Plastics revolutionized the design and manufacture of automobiles, from interior components and exterior trim to entire body panels and under-the-hood parts. This required the development of a whole range of new assembly techniques that replaced mechanical fasteners and adhesives and led to reduced costs, improved productivity, and increased worker safety. Today that revolution continues at an accelerated pace, as automakers take advantage of continued improvements in plastics processing and assembly technology, especially in electronics.
A good example of this is seen in the new center tail-lamp designs appearing on today’s automobiles. Small, relatively simple tail-light modules are giving way to highly stylish one-piece assemblies that can measure up to 1400 mm from side to side with complex multi-dimensional contours. And those are just the exterior housings. Inside, the electronic sophistication boggles the mind, with arrays of organic light-emitting diode (LED) lamps that can indicate braking and directional changes and illuminate the paths of cars moving in reverse. They may also house sensors, radar devices, and cameras, along with the associated circuit boards and wiring. These kinds of assemblies have spawned — and are made possible by — new plastic welding technologies that not only bond the complex shapes involved but also do so without damaging the delicate electronics inside.
Even as recently as 10 years ago, the typical car had a relatively small number of sensors, mainly aimed at monitoring the combustion engine and drivetrain components. Today the average number of electronic devices in a car can surpass 200 — sensors, radar, and cameras — all intended to connect the driver, whether human or automated, to information about the vehicle itself and also its surroundings, including lane markings, other automobiles, dangerous objects, and even human beings and animals. As in the center tail-lamp application, these electronic components are housed in, attached to, and protected by plastic structures, and their fragility poses a challenge when these modules are assembled.
Electric/Autonomous Vehicles Offer New Challenges
The situation is becoming even more challenging as electric vehicles (EVs) and autonomous cars become more commonplace. Today’s gas-powered automobiles are extremely connected, incorporating technology that will be essential in autonomous automobiles. This is why the current shortage of semiconductor chips is causing so many problems in vehicle production and driving up the prices of new and used cars.
At the same time, designers are trying to create a more customized and comfortable environment for drivers and their passengers. This trend is seen in interior lighting, where a few individual lamps, used to facilitate entry and exit or to illuminate maps, are giving way to mood and even smart lighting. As a driver approaches the car, key fobs communicate with sensors, turning on internal illumination to welcome him or her. These fobs also make extensive use of plastics in sealed assemblies. Driver-information displays are now a key design element in automobile interiors. From dashboard instruments to interactive maps and satellite radio selections, these displays are ultimately connected to almost every possible sensor and camera in the car. The outer plastic housings require joining, as do all the circuit boards and wiring inside the console.
Plastic Welding Technologies
Plastic welding is not one technology. The term encompasses a range of joining technologies that continue to evolve to meet the wide range of automotive assembly needs.
Ultrasonic welding is the most common technique and is still probably the most frequently applied in bonding automotive plastics components. The process, which creates a high-frequency heat-generating motion between components to be bonded, has been used for 75 years to join thermoplastic parts that would be too complex or prohibitively expensive to mold in one piece. Many automotive components are already ultrasonically welded. However, the complexity, fragility, and precision required by sensors, cameras, and lighting components have led to the development of a new “dynamic mode” that can automatically adjust itself to part-to-part variabilities and unique materials. For instance, this technique can safely weld small, thin, or complex plastic parts onto plastic structures directly atop sensors or delicate electronics without damage. It can weld parts atop plastic assemblies containing compressible internal elements, such as elastomeric seals or cores, and it can handle materials that vary in hardness or structural consistency, such as composites.
A new laser technology for clear-on-clear welding involves multiple beams, positioned on many axes so that energy can be applied along the full length of the weld surface, even when the assembly is large and multidimensional. Unlike trace or scan welding, which completes the weld a little at a time as a moving device brings the parts together under pressure and allows parts to be preassembled. One surface freely transmits the laser energy (without itself being affected) through to the second (laser-absorbing) surface where laser energy is converted to heat that is conducted across the interface, creating the weld.
Lasers are remarkably versatile. They can weld dozens of different polymers, including some of the most advanced engineering materials. They can sometimes even be used with otherwise incompatible resins, including crystalline and amorphous resins, as well as reinforced plastics. Usually, the transmissive surface is more or less clear and the absorptive layer is darker, but that does not always have to be the case. Using various coatings and additives, an otherwise laser-transparent material can be made to absorb laser radiation, making it possible to create clear-on-clear assemblies.
Clean vibration technology offers manufacturers another option for demanding automotive applications. In conventional vibration welding, the heat needed to create the weld is developed by the friction of the two surfaces to be joined moving against one another. In contrast, clean vibration is a two-step process. First, the components to be welded are positioned above and below a metal foil infrared emitter that exactly conforms to the joint lines. Second, the emitter preheats the plastics and, once the weld lines have begun to melt, the emitter is removed, the two parts are brought together under pressure and a gentle vibration begins. The result is a weld-free of particulates and other undesirable side effects or damage to sensitive electronic components.
Heat staking and swaging are two other proven welding technologies that have been shown to be especially effective at capturing and securing components that may be made of many materials: plastics, glass-reinforced polymers, metals, ceramics, fabrics, and filter media, even printed circuit boards (PCBs), switches and electronics. In conventional staking, components are placed onto small posts in a plastic part, and the exposed posts are reformed using heat and force to create flattened, rivet-like disks that lock the components in place.
A recent advance in this technology is referred to as “pulse staking.” Its primary advantage in automotive applications comes from the fact that precise heating and cooling are applied in a highly controlled and localized manner. It represents a significant improvement over earlier thermal staking tools that continuously radiated high heat in all directions before, during, and after a stake. Thus, pulse staking is readily applicable to securing multiple, closely spaced features on geometrically complex 3D parts. A single piece of tooling can accommodate multiple pulse staking tips, enabling them to perform multiple stakes on parts or assemblies (using different temperatures and cooling rates, if needed) at the same time. A single PulseStaking machine can support the operation of up to 60 different tips.
EV and Autonomy
With the rising popularity of electric and autonomous vehicles, the automotive industry is redefining itself. Adjusting, tracking, and strategizing, OEMs are determining the best approach to embrace these new megatrends. By understanding the joining application opportunities available within these segments, Tier 1 and Tier 2 suppliers can position themselves to deliver specific solutions that meet the demand for complex, multidimensional, and increasingly aesthetically focused applications.
Craig Birrittella is the Business Development Manager, Automotive, Branson Welding, and Assembly at Emerson. During his 25+ year career at Emerson, Craig has received a US Patent for lens adaptation to improve laser energy and has focused on a variety of additional technical areas, from vibration, clean vibration, and infrared welding. Birrittella has a BS in Mechanical Engineering from the State University of New York, Buffalo.