Assembly Innovations: New Process for Molding Auto Parts Uses Less Resin
December 19, 2008
Mazda Motor Corp. (Hiroshima, Japan) has developed a new plastic molding technology that substantially reduces the weight of plastic parts for vehicles. The technology lowers the amount of plastic resin needed to mold bumpers, consoles and other parts by 20 percent to 30 percent.
Mazda’s new process is a variation on traditional injection molding. The process involves mixing the raw plastic resin with a “supercritical fluid” (SCF) made from a common inert gas, such as nitrogen or carbon dioxide. A substance becomes an SCF when it’s exposed to such a high temperature and pressure that its liquid and gaseous phases become indistinguishable. An SCF can diffuse through solids like a gas, and dissolve materials like a liquid. As SCFs, nitrogen and carbon dioxide raise the fluidity of liquid plastic resin and cause the material to expand rapidly when injected into a mold. The resin forms a foam with a standardized microcell structure, so smaller amounts of resin are needed to fill the mold.
Mazda’s new technique also relies on the “core-back expansion molding process.” Once the foamed resin has filled up the mold, the volume of the mold is increased, causing the foam to expand. This means that large plastic parts, with low density and good rigidity, can be made from the same volume of resin.
Parts molded with the new process have a multilayer structure. The bubbles in the outer layer of plastic are kept microscopic, to ensure the part is strong and rigid, while the size of the bubbles in the core layer can be adjusted to reduce the part’s overall density as needed.
The technique can be used to mold nearly all the plastic parts in a vehicle. Besides producing stronger, lighter structures with less material, the new process also enhances the thermal insulative and acoustic characteristics of the parts.
Mixing gas with the liquid resin during molding is not new. Older plastic foaming methods use a gas formed through the thermal decomposition of organic and inorganic compounds. However, residual chemicals from the foaming agents can adversely affect some plastics and impair their ability to be recycled. Using SCFs to foam the plastic avoids these complications.
Mobile Robot Drills Holes in Airplane ComponentsA Spanish engineering team has developed a light, portable robot that precisely drills holes in wing spars and other large aeronautical components during the assembly stage.
Traditionally, such components are drilled using large, stationary machinery. In contrast, the robot moves over aircraft components while they are fixed to a tool holder.
Dubbed Roptalmu, the robot was designed for Airbus España (Madrid, Spain) by engineers at Fatronik-Tecnalia (San Sebastian, Spain), a private, nonprofit manufacturing research center. Roptalmu consists of an automatic moving platform and a three-axis drilling robot. Once the platform is positioned near the part to be drilled, the robot fixes itself to the tool holder of the part and automatically moves over it. The robot can drill a range of materials, including aluminum, titanium and carbon fiber. A set of sensors and control software ensure that the robot drills every point safely and automatically.
A key feature of the robot is its portability. “If the production system is fixed to the floor, like traditional machinery, it is very expensive and time-consuming to reallocate it throughout the shop floor,” says Valentin Collado, Fatronik-Tecnalia’s robot project manager. “With a small, portable system, such as Roptalmu, the production system is moved to the aerospace part to be manufactured.”
A conventional machine that can do the same job as Roptalmu could weigh 15 tons and require large amounts of electricity to move each of its axes. Roptalmu weighs only 3 tons and requires a fraction of the energy.
Another benefit of the robot is fully automatic operation. This is particularly important for large aircraft parts, which must be drilled with thousands of holes for assembly. Traditionally, this has only been done with manual or semiautomatic tools.
The main technical challenge of the project was to develop a system that met the accuracy requirements for aerospace assembly and yet could also stand up to the reaction forces of drilling, says Collado.
The use of Roptalmu is not limited to aerospace production. It could also be used by manufacturers in the renewable energy, shipping and construction industries-any industry that needs to handle large components.
In September, the European Manufacturing Summit presented the robot with its International Strategic Manufacturing Award for 2008. The robot beat out a field of more than 100 entries.
