Hood design-Week 2

TITLE: HOOD ASSEMBLY DESIGN

Introduction:

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 now recently from aluminum too.

The hood of a car is a frontal BIW enclosure component.

Bonnets are designed to reduce air resistance as the air flows around the car. Apart from this, bonnets are also designed to meet several other requirements. It also acts as the cover for the engine.

They serve a great deal of purpose in protecting the passengers inside the car & the pedestrians in the event of an accident. 

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In this design, the given thickness, master section and the datas are followed throughout.

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SAFETY CONSIDERATIONS:

• The European New Car Assessment Programme (Euro NCAP) is a European car safety performance assessment program which has developed test specifications & rating systems for assessing pedestrian injuries during impacts with the front of vehicles such test include a series of tests using impacts designed to bio-mimic a collision at speed of 40 km/h.
• They describe a situation in which a pedestrian is situated laterally & a car first hits one of his legs. Test are conducted on the leg, upper leg & most importantly the head, as head trauma is most commonly responsible for casualties.
• So to avoid severe injuries to the head, the high impact area for adults & children are subjected to less thickness. Also no reinforcement should be provided in that area as during head collision, the hood will absrob the head impact energy leading to collapse of the hood & thus protecting severe head injury.
• Another important criteria for the hood design is the protection of the occupants inside the car during front collision. The design of the hood should be in a such a way that the during the collision, the force should travel in the upward direction through the embosses & directed towards the body of car. Thus protecting the occupants inside.

Following parts are using in hood assembly for this report,

1. Outer Panel 
2. Inner Panel 
3. Hinge Assembly
4. Striker Assembly

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Hood Thickness:

• Outer panel thickness= 0.75 mm
• Inner panel thickness= 0.75 mm
• Reinforcement thickness= 1.5 mm

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Inner Panel:

• In the inner panel, we can research, develope then implement the safety aspect of pedestrians & as well as the driver. In this panel, we attach the reinforcement, develop the emboss, and consider designing the mastic points etc.
• It is an object of the present invention to provide a hood inner panel capable of reduction of a reaction force of the hood inner panel even if a level of deformation of a hood of a vehicle increases, & ensuring a sufficient energy absorption capacity.

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Outer Panel:

We can also call it as cover of inner panel. It is the part, which gives luxurious look to the hood or bonnet. Outer & inner panel can not join by any welding process like spot welding or rivet, which spoils the look of a car.

The outer panel is generally extracted model from the prototype design. 

 

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Hinge Assembly:

Hinge is a component that fixes the hood to the fenders of the car.

The latch must be fixed perpendicular to the hinge axis so that the hood opens or closes properly.

  

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Striker Assembly:

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

  

The processes involved in designing of a hood as a sheet metal operations are as follows:

• Blanking
• Hemming
• Punch cutting or piercing
• Deep drawing
• Embossing

Here we go with Hemming:

• Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180 degree. Automotive body panels & parts such as deck-lids, trunk, doors, hoods & tailgates are formed by hemming processes.
• Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller & forms the flange. Roll hemming operation can also be divided into several pre-hemming & final hemming process steps.
• Coventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a forming operation in which the flange is formed with a hemming tool after the drawing & trimming operations have been completed.

 

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Deep Drawing:

• Deep drawing is a manufacturing process that is used extensively in the forming of sheet metal into a cup or box-like structures. Pots & pans for cooking, containers, sinks, automobile parts, such as panel & gas tanks, are among a few of the items manufactured by sheet metal deep drawing.
• A deep drawing of sheet metal is performed with a punch and die. The punch is the desired shape of the base of the part, once drawn. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. For many calculations, the sheet metal thickness is assumed to remain constant. There are changes in thickness in certain areas, due to force involved.

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Embossing:

• The sheet metal embossing operation is commonly accomplished with a combination of heat & pressure on the sheet metal, depending on what type of embossing is required.
• A sheet metal is drawn through the male & female roller dies, producing a pattern or design on the sheet metal. Depending on the roller dies used, different patterns can be produced on the sheet metal.

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Striker / Latch Trajectory to the Hinges:

While opening or closing the hood, the latch must be perfectly aligned to the fixing or striker point. For that, the latches trajectory must be perpendicular to the hinge axis.

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Hood Assembly:

  

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Conclusion:

• The hood of a car has been designed and assembled by using CATIA V5.
• Creation of Emboss and Design of Hinge and Striker.
• Mastic points has been created under the design consideration.
• Embosses in the inner panel diverts the force towards the frontal collision and also the side collision towards the hinge of the hood. So that it reduces the collision force to the rest of the car.
• By using trajectory method, the striker is placed and is done to follow the hood open and close radius and for the latch placement.