Hood design-Week 2

HOOD DESIGN:

AIM:

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.

DATA TO BE USED:

Hood Thickness Information

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

Master Section:

Hemming Data:

Relief rear section:

Front relief:

WHAT IS HOOD?

The hood of a car is the metal panel that covers the engine.

It is usually located at the front of the car, and it opens to provide access to the engine compartment.

The hood is an important safety feature, as it helps to protect passengers from being injured by the engine in the event of a collision.

In addition, the hood can also help to cool the engine by deflecting heat away from the cabin.

For these reasons, it is important to ensure that the hood is in good condition and properly secured before driving.

If you notice any damage or defects, be sure to have it repaired as soon as possible.

Not only does the car’s hood protect the engine from the elements, but it also helps to improve the car’s aerodynamics.

In addition, the hood can be used to provide extra storage space for small items such as maps and sunglasses.

But perhaps the most important use for the hood is as a safety feature.

In the event of a collision, the hood can help to absorb some impacts and reduce the risk of serious injury.

HOOD ASSEMBLY:

1.HOOD OUTER PANEL:

Hood outer panel provides aesthetic look to the vehicle.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 required hemming flange and reliefs for the hemming operation. We also provide mastic sealants between outer panel and inner panel to reduce vibration.

2.HOOD INNER PANEL

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. STRIKER AND HINGES 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 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.

4. LATCH TRAJECTORY

Latch trajectory is given by the circle drawn from the hinge axis point. Hinge axis point is the centre 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 condition the striker axis through the tip of the striker should be tangential to the latch trajectory.

5.RELIEF POINTS ON THE EDGES

Relief ponts provides the strenth to the outer panel which has lost due to hemming process.

6.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, to improve the appearance of a part and to 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 required reliefs at the corners.

7. MASTIC POINTS:

Hood commonly possess 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 spoil its aesthetic appearance. So, mastic sealants are used to stick the inner surfaces of outer panel and inner panel. Mastic sealants are elastic compound 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 are more vulnerable to vibrate.

8. EMBOSSES:

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 embosses also determines the direction of the force distribution resulted from 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 sides of the car.

9.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 which 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 a 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.

DESIGN CONSIDERATIONS OF A CAR:

STEPS FOR HOOD DESIGN:

First we need to download the skin data from given link.

Then from outer panel we need to take the inner panel skin data by offsetting it to 0mm and we should hide the outer panel to work on inner panel.

Then we have to work on inner panel according to the master section by creating embosses for hinges and striker.

Then by using hinge axis we need to draw a latch trajectory.

For removing sharp corners we should use blends wherever it is required.

Then we need to do the hemming and give relief points on the edges to strentghen the hood .

finally thicken the component by 0.75mm to covert it to sheetmetal.