Objective

To design and calculate the performance criteria for the Roof and Rail Reinforcement design, Adding necessary features to develop the strength of the roof.

Introduction

Roof is a part of an automobile essential to protect and keep the passenger safety from harsh weather condition, accidents etc. the conventional task of the roof panel is that of compartment shielding, passenger protection and connecting of the body sides, front and roof cross members, In case of roll over compartment integrity is provided by the compartment frames, while the roof target is only to avoid the ejection of the passengers, providing protection against hard local contact.

Correspondingly a wide selection of suitable materials are available: Steel, aluminum, thermosetting plastic sheet, glass. In case of steel grade FEP04, the usually thickness is in the range of 0.65 to 0.85mm. In all cases, any roof panel material requires braces to prevent panel flexing and vertical waviness, commonly known as oil canning: for this purpose light steel bows are introduced, which are welded or riveted or screwed to the body side and bounded to roof panel by smooth flexible adhesives such as butyl mastic (in order to avoid sink marks on roof surface), mainly providing a damping effect.

Another task of roof bows is to support the interior roof liner which requires a number of fittings both in central and boundary areas to avoid deflection and vibrations. Fittings are usually plastic clips or Velcro strips. Some roof liners, mostly on less expensive vehicles ae bonded directly to roof panel.

Figure 1 Car Roof

For the give Roof styling, develop the essential flanges and reinforcements, Provide appropriate dimension and check for Draft analysis and also submit your section modulus report on 0-Y section.

Start with the creation of roof ditch area the tool opening angle is only 3 degree.

Do a curvature study on the roof and perform calculations to determine the position of the Bow-roof.

Bow – roof prediction Formula:

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

Judgement 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]

I = Bow Roof Span [mm]

W = displacement in [mm]

S.NO	BOWS	Rx	Ry	R	I	L	t	(R^2)/t	W	OK/NG
1	FRR & CTR	0	0	0	608.93	2027.08	0.7	0	1.4966714	ok
2	CTR& BR1	5534.8	6558.4	6003.27991	0	2027.08	0.7	51484813.9	1.779317457	ok
3	BR1 & BR2	5234.2	9425	6730.56306	257.5	2027.08	0.7	64714970.1	2.307325348	ok
4	BR2 & RRR	4155.6	11566.5	6114.41823	507.65	2027.08	0.7	53408728.9	2.373324885	ok

Figure 2 sunroof with Emboss

By noticing above table at s.no 1 between the front roof rail and central roof rail the Rx and Ry values are zero has there is a presence of sun roof cut out. And in s.no 2 the bow roof 1 is presented within the central roof rail, hence the bow span is consider as zero. This will help the have additional support to roof due to presence of sun roof.

Figure 3 cross section of the roof

Important Types of Roof Reinforcements:

• Front Roof rail Reinforcements
• Central-Bow Roof rail Reinforcement
• Bow Roof rail Reinforcement
• Rear roof rail Reinforcement

Figure 4 Roof Reinforcement

Draft Analysis

Front Roof rail Reinforcement

This would get fixed on the front of the roof which provides the strength and also helps to hold the wind shield glass. Here the draft analysis showed in the below picture shows the design is green in colour which means it means all bends are proper with 5 degrees angle and part is completely producible without any issues.

Figure 5 Front roof rail draft analysis

Centre bow roof rail Reinforcement

In this centre Roof rail are generally located in the centre of the roof which supports the structure to withstand the loads. In this design it is collaborated with the bow roof in between the centre roof rail and roof. Which provides an extra structural support as there is sun roof integrated in the design to compensate both the roofs are together.

Figure 6 Centre Bow roof rail

Draft analysis for this case is done separately first let’s do for the bow roof and go to Centre roof rail. By looking at the Figure 7 the bow roof rail 1 could be producible and it completely green in the analysis which it makes easer at production. Here at figure 8 the centre roof rail is also completely in green in colour which is properly producible.

Figure 7 Bow roof rail 1 draft analysis

Figure 8 Centre Roof rail draft analysis

Bow Roof Rail

This is located in between the rear roof rail and centre roof rail, which plays the major role in adding strength locally and helping the roof to maintain without any deformation. Where is attached to the roof by mastic seal has it roof is the styling component of the car. In Figure 10, draft analysis results are pretty positive which means even this is producible without any difficulties.

Figure 9 Bow roof Reinforcement

Figure 10 Draft Analysis of Bow roof Rail

Rear Roof Rail

This is located at the back of the roof which bears the edge load and strengthens the roof from the rear side. In the draft analysis in the figure 12 all the faces are shown in the green colour and even this part is quiet producible without any strain.

Figure 11 Rear Roof Rail

Figure 12 Draft Analysis of Rear Roof Rail

Draft Analysis of the Roof

In figure 13 shows that roof is completely producible with an easily produced without any issues. This has embosses on the roof to create extra strength and with stand loads and heat distortion.

Figure 13 Draft Analysis of the roof

Section Modulus and Moment of Inertia Details:

Section modulus of entire Roof

Figure 14 Section modulus of roof

By seeing the results it has maximum Inertia of 5.81x10⁷ and minimum Inertia 1.36x10⁰⁵. it has section area of 143.41 mm².

Section Modulus of Front roof rail

Figure 15 Section Modulus of Front Roof rail

By seeing the results it has maximum Inertia of 5.88x10⁴ and minimum Inertia 1.13x10⁰³. It has section area of 17.46 mm².

Section Modulus of Centre Roof Rail

Figure 16 Section Modulus of Central Roof Rail

By seeing the results it has maximum Inertia of 6.48x10⁴ and minimum Inertia 2.56x10⁰³. It has section area of 19.67 mm².

Section Modulus of Bow Roof Rail

Figure 17 Section Modulus of Bow Roof Rail 1

By seeing the results it has maximum Inertia of 5.94x10⁴ and minimum Inertia 0.538x10⁰³. It has section area of 17.97 mm².

Section Modulus of Bow Roof Rail

Figure 18 Section Modulus of Bow Roof Rail

By seeing the results it has maximum Inertia of 4.31x10⁴ and minimum Inertia 2.05x10⁰³. It has section area of 17.50 mm².

Section Modulus of Rear Roof Rail

Figure 19 Section Modulus of Rear Roof Rail

By seeing the results it has maximum Inertia of 3.84x10⁴ and minimum Inertia 3.19x10⁰³. It has section area of 16.71 mm².

Conclusion

Using roof styling, developing the essential flanges and reinforcement. Designed is provided at appropriate dimension and checked with Draft analysis and also made the section modulus report on 0-Y section.