Hood Design for the Car that Satisfies the Industry’s Manufacturing Requirements, Functional Requirements, and As Well As European N.C.A.P Standards Using Siemens NX CAD.

Project Objective: In this Project, I am going to Design the Hood of the Car and The Main Purpose to Improve Strength of Body, Reduce the Material weight of Body and Improve Mailage of Car and Saftey Purpose Using Different Types of Sheet Metal Operation and Design Shape on Front  Hood Car Body.

01. About of Hood(Bonnat) Design: 

• The hood may be hinged at either the front or the rear edge, or in earlier models. It may be split into two sections, one each side, each hinged along the centerline. A further variant combines the bonnet and wheel arches into one section and allows the entire front bodywork to tilt forwards around a pivot near the front of the vehicle.
• 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.
• Hood generally is used to covering car engines, radiators, and many other parts, therefore, the hood must be designed in such a way that all the maintenance on the engine. 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.
• Hoods are typically made out of the same material as the rest of the bodywork. This may include steel and Aluminum  However, some aftermarket companies produce replacements for steel hoods in fiberglass or carbon fiber to make the vehicle lighter.

02. Purpose of Hood Design:

• Save and safety of purposes inside the car.
• Cover all engine parts and radiators. 
• Reduce the Air effect due to design aerodynamic shape.
• provide access to the engine for repair and maintenance. 
• reduces engine noise, providing you with a quieter drive.
• It can also help keep the paint underhood last longer. 
• it can give motorists more time to get out of the car before the fire blazes out of the hood. 

03.Material Selection of Hood Design Assembly: 

Hood is typically made out of steel or aluminum, although aftermarket manufacturers may manufacture hoods out of fiberglass, carbon fiber, or dry carbon.

• Grade 304 stainless steel and Grade 302 mild steel for the outer and inner panel.
• Flex fiber or reinforcement vinyl ester composite for Latch.
• Elastomer /silicon Polymer and Silicon copper paste for mastic seal. 

04.Properties of Hood Material Stainless steel G 304:

• Good Corossion resistance.
• Good Modulus of elasticity (Gpa-200). 
• Good maintaining for mobility and weldability.  
• High yield Strength(Mpa-205).
• High endurance limit (Mpa259).
• Good Hardness (HB-201).

05.Design Consideration of Hood Design:

Observation of Adults, Childs, and lower Impact on Car Hood Body:

• The 1st and most important safety requirement to be considered while designing the Bonnet is the Pedestrian Safety from a frontal collision.
• The European New Car Assessment Program (Euro NCAP) is a European car safety performance assessment program which has developed test specifications and rating systems for assessing pedestrian injuries during impacts with the front of vehicles Such tests include a series of tests using impactors designed to mimic a collision at a speed of 40 km/h. They describe a situation in which a pedestrian is situated laterally and a car first hits one of his legs. Tests are conducted on the leg, upper leg, and most importantly, the head, as head trauma is most commonly responsible for casualties.

• Thus to avoid severe injuries to the head, the high impact area for adults and children is subjected to less thickness. Also, no reinforcement should be provided in that area as, during the head collision, the hood will absorb the head impact energy leading to the collapse of the hood and thus protecting the severe head injury.
• Another important criterion for the hood design is the protection of the occupants inside the car during the front collision. The design of the hood should be in such a way that during the collision, the force should travel in the upward direction through the embosses and directed towards the body of the car. Thus protecting the occupants inside.

06.Purpose of Sheet Metal Operation Sequence Wise for Hood Design: 

• Blankingand Punch.
• Deep drawing.
• Embossing.
• Hemming.

6.1.Blanking and Piercing Operation:

Blanking and piercing are shearing processes in which a punch and die are used to modify webs. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap. The process for parts manufactured simultaneously with both techniques is often termed "pierce and blank." An alternative name of piercing is punching.

Purpose of Blanking and piercing:

• Reduce the Body of weight.
• Improve the Strenght of the Body. 
• Distribute Impact Force.
• Improve Mileage of Car. 

       Figure: Blanking  

      Figure: Piercing             

6.2.Deep Drawing Operation:

• Deep Drawing of sheet metal is used to form contains or object with depth. it is a Plastics deformation in which a flat sheet or plate is formed into a recessed three-dimension part with a depth several times the thickness of the metal. The process of deep drawing begins with a flat sheet metal blank held on the upper surface of the die.
• A deep drawing process is used for the manufacturing of the inner panel. The material used is aluminum as it can absorb twice the crash energy of mild steel, lighter, dent free, and can make body panels thicker while still lowering the weight.

Purpose Deep Drawing Operation:

• Operation in which the thickness of the shell wall is reduced and it's surface smooth. When materials get compress between the punch and die, which reduce the thickness and increase the height of the cup.   

     

6.3.Embossing Operation:

• 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.
• Embossing is done by pressing a sheet of paper (or another substrate) into a female die, that has a design engraved or etched into it. This is usually done with a male counterpart underneath the paper so that the paper is sandwiched between the two and the design is transferred to the paper.

Purpose of Embossing Operation:

• Embossing enables you to highlight important elements of your printed products, such as letters (company name) and designs (your corporate logo), to make sure they stand out. Embossing can also be combined with foil stamping to help create the effect of a 3d image on printed paper that really shines.

       Figure: Embossing

6.4.Hemming Operation:

• Hemming is a sheet metal forming process in which sheets are joined by bending it to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods, and tailgates are formed by the hemming process. In this process, usually, a sheet is bent with the help of the inner sheet in three different stages.
• 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.                                                                                                                                                    

Figure: Hemming

Purpose of Hemming Operation:

•  Hemming is a sheet metal forming operation in which the edge of the sheet is folded back on itself. It serves several purposes: to fasten two sheet metal parts, to improve the appearance of edges (remove burrs and rough edges), and to increase the part stiffness.

         Figure: Hemming

07.Hood Design Process Steps:

     

• No sharp corners inside the panel.
• No negative draft.
• Provide appropriate corner relief on the area of curvature.
• Outer Panel Thickness = 0.75mm.
• Inner Panel Thickness = 0.75mm.
• Reinforcement Thickness = 1.5mm.
• Minimum Filet Radius = 0.3mm+thickness(Example,thickness of outer/inner panel),0.3+0.75=3.75mm.

 7.A.2  Hood Inner panel Design:

• The initial design was created from the master section that was already provided. Embossing is a metal forming process for producing raised or sunken designs or relief in sheet material by means of matched male and female roller dies, theoretically with no change in metal thickness. Embosses are created to provide additional strength and to direct the forces from the front collision towards the hinge and body of the car.

Part Navigators:

Sketch.

Extrude. 

Offset.

Law of Extension. 

Time Sheet. 

Face Blend.

Edge Blend.

Mirror geometry.

Extract Body

Extended Sheet.

Sweep. 

 7.A.3 Mastic Data Design:

• The main purpose of the outer panel is for the aesthetic looks. Thus we cannot use bolts or welding. This has to be done with the help of the hemming and mastic sealants. Mastic sealants are elastic compound that behaves like the rubber. It is placed between the outer and inner panels. Initially is it in paste form, but after the hot furnace bath, it gets hardened thus joining the outer and inner panel. Mastic sealant has the tendency to increase the strength of the panel and has the influence of 80mm diameter.

7.A.4 Latch And Hinge Reinforcement:

• To furthermore reduce the impact to the occupants inside the car, additional latch and hinge reinforcement to the hood. When latch and striker are placed, there is a drop in strength at that position thus reinforcement is required. Also, stiffness pads are placed to reduce NVH. Hinge and latch reinforcement thickness is kept at 1.2 mm but it may vary.

7.A.5 Hinge and striker:

• For the proper opening and closing of the hood, the striker should be perpendicular to the trajectory of the hood. For this, the hinge is assembled at its position. Once it is placed, the hinge axis is drawn. Using the hinge axis as the center we draw a big circle to the position the latch in such a way that it is perpendicular to the hood trajectory.

7.A.6 Force Distribution in an Inner panel:

7.B.1 Design of Outer panel:

7.B.2 Hemming Provide in Hood:

• Hemming is the process in which the edge is rolled flush to itself, while a seam joins the edges of two materials. Normally hemming operations are used to connect parts together, to improve the appearance of a part, and to reinforce part edges. In hood design, 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. Dimensions of hemming are given below.

7.B.3 Relief data:

• Relief is provided onto the part or component in order to remove any stresses developed in a particular area i.e sharp corners that take place during the hemming process are carried out. Thus corners are rounded or chamfered

 08. Draft analysis:

• Draft analysis is carried out to see that the panel can be drawn or not. It also helps to find the negative draft present in the component which can cause difficulty in manufacturability. 

 09.Moment of Inertia of Hood Assembly:

 10.Conclusions:

Thus I have designed the hood of the car that satisfies the industry’s manufacturing requirements, functional requirements, and as well as Euro NCAP standards using NX CAD.

Thanks & Regards

 Rajnish Kumar