Hood design-Week 2

Design Hood Outer Panel, Inner Panel and the necessary reinforcements by following the Master Section,

Hood is also referred as bonnet. Hood is the one of the major BIW component of the car. It acts as a styling surface of the car. In designing the hood, the designer should not only focus on the aesthetics of the hood but also should consider the passenger safety in case of collision with other vehicle or the poles, pedestrian safety in case of collision with pedestrians and the safety of engine and other components in the engine compartment in case of a solid body falls on the hood.

                Styling engineer will provide the outer surface of the hood to the design engineer, as a design engineer, we need to optimise the hood design such that the components meet all the safety criteria mentioned above without disturbing the styling surface.

                A typical Hood or Bonnet usually consists of Outer Panel, Inner Panel, Hinge Reinforcement, Hinges, Striker and Striker reinforcement. Outer panel is the styling surface where any of the operation that involve in deformation of the surface for example, joining methods like spot welds and riveting is not allowed on the styling surface. Disturbing the outer panel also disturbs the aerodynamics of the vehicle.

DESIGN CONSTRAINS TO BE FOLLOWED:

• Passenger safety
• Pedestrian Safety
• Manufacturing Feasibility
• Positioning the striker along the Trajectory of the Centre of Hinge axis
• Joining techniques of inner and outer panel.

POSITIONING THE STRIKER:

                The striker needs to be place on the trajectory of the centre point of the hinge axis to ensure that it fix perfectly on the latch, if not locking will not be smooth and affects the comfort and also it will create NVH problems.

The striker is aligned using following steps

1. Drawing the line along the axis of the hinge.
2. Creating the point on the mid-point of the line.
3. Drawing the circle from the mid-point of the line to the latch where the striker will be mounted.
4. Drawing the line from centre point to the mid-point of the striker rod.
5. Aligning the line’s end point and the mid-point of the striker to the circle.
6. Angle need to aligned so that the angle of the striker is perpendicular to the line drawn from mid-point of the axis line to the mid-point of the striker.

JOINING THE INNER AND OUTER PANEL OF THE HOOD:

                Inner panel and outer panel of the hood should be joined rigidly without disturbing the styling surface of the hood which is the outer panel. Here we use special joining methods known as Hemming and Mastics.

Hemming:

                Hemming is the process of wrapping the flange of the outer panel to the flange of the inner panel so that they are fitting rigidly. After hemming process, the sealants were applied along the edge of the flange of outer panel so that water tightness is achieved.

MASTIC POINTS:

                Mastic points were the gluing points where the paste is applied between the inner and outer panel to join the panels. Each mastic point will stiffness up to 80mm surrounding. So mastics to be added in such a way that it covers entire surface of the hood. If the gap is less than 5mm between the outer and the inner panel without mastic points it will cause vibration resulting in NVH problem.

CONCLUSION:

                Thus the hood is designed considering passenger and pedestrian safety as per the master section and striker also place in the path of trajectory of the hinge axis.

SIR MEDAM Aything else Please check the part when you check the assemble like hinges and striker.