Hood design-Week 2

Design of Hood

A car hood is defined as the hinged cover that rests over the engine bay of a front-engine vehicle. The car hood protects the engine and connected parts from the elements while providing easy access for repairs and maintenance.

The design of a car hood involves several factors, including aerodynamics, aesthetics, and functionality. Here are some general considerations that go into designing a car hood:

1. Aerodynamics: The shape of the hood should be designed to minimize wind and performance.
2. Cooling: The hood should have sufficient ventilation to allow air to flow through the engine compartment and cool the engine. This can help prevent overheating and improve engine performance.
3. Material: The material used for the hood should be strong, lightweight, and durable. Common materials include aluminium, carbon fibre and steel.
4. Aesthetics: The hood should be designed to complement the overall look of the car. This can include features like sculpted lines, a distinctive shape, and a stylish finish.
5. Functionality: The hood should be easy to open and close, and should provide easy access to the engine compartment for routine maintenance and repairs.
6. Safety: The hood should be designed to provide adequate protection in the event of a collision, and should meet applicable safety standards.
7. Resistance and turbulence: The vibreations and noices should be reduced around the engine compartment. This can help improve fuel efficiency.

When designing a car hood, all of these factors need to be taken into consideration to ensure that the end result is both functional and visually appealing.

A hood stay is a mechanism used to hold the hood of a vehicle open while the user is performing maintenance or repairs.

There are generally two types of hood stays are  manual and hydraulic.

Manual hood stays

These are the most common type of hood stay and are generally found in older vehicles. They consist of a metal rod that is held in place by a bracket on the hood and a support bracket on the engine compartment. The rod can be removed or adjusted to keep the hood in a desired position.

Hydraulic hood stays

 These are becoming more common in modern vehicles. They use a gas-filled strut that is mounted on the hood and a support bracket on the engine compartment. When the hood is opened, the strut extends, providing support to hold the hood open. The strut can be adjusted or replaced if necessary.

In addition to these two main types, there are also other variations of hood stays that may be used in certain vehicles. For example, some vehicles may use a spring-loaded mechanism that keeps the hood open, while others may use a cable system. However, manual and hydraulic hood stays are the most common and widely used types.

The curvature of the support rod during the open position should be less than 35mm to prevent further bending of the rod due to the weight of the hood. Both the inner panel and outer panel of the hood are generally designed with a thickness in the range of 0.65-0.75mm.

 The Components of a car hood includes

1.Outer panel

The outer panel of a car hood is the visible, outermost layer of the hood that covers and protects the internal components of the hood. It is typically made of metal or a composite material such as carbon fibre and is designed to be lightweight, strong, and durable.

The outer panel of a car hood is responsible for protecting the engine and other components located under the hood from damage due to external factors such as weather, debris, and collisions.

In terms of design, the outer panel of a car hood can vary greatly depending on the make and model of the vehicle, as well as the intended use of the vehicle. Some hoods feature a simple, flat design, while others may have raised areas or sculpted shapes to improve the vehicle's appearance or provide additional airflow to the engine.

Overall, the outer panel of a car hood plays an important role in protecting and enhancing the performance of a vehicle, while also contributing to its overall aesthetics.

 2.Inner panel

The inner panel in car hood design refers to the metal sheet which is inside the outer surface of the car hood. It provides additional support to the hood, which helps to maintain the shape of the hood and prevent it from flexing or bending under various driving conditions.

In addition to providing structural support, the inner panel may also include various components, such as insulation, sound-deadening material, or even air vents, depending on the specific design of the car hood. These components help to reduce the noise and heat transfer to the cabin.

Overall, the inner panel plays an important role in the design and function of the car hood, helping to ensure that it provides the necessary support and protection to the engine and other components underneath.

3.Hinge and striker assembly

  Hinge and striker assembly to open and closed our hood whenever required . This part should be strong enough to take the load of the hood and also the forces which act upon the hood in case of crash. So, this part should be designed with utmost care that it should not fail during its operation.

