Hood design-Week 2

Hood design

Objective:

 To Design Hood outer panel, inner panel and the necessary reinforcements by following the Master section with the design parameter.

Introduction:

An automobile hood, also known as a bonnet in some countries, is the hinged cover that covers the engine of a front-engine vehicle, which in many countries is called a bonnet. Basically, it is used for accessing the engine in order to conduct repairs and maintenance on it. To hold the hood down, it is typically used a concealed latch or latches that are hidden behind the hood. A hood pin may be used to hold the car hood down on cars with aftermarket hoods and race cars.

A hood may also contain an ornament on top, a hood scoop, wiper jets, power bulges, or even a power bulge with wipers. Steel and aluminum are the most common materials used to construct car hoods, but they may also be made of other materials. As well as carbon fiber, fiberglass, and dry carbon, aftermarket car hoods may also be constructed from a wide variety of other materials.

On most vehicles, there is a system for releasing the hood called a hood release, which is usually composed of an inner hood latch or lock handle, a cable used to open the hood, and a lock that secures the hood. In most cases, the hood lock handle is located on the same side of the steering wheel as the driver’s seat, or it can be located in the door frame on the opposite side.

Importance of Hood in a Car:

• In simple words, the hood of the car is responsible for the safety of the car.
• All engine parts and radiators of the car are protected by the hood or bonnet.
• Car hoods are also used in sports cars as an aerodynamic mechanism by reducing the Air effect.
• Car hoods provide relatively easy access to the engines in case any maintenance is required.
• Having a hood on your car also reduces engine noise, which helps you drive more quietly.
• Keeping the paint under the hood longer can also help keep it in good condition.
• Getting out of the car before the hood catches fire can give motorists time to escape that is why a proper and strong hood is necessary.

     while access for repairs and maintenance Hood can fix by two methods 

    1. Support Rod

    2. Gas Stay

Components

1.Hood outer panel

Outer panels are the aesthetic elements of a car. It is the styling team who provides the skin for the outer panel. The shape, position and size of the hood should satisfy the safety norms. So while designing the hood we should give more importance to pedestrian safety. The outer panel is attached to the inner panel by hemming. So, it is necessary to provide required hemming flange and reliefs for the hemming operation. We also provide mastic sealants between outer panel and inner panel to reduce vibration.

                               Hood - Outer panel

Master Section:

2.Hood inner panel

Inner panel is the part that gives strength and rigidity to the outer panel. The master section represents the initial emboss shape and size. Then we provide the emboss for the latch and hinge elements after fixing the location.

3.Reinforcement

Reinforcements are provided according to the design requirements. Mainly it is provided at the hinge and latch regions to improve the strength locally. Usually thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirement. According to the design requirement here it is given 1.5mm thickness to both hinge and latch reinforcements.

                             Striker & Hinge Assembly                                         

4.Latch Trajectory

Latch trajectory is given by the circle drawn from the hinge axis point. Hinge axis point is the centre point of the hinge axis. First, we can fix either the latch or the hinge. If we have fixed the hinge position then we should plot the Trajectory circle for the latch. For proper mating condition the striker axis through the tip of the striker should be tangential to the latch trajectory.

                                Latch Trajectory

5.Emboss Area

Throughout the inner panel we provide different embosses. We can increase the stiffness of the inner panel through these embosses. The shape and size of the embosses also determines the direction of the force distribution resulted from frontal collision. The force should be always distributed away from the passengers. Here in the figure the embosses are designed in such a way that the force is directed to either sides of the car.

 

6.Mastic Area

Hood commonly possess large surface area and hemming can only be provided through its boundary. We cannot use other joining techniques like welding, riveting etc because they leave marks on the outer panel which spoil its aesthetic appearance. So, mastic sealants are used to stick the inner surfaces of outer panel and inner panel. Mastic sealants are elastic compound that behave like rubber. It is applied between the inner and outer panels at specified spots. Each spot of mastic sealants has its effect around a circular region of 80mm diameter. Thus, the mastic points are arranged in such a way that it covers the areas away from the hemming which are more vulnerable to vibrate.

                             Mastic Area -  Hood Inner panel 

7.Deep-Drawing process:

Deep drawing is a metal forming operation in which the sheet metal is stretched into a desired shape by the mechanical action of a punch.The punch pushes the sheet metal blank downward and forces it into a die cavity which ultimately forms a shape of the desired part.During the deep drawing operation, the tensile forces cause the sheet metal blank to plastically deform into a cup shaped part.Generally the term deep drawing is referred to a drawn part which has depth more than its diameter.The parts drawn by using a deep drawing process can have different cross sections like straight cross section, tapered cross section as well as cylindrical and rectangular parts can be drawn.For deep drawing operation, the ductile metals like brass, copper, aluminum and mild steel show good drawability even at room temperature.

 8.Hemming process:

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.

In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas or material roll-in. This is why it is important to use simulation tools in order to, on the one hand, better understand the hemming process and, on the other hand, significantly reduce the number of “trial and error” loops during tryout und production.

There are various types of hemming operations:

• Conventional die hemming
• Roll hemming