Designing and assembly of BIW component

Objective

To understand and study the design methodology and mechanism that goes under designing and developing an automotive hood to achieve maximum safety for everyone in and around the vehicle.

Introduction

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. Hood is one of the other major closure systems in a vehicle and is fundamentally a reinforced skin with many design quality and safety regulations
Hood may come with several subcomponents, but the two most important ones are the outer and inner panels.

The inner panel serves as a structure for the vehicle to dissipate and channel shock waves at the event of a crash while the outer panel serves more as an aesthetic for the automobile’s overall presentation and to channel airflow over the vehicle. Hence, both require critical precision as well as a dedicated strategy right from the design conceptualization to the production step.

Once the design of the outer and inner panel is finalized the manufacturing process begins. They are generally manufactured by the deep drawing process. Once manufactured, the outer and inner components are united to form one unit by one or combination of several types of joining methods such as hemming, riveting, gluing, and spot welding to name a few.

However, for joining of inner and outer panel Hemming process is used. Hemming is done with the help of rollers for maintaining the consistent surface joining methods after the part has been deep drawn and trimmed.

Hemming

Hemming is widely used in the automotive manufacturing industry to assemble an outer closure panel and an inner
closure panel by folding the flange of the outer panel over the edge of the inner panel. This process is performed by
material suffered a plastic deformation. The neat and compact combination of these methods that do not show up to join the resistance welding. Sometimes used special adhesives to improve strength.

The purpose of Hemming projects is to fold and fold the outer sheet metal panels on the inner sheet metal panels in various parts, such as the vehicle's door, engine hood, trunk lid, usually composed of two sheet metal panels, and to join the two panels together

Hemming Stages

1.Before Hemming:-

The production process of a system starts with the method of deep tensile on the press lines of its components. After the component is formed on the press lines, the outer sheet is crimped to the edges to be hemming. This process is called flanging

2.Bonding Process:-

Bonding is the joining process by applying adhesive to the inner panel or the outer panel in various chemical properties before joining by the hemming method. The purpose of the bonding process is to strengthen the consolidation process, prevent corrosion problems by providing tightness, and during the use of the vehicle.

3.Marriage Process:-

The marriage process is to bond the inner sheet and outer sheet together after bonding. The marriage process can be done by the operator or by robotics. Depending on the need of the process, additional spot welding can be done after the marriage process. After completing the marriage process, it goes to the hemming phase

Hemming Methods

1. Die Hemming Method

It is the oldest automatic hemming method. the bend is made by press force. Hemming is performed in two steps: Pre-hemming and Final-hemming.

2. Table Top Hemming Method

It is a method of hemming using a table-top mold specially designed for the product to be fully produced. the bend is made by press force.

3. Robotic Roller Hemming Method

Robotic Roller Hemming method is a method that is not similar to other methods, is accompanied by a cylinder mechanism operating in a circular motion on the 6th axis of an industrial robot. Robotic roller in the hemming application,
cylinder mechanisms are used at different diameters according to process needs. These are called hemming heads.

Hemming heads can be purchased as standard or specially designed according to process requirements. The geometric
differences of hemming heads have an effect on the bending process. Hemming heads should be designed and manufactured in the form of the corner of the part to be hemmed, differently from the form of the twist, or supplied from suppliers on the market according to their suitability

Die hemming and table-top methods, although not economical in terms of initial investment cost, in terms of process efficiency and faster processing times. Therefore, they are preferred in high-capacity production

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 bypassing sheet or a strip of metal between rolls of the desired pattern.

Deep Drawing

The deep drawing process is a forming process that occurs under a combination of tensile and compressive conditions. A flat sheet metal blank is formed into a hollow body open on one side or a hollow body is formed into a hollow body with a smaller cross-section. [DIN 8584]

Deep drawing processes are divided into three types:

• Deep drawing with tools
• Deep drawing with active means
• Deep drawing with active energy

Bonnet influence the following performance measures:

• Overall vehicle mass
• Weight distribution
• Height of vehicle center of gravity (the bonnet and the boot lid are usually located
  above the C of G of the vehicle, hence weight reduction is beneficial)
• Vehicle drive-by noise intensity

Purpose of Hood

The bonnet system is an access panel to the engine compartment to enable maintenance of power train, drive belts, battery, fluid levels, and lamp units. It is fundamentally a reinforced skin panel with many safety and quality requirements.

Design Boundary Conditions for Bonnet

Design options assessment -Design Failure Modes and Effect Analysis

The height, weight, and age of the pedestrian all play a role in the kinematics of the event and
in his ability to survive. Most fatalities for the younger population are related to brain damage
caused by head impact on the bonnet.

Evaluation of pedestrian safety for a bonnet must be carried out in the context of its
surrounding elements:

-Vehicle styling, size (wrap around distance “WAD”) and under bonnet clearance to
other elements (considered as hardpoints).
-Local bonnet stiffness is influenced by mounting point stiffness such as hinges, bump
stops and latches.
-This is better understood by superimposing the kinematics of a dummy onto the test
conditions

Priorities Matrix while Designing Both outer and Inner Pannel

Design Data

As per the standard data as given

Hood Thickness Information

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

Master Section and Specification :

Upon designing the initial structure based on the master section, embossing was performed to strengthen the structure as well as to integrate channels to direct shock flow and dissipate maximum energy away from the cabin. With successful designing of these channels using the process of embossing, latch and hinge placements are designed for attachment of this structure to the vehicle.

Once the structure for the inner panel is prepared, reinforcement is provided to compensate for the strength drop which occurred due to the inclusion of latch and hinge placement. At this stage, the NVH team also contributes to implementing
major design changes and the inclusion of components to reduce vehicle vibration and noise control.

Apart from hemming, the center region of the inner panel structure is kept in contact with the outer panel using mastic sealants. Mastic sealants are rubberized components placed between the outer and inner panel to provide annexed contact. These sealants help maintain the outer panel aesthetically pleasing as well due to the absence of welds, nuts or bolts in the process of consolidation

Design

Hood Assembly

Outer Panel

Inner Panel

Cross Section

Hemming

Mastic Sealant

Mastic Sealant generally have an influence of about 80 mm

Striker Mechanism

Reinforcement Area:-

Hood Opening and Closing Trajectory

The trajectory for opening and closing the hood is considered to be an important factor where the striker center axis is coincidental with the hood center axis . The striker axis is perpendicular to the circle which is drawn by considering the center of the two hinge axis.

Shock Flow

For minimizing the impact of injury when collision with the hood a flow pattern is provided to minimize the impact of injury so that there is minimum damage. This is done for forcing the forces towards outwards with the help of this internal flow structure.

Conclusion

1. The following factors are considered while designing and manufacturing the hood inner and outer panel as per EuroNcap safety standards.

2. Then only it works well in terms of pedestrian and occupant safety. EuroNCAP (European New Car Assessment
Program) and other independent vehicle assessment bodies have been instrumental in increasing public awareness of the effectiveness of design for pedestrian safety.

3. Additionally, their test results are factored into the insurance ratings that are delivered for new vehicles. The objective of these measures is to reduce the number of road accident fatalities and the severity of injuries sustained by pedestrians involved in a collision with a vehicle in urban traffic.

References

1.Design case study Bonnet and Boot Lid - The Aluminium Automotive Manual