Handheld Ultrasonic Instrument Reads Hidden Matrix CodesData Matrix codes can be read by laser scanners, vision systems and even magnetic sensing equipment. Now, researchers at NASA’s Marshall Space Flight Center (Huntsville, AL) have developed a way to read hidden matrix symbols using a handheld ultrasonic instrument.
The portable, battery-powered device operates without mechanical raster scanning. Instead, the instrument is placed directly on an area believed to contain a matrix symbol. Intimate contact between the instrument and the substrate is provided by a flexible membrane on the face of the instrument or a replaceable gel pad. Ultrasound pulses are transmitted from a transducer into the target through the membrane or pad. A portion of each ultrasonic pulse, modified by the matrix symbol, is reflected back to an ultrasonic sensor. The sensor then converts the resulting spatial variation of ultrasound pressure to voltages that are used to construct a video image of the symbol.
Once a video image of the symbol has been captured, a second set of electronics decodes it and registers the data.
Hybrid Material Combines Properties of Metal, PlasticA new hybrid material consisting of a polymer and a nanocrystalline metal alloy can be used to create lightweight components that have the strength and stiffness of metal, while offering the design flexibility and benefits of high-performance thermoplastics.
The material, MetaFuse, was developed by DuPont Engineering Polymers (Wilmington, DE), Integran Technologies Inc. (Pittsburgh), and PowerMetal Technologies Inc. (Carlsbad, CA). MetaFuse is made by depositing a thin layer of high-strength nanocrystalline metal-25 to 200 microns thick-onto a component molded from thermoplastic. The process allows engineers to create components in complex shapes that are stronger than magnesium or aluminum and just as stiff. The metal has an average grain size of 15 to 100 nanometers, about 1,000 times smaller than conventional metals. Together, the hybrid material is two to three times stronger than typical steels and decorative nickel-chrome. Other metal deposition techniques, such as electroplating and vapor deposition, can’t create structures that are nearly as strong.
A unique aspect of the technology is that it places the metal in the optimum location to increase stiffness. For bending loads, the placement of the nanometal coating is most beneficial at the outermost edges of the part, furthest from the neutral axis. This is where the maximum tensile and compressive stresses are experienced by a part. The bending stiffness, torsional stiffness and strength of the part all increase. The outer sections experience the largest loads, and this is where the nanometal is most beneficial.
The process reduces creep in plastic parts at elevated temperatures; adds a wear-resistant and potentially low-friction surface to plastics; and makes plastics more impermeable, conductive and dimensionally stable. It also improves aesthetics by giving the plastic a metal look.
In the automotive industry, the material can be used to make oil pans, cylinder head covers, water and oil pumps, gasket carriers, timing chain tensioner arms, transmission housings and components, fuel rails, electric motors, electrical housings and covers, steering components and control arms. It can also be used for sporting goods, appliances, furniture, power tools, and housings for handheld electronics.
Coating, Heal Thyself!Researchers in Germany have developed a self-healing, nanoscale coating for preventing corrosion in steel and aluminum parts for aerospace, automotive, maritime and energy applications. The environmentally friendly coating is seen as an alternative to hexavalent chromium and other coatings that, while effective, are also toxic.
The multilayer coating was created by Daria Andreeva, Ph.D., and a team of researchers at the Max Planck Institute of Colloids and Interfaces (Potsdam, Germany). Their process involves pretreating the surface by sonication and then depositing a series of oppositely charged polyelectrolytes and inhibitors layer by layer. All totaled, the coating is just 5 to 10 nanometers thick.
The process forms a “smart” polymer nanonetwork of environmentally friendly organic inhibitors. The various layers do more that act as a barrier to external impacts. They also respond to changes in their internal structure, and they can combine to create different mechanisms of damage prevention and reparation.
“Our novel coating [provides] very high resistance to corrosion attack, long-term stability in aggressive media, and an environmentally friendly, easy and economical preparation procedure,” says Andreeva.
