Concept
To unlock the full potential of the 2017 Acura NSX’s Sport Hybrid SH-AWD powertrain and fulfill the high targets set for its total dynamic performance, the engineering team took a bold and challenging new direction: a completely clean-sheet, multi-material approach that breaks new ground in the automotive realm—with new materials, new construction methods and new thinking in supercar body design.
By starting from scratch, the NSX development team was able to choose the optimal material application and construction methodology for each area of the body, targeting both low mass and ultimate rigidity while also satisfying other critical design objectives such as superior outward visibility, world-class crash safety performance and world-class quality and durability befitting a next-generation Acura supercar.
The end result is the NSX multi-material body, with its aluminum intensive space frame, designed to achieve structural rigidity far superior to its top-in-class competitors. This high level of dynamic rigidity provides a crucial foundation for the NSX’s instantaneous responses. As a result, drivers will feel their inputs directly translated to the car’s actions with incredible speed and fidelity, while simultaneously allowing the maximum potential of the Sport Hybrid SH-AWD system to be realized by the car and driver—the essence of the New Sports eXperience.
“The challenge for the body design team was to create a body with a high level of rigidity to be able to transmit the full feeling of this powertrain directly to the driver without delay,” said Shawn Tarr, chief engineer for the NSX body development. “While the all aluminum unibody of the original NSX was ahead of its time, we would need to look to world-first technology in order to achieve this new level of rigidity.”
The NSX body construction—performed entirely in-house at Acura’s Performance Manufacturing Center (PMC) using domestic and globally-sourced parts—is undertaken with innovative new techniques and technologies, and with a commitment to quality unmatched in the supercar realm. As one critical example, MIG welding of the aluminum-intensive space frame is performed entirely by high-precision robots, with all welds and body components undergoing a detailed inspection by highly skilled PMC weld technicians.
Building quality and accuracy into the space frame eliminates the post-construction machining activity that is common in low-volume vehicle manufacturing, including many competing vehicles. This same commitment to next-generation quality through the ideal blend of machine precision and human craftsmanship can be found in every aspect of NSX’s body construction, finishing/painting and assembly, and is readily identifiable in the final product.
Key Body/Frame Features
- Multi-material aluminum-intensive space frame
- Complex high-performance ablation cast aluminum nodes for front crush zone (world’s first automotive application)
- Three dimensionally bent and quenched ultra-high strength steel A-pillar structure (world’s first application)
- Carbon fiber core front floor panel
- Aluminum and low-density SMC outer panels
- Innovative construction techniques including high-accuracy robotic MIG
welding using rotating trunnion (rotisserie-type) weld fixtures (world’s first automotive application) - Additional advanced joining technologies including flow-drill screws and self-piercing rivets
- Environmentally-conscious zirconium space frame pre-treatment (Acura first)
Multi-Material Space Frame
The NSX multi-material body with aluminum-intensive space frame offered the development team the best structural rigidity and lowest platform weight along with superior packaging for the power unit. NVH is also greatly minimized by the NSX’s tremendous global rigidity benchmarks—two times static and three times dynamic levels of torsional rigidity demonstrated by the next highest competing vehicle evaluated by the NSX development team.
Highly rigid and reinforced extruded aluminum beams comprise the majority of the space frame and are utilized for the front and rear frame rails and cross members, front and rear bulkhead frame members, floor cross members and side rails. To further aid noise attenuation, a number of these aluminum extrusions are filled with acoustic spray foam, which is used in 38 different locations.
Cast aluminum nodes serve as joining points for the extruded aluminum frame members and as ultra-rigid mounting points for the vehicle’s front and rear suspension systems, as well as its rear power unit. These nodes are either gravity die cast or, in front and rear crush zones, formed using advanced new ablation casting technology, a world’s first automotive application (see below for additional detail).
In another world’s first, the upper portion of the A-pillars and roof rails, which comprise one continuous section, are formed using three dimensionally bent and quenched ultra-high strength steel tubing. This new metal forming process allows enhanced styling and outward visibility while providing for high roof-crush strength (see below for additional detail).
