Hood design-Week 2

AIM:

 

To design Hood Inner Panel, Outer Panel and the necessary reinforcements by following the Master section and design parameters.

 

 

 

INTRODUCTION:

 

Hood

Hood is the main component of a car at the front portion. It is used to decorate the car and add a luxurious look. The shape of the Hood is made aerodynamic in order to minimize the air effect. It is generally used to access the parts easily such as radiator, engine and many other parts. A car hood, also referred to as a bonnet in some other countries, is the hinged cover that rests over the engine of a front-engine vehicle. Its purpose is to provide access to the engine for repair and maintenance. A concealed latch is typically used to hold down the hood. On vehicles with an aftermarket hood and on race cars, hood pins may be used to hold down the car hood. Hoods sometimes also contain a hood scoop, wiper jets, power bulge, and/or hood ornament. Car hoods are typically constructed from steel and sometimes from aluminium. Aftermarket car hoods may be constructed from various other materials, including carbon fibre, fiberglass, or dry carbon. The hood design may vary from one make and model to another.

 

 

 

Parts of Hood

 

Outer Panel:

 

Outer panels are the aesthetic elements of a car. It is the styling team who provides the skin for the outer panel. The shape, position and size of the hood should satisfy the safety norms. So, while designing the hood more importance is given to pedestrian safety. The outer panel is attached to the inner panel by hemming. So, it is necessary to provide required hemming flange and reliefs for the hemming operation along with mastic sealants between outer panel and inner panel to reduce vibration.

 

                      

Inner Panel:

The hood inner panel provides strength and rigidity to the hood. It also directs the force of the collision outwards instead of into the engine compartment of the car. It consists of embosses & holes which provide stiffness as well as dissipates energy towards reinforcement.

                      

 

Reinforcements:

 

Reinforcements are provided whenever there is an addition of material to the component there is a loss of strength locally. In this case, the additional material is the striker and hinge where additional reinforcements had to be attached due to loss of strength locally in the attachment areas. Usually thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirement.

 

Latch & Striker:

 

A hood latch is a very simple component. It's basically the fastener that keeps your hood closed shut. This latch ensures that your hood is securely connected to your vehicle and that it doesn't pop open unexpectedly. An engine hood latch mechanism for locking an engine hood in a closed position includes a striker fixed to the lower surface of the engine hood and a base member having a vertical slit into which the striker is dropped in response to closure of the engine hood. A locking mechanism engages with the striker in response to drop of the striker into the vertical slit and locks the striker in a closing position where it holds the engine hood in the closed position.

 

 

 

                    

Hinge:

 

Hinges are used to connect the hood & cowl panel of an automobile. It enables the opening & closing operation of the hood. The hinge should be made strong enough to handle the weight of the hood and also to handle the force action on it during the collision.

 

                                   

 

 

 

 

 

Positioning of Striker & Hinge:

 

The hinges should be positioned on the hinge tentatively such that they lie on the same plane. From the axis of the hinges create a midpoint, from that midpoint draw a circle with a radius from the midpoint to the center of the striker. The circle created is called the trajectory circle. With the trajectory circle, it is to be checked that the striker is tangent to the trajectory circle if not then the position of the hinge should be moved accordingly such that the striker is tangent to the trajectory circle. This is done because the latch where the striker strikes and locks the hood is positioned with respect to the trajectory circle. If the striker is not positioned accordingly then there will be difficulty in locking the hood.

 

                    

 

 

 

 

 

Hood Support:

 

There are two types of hood support used in automobile industry:

 

(1) Support Rod:

 

Most of the car manufacturers are used this only because of simpler and cheaper when compare to the gas stay. In this method we have to lift the hood by our own strength and fix the free end of the support rod to the provision which is given in the engine compartment or hood. It is suitable for the light weight and quite smaller hoods.

 

                                         

 

 

 

(2) Gas Stay:

 

In this method, once the hood is little bit lifted, then the gas stay can completely lift the hood entirely. It is done by the gas spring which is in inside the gas stay. If the hood is heavier and longer, then the gas stay pretty much makes the lifting process easier.

