Hood design-Week 2

CAR HOOD DESIGN USING NX CAD

OBJECTIVE:

To design Hood outer panel, inner panel and the necessary reinforcements by following the Master section mentioned with the design parameter.

ABSTRACT:

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. A concealed latch is typically used to hold down the hood. On vehicles with an aftermarket hood and on racecars, hood pins may be used to hold down the car hood. Bonnet is main component of a car at the front portion. It is used to decorate the car and add luxurious look. The shape of the bonnet is made aerodynamic in order to minimize the air effect. Bonnet is generally used to access the parts easily such as radiator, engine and many other parts. In automotive world the weight optimization plays an important role. In this paper material change is applied to the bonnet for the same design and finally showing the stiffest bonnet and less weight component.

DESIGN CONSIDERATIONS FOR CAR HOOD:

Head clearance zone:

Head clearance zone is the clearance such that when the hood is in fully open condition it does not hurt the head of the person that is standing next to the hood. This is controlled by the opening angle of the hood. The opening angle of the hood is decided for the region the car is manufactured. Some region may have people with average height of 5.5 ft and another region may have people with average height of 6 ft. so deciding the right opening angle for the hood is an important criteria.

Consideration of Noise Vibration Harshness (NVH):

NVH plays an important role in car design. The noise and vibration produced by the car should be minimized. in the hood , to avoid vibrations stiffener pads are provided . Mastic sealants also reduce the NVH. Stiffener pads and mastic are added between inner and outer panel of the hood.

Pedestrian safety:

Safety is the most important criteria in automobile designs which concentrates on both pedestrian and occupant safety. The pedestrians are the most vulnerable road users and are at high risk of traffic accidents. The major reason for the fatality of the pedestrian in traffic accident is due to the head injury resulting from the hard impact of the head against the stiffer hood or the ground. This leads to the necessity of new inner hood panel which is less stiffer and pedestrian friendly. The head impact analysis on the present hood of the car was done to study the response of the adult head form at two different locations.

Structural and model analysis for the same present hood assembly was done to observe the local and global stiffness. In order to reduce the head injury of the pedestrian the local stiffness over the area of head impact has to be reduced thus the new design of hood inner panel was focused on that and the structural and modal analysis was done for the new design. The design with lesser local stiffness and similar global stiffness compared to the existing hood was finalized. The head impact analysis for the new design of hood inner panel was performed. The HIC values of the adult head form for two different locations are found to be 706 and 948 which meets the safety limitations of the adult head acceleration during impact as proposed by EEVC WG17 and Euro NCAP regulations. Thus the new design of the hood is pedestrian friendly, considerably maintaining the overall global stiffness of the hood.

DIFFERENT METHODS OF MANUFACTURING FOR CAR HOOD:

Blanking:

Blanking is a metal fabricating process, during which a metal work piece is removed from the primary metal strip or sheet when it is punched. The control of the quality by the punch and die clearance. The ability to produce holes of varying shapes quickly.

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.

Trimming:

Trimming is a manufacturing process that is used as a finishing operation for forged parts, in order to remove flash. Most often it is desirable to perform this operation while the work is still hot for maximum efficiency, therefore it is usually incorporated into the larger production process.

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. 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.

DATA:

Inner hood has been designed by following the master data:

Master sketch:

Hood thickness:

Outer panel thickness- 0.75mm

Inner panel thickness-0.75mm

Reinforcement thickness- 1.5mm

HEMMING DATA:

DESIGN PROCEDURE FOR HOOD:

Inner Panel:

A hood inner panel for a vehicle is provided to improve rigidity, durability, and pedestrian protecting performance by comprising a composite structure in which a multi-cone structure and a frame structure are individually arranged on the front and the rear.

The present invention relates to a hood inner panel for a vehicle, and more particularly, to a hood inner panel for a vehicle for simultaneously improving hood rigidity and pedestrian protection performance. In general, the hood panel is installed in the front of the vehicle so as to protect parts in the engine compartment and the engine compartment and at the same time open and close the hood panel for replacement and repair of components in the engine compartment. The hood panel of the vehicle has a form in which an outer panel and an inner panel are combined, and has a frame structure for rigidity reinforcement in order to ensure hood rigidity and durability. The inner panel was designed by offsetting the given class A surface as per the given master section. The inner panel consists of Embosses and Mastics.

Embosses:

Embosses has been given to create extra strength in inner panel and embosses design needs to be inspired by force dissipation phenomena like here I have made embosses in a way if any object hit from front most of the force will get dissipated by its design towards the upper left & right corner so that less force reach at occupants end.

Mastics:

Mastic points are also given to apply mastic sealant. A white paste like sealant to join inner panel and outer panel with each other by providing some heat to it so that it gets hardened. The mastic point covers a radius of 80mm of surface. Thus, the mastic has to be placed within a radius of 80mm from each other.

Design of Outer Panel:

Design of outer panel is mainly inspired by aesthetic but there is some engineering also to it. Here main purpose of outer panel is to cover the inner panel to provide aesthetic look at the same time Panel must be curve & sleek so that it behave aerodynamically and air hitting from front reflect from it efficiently. So here rather than using seam and spot welding we use hemming method to join outer and inner panel. Hemming is a type of folding or wrap-around process in which roller bend and press the extrapolated flange in a way that it holds the inner panel firmly, then a sealant is also provided in between them under folds to get water tightening. The corners of the outer panel must be hemmed for 6mm as per given designed corners and provide a thickness of 6mm.

Reinforcements:

Reinforcements are used to provide more strength to the assembly.

1. Latch & striker
2. Hinge

Latch & striker:

Latch & striker is used for locking the hood with the car. It’s usually placed on the space provided on the inner panel.

Hinge:

Hinges are used to connect the hood & cowl panel of an automobile. it enable the opening & closing operation of the hood. the hinge should be made strong enough to handle the weight of the hood and also to handle the force action on it during the collision.

Position of Hinge & Striker:

The hinges should be usually placed on both sides of the hood in such a way that the strike fits exactly into the hole provided.

Condition for hinge and striker position is:

• Both the hinges should be on the same axis.
• The centre of the striker's circular trajectory should be always perpendicular to the hinge axis.

FINAL ASSEMBLY:

RESULT:

Thus, the car hood was designed as per the given class A surface and master section taking into considerations all the design parameters.