Challenge

Hood design-Week 2

KKonduru Yaswanth2 Mar 2021

HOOD-BONNET

Whats is mean by HOOD or BONNET

Bonnet is main component of a car at the front portion. It is used to decorate the car and add luxurious look. The shape of the bonnet is made aerodynamic in order to minimize the air effect. Bonnet is generally used to access the parts easily such as radiator, engine and many other parts. In automotive world the weight optimization plays an important role. In this paper material changes is applied to the bonnet for the same design and finally showing the stiffest bonnet and less weight component. For designing the hood 3D model CATIA V5 R19 OR UGNX is used, then import the cad model in to hypermesh and pre-processing is done using Hypermesh, solver is Optistruct Fea which helps to do the analysis for hood. For results visualization Hyperview and HyperGraph is chosen.

A car hood is the metal part that covers the engine of an automobile. The term car hood is a North American term, used primarily in America and Canada. Hood comes from the Old English word hod which means a hood, a soft covering for the head.A car bonnet is the metal part that covers the engine of an automobile

SAFETY REQUIREMENT WHILE DESIGNING HOOD

Safety is the most important criteria in automobile designs which concentrates on both pedestrian and occupant safety. The pedestrians are the most vulnerable road users and are at high risk of traffic accidents. The major reason for the fatality of the pedestrian in traffic accident is due to the head injury resulting from the hard impact of the head against the stiffer hood or the ground. This leads to the necessity of new inner hood panel which is less stiffer and pedestrian friendly.

The head impact analysis on the present hood of the car was done to study the response of the adult head form at two different locations. Structural and modal analysis for the same present hood assembly was done to observe the local and global stiffness. In order to reduce the head injury of the pedestrian the local stiffness over the area of head impact has to be reduced thus the new design of hood inner panel was focused on that and the structural and model analysis was done for the new design. The design with lesser local stiffness and similar global stiffness compared to the existing hood was finalized.

Vehicle safety factors should simultaneously consider occupant and pedestrian safety, given that pedestrians are the third largest category of traffic fatalities. Most pedestrian deaths occur due to traumatic brain injury, resulting from the hard impact of the human head against the vehicle's stiff hood or windshield.

Therefore, how to design a pedestrian-friendly vehicle and propose a new hood structure is a matter of urgency for minimising pedestrian head injuries.

In this study, three kinds of sandwich hood structures are proposed for reducing pedestrian head injuries, including carbon fibre-reinforced polycarbonate, carbon fibre-reinforced foam and aluminium-reinforced polycarbonate.

The finite element method is used to simulate the impact between the vehicle's hood and the headform impactor. The software used in simulation is LS-DYNA. The results predicted by the headform-hood tests show that the hood structure with aluminium-reinforced polycarbonate material provides enough absorption capability to protect pedestrians from the impacts of accidents. It is also stiff enough to keep pedestrians' heads away from the inner parts of the engine cavity.

PURPOSE OF HOOD

Bonnet is an important component of the front portion of the car which is used for many purposes. Bonnet is used to decorate front portion of the car and to add luxurious look.

It is made aerodynamic in shape to reduce air effect. Generally it is used to cover car engine, radiator and many other parts, therefore bonnet must be designed in such a way that all the maintenance parts should be ease of access and it should give a minimum impact of external disturbance on the engine.

When car come across any accident from the front portion most of the time bonnet system gets damaged and absorbs some part of impact energy resulting from crash.

SELECTION OF MATERIAL FOR HOOD

To simulate head impact phenomenon between head form impactors and composite bonnet. Then the behaviour of three identical bonnets made of steel, aluminium and composite have been investigated by the developed model.

WHY ALLUMINIUM for Car sheet metals

Due to its lower weight, the aluminium hood exhibits lower emissions during its use phase. Consequently, for indicators where the vehicle use phase is an important contributor to the environmental performance, the overall result of Aluminium hood exhibits a significantly lower impact than the steel one.

It is shown that the energy absorption of aluminium bonnet is smaller than steel and composite ones and for keeping the aluminium bonnet at the same level of stiffness, it is necessary to increase the thickness.

