Hood design-Week 2
INTRODUCTION:
Hood is an important component of car. It is used for various purposes such as decorating front part of the car and adding luxurious look to the front part. To reduce the effect of air it is generally designed aerodynamically. Hood is generally used to cover the engine, radiator and many other parts therefore it should be designed in such a purpose that there is an ease of access in maintaining the part and it should give a minimum external disturbance to the engine. It should also be designed in such a way that in case of any accident the bonnet should absorb the maximum impact of the clash.
DESIGN CONSIDERATION:
The most important safety requirement to be considered while designing a hood is the Pedestrian safety from front collision.
The European New Car Assessment program (Euro NCAP) is an European safety performance assessment program which has developed test specifications and rating system for assessing pedestrian injuries during impact with the front of vehicle. Such test includes series of test using impactors designed to mimic a collision at the speed of 40km/h.
They describe a situation in which a pedestrian is is situated laterally and a car hits one of his leg. The test are conducted on the leg , the upper leg and most importantly the head, because the head trauma is most commonly responsible for casualities.
Thus to avoid severe injuries to the head the high impact area for adults and children are subjected to less thickness. Also no reinforcement should be provided in such area . therefore it is designed in such a way that it should absorb the maximum impact during the frontal collision with the pedestrian.
The other important criteria for the hood design the safety of the occupant inside the car during collision. A hood should be designed in such a way that during any collision the force should travel in upward direction through the embosses and directed towards the body of the car thus protecting occupant inside the car.
MANUFACTURING REQUIREMENTS:
Deep drawing process is used.
Material generally taken is aluminium so that it can absorb twice the crash energy than Mild Steel, Dent free, and can make body panels thicker instead of having lower weight.
No sharp corners inside the panel.
No negative draft.
Provide necessary corner relief in the area of curvature.
Outer panel thickness = 0.75mm
Inner panel thickness = 0.75mm
Reinforcement thickness = 1.5mm
DESIGN OF INNER PANEL:
Master section
Master section and manufacturing requirements are generally provided by the marketability team.
Initial design are created with the help of master section .Embosses are created in the design to add the strength and to direct the force from the front collision towards the hinges and ody of the car.
Position of Hindge and Stricker :
For the proper opening and closing of the hood the stricker should be placed perpendicular to the trajectory of hood. So after placing the Hinge the Hindge axis is drawn. Using the hindge axis as the center we draw a big circle to postion the latch in such a way that it is perpendicular to the trajectory of hood.
Latch and Hindge Reinforcement:
To reduce the impact to the occupant inside the car an additional latch and hindge reinforcement is provided to the hood. When latch and hindge is placed there is a drop In the strength at that position thus reinforcement is required. Also stiffness pad are used to reduce the NVH.
Mastic Data:
Mastic sealant are elastic compound that behaves like a rubber. It is placed between inner and outer panel. Initially it is in paste form but after a furnace bath it become hard and joins the inner and outer panel of hood. It also have a tendency to increase the strength of the panel. Since hood not only covers the engine components and provides with collision safety , it but also makes the car look aesthetically beautiful, Since we cannot use welding and bolt on the hood we use mastic sealant.
Design of outer Pannel:
Hemming:
Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edge of the two materials. Normally hemming operations are used to connect parts together, to improve the appearance of the parts and to reinforce part edges. In hood design, 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. Dimensions of hemming are given below.
Relief Data:
Relief is provided onto the part or component in order to remove any stresses developed in a particular area that is sharp corner that takes places during the hemming process is carried out. Thus corners are rounded and chamfered.
Draft Analysis:
Draft Analysis is carried out to see that the panel can be drawn or not. It helps us to find the negative draft present in the component which can cause manufacturability.
Conclusions:
Thus we have designed the hood of the car that satisfies the industry’s manufacturing requirements, functional requirements as well as Euro NCAP standards using NX CAD.
