Fender Design Challenge

Objective: To design BiW fender mounting using sheet metal parameter on the Class A surface with given skin data and master section .using NX CAD.

Abstract:

Fender is body in white part of an automobile (vehicle body) which houses or frame wheels in order to prevent sand, mud, rocks, liquid and other road debris to throw into air when trye are in motion, which may lead to pedestrian accident and protect the engine compartment from damages. Apart from the pedestrian safety it serves the purpose of providing aerodynamic shape to car thus to perform better at higher speeds and give aesthetic look to body.

Shape of fender differ from vehicle to vehicle depending upon the body styling and purpose. It is mounted on the frame with fasteners and also provide provision for mounting of other part like bumper and baffle /mudguard on it to fit as assembly to the complete the car body. Front and back fender are represented in red colour in fig.1

Most passenger automobiles have four fenders, one over each wheel. For vehicles with narrow car body that exposes the tire, the fender is exposed curve over the top of the tyre. For wide body vehicle that cover the tire and is not directly visible from above the car body.

Wheel wells tend to be much larger than the diameter of the tire because they do not move with the tire suspension and consequently must be large enough to allow the full range of tire motion on the suspension without touching the interior of the wheel well.

2.1 Types of fender

Full bumper type:

Full bumper type is traditional type of fender where more surface area covered (fig.2). This type is used in old design of automobiles where it increases the overall weight and thus reduces performance.

Half bumper type:

Half bumper type is modern design which serve the technical requirement of full fender using less material (fig.3). Productivity of half bumper is more by reducing the size of blank and tooling cost. As the material consumption to produce the part is low result is reduction in overall weight of steel body thus increase the performance and aerodynamic aspects of car.

Fender are mounted on five important regions with car body i.e.

• Drip mounting area
• Sill mounting area
• Bumper mounting area
• A-pillar mounting area
• Splash/ Baffel mounting area

3. Design Methodology

Given data:

Step 1: Design of Drip area as per Master section

With the help of data given for Drip area in master section(fig.4), it is designed using curve and surface feature tool in NX CAD (fig.6).

• Two planes are drawn away from both ends on the offset surface face at 150mm and 200mm as per master section respectively. These are considered as clearance area for the mounting of front head light housing and cowl installation. Thus the effective length of the flange will be 79mm.
• The starting edge of flange is created by using curve on surface and trimmed it accordingly to obtain smooth curvature at the bending area.
• Using law extension command all surfaces from A to L are created with the draft parameter.
• Maximum depth allowed for the drip area in master section is 40mm. In order to be in safer side here we consider 34.86mm which is consider to avoid spring back effect during drawing operation in manufacturing and reduces tooling cost. Smaller drip area depth also help the fastening tool to reach easily while assembly process of fender at assembly line.
• Two darts patterns are added on the longer side in order to provide stiffness and add strength to part. So that during motion it does not vibrate and impart forces to fender outer surface.
• Three Nos. M4 holes are created inside the rectangular emboss with flat surface for mounting on engine compartment and sufficient bolt head clearance area also consider.
• All sharp edges are rounded off and recommended radius bends are given.

Step 2: Design of Bumper mounting area

In bumper mounting area also darts and embossed surface with bolting holes are provided. M5 bolt holes are consider to assemble the bumper and fender on the car (fig.7).

For reference we can see the assembly view of fender to bumper is as shown in the fig.8.

Step 3: Design of Baffle area mounting

Baffle mounting or mudguard are clip fit type of mounting on the inner side of the fender arch area over the tire(fig.9). It protects the car engine compartment and waking by pedestrian from causing injuries from chip out debris on road when car is in motion. It are mounted on the fender using special type of locking clips which are made up of plastics ( fig.10) Six mounting holes with surface resting projection of 5mm are provided over the arch area to give maximum strength to baffle during its fitting (fig.11).

Step 4 : Design of Sill mounting area

Sill is the panel (metal plate) directly below the bottom of door supporting the floor and may be used to combine floor and body (fig.12). Bottom end of fender is mounted on the sill body for reinforcement of fender panel, thus sill mounting position is designed with holes and emboss. M5 fasteners are used to fix fender on sill body (fig13.).

Step 5: Design of A-pillar mounting

The A pillar is the structural pillar that ties the body to the roof. This makes the sides of the windshield to rest. Front fender are fastened to the A pillar to form robust structure. In below image (fig.14) A,B,C and D represent different type of pillar used in car which sharing the load of roof and glasses fitted across the body. Sill mounting is designed in circular shape with embossed surface and M10 hole provision. Two dart stiffeners used in sheet metal parameter to add stiffness and strength at local area (fig.15).

Step 6: Adding Thickness to surface design.

Thickness of 0.75mm inward on the final sewed surface of fender to give the sheet metal parameter (fig16).

4.Conclusion:

Hence, all mounting points for fender designed from the skin data and master section received from styling team and material thickness of 0.75mm applied uniformly using NX CAD.