Hood design-Week 2
AUTOMOBILE HOOD DESIGN
Introduction:
Hood
The Hood is the outer panel covering the front engine of the vehicle. It opens to allow access to the engine compartments for the ease of maintenance or repair of the vehicle. Hood is also considered as another door as it consists of the outer panel, an inner panel like side doors of a vehicle.
Outer panel: It is the aesthetic part of the hood. In other words, it is the outer skin of the hood which provides a luxurious look to the vehicle.
Inner Panel: The hood inner panel provides strength and rigidity to the hood. It also directs the force of the collision outwards instead of into the engine compartment of the car.
Striker: It is U shaped bend that attaches to the latch in order to lock the hood and prevent any loose movement during the car motion.
Hinge: It is the pivoting point from which the hood opens and closes.
Pedestrian -Vehicle Collision
- India, however, ranks 1 in the number of road accident deaths across the 199 countries reported in the World Road Statistics, 2018 followed by China and the US. As per the WHO Global Report on Road Safety 2018, India accounts for almost 11% of the accident-related deaths in the World.
- Road transport remains the most favored mode of transport for both freight and passenger movement in India. The fast-growing population, exceptional rate of motorization coupled with the ever-growing urbanization has made people vulnerable to frequent road accidents resulting in fatalities, injuries/disabilities.
- the sequence of injuries and events in a pedestrian collision images are mentioned below.
Design specifications for the automotive hood component
Master section data was already provided by the support instructors of the course.
Hood Thickness Information
- Outer Panel Thickness = 0.75mm
- Inner Panel Thickness = 0.75mm
- Reinforcement Thickness = 1.5mm
The process involved in designing hood as a sheet metal operation is
- Blanking
- hemming
- Punch cutting or piercing
- Deep drawing
- Embossing
Design of hood
- Inner panel design
- 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.
- 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.
- 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.
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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.
- Hemming in sheet metals
- 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.
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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 hem when attaining at the corner of the sheet metals.
- 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.
Hood Components
- Latch
A hood latch is a very simple component. It's basically the fastener that keeps your hood closed shut. This latch ensures that your hood is securely connected to your vehicle and that it doesn't pop open unexpectedly
When tension is applied to the cable from the hood release handle, it pivots the secondary latch, which pulls away from a retaining seat located under the hood. By design, the secondary latch then releases the hood a few inches before a safety latch takes over.
- Hinge
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.
- Latch trajectory motion
The thickness of the reinforcements should be in the range of 1.5mm. This parameter can be obtained from the CAE team or with a carry-over study.
There is additional reinforcement called a stiffener pad which is attached between the hood inner and outer panel. This is done in order to reduce the noise and vibration during the motion of the car.
Distance between the outer and inner panel should be 5mm where mastic sealants are placed in the mastic sealant points to form a strong bond between them. This also reduces the noise and vibration in the hood in the car.
We are using sealants to join the hood outer and inner panel because the sheet metal used is 0.75mm thick and welding is not possible as it would affect the Class A surface.
Emboss
Sheet metal embossing is the stamping process to obtained raised or sunken edges for the desired design pattern on the sheet metal. This is done with help of male and female dies between which sheet metal is placed and the dies are pressed against the sheet metal to obtain the designed pattern. In some cases, roller dies are used to get the raised edges in the sheet metal.
Manufacturing considerations for the emboss creation
1. The distance between the outer edges of the emboss should be a minimum of 5mm.
2. Draft angle should be provided to the emboss with 7degree">degreedegree - 9degree">degreedegree for the easy removal of the part from the die.
3. No sharp corners to be provided in the emboss can it would lead to inefficient manufacturing.
4. The height of the emboss should not be more than 5mm.
Position of the hinge and Striker.
The hinges should be positioned on the hinge tentatively such that they lie on the same plane. The position of the hinge can also be decided based on the carry over study.
From the axis of the hinges create a midpoint, from that midpoint draw a circle with a radius from the midpoint to the center of the striker. The circle created is called the trajectory circle. With the trajectory circle, it is to be checked that the striker is tangent to the trajectory circle if not then the position of the hinge should be moved accordingly such that the striker is tangent to the trajectory circle.
This is done because the latch where the striker strikes and locks the hood is positioned with respect to the trajectory circle. If the striker is not positioned accordingly then there will be difficulty in locking the hood.
Note: For all the closure components the position of the hinge and hinge axis is important and it influences the position and orientation of the striker.
Design Standards
The most important criteria in designing a bonnet are pedestrian safety from a frontal collision.
The EURO NCAP has developed series of crash test and rating systems for assessing pedestrian, driver, and passenger injuries during impact with of the vehicle.
The below image illustrates a pedestrian is in standing perpendicular to the road and a crash test performed with a head-on collision.
Wrap around distance: It is the distance from the road to the point where the head of the pedestrian collides with the hood.
In the below images we can see the wrap-around distance for adults and children.
Side reference line: A line is drawn at 45degree">degreedegree from the ground such that it touches the end of the hood. This type of hood is called the inlaid hood. If the end of the point of the side reference line is at A-pillar then it is called the wrap-around hood.
The position of the side reference line is important because if the side reference line is on the hood resulting in a bigger hood the wrap-around distance will be less and hence the impact zone will be more. But if the side reference line falls on the fender which makes the size of the fender bigger resulting in a lesser hood size which in turn results in high wrap around distance and lowering the impact zone.
Another important aspect to be considered is the safety of the driver and passengers of the car. This is done by strengthening the inner panel by creating embosses and the design of the embosses should be such that the force due to impact should be directed outside the car rather than inside the engine compartments.
The arrows represent the direction of the force.
ISO VIEW
FRONT VIEW
SIDE VIEW
TOP VIEW
