Hood design-Week 2

Aim-

Design Hood Outer Panel, Inner Panel and the necessary reinforcements by following the Master Section mentioned with the Design parameters.

What is hood?

A car hood is also referred a bonnet, its is hinged cover that rests over the engine of a front engine vehicle. Its purpose is to provide access to engine for repair and maintenance.

Hood mainly consists 4 components - inner panel, outer panel, latch & striker, hinges. The outer panel is modelled in such a way that It gives good aesthetic looks and inner panel are provided with emboss for equal force distribution radially outward direction. And reinforcements for safety.

Automotive metal forming –

Automotive metal forming is the process of bending or shaping metal into a specific shape to create automotive parts. Metal can undergo something called plastic deformation. This means that the metal can take any shape you could imagine. Roll forming uses force to change the shape of the metal.

Bending

Bending is generally used to produce simple curved surfaces rather than complex ones. A mechanically operated press drives a punch against sheet metal, forcing it into a simple die with enough pressure to produce a permanent change in the metal's shape

Deep Drawing

Deep drawing 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. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter.

Hemming.

Hemming is a sheet metal forming process in which sheets are joined by bending it to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods and tailgates are formed by hemming process. In this process, usually a sheet is bent with the help of inner sheet in three different stages.

Some of the most commonly used features in designing Hood assembly are,

• Offset surface – creates a body by offsetting a set of faces.
• Trim sheet – trims of a portion of sheet body.
• Law extension – from the edge of sheet metal/ curve a extended sheet metal is created.
• Curve on surface – creates a surface spline on the face of sheet metal.
• Mirror Geometry - creates the exact mirror of sheet metal body.
• Face Blend – adds tangent blend faces between selected set of faces.
• Edge Blend – rounds sharp edges between the faces.
• Projected curve - projects the curve, edges, points on planes or on faces.
• Emboss – modifies a body with faces made by projecting a section along a vector.
• Extend sheet – extend a sheet body by a distance.
• Sew – combines two adjacent sheet bodies making it as one.
• Through Curves – creates a body through multiple sections where the shape changes through pass through each section.

Design parameters considered for Hood Design,

Hood thickness information -

Outer panel thickness - 0.75 mm

Inner panel thickness – 0.75mm

Reinforcement thickness – 1.5 mm

1. Hood outer panel –

Outer panel provided the aesthetic look for hood of car. Design styling team provides skin for outer panel. while designing pedestrian safety is considered. By hemming process, the outer panel is made to attach with inner panel.

Hemming relief image

2. Hood inner panel

It provides the strength and rigidity to outer panel. The emboss is done in order to give strength to the inner panel, cut is done on the inner panel to reduce the weight as well as to reduce the impact when the car front hits pedestrian. Edge blend and face blend is done on the corner and face to remove sharp edges/corners.

3. Latch Trajectory -

The latch trajectory is obtained by drawing the circle taking reference of hinge connecting line midpoint. After drawing circle, a tangent line is drawn on the circumference at require angle, and a mid-line is drawn to striker latch. The tangent line on circle at an angle and the mid line of striker latch are made coincident by applying constraints.

Image of Latch Trajectory –

Mastic data –

In order to join the outer panel to inner panel hemming is done but which provide support at the edges. So to join the inner and outer panel we cannot use spot welding/ mechanical fastners to join because if affects the aesthetics of outer panel and causes weight.

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