Car Hood or bonnet:

A car hood is a metallic part that is used to cover or protect the engine compartment of the car. It is usually hinged to the engine compartment and thus facilitating the open and close operation as per the requirement.

Car Hood Design:

For the design of the hood, three main factors play a major role as follows:

• Hood inner panel design with suitable embosses
• Hood outer panel with suitable hemming and relief
• Latch and hinge relationship
• Mastic seal arrangement between the hood outer and inner panels.

Design parameters:

Thickness:

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement (latch and hinge) Thickness = 1.5mm

Hemming total offset surface distance = 3.15mm

Rear relief distance = 29 mm

Front relief distance = 200mm

Average face and edge blend radius = 6mm

Hood inner panel

Most importantly, inner panel is designed first as it is responsible for determining the strength and weight of the panel. For my hood internal panel, I have used few embossed structures to facilitate more strength and thereby, having positive impact on the crash analysis report. From the below figure, we can see that, the designs are selected such a way that no force is acting towards the center but, divert outwards which gives more strength to the hood. The triangular structures are trimmed so that the hood becomes light in weight and also consumes less material which makes it easy for manufacturing.

Hood outer panel

The outer panel is a simple metallic part which is used to enclose the inner panel by using hemming phenomenon. The front and rear reliefs are given for more tolerance. This outer panel is usually painted and comes with different styles to improve the aesthetic factor.

Hemming:

It is the process where one sheet metal is folded over the another by rolling at its edge of the sheet. Here, the outer panel edge is rolled over the inner panel in order to cover the inner panel and provide thickness and more strength.

Rear relief:

Some portion of the outer hemmed panel is removed to facilitate the relief.

Hinge and Latch assembly:

The hinges and latch are assembled and constrained on the work part. Here, hinges are used to open / close of the hood and latch is used to lock / unlock the hood with respect to the engine compartment.

The hinge axis should be parallel to x-axis and hence, necessary hinge emboss design arrangement has been made.

Latch and hinge relationship:

The trajectory shown in the below figure determines the maximum distance up to which the hood can open. The distance between the midpoint of the hinge axis and the latch hook is the radius of the circle. This may vary country wise as per the average height of the respective citizens. The connecting rod which holds the hood against the engine compartment will be the important factor to determine the maximum height.

Mastic sealing:

The mastic seal is used to stick or combine the inner and outer hood panel firmly to reduce vibrations and noise. Also, it helps to give high strength to the part.

The above figure gives just an idea where the mastic seal is applied. The circled portions represent the mastic seal. Usually, it is more applied inside the embossed walls and areas and also on the edges of the panel for firm holding.

Conclusion:

The major design challenges faced is the inner panel as it is the main supporting strength for the hood which is followed by the outer panel. The hemming is most the important element used for tight covering of the panel, thereby minimizing vibrations and noise. The head-on impact is again the critical factor to be considered for designing the hood and internal structures. Further developments can be made in order to meet the challenging standards and improve aesthetics of the design.