Hood design-Week 2

AIM:

To Design Hood Outer Panel, Inner Panel and the necessary reinforcements by given Master Section and the Design parameters.

HOOD:

Hood is a main BIW component in front portion of a car. It is an opening body panel that covers the engine in front engine vehicle. It consist of an outer panel and inner panel. The inner panel provides the strength while the outer panel functions as the metal cover. It is an access panel to the engine compartment to enable maintenance of power train, drive belts, battery, fluid levels and lamp units. It gives good aesthetic look for a vehicle.

DESIGN CONSIDERATIONS:

The human comfort factor for automobile design is first consideration. It is a method to safeguard and protect space for the human user and necessary components that make up the vehicle being designed. All safety regulations are ensured during this process. Ergonomical consideration consist 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 decided by the average height of the human in that particular country.

There are two types of hood stay, they are Gas stay and Support rod.

GAS STAY:

It is used to lift the car hood, its purpose is to just give the lifting force to the hood, then it automatically opens the car hood by means of gas inside the cylinder of the gas stay. This is used where the car hood size is heavy to lift.

SUPPORT ROD :

This is widely used in most of the cars. In this type we have to lift the hood by ourselves and place the support rod in the space provided either in the hood or engine portion. This is mostly used for where the car hood weight is small.

PEDESTRIAN SAFETY :

1. Design of the hood should be in such a way that it should reduce the injuries to the pedestrians in the event of a pedestrian vehicle collision. The objective of these measures is to reduce the number of road accident and the severity of injuries sustained by pedestrians involved in a collision with a vehicle in urban traffic.
2. The height, weight and age of the pedestrian all play a role in the 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 risks include rupture of arteries in the lower limbs and pelvis from bumper and bonnet leading edges.Impact frequency and seriousness of injury has been studied for many years, resulting in rating systems and improved design.
3. Evaluation of pedestrian safety for a bonnet must be carried out in the context of its surrounding elements like Vehicle styling, size (wrap around distance “WAD”) and under bonnet clearance to other elements (considered as hard points). Local bonnet stiffness is influenced by mounting point stiffness such as hinges, bump stops and latches. This is better understood by superimposing the kinematics of a dummy onto the test conditions.
4. Wrap Around Distance (WAD) :- It is the geometrically traced distance from the contact point with the Ground Reference Plane, vertically below the front face of the bumper, to any point on the vehicle front structure.

• Child Head Impact Zone :- 1000 WAD to 1500 WAD.
• Adult Head Impact Zone :- 1500 WAD to 2100 WAD.

DESIGN OF HOOD:

MASTER SECTION:

Master sections are the guides for design requirements which decide the component packaging after technical (Styling, Concept or Class-A) surfaces.

Four main parts of Hood assembly are;

• Outer Panel.
• Inner Panel.
• Striker.
• Hinges.

Given Hood Thickness Information are;

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

OUTER PANEL:

The outer panel skin surface are given from the Styling department with proper aesthetic look. The shape of the Outer panel is made aerodynamic to develop efficiency of the vehicle. From the outer panel the inner panel is to be designed. The outer panel have a thickness of 0.75 mm.

INNER PANEL :

Hood Inner panel is main part in hood design. Hood consists of embosses which makes the incoming air to flow away from the body. It gives structural support and strength to the outer panel of Hood. The outer and inner panels of the Hood are typically attached together using a hemming operation at the edge.

LATCH AND STRIKER:

ThE LATCH and STRIKER is the attachment of hood assembly and vehicle body. The hood latch system must be able to catch the striker of the hood upon closing as well as automatically lock. Once in the locked state, it must remain locked and only unlock upon the operator’s control.

HINGE:

The hinges are used to guide and hold the hood while during opening and closing. Hinge assembly consists of two parts one is connected to the hood inner panel and second one is connected to the vehicle body.

REINFORCEMENT:

Reinforcements are provided mainly in hinge and latch region. When hinge and latch assemblies are attached to inner panel, strength of that area reduces locally so we add some additional material to increase the strength of the area locally. Thickness of reinforcement material is provided according to the design requirements. In this, 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 the latch trajectory. the position of latch striker follows the path of this circle.

MASTIC DATA:

Mastic sealants used between the outer and inner panel. Mastic sealants are the rubber like elasic compound which connects the outer and inner panels of car hood at specified points. Mastic sealants are used because other joining process like welding or riveting are not good for car asthetic design. It also helps in improving Noise, vibration, and harshness characteristics. Mastic salant points are effective around a circular region of 80mm diameter.

EMBOSS DEFINITIONS:

Embosses are provided to increase the strength of inner panel. Shape of embosses also determines the direction of collision force distribution. the shape of the embosses should be designed in such a way that, the collision forces should be directed towards outward side of the car (towards hinge side).

FINAL ASSEMBLY:

MANUFACTURING OF HOOD :

The most important design consideration of any component is manufacturing aspect. 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 aspect is to manufacture hood assembly with minimum operation sequence and process time.

DEEP DRAWING:

• The manufacturing of deep, cuplike products from thin sheet metal is known as deep drawing. The process involves a punch with a round comer and a die with a large radius. The punch-die clearance is slightly larger than the thickness of the sheet metal to be 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.
• The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions. A flat sheet metal blank is formed into a hollow body open on one side or a hollow body is formed into a hollow body with a smaller cross-section.
• Deep drawing creates a seamless effect on metal, allowing for the creation of a smooth, curved edge. Deep drawn metal parts are created using a single metal blank, not a repeated course of metal blanks as is typically the case with traditional metal stamping.
• Deep drawing is one of the most widely used processes in sheet metal forming. Apart from its use in many other sectors, it is applied in the automotive industry for the manufacturing of car body parts.
• When drawing complex car body parts in practice, there is usually a combination of stretch and deep drawing involved. It is necessary that the sheet metal is stretched as well as possible without reaching the material’s limits (e.g. splits, wrinkles).

HEMMING:

Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts. This assembly method is widely used in the final stages of production of automobile hoods, doors, or other closures for aesthetic purposes. It is a metalworking process that involves rolling the edge of sheet metal over and onto itself, essentially creating an area of two layers. During this process, the edge of sheet metal is folded over. The two newly formed layers then lie flush with each other. The typical three-step bending process of the hemming operation comprising of the flanging, pre-hemming, and final hemming process.

ROLL HEMMING:

Roll hemming is carried out 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.

HEMMING DATA FOR HOOD:

CORNER RELIEF:

FRONT RELEIF: