Challenge

Hood design-Week 2

TTrishul I S4 Nov 2021

HOOD DESIGN :-

HOOD AND ITS COMPONENTS :-

A typically hood assembly consists of hood outer panel, inner panel, latch and striker, hinge, hood stay. Hood stay is an apparatus for supporting the engine hood of a motor vehicle in its open position. The purpose of opening the engine hood is for inspecting engine room, replenishing cooling water and engine oil, changing parts and making the repairs etc. Common types of hood stay are Support rod hood stay and Gas stay. Support rods are operated manually and they are simple to design and cost effective whereas gas stays requires no man power but they are costly.

Hood are typically made out of the same materials as the rest of the body work. This may includes steel and aluminium. Deep drawing, Hemming, Blanking and Piercing are the common sheet metal operations that are used in manufacturing hood in automotive industries.

Design parameters :-

Hood Thickness Information

Outer Panel Thickness = 0.75mm

Inner Panel Thickness = 0.75mm

Reinforcement Thickness = 1.5mm

Master Section :-

Components :-

1) Hood Outer Panel :-

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

Fig.1 : Hood Outer Panel. Fig.2 : Reliefs for Hemming at the corners of Hood.

2) Hood Inner Panel :-

Inner Panel is the part of the hood that gives the strength and rigidity to the outer panel of the hood. The master section represnts the initial shape and size of the emboss. Then we provide the emboss for the Latch and Hinge components after fixing them in the perfect location of the inner panel.

Fig.3 : Hood Inner Panel.

3) Reinforcement :-

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

4) Latch Trajectory :-

Latch Trajectory is given by the circle drawn from the hinge axis point. The centre point of the hinge axis is the Hinge axis point. We can first fix either the latch or hinge. If we fix 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.

Fig.4 : Latch Trajectory.

5) Emboss definitions :-

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

Fig.5 : Inner Panel Embosses.

6) Mastic Data :-

Hood commonly possess large surface area and the hemming can only provided through the boundry of hood. We cannot use other joining techniques like riveting, welding etc because they leave the marks on the outer panel of the hood which spoils its aesthetic appearence. So, Mastic sealants are used to stick the inner surface of outer panel and the inner panel.

Mastic sealants are elastic compound that behave like rubber. It is applied between the inner and outer panels at the specified spots. Each spot of the mastic sealant 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, this reduces the NVH.

7) Deep Drawing :-

Deep drwing is one of the most widely used processes in sheet metal forming. Apart from its use in many other sectors, it is applied in the automotive industry for the manufacturing of car body parts. The Deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions.

Fig.6 : Deep Drawing.

8) Hemming :-

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve the tight fit of those parts. Normally, Hemming operations are used to connect parts together, to improve the appearance of the part and to reinforce part edges. In car part production, hemming is used in assembly as a secondary operation after the deep drawing, trimming and flanging operations to join the 2 sheet metal parts i.e., outer and inner together. Typical parts for this type of assembly are doors, hoods, fenders and trunk lids.