 

                                    

 

 

 

 

 

Design considerations for Hood

 

Hood Head Zone:

 

                   

 

 

 

 

 

In-vehicle to pedestrian collisions, the main reason for fatal injuries is the pedestrian to vehicle impacts, which are caused by the direct impact of the pedestrian head to the front part of the automotive hood during a collision. This paper deals with the development of a new finite element model to simulate the car-to-pedestrian front impacts between the adult head form and vehicle hood composite structures according to the EURO-NCAP requirements.

 

 

Pedestrian Safety:

 

                                 

The Pedestrian Protection System (PPS) is a system which, in certain frontal collisions, contributes to mitigating a pedestrian's impact with the car. In certain frontal collisions with a pedestrian, the sensors in the front of the car react and the system is activated.

 

In other words, A pedestrian can be defined as a vulnerable road user that is at risk when it comes to roads. Thus, the safety of such being is essential. The pedestrian safety and protection norms are aimed to do so. It will ensure that the new cars meet a minimum requirement of safety for the pedestrians.

 

                        

 

 

Emboss:

 

 

 

                            

 

Emboss is given so that during the crash the energy is dissipated outside or away from the vehicle occupants and along with the other cut outs to reduce the weight. Also, its help to improve the strength of the hood inner panel.

 

Another important aspect to be considered is the safety of the driver and passengers of the car. This is done by strengthening the inner panel by creating embosses and the design of the embosses should be such that the force due to impact should be directed outside the car rather than inside the engine compartments.

 

The arrows represent the direction of the force.

 

                      

 

 

 

 

 

Mastic Sealant:

Hood commonly possess large surface area and hemming can only be provided through its boundary. Other joining techniques like welding, riveting etc cannot be used because they will leave marks on the outer panel which spoil its aesthetic appearance. So, mastic sealants are used to stick the inner surfaces of outer panel and inner panel. These are elastic compound that behave like rubber. It is applied between the inner and outer panels at specified spots. Each spot of mastic sealants has its effect around a circular region of 80mm diameter. Thus, the mastic points are arranged in such a way that it covers the areas away from the hemming which are more vulnerable to vibrate.

 

                          

 

 

 

 

 

Manufacturing Techniques

 

Stamping Process:

 

 

 

                              

 

Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal. This process can be made by means of matched male and female roller dies, or by-passing sheet or a strip of metal between rolls of the desired pattern. It is often combined with foil stamping to create a shiny, 3D effect. 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 sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter.

 

                                   

 

 

 

 

 

Hemming:

 

Hemming is a technology used in the automotive industry to join inner and outer closure panels together (hoods, doors, tailgates, etc.). It is the process of bending/folding the flange of the outer panel over the inner one. The accuracy of the operation significantly affects the appearance of the car’s outer surfaces and is, therefore, a critical factor in the final quality of a finished vehicle

 

Different types of Hemming are:

 

Conventional Die Hemming

 

Roll Hemming

 

Flat or Closed Hem

 

Open Hem

 

Teardrop Hem

 

Rope Hem

 

Roll Hem

 

 

 

Roll Hemming:

 

                        

 

 

 

 

 

Generally, Roll Hemming is used to join the outer and inner panel of the hood. It 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. 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 Relief:

 

During the hemming operation rollers rolls over the outer panel surface to join to panels together with hemming glue. But at the corner, the roller could not produce perfect hemming due to the presence of curvature. To avoid overlapping some of the material removed it is necessary to provide some relief at corners.

 

                       

 

 

 

 

 

                       

 

 

Draft Analysis:

 

                        

 

 

 

 

 

Once the design was ready, the inner panel of the hood was analysed for manufacturability. here draft analysis shows that all parts are clearing when core is removed from cavity.

 

Different Views of Hood

 

 

 

Front View:

 

 

 

                        

 

 

 

Side View:

 

 

 

                        

 

 

 

Isometric View:

 

 

 

                        

NOTE:

Since the zipped folder size was more than 20 MB, so it could not be uploaded. Hence the google drive link is : https://drive.google.com/file/d/1PM8Iyt9YtWCKBobpj-MKoDtJjZlTGBMl/view?usp=drive_link