Hood design-Week 2

Hood Design

Hood

A car hood is also known as bonnet in the form of cover that is rested above the engine compartment with the help of hinges. Its purpose is to provide easy access to the engine for its repair and maintenance.

Types of Hoods

1. Inlaid Hood or Built in Type: A gap exists between the hood and the car body. The side reference line of the car is located on the fender which can cause additional damage to pedestrians and increase Euro-NCAP ratings.
2. Wrap Around Hood: This hood tends to wrap around the car body, with the end point of the side reference line of the car being the hood. This will reduce the head impact zone which means higher Euro NCAP ratings.

Classification on Hood Stay types

1. Support Rod Hood Type - A hood stay is a device for a car's engine room that can safely maintain an open engine hood if an external force is suddenly generated by wind or vibration. It can also make it easier to open and close the engine hood. Due to its inexpensive cost and widespread use, it serves as the hood's fundamental and most common support. The support rod used has been purposefully slightly twisted to increase its strength and rigidity so that it can hold the hood securely.
2. Gas Stay Hood Type - These types of hood supports are quite helpful when lifting the hood's heavier weight and do not demand a lot of manpower. It costs a lot and is typically found in larger cars. It is attached to the engine compartment on one end and the hood on the other of its two ends. The gas stay support is fixed by stud balls.

Components of the Hood

1. Reinforcements - We must remove some material from the hood to make space for the latch, striker, and hinges, that will cause a localized loss of material strength. Therefore, the reinforcements given in the latch and striker area and the hinge area are referred to as Latch and Striker Reinforcements and Hinge Reinforcements, respectively.

2. Stiffener pads - There will be vibration when the hood is in motion because of the sort of hard sponge that is used between the outer and inner panels to boost strength. Therefore, we utilize stiffener pads to prevent vibration. As a result, the car's NVH level is decreased.

3. Mastic Seal - These are materials of the hard rubber nature that are sandwiched between the outer and inner panel and ooze out to hold the two panels together. This is positioned inside panel so that it covers the entire hood. These seals can increase local strength by expanding roughly 50mm in diameter.

4. Embosses - It is crucial in preventing human life loss in frontal crashes. The embosses are shaped in a Y and V orientation such that during a collision, the forces spread out or move in the direction of the hinge which will have less impact. on passengers. Adding embosses also enhances traction, adds aesthetic value, and allows for efficient heat dissipation throughout the entire surface.

5. Hinges - The Hinges are used to open and close the hood that rotates about a certain axis.

6. Latch - There are two latches installed in the car for hood opening. One is under the driver’s seat that enables to open hood partially and another latch is under the hood which completely opens the hood.

Materials used in Hood –

1. Steel
2. Aluminum
3. Carbon fiber
4. Fiberglass

Design Considerations for Hood -

Based on the typical height of the population in that area or nation, the hoods are made to open at a certain angle.

HIC Criteria – More the green zone area, better will be the design.

= or < 1000 Rating: Green, 1000 ~ 1350 Rating: Orange, = or > 1350 Rating: Red.

The wrap around distance is the point from the ground to the end point of the hood. Never will the wrap-around distance change. However, the length of the hood is the sole factor that will affect the impact zones.

Master Section – The following significant features are indicated by the master section. There is a 25 mm gap between the hood's outer and innermost surfaces. This 25 mm surface is below the engine compartment. There is a minimum 2 mm space between the hood's outer and inner panels. Additionally, to allow the tool to stamp and exit the part, the geometry is specified at almost a 45-degree angle or inclined outwards.

Deep Drawing - It is a shaping procedure that takes place in a setting that combines compressive and tensile forces. A hollow body including one side opened is manufactured from a flat sheet of metal. Deep drawing is typically done with hard tools in the automobile sector.

Punch, die, and binder are the stiff tools. After inserting the metal sheet blank, the plate holder in deep drawing closes. The sheet is then held in position between the binder and the die. This procedure slows the sheet's flow as it is drawn, preventing wrinkles from accumulating underneath the binder. The sheet is stretched from over die radius by the punch before being formed in the die. Thus, up to the lower center line of the punch, the punch power required for formation is gradually increased.

Hemming - It is a common practice in the production of steel and aluminum bonnets. For panels which require flat hemming, specially produced variations of common automotive alloys are employed. The borders of the outer and internal panels of the hood are normally hemmed to join them together. The outer panel is always folded over the inner panel to hem the front and top edges. There are design solutions where the inside panel is folded around the outermost panel for the left and right sides. The fabric's outside surface is plastically stretched in hemming.

The plastic strain from the hemming operation increases whatever strain is already present in the flange area as a result of the panel stamping activities. The visible surface of the bent material gradually becomes rougher as the overall plastic strain rises, and in areas with high levels of embossing strain, fine surface fractures eventually turn into visible reliefs. In order to prevent problems like spring back, these reliefs are offered on the surfaces. The bonnet surface at the corners tends to bounce back to its original position as a result of the rollers' lack of pressure on the surface when they are made to roll on the surfaces to unite the outer and inner hood. Therefore, when relief is offered, there is no need for rollers to pass.

Striker Position - The striker must be perpendicular to the hood's trajectory for proper hood opening and closing. First, an axis is drawn, and the hinge is placed. The hinge axis and the center distance from the striker are used to calculate the trajectory. A circular trajectory is indicated for the closing and opening of the hood.

The assembly of the hood consists of outer panel, inner panel, hinge assembly, striker and mirror hinge assembly.

Inner panel

Latch and Stryker

Mastic positions

Embosses

Outer panel

Hinge Assembly

Hinge Axis