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Latest Trend for Auto Exterior Application: Polypropylene Solution for Thin Wall Design Arjun Jindal Machino Polymers Limited Introduction The first decade of the new millennium has seen a rapid growth of usage of plastics in the automotive industry. In Fig 1 is shown a trend of global plastics usage in automotives beginning since 1970. The year wise trend suggests a steady growth and there is a considerable change since 2006 and the trend predicted a dramatic jump by the year 2015.

Fig. 1: Year wise global trend of usage of plastics in automotives. [1] The increase in popularity of plastics in automotives is attributed primarily out the factors that are summarized as: Greater flexibility in terms of design, lightweight, offering fuel efficiency and several other excellent properties are stimulating the use of plastics in automotive parts. Buoyed by the rapidly growing high temperature plastics and lucrative long fiber and short fiber reinforced thermoplastics, automotive plastics are projected to increase its applications replacing steel and glass in automotive industry. Automakers today aim for manufacturing lighter vehicles and contribute to optimum fuel consumption. Plastics have emerged as a means for reducing the car weight and achieving fuel efficiency. Properties such as corrosion resistance, lightweight, durability, resiliency and

toughness have spurred use of plastics in automotive parts such as fenders, doors, and bumpers [2] There are some other attributes also play their role. Polymers have very distinct characteristics, but all have things in common. They are resistant to harsh chemicals; provide both thermal and electrical insulation; offer good noise, vibration, and harshness (NVH) characteristics; offer design flexibility; have an excellent strength to mass ratio; and offer a variety of production options. They can be molded into the body of a car, or mixed with solvents to become an adhesive or paint. Elastomers and some plastics are very flexible. Other polymers can be foamed, like PS and urethane. Polymers seem to have an unlimited range of characteristics and colors, with inherent properties that can be enhanced by a wide range of additives to broaden their uses [3]. Changes in Automotive Norms Since last couple of years the norms related to automotives have been changed markedly. The norms associated to automotives are broadly classified as safety related norms, interior emission norms and exterior emission norms. The later two are directly related to environmental standards. As the legislations related to environment getting stronger day by day, so is following automotive emission regulations. In the context of this article we feel to provide a brief outline of each of the norms. Interested reader may refer to many a number of articles available on line or in journals or monographs [4-7]. Automobile safety is the study and practice of vehicle design, construction, and equipment to minimize the occurrence and consequences of automobile accidents. (Road traffic safety more broadly includes roadway design.) Active and passive safety systems and accessories: The terms "active" and "passive" are simple but important terms in the world of automotive safety. "Active safety" is used to refer to technology assisting in the prevention of a crash and "passive safety" to components of the vehicle (primarily airbags, seatbelts and the physical structure of the vehicle) that help to protect occupants during a crash Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles (motor cars) and other powered vehicles but they can also regulate emissions from industry, power plants, small equipment such as lawn mowers and diesel generators. Frequent policy alternatives to emissions standards are technology standards (which mandate Standards generally regulate the emissions of nitrogen oxides (NOx), sulfur oxides, particulate matter (PM) or soot, carbon monoxide (CO), or volatile hydrocarbons. An emission performance standard is a limit that sets thresholds above which a different type of emission control technology might be needed. While emission performance standards have been used to dictate limits for conventional pollutants such as oxides of nitrogen and oxides of sulfur (NOx and SOx),[1] this regulatory technique may be used to regulate greenhouse gasses, particularly carbon

dioxide (CO2). In the US, this is given in pounds of carbon dioxide per megawatt-hour (lbs. CO2/MWhr), and kilograms CO2/MWhr elsewhere in the world. In addition the interior emission norms give importance on fogging index, volatile organic compound emission, stickiness on parts and odor behavior of interior automotive plastic parts. Volatile organic compounds (VOC) refer to organic chemical compounds which have significant vapor pressures and which can affect the environment and human health. VOC are numerous, varied, and ubiquitous. Although VOC include both man-made and naturally occurring chemical compounds, it is the anthropogenic VOC that are regulated, especially for indoors where concentrations can be highest. VOC are typically not acutely toxic but have chronic effects. Because the concentrations are usually low and the symptoms slow to develop, analysis of VOC and their effects is a demanding area. To meet the ever challenging emission related legislations automotive manufacturers relentlessly trying for alternate materials for making the vehicle lighter thus resulting in better fuel economy, together with maintaining or improving safety norms both for the vehicle, its passengers as well as pedestrians. Search for plastics to replace metals: It is very general misconception in the common people that usage of plastics to make a vehicle with improved aesthetic appeal together with making lighter in weight, more fuel efficient and making overall more value for money has something related to sacrifice in safety and security. However a closer understanding on the relative properties and performance of plastics and metals the scenario would change. In Fig 2 is shown the relative strength vs density zone distribution of different materials.

Fig 2: Strength vs density zone distribution of different materials.