ALUMINIUM MATERIAL PROPERTIES FOR HOOD

ANCAP

ANCAP provides measures for the assessment of pedestrian protection performance of a passenger car experimentally by firing subsystem impactors representing a child head, adult head, upper leg and lower leg at a specified angle and speed to the front end of a stationary vehicle. The resulting injury measures from these physical tests are assessed against the bounds specified by the protocols shown in Figure 1. This study focuses only on child pedestrian head impact to the outer hood panel and do not include inner hood, upper or lower leg impacts defined in these protocols.

As a result of the implementation of these regulations, vehicle manufacturers face technical challenges associated with the investigation of optimal hood panel configuration to meet the requirements of ANCAP while retaining or maximising styling flexibility with minimal modifications to the general architecture of the design.
HIC value are used to predict the risk of engine hood to the pedestrian and the level of severity of engine hood design when the collision occurs. The value of HIC depends onthe engine hood design, materials, impactor type and structure. HIC is calculated according to Equation be

'a' is the resultant acceleration in g

t1, t2 is two time instants in seconds

which define the start and end of the recording when HIC is at maximum. Values of HIC in the time interval t1–t2 is greater than 15 ms are ignored for the aim of calculating the maximum value. In this study, HIC value is calculated using DIAdem for the pedestrian head impact on automotive hoods.

ANCAP plays a vital role in not only informing consumers of the differences in safety performance of new vehicles entering the Australasian vehicle fleet, it also advocates for improved vehicle safety design and specification through public education campaigns, advocacy activities and engagement with governments, corporate fleets, the media and consumers.

BIW DESIGN CONSIDERATION

CONCEPT DESIGN PROCESS

Product proposal & planning:

Team of marketing evaluates product need & feasibility of product in market and finalizes product proposal document.

Product concept definition:

Requirements consideration of customer, legislative, organization.

Business case:

Target market, manufacturing, costing strategically considered for business case preparation.

Design Gate Review 1:

To review product concept sheet.

CFT team formation:

Benchmark:

Competitive vehicle are bench-marked to to target weight & cost.

Preliminary design concept:

Engineering converts customer, legislative, organization requirements into technical features.

Feasibility drawing:

Drawing release for feasibility study.

Make / buy:

To finalize design manufacturing & assembly process at supplier and OEM end.

PPAP (Production part approval process) plan.

Prototype build:

Preliminary concept evaluation, feasibility & testing.

Design Gate Review 2:

Prototype issues & action plan.

Production drawings:

Drawings released for tooling part development.

Legislative certifications:

AIS, CMVR, Homologation requirement fulfilled.

Design Gate Review 3:

DVP, part development plan, test reports, facility plan.

Pilot batch production:

Design improvements based on pilot batch feedback.

Design Gate Review 4:

Technical clearance.

Start of production

Design Gate Review 5:

Technical clearance

SHEET METAL DESIGN

While designing components top priority is for function and second is for cost effective manufacturing process selection.

This can be achieved in design by:

Keeping part simple
Lesser material yield
Consideration of minimum manufacturing stages

OBJECTIVES OF SHEET METAL DESIGN:

Function: Most low stress (and many high stress) components requiring moderate stiffness can be created from sheetmetal. Sheetmetal is particularly effective for parts that function as containers, chutes and gates, but can effectively be used for mounting brackets as well.
Attachment method: Sheetmetal parts are typically joined by welding, riveting or via fasteners.

DESIGN TIPS

Study Manufacturing process available.

Shape: Use simple shapes such as straight cuts, bends, and punched holes. Whenever possible, avoid internal cuts, curved cuts, and close-fit holes.

Simple: Complex sheetmetal parts are difficult to manufacture using tooling available. Typically, complex sheetmetal parts can be broken down into multiple simple parts.

Material specification: Choose a optimum material and thickness.

Tolerances: In modern industry parts are made using high precision CNC lasers and bending equipment. However, sheetmetal features are generally cut by aligning the layout lines by eye, so design sheetmetal parts to have large feature tolerances.

Order of operations: The order of forming operations is important for sheetmetal parts. Holes and cuts must be created prior to bending. The bending sequence can typically be performed in only one or two ways. Be familiar with the available tooling and processes and do not design parts that cannot be fabricated using the available tooling in lab.

HOOD DESIGN DATA

In this design i consider inner panel and outer panel thickness be 0.75 mm.

