Hood design-Week 2

Aim: To design car hood in NX using given master section and provided design parameters.

Hood and it’s components:

• Hood –

Car hood/bonnet is a hinged cover that rests over the engine in a front-engine car. A latch is provided under the hood in order to prevent accidental opening during driving. Purpose of hood is to provide access to the engine and battery for repair and maintenance. It also protects these parts from direct sunlight and dust.

Fig 1 Hood Assembly with hinge and striker

Components –

The car hood consists of following components,

1) Hood Outer Panel

The outer panel works as a metal cover. It is responsible for aesthetics of the vehicle.

Fig 2 Hood outer panel

2) Hood Inner Panel

The inner panel provides strength and supports the outer panel. It is where hood balancer and hinges are attached.

Fig 3 Hood outer panel

3) Hinges

Hinges allow the hood to rotate around a fixed axis for opening and closing movement. One part of the hinge is fixed with the engine compartment, while other part is connected to hood.

Fig 4 Right hinge assembly

4) Latch and Striker

Latch and striker mechanism is provided to lock the hood, in order to prevent accidental opening of the hood during driving. The latch is present on the engine compartment while the striker is attached to inner part of hood.

Fig 5 Stricker and latch assembly

Latch Trajectory:

It is the path along which the hood rotates during opening and closing movement. The striker on the hood follows a particular path while opening or closing the hood, which is along circumference of a circle with center at the hinge axis. This path is nothing but latch trajectory. It is a very important aspect in hood design, in order to decide hinge, latch and striker installation points.

Mastic Sealant:

Mastic sealant helps to locally improve strength of the hood. It is generally a hard rubber part, which is introduced as a paste in between inner and outer panel of the hood, which will get hardened inside the furnace. Every mastic sealant point will have a tendency to improve the local strength in around 80 mm diameter. Considering this, the mastic points are positioned such that most of the hood region is covered.

Design Methodology:

The procedure followed for designing the hood and its components is as follows,

• First the inner panel is designed from the given master section using the various commands and features. We create the embossing using the offset surface from the original master section. Similarly, we create the cuts on the emboss by sketching and using trim surface option.
• Then the outer panel is designed from the same master section. Here we are supposed to provide the hemming to outer panel. The parameters of hemming are taken as per given values.

Draft analysis

All parts should have a positive draft of min 5 degrees, so that the tool can come outside without any interference.

Latch and striker reinforcements:

Sheetmetal Operations in Car Hood Manufacturing Process:

• Deep Drawing –

It 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. The process is considered deep drawing when the depth of the drawn part exceeds its diameter.

• Hemming –

Hemming is a forming operation in which the edges of the sheet are folded over other part or simply folded in order to achieve a tight fit. 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.

• Embossing –

Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal. This process is carried out by means of matched male and female roller dies, or by passing the sheet or rolls of metal between rolls of desired pattern.

• Piercing –

It is a shearing process in which raw sheet metal is pierced with a machining tool, resulting in the creation in a particular shape hole in the sheet. The major difference between blanking and piercing is that in blanking the cut out is the workpiece and outer part is scrap, while in piercing, the cut out is scrap and the outer sheet is the workpiece.

Conclusion: I designed the car hood along with its components and assembled the same, using NX CAD, under given parameters.

Thanks,

Prasannavenkatesan R