Fig. 3 summarizes the relative specific strength properties of plastics and metals. Specific strength or specific modulus is obtained by dividing the respective strength or modulus

by specific gravity of the respective material. Fig 3 shows that invariably all plastics or polymers can not replace metals, but there is a definite merging zone. This zone is mainly governed by specially designed plastics or polymeric composite material.

A properly selected composite material from the merging zone can suitably be used for replacement of a metallic part depending on the functional requirement. Also Fig 3 clearly shows specially designed PA-6 or reinforced PP composites can even surpass metals such as cast iron or steel in terms of specific strength or modulus. Plastics such as PA-6 or PP based composites additionally provide more ductility that will act as a benefit in terms of high rate of shock absorption as is encountered in the event of a crash. This in summary thus clearly outlines there is no harm in replacing metal parts with plastic once with a good understanding on the design, functional attributes and suitability of the plastic part for that application [8,9].

Fig 3: Specific Properties of Different Materials. In Fig 4 is presented a comparative share of different plastics used in automotives. For the sake of simplicity elastomeric materials and thermosetting resins are excluded, since where absolutely required a thermoplastic material can never replace these eg. in tire tread. Fig. 4 clearly indicates polyolefin materials are miles ahead as compared to any all other thermoplastics in terms of usage in automotives. In fact polyolefin materials are taking a 50% share of the total thermoplastics and the share is likely to boom further. While talking about polyolefin family is generally meant PP, PE and TPOs. Wherein PP and TPO combined together takes more than 85% share.

ABS, 14

Others, 14 Polyolefin, 50

PU, 15 PVC, 7

Polyamide, 9

Fig 4: Share of various plastics in automotives

Thin wall Bumper Application The advent of plastic bumpers started in late 1980s and got into full fledged operation 1990s in Europe. Polyamide, Polycarbonate based alloys have seen the initial growth but soon have been taken over by PP-Elastomer blends and TPO. Earlier bumpers were used to have a thickness of 3.5 mm. Since the beginning of 2000 automotive manufactures are continuously trying to reduce the wall thickness of bumper materials. The main objective behind this was operational easiness while assembly stage, improved aesthetics, improved fitment the body and weight reduction. However reducing the wall thickness is not an easy job and has got many challenges as outlined below to deal with.

1. A reduction in wall thickness results in effective path length for shock absorption decrease. This is having a direct implication on safety.

2. Wall thickness reduction will reduce cross sectional area for each infinitesimal cross section of the bumper. That will lead to more stress concentration and reduced rate of stress dissipation in the event of sudden shock as is encountered in the event of a crash. This is having a direct implication on safety.

3. It is established by calculation that resistance to deformation on bending varies by cubic power of thickness. Thus automatically a wall thickness reduction has a negative effect on bending resistance.

4. Wall thickness reduction will need higher degree of support from the back in terms of ribs and boshes. This may lead to more proneness to sink marks. Aesthetic issue.

5. A reduced wall thickness part will naturally have lower self supporting capability and may undergo undue bending or sagging effect during post painting baking phase.

6. A reduction in part thickness will need a corresponding reduction in wall thickness in tool. That will automatically lead to faster cooling and reduced flow

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path in mold increase in resistance to flow. In that event extra pressure will be required and that may lead to flow marks or tiger stripes in the part.

7. Shear rate, hence, shear heating varies inversely with wall thickness and the melt front temperature falls off faster for the thinner part.

So in summary to achieve a reduction in part thickness fore a safety related functional component such as bumper the OEM and the material designer needs to encounter these challenges with the Tier-1. Now thanks to the new generation PP materials, elastomer and TPO and the new sets of technology that made the scenario come true. In Fig 5 is shown the comparative property chart of a traditional TPO based bumper used for 3.5 mm wall thickness and a new generation reinforced TPO alloy solution for a thin wall bumper. The said solution is seen to be successful up to 2.7 mm wall thickness. Further research is in progress to calculate the minimum achievable wall thickness and together with the impact of the same on other functional aspects. Fig. 5 clearly highlights a reduction wall thickness has necessitated changes in the material in terms of increase in flow ability, flexural modulus and tensile strength with minimum change in impact resistance. An increase in tensile properties on the other hand results in improved overall energy absorption criteria and hence toughness. Fig. 5: Property comparison of a standard traditional bumper compound and high profile reinforced TPO for thin wall bumper application. We have seen that impact resistance of a polyolefin falls off with material thickness or the path length behind the impacted spot. The trend is expressed in Fig. 6 and the relationship is expressed by equation 1 below [10]:

Fig. 6: Extrapolated plot for variation of impact energy with specimen thickness [10]

