Challenge

Hood design-Week 2

UUdhayakumar U21 Jun 2022

DESIGINING OF HOOD INNER PANEL, OUTER PANEL AND THE NECESSARY REINFORCEMENT BY FOLLOWING THE MASTER SECTION

OBJECTIVE

The main objective of the project is to designing of hood inner panel, outer panel and the necessary reinforcement following the master section and Euro NCAP standard that satisfies the manufacturing and functional requirements.

HOOD

A car hood also referred to as a bonnet in some other countries is the hinged cover that rests over the engine of a front-engine vehicle. Its purpose is to provide access to the engine for repair and maintenance. Car hoods are typically constructed from steel and sometimes from aluminum. The hood release system is common on most vehicles and typically consists of an inner hood latch/lock handle, a hood release cable, and a hood lock assembly. The hood lock handle is usually located under the steering wheel, next to the driver’s seat, or in the door frame.

Design constrains to be followed: -

Passenger safety
Pedestrian safety
Manufacturing feasibility
Latch trajectory must be center of hinge axis
Joining techniques of inner panel and outer panel

Passenger safety

Whenever the frontal crash occurs in a car, hood will be affected first. So, hood must design in such a way that the impact force should be dissipated towards the side panel of the car before reaching the driver’s cabin, thereby deflecting the force on to the body and not the passengers.

Pedestrian safety

While designing the hood pedestrian safety is also consider as per Euro NCAP standard. Hood is are of two types based on side reference line. "Side reference line" means the geometric trace of the highest points of contact between a straight edge 700 mm long and the sides of the vehicle, when the straight edge, held parallel to the transverse vertical plane of the vehicle and inclined inwards by 45°, is traversed down, and maintains contact with the sides of the front structure. If the line falls in fender, then the hood is inlaid hood, If the line falls on hood, then it is wrap around hood

Regarding the safety of the pedestrians. It is of utmost importance that we make sure not to place re-enforcement on the areas prone to high head impact. Also, the child impact area is designed with lesser thickness than the adult impact area so that in the event of a frontal collision where a child is involved, the bonnet will absorb the impact of the crash and crumble to protect the child’s head from absorbing the force.

Manufacturing feasibility

For manufacturing the hood, Stamping, deep drawing and hemming process are required.

Stamping

Metal stamping is a crucial element for various applications in the automotive industry. The metal stamping process produces components with extremely tight tolerances through the use of specialized stamping dies, which shape and cut the workpiece to the desired form and size. Typical stamped parts used in the automotive industry include fenders, hubcaps, and many other critical components.

Deep drawing

Deep drawing is a sheet metal forming process in which a 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.

For manfacture these part cetrain guideline to be followed:-

Minimum fillet radius required – 3mm + thickness of sheet

No sharp edges allowed inside the component

No curvature lesser than 5mm

Small embosses should not exceed the maximum depth of 6mm.

Provide mastic points to reduce NVH

Hemming

Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods and tailgates are formed by hemming process.

Provide appropriate corner relief along the hemming region.

Positioning of striker along the trajectory of center of hinge axis

To position the latch and striker effectively, we position the hinge and draw the hinge axis. Now, using the hinge axis as the center we draw a big circle to the position where we need the latch to be placed. Then, we draw a tangent line to the circle at that point and place the latch in that region.

Mastic Sealant:

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

Data given: -

Hood outer panel skin data from the styling team

Hood Thickness Information

Outer Panel Thickness = 0.75mm

Inner Panel Thickness = 0.75mm

Reinforcement Thickness = 1.5mm

Master Section:

Hemming Data:

Relief rear section:

Design Approach: -

Creating assembly file for the hood
Importing the stylish surface, name it as parent body. Make a copy of this start designing inner panel

Since it is symmetric in nature, designing off the body is enough. So, trim the surface into half.

Design the inner panel based on the given master section

After performing the initial stages of design, we will provide local embosses to strengthen the component. To join the inner and outer panel mastic paste is provided in-between, so these cutouts are made. Fillet radius of 3.75mm given for the manufacturing feasibility.

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 to divert the force away from the passengers into the hinges, as shown in the image below:

Assemble the hinge on emboss provide for the hinge.

To position the latch and striker effectively, we position the hinge and draw the hinge axis. Now, using the hinge axis as the center we draw a big circle to the position where we need the latch to be placed. Then, we draw a tangent line to the circle at that point and place the latch in that region.