Challenge

Hood design-Week 2

DDurvesh Naik21 Jan 2023

Aim :-

To design a Hood outer panel, inner panel and the necessary reinforcements by the given Master section and design parameters in NX CAD workbench,

Introduction :-

Hood is a main component of front portion of a car. It is an opening body panel that covers the engine in front engine vehicle. It consist of an outer panel and inner panel. The inner panel provides the strength while the outer panel functions as the metal cover. It is an access panel to the engine compartment to enable maintenance of power train, drive belts, battery, fluid levels and lamp units.

Hood design consideration:-

The hood of a car is considered as the frontal BIW enclosure component. Bonnets are designed to reduce air resistance as the air flows around the car. Apart from this, bonnets are also designed to meet several other requirements. They serve a great deal of purpose in protecting the passengers inside the car & the pedestrians in the event of an accident. It also acts as the cover for the engine.

The European New Car Assessment Programme (Euro NCAP) is a European car safety performance assessment program which has developed test specifications & rating systems for assessing pedestrian injuries during impacts with the front of vehicles such test include a series of tests using impacts designed to bio-mimic a collision at speed of 40 km/h.
They describe a situation in which a pedestrian is situated laterally & a car first hits one of his legs. Test are conducted on the leg, upper leg & most importantly the head, as head trauma is most commonly responsible for casualties.
So to avoid severe injuries to the head, the high impact area for adults & children are subjected to less thickness. Also no reinforcement should be provided in that area as during head collision, the hood will absrob the head impact energy leading to collapse of the hood & thus protecting severe head injury.
Another important criteria for the hood design is the protection of the occupants inside the car during front collision. The design of the hood should be in a such a way that the during the collision, the force should travel in the upward direction through the embosses & directed towards the body of car. Thus protecting the occupants inside.

Components of Hood

1. Outer Panel
2. Inner Panel
3. Hinge
4. Latch
5. Reinforcement

Outer Panel

A car hood panel is one of the most important components of the BIW (body in white), it is considered the closure sheet-metal component. The outer panel has the aesthetic look to it but on its own is very weak and not capable of handling force during impact. Most automobile hood outer panels are made of traditional steel plates, and their quality does not meet the needs of lightweight development. For this reason, it is necessary to obtain lightweight effects through the application of automotive aluminium sheets. The most widely used car aluminium alloys in the market are deformed aluminium alloys of 6111, 6016, and 5182. The production process of the outer panel of the hood mainly includes blanking, deep drawing, trimming, turnup, and side turnup. Among them, deep drawing is a key process to ensure the quality of parts.

Inner Panel

The inner panel of the hood is not visible to the customer, but this is the engineering feature of the outer panel. The hood panel 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. A hood inner panel according includes an inner panel main body forming part of a hood of a vehicle, a front bead provided on the inner panel main body and extending along a vehicle width direction, and a rear bead provided on the inner panel main body, located on a rear side of the front bead and extending along the vehicle width direction. The front bead includes a centre portion in the vehicle width direction that is curved toward the front of the vehicle and located in front of each end portion in the vehicle width direction, and the rear bead includes a centre portion in the vehicle width direction that is curved toward the back of the vehicle and located behind each end the portion in the vehicle width direction.

Hinge

A hinge is a machine element that connects two bodies allowing angular movement about a fixed axis of rotation, all the while preventing translations and rotations on the remaining two axes. A hinge can be considered as a journal bearing with only one degree of freedom where a shaft is rotating in a hole. Hinges only allow one rotation, either yawing (the most common), pitching, or rolling. Hinges are a jointed and flexible device that is attached to any swinging part. Hinges are mechanical bearings that are used to connect two swinging objects or points and give them the freedom to move relative to each other. Hinges have limited movement, allowing the joint to move only at one angle and restricting the other movements of swinging parts.

Latch

Latchesare mechanical components that allow the temporary joining of parts that are moving relative to each other. They are actuated to release the coupling and allow the two parts to separate. Latches are mostly seen on doors and enclosure openings. They are also used in devices such as seat belts, clamps, straps, and objects with retractable parts. Different designs feature various methods of actuation, holding style, and mounting. The hood latch is extremely simple. When the hood is closed, the latch slides over what is called a catch, and spring covers the latch to keep it snug. When we pull the knob inside the car to open the hood, the hood latch cable opens the latch, allowing it to bypass the catch and open.

Data used-

Hood Thickness

Outer Panel thickness=0.75 mm
Inner panel thickness-0.75 mm
Reinforcement thickness =1.5 mm

Master Sketch: -

Manufacturing aspects and design approach: -

The styling gathering will give us the skin data. The arranging engineer will mull over the engineering common sense of the part with furthermore considering the NCAP standards and will provide analysis so they can change the styling of the hood properly.

