Hood design-Week 2

Hood Design

Introduction:-

The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment, or trunk on rear-engine and some mid-engine vehicle for maintenance and repair.

Bonnet is an important component of the front portion of the car which is used for many purposes. Bonnet is used to decorate front portion of the car and to add luxurious look. It is made aerodynamic in shape to reduce air effect. Generally it is used to cover car engine, radiator and many other parts, therefore bonnet must be designed in such a way that all the maintenance parts should be ease of access and it should give a minimum impact of external disturbance on the engine. When car come across any accident from the front portion most of the time bonnet system gets damaged and absorbs some part of impact energy resulting from crash.

Design Consideration

The 1st and most important safety requirement to be considered while designing the Bonnet is the Pedestrian Safety from frontal collision.

The European New Car Assessment Programme (Euro NCAP) is a European car safety performance assessment program which has developed test specifications and rating systems for assessing pedestrian injuries during impacts with the front of vehicles Such tests include a series of tests using impactors designed to mimic a collision at a speed of 40 km/h.

They describe a situation in which a pedestrian is situated laterally and a car first hits one of his legs. Tests are conducted on the leg, upper leg and, most importantly, the head, as head trauma is most commonly responsible for casualties.

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 that area as during the head collision, the hood will absorb the head impact energy leading to collapse of the hood and thus protecting severe head injury.

Another important criteria for the hood design is the protection of the occupants inside the car during the front collision. The design of the hood should be in a such a way that the during the collision, the force should travel in the upward direction through the embosses and directed towards the body of the car. Thus protecting the occupants inside.

Design ForManufacturing requirements: -

• Deep drawing process is used for the manufacturing of the inner panel.
• Material used is aluminium as it can absorb twice the crash energy of mild steel, ligher, dent free and can make body panels thicker while still lowering weight.
• No sharp corners inside the panel.
• No negative draft.
• Provide appropriate corner relief on the area of curvature.
• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5 mm

Design of inner panel:

Master Section:

Master section is already provided by the marketability team and the manufacturing requirements.

Initial design was created from the master section that was already provided. Embossing is a metal forming process for producing raised or sunken designs or relief in sheet material by means of matched male and female roller dies, theoretically with no change in metal thickness. Embosses are created to provided addition strength and to direct the forces from the front collision towards the hinge and body of the car.

Position of hinge and striker: -

For the proper opening and closing of the hood, the striker should be perpendicular to the trajectory of the hood. For this, hinge is assembled at its position. Once it is placed, hinge axis is drawn. Using the hinge axis as the center we draw a big circle to the position the latch in such a way that it is perpendicular to the hood trajectory.

Latch And Hinge Reinforcement: -

To furthermore reduce the impact to the occupants inside the car, additional latch and hinge reinforcement to the hood. When latch and striker are placed, there is drop in strength at that position thus reinforcement is required. Also stiffness pads are placed to reduce NVH. Hinge and latch reinforcement thickness is kept at 1.5 mm but it may vary.

Mastic Data: -

As we know that the main purpose of the outer panel is for the aesthetic looks. Thus we cannot use bolts or welding. This has to be done with the help of the hemming and mastic sealants. Mastic sealants are elastic compound that behaves like the rubber. It is placed between the outer and inner panel. Initially is it in paste form, but after the hot furnace bath it gets hardened thus joining the outer and inner panel. Mastic sealant has the tendency to increase the strength of the panel and has influence of 80mm diameter.

Design of Outer panel: -

Hemming:-

Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edges of two materials. Normally hemming operations are used to connect parts together, to improve the appearance of a part 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 :

Relief is provided onto the part or component in order to remove any stresses developed in a particular area i.e sharp corners that takes place during the hemming process is carried out. Thus corners are rounded or chamfered.

Draft analysis-

Draft analysis is carried out to see that the panel can be drawn or not. It also helps to find the negative draft present in the component which can cause difficulty in manufacturability.

Thus from the above image we can conclude that the part can be drawn without any problems

Parts for Assembly

Latch Reinforcement

Hinges-2 nos

Component that attached with Hinges and Engine Compartment- 2 nos

Assembled Hood Design

Different Views of Hood

Conclusions:-

Thus we have designed the hood of the car that satisfies the industry’s manufacturing requirements, functional requirements and as well as Euro NCAP standards using NX CAD.