Hood design

OBJECTIVE:

Designing of Hood Assembly

DESCRIPTION:

Hood:

A car hood is the metal part that covers the engine of an automobile. The term car hood is a North American term, used primarily in America and Canada. Hood comes from the Old English word hod which means a hood, a soft covering for the head. Interestingly, hood is used by British English-speakers to refer to the waterproof cloth top covering the passenger compartment of a car or pram.

The components associated with hood are,

• Outer panel
• Inner panel
• Hinges
• Latch & striker

Design Parameters:

For this project, the design parameters are already given to complete the design and development of hood. Those parameters are as follows,

Hood Thickness Information 

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

Master Section:

Master sections are the guides for design requirements which decide the component packaging after technical (Styling, Concept or Class-A) surfaces. Concept development in BIW.

Hemming Data:

Hemming is a technology used in the automotive industry to join inner and outer closure panels together (hoods, doors, tailgates, etc.).

Hemming reliefs:

Design procedure:

The following procedures are followed to design the hood according to the OEM standards. The design starts with the styling class A or skin data of the hood which is given by the styling team.

1. Outer Panel: 

• Outer Panel is a Covering part for Inner Panel which is given as a input.

Hemming:

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.

• in this project we jus needed to perform hemming on outer panel.
• for hemming hemming data is given
• first outer surface is offsett to 2.65mm as master section and curve face used to to make trim sheet and about that trim sheet law extension feature applied.
• and finally three face blend comand applied.

• now relief for inner panl created by curve on face and trim it.

• after applying mirror geometry by midplane full body is formed.
• and finally 0.75mm thickness is applied to inwards direction and finally colour is applied.

2. Inner panel:

Inner panel of the hood provides strength to the hood and provides the reinforcements for rod / gas stay, hinges and latch & striker which are all used to attach the hood with the engine compartment.

• The outer surface of hood skin data is given by the styling team. With that skin data the design process of inner panel starts.
• Copy of Outer panel created as Inner panel and link between breaked
• and now for clear understanding this inner panel trim with middle plane. 
• Then using the given master section, the trimmed surface is offset to further and further to the required dimensions.

• After offsetting those surfaces, the required curves were offset on the surface faces and new sketches were created to according to the requirements.
• With the help of these curves and sketches, those surfaces were trimmed and joined using the commands like through curve, law extension and trim & extend.
• and now some flanges formed.

Emboss:

Embossing is a metal stamping process for producing raised or sunken designs or reliefs by passing metal sheet or strip between rolls of the desired pattern. The process enables repeated production without variation and does not change the metal's wall thicknesses.

• Then the emboss were created using the new sketches created in the required planes, through the commands like emboss and law extension etc. with required drafts in the positive direction.
• for creating emboss we need tooling axis because draw direction is our tooling axis, so first tooling axis created which is perpendicular to side view.

• Then the edges and corners were blended using the commands like face blend and edge blend to avoid the sharp edges and corners.

Mastic Data:

Mastic sealants are the materials which is like a rubber or sponge used to seal the gap between the hood inner and outer panels to avoid NVH and improve strength to the outer panel. This mastic sealants are placed in the hood inner panel and the points where the sealants placed are called mastic points. Each mastic sealants covers 80mm diameter of space to serve its purpose. These mastic points are said to be the mastic data.

• after that some cutout made for reducing stress concetration.

• The emboss for hinges and striker were created with the reference taken from the other parts using the command like wave geometry linker, datum plane, emboss and law extension etc.

• After creating required embosses and mastic points, the whole surface is mirrored about yz plane and sewed together to complete the hood inner panel surface.
• When the inner panel is completed, then it is thickened according to the design parameters of 0.75mm to create the inner panel.
• Then the latch trajectory were created with the help of hinge axis which used to assemble the striker in the future.

3. Hinges:

A hinge is a mechanical device that joins together two solid pieces to allow for rotating or opening between both parts. So hinges are commonly used to create a door or a lid which will give you easy access to the components that are going to be inside your enclosure.

For this project, the hinge part file is already given.

to mount hinge on inner plane just assembly constrain used.

                             Hinge assembly is shown.

4.Latch & striker:

Latches or striker are mechanical components that allow the temporary joining of moving parts relative to each other. They are actuated to release the coupling and allow the two parts to separate. They are mostly seen on doors and enclosures. They are used in devices such as seat belts, clamps, straps, and objects with retractable parts. Different designs feature different methods of actuation, holding style, and mounting.

For this project, the striker part file is already given.

Latch Trajectory:

Latch trajectory is the path which decides the striker movement when the hood is opened/closed. This trajectory is created with the help of hinge rotation axis. With reference to the hinge axis a circle is drawn with required dimension and then a tangent line is created which is perpendicular to the reinforcement. This line and circle is said to be the latch trajectory.

while opening or closing the hood, the latch must be perfectly aligned to the fixing or striker point. For that, the latches trajectory must be perpendicular to the hinge axis.

For mount Latch or striker on inner panel we drawn a sketch with reference to this sketch using wave geometry linker this latch striker is mounted.

Final Assembly:

In final assemby verified it with clip view whether inner panel and outer panel are at right place

but due to student version of NX CAD software found some graphical error.

Draft Analysis:

CONCLUSION:

The parameters, standards, procedures and manufacturing process involved in design and development of hood and its assembly which is followed in the OEMs and automotive industries is explained in detail with reference images.