Hood design-Week 2

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

Introduction:The Hood is the hinged cover over the engine of motor vehicles . Hoods can open to allow access to the engine compartment,on rear-engine and some mid-engine vehicle for maintenance and repair.

Hoods are typically made out of the same material as the rest of the body work. This may include steel, aluminium, fiberglass or carbon fiber. However, some aftermarket companies produce replacements for steel hoods in fiberglass or carbon fiber to make the vehicle lighter.

Parts of Hood: Hood assembly is the assembly of four parts like outer panel, inner panel, latch system, and Hinge system in hood assembly design.

• Outer Panel: The outer panel skin surface.It follows the aerodynamic criteria.

• Inner Panel: Inner Panel of the hood is 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 an accident. It also acts as the cover for the engine.

• Hinge and striker: Hinge is used to control the opening and closing of the hood.It connects the hood and engine compartment of a car. one other purpose of hinge is if in case your hood striker would fail ,the hinges keep the hood attached to your car.

A latch and striker mechanism os provided to lock the hood the latch and stricker ensure that your hood is securely connected to the vehicle and its does not open unexpectedly which driving,the latch is present on the engine compartment while the striker is attached to the inner part of the hood.

• Latch Trajectory

When the hood is closed, the ideal position for latch (striker) will be perpendicular to the locker. Therefore, latch trajectory should always be tangent to the striker when you open or close the hood. To achieve that, the hinges are located along the axis passing the center of this circular trajectory.

Pedestrian safety consideration :

When a car crashes on the pedestrian, the whole human body wraps around the front shape of the car and the head impacts on the bonnet or the windscreen. The distance on which the head impacts on the car from the ground is called as the Wrap Around Distance (WAD). To be specific the Wrap Around Distance is a measurement of distance from the ground to the head impact zone over the outer surface of the car. The wrap around distance is measured longitudinally in the center of the vehicle from the ground.

Mastic data: Hood commonly possesses a large surface area and hemming can only be provided throught its boundary.we cannot use other joining techiniqes like welding,riveting.etc because they leave marks on the outer panel which spoils its aesthetic apperance.so,mastic sealantare used to sticks the inner surface of the outer panel and inner panel.We have used mastic circles in the hood inner panel because these mastic data has tendency to increase the strenght of the pannel and has influenceof 80mm diameter.

Emboss: Emboss is added to inner panel to distribute an impact force away from the passenger during a crash. Emboss redirects force to hinges, latches and other reinforcements. Most of emboss face near to outer panel, except the area for mastic seals, are cut out to reduce the weight.

Manufacturing process used

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.

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.

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

Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation 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 as compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller which follows a defined path.

Conclusion: Following all above given data details we have started the design of hood.