the production of instrument panel substrates and other parts for automotive interiors.

LFI-PUR Process

The glass fibre rovings are chopped to a set length in a chopper immediately upstream of the mixing head. They are wetted with PUR reaction system in the mixing head. The mix is discharged into the open mould, the mould closes and the part is shaped under pressure, causing the fibres and the PUR matrix to bond into a high-strength composite. Characteristics of LFI parts are high strength are high strength and low thermal expansion. Fibre length and concentrations can be varied during pouring to locate strength and stiffness as required, by adjusting fibre

concentrations/Fibre length. The parts will be moulded by Reinforced Reaction Injection Moulding method (RRIM).

REINFORCED REACTION INJECTION MOULDING(RRIM) The term RRIM, designates the process when granular, flake or fibre additives(fillers) are incorporated to modify the properties of Polyurethane.

A. Metering and Mixing Technology

The two primary components (Polyol & Polyisocyanate) are transferred from storage tanks to working vessels called feed tanks. Often strictly when two-component systems are processed (i.e) all additives such as activators, stabilizers, flame retardants, pigments that are essential for the reaction are already contained in the two primary components. It is also possible to have premix stations inject the additives directly into the lines connected to the meeting pumps convey the components in exact ratios from the feed tanks to the mix-head. The mixture is then discharged from the mixhead into either an open mould or into cavity of a closed mould along with glass fibre rovings.

Fig 1.2. Piston type mixing head

a.Impingemnt mixer b.Control & cleaning piston

c.Injection Nozzle d.Mixing Chamber

e.Discharge channel f.Discharge cleaning piston

g.Throttle adjusting mechanism

h.Throttle

International Journal of Conceptions on Mechanical and Civil Engineering Vol. 1, Issue. 1, Dec’ 2013; ISSN: 2357 – 2760

123 | 1 3 3

B. Mix Head The mix heads in the RRIM can accomodte fibres of length 0.1 to 0.2 mm. But for processing long fibres a special type of mix head is attached to the moulding machine. This L-type mixing head will process glass fibres of lengths upto 100mm. Thus this mixing head will provide long continuous fibres for the moulding of components. Fig 1.3. Mix head for Long fibres (L-Type) Manufactutrer (Krauss Maffei) Right: Sectioned 3-D CAD model

Left:

a: impingement mixer

b: control and cleaning piston

c: injection nozzles

d: Mixing chamber

e: discharge channel

f: discharge cleaning piston

g: mechanism for adjusting annular (ring) channel

h: coaxial sleeve Advantages

Higher strength

Low weight to strength ratio

Partially automated

No hazardous chemical exposure to environment and labour

Improved productivity(20 parts/hour) machine

Low tool cost

Parts integration

Finished part manufacturing

Both side finish

Fully automation possible

Applications

Due to its high gloss and good surface finish, it is used to make,

Tractor Baoonets

Automotive Interiors

Panel Substrates

Door Panels

Dash Board of automotives

Fig 1.4. Panel substrates made of LFI.

International Journal of Conceptions on Mechanical and Civil Engineering Vol. 1, Issue. 1, Dec’ 2013; ISSN: 2357 – 2760

124 | 1 3 3

Left : Body panel Substrate Right : Tractor Bonnet

Conventional Materials The materials now used for making autobody panel is nothing but steels i.e., plain carbon steel with carbon content upto 0.2 %. Steel vs LFI Table 1.2. Physical Propeties

Properties Steel LFI

Tensile Strength MPa 350 298

Thermal Expansion 10-6K-1 11.7 4.5

Thermal Conductivity Jm-1K-1 50 17.5

Impact strength J 170 155

% Elongation 30 4-5

Plain Carbon Steels Carbon Steel is by far the most widely used kind of steel. The properties of carbon steel depends primarily on the amount of carbon it contains. Most carbon steels contain carbon upto 1 %. Carbon Steel is made into wide range of products including structural beams, car bodies, kitchen appliances, cans etc. Steel containing carbon upto 0.2 % are called as mild steel and are used for making bodies of most of the automotives in the world. It has good mechanical and as well as chemical properties.

II. CONCLUSION Thus the LFI moulds will have good mechanical

properties in comparison with steel. Also LFI moulds provides 20% reduction in weight of the component made of steel. Thus the LFI will be a good choice for making auto body panels and reduces the weight of the vehicle.

REFERENCES [1] O.P.Khanna. “Engineering materials and metallurgy” [2] Krauss maffei- People for plastics, “kraussmaffei.com” [3] Krauss Maffei, “The process for high quality long fibre glass reinforced

Polyurethane parts”. [4] Prof.J.S.Calton, “ME4210: Manufacturig process and Engineering”. [5] Owens Corning , “ME1020: Roving designed for LFI operations”. [6] Bayer Material Science, Polyurethane Information.