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The Honda Insight's body is made of aluminum, offering light weight and a high level of body rigidity to enhance overall fuel economy, handling and passenger safety.
Aluminum weighs only one-third as much as steel. In addition, aluminum alloy is highly versatile and readily lends itself to a wide variety of manufacturing techniques. Lastly, aluminum is extensively recycled, which helps lower its cost. The Insight's aluminum body in white (just the sheet metal: doors, hood, etc.) is roughly 40 percent lighter than a comparable steel body.
The basic structure is a new, lightweight aluminum monocoque, reinforced in key areas with aluminum extrusions joined at cast aluminum lugs. Stamped aluminum panels are welded on to this structure to form an extremely light and rigid platform for the drivetrain and suspension.
The resulting body structure has 13 percent more bending strength and an impressive 38 percent more torsional rigidity than a comparably-sized steel body, despite weighing 40 percent less. The unit-body part of the Insight's body uses stressed sheet-metal panels to absorb and distribute structural and suspension loads, much like an ordinary steel unit body.
From their experience building the Acura NSX - the world's most produced aluminum-bodied car - Honda engineers have gained extensive knowledge of aluminum. However, the Insight is designed for a very different purpose.
Market requirements dictated the development of new, more cost-effective techniques for manufacturing the Insight's aluminum body. In response to this challenge, Honda engineers developed the Insight's innovative unit-body/space-frame construction.
The unit-body part of the Insight's body uses stressed sheet-metal panels to absorb and distribute structural and suspension loads, much like an ordinary steel unit body. However, with the Insight's body all of these panels, including the roof, floor, front and rear wheel wells, rear quarter-panels, bulkhead, and even the doors and hood, are made of aluminum alloy. These stressed panels are reinforced in key areas by aluminum-alloy frame members.
It is these aluminum frame members and their cast-aluminum connecting joints that make the Insight's hybrid body so unique. In a steel unit body, frame members are formed by stamping in large presses and then joined to the body by welding. However, the Insight uses extruded frame members. Extrusions are drawn from a die in much the same way that tubing is made, and like tubing are of constant cross section. Once formed, extrusions can be easily made into complex three-dimensional pieces, such as a curved windshield frame. They also do not require any additional machining or finishing after they are formed.
On the Insight, each frame member's size and strength is optimized so that the frame is strong where it needs to be, and lighter in less critical areas. A variety of shapes are used, including hexagons, ovals, H-sections and reinforced box-sections. The door and windshield pillars, front and rear side-frame members, lower body sills, cross members and floor frame members are all formed in this manner.
In more highly loaded areas of the body (such as the front and rear sub frames), larger, internally ribbed, hexagonal aluminum frame members are used. These are joined to other frame members via rigid, die-cast aluminum joints. Die-castings are also used at engine and suspension mounting points. These die-castings offer versatility and cost savings, because they can be designed to suit specific size, space and strength requirements.
Thixotropic Die Casting
Some of the die-cast joints used in the Insight's aluminum body are made using a newly developed casting technology invented by Honda engineers, called Thixotropic Die Casting. Thixotropic Die Casting uses aluminum alloy that has been heated to a semi-solid condition, instead of the molten, liquid state normally used in die casting. Pieces made with molten aluminum must be more highly processed and refined before casting; however, Thixotropic Die Casting requires less energy for smelting (an important consideration since aluminum is more expensive than steel), and owes much of its strength to the controlled formation of discrete aluminum crystals within the metal casting.
The Insight was designed to meet or exceed the latest U.S., European and Japanese safety standards. The interior is designed to meet the 2003 safety standards for side-impact and head-injury protection.
The Insight's aluminum body and frame are designed to meet the safety and impact-protection standards Honda engineers set for it. At the heart of this design is a newly developed Honda technology called G-Force Control Technology, or G-CON. G-CON optimizes each part of the Insight's aluminum body and frame to best absorb a specific type of impact. The cabin floor, for example, forms a strong and rigid foundation, designed to minimize deformation in an impact. Outside of this area, the surrounding aluminum frame members have been tailored to control impact forces.
Full-frontal and offset-frontal impacts are first absorbed by the large-section, hexagonal extrusions that serve as the front-side frame members. These hexagonal sections are made up of six individual equilateral triangles and are designed to progressively collapse like the bellows of an accordion in an impact. A die-cast aluminum joint connected to the rear of these extrusions transfers any additional impact energy rearward to an oval-shaped, curved hexagonal extrusion, which further absorbs energy by bending upward.
The aluminum extrusions that extend from the passenger compartment all the way back to the rear of the Insight on either side are also designed to progressively absorb rear-impact energy. In addition, the spare tire and wheel, and the Insight's aluminum suspension, including the tires and wheels, are designed to aid in rear-impact energy absorption.