Hood design-Week 2

Components

1. HOOD OUTER PANEL

Outer panels are the aesthetic elements of a car. It is the styling team will provide 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. Therefore, it is necessary to provide the required hemming flanges 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 strength locally. Usually 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 requirements here it is given 1.5mm thickness to both hinge and latch reinforcements.

4. 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 cycle for the latch. In proper mating conditions, the striker's axis through the tip of the striker should be tangential to the latch trajectory.

5. 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 determines 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.

6. MASTIC DATA

Hood commonly possesses a large surface area and hemming can only be provided through its boundary. We cannot use other joining techniques like welding, riveting, etc because they leave marks on the outer panel which spoils its aesthetic appearance. So, mastic sealants are used to stick to the inner surfaces of the outer panel and inner panel. Mastic sealants are elastic compounds that behave like rubber. It is applied between the inner and outer panels at specified spots. Each spot of mastic sealants has its effect around a circular region of 80mm diameter. Thus, the mastic points are arranged in such a way that it covers the areas away from the hemming which is more vulnerable to vibrating.

7. HEMMING

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, improve the appearance of a part, and reinforce part edges.

In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming, and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids, and fenders.

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas, or material roll-in. This is why it is important to provide the required relief at the corners.

There are two types of hemming operations,

CONVENTIONAL DIE HEMMING

In conventional die hemming, the flange is folded over the entire length with a hemming tool.

ROLL HEMMING

It is the roll hemming process is used for automotive sheet metals. Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operations can also be divided into several pre-hemming and final hemming process steps. Roll hemming is very flexible to use and tool costs are significantly lower compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller that follows a defined path.