"Vehicle weight reduction not only has positive impacts on performance, such as acceleration, deceleration, and cornering, but can also reduce its environmental footprint through improved fuel economy and reduced material use. That's why engineers are so keen to make cars lighter. However, we've also found that some technologies introduced to make car bodies lighter can, in some cases, actually increase waste. That a technology designed for its ecological benefits could have the opposite effect of increasing environmental impacts is a point that I find intolerable as an engineer. I came up with the idea for the alternating blank stamping technology because I deeply wanted to resolve this issue.
Speaking on his motivations for developing the 'alternating blank' stamping technology is Teruo Kamada, a Senior Staff engineer in the Reserch and Deveropment Division of Honda Engineering (EG), a company that conducts research and development on production technology and also manufactures the production facilities used at Honda. For years Kamada has been involved at EG in the development of production technologies for metal stamping operations. Given the possibility that tailored blanks—a technology that reduces the weight of a vehicle's body panels by combining two varieties of sheet metal with different material properties—could increase the environmental impacts of the stamping process, Kamada designed the basic construction of the alternating blank stamping technology to resolve this issue.
Immediately after laying out the vision for this new technology, Kamada left the project for an assignment overseas. The developers who succeeded him, however, carried on his vision and, after overcoming numerous obstacles, achieved practical application of the technology. In 2015 they adopted the technology in the stamping operations for manufacture of "side panel outer" (a side body panel) for the N-WGN. The result was a dramatic improvement in process yield (the amount of raw material in the final product relative to how much was put into the process of making it), along with a variety of other beneficial outcomes, including a reduction in the amount of scrap generated, a reduction in carbon dioxide emissions, and a reduction in raw materials use.
In the automotive stamping process, workpieces called blanks are made by cutting sheet metal with a die. These blanks are then pressed and formed into a three-dimensional body component. Blank fabrication, the first stage, involves passing rolled metal sheets called coils through a stamping press, which punches them out with dies located above and below the metal. Sheet metal remaining after the blank is cut out becomes scrap. Since roughly half of the coil is transformed into scrap, stamping operations tend to account for about two-thirds of all scrap produced in Honda automobile production.
Of course, this scrap is collected and reworked into other metal products, so not all goes to waste. But the added resources and energy used to do so makes this system far from ideal. Scrap reduction is also a socially desired goal in Japan. For example, the Act on the Promotion of Effective Utilization of Resources, an environmental regulation colloquially known as the 3Rs Law, requires businesses to plan and report on activities to reduce scrap.
In this light, the possible increase in scrap from stamping—a process for which a scrap reduction was desired, other factors notwithstanding—was a major cause for concern, regardless of its advantages for making vehicles lighter. The alternating blank stamping technology devised by Kamada, therefore, is attracting a great deal of attention due to its potential to dramatically reduce scrap, not only in the fabrication of tailored outer panels, but for stamping processes overall.
Teruo Kamada, Senior Staff engineer, Reserch and Deveropment Division, Honda Engineering Co., Ltd.
"Side panel outer" of the N-WGN
Material begins as a thin steel sheet rolled in a coil. One coil provides enough material to produce 500 cars' worth of blanks
Stamping press cuts out the blanks. Dies above and below are pressed together to punch out the desire shape
Light blue indicates sections used for parts, while gray indicates areas that become scrap. A large portion of this metal sheet will become scrap
Blanks cut out by the stamping press. These are pressed again, forming three-dimensional parts that become the side panel outer
Outer body panel is manufactured by combining two types of material: thin steel sheet and high-tensile steel
Replacing the red section, previously used, with high-tensile steel turns this area into scrap
Nesting blanks in this way not only minimizes scrap, but also allows more blanks to be cut from fewer coils, increasing the number of blanks extracted from each coil by about 20 percent
The ideal pattern can't be stamped, since the required die goes past the edges of the stamping press
A stamping press. People nearby provide a sense of scale for how large it is
Tailored body panels, the motivation behind development of the alternating blank stamping technology, are a new technology for reducing vehicle body weight. Compared to conventional body panels, which are made from one type of steel, these panels combine two types of metal with different material properties, making them lighter while also maintaining or even improving strength and rigidity. Tailored side body panels, for example, are made by substituting only the lower portion—the part subject to strong forces—of a part typically made entirely from thin steel sheet with high-tensile steel, a strong and lightweight material.
This technology also presented an unexpected problem: Replacing part of the sheet (the red area in the figure) with high-tensile steel meant this section would not be used, thereby increasing the amount of scrap generated in blank production. One way to solve this problem is to design the sheet layout (the pattern determining which sections of the sheet material to punch out for parts) to reduce waste by nesting multiple parts in the same sheet. However, since the shape of panels and other components vary widely between car models, an optimally efficient sheet layout is not necessarily possible for all models; it can actually reduce process yield depending on the model.
"With societal requirements on energy and resource efficiency becoming more strict, improving the yield of a stamping process where only about half of the material appears in the final product was an important company priority. And since scrap is a byproduct we are legally required to reduce, we couldn't allow an increase in scrap, no matter how it helped to reduce vehicle weight," says Kamada. "We had to develop a technology or method that would enable efficient sheet layout in every situation. That was the idea that got me thinking."
In the case of blanks used for the tailored outer panel, rotating a blank 180 degrees would result in an efficient sheet layout that minimized scrap. This sheet layout was not possible, however, as it would make the stamping die too big for the press. Kamada saw this as just another example of a situation in which an ability to fit a large sheet layout onto a smaller die would dramatically increase the number of layout possibilities, while also significantly improving process yield.
"We could have gotten a bigger stamping press that fit bigger dies, of course," he says. "But stamping presses are huge machines; one press alone is about as large as a two-story building. From a cost-benefit perspective, replacing or adding a stamping press is not so simple. In the end we needed a technology or method we could deploy with existing facilities. I spent many days trying to work out a good solution."
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