Hood design-Week 2

Objective: To design the outer panel of the hood with hem and develop the inner panel with all the necessary reinforcement definition then positioning of the hinge, striker, and creating provision for mastic sealant points.

Theory: The hood or the Bonnet of a car is considered as the frontal BIW enclosure component. Bonnet is 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, bonne is also designed to meet several other requirements. They serve a great deal of purpose in protecting the passenger 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 stays 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 + Sheet thickness
• No sharp corners inside the component
• No curvature 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 frontal collision requirement is that the hood crushes and dissipates forces in the upward direction and to the hardpoints on the hood thereby deflecting the forces onto 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 where we need to place the latch.

 

Procedure:

1. Master Section Creation:

The master section is created based on the requirements from the marketability team and the manufacturing requirements.

2. The geometry is created based on the master section that was provided above. After performing the initial stage of the design, we will provide local embosses to strengthen the component. The component will be strengthened based on the master section. When the force impacts the hood from the front, it travels in an upward direction, but the component is designed in such a way to divert the impact force directed away from the passengers, as shown in the image below.

The 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 Reinforcement:

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

The reinforcement plate is placed on the back side of the latch and hinge. In the below image the outer panel is removed to show the reinforcement plate.

4. Provision for mastic sealant Points:

The mastic sealant or the mastic point is an elastic compound that behaves like rubber. The mastic points are defined on the hood inner panel where the hood can easily be deformed. 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.

Hemming and corner reliefs for the outer panel:

Hemming is the process of joining both the outer and inner panels 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 flange of the hood outer panel to the inner panel will be filled with sealants to make the joints waterproof. After the hemming is done, we need to provide the corner relief at the corner of the hood so that the parts can be produced without any defects.

Hemming:

Corner Relief :

Conclusion:

          I learned to design of hood that satisfies the industry manufacturing, functional requirement, and as well as Euro NCAP (New car assessment program) standard which defines the automotive safety regulations. To develop the Hood design, I used NX12.