Hood design-Week 2

Aim :- To Design Hood Outer Panel, Inner Panel and the necessary reinforcements by following the Master Section with design consideration in NX CAD Software.

Hood :-

A car hood, also referred to as a “bonnet” in some countries, is the hinged cover that rests over the engine bay of a front-engine vehicle. The car hood protects the engine and connected parts from the elements while providing easy access for repairs and maintenance.

Car hoods are typically constructed from steel and sometimes from aluminum. Aftermarket car hoods may be constructed from various other materials, including carbon fiber, fiberglass, or dry carbon.

Master section of car hood :-

Design parameter :

Hood Thickness Information

Outer Panel Thickness = 0.75mm

Inner Panel Thickness = 0.75mm

Reinforcement Thickness = 1.5mm

Components of car hood :-

Outer panel :-

A car hood panel is one of the most important components of the BIW (body in white), it is considered as the closure sheet-metal component. A hood panel consists of two panels that are hemmed together to form the automotive hood assembly. The inner panel of the hood is not visible to the customer but this is the engineering feature of the outer panel. The outer panel has the aesthetic look to it but on its own is very weak and not capable of handling force during impact.

Inner panel :-

A hood inner panel for a vehicle is provided to improve rigidity, durability, and pedestrian protecting performance by comprising a composite structure in which a multi-cone structure and a frame structure are individually arranged on the front and the rear. 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.

Latch :-

Under the hood of most cars, trucks, vans and even tractors is a latch. Known as a hood latch, it temporarily holds the hood down. Hood latches are connected to a handle. When you pull or engage the handle, the hood latch will release. It plays a major role in opening and closing hood for maintenance of car engine and gives a tight locking position not to create undisturbed noises when the vehicle is running.

Hings :-

The hood hinge is a pivot and bracket mechanism that makes it possible for you to open and close your hood. hinges are mounted on fix parallel axis on car compartment. This coupling allows the hood to open and close, as well as makes contact between the engine block to the hood. It also controls the lifting of the bonnet mitigates the consequences of a collision between a pedestrian and a vehicle.

The Reinforcements :-

The area near hinge and latch has more chances of failure in the hood panel. Hence to avoid any failure, the hinge and latch areas are reinforced with extra material whose thickness is usually determined by the type of vehicle. 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 Trajectory :-

The latch trajectory is the path which the striker will follow when the hood is open/closed while pivoting on the hinge axis. The latch trajectory is taken as a circle with the hinge axis as the center of the circle. The striker is placed 90 degree such that it is tangent to the circle. The radius of the circular trajectory is determined by the set standard based on the average height of a person. The radius is measured from the hinge axis up-to the latch.

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. mastic sealent is an elastic compound that behaves like a rubber. These points are defined on the hood inner panel where hood easily can deform. It helps hood outer panel to come back to its original shape after getting deformed. It also helps the inner panel fixed with the outer panel.

Emboss :-

Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal.This process can be made by means of matched male and female roller dies or by passing sheet or a strip of metal between rolls of the desired pattern. In Hood design the inner panel of the hood has more embosses to improving the strengthening of the panel.

Manufacturing Process :-

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. A flat sheet metal blank is formed into a hollow body open on one side or a hollow body is formed into a hollow body with a smaller cross-section.

Deep drawing processes are divided into three types:

• Deep drawing with tools
• Deep drawing with active means
• Deep drawing with active energy

The figure illustrates the deep drawing process. The rigid tools consist of a punch, die and binder. In deep drawing, the plate holder closes after the metal sheet blank has been inserted. Next the sheet is clamped between the die and the binder. This process slows down the flow of the sheet while it is being drawn and thereby prevents wrinkles from forming under the binder. The punch stretches the sheet over the die radius and forms it in the die. The amount of punch force necessary for forming is thereby continually increased up to the lower dead center of the punch. Whereas in pure deep drawing there is no reduction of sheet metal thickness, forming is achieved in stretch forming purely as a result of a decrease in sheet metal thickness. Stretch forming is extensively used for the forming of only slightly curved parts with low depth of draw (e.g. roofs, doors).

Hemming :-

Hemming is a technology used by the automotive industry to join inner and outer closure panels together (hoods, doors, tailgates, etc.). It is the process of bending/folding the flange of the outer panel over the inner one. Normally hemming operations are 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 use simulation tools in order to, on the one hand, better understand the hemming process and, on the other hand, significantly reduce the number of “trial and error” loops during tryout und production.

There are various types of hemming operations:

• Conventional die hemming
• Roll hemming

Conventional die hemming

Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool.

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.

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.

Assembly of Hood :-

Conclusion :-

The hood design has been completed by considering the criteria , dimensions , procedures and standards . By the process of this design, have learnt about the hood mountings, sheet metal operations like hemming, embossing, deep drawing, piercing, Pedestrain safety and its ratings.