Hood design-Week 2

DESIGN OF HOOD BY USING MASTER SKETCH

OBJECTIVE:Design Hood Outer Panel, Inner Panel and the necessary reinforcements by following the Master Section mentioned with the Design parameters explained in the videos.

Submit an ASSEMBLY of Hood Inner Panel, Outer Panel, Latch, Hinge and the Reinforcements.

A detailed report about the Hood Design which includes a detailed explanation about hood and its components, Latch Trajectory, Mastic Data, Emboss Definitions, Manufacturing process like Deep-Drawing and Hemming, and all the parameters followed in the design.

The report should be well-formatted and should have a good flow of content. Add all the relevant images

Data to be used:

Hood Thickness Information

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

INTRODUCTION:

The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment (or trunk on rear-engine and some mid-engine vehicles) for maintenance and repair. From a design perspective, the hood should meet some specific conditions like pedestrian safety, a hood head zone for the lock striker, force distribution when subjected to frontal collision (occupant safety), manufacturability, etc. A typical hood assembly consists of a hood outer panel, inner panel, latch and striker, hinge, and hood stay. Hood stay is an apparatus for supporting the engine hood of a moto vehicle in its open position. The purpose of opening the engine hood is for inspecting the engine room, replenishing cooling water and engine oil, changing parts and making repairs, etc. Common types of hood stays are Support Rod and Gas Stay. Support rods are manually operated and they are cost-effective and simple to design whereas gas stays require no manpower but they are costly. The Hood is typically made out of the same material as the rest of the bodywork. This may include steel and aluminum. Deep drawing, hemming, blanking, and piercing are the common sheet metal operations that are used in manufacturing hoods in automotive industries.

THEORY:

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-enforce components

1. • Hood outer panel
   Outer panels are the aesthetic elements of a car. It is the styling team who provides the skin for the outer panel. The shape, position, and size of the hood should satisfy the safety norms. So while designing the hood we should give more importance to pedestrian safety. The outer panel is attached to the inner panel by hemming. So, it is necessary to provide the required hemming flange and reliefs for the hemming operation. We also provide mastic sealants between the outer panel and inner panel to reduce vibration

2. Hood inner panel

   The inner panel is the part that gives strength and rigidity to the outer panel. The master section represents the initial emboss shape and size. Then we provide the emboss for the latch and hinge elements after fixing the location

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

   • Latch Trajectory

     Latch trajectory is given by the circle drawn from the hinge axis point. The hinge axis point is the center point of the hinge axis. First, we can fix either the latch or the hinge. If we have fixed the hinge position then we should plot the Trajectory circle for the latch. For proper mating conditions, the striker axis through the tip of the striker should be tangential to the latch trajectory.

Emboss definitions

Throughout the inner panel, we provide different embosses. We can increase the stiffness of the inner panel through these embosses. The shape and size of the emboss also determine the direction of the force distribution resulting from a frontal collision. The force should be always distributed away from the passengers. Here in the figure the embosses are designed in such a way that the force is directed to either side of the car.

Deep Drawing

Deep drawing 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 that occurs under a combination of tensile and compressive conditions.

Sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter. This is achieved by redrawing the part through a series of dies. The flange region (sheet metal in the die shoulder area) experiences a radial drawing stress and tangential compressive stress due to the material retention property. These compressive stresses (hoop stresses) result in flange wrinkles. Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

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 the thickness of inner panel is 0.75mm we need to maintain a minimum fillet radius of 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 frontal 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 onto the body and not the passengers.

2. The second major function of the hood is the opening and closing 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 center we draw a big circle to the position where we need to place the latch.

Master Sketch

The master sketch utilized for designing the hood is shown below.

Embosses

Various embosses were made in the hood inner panel by keeping in mind the following design considerations

• Pedestrian safety during the frontal crash.
• To improve the strength and stiffness of the body.
• the embosses were designed in such a way that the distance between the hood inner panel and the outer panel was kept 5 mm from the points it had to be attached to each other.
• Hinge emboss was done keeping in mind the striker and hinge axis correlation.

Mastic Data

Mastic points are those points of the hood inner panel which are in contact with the hood outer panel with the help of sealants so as to minimize the effect of the vibrations produced by the engine.

Following are the design considerations for the mastic points

• The diameter of the mastic points was taken as 5mm.
• The distance between the mastic point and the hood outer panel is 5mm.

The distance between two mastic points was kept in such a way so as to minimize the vibrational effects

Hemming

Hemming is the process of joining the hood inner panel and the hood outer panel. Due to the styling finish of the vehicle both the panels cannot be joined using the welded joints so in order to avoid these joints hemming is used. Hemming for the hood was done with the help of the hemming data as shown.

In the corners a relief is to be provided during hemming and for this relief following data was used.

BELOW ARE MODEL FIGURES:

CONCLUSION:The design of reinforcement and hemming of hood using master sketch.