Hood design-Week 2

Aim:

To create an outer and inner hood panel, positioning the stiker, hinge and their reinforcements.

Theory:

Hood plays a major role in pedestrians safety as well as car safety. It covers entire engine components and also acts as a shield to the pedestrians from the major injury. Hood has different styles.On front-engined cars, the hood may be hinged at either the front or the rear edge, or in earlier models it may be split into two sections, one each side, each hinged along the centre line. A further variant combines the bonnet and wheel arches into one section and allows the entire front bodywork to tilt forwards around a pivot near the front of the vehicle.

Hoods are typically made out of the same material as the rest of the body work. This may include steel, aluminum, fiberglass or carbon fiber. However, some aftermarket companies produce replacements for steel hoods in fiberglass or carbon fiber to make the vehicle lighter.

The boundary conditions for commencing a new design process using aluminium can be identified and analysed by grouping together requirements using affinity matrix methods. Bonnet and boot lid are treated separately and are then compared to highlight major differences.

The functional requirements, the design options and the system considerations have now been formalised. Each element of the design may now be assessed for materials’ selection using a simple prioritisation matrix. In this case study, we first consider the system requirements, then the requirements of each constituent part separately.

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. All major insurance and regulating authorities have studied this topic in order to put in place a range of measures to reduce mortality rates and the severity of injury resulting from pedestrian impacts. These studies have produced test procedures and systems to rank and regulate vehicles for pedestrian safety.

Evaluation of pedestrian safety for a bonnet must be carried out in the context of its
surrounding elements:
 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.

Procedure:

Inner Hood Panel:

• Spilt the outer hood panel Class A into half and copy it in the newly created geometrical set ‘Inner Hood’.
• Create surfaces using offset, spilt options as per Master Section given for inner hood panel.

• Use Edge Fillet option by joining the surfaces, to minimise the errors.
• Use Boundary option for any discontinuity around the surfaces.

Embossments:

Embossments are created on the inner hood panel as it gives strength and also reduces production cost. As the outer panel has a thin layer sheet,it has less strength. Holes are made in between because of pedestrians safety.

• Design a new sketch and project it on the surface using the Projection option.
• Sweep the projected curve with a 7degrees draft angle in draft direction.
• Offset the extracted surface to the required embossment length.
• Trim the unwanted surface and join all the surfaces.
• Repeat the same steps for required embossment shapes.
• After completion of creating embossments, Join all the surfaces and Mirror it.
• Use the Boundary option for the perfect inner hood panel.
• Thicken the entire surface in the new body created.

Outer Hood Panel:

• Spilt the surface into half and offset it to 2mm.
• Extract the edge of the surface and use Parallel Curve to move a distance of 6mm.
• Now spilt the surface with a parallel curve as a cutting element.
• Extract the edges of both surfaces, use Multi Section Surface to create a connecting surface.
• Join all the surfaces and give edge fillet to all sharp edges.
• Create a new body and thicken to 0.75mm.

Reinforcements:

• Extract the hinge bottom surface and thicken it to 1.75mm.

• Repeat the same for the latch part.

Assembly:

• Import the parts into Assembly workbench.
• Select hinge part and set in required position by Manipulate option.
• Once part is posritoned, Use offset option to get attached by 0 mm distance.
• Select axis hinge part and axis of inner hood panel then use Coincidence Constraint.

Result:

Hood was created and attached with hinges, stickers and the reinforcements to it.

• Opening angle of latch is created.