Hood design-Week 2

Title- Hood Design

Objective :

Design a hood with the given input data to satisfy the engineering, manufacturing and functional requirements.

What is hood?

Hood is basically one type of door which is used to close the engine compartment. Hood basically consists of two main parts: inner panel and outer panel where inner panel gives strength to the outer sheet and outer sheet is just a sheet with curves for aesthetic purpose.

Basic components of hood :

• Outer Panel
• Inner Panel
• Hinges
• Stricker(Locking Mechanisum)
• Stay rod or Gas stay
• Mastic seal
• Reinforcement

Details of every componens

Outer Panel :

As discussed earlier, the outer panel is a sheet which is for aesthetic purpose. Generally we get this surface to design the remaining parts of the hood. Generally the main shape the outer panl comes from the basic sketch of the car. As a BIW designer we get the class A surface as an input. This class A surface consists of all the aesthetic shapes and boundaries of the hood i.e. maximum size of hood. while designing hood we need to make sure we are no disturbing the outer shape of the hood. As a BIW designer we need to give strength to the outer surface without disturbing its shape.

Manufacturing process for outer panel

First step is blanking in this process the main sheet is cut into perticular shape and size then stamping process is used to give basic shape to the sheet by pressing sheet metal in to the die where die is havig the same size and shape of the outer panel.

Class A surface of outer panel

Inner Panel :

This is the main structure of the hood which gives strength to the outer surface. While designing the inner panel the main thing we need to make sure is uniformity and symmetry. The main input to design the inner panel is the class A surface of the outer panel. We need to take all the references from that class A surface. Inner panel consists of various types of embassed to get strength. It also has various cutouts for mounting and holding purpose like cutouts for support rod or gas stay etc.

Manufacturing process for outer panel

The manufacturing process is quite similar to the outer panel. First step is blanking in this process the main sheet is cut into perticular shape and size then stamping process sheet metal into the die. With addition to that various cutouts are there in the inner panel.

Hinegs :

Hinges are the standard parts used in the hood assembly: the main purpose of hinges is to give opening and closing to the hood. The one side of the hinge is mounted on the engine comparment and the other side is mounted on the hood. The axis of 2 hinges must be the same; this is the important criteria we need to consider while mounting the hinges. Based on the hinge position we need to do embosses to the inner panel of the hood.

Stricker (Locking mechanisum) :

In simple language stricker is the one part of the locking mechanisum which helps to lock the hood to the engine bay. a stricker is also the standard part which mounts on the inner panel of the hood and the other part of the locking mechanisum is mounted on the engine bay. Like hinges we need to give curtain height and angle to the stricker by providing embosses to the inner panel. The main criteria to mount the stricker on the inner panel is that the axis of the stricker must be tangent to the rotational curvature of the inner panel.

Stay Rod or Gas stay :

The basic application of a stay rod or gas stay is hold the hood in open position. Stay rod is the rod with a slightly bended in shape to get good strength and can provide support to the hood when it is in an open position. The bend should not be more than 35mm. Similar to the stay rod gaas stay is used. The main advantages of using gas stay is that you didn't need to apply effort to open the hood. Gas stay is generally used where the weight of the hood is more to reduce efforts we use gas stay instead of stay rod. While positioning the stay rod we need to make sure it is opposite to the battery of the car so it is easy to put and remove the battery without any obstacle.

Stay Rod

Gas stay

Mastic seal :

Mastic seal is basically the glue used between the outer panel and inner panel. we can apply a mastic sseal where we need to provide stiffness. Mastic seals help with noise and vibration cancellation. The mastic seal gives stiffness in 80mm diameter. We have to make sure we apply mastic seal a way all the area covered of the inner panel to give better results.

Reinforcement :

This is added material to provide stiffness in specific areas like under hinges and stricker etc. these are the simple strips which are added to the inner panel.

