Hood design-Week 2

OBJECTIVE:

 To understand and designing of Hood assembly consists of Hood Outer panel, Hood Inner panel joined with Hem and develop the Inner panel with all necessary reinforcements definition of the positioning Hinge, striker parts and create provision for mastic sealant points.

HOOD

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 (boot) on rear-engine and some mid-engine vehicles for maintenance and repair.

THEORY:

The Hood or Bonnet of a car is considered as the frontal BIW enclosure component. Bonnets are designed to reduce air resistence as the air flows around the car. The design of the Bonnet is vital since it affects the aerodynamic flow around the car. Apart from this bonnet are also designed to meet several other requirements. They serve a great deal of purpose in protecting the passengers inside the car and the pedestrians in the event of the accident. It also acts as the cover for the engine.

The Hood or Bonnet consists of following parts :

1. Hood outer panel
2. Hood inner panel
3. Latch and striker re-enforcement
4. Hinge re-enforcement
5. Gas stay re-enforcement

 HOOD THICKNESS INFORMATION

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

MASTER SECTION USED

FUNCTIONAL AND SAFETY REQUIREMENTS :

1. The most important safety requirement to be considered while designing the Bonnet is the frontal collision requirements.

 The design intention of the hood according to the frontal collision requirement is that the hood ccrushes and dissipates forces in the upward direction and to the hard points on the hood thereby deflecting the force on the body and not to the passengers.

2. The second major function of the hood is the opening and closing of the hood. This is done with the help of the latch and striker. The hood pivot axis should align with hinge axis.  

The latch and striker trajectory for inner panel is shown below

  The processes involved in designing hood as a sheet metal operation are

• Blanking
• hemming
• Punch cutting or piercing
• Deep drawing
• Embossing

Designing of Hood:

Inner panel

• The hood inner panel is required to have a high initial reaction force against the impact exerted on the hood to enhance the energy absorption capacity. The hood is further required to minimize a reduction of a reaction force by deformation in a collision.
• It is an object of the present invention to provide a hood inner panel capable of reduction of a reaction force of the hood inner panel even if a level of deformation of a hood of a vehicle increases, and ensuring a sufficient energy absorption capacity.
• In the inner panel only we can research and implement the safety of pedestrians and as well as the driver. In this panel only we can attach the striker & hinge reinforcements, emboss, mastic points, etc.

Sheet metal emboss:

• The metal sheet embossing operation is commonly accomplished with a combination of heat and pressure on the sheet metal, depending on what type of embossing is required. Theoretically, with any of these procedures, the metal thickness is changed in its composition.

Deep Drawing:

• Deep drawing is a manufacturing process that is used extensively in the forming of sheet metal into a cup or box-like structures. Pots and pans for cooking, containers, sinks, automobile parts, such as panels and gas tanks, are among a few of the items manufactured by sheet metal deep drawing.

• A deep drawing of sheet metal is performed with a punch and die. The punch is the desired shape of the base of the part, once drawn. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. For many calculations, the sheet metal thickness is assumed to remain constant. However, there are changes in thickness in certain areas, due to the forces involved.

The below Figure showing Hinge placement emboss 

The below Figure showing Striker and latch placement emboss 

Mastic points:

The mastic sealant or mastic point is an elastic compound that behaves like a rubber. The mastic points are defined on the hood inner panel where the hood can easily deform. They help the hood outer panel to come back to its original shape after its gets deformed. 

A mastic sealant data is used to fix or combine the hood outer panel and hood inner panel. 

They can provide thermal and acoustical insulation, and may serve as fire barriers. They may have electrical properties, as well. Sealants can also be used for simple smoothing or filling. They are often called upon to perform several of these functions at once.

A sealant has three basic functions: It fills a gap between two or more substrates; it forms a barrier through the physical properties of the sealant itself and by adhesion to the substrate; and, it maintains sealing properties for the expected lifetime, service conditions, and environments. The sealant performs these functions by way of correct formulation to achieve specific application and performance properties.

The mastic has an influence area of 80mm. See below picture where the mastic provision is given in the current design of hood.

 Hemming in sheet metals

• Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods, and tailgates are formed by hemming processes.

• Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a forming operation in which the flange is formed with a hemming tool after the drawing and trimming operations have been completed

• Roll hemming is carried out incrementally 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.
• If weld or bolts were used to join the hood panels then the design and the aerodynamic features would get damaged so hemming is more significant to use.

Corner Reliefs

Fig Rear Corner relief

Fig Front Corner relief

Final Assembly Design

Conclusion: I understood the design concepts of Hood Assembly and its components according to rules and regulations. Used NX CAD student version to design this hood assembly.

Note: Unable to export STEP (.stp) file of assembly design due to version used (NX CAD Student version)