Material Innovations
MSC's Quiet Steel BIW part
 By using laminated steel, several components were eliminated from the dash panel without the loss of structural integrity or safety requirements. |
Key engineering targets for the 2001 Ford Explorer Sport Trac were to provide a high level of riding comfort along with noise, weight, and cost reductions in a rugged SUV. One way that the engineers met their targets was through the use of MSC Laminates and Composites' Quiet Steel (covered in AEI in March 2000) for the instrument panel.
Quiet Steel is comprised of two metal skins surrounding a 25-µm (985-µin) weldable viscoelastic polymer core. Manufactured in a continuous coil, the material can be used in standard transfer press operations. Metal skin type and thickness can be optimized at the design engineer's discretion to ensure structural integrity of the part, while the viscoelastic polymer can be tailored to meet the specific noise reduction needs of the application.
"We've had success with our Quiet Steel materials in powertrain applications for 15 years," said Jim Carlen, Vice President of MSC Laminates and Composites. Carlen is optimistic that Ford's use of the material in a body-in-white (BIW) application will set the stage for additional implementation into other light BIW applications, not only at Ford but at GM and DaimlerChrysler as well. Current powertrain applications include valve covers, oil pans, transmission pan covers, and disc brake dampers.
 The Aachen Head matches human sensitivity to acoustic input. When MSC Laminates and Composite's Quiet Steel was tested as part of the Ford Explorer Sport Trac, it achieved an overall 95% rating at 56 km/h (35mph). |
In the Sport Trac application, Quiet Steel satisfied the structural needs of the vehicle while providing enhanced NVH benefits, allowing engineers to remove additional add-on materials and simplify the entire vehicle assembly process. To quantify the performance of the Quiet Steel and other interior improvements, Ford engineers used the "Aachen Head," named for the university in Germany where it was developed. The head replicates how a human picks up sound. During testing, the ears "hear" interior noise and record it on a digital tape stored inside the head for later replay and assessment in the test lab.
Sound tests were conducted in all road conditions, from acceleration to cruising speeds. Engineers plotted the sounds and evaluated the interior's performance to reduce unwanted noise. By reducing structure-borne noise in the vehicle, engineers achieved a score of 95% in speech intelligibility testing at a steady driving speed of about 56 km/h (35 mph). A 100% rating can only be achieved in a fully insulated sound room.
Another target for Ford engineers was to reduce the weight of the overall dash panel system. A conventional system, which had a mass of 12 kg (27 lb), required the assembly of a dash insulator, steel dash doubler, mastic deadener, steel dash panel, and engine-side fiberglass dash insulator. In contrast, the new system required only a Quiet Steel laminated dash panel and fiberglass dash insulator, reducing assembly time and space requirements at a mass of 9 kg (20 lb). Because of the reduced manufacturing and assembly steps of the new system, costs were reduced.
According to Carlen, other body applications under development for new vehicles include other dash panels, floor pans, roof panels, and truck floors.
- Jean L. Broge
TIMET's titanium alloy for springs
 Springs made with TIMET's titanium alloy do not require as many turns as a steel spring, and because titanium has about half the density of steel, it does not require as much material to make a titanium spring that can perform the same task. |
Among engineering alloys, titanium possesses the strength, density, and modulus to make the "ideal" spring for virtually any weight- or space-sensitive application, according to the Titanium Metal Corp. (TIMET) of Aspen, CO. Various titanium alloys are suitable for making springs, including Beta-C (Ti-3Al-8V-6Cr-4Mo-4Zr), which has been used in the aerospace industry over ten years in spring applications similar in scale to those used in automobiles. The expense of producing Beta-C has precluded its use in automotive applications. By altering the alloy formulation through the use of a much less expensive Fe-Mo master alloy, TIMET has produced a material (Ti-6.8Mo-4.5Fe-1.5Al) called TIMET LCB (Low Cost Beta) that retains the spring characteristics of Beta-C, but at a cost affordable to automakers.
The use of TIMET Exhaust Grade titanium for the exhaust system of the 2001 Corvette Z6 was the first significant appearance of titanium on a volume production car (covered in AEI in October 2000). The first production cars to ride on titanium springs are now on the road, with the rear suspension of the 2001 Volkswagen Lupo FSI fitted with these springs. Muhr und Bender of Attendorn, Germany, manufactures the springs on standard high-volume production equipment from an alloy supplied by TIMET.
