Roof challenge

Objective:

To design the Automotive Roof based on the given styling surface and to analyze the prepared model to check the manufacturability and the feasibility of the design.

Introduction:

The Roof of a vehicle is the part which encases the traveler compartment from the top. It ensures the Passengers and the inside of the vehicle from outer situations consequently giving a sheltered and secluded lodge. The rooftop assumes a significant job in the security, particularly on account of turn over mishaps. To accomplish better security results the rooftop is planned with fortification structures, for example, rails.

The major components of the Roof are

1. Outer panel/ Shell
2. Front roof rail
3. Rear roof rail
4. Bow roofs
5. Central roof reinforcement rail.

Every one of these parts are intended to fulfill the essential elements of the rooftop, to meet the security prerequisites and to improve the exhibition of the vehicle by weight advancement.

1) Outer Panel / Shell

The outer panel is the A-class surface of the rooftop which encases the highest point of the traveler compartment. It is intended to coordinate the information styling surface, along these lines showing signs of improvement streamlined execution as proposed. It additionally has a noteworthy job in the style of the vehicle. The external board is mounted to the rooftop rails with the assistance of mastics and the discard territories are mounted with spot welds. The normally utilized materials for the external board are Steel and Aluminum compounds

Design Considerations

Geometric requirements:

1. Thickness: 0.75 mm
2. Ditch area-minimum flange width: 15 mm

Manufacturing requirements:

1. Small emboss depth should be less than 5 mm
2. Mounting and welding areas should be flat
3. Minimum fillet radius should be 3mm+thickness
4. Tool opening angle is 3 degrees

Functional Requirements:

1. Provide adequate space for windshield glass supporting elements
2. Space for the hinges of backdoor and allow the swinging of backdoor

Design methodology

1: Creating the Outer panel surface from the given input skin.

2: Developing the ditch area

Spines are made on four sides of the rooftop according to the previously mentioned necessities. The front end rib is given with a width of 21.50 mm to give sufficient space to the elastic fixing, mounting of windshield glass, and so forth. The back discard region is made to allot the pivots of the secondary passage and to permit the swinging of the indirect access to the necessary opening point. Some decorates are additionally given on the back to expand the quality locally.

The thickness of 0.75 mm is given according to the geometric prerequisites.

2) Front Roof Rail

The front rail underpins the rooftop external shell at the front end. It is mounted with support rooftop rail fortification on the two closures. The rails are furnished with emblazons to improve the quality and the rail is associated with the external board utilizing mastic sealants on one side and the other joinery is spot welded.

Design Considerations:

Geometric requirements:

1. Thickness – .75 to 1.5 mm

Manufacturing requirements:

1. Small emboss depth should be less than 6 mm
2. Mounting and welding areas should be flat
3. Minimum fillet radius should be 3mm+thickness

Functional requirements:

1. Headroom clearance: 80 mm minimum
2. Front visibility criteria
3. Enough flange length to support the windshield glass & its components

2 mm clearance at the flange edge for trims.

Design methodology

1: Creating the swept surface that meets the design requirements with the outer surface geometry as reference.

The section is created by considering the front visibility criteria and minimum headroom clearance of 80mm. A flange of 15 mm is provided to support the windshield glass & its components,

And 2 mm clearance is provided at the flange edge for allocating the trims.

3) Rear Roof Rail

The rear roof rail is similar to the front rail. It is designed to support the back end of the roof and the hinge of the backdoor is also mounted on it.

Design Considerations

Geometric requirements:

1. Thickness – .75 to 1.5 mm

Manufacturing requirements:

1. Small emboss depth should be less than 6 mm
2. Mounting and welding areas should be flat
3. Minimum fillet radius should be 3mm+thickness

Functional requirements:

1. Rear headroom clearance: 80mm minimum
2. Rear visibility criteria
3. Space for mounting the backdoor hinge.

Design methodology

1: Creating the swept surface that meets the design requirements and the outer surface geometry as reference.

The section is developed by considering Rear headroom clearance of 80mm, Rear visibility criteria, and space for mounting the backdoor hinge is also given.

4) Reinforcement roof CTR

The reinforcement roof at the center is the supporting member at the middle which is mounted to the B pillars on either side. They are attached to the outer panel using mastic sealants. Sometimes it acts as bow roof and sometimes bow roofs are also provided with the reinforcement roof center. In some vehicles a room lamp mounting provision is also given on this part.

Design Considerations:

Geometric requirements:

1. Thickness: 0.75 to 1.5 mm

Manufacturing requirements:

1. Small emboss depth should be less than 6 mm
2. Mounting and welding areas should be flat
3. Minimum fillet radius should be 3mm+thickness

The strength can be further improved by giving separate mastic points that extend outwards.

Design methodology

1: Creating the offset surface that meets the design requirements, with the outer surface geometry as reference from bow roof.

