Hood design-Week 2

HOOD:

       A car hood is also called as "BONNET" in some countries is the hinged cover that rests over the engine bay of a front-engine vehicle. The car hood protects the engine and connected parts from the elements while providing easy access for repairs and maintenance.

STUFFS UNDER THE HOOD:

• Engine

• Alternator

• Battery

• Belts

• Cylinders and Spark Plug Wires

• Piston and Crankshaft

• Oil Fill Cap and Dipstick

• Radiator

• Transmission

• Reservoirs

BiW CLOSURES CATAGORY:

• HOOD/BONNET
• FENDARS
• REAR DOOR
• FRONT DOOR
• TAIL GATE/TRUNK LID.

MAIN FUNCTION IN HOOD:

The hood (American English) or bonnet (Common English) is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment, or trunk (boot in Common English) on rear-engine and some mid-engine vehicles) for maintenance and repair.

Design parameters

Hood Thickness Information

    Outer Panel Thickness = 0.75mm

    Inner Panel Thickness = 0.75mm

    Reinforcement Thickness = 1.5mm

Master Section

DESIGN PROCEDURE:

1. Open all the (.igs) & (.stp) file and save it as cat prt file.
2. Create an Assembly part file.
3. Open all the cat part file, Create tooling axis and copy the Outter pannel and paste special as link as inner pannel. 
4. According to the given master section, start creating the Hood inner pannel.
5. Create Primary emboss, secondary embose and Mastic.
6. Create Deboss for Hinge.
7. Convert the Hinge part from Surface to solid.
8. Using the Trajectory method Align the striker according to the primary emboss and secondary emboss.
9. Create the deboss for striker.
10. Create reinforcement for hinge and striker.
11. Create Hemming operation for outter pannel.
12. Create corner relief at the bend.
13. Finally make it as solid using thicken method.
14. And create intersection for both inner pannel and outter pannel. verify using the intersection.

Tooling Axis:

Tooling axis is created along Angle/normal to curve, This tool is created along in line created between two points ploted at the outter pannel of the given class A surface hood. (note; The angle given is 90 deg).

1.Hood outer panel

Outer panels are the aesthetic elements of a car. It is the styling team who provides the skin for the outer panel. The shape, position and size of the hood should satisfy the safety norms. So while designing the hood we should give more importance to pedestrian safety. The outer panel is attached to the inner panel by hemming. So, it is necessary to provide required hemming flange and reliefs for the hemming operation. We also provide mastic sealants between outer panel and inner panel to reduce vibration.

 

2.Hood inner panel

Inner panel is the part that gives strength and rigidity to the outer panel. The master section represents the initial emboss shape and size. Then we provide the emboss for the striker and hinge elements after fixing the location.

Hinge:

    The hood hinge is a pivot and bracket mechanism that makes it possible for you to open and close your hood. Each car typically has a pair of hood hinges installed in the front of the vehicle.

Striker: 

Striker is used to lock the hood with latch body.

 

3.Reinforcement

Reinforcements are provided according to the design requirements. Mainly it is provided at the hinge and striker regions to improve the strength locally. Usually thickness of reinforcements will be higher than that of the inner panels and the value varies according to cost and requirement. According to the design requirement here it is given 1.5mm thickness to both hinge and striker reinforcements.

 

4.Striker Trajectory

Striker trajectory is given by the circle drawn from the hinge axis point. Hinge axis point is the centre point of the hinge axis. First, we can fix either the striker or the hinge. If we have fixed the hinge position then we should plot the Trajectory circle for the striker. For proper mating condition the striker axis through the tip of the striker should be tangential to the striker trajectory.

5.Emboss definitions

Throughout the inner panel we provide different embosses. We can increase the stiffness of the inner panel through these embosses. The shape and size of the embosses also determines the direction of the force distribution resulted from frontal collision. The force should be always distributed away from the passengers. Here in the figure the embosses are designed in such a way that the force is directed to either sides of the car.

6.Mastic Data

Hood commonly possess large surface area and hemming can only be provided through its boundary. We cannot use other joining techniques like welding, riveting etc because they leave marks on the outer panel which spoil its aesthetic appearance. So, mastic sealants are used to stick the inner surfaces of outer panel and inner panel. Mastic sealants are elastic compound that behave like rubber. It is applied between the inner and outer panels at specified spots. Each spot of mastic sealants has its effect around a circular region of 80mm diameter. Thus, the mastic points are arranged in such a way that it covers the areas away from the hemming which are more vulnerable to vibrate.

7.Deep Drawing

Deep drawing is one of the most widely used processes in sheet metal forming. Apart from its use in many other sectors, it is applied in the automotive industry for the manufacturing of car body parts. The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions.

Sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter. This is achieved by redrawing the part through a series of dies. The flange region (sheet metal in the die shoulder area) experiences a radial drawing stress and a tangential compressive stress due to the material retention property. These compressive stresses (hoop stresses) result in flange wrinkles. Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

 

8.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 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. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas or material roll-in. This is why it is important to provide required reliefs at the corners.

There are two types of hemming operations,

1. Conventional die hemming

In conventional die hemming, the flange is folded over the entire length with a hemming tool.

2. Roll hemming

It is the roll hemming process that is used for automotive sheet metals. Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps. Roll hemming is very flexible to use and tool costs are significantly lower as compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller which follows a defined path.

CORNER RELIEF CUTOUT:

sheet metal sections are removed from the model. You can apply corner relief automatically to all corners or manually to individual sets of corners. Relief helps to control sheet metal material behavior and to prevent unwanted deformation during unbend operations.

Final Assembly:

Daft Analysis: