Hood design-Week 2

Aim :

To design & Assemble Hood outer panel, ineer panel and the neccessary reinforcements by following the design parameters & master section which is given to us as an inputs.

Software Used : CATIA V5

Abstract :

 The project report details with the explanation of the steps and procedure followed while developing the HOOD Assembly of a car using a CATIA V5. using the styling surface and master section as input, we were able to create HOOD outer panel and inner panel with features like embossements and mastic points. After creating the HOOD inner and outer panels, we have created a complete HOOD assembly consisting of the outer panel, inner panel, latch, hinge & reinforcements. in the end, a Draft Analysis has also been perfomed using the tooling axis to check the manufacturability of the components.

Methodology :

• Creating hood inner panel
• Creating hood outer panel
• Creating embossment for hinge
• Creating embossment for latch
• Creating reainforcements
• Assembling the components
• Performing Draft Analysis on CAD model

Theory :

HOOD :

The hood or bonnet is the hinged cover over the engine of motor vehicles. Hood can open to allow access to the engine compartment or trunk on rear-engine and same mid-engine vehicles for maintenance and repair. it generally covers the engiine and other essential accessories likr battery, Radiator, electrical components, etc. of the car which are exposed outside. The hood consists of an outer panel and inner panel. The inner panel provides stength and support, where the outer panel is a metal cover that as styling factors. Whille desiging the hood, a designing engineer needs to make sure that the following design requirements are followed.

• Pedestrain safety Occupant safety
• Vehicle quality
• Ability to manufacture

Out of these requirements, pedestrain safety & Occupant safety are the must important factors. Euro NCAP is a voluntary vehicle safety rating system that will provide european consumers with information regarding the safety of passengers vehicles. The more stars, the better safety will be provided to the customers. Thus design engineer must need to follow these requirements to provide better safety to the customers.

Vehicle design are usually on understanding the car-pedestrain interaction, which is characterized by the following sequence of events : the vehicle bumper first constacts the lower limbs of the pedestrian, the leading edge of the hood hits the upper thigh or pelvis, and the head and uooer torso are struck by the top surface of the hard impact of the head against the stiff hood or windshield. in addition, allthrough usually non-fatal, injuries to the hard impact of the lower limb (usually to the knee joint and long bones) are the most common cause of disabilities. The hood of most vehicles is usually fabricated from sheet metal, which is a compliant energy-absorbing structure that poses a comparatively small threat. Most serious head injuries occur when there is insufficient clearance between the hood and stiff underlying engine components. A gap of approximately 10cm is usually enough to allow the pedestrain's head to have a controlled deceleration and a significantly reduced risk of death. Most limb injuries occur due to a direct blow from the bumper and the leading edge of the hood. Wrap Around Distance(WAP) is the distance from the ground level to the end of the hood as shown in the image.

                                                                                                    Fig : WAD zones

There are two main zones that are conidered while the designing stages; The Child head impact zone ( 1000mm to 1700mm WAD) and the adult head impact zone. ( 1700mm to 2100mm WAD). If the side reference line is on the fender, the WAD will be more and the impact zone will be less and vice versa.

The hood panel should be designed in such a way that it diverges the impact forces during a collision away from the occuparts inside the cabin. The forces should be damped properly to avoid or reduce the risk of inuries and death.

Types of Hood Support :

Support Rod :

A hood rod is designed to hold your hood propped open whenever you need to do some work in yours car's engine bay. when used, it must be firmly secured to ensure that it provides a stable hold on the hood. Meanwhile, when not is used, it must be kept stable in place and must not movie around. The rod clip is the part assigned with that function. This clip clamps onto the rod and in ensures that it is firm in its place when not is used. It keeps the rod from moving around under the hood and from causing trouble.

Gas Stay :

This are used to lift the car hood or bonnet, its purpose to just give the lifiting force to the hood, then it automatically opens the car hood by means of gas pressure. This is used where the car bonnet size is heavy to lift.

Components of Hood :

The components of the hood includes hingre, latch and reinforcements which are attached to the inner panel of the hood. The basic definitions of these parts are given below.

Hinge : 

A hinge is a piece of metal, wood, or plastics that is used to join a door to its frame or to join two things together so that on of them can swing freely.

Latch : 

The hood latch helps to keep your hood closed. when the hoods is closed, the latched sides over the what is called a catch, and the spring covers the latch to keep it sung. When you pully the knob inside the car to open the hood, the hood latch cable opens the latch, allowing it to bypass the catch and open. There is, however the the second hood latch, to keep the hood from flying up if  accidentially unlatched. That latch will need to be opened with your hand to get the hood fully open.

Reinforcements :

The purpose or reinforcement is to provide additional strength for the hood where it is needed. When the latch and striker attached to the panel, the Strength will be reduced in that area. To the strength that area the reinforcement is added.

Latch Trajectory :

Latch Trajectory is the orbital path in which the latch should be positioned to the lock hole. The trajectory is drawn based on the reference of the hinge joint central axis.

Mastic Data :

Mastic is common as an adhesive and sealant. A mastic sealant is a type of liquid sealant that cures in an elastic state, thus making it flexible while holding the bond of the surfaces that have attached. it adheres to just about any material making and all - purpose type of sealant wood, aluminium, glass, marble, and even dust board are all standard application for mastic sealant.

Embossments :

Embossing is an operation used in making raised figures on the sheets, with corresponding relief on the other side. The process essentially involves drawing and bending the metal. The die set consists of a die and punch with the desired contours so that when the punch and die meet the clearance between then is the same as that of the sheet thickness. Embossing operation is generally used for providing dimples on sheets to increase there rigidity and for decorative sheet work used for panels in houses and religious places. Stretch forming operation is a relatively less several operation.

Manufacturing Process :

The manufacturing process involves turning raw materials into finished products which are used for some purpose. The economics of the manufacturing operation is a very improtant consideration. To be viable in the modern environment a product as to be competitively priced besides having functional and aesthetic appeal. There are diiferent processes available for manufacturing. This are classified as casting process, forming processes, Fabrication process, Material removal process.

Deep Drawing :

  Drawing is the process of making Sheels, and similar articales from metal blanks. Drawing when cup height is more then half the diameter is termed deep drawing. Ductile materials are easier to be drawn into deeper cups. In the drawing , because of the radial flow of materials, the sidewells increase in thickness as the height is increased. There would be a slight thinning of metal at the bottom corners.

Hemming :

Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180 Degrees. Automotive body panels and automotive parts such as deck lids, trunks lids, doors, hoods, and tailgates are forming by hemming process.

Procedure :

Data to be used :

Hood Thickness Information 

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

Design :

Inner Panel :

First open the given model i.e, Hood styling surface in CATIA V5 and Extract the surface

Now following  the Master section, offect the surfaces

After offsetting the surfaces, use the boundary option to create boundaries of the surfaces and use the parallel curve option, offset the boundary on the surfaces.

Now split this surfaces with boundary which we offset to get the first inner portion surface of the hood 

 Similarly, we need to create all other inner portion surfaces for the hood inner panel at different offset values by following the master section.

Offset the split surfaces (the main surface which we split with the yz plane) to 4mm and again by extracting the boundary, offset it to 22mm on the surface. split the surface using this boundary and this will give as our second portion of the inner surfaces.

Then need to offset the boundary to 35mm and split the second portion surfaces with it to get the inner edge of the surface.

Create a surface between the first second inner portion surfaces (by selecting inner edges) using the the blend are multi-section option.

Now again offset the main split surface to 20mm and offset its boundary to 50mm and split the surfaces. This will give us the third and final inner portion of the hood inner panel.

Similarly, create a surface between the second and third inner portion surfaces using the blend or multi-section option and give the required fillets to the edges by following the master section.

Now to create Embossment, create a sketch ( no specific dimensions is needed) and project this sketch on the inner panel surfaces.

Necessary cuts are needed for the embossements and they should be in such a way that the stress in the body that develops during an impact should not affect the occupant heavily. After creating the embossements, mastic points are to be included near the hole regions such that these points are used to make sure that there is no gap between the outer and inner panels.

Now using the symmetry option create a surface on the other side. join these surfaces and if there is a gap between the surfaces, we need to create a surface in between them.

Creating Hood Outer Panel :

To create the hood outer panel, the below the inputs needs to be followed.

Using the main split surface, create the outer panel by first extraploating it to 2.75mm.

Now offset is extrapolated surface to 2.45mm and extra its boundaries and using the parallel curve option, offset the boundary to 6mm split the surface using it.

Create a surface between the extrapolating surface and split surface using the blend or multi-section option. join the surfaces and given and edge fillet to them.

According to the requirement we need to given 3mm cutouts at hemming regions.

Extract & offset the boundary to 3mm and using spline create the cutouts of 3mm.

Project this cutouts lines on the surfaces and split the surface using it.

Using the symmetry option create a surface and other side join this surfaces with a max merge.

Creating a solid body with a thickness of 0.75mm using thicken option in the part workbench.

Creating Embossement for Hinge :

To create the embossement for hinge, use the assembly workbench to adjust the hinge part near the hood part using the manipulate tool.

Now , go to the hood model part workbench and create a sketch using the hinge such that the embossement area can cover the hinge part.

Onces the sketch is created project it to the surface and split the surface using it.

Use the sweep option to create the surface with draft valve of more then 7 degrees.

Now extract the lower surface of the hinge part and extrapolate it. trim the sweep and extrapolate surface to get the final output.

Mirror the hinge surface on to the other side and join this hinge with the main surface (inner panel).

 Create a point at the centre of the hinge circle at both ends and create a line using the two points.

Create the middle point using the two points created and create a circle using the middle point created. The circle trajectory should be tangent the latch part.

Creating Embossement for Latch :

Creating embossement for latch is similar to that of the hinge part but in this case, the latch part strier should be tangent to the circle.

Use the striker to create a sketch and project it to the surface and split it.

Now extract the lower surface of the striker part and extapolate it.

Trim the sweep and extrapolated surface to get the final output.

 

Finally, join this surface with the inner panel surface and thicken it in the part workbench with a thickness value of  0.75mm.

 

Assembling the Componements :

To assembly the components, go to the assembly workbench and constraint the parts using upset constraints. Given offset value of '0' by selecting the embossement surface of the hinge and the lower part of the hinge. A similar operation needs to be performed for constraining the latch.

 Use explode and update option to check if all the parts are assembled properly or not.

Draft Analysis on CAD Model :

The draft analysis of the hood inner panel was successfully performed with a minimum angle of 7 degrees with respect to the tooling direction.

 Tree Structure :

Result : 

The design and developement of the hood inner panel, outer panel, latch, hinge and reinforcements in completed following the design parameters and also successfully assembled.

Final CAD Model :