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October 2003
Composites Open Road To Innovation In India

Railway and automotive applications point the way to composite mass production.

Author:
Posted on: 10/1/2003
Source: Composites Technology

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The three-wheeler's entire body, including rear bumper and seat pedestals, is a composite construction, optimizing the HEV's weight for fuel economy.

Source: TVSMThe three-wheeler's entire body, including rear bumper and seat pedestals, is a composite construction, optimizing the HEV's weight for fuel economy.

The composites industry in Asia currently accounts for 30 percent of the global market, growing annually at at rate of 7 percent, while worldwide growth averages 4 percent. Asia's two growth leaders, China and India, maintain double-digit expansion (15 percent and 12 percent, respectively). China, however, has surged ahead in composites usage with a 25 percent share of the Asian market compared to a paltry 4 percent for India. If India is to take a place next to China at the forefront of the Asian composites sector, composites must find applications in volume production markets. India time may have finally come, as growing financial and environmental pressures spur development of composite solutions to meet challenges faced in this populous nation's public and personal transportation arenas.

SMC AXLE BOX COVERS FOR INDIAN RAILWAY COACHES

The Indian Railways (IR) is a vast network with laid track in excess of 100,000 kilometers/62,000 miles. To date, however, the application of composites in rolling stock construction in India is abysmally low even in comparison to Japan. But the high incidence of pilferage of stainless steel, aluminum and cast-iron components used in railway coaches continues to plague the IR, and is a factor driving increased interest in composites. Since thermosetting composites have no resale value, they are a viable anti-theft alternative.

It was against this backdrop that the IR considered development and commercialization of axle box covers in sheet molding compound (SMC). The disk-shaped axle box covers house the wheel bearings on railway coaches. There are four wheels per coach and each wheel has a front and rear axle box cover. Theft of the easily accessible, 4.5 kg/9.9 lb die-cast aluminum front covers resulted in heavy revenue losses.

When the SMC concept was first put forward, the RDSO (Research, Design and Standards Organization), Ministry of Railways (the approving authority for any new construction material used in railway applications) voiced a concern about the resistance of SMC to the grease used to lubricate the bearings, which is alkaline in nature. If an SMC cover could be attacked by grease while in service, glass fibers might invade the grease, inhibiting its lubricating performance and resulting, eventually, in a "hotbox" effect (overheating of the bearings). If not remedied, the condition could result in train derailment.

To convince Railway authorities that SMC posed no hazard, a prototype was developed at one of the Railway's coach repair workshops, in Hyderabad, South India. The design and fabrication of the chrome-plated steel dies was done in the workshop's own tool room. An existing hydraulic press (used for cold stamping of metal products) was modified to suit compression molding requirements of SMC with respect to pressure and temperature controls, closing speeds, provision of ejection pins, etc. To comply with fire safety regulations for railway coaches, fire retardant-grade SMC with a glass content of 25 percent was supplied by Devi Polymers (Chennai, India) a leading Indian manufacturer of SMC and BMC (bulk molding compound). The product combined glass fiber in the form of chopped strand mat, manufactured by FGP Ltd., (Bombay, India; now a Saint-Gobain company), with unsaturated isophthalic polyester resin supplied by Naptha Resins and Chemicals (Bangalore, India) a leading polyester resin manufacturer in South India. The cover was compression molded at a temperature of 120°C at a pressure of 120 kg/cm2 (1,765 psi). Total cycle time (including charge placement and demolding) was 15 minutes, which included an 11-minute cure. The average weight of the SMC cover was 4.0 kg (8.8 lb), 0.5 kg/11.1 lb less than the aluminum cover, with a maximum thickness of 10 mm (0.39 inch) along its periphery.

In Indian Railway composites development, the common practice is to subject the product to field trials and observe its performance over a period of time. Sixteen SMC front axle box covers were installed on four coaches and, after 18 months of service, were subjected to tests at the RDSO Central Testing Laboratory. Since the primary concern was the ability of SMC to resist attack by grease (i.e., the possibility of migration of glass fibers into grease); the penetration test was carried out at 25°C/77°F using new (fresh) grease and grease removed from the SMC axle box cover. While fresh grease gave penetration index values in the 220 to 250 range, grease removed from the SMC cover gave values in the 240 to 265 range. Another test determined the drop point for grease used in bearing applications. While the minimum value should be 180°C/64.4°F with fresh grease; the grease removed from the SMC cover registered a temperature of 190°C/66.2°F. The tests demonstrated that SMC covers were unaffected by grease.

