Hood design-Week 2

HOOD DESIGN USING NX

In this report, the flow of information will be as follows:

• Objective
• Introduction
• Data
• Design of components
• Analysis
• Conclusion

OBJECTIVE

Design hood outer panel, inner panel, and reinforcements with the given outer hood skin, master section and design parameters.

INTRODUCTION

The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment (or trunk on rear-engine and some mid-engine vehicles) for maintenance and repair. In design perspective hood should meet some specific conditions like pedestrian safety, hood head zone for the lock striker, force distribution when subjected to frontal collision (occupant safety), manufacturability, etc.

A typical hood assembly consist of hood outer panel, inner panel, latch and striker, hinge, hood stay. Hood stay is an apparatus for supporting the engine hood of a motor vehicle in its position. The purpose of opening the engine hood is for inspecting engine room, replenishing cooling water and engine oil, checking battery condition, changing the parts, and repairs, etc. Common types of hood stays are support rod and gas stay. Support rods are manually operated and they are cost effective and simple to design and manufacture. Whereas gas stay requires no man power but they are costly.

Hoods are typically made of the same material as the rest of the bodywork. This may include steel, aluminum, fiberglass, or carbon fiber. However, some aftermarket companies produce replacements for steel hoods in fiberglass or carbon fiber to make the vehicle lighter. Blanking, piercing, drawing, deep drawing, embossing, and hemming are the common sheet metal operations that are used in manufacturing hoods in automotive industries.

DATA

Hood thickness information

Outer panel thickness - 0.75 mm

Inner panel thickness - 0.75 mm

Reinforcement thickness - 1.5 mm

Master section

DESIGN OF COMPONENTS

HOOD OUTER PANEL

Outer panel is the aesthetic element 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.

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. It is required to have a high initial reaction force against the impact exerted on the hood to enhance the energy absorption capacity. The hood is further required to minimize a reduction of a reaction force by deformation in a collision.

It is an object of the present invention to provide a hood inner panel capable of reduction of a reaction force of the hood inner panel even if a level of deformation of a hood of a vehicle increases, and ensuring a sufficient energy absorption capacity. Here only we can research and implement the safety of pedestrians and driver.

RENIFORCEMENT

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.

LATCH AND STRIKER

Latch & striker is used for locking the hood with the car. it's usually placed on the space provided on the inner panel. Striker is U shaped bend that attaches to the latch in order to lock the hood and prevent any loose movement during the car motion.

HINGE

It is the pivoting point from which the hood opens and closes. Hinges are used to connect the hood & cowl panel of an automobile. it enables the opening & closing operation of the hood. the hinge should be made strong enough to handle the weight of the hood and also to handle the force action on it during the collision.

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.

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.

MANUFACTURING METHODS

BLANKING It is the process where the required sheet metal material is cut from the sheet metal coil for the manufacturing of the hood using a blanking die. Blanking is a punching operation in which entire periphery is cut out and the cut-out portion required is known as STAMP OR BLANK.

• When a component is produced with one single punch and die where the entire outer profile is cut in a single stroke the tool is called a blanking tool.
• Blanking is the operation of cutting flat shapes from sheet metal.
• The outer area of metal remaining after a blanking operation is generally discarded as waste.
• Size of blank or product is the size of the die & clearance is given on punch.
• It is a metal cutting operation.

TRIMMING

When cups and shells are drawn from flat sheet metal the edge is left wavy and irregular, due to uneven flow of metal. Shown is flanged shell, as well as the trimmed ring removed from around the edge. While a small amount of Material is removed from the side of a component in trimming tool.

DEEP DRAWING

Deep drawing is one of the most widely used processes in sheet metal forming. Apart from its use in many other sectors, it is applied in the automotive industry for the manufacturing of car body parts. The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions.

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. This is achieved by redrawing the part through a series of dies. The flange region (sheet metal in the die shoulder area) experiences a radial drawing stress and a tangential compressive stress due to the material retention property. These compressive stresses (hoop stresses) result in flange wrinkles. Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

EMBOSSING

Sheet metal embossing is the stamping process to obtained raised or sunken edges for the desired design pattern on the sheet metal. This is done with help of male and female dies between which sheet metal is placed and the dies are pressed against the sheet metal to obtain the designed pattern. In some cases, roller dies are used to get the raised edges in the sheet metal.

Manufacturing considerations for the emboss creation

• The distance between the outer edges of the emboss should be a minimum of 5mm
• Draft angle should be provided to the emboss with 7degree- 9degree for the easy removal of the part from the die
• No sharp corners to be provided in the emboss can it would lead to inefficient manufacturing
• The height of the emboss should not be more than 5mm

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.

Different types of hemming methods are

Die hemming method

Table-top hemming method

Robotic Roller hemming method

CORNER RELIF
There are many types of Hemming process but in Hoods Roller hemming is used. In this process the roller will be rolling over the edges of the Outer panel to close it with the inner panel. These rollers will be rolling over 2-3 time for perfect closing. so, the certain force is being used by rollers to all the corners but there are some areas where the roller cannot tighten the part properly so that’s why we give some relief to the corners.

FINAL ASSEMBLY

CONCLUSION

• The design considerations for the Hood is taken are discussed and taken into consideration while designing the hood.
• The manufacturing feasibility of the hood is taken into consideration.
• Draft Analysis is performed to check if the faces are clearing for the required draft angle for manufacturing the emboss.