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Lightweighting Heavy on History

 Ellen Kehoe

 

 

 

 

 

 

 

By Ellen Kehoe
Senior Editor

Maybe the desire to lose weight doesn’t go back as far as Atlas in Greek mythology, but for decades materials experts have sought lighter weight with strength and economy in the more well-known applications of autos and airplanes as well as in such products as metal cans and bicycles.

Atlas; Image from Houzz.com
Magnesium

Lightweight, low-cost magnesium tooling was an early success. A radar component manufacturer mentioned in a 1955 SME Technical Paper recognized the economy of using magnesium tooling, expressing its workability by saying, “we use it like lumber.” Aside from its light weight, magnesium’s advantages are dimensional stability, tight tolerances, high strength properties and superior elongation, toughness and stiffness. Machinability, weldability, fine grain size and freedom from porosity, and alkaline resistance are also key benefits. The paper goes on to describe representative designs of various inspection, testing and quality control checking and tooling fixtures. Other tooling uses of magnesium include stretch forming dies, rubber pad form blocks, assembly and locating jigs, welding fixtures, plastic dies and molds and drilling, routing and fly-cutting jigs.


Martensitic Stainless Steels

Stainless steels are commonly divided into five groups, classified by their microstructure at room temperature: austenitic, ferritic, duplex, precipitation hardenable and martensitic. Martensitic stainless steels (MSS) are a low-cost, high-strength, lightweight alternative to costly high-alloy materials. With excellent mechanical properties of specific strength, toughness and fatigue performance, in addition to corrosion resistance, MSS are easy to process in the annealed state and compatible with all existing forming and fabrication methods.

Historically, applications of martensitic stainless steels include surgical instruments, cutlery, gears, shafts, fasteners, steam, gas and jet turbine blades, and valves. Typical new applications are for structural components, tube, pipe and assemblies.


Can Manufacturing

Reducing the weight and metal cost of cans and other effects of lightweighting on can manufacturing methods are discussed in papers from several can-making seminars. Selecting the best and cheapest way to produce cans is a complex problem, requiring a detailed study of metal, equipment and labor costs. With 75% of the metal in a can in the sidewall, reducing the thickness makes sense, but a thinner can is not always more economical and is susceptible to damage in the customer’s plant, such as in beverage can filling and handling.

Drawn and ironed (D&I) cans are ideal where a substantial difference is required between bottom and wall thickness. The absence of a solder joint can be an important factor also. As the technology for producing D&I cans progressed, it was “recognised that metal forming difficulties may prevent the full exploitation of the increased material strength.” Maintaining control of wrinkling and tooling geometry are important aspects discussed.

Martensitic stainless steel automotive subframes and suspension components (D. Codd, TP08PUB118).

For other kinds of cans, D&I can offer enough metal savings to offset higher equipment and labor costs. The essential considerations are reducing the scrap skeleton weight/width, increasing the (coil) width of the starting metal (to increase the number of cups produced per stroke of the press), reducing the can wall thickness, reducing the gauge of the starting metal and changing the configuration of the can.

Numerical simulation to optimize both the can profile and can manufacturing conditions with aluminum was presented by a researcher from Kobe Steel in Japan. In the necked-in process, the necking load is reduced to 85% of the conventional load by an optimum die profile. In the scoring process on the can end, the optimum profile and surface condition of the die are clarified to obtain a better condition of the score.

Bicycle Parts

The use of composite materials in the bicycle industry has increased significantly. The fork is a critical component and a major influence on the ride quality of a bicycle. The response of the bicycle to the road and during turning depends greatly on the stiffness and damping of the fork, and the fork undergoes many types of load during use. Failure of the fork would be catastrophic, so high impact resistance and long fatigue life must be assured.
Finite element meshing of crown region of bicycle fork (M-A. Octeau and L. Lessard, TP01PUB279).
At the 13th International Conference on Composite Materials (ICCM-13) in 2001, Canadian authors presented a new structure for a carbon fiber fork with reduced weight and increased performance. This type of composite fork is for use on high-end racing bicycles, where stiffness, strength and light weight are all critical design parameters. The design was also developed to be easily produced—by resin transfer molding—at minimum cost with high quality and repeatability.

The first “safety bikes”—in today’s familiar configuration with two equal-sized wheels—developed in the late 1800s-early 1900s in response to head injuries when riders flew head-first over the large front wheels of old-time contrivances. Diamond-shaped frame tubes, which are still in common use today, were initially quite heavy.

Materials for bicycles has evolved with increasing sophistication from steel to wood and bamboo to aluminum, magnesium, plastic and graphite-carbon. The first molded, advanced composite frame—the Kestrel 4000—was introduced in 1987 by Cycle Composites Inc. Unlike any other carbon frame before it, the Kestrel did not use metal lugs to connect tubes together. Without the constraints and high stresses commonly found in previous tube and lug designs, an aerodynamic model with a superior strength-to weight ratio could be easily created. The company also introduced a carbon fiber road fork, molded in one piece. The fork was lighter than the current production aluminum forks but offered the safety and handling of a heavy steel fork.

 

P.S.-Cars and Planes

Among the offerings on lightweighting automotive and aircraft components in SME's knowledge resource of 16,000 technical papers are these on: aircraft and missile parts (TP58PUB61), missile case materials (TP63PUB113), composite aerospace tooling (TP89PUB689), performance of Twintex prepreg for automotive applications (TP01PUB108) and design approach to an atmospheric re-entry vehicle (TP04PUB60).

 


Published Date : 2/23/2015

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