Hood design-Week 2

OBJECTIVE : 

Design Hood Outer Panel, Inner Panel and the necessary reinforcements by following the Master Section

 

PROCEDURE : 

1. Introduction

2. types of hood stay

3. Design consideration

4. Design approach

5. Manufacuturing paramters

6. trajectory line

7. assembly of hood

8. conclusion

 

1. INTRODUCTION

Hood is the opening body panel that covers the engine in the front engine vehicle. it also considered as the another door , since it has outer panel and the inner panel. the inner panel is for provides the strenght and the outer panel acts as a metal cover. the main purpose of the hood to provide the access of the engine for repair and maintenance. hood is also called a bonnet is some other countries. on the frront engine vehicle hood may either hinged at the front or the rear edge. the hood are typically made out of the steel, aluminium, carbon fiber, fiber glass. aftermarket companies provides the replacement of steel hood in fiber glass or carbon fiber to make the vehicle lighter. 

 

2. TYPES OF HOOD STAY 

Hood stay is an apparatus for an engine of a car to keep safe the hood even if it in open conditions. by using this hood stay we can easy to access the engine compartment for any service or maintenance purpose. 

• support rod
• gas stay 

 

SUPPORT ROD

The device which is used for holding the hood in the car engine compartment in the open state by means of rod. the bend in the support rod gives the more strength and less fatigue failure. but the support rod bend must not greater than 35mm. this is due the more the bend can cause the bending deflection in the rod and also for the consideration of space inside the engine compartment. 

PROS : 

• cost effective 
• simple

CONS : 

• the metal rod can cause scratches and rust while in rough contact with the panel and other components
• It also hot to handle when the engine is running for very long time, the heat from the engine will also transfer some amount to the support rod

 

GAS STAY

The device which is used for holding the hood in the car engine compartment in the open state by means of actuator activated by gas. they are used to support the counterbalance of the masses. the little amount of force is required to actuating the hood when the gas stay is used, after that the gas gets exerted in the piston then the hood will be automatically uplift or downlift in fully opened or closed condition.

PROS :

• No man power is required.
• easy usage

 

CONS :

• costlier

 

3. DESIGN CONSIDERATION OF HOOD

3.1 HOOD HEAD ZONE FOR LOCK STRIKER :

the first important criteria to design a hood is a opening angle of the hood.  this will varies from region to region, this is because the average human height may be vary in various region. the opening angle is controlled by the gas stay or the support rod. there must always the certain clearance between the head tip to the striker to avoid collision. 

 

3.2 BETTER PEDESTRIAN RATING

INLAID HOOD 

 When the end point of the car lies on the fender , then it is called as inlaid hood . it is also defined using the side reference line, the 45 degree tangential line where the end point touches the hood is said to be inlaid. 

 

WRAP AROUND HOOD

When the end point of the car lies on the hood , then it is called as wrap around hood, it is also defined using the side reference line, where the tangential 45 degree line meets in the car body i.e hood is said to be wrap around hood.

 

TEST IS TO CARRIED OUT FOR EURO - NCAP ASSESSEMENT 

WRAP AROUND DISTANCE : 

the trace point which is recieved from the front structure, the tape of one end with the requried lenght and the tape of another lenght is said to touches the front end strcuture of the hood 

 

Child impact zone - 1000 WAD to 1500 WAD

Adult impact zone - 1500 WAD TO 2100 WAD

 

SIDE REFERENCE LINE : 

The trace of the highest contact between the straight inclined line and the vechicle contact point. 

 

When ths side reference line lies on the fender, then the wrap around distance is more, when the side reference line lies on the hood, then the wrap around distance is less. 

More the wrap around , distance lesser the head impact zone. 

 

4. DESIGN APPROACH 

In this project of HOOD DESIGN , Siemens NX is used for designing and the development of the hood. the hood basically consist of inner panel, outer panel, latch and striker, hinges , hinge reinforcement and latch and striker reinforment. 

 

THICKENSS : 

HOOD INNER PANEL : 0.75 MM

HOOD OUTER PANEL : 0.75 MM 

REINFORCEMENTS : 1.5MM 

 

INNER PANEL :

Inner panel is also known as the structural region of the hood. this panel design plays an important role in EURO NCAP design consideration. for the safety and NVH, the engineers are more focused on the hood inner panel. embosses in the inner panel gives more strenght and toughness to the hood. but the embosses are to transfer the force impact during the accident must be more over away from the frontal area . so embosses must be placed in such a direction where the forces of impact must tranfer away from the frontal region to avoid impact to the driver and passenger. 

 

OUTER PANEL : 

outer panel is said to the skin of the metal body. it is mainly for styling purpose. the outer panel is assembled with the inner panel where the hemming is provided in the outer panel to get closely assembled without using any fastners or welding purpose and also for the water leakage purpose. 

 

LATCH AND STRIKER :

 this is used as a secondary locking of the hood. where as the primary opening is placed under the driver seat, the primary opening helps to access the latches with the small opening. the latch is placed in the engine compartment where as the striker is placed in hood. 

 

HINGES : 

hinges are used to join the parts together and revolute together along the trajectory path.

 

REINFORCEMENTS :

when ever there is any addition of weight added to the particular region , there will be some losses of material strenght in that region to over come that reinforcements are used. the thickness of the reinforcement may vary from 1mm to 1.5 mm accoring to the weight acting.

 

5. MANUFACTURING PARAMETERS

5.1 DEEP DRAWING :

punching or blanking is removing a large piece or strip of a sheet metal during forming operation. where the small piece is discarded then it is called puching operation, where as a large piece is made as scrap and small piece is made for usage then it is called blanking.

deep drawing is the one of the sheet metal forming operation in which the sheet metal blank is drawn into desiered shape with the help of its tensile and compressive forces.

PROCESS : 

step 1 : after the blanking process the sheet metal blank is placed inside the die. 

step 2 : the shank holder grips the sheet metal blank, in between the punch and die with required amount of pressure. 

step 3 : after gripping the blank, the deep drawing punch stretches the blank inside the die, during this operation the shank holder pressure is continusly maintained with free movement of material.

step 4 : after the sheet metal drawing operation, remove the finished part from the die. 

5.2 HEMMING 

It is the forming operation in which the edges of the sheet metal are folded or get folded over another part to get a tight fit. this is also used as adding strenght to the material and removing the sharp edges. 

 

design consideration of hems : 

open hem : 

open hem radius / sheet metal thickness >= 0.5

return flange height / sheet metal thickness >= 4

rolled hem :

external radius of rolled hem / material thickness >= 2

rolled hem opening / material thickness >= 1

tear drop hem : 

radius of tear drop hem / material thickness >= 0.5

return flange height / sheet metal thickness >= 4

hem opening / material thickness >= 0.25

closed hem : 

return flange lenght from outside the bend => 4 x material thickness 

5.3 EMBOSSING

It is a stamping process for producing a relief in sheet metal, raising or an sunken design. this process is made by means of male and female dies inbetween which by passing sheet which forms a desired shape. 

design consideration of embossing :

 

5.4 MASTIC DATA / GLUE 

Mastic is a fibrous adhesive which hardens into a long-term seal . it is used to bond the automotive exterior panel to the interior panel 

   

 

 

6. TRAJECTORY LINE 

the trajectory of the latches is the path where the motion hinges rotates in the parabolic path, this trajectory line defines the path of the latch and striker to get correctly engaged each other. 

 

7. ASSEMBLY OF HOOD 

     

 

8. CONCLUSION 

hence hereby the design of hood with the various design paramters and manufacturing feasibility of hood is shown and designed under the regulation of EURO NCAP standards.