Hood design-Week 2

Aim :- Design a car hood in NX by using the given master section.

Theory :-

Hoood and It's parts :-

Defination :-

• Car hood is a hinged metal cover placed  over the engine in a front-engine car.
• A latch is provided under the hood in order to prevent accidental opening during driving.
• Purpose of hood is to provide access to the engine, battery , Radiator and air condicener for repair and maintenance.
• It also protects these parts from direct sunlight,Rain and dust.
• Hood is made aerodynamic in shape to reduce air effect and used to decorate the front portion of the car and to add a luxurious look of cars.
•  When cars come across any accident from the front portion most of the time the hood system gets damaged and absorbs some part of the impact energy resulting from the crash.

Hood Outer Panel :-

• The outer panel works as a metal cover. It is responsible for attractiveness of the vehicle.

Hood inner panel :-

• The inner panel provides strength and supports the outer panel.
• It is where hood balancer and hinges are attached.
• 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.
• It also consists of different embosses and hole at different places. Embosses provide stiffness as well as dissipate energy towards hinges.

Hinges :-

• Hinges allow the hood to rotate around a fixed axis for opening and closing movement.
• One part of the hinge is fixed with the engine compartment, while other part is connected to hood.
• The active hinge must lift up the rear part of the hood in appropriate short time to extend the deformation space between the hood and the rigid parts of the engine compartment.

Latch and striker :-

• latch system ensures that the hood stays locked, therefore protecting the engine and the many other parts that reside within the hood of the car. 
• Latch and striker mechanism is provided to lock the hood, in order to prevent accidental opening of the hood during driving.
• The latch is present on the engine compartment while the striker is attached to inner part of hood.

Support Rod :-

• It is a component that supports the hood in open position.It is also called as hood balancer rod.
• Now days instead of support rod we used Gas stay.
• It also doing same work as supporting Rod by mean of an accuator which is activated by gas.
• This is mostly used in the suv type cars where the hood  is heavy, which cannot be handle easily. This works with a hydraulic mechanism through whih the hood can lift itself without any external force.

Reinforcement of Hinges:-

• The reinforcements are provided to add material to the inner panel to provide extra strength to the hood to compensate for loss of strength near component installation regions.
• It also  provided to reduce imapct in collisions to passangers.
• Generally reinforcement of hinges are made around to 1mm and 1.5mm thickness.

Latch trajectory :-

• It is the path along which the hood rotates during opening and closing movement.
• The striker on the hood follows a particular path while opening or closing the hood, which is along circumference of a circle with center at the hinge axis.
• This path is nothing but latch trajectory. It is a very important aspect in hood design, in order to decide hinge, latch and striker installation points.

Design consideration for making Hood :-

1.Hood types :-

1.wrap around hood :-

When the end point of the cars lies on the hood then it is called as arap around hood . Wrap around distance is the trace of the points recived on the front structure when one end of flexible tape of required length held at ground level and another end is in contact with the front structure.

Side reference line :- It means the heighest contact point between the stright edge inclined at an angle of 45 degree and the side of the vehicle.

2. Inlaid hood :-

When the end point of the car lies on the fender then it is called Inlaid hood.

2.For better pedestrain rating :-

3.Head Clearance :-

It is the one of the main criteria while designing a hood of a car. The opening angle of the Hood varies from place to place and to country to country. This design based on the average heaight of the people in that country.

4.Latch trajectory :-

• It is the path along which the hood rotates during opening and closing movement.
• The striker on the hood follows a particular path while opening or closing the hood, which is along circumference of a circle with center at the hinge axis.
• This path is nothing but latch trajectory. It is a very important aspect in hood design, in order to decide hinge, latch and striker installation points.

5.Mastic Sealant :-

• Mastic sealant helps to locally improve strength of the hood.
• It is generally a hard rubber part, which is introduced as a paste in between inner and outer panel of the hood, which will get hardened inside the furnace.
• Every mastic sealant point will have a tendency to improve the local strength in around 80 mm diameter. Considering this, the mastic points are positioned such that most of the hood region is covered.

