Hood design-Week 2

Hood Design in NX CAD.

Objective:

Design hood outer panel, inner panel and reinforcements with the given outer hood skin, master section and design parameters.

Introduction:

The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment (or trunk on rear-engine and some mid-engine vehicles) for maintenance and repair. In design perspective hood should meet some specific conditions like pedestrian safety, hood head zone for the lock striker, force distribution when subjected to frontal collision (occupant safety), manufacturability etc.

A typical hood assembly consist of hood outer panel, inner panel, latch and striker, hinge, hood stay. Hood stay is an apparatus for supporting the engine hood of a moto vehicle in its open position. The purpose of opening the engine hood is for inspecting engine room, replenishing cooling water and engine oil, changing parts and making repairs etc. Common types of hood stays are Support Rod and Gas Stay. Support rods are manually operated and they are cost effective and simple to design whereas gas stays require no man power but they are costly. Hood are typically made out of the same material as the rest of the bodywork. This may include steel and aluminium. Deep drawing, hemming, blanking and piercing are the common sheet metal operations that are used in manufacturing hoods in automotive industries.

Requirements:
Hood Thickness and manufacturing considerations.

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm
• Minimum fillet radius = 3mm+Thickness (example: When thickness of inner panel is 0.75mm we need to maintain minimum fillet radius 3+0.75=3.75mm)
• No sharp corners inside the component
• No curvatures lesser than 5mm
• Small embosses should not exceed the maximum depth of 6mm (staying on the safe side)
• Mounting areas and welding areas need to be flat
• Provide appropriate corner relief on the area of curvature

FunctionalAndSafetyRequirements:

1. The most important safety requirement to be considered while designing the Bonnet is the frontal collision requirements.
   The design intention of the hood according to the frontal collision requirement is that the hood crushes and dissipates forces in the upward direction and to the hard points on the hood thereby deflecting the force on to the body and not the passengers.

2. The second major function of the hood is the opening and closing of the hood. This is done with the help of the latch and striker. To position the latch and striker effectively, we first position the hinge and draw the hinge axis. Now, using the hinge axis from the centre we draw a big circle to the position there we need to place the latch.

Following parts are using in hood assembly for this report:

1. Hood outer panel

1. Hood inner panel
2. Hinge assembly
3. Striker assembly

Inner Panel:

• In the inner panel only we can research & implement the safety of pedestrians & as well as the driver. In this panel only we can attach the reinforcement, embossed, mastic points etc.
• It is an object of the present invention to provide a hood inner panel capable of reduction of a reaction force of the hood inner panel even if a level of deformation of a hood of a vehicle increases, & ensuring a sufficient energy absorption capacity.

Outer Panel:

We can also call it as cover of inner panel. It is the part, which gives luxurious look to the hood or bonnet. Outer & inner panel can not join by any welding process like spot welding or rivet, which spoil the outer look of a car. The outer panel is generally extracted model from the prototype design.

Hinge Assembly:

Hinge is a component that fixes the hood to the fenders of the car. The latch must be fixed perpendicular to the hinge axis so that the hood opens or closes properly.

Striker Assembly:

Latch & striker is used for locking the hood with the car. It is usually placed on the space provided on the inner panel.

The process involved in designing hood as a sheet metal operations is:

• Blanking
• Hemming
• Punch cutting or piercing
• Deep drawing

• Embossing

Hemming:

• Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180 degree. Automotive body panels & parts such as deck-lids, trunk-lids, doors, hoods & tailgates are formed by hemming processes.
• Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller & forms the flange. Roll hemming operation can also be divided into several pre-hemming & final hemming process steps.
• Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a forming operation in which the flange is formed with a hemming tool after the drawing & trimming operations have been completed.

While doing the hemming process a relief angle is formed as a product of hemming when attaining at the corner of the sheet.

Deep Drawing:

• Deep drawing is a manufacturing process that is used extensively in the forming of sheet metal into a cup or box-like structures. Pots & pans for cooking, containers, sinks, automobile parts, such as panel & gas tanks, are among a few of the items manufactured by sheet metal deep drawing.
• A deep drawing of sheet metal is performed with a punch and die. The punch is the desired shape of the base of the part, once drawn. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. For many calculations, the sheet metal thickness is assumed to remain constant. There are changes in thickness in certain areas, due to force involved.

Embossing:

• The sheet metal embossing operation is commonly accomplished with a combination of heat & pressure on the sheet metal, depending on what type of embossing is required.
• A sheet metal is drawn through the male & female roller dies, producing a pattern or design on the sheet metal. Depending on the roller dies used, different patterns can be produced on the sheet metal.

The embossing process can produce a variety of patterns. Some of the most common patterns include stucco, leather grain, wood grain, weather grain, and rough sawn cedar. Most embossers will tool to form any needed pattern, depending on the cost parameters involved.

Materials commonly used in the metal embossing process include:

• Aluminium (All Alloys)
• Aluminium (T1/T2)
• Brass
• Cold rolled steel
• Copper
• Galvanized steel
• High strength, low alloy, steel
• Hot rolled steel
• Steel (All Alloys)
• Zinc

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.

Mastic Sealants:

The main purpose of the outer panel is for the athletic looks. Thus, we cannot use bolts for welding. This has to be done with the help of hemming and mastic sealants. Mastic sealants are elastic compound that behaves like the rubber. It is placed between the outer and inner panels. Initially it is 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 80 mm diameter.

Draft Analysis:

• 5 degrees of draft analysis is made to the inner panel to find any negative draft. this process is done because we need to develop and submit a positive design to the manufacturers.
• we can see that there are no negative drafts by the inner panel, hence the design is positive and ready to manufactured.

Conclusion:

In this project complete hood assembly is designed by designing inner and outer panel which meets manufacturing requirements. Inner panel is designed with reference of master sketch. Hinge and latch striker reinforcements are designed and all components are assembled together.