Design consideration for hood

Hood opening angle:

The angle at which hood is opening should be sufficient that it should not stricke the person who is checking the engine. the opening angle varies region to region it is basically depends on the average height of the person.

Force Distribution:

While designing the hood we need to consider that after impact like front impact to the hood the force should be distrbuted towards the hinges and not towards the person who is sitting in the vehicle. we need to design an emboss in such a way that is to transfer a load to the hinges and absorb the load.

Placement of stay rod or Gas stay

As discussed earlier the placement of stay rod should not comes between the battery removal and refit. also need to consider the height of the rod os depends on the angle at which the hood need to open.

Placement of mastic seal.

The mastic seal gives stiffness in 80mm dia. We have to make sure we apply mastic seal in such a way all the area covered of the inner panel to give better results.

Pedestrian safety :

In pedestrian-car accidents, head injuries are common cause of death. The acceleration of the heads center of gravity (henceforth, head center) resulting from a head hit is used to determine the HIC (Head injury criterion) value, which is a meaure of the morality risk of a head injury. The pedestrian's head does not strike the hood in a normal to the hood's surface direction.

During the majarity of pedestrian-vehicle collisions, the pedestrian's entire body wraps aroung the car's front form. This has an effect on the vehicle's head Impact. Meanwhile, the windscreen is a significant impact point that has undergone NCAP testing. car contact spped, vehicle type, rigidity and shape, nature of the front (such as bumper height, bonnet height and length, windscreen frame), pedestrian age and body height, and standing posture of the pedestrian relative to the vehicle front all influence the degree of injuries. One of the most essential parameters for assessing pedestrian protection is the wrap around distance WAD.

Input Data

Master section:

Master sketch:

Hemming data:

Front relief:

Relief rear section:

How to draw latch trajectory

Latch trajectory is used to place the stricker in such a way that hood will lock properly

Step1- Draw the axis of the higes

Step2- Draw a circle with the hinge axis as a center and draw the tangent line to the circle.

Step3- Draw a centerline of a stricker U clamp

Step4 - Constraint hinge axis to the X axis and also constraints to the tangent line of the circle and center line of a U clamp.

What is Emboss:

Sheet metal embossing is a stamping technique that creates raised or sunken images in sheet metal. This procedure can be accomplished using matched male and female roller dies, or by sliding a sheet or a strip of metal between the desired pattern's rolls. The geometry is based on the master section that was developed previosly. We will supply local embossed to strenghthen the component when we complete the basic design stages. The master portion will be used to reinforce the component. When a force strikes the hood from the front, the force travels upwards. As seen in the illustration below, the component is designed to redirect force away from the passengers and into the hinges.

Deep drawing:

Deep drawing is a sheet metal forming technique in which a sheet metal blank is mechanically pulled radially into a forming die. As a result, its a shape transition with material retention. When the depth of the draw part exceeds its diameter, the procedure is called "deep drawing". This is accomplished by using a sequence of dies to redraw the part. Due o the material retention properly, the flange, the flange region (sheet metal in the die shoulder area) experiences radial drawig stress and tangential compressive stress. Flange wrinkles are caused by compressive stresses(hoop stresses) A blank holder, whose purpose is to permit controlled material flow, can help prevent wrinkles.

Hemming:

Hemming is a shaping process in which the sheet's edges are folded over another section to create a snug fit, Hemming procedures are commonly used to join parts, Improve the look of a part, and reinforce part edges.

Hemming is a secondary technique used in automotive part assembly after deep drawing, trimming, and flanging operations to unite two sheet metal sections (outer and inner). Hoods, doors, trunk lids, and fenders are common parts for this type of assembly.

Roller hemming :

Hood Design Result

Front View

Side view

Hemming dimensions:

Conclusion :

In this project we learned about different engineering parametrs we need to consider while designing the hood, learned about different CATIA tools used to create hood cad model. we also learned about safety parameters we need to consider while designing the hood.