I = 0.0158 x^3 - 1.2136 x^2 + 3.8677 x – 1.138 In equation 1 and 2 x is the thickness, I is the impact resistance at thickness of specimen. As stated earlier as we go down to reduce part thickness the effective path for crack propagation behind the surface undergoing impact decreases and consequently stress at the point increases making thinner sections more vulnerable to crack propagation and a catastrophic failure. However for a properly designed TPO material it is observed that all the compositions are capable to withstand the shock associated to impact without catastrophic failure as a bumper material up to at 2.0 mm or at least 2.5 mm. it is stated that when a car undergoes a crash the overall energy that is encountered first by the bumper is transmitted in several ways first of which is impact and then comes the stretching forces in localized unit cross sections and localized deformation. Accordingly we have analyzed for crashworthiness of the materials by stress strain measurements. Summary and Conclusions: Thermoplastic materials are being used more and more in automotive structural applications. Sometimes, specific responses of thermoplastic components are required when they are subjected to impact conditions. In today date PP and TPO materials are emerging at a rate without any bounds to fill the emerging norms and automotive part requirements. Properly designed PP, TPO materials can be and actually successfully are applied for thin wall applications from bumpers to dashboards or even body side claddings and body panels. In order to reduce part thickness we need to increase both the bending elastic modulus without sacrificing impact resistance, and the overall energy

consumed during deformation. A forward integration of the basic idea led to successful development of a series of solutions for:

1. Thin wall bumper and exterior parts. 2. Thin wall bumper thickness achieved is up to 2.65 mm and still work is going on. 3. Thin wall Interiors including Dashboard and Door trim materials. 4. Soft feel and high scratch resistant Interior solutions for dashboard and door trim

with a reduced stress whitening effect. 5. High profile engineering application such as front frame carriers and front panels. 6. Exterior body panels with molded in colour that does not need a painting

operation. 7. The newer generation materials comply with all safety norms, ELV norms and

emission regulations. References:

1. Engineering Plastics and Plastic Composites in Automotive Applications, Kalyan Sehanobish, SAE International, April 2009

2. http://www.thomasnet.com/articles/custom-manufacturing-fabricating/plastic-fab-metal-fab

3. http://www.tms.org/pubs/journals/jom/9607/alvarado-9607.html 4. http://en.wikipedia.org/wiki/Emission_standard 5. "Rapid - Press Releases - EUROPA". Europa.eu. 2008-10-22, Retrieved 2009-06-29. 6. http://en.wikipedia.org/wiki/Automotive_safety 7. Bunketorp O, Romans B, Hansson T, Aldman B, Thorngren L, Eppingen R H.

"Experimental Study of a Compliant Bumper System". Proceedings of the 27th Stapp Car Crash Conference. SAE Paper No. 831623

8. Michael Sepe, Plastic to Metal Replacement (Part 3), http://www.ides.com/articles/design/2008/sepe_03.asp

9. Michael Sepe, Plastic to Metal Replacement (Part 4), http://www.ides.com/articles/design/2008/sepe_03.asp

10. Crash worthiness analysis of Polypropylene Composite used for Designing Automotive Bumpers, ANTEC-0611-2009.R2

11. Integrating Thin Wall Bumper Moulding into Resin Properties: Effect of Impact-Stiffness-Tensile Balance, ANTEC-0614-2009.R1

Arjun Jindal Director Machino Polymers Ltd Arjun Jindal, a young, dynamic achiever is one of the most sought after entrepreneurs in the country. After

successfully completing higher education from Babson College, U.S.A., he came back to India to join Machino

Group Industries as one of the Directors. Machino Polymers Ltd (MPL), India’s leading manufacturer and

supplier of highly engineered and advanced Polypropylene (PP) composite Material to Original Equipment

Manufacturers (OEMs) and Tier 1 Vendors (molders) in automobile industry.

Witnessing the vast scope of automotive component industry in India, Mr. Jindal worked towards setting up an

ultra modern R&D facility manned by eminently talented, experienced and dedicated research team to provide

a distinctive edge. The highly engineered PP compounds from MPL have sought QS – 9000 certification

pronouncing its products as of best and consistent quality.

Apart from his professional commitments, Mr. Jindal also engages himself in various social welfare activities.

Mr. Jindal is among the Committee Members of Young Leaders’ Forum, Indian Chamber of Commerce as well

as the Committee Member of FICCI. Also he holds a special interest in Animation; therefore he is also a

member of Animation and Gaming Forum. He also owns an animation institute in Kolkata named ‘Ready to

Go Animate’. About Machino Polymers Limited Machino Polymers is a state of the art polypropylene compounds manufacturer for the automotive industry in India. They are a leading supplier with global approvals in supplying to all leading car manufacturers with presence in India as well as abroad. It was established in the year 1994 and today has an installed capacity of 40,000 tonnes per year per year at its 5 acre plant in Gurgaon, Haryana, in North India. The company plans to be multi location with facilities coming on line in Pune and in Chennai within the next financial year. By becoming a regional supplier to their customers the company will be even closer to meet their individual requirements. Machino Polymers’ core strengths lie in its production quality and commitment to research and development of advanced PP compounds for future needs of the automotive market. The Machino Innovative Research Applications Centre (MIRAC) is recognized by the Indian Government’s Department of Science and Technology (DSIR). For more information visit, www.machinopolymers.com