Hood design-Week 2

AIM: Design Hood Outer Panel, Inner Panel and the necessary reinforcements.

INTRODUCTION: This Project is about car hood design assembly. We can understand the different parts of car hood like hood outer pannel, hood inner pannel, hinge assembly and striker. We can also see the step by step processes involved in this project. Designing of the model is carried out in Siemens NX-10. 

Following are the definitions of different parts and oprations involved in the project: 

HOOD: Hood, also known as bonnet is a hinged cover over the engine compartment of the motor vehicle. Hoods can open to allow access to the engine compartment, maintenance and repair. 

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

Different Components of hood: 

Outer Panel:  It is the aesthetic part of the hood. it is the skin of hood and provide a suitable and luxurious  look.

Inner Panel:  The hood inner panel provides strength and rigidity to the hood. It also directs the force of the collision outwards instead of into the engine compartment of the car. 

Striker:  It bolts to the underside of the hood at the front. It engages the hood latch when closed.

Hinge assembly: Hinges are used to keep smooth opening and closing of hood to do maintenance of engine and engine parts.

Support rod and Gas stay: The bonnet stay rod is a sturdy metal rod (often with a rubber sleeve which stops it rattling against the bonnet when the car is in motion) which functions to prop the bonnet open and hold it in place.

Design Considerations in Hood:

While designing a hood several design parameters are to consider such as the opening angle of the hood, Support system for the hood, Pedestrian safety rules, etc.

• Hood head zone for striker locking: While designing the hood this parameter should be taken into consideration because when we open the hood to get access to the engine compartment to perform any operation while the hood is in open condition the minimum height of the hood should be such that it does not collide or hit to head of the person who is operating. So, the height of hood in open conditions should be more than the average height of humans in that region thereby no human gets hurt.

•  Pedestrian safety: While designing the hood, it is vital to consider the safety of pedestrians as when your car hits the pedestrian during a crash, it is very important to study the areas over the hood where different body parts of pedestrians are going to hit. we should also take into account the average height of adults and children while designing our hood. So, whenever a new car is been launched, all these safety parameters are checked by taking a crash test and studying the data obtained from it to make changes accordingly to follow pedestrian safety.

• Mastic Data: We know that the hood comprises two main parts: a hood inner panel and a hood outer panel. The hood inner panel is enclosed below the outer panel and thereby provides rigidity to the hood. When these parts are assembled to form a hood a small gap remains between these two parts as they are both metal parts this may lead to noise and vibrations when the vehicle is in running condition which is undesirable to avoid this mastic sealant is filled between this small gap.

  Mastic sealant is a paste-like material that is applied on a surface and is hardened by heating.

• Force Distribution:

  A good designer should always consider the safety parameters as a top priority, In the case of hood design, one should design the hood in such a manner that if the vehicle gets a frontal crash then all the forces must be distributed towards the hinge of the hood, as it is important to reduce the impact of the crash by diverting the force towards the hinges and thus safeguard the passengers in the vehicle.

 Hood Design Process:

      Rear Relief :                                                 Front Relief :

Manufacturing processes for production of hood inner & outer panel:

• Deep Drawing: Deep drawing is a sheet 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. This is achieved by redrawing the part through a series of dies.

• Heming: 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.

        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 use                    simulation tools in order to, on the one hand, better understand the hemming process and, on the other          hand, significantly reduce the number of “trial and error” loops during tryout and production.

        There are two types of heming process use:

           a) Conventional die Heming 

           b) Roll Heming

Deciding placement of Striker:

To decide the position of the striker on the hood inner panel, first we have to fixed the position of hinges on the hood inner panel. Once it is done then take construct two points one on each hinge by taking centre point of hinge. Then draw a line starting from one point to another point of hinge, this line forms our hinge axis along which our hood will rotate when we open or close the hood.

Now, by taking midpoint of this line draw a circle normal to the line take approximate diameter of the circle initially, after that draw a line which is tangent to the circle also draw a vertical line whose one end gets coincident with the end point of tangent line. This forms the trajectory path of our hood.

Furthermore, construct similar line on striker taking midpoint and constraint this line with the trajectory path as shown below.

• Latch Trajectory:  While assembling the latch with the hood panel it is strictly recommended that the position of latch striker should be placed such that the latch striker exactly fit into the lock hole in the engine compartment. Keeping this in mind, the latch striker is placed on the inner hood panel using latch trajectory path. This path is created using the the hinge axis taken as reference to draw a big trajectory path.

• Embossed Surface:  Embossed surface plays an important role in car hood panel while crashing or accident of car. Because during the collision, hood is most affected part which sustains all the impact forces while crashing. most of the impact forces are directly flows in the direction of collision & thus can harm the driver sitting under the car, thus to overcome this problem generally, V or Y shaped embosses are given in inner hood panel. so that, the impact forces coming in the direction of collision is diverted towards the corner point of the hood & driver couldn't be harmed.

Images of final assembly of hood:

Conclusion: Hence the modeling of hood assembly completed and I have attached two saperate files of hood assembly and one Zip file in which all part files and step filles are included. all the neccessary definitions and process are explained in the report.