Hood design-Week 2

HOOD ASSEMBLY

INTRODUCTION

Hood / Bonnet is main component of a car at the front portion. It is used to decorate the car and add luxurious look. The shape of the bonnet is made aerodynamic in order to minimize the air effect. Bonnet is generally used to access the parts easily such as radiator, engine and many other parts.

HOOD DESIGN CONSIDERATION

The Hood of a car is considered as the frontal BIW enclosure component. Bonnets are designed to reduce air resistance as the air flows around the car. The design of the bonnet is vital since it affects the aerodynamic flow around the car. Apart from this, bonnets are also designed to meet several other requirements. They serve a great deal of purpose in protecting the passengers inside the car and the pedestrians in the event of an accident. It also acts as the cover for the engine.

• The 1st and most important safety requirement to be considered while designing the Bonnet is the Pedestrian Safety from frontal collision.
• The European New Car Assessment Programme (Euro NCAP) is a European car safety performance assessment program which has developed test specifications and rating systems for assessing pedestrian injuries during impacts with the front of vehicles Such tests include a series of tests using impacts designed to bio-mimic a collision at a speed of 40 km/h.
• They describe a situation in which a pedestrian is situated laterally and a car first hits one of his legs. Tests are conducted on the leg, upper leg and, most importantly, the head, as head trauma is most commonly responsible for casualties.
• Thus to avoid severe injuries to the head, the high impact area for adults and children are subjected to less thickness. Also no reinforcement should be provided in that area as during the head collision, the hood will absorb the head impact energy leading to collapse of the hood and thus protecting severe head injury.
• Another important criteria for the hood design is the protection of the occupants inside the car during the front collision. The design of the hood should be in a such a way that the during the collision, the force should travel in the upward direction through the embosses and directed towards the body of the car. Thus protecting the occupants inside.

Following parts are using in Hood Assembly in the report,

• Hood outer panel
• Hood inner panel
• Hinge assembly
• Striker assembly

HOOD THICKNESS INFORMATION

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

INNER PANEL

• The hood inner panel is required to have a high initial reaction force against the impact exerted on the hood to enhance the energy absorption capacity. The hood is further required to minimize a reduction of a reaction force by deformation in a collision.
• It is an object of the present invention to provide a hood inner panel capable of reduction of a reaction force of the hood inner panel even if a level of deformation of a hood of a vehicle increases, and ensuring a sufficient energy absorption capacity.
• In the inner panel only we can research and implement the safety of pedestrians and as well as the driver.in this panel only we can attach the reinforcement, embossed, mastic points, etc

OUTER PANEL

Outer panel is nothing but a outer skin of inner panel. Otherwise called as a cover of inner panel. It is the part, which gives luxurious look to the hood or bonnet. Outer panel and inner panel cannot join by any welding process like spot welding or rivet, which spoil the outer look of a car. The outer panel is generally extracted model from the prototype design.

HINGE ASSEMBLY

Hinge is a component that fixes the hood to the fenders of the car. The latch must be fixed perpendicular to the hinge axis so that the hood opens or closes properly.

STRIKER ASSEMBLY

Latch & striker is used for locking the hood with the car. it's usually placed on the space provided on the inner panel.

The process involved in designing hood as a sheet metal operation is

• Blanking
• Hemming
• Punch cutting or piercing
• Deep drawing
• Embossing

HEMMING

• Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods, and tailgates are formed by hemming processes.
• Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a forming operation in which the flange is formed with a hemming tool after the drawing and trimming operations have been completed
• Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps.
• If weld or bolts were used to join the hood panels then the design and the aerodynamic features would get damaged so hemming is more significant to use.

While doing the hemming process a relief angle is formed as a product of hemming when attaining at the corner of the sheet

DEEP DRAWING

• Deep drawing is a manufacturing process that is used extensively in the forming of sheet metal into a cup or box-like structures. Pots and pans for cooking, containers, sinks, automobile parts, such as panels and gas tanks, are among a few of the items manufactured by sheet metal deep drawing.
• A deep drawing of sheet metal is performed with a punch and die. The punch is the desired shape of the base of the part, once drawn. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. For many calculations, the sheet metal thickness is assumed to remain constant. However, there are changes in thickness in certain areas, due to the forces involved.

EMBOSSING

• The metal sheet embossing operation is commonly accomplished with a combination of heat and pressure on the sheet metal, depending on what type of embossing is required. Theoretically, with any of these procedures, the metal thickness is changed in its composition.
• A metal sheet is drawn through the male and female roller dies, producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet.
• The pressure and a combination of heat actually "irons" while raising the level of the image higher than the substrate to make it smooth. The term "impressing" refers to an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material.

LATCH TRAJECTORY

While opening or closing the hood, the latch must be perfectly aligned to the fixing or striker point. For that, the latches trajectory must be perpendicular to the hinge axis.

MASTIC DATA

A mastic sealant data is used to fix or combine the hood outer panel and hood inner panel.

• They can provide thermal and acoustical insulation, and may serve as fire barriers. They may have electrical properties, as well. Sealants can also be used for simple smoothing or filling. They are often called upon to perform several of these functions at once.
• A sealant has three basic functions: It fills a gap between two or more substrates; it forms a barrier through the physical properties of the sealant itself and by adhesion to the substrate; and, it maintains sealing properties for the expected lifetime, service conditions, and environments. The sealant performs these functions by way of correct formulation to achieve specific application and performance properties.

IMPACT FORCE DISTRIBUTION IN HOOD/BONNET

A hood design must be made in such a way that when a force is impacted in the front of the hood, all the force must be directed outwards from the vehicle. And the distribution of the force must be controlled along with the hood.

HOOD ASSEMBLY_OUTPUT MODEL

CONCLUSION

Therefore, we have designed a hood that falls under the rules and regulations of the manufacturer's standards.