The axle box cover is bolted in position on the wheel with four lugs, through holes drilled for the purpose. There should be no eccentricity during drilling of holes on the four lugs of the SMC cover, because this will cause the steel bolts to shear off in service, and dislodge the cover. A critical mechanical trial tests the bolt pullout load, which determines the ability of the lugs to hold individual bolts securely in position. When the lugs were tested, the pullout load for SMC covers was found to be 1,000 kg/2,200 lb per lug, double the load for conventional aluminum covers (500 kg/1,100 lb).

At high train speeds, trackbed ballast tends to hit the cover and could lead to cracking or breakage. A final test simulated the effect of ballast impact, using a steel indenter with a 6 mm/0.25-inch radius. The indenter was dropped onto the cover from a height of 0.85m/33.5 inches, with successively greater applied loads. The SMC cover matched die-cast aluminum, withstanding the same load of 10 kg/22 lb.

Though the tests proved conclusively SMC front axle box covers were a viable alternative, the IR's customary "play-it-safe" approach delayed formal approval for use on refurbished coaches for eight years following the initial field trials! RDSO has since framed technical specifications for the SMC covers that are now used by most of the zonal railways in India. The product is supplied by RDSO-approved molders who make the SMC in-house and subsequently carry out compression molding, using their own hydraulic presses. The number of new coaches produced by the Indian Railways annually is 2,400 to 2,500, with an equal number of old coaches being refurbished.

This successful application has provided the impetus for a multitude of new and potential load-bearing applications in composites, including insulated track rail joints, sleeper berths and main doors of coaches.

GLASS FIBER-BASED AUTOMOTIVE BRAKE LININGS

Traditionally, asbestos has been the fibrous reinforcement for brake linings in India. Several years ago, Sundaram Brake Linings (SBL, Chennai, South India), a leader in India's friction materials market, pioneered the development of asbestos-free, glass fiber-based brake linings in India, benefiting from a policy decision by India's leading automotive manufacturer TELCO to use eco-friendly products in all its vehicles. SBL, one of the TVS Group of Companies (Bangalore, India) that has been manufacturing automotive components for several decades, accounts for more than $16 million (USD) of TVS's current $1 billion per yearly turnover.

SBL's brake linings for commercial vehicles, passenger cars and two-wheelers use glass fibers in the form of chopped strands with phenolic resin as the matrix, with fiber content varying, based on vehicle type. India's commercial vehicles can be broadly classified as Light Commercial Vehicles (LCVs, with gross vehicle weight to 6 metric tonnes/13,228 lb or Medium and Heavy Commercial Vehicles (MCVs and HCVs, gross weight exceeding 6 metric tonnes). Glass content ranges from 5 to 10 percent in LCV and passenger car applications to 9 to 13 percent for MCV and HCV brake linings.

Glass fiber, sourced from indigenous manufacturers, and phenolic resin in powder form (binder) are the principal ingredients. These and other raw materials, such as friction modifiers, (normally based on cashew nut shell liquid in the polymerized form), fillers and metal powders (for heat dissipation) are weighed and mixed, based on a proprietary formulation. The mixture is compression molded at pressures that vary with ram diameter (typically in the range of 100 to 200 kg/cm2 or 1,470 to 2,940 psi). The temperature range varies from 135°C to 150°C (275°F to 302°F) and press cycle time varies from 10 to 20 minutes. After curing in the press, the brake linings are postcured in ovens for 6 to 15 hours at temperatures ranging from 150°C to 170°C (302°F to 338°F). Afterward, brake linings are cut to size; outer and inner diameters are machined to size and drilled in accord with design specifications.

The glass/phenolic composite makes a lightweight brake lining. The heavy-duty composite blocks for HCVs and MCVs weigh 0.8 to 1.2 kg (1.76 to 2.64 lb), while LCV brake linings weigh only 0.3 to 0.5 kg (0.66 to 1.10 lb). Passenger car linings normally weigh-in between 0.07 to 0.12 kg (1.54 to 2.64 lb). For two-wheelers, the weight is in the 0.03 to 0.04 kg (0.066 to 0.088 lb) range.

