Hood design-Week 2

Aim: Design Hood outer panel, inner panel and the necessary reinforcements by following given Master section.

General Design Information:

Master Section:

Hood Thickness Information:

Outer panel thickness = 0.75mm

Inner Panel Thickness = 0.75mm

Reinforcement Thickness = 1.5 mm

Objective:

A detailed report about the Hood Design which includes a detailed explanation about hood and its components, Latch trajectory, Mastic data, emboss definitions, manufacturing process like deep drawing and hemming, and all the parameters followed in the design.

Introduction:

A car hood, also referred to as a bonnet in some other countries, is the hinged cover that rests over the engine of a front-engine vehicle. Its purpose is to provide access to the engine for repair and maintenance. A concealed latch is typically used to hold down the hood.

A car hood is meant to protect the performance parts of your vehicle, including the engine, while also providing easy access for repairs and maintenance. It is possible for the hood to incur damage as well. One of the most common types of damage is to the hinge, which is the device that connects the hood to the body of the vehicle. Over time, the hinge can become loose or may fall off completely. The hood is also prone to receiving scratches and dents. Although this might appear to be a minor problem, dents and scratches can lead to depreciation in the value of your vehicle. Scratches and dents can also lead to exposure to the elements that can result in rust and corrosion. This can be a serious problem that can ultimately expose the engine in your car to snow, sunlight, and rain. When this happens, it can impact the performance of your car's engine.

Inner panel of Car hood:

Car hood is a forming of both inner and outer panel. The main purpose of the inner panel is to maintain strength of the outer hood towards crash. Not only that the embosses present on the inner panel used to resist the impact force by simply dissipating the impact force towards side of the car.

By providing the structural embosses on the inner panel we can reduce the weight of the panel as well as we can provide the way to dissipate impact force towards side of the car.

Mastic points:

Despite of spot welding and other forming processes are not used to join both inner and outer hood. To join or to fill the gap between the outer and inner panel mastic points were used which Provides strength to its surroundings.

Deep Drawing Process:

Deep drawing is a process of converting metal sheet into cylindrical or box shaped structure with or without changing its length and thickness. Many cylindrical parts like metal can, pots, container for food and beverages, kitchen sinks, automobile fuel tank etc. are deep drawing product.

Before discussing its working process, first we should learn about main part used in drawing process. These parts are as follow.

The blank is placed over an open circular die with the help of blank holder. The blank holder provides a necessary force to hold the blank. The punch which is attached with a mechanical or hydraulic press moves downward and provide a necessary drawing force at blank. This force tends to deform metal sheet and forces it into the die cavity and convert it into a cup shape structure.  If this force is high it causes elongation of cup wall to thin and if excessive, it causes tearing of sheet. So the punch force should remain a certain limit to avoid tearing during operation.

Hemming: Hemming is one of the forming processes which is used to join outer and inner panel without effecting look of the Hood.

Roller hemming:

Robot hemming is utilized for the manufacture of Low to medium production volumes. It uses a standard industrial robot integrated with a roller hemming head to provide a flexible method for forming closures. The flange of the outer panel is bent over the inner panel in progressive steps, by means of a roller-hemming head.

One advantage of this process is that it can use the robot-controlled hemming head to hem several different components within a single cell. Another is that minor changes or fluctuations in panel-hemming conditions can be quickly and cost-effectively accommodated. If equipped with a tool-changing system, the robot could serve a variety of additional functions within the same assembly cell, such as operating dispensing equipment for adhesives and sealants, or carrying out panel manipulations, using a gripper unit.

EURO NCAP:

The hood is designed according to the EURO NCAP (European car safety performance assessment programe) Standards, The adult and child impact zones were taken in to consideration while designing the car Hood, EURO NCAP Provides consumers with an independent assessment of the safety level of the most popular cars available in the EUROPE. EURO NCAP basically provides the information about the safety level of cars to the consumers in terms of Star ratings.

Pedestrian safety test:

The below shown image gives information about how the pedestrian safety test is carried out by the EURO NCAP team. The leg and head impactors were used in the place of child head, adult head, Upper leg and lower leg at specified angle and speed to the front end of a Stationary vehicle. The stars were given according to the impact registered.

Side reference line:

The Bonnet Side Reference Line is defined as the geometric trace of the highest points of contact between a straight edge 700mm long and the side of a bonnet, as defined in Section 3.3.1 and A-Pillar, when the straight edge, held parallel to the lateral vertical plane of the car and inclined inwards by 45° is traversed down the side of the bonnet top and A-Pillar, while remaining in contact with the surface of the body shell, any contact with door mirrors is ignored. See Figure. Where multiple or continuous contacts occur the most outboard contact shall form the bonnet side reference line.

Wrap around distance:

When a car crashes on the pedestrian, the whole human body wraps around the front shape of the car and the head impacts on the bonnet or the windscreen. The distance on which the head impacts on the car from the ground is called as the Wrap Around Distance (WAD).

To be specific the Wrap Around Distance is a measurement of distance from the ground to the head impact zone over the outer surface of the car. The wrap around distance is measured longitudinally in the center of the vehicle from the ground.

The severity of the injury caused by the frontal crash depends on the type and shape of the vehicle, speed of the vehicle and the movement of the pedestrian relative to the vehicle. In addition to these parameters, the wrap around distance plays a major role in the safety measurement of a pedestrian.

During the crash analysis, based on the Wrap Around Distance (WAD), two test areas will be created namely Child head impact zone and the Adult head impact zone. The child head impact zone is between 1000 to 1700 mm WAD and the adult head impact zone ranges between 1700 to 2100 mm WAD.

Latch trajectory: Latch trajectory tells us about the fixing position and movement of the hood to the latch.

In this above shown figure the latch trajectory of hood is defined.

Design Procedure:

The Class A Surface is given to create the hood outer and inner panels.

First, we need to trim the surface in to two halves’ by selecting Trim option. Later we need to offset the Trimmed portion of the hood in order to create inner panel.

The two offset regions are joined by using Through curve option available in NX CAD. The same operations were repeated until the required given master gets fulfilled.

Embosses were created by using emboss options or by using Law Extinction option provided in the NX CAD. The required Emboss sketch were created and projected on the inner panel hood surface.

Hemming:

Robot hemming is utilized for the manufacture of Low to medium production volumes. It uses a standard industrial robot integrated with a roller hemming head to provide a flexible method for forming closures. The flange of the outer panel is bent over the inner panel in progressive steps, by means of a roller-hemming head.

Conclusion:

The required Car hood is designed according the given master section and safety parameters.