The master sketch territory is obliged different areas. Moreover, various predefined values are given to us as demonstrated by which we need to engineer and plan the sketch and model the hood.

Starting there forward, the CAE engineer will do an examination and testing on the part shown and subsequently report analysis to the hood engineer and make the significant changes.

Deep drawing

In this corporation, a sheet is pulled into the ideal shape using a punch and pass-on gadget. The sheet is outlined in the condition the pass on by driving the punch down on it. To avoid the sheet wrinkling itself, the sides of the sheet are held someplace close to folios. In the automotive industry, deep drawing is usually carried out using rigid tools.

Piercing :-

Piercing is a shearing process in which raw metal is pierced with a machining tool, resulting in the creation of a circular or other shaped hole.

Hemming :-

Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts..

This assembly method is widely used in the final stages of production of automobile hoods, doors, or other closures for aesthetic purposes.

It is a metalworking process that involves rolling the edge of sheet metal over and onto itself, essentially creating an area of two layers. During this process, the edge of sheet metal is folded over. The two newly formed layers then lie flush with each other.

The typical three-step bending process of the hemming operation comprising of the flanging, pre-hemming, and final hemming process.

Roll hemming :-

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.

Latch Trajectory

The latch trajectory shows the striker's way when the hood is opened and shut on a vehicle. The range of the round Trajectory is controlled by the set standard dependent on the typical stature of an individual. The range is estimated from the pivot hub up to the Latch. It is the Trajectory on which the movement of the hood (opening and closing are dependent). This circular Trajectory has a radius equal to the length from the centre point of the centre axis of the Hinge to the striker point on Latch. The striker point is also tangent to the Trajectory.

Mastic sealant

The mastic points are regions where mastic interferes with the outer panel to the inner board. We can't use spot welding because this gives less elegantly fulfilling results. Accordingly, mastic is used to join the panel as it doesn't modify the actual metal.

Embosses

The design of embosses is done by the force distribution of frontal impact. It is designed so that the reduction of force starts when it is directed till the corner, i.e., up to the hinges, and loses the maximum amount (of force) till the end.

Force Distribution

Reinforcement

The Zone near the turn and Latch has more chances of disillusionment in the hood panel. Consequently, to avoid any failure to rotate and latch region upheld with extra materials whose thickness is regularly directed by the vehicle. The reinforcements give additional fortitude inner panel of the centres where various parts, for instance, the lock and rotate, will be put. The reinforcement ensures that the turns and the snare have better assistance to avoid frustration.

Corner Reliefs and Front Reliefs

Reliefs are provided at the front and side portion of the panel for smooth rolling operation .so that no tearing of the sheet happens when the roller passes through a specific portion.

Tools:

Offset surface- The offset surface gadget copies the picked surface at a provided distance and guidance.
Emboss- The embossing contraption makes a punched surface of the picked shut contour. The punch is produced using a chosen surface containing the contour surface. Sketch. a draft can be obliged the punch from either the end cap or the base surface.
Trim sheet- The trim sheet gadget parts the target surface along the intersection curve of the target surface and the gadget surface. The piece of the cover on either side of the intersection can be either discarded or retained according to need.
Through curves- This contraption creates a surface between two various surface sections where the shape can change in section.
Law Extensions- Creates an extended surface subject to an open-chain contour or a shut contour on the picked target surface. A draft can be obliged by the extension.
Face blend- Creates a curved blend or fillet along two picked surfaces in gave direction vector. The blend curve can be changed regarding reach, width, and continuity.
Extend sheet- Creates an extension of the picked sheet up to a given distance.
Offset in the face- Creates an offset in the front or edge on the target face up to a provided distance.
Bridge curve- Create a roundabout portion between two intersecting and non-intersecting curves. The beginning and endpoint of the roundabout changed by providing distance.
Projected curve- Creates a projection of a curved profile onto a goal surface. The surface can be linear and curved. The direction can be changed by a reasonable vector.
Sew- combines sheet bodies by sewing common edges together or combines solid bodies using sewing faces. Any opening between the surfaces can be closed.
Mirror Geometry- Mirror a geometry along a face.
The curve on the surface- Creates a surface spline feature directly on the face.
Thicken- creates a strong body using thicken.
Extracted body- Creates a body of picked geometry that can be changed by editing the parent feature and rebuilding the extracted feature.

HOOD INNER PANNEL

TREE STRUCTURE

HOOD OUTER PANNEL

TREE STRUCTURE

Hood Design Assembly

The hood is designed or modified by different tools like offset surface, offset curve in the face, projected curve, the curve in the face, through curves, face blend, edge blend, sew, law extension, mirror geometry, trim sheet, trim body, thicken which provide desire shape and size to unexpected deformation.

ASSEMBLY TREE STRUCTURE