SBL's glass fiber-based brake linings conform to automotive brake manufacturing standards set forth in IS 11852 (Indian Standard) and meet critical tests for friction coefficient, such as the Chase test (based on a procedure outlined in SAE J661a, and adapted for the Indian Standard IS 2742-1994). The Chase test checks the friction rating on a small sample cut from the full lining, while dynamometer trials subject the finished product, mounted in a complete brake assembly, to simulated driving conditions. Glass linings also meet or exceed minimum values for cross-breaking strength for HCVs and LCVs (300kg/cm2 or 4,410 psi) and rivet-holding strength (200 kg/440 lb per rivet for LCVs; 400 kg/880 lb for HCVs).

Most importantly, brake linings made with glass reinforcement have a service life 20 to 30 percent longer than asbestos-based linings. Since SBL's pioneering work in development and successful commercialization of the concept, that fact has helped motivate 40 percent of the automotive industry in India to shift to glass fiber-based brake linings resulting in the use of approximately 750 metric tonnes (1.65 million lb) per year of glass fiber.

ECONOMICAL COMPOSITE THREE-WHEELER

India's three-wheeled taxis, a common sight in most cities and small towns, are inexpensive compared to the conventional taxi and a quicker (though more expensive) means to one's destination than the common bus. Although composites were introduced to three wheelers in the mid-'80s, they were used solely to make replacement hard tops for existing metal or canvas/PVC-coated fabric tops. Three-wheelers accommodate a driver and as many as three passengers, but their gasoline engines are a major source of air pollution. Therefore, in 2001, TVS Motor Company Ltd. (TVSM), part of the TVS Group and a leading manufacturer of motorcycles, scooters and mopeds in India, teamed with Owens Corning (OC), India, to explore the feasibility of manufacturing a three-wheeled Hybrid Electric Vehicle (HEV) with its entire body made from composites. HEV vehicles are equipped with electric motors powered by batteries and gasoline engines that serve the dual-purpose of charging the onboard battery pack and providing motive power at high speeds or when batteries are low. Typically, HEVs operate on electric power at low speeds in heavy traffic (0 to10 kmh or 0 to 6.25 mph); the gasoline engine is used at higher speeds (40 to 45 kmh or 25 to 28 mph).

A joint study showed that a gasoline/electric powered three-wheeler with a lightweight composite body had potential for greater fuel efficiency and significant savings in tooling costs and tare weight without sacrificing functional requirements of strength, stiffness and structural integrity — a necessary outcome in view of the fact that the heavy HEV traction battery accounts for 10 to 12 percent of the vehicle's tare weight.

With fuel efficiency as a priority, the prototype goal was a tare weight of 330 kg/726 lb and payload weight (including passengers and luggage) of 320 kg/704 lb. TVSM initiated a total change in body design, conducting wind tunnel tests on scale models with different styling and shapes calculated to reduce the aerodynamic drag by 10 percent compared to the benchmark vehicle.

For the prototype, called TVSM-HEV, the partners abandoned the conventional three-wheeler chassis for a new ladder-type steel chassis designed in-house by TVSM after a thorough finite element analysis (FEA). Finite element modeling (FEM) was used to optimize body panel thickness and mounting locations on the chassis, check composite parts for shock loading (when the vehicle is in motion) and stress-check part assemblies under combined load conditions in static. After the completion of FEM analysis, a CAD model was generated that led to the fabrication of a full-scale wooden solid model integrated with other accessories such as head/rear lamps, indicators, wipers and rearview mirrors to evaluate outside size, shape and styling. The next stage was the fabrication of a hollow mockup to enable study of internal layout, functional requirements and ergonomics. Feedback from the hollow mock-up assisted in finalizing the size and shape of the front fender, cowl and rear panels.

