Hood design-Week 2
AIM
To create a complete hood assembly from the given Master sketch and skin data of the Hood outer panel using Siemens NX-CAD.
THEORY
Car Hood or Bonnet is one of the important BIW parts of the car. It is the hinged cover that rests over the engine of a front-engine vehicle. There are two different types of hoods, they are Inlaid/ Built-in hood and wrap around hood. In Inlaid type the hood spreads only on the engine compartment whereas in wrap around type the hood spreads furthermore pushing the fender downwards and taking its space. Wrap around hood is better in terms of pedestrian safety.
There are mainly 4 components that constitute a car hood. They are:
1.Hood outer panel- It gives the aesthetic and stylish look to the car.
2.Hood Inner panel- It provides the necessary strength and rigidity to the outer panel.
3.Latch striker- It is the mechanism used to close the hood.
4.Hinges- They provide the support for the hood while opening and closing
and in some cases, Support rod is also mounted on the car hood itself.
IMPORTANT CONSIDERATIONS WHILE DESIGNING A HOOD
Important considerations that an engineer must keep in mind while designing a hood are:
1.Pedestrian Safety:
It is the most important factor that decides whether the hood you design is a good one or a bad one. Euro NCAP safety assessment program in which the pedestrian safety is tested while the car is moving at a standard speed of 40kmph and side reference line which is at an angle of 45 degrees to the ground level is projected up to where it touches the car hood or the fender on the both sides and the whole area from left to right is marked and a thread which is fixed on the ground is taken and wrapped around the impact area of the hood and the child head impact and adult head impact areas are marked so we have to make sure that in these areas the hood thickness is as less as possible and no reinforcements are given so that during collision the hood absorbs the most of the energy and breaks thus preventing the pedestrians from severe head injuries.
2.Occupant Safety:
Another important criterion that a good hood must satisfy is the good occupant safety because hood will be the one of the first one to hit in an accident/collision. So, we as an engineer must make sure that the forces that impact the hood are not transmitted to the passenger compartment. We can achieve this by giving the appropriate embosses while designing the inner panel of the hood and we also provide a pre-defined line along which the hood collapses during the time of frontal crash.
3.Latch trajectory:
It is important to consider this while placing your striker at the time of hood assembly. what it says is that for the latch and striker mechanism to lock properly while closing the hood, when a circle is drawn with the midpoint of the line joining the two hinge axes as its center and connecting the striker that the latch must be tangent to this circle.
4.Deep drawing:
Hood of a car is manufactured using a sheet metal operation known as Deep drawing. It is a sheet metal forming operation in which a sheet blank is radially drawn into required shape by the mechanical action of punch. So for a hood design to manufacturable all the embosses that are created on the inner panel must be made with a positive draft angle.
4.Vehicle quality:
It involves all other factors that decide how good a hood is like torsional stiffness, dent resistance (Chipping due to stones in the road), corrosion resistance and noise and vibration attenuation.
GIVEN PARAMETERS FOR DESIGNING THE HOOD:
- Outer panel thickness= 0.75mm
- Inner panel thickness= 0.75mm
- Reinforcement thickness= 1.5mm
MASTER SECTION
HEMMING DATA
REAR SECTION RELIEF
FRONT RELIEF
HOOD INNER PANEL
Hood inner panel should be designed in such a way that it will provide the required stiffness to the hood and also absorb the energy during collision with pedestrian in order to increase pedestrian safety. To increase the stiffness, we provide the multiple embosses on the inner panel surface.
To make the vehicle safe for the pedestrian we remove some amount of material from the inner panel so that on collision the outer panel can deform and absorb the impact.
To provide the firm and strong support at the hinge and striker location, we provide the reinforcement of 1.5mm thickness. Striker mount is designed considering the latch trajectory and the head zone after opening of the hood as below.
HOOD OUTER PANNEL
The outer panel, used to cover the inner panel of the hood. It is also considered as the class-A type of the car body, because it is visible from the outside. This component must be considered for the styling. It is first component that subjected to any type of impact. This part is intact with inner panel so to have a perfect combination its edges are wrap around inner panel this type of wrap called hem operation.
Mostly all the automobile industries use Hemming process to join the outer and inner panel. Keeping the same in the consideration hemming glue clearance of 0.2 mm on each side of inner panel is maintained. Also, mastic clearance of 5mm is kept between two panel as below for joining process. End relief are provided as per the given data.
CONCLUSION: -
Creation a complete hood assembly from the given Master sketch and skin data of the Hood outer panel using Siemens NX-CAD is done.
NOTE :- BECAUSE OF THE FILE SIZE LIMITATION UPTO 20 MB IM UNABLE UPLOAD THE FILE IN THE BROWSE OPTION ON THE WEBSITE. SO IM ATTACHING HERE BELOW THE GOOGLE DRIVE LINK FOR THE FILE.
https://drive.google.com/file/d/1ICAjaseHO3-FCzTAY30HWz_IpS2Clnk7/view?usp=sharing