The researchers tested their process on aluminum aerospace components, so the ultrasonic pretreatment process was particularly important. Although aluminum surfaces are typically covered by 3 to 7 nanometers of natural oxide film, this thin layer provides insufficient protection against corrosion and actually inhibits the adhesion of protective coatings.
“Ultrasonic pretreatment is crucial for formation of a uniform film,” says Andreeva. “The surface of ultrasonically pretreated samples exhibits better wettability, adhesion, and chemical bonding with the polymer layers of subsequent coatings. It results in a homogeneous distribution of the polymer film on the aluminum surface.”
According to the researchers, the coating provides several mechanisms of corrosion protection. Controlled release of the inhibitors is stimulated by the presence of corrosive agents, while the polyelectrolyte layers buffer pH changes at potentially corrosive areas. In addition, because the polyelectrolyte constituents can move from layer to layer, the coating can heal itself when damaged.
The chemistry of the process is versatile. The mix of polyelectrolytes and inhibitors can be adjusted to suit a variety of surfaces and applications. “Although we concentrated on corrosion, our method could also be...applied to self-repairing coatings for antifungal or antifriction applications,” says Andreeva.
One practical problem the Max-Planck team is still working on is how to automate the layer formation procedure for mass-production applications. Beyond that, they are already developing other anticorrosion formulations.
Bolt Reports How Much Load It's ApplyingWhether a bolt is tightened by an air tool, a pulse tool or a computer-controlled electric tool, engineers can never be absolutely certain how securely the joint has been fastened. That’s because engineers measure torque to assess the tightness of the joint, when what they really want to measure is clamp load.
Now, Load Control Technologies (King of Prussia, PA) has introduced a way for engineers to measure exactly how much clamp load a bolt is applying to a joint. It’s called i-Bolt, and it works like this: Load Control Technologies equips the assembler’s bolts with a permanent, inexpensive ultrasonic transducer. The transducer can be located at the top, bottom or both ends of the fastener.
During assembly or auditing, sensors directly measure the clamp load via the pulse echo technique. A voltage pulse is applied to the transducer to generate a longitudinal ultrasonic wave. The wave travels the length of the fastener, reflects off the end, and returns to the transducer. A sensor measures how much time it takes for the wave to return. This measurement is taken continuously during tightening, beginning at zero load.
Every bolt stretches when it’s tightened-that’s the source of clamp load. As the fastener elongates, it takes longer for the ultrasonic wave to make its round trip. Thus, a change in time is directly proportional to the clamp load applied by the bolt. Load measurements made via the pulse echo technique are accurate to ±3 percent at 3 sigma.
The transducer attached to the bolt is only 50 microns thick, and it does not affect the form, fit or function of the fastener. The transducer is permanent. It can be tightened, retightened and inspected for the life of the joint at any time with near-perfect repeatability.
In addition to the transducer, each bolt receives a 2D bar code for traceability and data logging.
Before shipping i-Bolts to an assembler, Load Control Technologies replicates the assembler’s joint, generates the ultrasonic parameters, and stores the ultrasonic signatures-including the zero load reading-of each individual bolt to its unique bar code. So, once the assembler receives the i-Bolts, they are ready to be used.
Any hand tool or power tool can be adapted for use with i-Bolts. The transducer is configured so it can be pulsed and read using a single, inexpensive, spring-loaded contact integrated into the drive of the tool. The return path of the signal is provided through the tool’s socket.
The controller can be programmed to shut off the tool when a specific clamp load is reached. It can also record and display curves of load vs. time or torque vs. tension. During auditing, data is taken in the actual joint without turning, drilling or otherwise disturbing the fastener. All measurements are automatically recorded and converted into Excel spreadsheets along with analytical templates for curve plotting, including graphical representation of friction parameters.
For more information, visit www.innovationplus.com or call 610-272-2600.