After careful consideration of functionality, tooling and assembly requirements the number of composite body panels was reduced to 10 major assemblies, compared to 21 with the conventional steel version, shortening assembly time. For safety, the front cowl was designed with integrated "A" pillars to provide added protection against frontal impact. Specially designed "B" pillars provide protection against side collision and vehicle overturn, and built-in, soft "Z" sections between body panels and chassis cushion impact. Sidewall protection also was provided in the passenger cabin. Parts consolidation kept manufacturing costs for the prototypes comparable to those for steel bodies.

For the prototype, called TVSM-HEV, the partners abandoned the conventional three-wheeler chassis for a new ladder-type steel chassis designed in-house by TVSM after a thorough finite element analysis (FEA). Finite element modeling (FEM) was used to optimize body panel thickness and mounting locations on the chassis, check composite parts for shock loading (when the vehicle is in motion) and stress-check part assemblies under combined load conditions in static. After the completion of FEM analysis, a CAD model was generated that led to the fabrication of a full-scale wooden solid model integrated with other accessories such as head/rear lamps, indicators, wipers and rearview mirrors to evaluate outside size, shape and styling. The next stage was the fabrication of a hollow mockup to enable study of internal layout, functional requirements and ergonomics. Feedback from the hollow mock-up assisted in finalizing the size and shape of the front fender, cowl and rear panels.

After careful consideration of functionality, tooling and assembly requirements the number of composite body panels was reduced to 10 major assemblies, compared to 21 with the conventional steel version, shortening assembly time. For safety, the front cowl was designed with integrated "A" pillars to provide added protection against frontal impact. Specially designed "B" pillars provide protection against side collision and vehicle overturn, and built-in, soft "Z" sections between body panels and chassis cushion impact. Sidewall protection also was provided in the passenger cabin. Parts consolidation kept manufacturing costs for the prototypes comparable to those for steel bodies.

Apart from the hard top, which was sprayed up, glass-reinforced plastic (GRP) components were layed up by hand on open molds, with tooling and part development carried out at the Market Development Center of OC, India. Body panels, including the front cowl, passenger cabin, A and B pillars, floor, front and rear fenders, rear bumper, tail door and door frame and fascia, were molded from GRP. The use of GRP for the engine compartment provided damping for NVH (Noise Vibration Harshness). For hand layed components, TVSM used a combination of woven fabric and chopped strand mat from OC, India, wetout with orthophthalic-grade polyester resin, sourced locally. The average GRP thickness for the components varied between 2.5 to 3.5 mm/0.098 to 0.138 inch), using three to five layers of reinforcements.

Sub-assemblies were bonded with cold-bond methacrylate adhesive from ITW Plexus (Kettering, Northants, U.K.). The composite body panels were assembled on the steel chassis using steel brackets and rubber shock mounts. Integrated steel inserts and collared bushings, embedded in the composite body panels, facilitated mounting of functional units, accessories and brackets. The passenger cabin, consisting of rear panels, seat base and tail doorframe, was assembled using cold-bonded adhesive fixtures.

The TVSM-HEV design optimized vehicle weight (a 30 percent reduction, compared to steel) and reduced drag co-efficient, enabling the prototype to achieve the targeted 25 percent increase in fuel efficiency using HEV motive power. Insights gained during successful road tests of the prototype's structural integrity and in-service handling led to a few modifications, including a decision to use flexible-grade polyester resin for the composite panels in the next step toward commercialization.

TVSM has not yet commenced commercial production, but the company plans to manufacture the vehicle's special chassis while subcontracting bodywork to competent molders who would be trained by TVSM in regard to fabrication and assembly. The company envisions resin transfer molding (RTM) as the production method when volumes ramp up. TVSM anticipates production startup within a 48-month timeframe.

Once in production, the company anticipates that the TVSM-HEV will minimize the financial risk that accompanies changes in vehicle design or body style because tooling costs are as much as 60 percent lower than steel, thereby resulting in lower breakeven volume.

This successful joint venture should set the trend for similar efforts by other companies in developing innovative applications for composites, and pave the way for a quantum increase in glass fiber use in India.

TRAVELING TOWARD NEW HORIZONS

The Indian composites industry has the potential to grow 25 percent per annum. For this to be a reality, however, the growth drivers will be commercialization of volume applications and emphasis on automated processing techniques. If India perseveres toward these goals, the country has the wherewithal in composites design coupled with entrepreneurial flair to live up to its true potential in the Asian composites market.


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