Aluminum stampings are utilized as lightweight closure panels for the rear floor, rear bulkhead and B-pillars. The front floor panels are constructed of carbon fiber for strength and low weight.
Ablation Cast Nodes
One of the most difficult design challenges in the development of the all-new Acura NSX was to minimize the front and rear overhangs of the vehicle while managing collision energy absorption in key areas for crash safety performance and maintaining optimal structural rigidity. To solve these complex and competing design imperatives, Acura engineers developed innovative new technology called ablation casting, an all-new material application and a world’s-first application in the automobile industry. Ablation casting was matured from a fundamental research theme to production vehicle application within the development cycle of the new NSX—a major design, engineering and manufacturing achievement.
Ablation cast aluminum nodes within the NSX space frame shown in yellow.
Ablation casting is utilized in the creation of six joining members, or nodes—two upper and two lower nodes in the front frame, and two nodes in the rear frame. These nodes also serve as ultra-rigid mounting points for both the front and rear suspensions. The front upper nodes are designed to absorb and dissipate energy in a frontal collision. The two ablation cast nodes at the rear of the vehicle are designed for high strength to mitigate forward movement of the power unit in the event of a severe rear collision.
Ablation casting involves the rapid cooling of a sand-cast aluminum component via the precise application of water jets, which ablate the sand mold while cooling the part. This process allows for the fine-tuning of both the cast part’s shape and its material properties while minimizing weight with hollow forms and optimized wall thicknesses. Unlike traditional castings, the high-strength and ductile properties of the ablation cast members allow these sections of the space frame to progressively crush at 155 kN of load; and the rear frame nodes are designed to withstand up to 210 kN of load.
The ablation cast nodes are produced in-house at the company’s Anna, Ohio engine plant, which has extensive experience with precision casting. The Anna Engine Plant is the only automotive production facility in the world utilizing ablation casting technology.
3-Dimensional Bent and Quenched Ultra-High Strength A-Pillar
The original NSX was known for its outstanding forward visibility, giving drivers a feeling of being connected to the road while optimizing visibility, and this design attribute was considered essential to preserving a core characteristic of the NSX driving experience. For the next-generation NSX A-pillars, new advancements in forming ultra-high strength steel parts provided the ideal solution, meeting the engineering team’s goals for safety performance while maximizing forward visibility.
The NSX’s A-pillars have been precisely crafted using an all-new, three-dimensional forming and tempering process that allows for a complex part shape with ultra-high tensile strength. This “3D bent and quenched” component is heated and then shaped in three dimensions by an articulating robotic arm, after which the part is quenched using water jets to achieve an ultra-high tensile strength of 1,500 megapascals. This process enables a very thin cross-section with precise shape specification and tolerances, while also meeting the increased structural rigidity standards for roof-crush performance. Utilization of this process reduced the width of the A-Pillar—at just 3.5 inches (89 millimeters) in width—by one inch (25 mm) compared to a conventional construction process; the view is a full 36 percent less obstructed than the next-best supercar evaluated by the Acura team and even better than the original NSX.
To prevent galvanic corrosion, the component receives an electro-deposited coating before being joined to the stamped steel structure at the base of the A-pillars.
Carbon Fiber Floor
When evaluating material composition and placement throughout the body, the design team determined that carbon fiber would serve as the ideal material for the driver and passenger floor section. In addition to its light weight, the material is strong enough to handle the loads occupants place on the floor during vehicle ingress/egress. Aluminum sheeting would have required additional cross-member frame support beneath it which would have in turn added additional weight.
Space Frame Construction
A number of advanced technologies and techniques are used in the construction of the NSX space frame, which is conducted entirely in-house at the company’s new Performance Manufacturing Center in Marysville, Ohio. The NSX development and manufacturing teams were determined to maintain in-house control of the complete body construction process to ensure the highest levels of quality and performance for Acura customers.