6.Force Distribution :-

• A hood design must be made in such a way that when a force is impacted in the front of the hood. All the forces must be directed towards outside of the vehicle. And the distribution of the force must be controlled along with the hood.

Design Methodology :-

• First the inner panel is designed from the given master section using the various commands and features.
• We create the embossing using the offset surface from the original master section. Similarly, we create the cuts on the emboss by sketching and using trim surface option.
• Then the outer panel is designed from the same master section. Here we are supposed to provide the hemming to outer panel.
• The parameters of hemming are taken as per given values.
• Now, on the inner panel, the embossing for hinge and striker are produced by considering their respective dimensions and assembly positions.
• First the emboss for hinge is created and then by fixing the hinge into its position, we draw an axis passing through both side hinge axes to form a common axis. And then we position the striker such that it will move along circumference of a circle whose center is at midpoint of the common axis. Thus, position of striker is decided and we can create emboss for the same.
• Using the hinge emboss we created, we can create our hinge reinforcements by creating new parts in the assembly itself.

Data Povided –

Outer Panel Thickness – 0.75mm

Inner Panel Thickness – 0.75mm

Reinforcement Thickness – 1.5mm

Tool used in during design of hood :-

• Offset Surface – It allows you to offset one or more existing surfaces.
• Offset in Face – This command will allow you to offset particular edges or curves on selected faces.
• Trim Sheet – It is used to trim off a portion of a sheet body using curves, faces, edges or planes.
• Trim Body – It is used to trim one or more bodies using a face or plane. You can also specify the bodies to retain and the bodies to discard.
• Projected Curve – It is used to project an existing curve/curves on a selected plane or surface by selecting a direction for projection
• Through Curves – It will allow you to create a body Through multiple sections, where it’s shape changes to pass through each section.
• Law Extension – This command extends a curve or edge to create a sheet body at desired angle length by changing the rules under angle law and length law.
• Extend Sheet – It will allow you to extend an existing surface to required distance.
• Emboss – Emboss command creates an embossing by modifying a body with faces created by projecting a curve/section along a direction. You can modify the emboss using options like endcap location and draft angle
• Sew – It combines sheet bodies together by sewing their common edges. There shouldn’t be any gaps larger than specified tolerance.
• Trim and Extend – It helps you to trim and extend intersecting surfaces and make corner at their intersection.
• Face Blend – It creates fillets between faces.
• Edge Blend – It creates fillets on edges.
• Mirror Geometry – As name suggests, it allows you to mirror geometries about selected plane or surface.
• Extrude – It helps you to create a feature from a sketch. You are also able to create thin feature using a sketch or curve under this command.
• Wave Geometry Linker – With this you can create, associative or linked copies of any entity of a part into other parts. It may be a surface, edge, curve, body, sketch etc. The changes made to the original entity will be reflected in the copy of that entity.

Manufacuring Process used in making Hood :-

Hemming –

• Hemming is a forming operation in which the edges of the sheet are folded over other part or simply folded in order to achieve a tight fit.
• 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.

Deep Drawing :–

• It 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.

Piercing :-

• It is a shearing process in which raw sheet metal is pierced with a machining tool, resulting in the creation in a particular shape hole in the sheet.
• The major difference between blanking and piercing is that in blanking the cut out is the workpiece and outer part is scrap, while in piercing, the cut out is scrap and the outer sheet is the workpiece.

Embossing:-

• Embossing is a forming process in which a high pressure is applied on a surface sheetmetal to change it's shape.
• Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal.
• This process is carried out by means of matched male and female roller dies, or by passing the sheet or rolls of metal between rolls of desired pattern.

Reference :-

•  Google Image
• wikipedia

conclusion :-

• The car hood design is completed with the full design consideration and the Requirment of
  using of Nx .