Roof Design

Roof Design

Aim: To design a roof and its parts using NX or Catia and calculate the ‘Heat Dissertation criteria’ and ‘Snow Load Condition’ along with the draft analysis of each part.

What is Roof?

Roof is a portion that sits over the car. Its function is to protect the passenger from wind, sun, storm, rain etc.

The image shows the hood that we design using NX siemens software. The roof can be of various type like convertible, with sun roof, of different material and so on. We are designing a standard roof.

Parts Of Roof:

1. Roof outer body
2. Front roof rail
3. Rear roof rail
4. Bow roof rail
5. Center roof rail
6. Roof outer body: This is the outer cover of the body on which different rails or reinforcement will be added
7. Front roof rail:

This is the front roof rail and this is mounted on the front of the roof on which wind shield glass and front body will be joined. This front roof rail is created with given master section view.

3. Bow roof rail: The bow roof are given to improve the torsional stiffness and load bearing capacity of the roof. The number bow roof will depend on the size of the roof, some times there will be no bow roof if the roof is too small for example in Alto, Mini Cooper etc., and it is not necessary that bow roof will always be in same place it will vary from design to design, in our design we take two bow roof one in front and another in back between center and rear roof rail.

Bow roof front

bow roof rear

4. Center roof rail: Center roof rail plays crucial role because this will provide support to the roof in center. This also help during rool-over test. The center roof rail is connected to the B-Pillar.

Center bow roof rail

5. Rear roof rail: Rear roof rail is at end of the roof and rear glass and side body.

The next image shows the master section of the rear roof rail.

Heat distortion study of the roof:

The heat is the one method to calculate whether the position of the roof is correct or not. Here is the image of the of the formula.

Bows	Rx	Ry	R	I	L	t	R^2/t	W	Result
FR-1	3071.04	3272.75	6343.79	437.3	2122.6	0.75	53658228.7521	2.46	Ok
1-CTR	3328.15	6053.83	9381.98	334.6	2122.6	0.75	117362064.9605	3.5	NG
CTR-2	4119.58	9871.22	13990.8	471.8	2122.6	0.75	260989979.52	2.3	Ok
2-RR	3407.01	13771.05	17178.06	418.1	2122.6	0.75	393447660.4848	2.4	Ok

Similarly we will calculate,

Snowed Criteria:

Snowed criteria is calculated for snow load that roof can withstand during snowing season when cars are left outside under the snow.

Bows	Iy	t	α	Lx	Ly	s	Rx	Ry	Qr
FR-1	0.439	0.75	0.981	1154	2122.6	385.95	4261	14539	0.73
1-CR	2.86	0.75	4.85	1131	2122.6	403.2	4189	10109	0.46
CR-2	0.439	0.75	0.946	1103	2122.6	444.95	3373	6296	0.54
2-RR		0.75		1071	2122.6		4187	3195

Result: from the above result snow load will fail in all condition and heat distortion will fail in 1-CTR. So we have to change the position of bow roof rail.

Draft analysis:

In NX we have a software draft analysis which will calculate all the constrain and see if there is any negative draft is there or not. Before giving it for manufacture we have to check draft analysis.

Rear rail:-

Bow roof 1:-

Center roof rail:-

Bow roof rail 2:-

Front roof rail:-

Outer body:-

As we can see that all the parts has passed the draft analysis so we can draft this parts.

Conclusion

We had successfully created the parts of roof and also check the design, according to the result we can send part for drafting but before that we have to change the position of the bow roof rail to get under control heat distortion and snow load resistance.