Objective

            To know the design strategy for the hood to attain maximum safety for the hood. Using NX software to model the hood with the essential embosses and mastic points.

Introduction

            Bonnet is also called hood. It is hinged thin sheet which shields and guards the main parts of car like engine. Its foremost function is to direct access to the engine, battery and other vital parts of the cars for repair and maintenance and to protect these parts from direct sunlight and dust. It also gives good looks and, help to design car aerodynamically stable.

The Car hood design consists of following parts

• Outer Panel
• Inner Panel
• Hinge
• Latch and Striker

Designing

Data provided for design

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

Master Sketch

Figure 1 Master Sketch

            A master sketch will provide the necessary dimension to design the hood. This the cross section for the inner panel and outer panel.

Outer Panel

Figure 2 Outer Panel

Outer Panel is the outer skin of the hood which is holding the inner panel by hemming and mastic seal. Outer panel is not welded or rivet with the inner panel as it’s the luxurious outer look of the car. Thickness of the outer panel is 0.65 to 0.75mm.

Hemming

          Hemming is a technic in automotive Industry to join inner panel and outer panel together. It is the process of bending and folding the flange of the outer panel over the inner panel.

Figure 3 Hemming cross section

Relief Corner

Figure 4 Relief at Corner

Figure 5 Front Relief

            At the corners the relief is provided to ease the process of joining the outer panel and inner panel by rolling. Which will help the assembly to be installed properly and easily.

Inner Panel

Figure 6 Inner panel

            Inner panel is the support of the outer panel which consists of holes and embosses at different places. Embosses will help in providing the stiffness and dissipating the energy towards the hinges. Thickness vary from 0.65 to 0.75mm. There is a gap of 2mm between inner and outer panel for mastic seal.

Mastic Seal Data

Figure 7 Mastic Data

            As above figure shows the mastic sealants data point, which hold the outer panel together with the inner panel in the form of paste. It is made of the hard rubber and used for noise reduction and vibration. This points are located on top of embosses and holds the outer panel with 80mm dia.

Emboss

Figure 8 Emboss

            Embossing is a process in which sheet metal is drawn to shallow depth. The operation is carried out mostly for the purpose of stiffening flat surface and design in inner panel. At the time of the crash these embosses divide forces as divert it to the hinges. So, that passengers inside the car will be safe.

Reinforcements

Figure 9 latch Reinforcement

            Latch and striker is the used for locking the hood with engine compartment. It is placed with respect to the trajectory obtained perpendicular to the hinge axis. Latch and striker is reinforcement part.

Figure 10 Hinge

            Hinge is the assembly that helps in closing and opening of the hood. This also controls how much the hood should be opened when it is in the open condition. Hinge and striker assembly is placed by the data, considering the height of the normal adult height such that it is easy for a person to work normally on the engine or other parts without the hood hitting the head of the person.

Figure 11 Hinge and striker Representation

For positioning hinge and striker, to place hinge tentatively and hinge axis point and place striker position from data taken from parent car or our own. Take the hinge axis point and striker point as radius and draw a circle. From a circle we conclude two points.

• Whether a circle is trajectory of hood opening and closing.
• At this position striker is exactly perpendicular to trajectory locally.

Assembly

Figure 12 Hood

            Finally outer panel and inner panel would be joined by mastic seal then at edges the hemming is used. Additional reinforcement are added such as latch and striker, Hinge mountings.

Conclusion

Hood is completely designed in NX software, by end of the design I have learned new features such as hemming, embossed, offset curve on the face, bridge curve, law extension and through curves. Which also gave me a greater understand of the manufacturing the hood in the industry.