Hood design-Week 2
Detail report on Hood Assembly-:
Hood Introduction-:
The hood is a top component of the body in white (BIW). In certain countries, a car hood is also known as a Bonnet. It protects the engine and other accessories as well as it absorbs the most impact force across the body which provides safety to the vehicle. It also allows access to the engine and its components for maintenance and repair works. On front-engine automobiles , the hood may be hinged at either the front or rear edge, or it may be divided into two portions, one on each side, each hinge along the centreline, as on older models. Another variation merges the bonnet and wheel arches into a single piece, allowing the entire front bodywork to tilt forward around a pivot at the vehicle's front. It is a front class-A body of the car. Because of these all consideration, a proper design must be considered. The hood design must be in aerodynamic shape, fancy and luxurious looks.
Reduction of weight of car and especially from the front of the vehicle is very significant to improve the performance and efficiency of any automobile as well produces low emission. Considering these all parametres, Hoods are usually made from the same material as the rest of the body. This can be steel, aluminium, fiber glass or carbon fibre.However, some aftermarket companies produces fiberglass or carbon fibre steel hood replacements to mkake the vehicle lighter. The hood release system is the most common on most vehicles and typically consists of an inner panel, outer panel, Hood latch/Lock handle, a hood release cable, and hinge assembly. The hood lock handle is usually located under the steering wheel, next to the driver's seat, or in the door frame.
Hood Design Considerations-:
The hood of a car is considered as the frontal BIW fully enclosure component. It design must follow the aerodynamic shape to avoid the air resistance from the car. It design also considered for protecting the passenger seating inside as well as the pedestrains in the event of accident. The engine noise and vibration also must be considered, and it should be avoid or reduced.
The Hood consists of following major components-:
The Outer Panel
The outer panel, used to cover the inner panel of the hood. It is also considered as the class-A type of a car body, because it is visible from outside. This component must be considered for the styling. It is the first component, that subjected to any type of impact. This part is intact with inner panel so to have a perfect combination and its edges are wrap around inner panel this type of wrap is called hem operation.
Outside view
Inner view
The Inner Panel
This is a class-B surface, which cannot be visible directly from the outside. The top and bottom section of the inner panel are presented below. Fror this hood part, many factors must be considered for designing such as: less weight, high stiffnes, good force distribution at the time of impact, good heat remover, minimal harness and vibration. The steps embosses were provided for good stiffness and avoid localization of forces. The sticker and the hinge are also attached to it. The half circle space presented in the figure marked with the red line circle also provided for the mastic to provide the proper contact between outer and inner panel.
Inner section
Outer section
MASTIC-:
The outer panel cannot be bolted or welded to the inner panel, because of the esthetic requirements. This can be overcome by providing the suitable mastic sealant. An excellent anti-flutter compound, Elastic mastics are an extruded product made in standard, custom, or complex die cut shapes and thickness to meet customer requiremnets for sealing, noise dampening, and vibration reduction. This sealant also increases the strength of the system and has a influence around 80mm in diameter.
Latch and Striker Assembly-:
These both, together used to lock the hood to the body of the car. The reinforcement is provided to compensate the loss of the strength.
Hinge Assembly-:
Hinges are provided with the hood assembly on the both corner as shown below. It is used to connect the hood and fender and also it provide the rotation to the hood assembly, so as to open and close hood frequently. It allow only one degree of freedom.
Opening of the Hood-:
On newer models, the hood release is often located inside the vehicle, somewhere near the steering coloumn, or on the floor next to the driver's seat. On older models, the hood release is behind the grill or bumper. With the hood release inside the vehicle, press, push or pull until the hood pops open. Then push, press or pull from front to back and side to side until it releases the hood. THhe hood opens a little but is likely to be stopped by the safety lock of a metal lever, when pushed in one direction or other, release the hood so it can be fully opened.
Latch Trajectory-:
Latch trajectory is a path that hood folloe for its working i.e., opening and closing operations. The proper working of hood can be achieved by positioning the striker tangential to the trajectory path of the hood. The trajectory path must be drawn from center of the hinge axis on the mirror plane.
Emboss Definition-:
Sheet metal embossing is a stamping technique that creates raised or sunken images in sheet metal. This procedure can be accomplished using matching male and female roller dies, or by sliding a sheet or a strip of metal between the desired pattern's rollers. It is frequently used in conjuction with foil stamping to produce a gleaming, three-dimensional impression.
Hemming Operation-:
Hemming is a sheet metal forming method that involves bending sheets to an angle of 180 degrees. The hemming technique is used to create automobile body panels and pieces such as deck lids, trunk lids, doors, hoods and tailgates. In this operation sheets are folded over another part in ordre to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appereance of a part and to reinforcepart edges.
Deep drawing-:
Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. 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 experiences a radial drawing stress due to the material retention property. These compressive 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.
Commands used for designing Hood Assembly in NX-CAD-:
Surface commands: Offset surface, trim sheet, face and edge blends, through curve, extract geometry, law extension, thicken, trim and extend sheet, extend sheet, sew.
Curve commands: Curve on surface, offset curve, project curve, bridge curve, offset curve in face.
Assemblies commands: Add component, move component, assembly constraints, Mirror assembly and wave geometry linker.
Views of Hood Assembly-:
Top view
Left side view
Front view
Back view
Isometric view
Conclusion-:
All the parts of the hood are designed based on the required conditions and assembled together for getting a complete Hood Assembly.