Hood design-Week 2
HOOD DESIGN
OBJECTIVE
Design outer panel with the hem, develop the Inner Panel, develop all the necessary Reinforcements, Mirror and position the Hinge & Striker, provide Mastic Data, and provide the required Emboss definition.
With this understanding, an industry-standard hood panel is to be designed which can very well be manufactured and assembled. In other words, the design has to follow DFM and DFA standards as well.
Software used: Siemens NX 11
In this report, the flow of information will be as follows
1. Understanding
2. Design Consideration
3. Design
4. Draft Analysis
5. Conclusion
6. Reference
ABOUT HOOD
Hood is an important component of the front portion of the car which is used for many purposes. It is made aerodynamic in shape to reduce air drag. Generally, it is used to cover car engines, radiators, and many other components, the design must meet pedestrian's requirements and design should be satisfying serviceability and also design should be made in a way that when an accident occurs the energy absorption should no reach to passengers.
DESIGN DATA
- Outer Panel Thickness = 0.75mm
- Inner Panel Thickness = 0.75mm.
- Reinforcement Thickness = 1.5mm
MASTER SKETCH:
1.Understanding
Hood, which also goes by the term bonnet, mostly in the commonwealth countries, is essentially a type of door that covers the powertrain and other vehicle propulsion system components such as drive belts, battery, fluid levels and lamp units in the frontal (or rear, based on the engine placement) region of an automobile. Aside from being a hinged cover to engine providing easy access to maintenance and repair, it acts as a critical safety component both for the vehicle occupant as well as the pedestrian.
Hood is one of the other major closure systems in a vehicle and is fundamentally a reinforced skin with many design quality and safety regulations.
2.Design Consideration
As discussed in the earlier section, the hood plays a critical safety function in an automobile, not only for the occupants of the vehicle but also for the pedestrian. Hence, a lot goes in while designing the hood and must be compliant with the standards and considerations. In this project, the European New Car Assessment Programme, popularly know as EuroNCAP, was followed to understand the consideration and standards one must follow while designing a hood. EuroNCAP plays an instrumental role in raising awareness on safe and effective design for the pedestrian. It programs and develops test series and rating systems for accessing design safety for pedestrian during impact with a vehicle. The tests are generally executed for vehicle hit speed at around 40 km/h and covers the pedestrian body interaction with the vehicle upon collision.
As we could see the impact region, based on these impact regions the thickness of the hood at those regions are reduced to allow softer landing and lower impact. Upon impact of the pedestrian, the hood in those regions absorb and dissipate the energy allowing deformation and hence collapsing, which in turn would result in a lower impact on the pedestrian.
At the same time, the impact on the vehicle should be channeled outside the vehicle to safeguard the occupants from severe injuries. Based on these considerations, the inner panel should be embossed with strategized channels and empty cut-outs to allow for maximum absorption of such impacts.With this understanding, the below-provided design was executed using Siemens NX 11.
Design
Components
1.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 we should give more importance 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. We also provide mastic sealants between outer panel and inner panel to reduce vibration.
2.Hood inner panel
Inner panel is the part that gives strength and rigidity to the outer panel. The master section represents the initial emboss shape and size. Then we provide the emboss for the latch and hinge elements after fixing the location.
3.Reinforcement
Reinforcements are provided according to the design requirements. Mainly it is provided at the hinge and latch regions to improve the strength locally. Usually thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirement. According to the design requirement here it is given 1.5mm thickness to both hinge and latch reinforcements.
3.Latch Trajectory
Latch trajectory is given by the circle drawn from the hinge axis point. Hinge axis point is the centre point of the hinge axis. First, we can fix either the latch or the hinge. If we have fixed the hinge position then we should plot the Trajectory circle for the latch. For proper mating condition the striker axis through the tip of the striker should be tangential to the latch trajectory.
4.Mastic Data
Hood commonly possess large surface area and hemming can only be provided through its boundary. We cannot use other joining techniques like welding, riveting etc because they 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. Mastic sealants 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.
5.Emboss definitions
Throughout the inner panel we provide different embosses. We can increase the stiffness of the inner panel through these embosses. The shape and size of the embosses also determines the direction of the force distribution resulted from frontal collision. The force should be always distributed away from the passengers. Here in the figure the embosses are designed in such a way that the force is directed to either sides of the car.
6.Hemming
Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.
In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.
The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas or material roll-in. This is why it is important to provide required reliefs at the corners.
There are two types of hemming operations,
1.Conventional die hemming
In conventional die hemming, the flange is folded over the entire length with a hemming tool.
2.Roll hemming
Hemming relief
Hemming is a forming operation in which the edges of the sheet are folded or folded over another part to achieve a tight fit. Normally hemming operations are used connect two different sheets.
Draft Analysis
Once the design was ready, the complete hood was analyzed for manufacturability. Using the Draft Analysis function from Siemens NX, it could be seen that the designed part can be manufactured without any difficulties.
Final Assembly
Side View
Front view
Back View
Isomatric View
Conclusion
With the completion of the design and analyzing it for successful manufacturability, we can conclude that this can be utilized for a vehicle. Also, the design was executed under the EuroNCAP safety standards and hence satisfies hood safety both for occupants and the pedestrians.