Striker reinforcement thickness be 1.5 mm.

Tolerance value between outer panel and inner panel be 0.2 mm.

EMBOSSING

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, or by passing sheet or a strip of metal between rolls of the desired pattern.

Metal sheet is drawn through the male and female roller dies producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet.
Emboss should be in 7 degree to 25 degree inclinte in angle and it should not be in 90 degree angle,why because when we do stamping in manufacturing the stamping tool fits the sheet metal hence it will not come out of that sheet metal,So this is the main reason why the emboss face is in angle.

Characteristics of the metal embossing process include:

Its ability to form ductile metals,
Its use in medium to high production runs,
The ability to maintain the same metal thickness before and after embossing,
The ability to produce unlimited patterns, depending on the roll dies, and
The ability to reproduce product with no variation.

Located within the embossing stand itself are two engraved and mated hardened steel rolls, geared together to maintain top-to-bottom pattern registration. The width and diameter of these rolls depends on the strip width, material thickness, pattern depth, and material tensile strength and hardness.

In most machines, the upper roll blocks are stationary, while the bottom roll blocks are movable. The pressure with which the bottom roll is raised is referred to as the tonnage capacity. This figure also depends on the aforementioned parameters.

Embossing machines are generally sized to give 2" of strip clearance on each side of an engraved embossing roll. Many embossing machines are custom-manufactured, so there are no industry-standard widths. It is not uncommon to find embossing machines in operation producing patterns less than 6' wide all the way up to machines producing patterns 70"+ wide.

The illustration that follows provides a two-dimensional look at a typical embossing line setup with an embossing roller in the middle. The illustration shows the metal sheet entering the roller, and then the embossed sheet leaving toward the drawing rollers.

Embossed metals are used in industry for two reasons: aesthetic and functional. Aesthetic applications also include appliance panels, building products, elevator panels, garage door panels, automotive trim, metal office furniture, and others.

Functional applications are those in which a performance characteristic is enhanced. This can include a metal products ability to disperse liquid more effectively, reduction friction and static, increase a metal panel’s stiffness and rigidity, increase a metal surface area for acoustic or heat transfer applications, and improve traction.

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:

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

MASTIC SEALANTS

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 has attached together. It adheres to just about any material making an all-purpose type of sealant.

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 panel. 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 influence of 80mm diameter.

PROS

One positive characteristic of mastic sealant is that it has a very smooth exterior while keeping its rigid form underneath.

Surfaces do not have to be primed when using this type of sealant, and although applied thick, it adheres smoothly to any surface. It is important that the area to be joined or sealed be clean and dry, just like any other sealant on the market.

Mastic sealant may be used outdoors as well because of its waterproof quality. It can be applied on rain duct leaks outdoors, for example.

It is also favored for areas under high or low temperatures such as heater vents or drier vents and contains ultraviolet inhibitors to make sure that it is protected from damaging effects of the sun that will often weaken other types of sealants. That makes it a good choice for use on roofs, or any surface that is constantly exposed to sunlight. Most mastic sealants will also work well with metal because they do not corrode over time.

it functions well in areas with mild vibration and heat, like heating ducts.

CONS

Mastic sealant is not recommended for areas that have too much joint movement, or anything that will be moved a long length.

It works well with constant pressure on it, but not constant movement.

It also works best when applied thickly and is not recommended if only a thin layer is needed such as touch ups. Another sealant is a better choice for those types of repairs

HEMMING PROCESS

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. Conventional die hemming.

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.

In between the outer panel and inner panel there will be glueing after or before hemming process because to reduce NVH and also sticking the two panels.

Types of Hemming

conventional die hemming

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

Roll hemming

In roll hemming, the hemming roller is guided by an industrial robot to form the flange.

While manufacturing the hood we choose Roll hemming only.

RELIEF CORNER

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

We leaving 2 mm from sheet metal for Roll hemming process.

POSITION OF STRIKER AND HINGE

For the proper opening and closing of the hood, the striker should be perpendicular to the trajectory of the hood. For this, hinge is assembled at its position. Once it is placed, hinge axis is drawn.

To check 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.

In between the two hinges the striker is perpendicular to the midpoint of two hinges,Why because while closing and opening of latch and striker the opening position be similar actions.