Hood design-Week 2

Objective:

To design outer panel of Hood with Hem and develop the Inner panel with all necessary reinforcements definition then positioning of Hinge, striker and create provision for mastic sealant points.

Theory:

The Hood or the Bonnet of a car is considered as the frontal BIW enclosure component. Bonnets are designed to reduce air resistance as the air flows around the car. The design of the bonnet is vital since it affects the aerodynamic flow around the car. Apart from this, bonnets are also designed to meet several other requirements. They serve a great deal of purpose in protecting the passengers inside the car and the pedestrians in the event of an accident. It also acts as the cover for the engine.

The hood or the Bonnet consists of the following parts.

1. Hood outer panel

2. Hood inner panel

3. Latch and Striker re-enforcement

4. Hinge re-enforcement

5. Gas stay re-enforcement

Requirements:

Hood Thickness and manufacturing considerations.

• Outer Panel Thickness=0.75mm

Inner Panel Thickness=0.75mm

• Reinforcement Thickness = 1.5mm

• Minimum fillet radius = 3mm+Thickness (example: When thickness of inner panel is 0.75mm we need to maintain minimum fillet radius 3+0.75-3.75mm)

. No sharp corners inside the component

No curvatures lesser than 5mm

• Small embosses should not exceed the maximum depth of 6mm (staying on the safe side)

• Mounting areas and welding areas need to be flat

• Provide appropriate corner relief on the area of curvature

Functional and Safety Requirements:

 

1. The most important safety requirement to be considered while designing the Bonnet is the frontal collision requirements.

The design intention of the hood according to the fronal collision requirement is that the hood crushes and dissipates forces in the upward

direction and to the hard points on the hood thereby deflecting the force on to the body and not the passengers.

2. The second major function of the hood is the opening and closing of the hood. This is done with the help of the latch and striker. To position the latch and striker effectively, we first position the hinge and draw the hinge axis. Now, using the hinge axis from the centre we draw a big circle to the position there we need to place the latch.

Procedure:

1. Master section creation:

The master section is created based on the requirements received from the marketability team and the manufacturing requirements that we saw before. Below is the image of the master section used for the design.

2. Geometry and

Embosses in the inner panel are made according to the diversion of the load path. The emboss depth is kept at a maximum of 5mm to be on the safer side so that the part can be manufactured without any problems.

3. Latch and Hinge reinforcements:

After designing the hood inner panel, we need to place the Latch and hinge as explained in functional requirements section, while the development of the inner panel, we also need to develop some additional reinforcements for strengthening the area where we are going to mount the Latch and Hinge parts. These re-enforcements are made from sheet metal of thickness 1.5mm.

See the below picture where the Latch, striker and Hinge are assembled for your reference

Reinforcement plates of Hinge and Latch are added on the backside of latch and hinge which can be seen in the below image, in this image outer panel is removed to show the reinforcement plates.

4. Provision for Mastic Sealant Points: The Mastic sealant or the Mastic point is an elastic compound that behaves like a rubber. The mastic points are defined on the hood inner panel where the hood can easily deform. They help the hood outer panel to come back to its original shape after it gets deformed. The mastic has an influence area of 80mm. See below picture where the mastic provision is given in the current design of Hood.

5. Hemming and Corner Reliefs for the outer panel design:

Hemming is the process of joining both the outer and inner panel together. The hemming process roles and wraps the hood outer panel around the inner panel and holds it tightly together. The gap between the hemming flanges of hood outer panel to inner panel will be filled with sealants to make the joint as waterproof. After the hemming is done, we need to provide corner relief at the comers of the hood so that the part can be produced without defects. See the below pictures of Hemming and the reliefs provided at the corners.

*Hemming:

Corner Relife

Conclusion:

I learned to design of Hood or Bonnet that satisfies the industry manufacturing, functional requirements and as well as Euro NCAP (New Car Assessment Program) standards which defines the automotive safety regulations. To develop Hood design I used cad software NX CAD .