Hood design-Week 2

Theory of Hood:

Hood is main component of front portion of car. It is an opening body pannel that covers the engine, It consists of Inner pannel that provides the strength while outer Pannel functions as the metal cover. It is an access pannel to the engine compartment to enable maintenance of power train, drive belts, battery, fluid levels, lamps unit etc.

Hood consists of

• Outer Pannel
• Inner pannel
• Hinge Reinforcement
• Stricker Reinforcement

Factor Considered while designing the Hood.

• NVH (Noise vibration & harness)
• Hinge axis
• Latch and striker Point
• Deformation Bracket
• Gas stay requirement
• Euro Ncap regulations
• Pedestrain Rating

Data Given for Designing Hood

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

Design considerations:-

The Human comfort factor for automobile designs is first considerations. it is a method to safeguard and protect space for the human user & necessary components that make up the vehicle being designed. all safety regulations are ensured during this process Ergonomical considerations consists of hood clearance, Hood opening angle and location of support rod or gas stay.

Hood opening angle is different for different regions or countries. It is desided by the average height of the human in that particular country.

There are two types of hood stay, support rod & Gas stay which holds the position of hood at desired angle.

Support Rod: It is simple metalic rod it is not usually made linear to increase rigidity of rod but the length from line connecting support rod retaining point with reating point on a body side to maximum bending point should be less than 35mm to ensure the strength of support rod.

groomet are provided to keep the support rod rest.

Gas stay: It is a device used for supporting the engine hood of a vehicle in its open position by means of an actuator which is activated by gas.

In case of gas stay only initial force is required to open the hood then it automatically opens at desired angle with extension of pneumatic piston in cylinder of gas stay assembly.

Safety Requirements: The most important safety requirement is regarding the frontol collision. It should withstand in high collosion forces as well as it should divert the forces in outward direction so intensity of collosion forces would be reduced to cabin side of car.

Pedestrain Safety: Design should be such way that it should reduce the injuries to the pedestrain in the event of a pedestrain vehicle collosion. The objective of these measures is to reduce the number of a road accident fatalities and the severty of injuries sustained bt pedestrains involved in a collosion with a vehicle in urban traffic.

The height, weight and age of the pedestrain all play a rolenin kinematics of the event and in his ability to survive. most fatalities for the younger population are related to brain damage caused by head impact on the bonnet. for older people additional risk include repture of arteries in the lower limbs and pelvis from bumper and bonnet leading edges., impact frequency and seriousness of injury has been stuided for many years, resulting in rating systems and improved design.

evaluation of pedestrain safety for a bonnet must be carried out in the context of its surroundings elements like vehicle styling, size (wrap around distance) WAD and under bonnet clearance to other element (considered as hard points).

Wrap around distance (WAD) :- It is geometrically traced distance from the contact point with the ground refrence plane, vertically below the front face of the bumper, to any point on the vehicle front structure.

Side refrence line:- The geometric trace of the heighest points of contact b/w a straight edge, held parallel to the lateral vertical plane of the vehicle and inclined 45 degree is traveresed down the side of the front structure, and the side of the front structure.

Child Head Impact Zone:- 1000 WAD to 1500 WAD.

Adult Head Impact Zone:- 1500 WAD to 2100 WAD.

As we know these are the four main parts of hood assembly are as follow:-

• Outer Pannel
• Inner pannel
• Latch and striker system
• Hinge system

Outer Pannel:- We get the outer pannel skin surface from style dept with proper aesthetic look, gap etc. the shape of the outer pannel is made aerodynamic in order to minimize the air effect. Shape of the outer Pannel is reffered as a base to design a inner pannel..

Inner Pannel:- Hood inner pannel is a main functional part in hood design. it gives structural support and strength to the outer pannel of hood. the outer and inner pannels of the hood are typically attached using a hemming operation at the edges.

Latch & striker:- This system is the attachment of the hood assembly and vehicle body. The hood latch system must be able to catch the striker of the hood upon closing and instantaneiusly, as well as automatically, lock. Once in the locked state, it must remain locked an only unlock upon the operator's control.

Hinge system:- The hinges are used to guide and hold the hood when open & close. Hinge assembly consists of two parts one i sconnected to the hood inner pannel and second is connected to the vehicle body.

Reinforcements:- Reinforcement is provided mainly in hinge and latch region. when hinge and latch assembles are attached to the inner pannel, strength of that area reduces locally so we added some extra material to increase the strength of the area loaclly. thickness of reinforcement material is provided according to the design requirements. in this project, 1.5mm thickness has been given to both latch and hinge reinforcement.

Latch Trajectory:- Circle is drawn from the hinge axis center so we can finalize the position of latch striker for proper mating, the tip of the striker should be tangential to latch trajectory. the position of latch striker follows the path of this circle.

Emboss:- Emboss are provided to increase the strength of inner pannel. Shape of emboss also determines the direction of collosion for force distribution. the shape of emboss should be designed in such a way that, the collosion forces should be directed towards & outwards side of the car.

Mastic data:- Mastic sealants used between the outer and inner pannel. mastic sealants are the rubber like elastic compound which connects the outer and inner pannels of car hood at specified points. mastic sealants are used in the region between the inner and outer pannel because other joining process like welding and riverting are not good for car asthetic design. it also helps in improving NVH (Noise,Vibration, harshness) characteristics.

Manufacturing Aspects:- The most important design consideration of any components is manufacturing aspects. In sheet metal, the component is manufactured by press tool dies. The press tool is stamping which includes cutting operations like shearing, piercing, etc . and forming operations like bending, deep drawing, hemming etc the main focus of manufacturing aspects is to manufacture hood assembly with minimum operations sequence & process time.

Deep Drawing:- The manufacturing of deep, cuplike product from thin sheet metal is known as deep drawing. the process involves a punch with a round conner and a die with a large radius. the punch- die clearance is slightly larger than the thickness of the sheet metal to a deep drawn.

As the load applied through the punch, the sheet metal is forced to flow radially and sink into the die cavity to form a cup. the process is best suitable for complex shaped problems.

deep drawing process is a forming process which occur under a combination of tensile and compressive conditions. A flat sheet metal blank is formed into a hollow body with a smaller cross section.

Piercing:- Piercing is a shearing process in which raw matel is pierced with a machining tool, resulting in the creation of a circular or other shaped hole.

Hemming:- Hemming is a sheet metal forming process in which sheets are joinned by bending it usually to 180 deg.

This assembly method is widely used in the final stage of production of automobile hoods, doors, or other closures for aesthetic purpose.

It is a metal working process that involves rolling the edges of sheet metal over onto itself, essentially creating an area of two layers. during this process, the edges of sheet metal is folded over. the two newly formed layers then lie flush with each othe.

the typically three- step bending process of the hemming operation comprising of the flanging, pre-hemming, and final hemming process.

Rolling Hemming:- Rolling 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.

Corner Relief:-

Final assembly:-

Note:- Dear teacher I made a mistake in this design that my emboss direction is inward instead of outward. I don't notice while designing. actually I have an idea of make it correct but I don't have a much time to correct it as I allready very slow in this course due to office work. So please considered it as correct design and please forgive me this time, for the next i'll take care of this type of mistake and make sure that it can't be repeat it future.