Through the implementation of strict manufacturing/build processes and quality controls, the dimensional accuracy of the multi-material body is maintained throughout the construction process, eliminating the need for post-process machining. This is a unique manufacturing system and a great point of pride for Acura, allowing the team to achieve quality and accuracy levels superior to its competitors.
Metal Inert GAS (MIG) Welding
Metal Inert Gas (MIG) welding is utilized for the majority of the aluminum space frame construction. The frame contains more than 860 MIG weld points, where more than 112 feet (34 meters) of MIG wire is applied. Most welding is done by fully automated robotic weld arms which offer exceptional precision and control.
For the underbody section of the space frame, construction is done in a series of four stations, where highly skilled weld technicians work in tandem with automated robotic weld machines to ensure the highest quality parts. Specialized picture frame-style fixtures, developed in-house, are used to hold the component pieces, allowing for precise control of the weld process and dimensional accuracy of the part. Four of these fixtures are able to rotate 360-degrees to improve the access of robotic weld arms to the part and to allow for full datum referencing (highly accurate measurements between lines on a three-dimensional X, Y and Z axis) of the part.
Strategic sequencing of the numerous weld processes mitigates the potential for parts deformation from heat buildup, a common challenge in the welding of aluminum components. The quality of welds and dimensional accuracy of the part are confirmed at each station by technicians through visual inspection.
The floor and upper components of the space frame are then joined by large, fully robotic general welders, which also utilize rotating trunion-type fixtures with 360-degree movement. Twin robotic weld arms are able to conduct welding processes simultaneously to aid in both manufacturing efficiency and in the uniform distribution of heat, mitigating the potential for part deformation.
Additional body joining technologies including self-piercing rivets, flow-drill screws, and roller hemming, each chosen for its specific and unique qualities within a given element of the overall space frame construction.
Self-piercing rivets (SPR) allow for the joining of two or more layers of material without having to pre-drill or punch a hole and are ideal for joining sheet materials while providing an exceptionally watertight joint. The NSX space frame contains more than 345 self-piercing rivets.
Flow-drill screws (FDS) are used in the place of a nut-and-bolt application in numerous areas of the space frame, reducing both weight and parts complexity. FDS are also particularly well suited to areas of the body where one side of the part is inaccessible by conventional tools, such as in an extruded component. More than 245 flow-drill screws are applied to the NSX space frame.
Roller Hemming joins two pieces of sheet metal by creating a sharp-angle bend, allowing the metal to be folded back over itself, creating a strong and tight joint with a clean and finished edge. There is nearly 60 feet (18 meters) of roller hemming edge on the NSX space frame.
Space Frame Advanced Conversion Coating
Prior to final assembly—where the space frame is fitted with the suspension, powertrain, electrical, interior and other componentry—the fully constructed space frame undergoes an advanced conversion coating process using a zirconium pre-treatment material and an e-coat process as an additional barrier to galvanic corrosion while maintaining a low environmental impact.
The use of zirconium, an Acura and Honda company first, eliminates more than 90 percent of the waste byproduct that results from the use of more conventional zinc-phosphate material. This byproduct, which contains heavy metals, must be disposed of in landfills, creating a significant waste stream. The use of a zirconium conversion coating is part of the effort to create a manufacturing process with a low environmental impact, consistent with the ideal of a next-generation hybrid supercar.
Body Repair and Serviceability
To assist in the ease and cost of collision repair, as well as to protect to a high degree the dimensional accuracy and integrity of the NSX space frame during a collision repair, the NSX development team worked closely with Acura service engineering team members to implement an overall modular construction concept: Space frame components can be purchased and replaced individually or as pre-assembled modular replacement sections. For example, there are “light-collision” and “medium-collision” replacement sections for both the front and rear sections of the vehicle, which are designed to minimize the amount of welding activity required.
For extensive servicing of the powertrain (engine, rear motor and transaxle), the team designed a modular rear inner body section—once the rear fascia panel is removed, the entire trunk section of the vehicle can be removed as a single unit to permit easy and unrestricted access to the mid-mounted V-6 engine. The trunk structure also helps locate outer body panels.