VEHICLE HOOD DESIGN.

TITLE: DESIGN AND ASSEMBLY OF VEHICLE HOOD.

OBJECTIVES:

• To design and assemble the vehicle hood.
• Learning the industrial approach of how vehicles sheet metal parts are designed in industry.
• To be industry ready for the role of Mechanical Design Engineer.

INTRODUCTION:

Hood is use as an engine cover for motor vehicles. Hood is connected by two hinges to the engine compartment. Hood can open to allow access to the engine compartment for maintenance and repair. While designing a hood in industry specific manner hood should meet the following conditions.

1. Pedestrians safety
2. Force distribution when subjected to frontal collision (Passenger Safety)
3. Placement of latch on latch trajectory
4. Manufacturability

A typical hood assembly consist of outer panel, inner panel, hinge assemblies, latch and striker mechanism and hood stray. All the parts have their different functions. Mine main focus during this project is ion designing the inner panel in industry manner and placing the latch and striker mechanism on latch trajectory. Hood are typically made out of the same material as the rest of the body in white of car. Deep drawing, hemming, blanking and piercing are the common sheet metal operations that are used in manufacturing hoods in automotive industries.

DESIGN METHODOLOGY:

Pedestrian safety and the awarding the flow of forces to the side of hood in case of vehicle crash for the safety of passenger or occupants are the two main aspect taken into the account while designing hood. Total design of this hood assembly is designed using Siemens NX Software.By the help of following operation Hood assembly is designed.

DESCRIPTION:

Inner Panel:

The inner surface is to be designed like master section. So i first started with creation master section by creating three offset surface and by using trim sheet, through curve and law extension. after that main emboss is created by emboss feature. After creating main emboss i create various small emboss for easy flow of frontal forces to the side in case vehicle crash. This emboss should be in Y or V shape so that forces can transfer easily. then i created emboss seat for the latch and striker, this emboss were different from other embosses as this embosses were created by using end cap condition as datum plane. That's why the upper surface of this emboss is parallel to the hinge and latch surface. Blend with appropriate dimensions were created at every edge so that there should no stress concentration. After all this process the part is thicken so that it is converted into solid one.

Outer panel:

Outer panel is the aesthetic part in hood of the car. As for joining the inner panel with outer panel i used the hemming technique. For creating i first offset outer panel surface and then apply symmetrical law extension command on the edge of the offset surface. After that by using three face blend hem is created.

Latch trajectory:

Latch trajectory plays an important role in assembling the latch with the inner panel. For this I created a circle of 511mm while taking the hinge axis as the central axis. After that I created a line tangent to the circle. And attach this line with the line drawn on to the latch by using prefer touch constrain. For proper mating condition the striker axis through the tip of the striker should be tangential to the latch trajectory.

Reinforcements:

Reinforcements are usually provided to increase the strength of sheet metal part in that region. In this project of hood designing at hinges and at latch reinforcement were provided with thickness of 1.5mm. usually, the thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirements.

Mastic data:

As we know the main purpose of outer panel is for the aesthetics looks. Thus, we cannot use bolts or spot welding because they will leave mark on the outer panel. Hood commonly possess large surface area and hemming can only be provide at the boundaries. So, mastic sealants are used to stick inner surface of outer and inner panel. Mastic sealants are elastic compound that behaves like rubber. Initially they are in pastel form, but after the hot furnace bath it gets hardened thus joining the outer and inner panel. 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.

The main function of the emboss is to provide the stiffness to the inner panel and directing the forces to the side of the hood in case of the frontal collision. Shape and size of embosses is totally decided by the design engineer while deciding the shape force distribution should be taken into account. Mostly Y and V shaped embosses are preferred.

I first created a large base emboss having depth of 10mm. after this over this large emboss I created different small embosses according to the requirement. Then I applied the blends at the edge of the embosses in order to reduce stress concentration.

Deep drawing:

The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions.

Deep drawing process start with a metal blank, the disc of metal cut from a larger sheet is pushed into a cavity around a die, which begins the deep drawn process of drawing the blank into the desired shape. This is completed in gradual steps to ensure an even distribution of the metal across the final shape, which is important for preserving the integrity and strength of the finalised deep-drawn component.

Features like emboss, dimple and bead are used in Siemens NX for representing the deep drawing on software level.

Hemming:

For joining the inner panel with the outer panel, we cannot use spot welding as spot welding would leave weld marks on the outer panel. As out panel is an aesthetic part off the hood so it should be free from any marks. That’s why we use hemming process for joining inner and outer panel. Hemming is a forming operation in which the edges of the sheet are folded over another sheet metal part in order to achieve a tight fit. Normally hemming operation is used to connect parts together, to improve the appearance of a part and to reinforce part edges.

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 relief at the corners.

I created the hem in NX by creating a offset surface to the outer panel and then symmetrical law extension on the edges of offset surface. After that by using a three faced blend I blended this surfaces in the shape of hem.

Assembly:

While assembling the hood first step is to make the outer panel fixed. As inner panel is created by taking reference of outer panel that’s why inner panel is also get fixed with the outer panel. For joining the hinge assembly, I first make axis of hinge parallel to the X- axis. After that by using distance constrain hinge is joined to the inner panel. Striker is assembled to the inner panel by using Prefer touch constrain twice.

Isometric view:

Front view:

Top view:

side view:

CONCLUSION:

Successfully designed, assembled Hodd assembly. learned Siemens NX software as a design tool in industrial manner. This project really helps me to enhance my designing skill and help me to become industry ready for the role of Mechanical Design Engineer. Overall, the project was successful.