Hood design-Week 2

AIM - TO DESIGN CAR HOOD ASSEMBLY.

In this report we are going to study about Hood Outer Panel, Hood Inner Panel, Hinges , Striker in NX. Using the CAD we are going to design and develop the model with design consideration.

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. It generally covers the engine and other essential accessories of the car. The Hood consists of Hood Outer Panel and Hood Inner Panel. The Inner panel provides the strength and support and the Outer Panel provides the aesthetic look. while designing the Hood a Design enginner needs to make sure that the following design parameters are followeed.

• Pedestrian Safety
• Occupant Safety
• Styling
• Manufacturibility

Points to be consider while designing the hood:

• Opening angle of Hood
• N CAP crash Test
• Wrap Around Distance (WAD)
• NVH (Noise, Vibration, Harshness)

Design considerations :-

The human comfort factor for automobile design is first consideration. It is a method to safeguard and protect space for the human user and necessary components that make up the vehicle being designed. All safety regulations are ensured during this process. Ergonomical consideration consist of Hood clearance, Hood Opening angle and location of support rod or gas stay.

Hood opening angle is different for different regions or countries. It is decided by the average height of the human in that particular country. 

                                                

There are two types of hood stay, support rod and Gas stay which holds the position of hood at desired angle.

1) Support rod :-

It is a simple metalic rod. It is not usually made linear to increase rigidity of rod but the length from line connecting support rod retaining point with retaing point on body side to maximum bending point should be less than 35mm to ensure the strength of support rod.

It should have sufficient clearance with other engine components to avoid rattling noise.

Gourmets are provided to keep the support rod in rest condition.

                                      

Advantages of support rod are as follows

• They are economical 
• Light in weight.

Disadvantages of support rod are as follows

• When striking with the automotive body panel to leave scars which are very likely to cause rust.
• The metal rod is often too hot to be gripped by hands immidiately after the vehicle has been stopped.

2) Gas stay :-

It is a device used for supporting the engine hood of a vehicle in its open postion by means of an actuator which is activated by gas.

In case of gas stay only intial force is required to open the hood then it automatically opens at desired angle with the extension of pneumatic piston in cylinder of gas stay assembly.

Advantages of Gas stay are as follows

• No human effort is required
• Easy to operate 

Disadvantages of Gas stay are as follows

• They are heavy in weight compared to support rod.
• Cost is more.

                                         

Safety requirements :-

The most important safety requirement is regarding the frontal collision.

It should withstand in high collision forces as well as it should divert the forces in outward direction so intensity of collision forces would be reduced to cabin side of car.

                              

Pedestrian safety :-

Design should be such way that it should reduce the injuries to the pedestrians in the event of a pedestrian vehicle collision. The objective of these measures is to reduce the number of road accident fatalities and the severity of injuries sustained by pedestrians involved in a collision with a vehicle in urban traffic.

The height, weight and age of the pedestrian all play a role in the kinematics of the event and in his ability to survive. Most fatalities for the younger population are related to brain damage caused by head impact on the bonnet. For older people additional risks include rupture of arteries in the lower limbs and pelvis from bumper and bonnet leading edges.Impact frequency and seriousness of injury has been studied for many years, resulting in rating systems and improved design.

Evaluation of pedestrian safety for a bonnet must be carried out in the context of its surrounding elements like Vehicle styling, size (wrap around distance “WAD”) and under bonnet clearance to other elements (considered as hard points). Local bonnet stiffness is influenced by mounting point stiffness such as hinges, bump stops and latches. This is better understood by superimposing the kinematics of a dummy onto the test conditions.

Wrap Around Distance (WAD) :- It is the geometrically traced distance from the contact point with the Ground Reference Plane, vertically below the front face of the bumper, to any point on the vehicle front structure.

Side Reference line :- The geometric trace of the highest points of contact between a straight edge, held parallel to the lateral vertical plane of the vehicle and inclined 45 deg. is traversed down the side of the front structure, and the side of the front structure.

Child Head Impact Zone :- 1000 WAD to 1500 WAD

Adult Head Impact Zone :- 1500 WAD to 2100 WAD 

                                  

                                        

Besides functioning as an engine compartment cover, the hood of modern vehicles can also help manage the impact energy of a pedestrian’s head in a vehicle-pedestrian impact. However, a hood’s ability to absorb impact energy may be impeded by the proximity of the hood to components packaged inside the engine compartment, i.e., by its underhood clearance.

For example, for a given hood design, the hood’s ability to absorb impact energy through deformation can be significantly reduced when the hood and engine block are in close proximity.

Therefore, a large underhood clearance would be preferred for pedestrian protection.

The predicted level of protection offered by the vehicle is verifiedby EURO-NCAP

HOOD OUTER PANNEL

HOOD INNER PANNEL

SHEET METAL OPERATIONS 

1. Blanking & Piercing  - 

Blanking and piercing are shearing processes in which a punch and die are used to produce parts from coil or sheet stock. Blanking produces the outside features of the component, while piercing produces internal holes or shapes. The web is created after multiple components have been produced and is considered scrap material. In blanking, the piece is cut off from the sheet, and it becomes a finished part. In piercing, the cutout portion is scrap which gets disposed off while the product part travels on through the remainder of the die. The terminology is different here, though both processes are basically the same and therefore belong to the same category, which is the process of metal cutting.

                         

2. 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. 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. 

        

3. Embossing -

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. 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.

4. Hemming  - 

Hemming and seaming are two similar metalworking processes in which a sheet metal edge is rolled over onto itself. Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edges of two materials. Hems are commonly used to reinforce an edge, hide burrs and rough edges, and improve appearance. Hemming is a sheet metal forming process in which sheets are joined by bending it to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods and tailgates are formed by hemming process. In this process, usually a sheet is bent with the help of inner sheet in three different stages.

5. Mastics Point -

Mastic adhesive was developed specifically to bond exterior automotive panels to the vehicle’s inner panel structure, such as on roofs, doors, and hoods. This one‐component synthetic rubber sealer remains elastic after curing to reduce panel flapping and to prevent panel distortion.

The Hood Assembly consists of -

1. Hood Outer Panel

2. Hood Inner Panel

3. Hinge Assembly

4. Latch & Striker

MASTER SECTION

 

 INFORMATION PROVIDED FOR HOOD THICKNESS

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

HOOD OUTER PANEL DESIGN -

As input got class A surface. Draw Tooling direction and check for Draft Analysis. when class A is clearing in Draft Analysis then proceeded with the Outer panel creation.

 

Firstly, we cut the class A in two symmetrical halves with the Y-Z plane. Then we took the offset and turn all the sharp corner into the round. After that we have created that surfaces through offset and draw the hemming flange through log extension. At last we use face blend command to create the outer panel and then we mirror geometry  to form a thick body..

HOOD INNER PANEL DESIGN -

As input we receive the offset data of Hood Outer Panel. We offset the outer edge and made all the sharp corner to the round one then, trim the geometry to syemmetry by Y-Z plane. we offset all the necessary surfaces which is mention in the sketch and trim it. After creating the required surface we created the firts emboss then, second emboss and remove all the material. Now we linked the Hinge Assembly created emboss for the Hinge.

STRIKER ASSEMBLY

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HINGE ASSMBLY

COMPLETE ASSEMBLY

CONCLUSION -

In this challenge Hood is created successfully in Top-Down Assembly approach with Hood Outer Panel, Hood Inner panel, Hinge Assembly amd Striker with the given sketch and all the design considerations.