Hood design-Week 2

                                                                   DESIGN OF HOOD USING NX CAD                                                  

OBJECTIVE :

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

THEORY :

The Hood or Bonnet of a car is considered as the frontal BIW enclosure component. Bonnets are designed to reduce air resistence 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 bonnet 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 the accident. It also acts as the cover for the engine.

The Hood or Bonnet consists of 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 min fillet radius 3+0.75=3.75mm)
• No sharp corners inside the components
• No curvatures less than 5mm
• Small embosses should not exceed the maximum depth of 6mm (staying on the safe side)
• Mounting area and welding areas needs to be flat
• Provide appropriate corner relief on the area of curvature

FUNCTIONAL AND SAFETY REQUIREMENTS :

1. The most important safety requirement tombe 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 ccrushes and dissipates forces in the upward direction and to the hard points on the hood thereby deflecting the force on the body and not to 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, uisng 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 fom 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 EMBOSS CREATION :

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

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 referrence.

Reinforcements plates of hinge and latch are added on the backside of the 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 mastcic 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 its 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 tightely together. The gap between the hemming flanges of the 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 as the corner of the hood so that the part can be produced without any defects. See the below picture of hemming and the reliefs provided at the corners. 

HEMMING :

CORNER RELIEFS :

CONCLUSION :

I learned the design of hood or bonnet that satisfies the industry manufacturing, functional requirements and as well as EURO NCAP (New car assessment program) standard which defines the automative safety regulations. To develop Hood design I used NX CAD software.