Hood design-Week 2

Note: I cannot upload more than one photo here in the box. So i have uploaded the report in the zip file. Kindly have a look.

Hood design-Week 2

Hood Is also called as bonnet. It covers the engine compartment. This component is important because it responsible for frontal crush and pedestrian safety. This is also used to dissipate the energy outside of the car body. Designing a hood has a important element to be considered and that is the opening angle this varies from place to place. As the height of people in each country vary this opening angle should be adaptable or varied. This opening angle is controlled by support rod or gas stay.

Support rod and gas stay:

Support rod or gas stay are used to open the back door as well as the hood. Choosing that our car needs support rod or gas stay depends on the weight of the hood. The length of the support rod is predefined with the angle of opening the hood. The rod can be either mounted on the hood or in the engine compartment. The rod will be not in a straight shaft it will be having bends and those are designers wish to design. There is no specific rules to control the design. But we need to consider that the design must not affect the engine compartment parts. The straightness is avoided because it may lead to wobbling effect and lead to bending of the rod. And also it should not be so curvy that above 35mm will lead to bending due to the weight of the hood. Grommets are used to keep the support rod in the respective places. In gas stay the piston rod is used to open and close the hood. The extended position makes the hood open and vice versa. Ball stud is used in gas stay as like grommets in support rod to hold the gas stay. To attach this gas stay a bracket is introduced to hold the gas stay.

                          Support Rod                                                                                     Gas Stay

                        Grommets                                                                                            Ball Stud

Reinforcement:

Reinforcement are things that are added to increase or compensate the lost strength in the component. Here in hood we remove sections to attach hinges, latch and striker to accommodate those parts in the hood. So now these parts are reinforcements as they are added in place of removed section to add strength to the hood.

Stiffener pads:

These are sponge like structures which is placed between the engine compartment and the hood. Stiffener pads are used to decrease the vibrations caused by the surrounding while driving. This improves the NVH of the car. This also increases the rigidity of the component.

Mastic sealants:

These are small hard rubber parts that are introduced between the inner and outer panel of the hood which increase the NVH of the car. These mastic sealants are placed in pre defined mastic points. Those give 80 mm diameter of strength to the hood. The rubber material gets into the heat bath where it becomes as paste and holds the inner and outer panel. So this way we join the inner and outer panel without spot welding operation

Emboss:

Embosses are used to give strength to the hood and the way the design of the emboss defines the flow of energy dissipation during a frontal collision. Show sure by we ensure the safety of the passenger in the car the emboss are placed so that the force is diverted to the hinge area or the outwards region of the car.The design should be also manufactureable high Complex emboss cannot be manufactured, maximum of 5 mm should be kept for the depth to be on a safer side.

Latch and striker:

This is the part which is responsible for locking and unlocking the hood to the engine compartment. The latch and striker must be perpendicular to each other and this defined by the trajectory angle. This angle of rotation is based on the hinge axis. The to and fro motion of the axis can change the angle of rotation and mix engaging of latch and the striker. To position the large and striker effectively We draw a circle with hinge access centre and draw a tangent line and here where the latch is placed

Manufacturing Process of hood:

Automotive parts mostly uses sheet metal for their components. Initially a blank is taken and that will undergo on a series of forming operation like bending, drawing, Stamping, forging and hemming. These process depends on the component we manufacture.

In bending the sheet metal is bend to a defined curvature. Here simple curve surfaces are produced this becomes the base surface of the component. A Die and Press arrangement applies pressure on the sheet metal which changes the curvature of the blank permanently. And applying of pressure must be careful that the metal should not spring back to its original shape.

Next after the bending process drawing operation is done here Complex curvature can be produced. the die and the mould create the desired shape which we predefined for the blank the pressure is applied hydraulically or mechanically that forces the punch to the die and forms the shape in the sheet metal. Negative draft angle is avoided because it cannot be manufactured. 

One of the drawing process is Deep drawing deep drawing is a forming operation the is a combination of tensile and compression. 

Stamping is done with the help of Stamping press machines share a series of dies or a single die with various cuts or formed on the metal

Hemming:

Hemming is a type of forming operation in manufacturing components. Here the edges of the sheetmetal is folded on the other part achieving tight fit. This joins the both parts without affecting the appearance and hence it is used in hood, doors, fenders, tailgates etc,. In Hood it is used to join the inner and Outer panel of the Hood. 

There are various types of heming operations

• Conventional Dai Hemming
• Roll Hemming 

Conventional Dai Hemming:

This is used it for mass productions. Here a hemming tool is used to fold the entire length of the sheet metal. Depending on the opening angle that will be several steps of Hemming process. But this is a expensive process and it is restricted to flat and complicated profiles cannot be made in hemming. 

Roll hemming:

After name says rollers are used in the hamming process and industrial robots are used to get the rollers over the part to fold over the other part and hemming his done. Comparing to the conventional die hemming the tool cost are significantly low the old hemming but the cycle time is higher the roll hemming

Here are some photo copy of my hood design mentioning the above points

Hemming

Emboss

Hinge

Mastic points

Trajectory