Hood design-Week 2

AIM: 

To design car hood in NX CAD using given master section and analysis it's components.

INTRODUCTION:

A car hood is the metal part that covers the engine of an automobile. The term car hood is a North American term, used primarily in America and Canada. Hood comes from the Old English word hod which means a hood, a soft covering for the head. Interestingly, hood is used by British English-speakers to refer to the waterproof cloth top covering the passenger compartment of a car or pram.

A car hood, also referred to as a “bonnet” in some countries, is the hinged cover that rests over the engine bay of a front-engine vehicle. The car hood protects the engine and connected parts from the elements while providing easy access for repairs and maintenance power train, drive belts, battery, fluid levels and lamp units.Car hoods are typically constructed from steel and sometimes from aluminum.

 HOOD:

The HOOD is an opening body panel that covers the engine in front engine vehicle.It gives access to the vehicle's engine and is also vital for the safety against the frontal impact of the car and while providing easy access for repairs and maintenance power train, drive belts, battery, fluid levels and lamp units.

DESIGN PARAMETERS:

Hood Thickness Information

    Outer Panel Thickness     = 0.75mm

    Inner Panel Thickness      = 0.75mm

    Reinforcement Thickness  = 1.5mm

PURPOSE OF HOOD :

The major purpose of  Hood  are save and safety of purposes inside the car. Cover all engine parts and radiators. Reduce the Air effect due to design aerodynamic shape. provide access to the engine for repair and maintenance.

• Functional and Safety Requirements

Frontal collision is the most important safety requirement to be considered while designing the Bonnet.

Hood design according to the frontal collision requirement is that the hood crushes and dissipates forces in the upward direction and to the hard points on the hood, thereby deflecting the force on to the body and not the passengers.

The above image from Euro NCAP shows the area of impact for a child and an adult.It shows that the child impact area is designed with lesser thickness than the adult impact area so that in the event of a frontal collision where a child is involved, the bonnet will absorb the impact of the crash and crumble to protect the child’s head from absorbing the force.

Components Of Hood:

The car Hood consists of following components,

• Hood inner panel

Inner panel is one of the main functional part in hood design.The hood inner panel provides strength and rigidity to the hood.It also directs the force of collision outwards instead of into the engine compartment of the vehicle.It is where hood latch and hinges are attached.

• Hood outer panel

it is the outer skin of the hood which provides a cover to the front engine vehicle.It is the aesthetic part of the hood,its creating a premium look. The outer panel is attached to the inner panel by hemming. We also provide mastic sealants between outer panel and inner panel to reduce vibration.

• Latch and Striker

It is a part that helps in locking the hood with the striker which is mounted on the engine block when it is not in use. It plays a major role in opening and closing hood for maintenance of car engine and gives a tight locking position not to create undisturbed noises when the vehicle is running. 

• Hinges

Hinge assembly consists of two parts one is connected to the hood inner panel and second is connected to the vehicle body.A Bonnet Hinge is a bracket system that facilitates the opening and closing of a car bonnet.

• Reinforcement

The reinforcements provided to add material to the inner panel to provide extra strength to the hood,Mainly it is provided at the hinge and latch regions to improve the strength locally.

Types of Hood stay:

The hood supported by two type of stay

• Support Rod

It is a  metalic rod used to lift the car hood.It is the cheapest method to lift the hood.In this type we have to lift the hood by ourself and place the support rod in the hood.it is one of the effective cost cutting method, widely use in many cars.

• Gas Stay

It is the most effective method to lift the car hood.Its purpose to just give the lifting force to the hood then it's automatically opens due to gas pressure.

CONSIDERATIONS FOR DESIGNING THE HOOD:

• Latch Trajectory

Latch trajectory is the path which the hood rotates during opening and closing movement.The radius of the circular trajectory is determined by the set standard  based on the average height of a person. The radius is measured from the hinge axis up to the latch.

• Mastic Data

Mastic point helps to locally improve strength of the hood.In the mastic point areas where the mastic is placed to attach the outer panel to the inner panel.Each spot of mastic sealants has its effect around a circular region of 80mm diametere.We cannot use spot welding because they leave marks on the outer panel,Hence the mastics are used to join the panels together as it does not melt the metal itself.

• Emboss definitions

In the  the inner panel we provide different embosses, which help to dissipate the force during frontal collision.The force should be always distributed away from the passengers.We can also increase the stiffness of the inner panel through these embosses.

In this image, you can see the force as it branches out on the hood, avoiding the passengers.

MANUFACTUREING REQUIREMENTS :

• Deep Drawing

While designing the inner panel hood that will be manufactured using the deep drawing process, there are some minimum requirements that we need to fulfil:

1. Minimum fillet radius = 3mm+Thickness
2. No sharp corners inside the component
3. No curvatures lesser than 5mm
4. Small embosses should not exceed the maximum depth of 6mm (staying on the safe side)
5. Mounting areas and welding areas need to be flat
6. Provide appropriate corner relief on the area of curvature.

It is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. The process is considered deep drawing when the depth of the drawn part exceeds its diameter.Deep drawing is one of the most widely used processes in sheet metal forming. The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions.

                   The process is presented in the picture

Deep drawing is a cold metal forming process, in which a flat metal blank is forced into a die cavity by hydraulically driven punch.
A cup-like cylindrical part, having the depth greater than its diameter, is formed as a result of deep drawing.

• Hemming

Hemming is the process of joining both the outer and inner panel together. The hemming process roles and wraps the hood outer panel around the inner panel and holds it tightly together.In the process which sheets are joined by bending it usually to 180°.

Hemms are commonly used to reinforce an edge, hide burrs and rough edges, and improve appearance.Hemmsare commonly used in the food industry on canned goods, on amusement park cars, in metal roofing (with a roof seamer), and mainly in the automotive industry.

After the hemming process is done, now we need to provide corner relief on the corners of the hood so that the part is manufactural.

There are two types of hemming operations,

• Conventional die hemming

In conventional die hemming, the flange is folded over the entire length with a hemming tool.

• Roll hemming

Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange.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.

CONCLUSION:

In this challenge I learn about Hood and design the hood assembly with the help of master sketch in NX CAD And also learnt the assembly of Hood inner panel, Outer panel, and the reinforcements like latch and hinge assembly.