Roof challenge

Objective: The main Objective of this work is to increase the resistance towards the force acting on the roof, during Snow load and other test conducted by BNVSAP(Bharat new vehicle safety assessment Program) and National Highway Traffic Safety Administration Program.

Roof: An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.

The basic BIW structure of the Roof contains different components which provides strength to the Roof, they are going to help further Heat distortion and snow load test conducted on it.

Components of Roof BIW structure are:

• Front Roof Rail
• Rare Roof Rail
• Reinforcement Bow Roof
• Bow Roof

All the above components are not only helps to provide strength to the component, but also, they help to hold other components of the car.

Front Roof Rail:

 We Know that the windshield is connected to the roof with the help of Front Roof rail and the back door and body side part is connected with the Rare Roof Rail.

The count of both bow roof and the Reinforcement bow roof can be increased and decreased according to the roof length, and the conditions it has to resist to protect the passengers inside the car.

Rare Roof Rail:

As we know rare roof rail not only provides the strength to the roof, but also it is provided to handle some back door features on to it for ex: hinge of the back door.

 

Bow Roof’s:

The above shown pictures are the bow roofs modeled using NX-CAD, the shape of the bow roof will be changing according to the strength roof needs to withstand, and to joining with the roof.

Reinforcement bow Roof:

This type of bow roof is used to withstand to the more deformation occur while applying load on to it. Usually, this type of support is used at the curvy location of the roof.

Draft analysis:

Tooling Axis:

Tooling axis of the product tells us the direction of movement where the part is being produced effectively.

There are Some advantages, if we follow the effective tooling axis like

The side cores and other things can be reduced.

Tooling axis has to be produced by considering some criteria’s like

• Direction of movement
• Bosses and other references have to be considered.

Creating Tooling axis by using Catia V5:

The above image shows different direction where the tooling axis possible to produce.

Tooling axis is not restricted to particular direction. It can be produced in that direction where the product can be produced easily.

Draft angle: Usually draft angle is provided on the part, as well as the core and cavity, in order to reduce the wear and tear of the product while ejecting from the mould.

Draft analysis is northing but the analyzing the draft angle provided on the part as well as the core and cavity of the injection mould by the Engineer

Draft angle allows ejector to simple push, to pop out the part from the mould

 

There are certain standards should be followed to provide the draft angle on the parts, core and cavity.

• Usually, the nominal draft angle 3deg is provided on the part
• Providing the nominal draft angle is easy and very economical.

Draft angle is depending on the material which is being used to prepare the product.

Ex: Textured parts required the more draft angle than the usual

Front Roof Rail Draft analysis:

Rare Roof Rail Draft analysis:

 

Reinforcement Roof Rail:

Bow Roof   Draft Analysis:

Roof Draft analysis:

Curvature Study of the Roof:

Heat distortion Test:

This test is usually conducted on the roof, to predict whether the roof can with stand to the suitable given temperature conditions with-out undergoing any bending and softening of the material. There is formula to predict weather the curvature of a roof, which can further gives information about the roof capability.

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8)  x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68           

Judgement Condition: OK< 2.7> 3.1

Were

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]

Sr no	Components	Rx(mm)	Ry(mm)	L(mm)	t(mm)	W	Judgement
1	Frr – Rr1	5658.7	2368	319.39	0.75	1.30	OK
2	Rr1-Br2	4820	5242	365.47	0.75	1.35	OK
3	Br1 – Br2	4067	9147	429.68	0.75	1.42	OK
4	Br2 – Rrr	3391	15174	550.68	075	1.55	OK

Snow load Prediction formula

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

 

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where

α = My x Lx2 x 10-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

               250 ≤ s ≤ 380

t = Roof plate thickness [mm]

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

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

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 = L1/2 + 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]

        Roof panel X curvature radius of length s in Side view

Sr no	Components	Rx1	Ry1	I(mm4)	Lx	Ly	s	Qr	Judgement
1	Frr – Rr	4167	3331	9260	1123	2100	2.7.49	20.4	OK
2	Rr – Br1	3799	6347	2103	1085	2100	238.36	46.5	OK
3	Br1 – Br2	4250	10434	6748	1063	2100	325.73	24.7	OK
4	Br2 - Rrr	4155	15493	-	1050	2100	-	-	-

 

Section Inertia Analysis:

Rare Roof Rail:

 

Bow Roof:

Reinforcement Bow Roof:

Front Roof Rail:

Conclusion:

The above BIW Components were designed and assembled according to the given master section’s, and found the ability of the roof to with stand both heat distortion and snow load conditions.