2: Providing separate mastic points.

The mastic sealant holds the bows and outer panel together. Each point will have an effective circular area of 80 mm in diameter. The mastic sealant helps to improve the elasticity of the outer panel. They also improve the NVH characteristics of the roof.

5) BOW roofs

The Bow roofs are given to improve the torsional stiffness and load-bearing capacity of the roof structure. The number of bow roofs provided will depend upon the overall dimensions of the roof. They are attached to the outer panel using mastic sealants. Each mastic point will have up to 80 mm circular effective area. The positioning of bow roofs is done based on curvature study. The heat distortion criteria and snow load criteria are checked to analyze the position of the bows in various conditions.

Design Considerations

Geometric requirements:

• Thickness – 1.5 mm minimum

Manufacturing requirements:

• a) Mounting and welding areas should be flat

• b) Minimum fillet radius should be 3mm+thickness

Design methodology

1: Creating the swept surface that meets the design requirements with the outer surface geometry as reference.

2: Providing separate mastic points.

The mastic sealant holds the bows and outer panel together. Each point will have an effective circular area of 80 mm in diameter. The mastic sealant helps to improve the elasticity of the outer panel. They also improve the NVH characteristics of the roof.

The rail surface is thickened by 1.5 mm

One BOW roof is also provided within the reinforcement roof CTR

Curvature Study

To fulfill heat contortion and snow load execution of the rooftop, we need to decide the ideal area of bow rooftops and rooftop plate thickness. In the event that the rooftop is presented to high temperatures for quite a while the rooftop structure will in general disfigure. This investigation will assist with checking whether our structure is substantial and if not will assist with deciding the ideal situation of the rails to dodge the disfigurement of the rooftop. Correspondingly if the rooftop is exposed to the overwhelming heap of day off, will in general twist or fall flat. To improve the quality under the snowed condition we need to situate the rails at wanted explicit areas.

Heat distortion criteria:

W = [1.73x10^-3 x L]+[1.85x10^-8 x (R^2)/t] +[ 1.10x10^-3 x l]-2.68

Judgment Condition: OK<2.7mm<NG

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

However if 2.7 W< 3.5, then provide the outer panel reinforcements to improve the strength.

Results:

s.no	Bows	Rx	Ry	R	l	L	T	R^2/t	w	ok/ng
1	Fr & 1st	5806.688	2824.59	3800.483047	221.282	2026.635	0.75	19258228.52	1.425765978	OK
2	1st & Ctr	5068.628	5714.498	5372.220369	308.886	2026.635	0.75	38481002.26	1.877751692	OK
3	Ctr & 2nd	4176.67	9921.094	5878.540126	295.43	2026.635	0.75	46076312.01	2.003463322	OK
4	2nd & rear	3392.802	15534.634	5569.263296	404.138	2026.635	0.75	41355591.55	2.035708794	OK

Snow load criteria:

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

Where

α = My x Lx2 x 10-12

My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

250 ≤ s ≤ 380

where;

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along 0Y[mm]

• Length of Roof panel with the center point between Roof rail Front /Rear as the reference point of the front and the rear.

Lx= Distance between the Left and Right end of the roof on the Roof BOW [mm]

• Width of the roof panel exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s= Distance for which Roof BOW bears divided load [mm]

• s = L1/L2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

• Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

Results:

S.NO	BOWS	lY	alpha	LX	LY	MY	Y	s	Rx	Ry	t	Qr
1	Fr & 1st	6898	0.6947748735	1100.948	1696.165	573205.6865	465.933	422.247	5806.688	2824.59	0.75	71.01413838
2	1st & Ctr	26520	0.5723609704	1071.21	1696.165	498793.4878	378.561	422.852	5068.628	5714.498	0.75	212.035353
3	Ctr & 2nd	8302	0.6324215568	1049.539	1696.165	574129.0241	467.143	531.161	4176.67	9921.094	0.75	27.97898337
4	2nd & rear				1696.165			297.59	3392.802	15534.634	0.75

In the heat distortion study, the 3ed section (between RR CTR & Rear Rail) came out to be (NG) not good. Also, In the snow load study the value of 'S' (the distance of bearing divided load) for RR CTR appeared as more than the desired range. So to improve the heat distortion and snow load performance of the roof at the rear section I gave emboss to the outer panel.This Will reduce by increasing the Bow Roofs.

Draft analysis:

We use Draft analysis to see that the part can be drawn or not. It helps to find the negative draft present in the component which will cause difficulty in manufacturing.

Draft analysis done on roof rails:

Final Model :

Result :- The Roof assembly is designed based on the given styling surface, considering all the geometric, manufacturing, and functional requirements.

Google Drive Link:- https://drive.google.com/file/d/1zFIaxJaPeRU7fGCxK7WkyBOCPWZvb021/view?usp=sharing