The cold spring winding, cold setting (blocking), and shot peening process steps are basically the same for titanium springs as for steel. The learned process differences included minor adjustments - such as determining the optimum heat treatment approach and the optimum aging time - rather than substantial changes, which were largely necessitated by low production volumes. The lower volumes, however, made the Lupo FSI spring application suited for both Volkswagen and Muhr und Bender to gain design, production, and process engineering experience with an unfamiliar material.
 TIMET has many automotive plans for their titanium alloys. Click to enlarge |
Because of titanium's low shear modulus, there are not as many turns required for titanium springs as steel springs. Even if the two materials have the same density, the titanium spring would be lighter because it does not use as much material. Since the density of titanium is about half that of steel, titanium can perform the same task as steel springs in most applications while weighing 60-70% less.
The low modulus and low mass of titanium springs enable them to be designed for smaller spaces so that engineers can reduce the free height of the spring to 50-80% that of a comparable steel spring. This can translate into greater styling and structural design freedom as well as improved passenger compartment and payload space design flexibility.
An added advantage of titanium is its inherent corrosion resistance. In standard salt-spray exposure fatigue tests, the typical fatigue strength of a steel spring, coated or uncoated, is reduced by up to 50% over that of the same spring tested in air. In the same tests, the life of the titanium springs in salt spray was reduced by less than 4% over the tests done in air. Unlike steel springs, titanium springs do not require protective coatings. A primary mechanical engineering property considered in the design of steel suspension springs is corrosion fatigue strength.
- Jean L. Broge
3M's hard-to-bond solution
 New acrylic pressure sensitive adhesion (PSA) technology from 3M can be used for bonding carpeting to an unprimed polypropylene automotive door panel. |
As design and production engineers increasingly shift to low surface-energy (LSE) plastics, they need better and more efficient ways of attaching LSE plastics to themselves, to metals, or to other materials. Surface energy defines the ability of adhesives and pressure sensitive adhesive (PSA) tapes to "wet-out" plastic surfaces and allow adhesion. Surface wet-out refers to how a liquid or viscoelastic solid flows and covers a surface. Maximum adhesion develops when adhesive or viscoelastic pressure sensitive tape thoroughly wets-out the surface to be bonded. The greater the wet-out, the better the surface contact and the greater the attractive force between the adhesive and the plastic surface.
LSE plastics are difficult to bond because they cannot be wet-out by conventional adhesives and tapes, resulting in minimal contact with the plastic surface and unsatisfactory bonds. Bonding LSE plastics such as polypropylene or other thermoplastics typically requires the surfaces to be primed and flame treated or corona treated to convert the low energy of the material to a higher surface energy better suited for most bonding. Plastics with a high-energy surface such as ABS and polycarbonate are easier to wet with conventional adhesives and tapes than are LSE plastics.
According to Barry Kostyk, Key Account Manager at 3M Bonding Systems Division, a recent advance in adhesive technology allows structural bonding (in excess of 6900 kPa (1000 psi) in overlap shear) of LSE plastics without priming or other pretreatments. 3M Scotch-Weld Structural Plastic Adhesive DP-8005 uses an innovative two-part solvent-free acrylic adhesive technology that does not require pretreating. "The structural bond that results is often greater than the strength of the substrates joined," said Kostyk. The adhesive cures at room temperature and resists many chemicals, water, humidity, and corrosion.
 Surface wetting affects contact area and therefore adhesion between adhesive and bonding surface. Click to enlarge |
Sprayable hot-melt adhesives, including 3M Spray-Bond 6111 HT bond LSE plastics without pretreatment, combine high heat resistance with high strength and low creep. These adhesives are used for light- to medium-weight bonding. Applications include vehicle interior manufacturing to bond fabric to polypropylene or polyethylene foams, or foam to foam.
Acrylic PSA technology has been used to bond LSE plastics. However, "often the PSAs compromised the ability to withstand high heat and chemical exposure," said Kostyk. He claims that the proprietary 3M adhesive technology used in 3M Laminating Adhesive 300LSE is suitable for light- to medium-weight bonding applications requiring extremely high peel-bond strength, high temperature, and chemical resistance. Available as an adhesive tape or a double-coated tape, the adhesive can be used to bond nameplates to LSE plastic parts or carpet onto polypropylene door panels.
- Jean L. Broge