4.reinforcements 

Mastic sealant

An important feature we provide between the inner panel and outer panel is the Mastic sealant. It also helps to reduce the NVH (noise, vibration and harshness) of the vehicle. Every region where the mastic sealant is added will have the ability to improve the strength at a distance of about 80mm. Mastic is added in the form of a paste at the respective points. When it gets heated in the hot bath, it gets hardened and joins the outer panel and the inner panel. Spot welds and rivets should not be used here since the outer panel is a styling surface and the use of such techniques will affect the aesthetics of the part.

Emboss

When a collision occurs on the front, the forces should be dissipated to the outside of the car. In order to do that, we create embosses along the respective directions and the force of the impact gets dissipated to the outside and along the hinges. So, the embosses enables the forces entering the cabin to be reduced drastically and helps in providing passenger safety. It also considers the safety of the pedestrian who will be badly affected during collisions.

Embossing is typically done using a hydraulic press or other specialized equipment that can apply the necessary pressure to create the design. The process can be relatively quick and straightforward, but it requires a high level of precision and attention to detail to ensure that the embossed design is consistent and accurate.

Latch and striker trajectory

For the striker emboss and to fix the striker, the trajectory of the striker should be determined. Therefor the following steps should be done to determine the trajectory.

1) Select the hinge axis by joining the centre line of two hinges by a line and take the midpoint of the axis.

2) Draw a circle with the midpoint of the axis as the centre and the circle should be passing though the predefined position of the striker and that should be considered as the trajectory.

3) Check whether the striker location is perpendicular to the trajectory at the area locally. If so, the circle can be the real trajectory. If not the position of the hinge should be modified, and new trajectory should be sketched.

If the trajectory is correct, then the closing of the hood would be smooth, and no problem arises. The striker reaches the latch which is mounted below in the correct position and the hood is closed.

Hemming

Hemming is a manufacturing process used in car hood design to create a folded edge that provides stiffness and rigidity to the hood. The process involves bending the edge of a sheet metal panel over onto itself to create a smooth, rounded edge.

The purpose of hemming is to create a strong and durable connection between two panels, while also providing a finished appearance to the edges of the hood. This technique is commonly used in automotive body manufacturing to join two panels of metal together and create a uniform appearance.

The hemming process typically involves a special tool or machine that is used to fold the edge of the metal panel over onto itself. This creates a double-layered edge that is more resistant to bending and deformation than a single-layered edge. Hemming also helps to reduce sharp edges that could be dangerous or cause injury.

Overall, hemming is an important process in car hood design, as it helps to improve the strength, durability, and appearance of the hood. It is a key step in the manufacturing process of automotive bodies and is used extensively in the automotive industry.

The corners of the hemming are likely to have spring-back that is, the force by the rollers creates changes in the design of the outer panel. So, we provide reliefs to the corners by avoiding some sheet there and thus prevents the deformation.

There are various types of hemming operations

 1) Conventional die hemming      

 In conventional die hemming, the flange is folded over the entire length with a  hemming tool. The steps include, for example, the pre-hemming and final hemming depending on the respective opening angle of the flange. Production plants for conventional die hemming are very expensive, but the cycle times are very low.

2 Roll hemming

In roll hemming, the hemming roller is guided by an industrial robot to form the flange.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. 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.

Deep drawing

Deep drawing technique is used in the manufacturing of hood which is basically a sheet metal. 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. 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. This setup is similar to sheet metal cutting operations. As in cutting, clearance is the lateral distance between the die edge and the punch edge. The sheet metal work piece, called a blank, is placed over the die opening. A blank holder, that surrounds the punch, applies pressure to the entire surface of the blank, (except the area under the punch), holding the sheet metal work flat against the die. The punch travels towards the blank. After contacting the work, the punch forces the sheet metal into the die cavity, forming its shape.