Material and processing advances in the thermoplastic and thermoforming industries are creating new design possibilities for mass transit interiors. “Until recently, thermoplastics were considered late in the design process and only selected on the basis of price, quantity and compliance,” says Rich Cort, mass transit business manager at Sekisui Polymer Innovations (SPI), a thermoplastic manufacturer. “Designers are now considering thermoplastics at the beginning of the design process. This early collaboration between manufacturers and suppliers is yielding efficiencies in the process and improving overall interior design.”
So why does Cort believe designers are choosing thermoplastics? “The requirement to minimize weight has become more common in the mass transit industry, and toxicity and environmental regulations have become more stringent,” says Cort. “The indications are that regulations will rapidly become stricter. The desire to improve the passenger experience is also driving innovation. As these factors converge, project teams are turning more frequently to thermoplastics over fiberglass.”
Thermoplastics versus fiberglass
Thermoplastics are made of polymers that become pliable or moldable above a certain temperature and solidify upon cooling. “Designers, OEMs and transit authorities are realizing the advantages that thermoplastics have over fiberglass,” says Cort. “They are lighter in weight, enable a more detailed design and are cheaper to fabricate. Parts retain mechanical properties such as durability, which decreases replacement and out-of-service costs. Integral color thermoplastic parts don’t need secondary finishing and require little cosmetic maintenance because they are resistant to chipping, cracking and discoloration. As such, during refurbishment projects they are often selected by transit authorities to replace worn-out parts made of other materials. Furthermore, unlike fiberglass they are VOC-free, so when parts are eventually replaced they can be recycled directly into the production stream.” Cort also says the thermoforming process can yield savings.
“The process typically generates more parts per hour per mold than fiberglass, often in ratio of 8:1,” he says. “In addition, prototyping molds are cheaper, making more design iterations possible and delivering a quicker time-to-market. Production molds are also cheaper, given that they often produce more than 20,000 parts before they need to be replaced.”
Vacuum versus pressure forming
There are two main ways to form parts from thermoplastic. “With traditional vacuum thermoforming, wall thinning can be a problem because variations in the sheet material occur as it is stretched over the tool,” says Cort. “With pressure forming, a combination of air pressure and vacuum, plus more sophisticated process controls for monitoring tool and sheet temperature, result in more consistent parts and make it possible to create precise details and intricate undercuts. The air pressure forces the thermoplastic into the minute crevices of a mold so that tight corners, vents and ribs, logo silhouettes and assembly points can be formed accurately.”
Cort reports that although temperature-controlled molds have been around for decades, in recent years they have been much more widely adopted. “Evenly cooling the formed part delivers a more stable part in the end, aiding consistency and enhancing quality,” he says.
Pressure forming also enables designers to selectively texture parts of a surface on a single part by applying the texture directly to the mold, which transfers directly to the primary surface of the part. “In vacuum forming, this is accomplished by embossing a texture on the extruded sheet, which can introduce inconsistencies in parts as the material is stretched or distorted,” says Cort.
“Pressure forming produces low-cost, aesthetically refined parts that rival those made using other types of forming,” says Cort. “As designers and manufacturers discover what they can accomplish with pressure forming, we are bound to see it used more for the mass transit interior industry.”
Cort is a strong believer in the power of early collaboration. “Designers are collaborating with thermoformers and manufacturers earlier, and so we’re seeing an increase in awareness of these new capabilities and technologies,” he says. “That improvement in the collaboration process has had a big impact on the passenger experience. The worlds of design and manufacturing are intersecting more powerfully than ever before because thereis much to be gained by it. Consider the many suppliers that contribute to a mass-transit interior. If each of those contributors works in isolation, the overall design quickly degrades. If colors and materials are chosen as part of a cohesive design, then components are able to interplay, complement and make sense with each other. Carpet, seat coverings and lighting all contribute to the passenger experience, enhancing the brand and the overall enjoyment of travel.”
Cort also contends that there are financial benefits to the collaborative approach. “It can lower costs,” he says. “Collaborating on a mass transit interior design earlier in the project development process translates to better results, often in a shorter time. As material suppliers, we all have the privilege and responsibility to continue the journey of developing mass transit products that exceed and anticipate increasingly stringent regulations while improving the passenger experience with refined design. Pressure forming is a game changer when combined with thermoplastic’s light weight and recyclability.”
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Article published by kind permission of Railway Interiors International, Annual Showcase 2015