Hood design-Week 2

HOOD DESIGN

Aim:- Create a hood assembly from the hood outer panel which is provided as an input surface to us according to the master section sketch.

Introduction:- The hood is the hinged cover over the engine of motor vehicles. Hoods can open to allow the engine compartment for maintenance and repair. From a design perspective, the hood should meet specific conditions like pedestrian safety, a hood head zone for the lock striker, force distribution when subjected to frontal collision, manufacturability, etc. A typical hod assembly consists of an outer hood panel, inner panel, latch and striker, hinge, and hood stay. A hood stay is an apparatus for supporting the engine hood of a motor vehicle in its open position. It is the most critical part of the car as it is always exposed to the frontal crash, climate conditions, heat generation by the engine compartments, etc. This gives access to the engine, battery, and other components which are always needed to be inspected at regular intervals. The time of inspection could be a maintenance, repair, or replacement of the parts. The Hood is the combination of an outer and inner panel and as per its design consideration, it also dissipates energy outside the car body.

Hood mainly consists of 4 components:

The inner panel, Outer panel, Hinges, and Latch striker.

The outer panel gives the aesthetic look whereas the inner panel has some embossing on it according to the force distribution and safety requirements.

Design Considerations for car hood: 

• Head clearance zone
• Consideration of Noise Vibration Harshness (NVH): Noise, Vibration(N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured harshness is a subjective quality, and is measured either via “jury” evaluations or with analytical tools that can provide results reflecting human subjective impressions.
• Pedestrian safety: Pedestrian safety is an important consideration while designing the hood. According to the wrap-around distance and pedestrian head impact zone, the hood is designed. Safety is the most important criterion in automobile designs which concentrates on both pedestrians being the most vulnerable road users and being at high risk of traffic accidents. The major reason for the fatality of the pedestrian in a traffic accident is the head injury resulting from the hard impact of the head against the stiffer hood panel which is less stiff and pedestrian-friendly. The area at the head impact zone is made softer to reduce the impact force during an accident.

Design Parameters

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

master sketch

Procedure:

Hood outer panel: Outer panels are the aesthetic elements of a car. It is the styling team that provides the skin for the outer panel. The shape, position, and size of the hood should satisfy 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 the required hemming flange and relies on the hemming operation. We also provide mastic sealants between the outer panel and the inner panel to reduce vibration.

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.

Reinforcement: Reinforcement is provided according to the design requirements. Mainly it is provided at the hinge latch regions to improve the strength locally. Usually, the thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirements. According to the design requirement here, it is given 1.5mm thickness to both hinge and latch reinforcements.

Latch Trajectory: Latch trajectory is given by the circle drawn from the hinge axis point. The hinge axis point is the center point of the hinge axis. First, we can fix either the latch or the hinge. If we fixed the hinge position then we should plot the trajectory circle for the latch. For proper mating conditions, the striker axis through the tip of the striker should be tangential to the latch trajectory.

Emboss: We provide different embosses throughout the inner panel. We can increase the stiffness of the inner panel through these embosses. The shape and size of the emboss also determine the direction of the force distribution away from the passengers. Here in the figure the embosses are designed in such a way that the force is directed to either side of the car.

Mastic sealant data: Hood commonly possesses a 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 spoils its aesthetic appearance. So, mastic sealants are used to stick to the inner surface of the outer panel and inner panel. Mastic sealants are elastic compounds 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 is more vulnerable to vibrating.

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, improve the appearance of a part, and 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 hemming operation are 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. It is important to provide the required relief at the corners.

There are two types of hemming operations:

1. Conventional die Hemming
2. Roll hemming

Conclusion:

In this challenge, I learned to design the hood inner panel, and Outer panel with the help of the master sketch and the styling surface. And also learned reinforcements like in latch and hinge assembly.

Front view

Side View

Back View