Challenge

Hood design-Week 2

AAditya Raj16 Feb 2023

Hood design-Week 2

AIM:- To Design Hood outer panel, inner panel and the necessary reinforcements by following the Master section mentioned with the design parameter, (Hinge,Striker) included.

Design Methodology

1. Develop the inner panel with

Embossing (with minimum 7 Degrees Draft)
Mastic Points

2. Develop the Outer Panel with

Hemming

3. Positioning the reinforcements

Hinges
Striker for Latch

Given data for Hood Creation

MasterSection

It has played very important role as it has every general design information considered for a hood. It shows general dimensions and structural shape of general hood design.

Hemming Data:

Relief rear section:

Front relief:

Data To be used

Outer Panel Thickness 0.75mm

Inner Panel Thickness 0.75mm

Reinforcement Thickness 1.5mm

Hood Introduction

The hood (North American English) or bonnet (Commonwealth English) is the hinges cover over the engine of the motor vehicles. Hoods can open to allow access to the engine compartment, or trunk (boot in Commonwealth English) on rear-engine and some mid-engine vehicles) for maintenance and repair.

Hood Design Facilitates

Hood Covers all engine components
Easy access in engine compartment
Frontal Crash impact forces absorption
Reduce Engine Noise
Aerodynamic Shape
Safety of Pedestrain
Good Aesthetic appearence

Design requirements for Car Hood

MANUFACTURING PROCESS

POINTS CONSIDERED FOR FEASIBLE MANUFACTURING

Minimum Draft of 7 Degrees given for sheet metal - For easy removal of component from tool(Die)
Sharp edges are avoided for easy manufacturing
Complex shape is avoided.
Opening Angle of Hood
NCAP Crash Test Ratings For Strength
Wrap Around Distance (WAD) for Pedestrian Safety
NVH (Noise, Vibration, Harshness) For Consumer/Customer/User/Buyer

Opening Angle of Hood

This is one of the main criteria in designing of hood. This opening angle varies from person to person and country to country. In India, the average height of a person is 5.8 feet/ 177 cm (Current data) whereas in the European countries the average height is 6 feet, these points refers variation in opening angle of hood.

Opening angle is considered as an important criteria, when the opening angle is less than required there are possibilities of human head injury.

Types of Hood Support

Support Rod- These support rods are widely used in cars to support the hood in open Position. These support rods are cost effective compare to gas stay. In this type of hood support the hood opens manually. The support rod is fixed on the hood or the engine compartment, to hold hood (in Open Position) the support rod needs to positioned(manually) on the supporting rod point which is opposite to the support rod position. Generally these support rods are used only in the lighter weight hood Vehicles.

Gas Stay - These Gas stay are type of support rods which is used for heavy weight hoods. In these gas stay rods, pressurized gas is filled which helps to hold the hood in open position. Gas stay just needs the initial force to open the hood. Gas stays are convient to use but these are expensive when compared to support rods.

Features and tools used for this model:-

1)Sketch

2)Offset surface

3)Offset curve in face

4) Through curves

5) Trim sheet

6) Trim and extend

7) Law extension

8) face blend

9) extend sheet

10) edge blend

11) Face blend

12) mirrior geometry

13) emboss

14) sew

15) Thicken

Hood outer panel

Outer panels are the aesthetic elements of a car. It is the styling team who provides the skin for the outer panel. The shape, position and size of the hood should satisfy the safety norms. So while designing the hood we should give more importance to pedestrian safety. The outer panel is attached to the inner panel by hemming. So, it is necessary to provide required hemming flange and reliefs for the hemming operation. We also provide mastic sealants between outer panel and inner panel to reduce vibration.

Relief:-

Hood inner panel

Inner panel is the part that gives strength and rigidity to the outer panel. The master section represents the initial emboss shape and size. Then we provide the emboss for the latch and hinge elements after fixing the location.

Emboss definition: Throughout the inner panel we provide different embosses. We can increase the stiffness of the inner panel through these embosses. The shape and size of the embosses also determines the direction of the force distribution resulted from frontal collision. The force should be always distributed away from the passengers. Here in the figure the embosses are designed in such a way that the force is directed to either sides of the car.

Mastic Data

Hood commonly possess large surface area and hemming can only be provided through its boundary. We cannot use other joining techniques like welding, riveting etc because they leave marks on the outer panel which spoil its aesthetic appearance. So, mastic sealants are used to stick the inner surfaces of outer panel and inner panel. Mastic sealants are elastic compound that behave like rubber. It is applied between the inner and outer panels at specified spots. Each spot of mastic sealants has its effect around a circular region of 80mm diameter. Thus, the mastic points are arranged in such a way that it covers the areas away from the hemming which are more vulnerable to vibrate.

HINGE ASSEMBLY

Hinges is the assembly of components connected to the door and body of the vehicle, linked to each other and capable of rotating around the same axis. Conventional system consists of two hinges for each door, an upper hinge and a lower hinge.

Latch Trajectory

Latch trajectory is given by the circle drawn from the hinge axis point. Hinge axis point is the centre point of the hinge axis. First, we can fix either the latch or the hinge. If we have fixed the hinge position then we should plot the Trajectory circle for the latch. For proper mating condition the striker axis through the tip of the striker should be tangential to the latch trajectory.

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 forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.

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. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas or material roll-in. This is why it is important to provide required reliefs at the corners.

There are two types of hemming operations,

Conventional die hemming

In conventional die hemming, the flange is folded over the entire length with a hemming tool.

Roll hemming

It is the roll hemming process that is used for automotive sheet metals. Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps. Roll hemming is very flexible to use and tool costs are significantly lower as compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller which follows a defined path.

Reinforcement

Reinforcements are provided according to the design requirements. Mainly it is provided at the hinge and latch regions to improve the strength locally. Usually thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirement. According to the design requirement here it is given 1.5mm thickness to both hinge and latch reinforcements.