Design of backdoor

Aim :

Use the provided styling surface to come up with a back door design, use appropriate design methodologies, and provide the necessary reinforcements and embosses.

Solution :

Now we will discuss about geometric dimensioning :

The most common way of showcasing the dimensions of the part are the plus minus signs .It consists of the following :

1. Basic Dimensioning : A numerical value that is used to describe the theoretically exact profile , orientation or location of a feature . Basic dimensions have no tolerance and can not be rejected .

There is a certain standards for the symbols in dimensioning which is used worldwide for easy intrepretation .

Types of geometric dimensioning : 

1. Form : This consists of the following : flatness , circularity ,cylinderity , flatness , straightness and it is applicable for only individual features .

 2. Profile : It consists of profile for line and profile for surface . It is used for related features .

3. Orientation : It consists of angularity , parallelism and perpendicularity .

4.Location : It consists of position , concentrity , symmetry.

Manufactured items differ in size and dimensions from the original CAD model due to variations in the manufacturing processes. To optimally control and communicate these variations, engineers and manufacturers use a symbolic language called GD&T, short for Geometric Dimensioning and Tolerancing.

With functional assemblies, multi-part products, or parts with complex functionality, it is crucial that all components work well together. All relevant fits and features need to be specified in a way that impacts the manufacturing process and its related investments the least, while still guaranteeing functionality. Tightening tolerances by a factor two can raise the costs twofold or even more, due to higher reject rates and tooling changes. GD&T is the system that allows developers and inspectors to optimize functionality without increasing cost.

For example, a feature standing at 90 degrees to a base surface can be toleranced on its perpendicularity to that surface. This will define two planes spaced apart, that the center plane of the feature must fall within. Or, when drilling a hole, it makes the most sense to tolerance it in terms of alignment to other features.

Engineering drawings need to show the dimensions for all features of a part. Next to the dimensions, a tolerance value needs to be specified with the minimum and maximum acceptable limit. The tolerance is the difference between the minimum and maximum limit. For example, if we have a table that we would accept with a height between 750 mm and 780 mm, the tolerance would be 30 mm.

However, the tolerance for the table implies that we would accept a table that is 750 mm high on one side and 780 mm on the other, or has a waved surface with 30 mm variation. So to appropriately tolerance the product, we need a symbol communicating the design intent of a flat top surface. Therefore we have to include an additional flatness tolerance in addition to the overall height tolerance.

Besides individual tolerances, engineers must take into account system-level effects. For example, when a part comes out with all dimensions at their maximum allowed value, does it still meet overall requirements such as product weight and wall thicknesses? This is called the Maximum Material Condition (MMC), while its counterpart is the Least Material Condition (LMC).

Now we will work on the following part :

Following are the regions of a car : 

1. A Pillar : This takes consideration of the following :

Side Head Room : It is important to have enough side head room so that the driver can have good visibility 

Front Pillar Obstacle Angle : This should be taken into account so that the driver can have good visibility.

Glass Stroke : This is the reachibility of the glass from where the person is sitting in the vehicle .If the glass is too close to the person chances of injury during  a crash are high . If the A pillar is more inclined , more close the glass is to the person.This also depends on the seating .

2.A Centre Region : This is the region where the  steering column is attached  as well as cockpit etc . The air vents also come through this region .

3.A pillar Lower region : This is the place where the lower hinges of the door are mounted .

4.Sill : This is the bottom most part of the car and keeps the harness .

5.Front Door : There are conditions in which the hinge axis of the door is inclined :

a. Forward Inclination : This is the condition in which the hinge axis is inclined wrt to the car vertical axis 

b.Vertical Condition : This is condition in which the hinge axis is parallel to the vertical car axis and the amount of force required to open and close the door are similar .

c.Inward Inclination : In this condition the dead weight acts towards closing condition as the majority of the weight is inclined downwards .

d.Outward Inclination : In this condition the dead weight  acts outward during the opening condition and an additional amount is required while openining.

6.Center Pillar or B Pillar : This is the pillar which is joining the upper and bottom of the car .This pillar is the region which holds the striker that enables the closing of the door.

Sometimes checklinks are installed on the a pillar so that the door is opened in intervals so that the user does not have to apply a lot of efforts in opening the door.

 The assembly sequence for aluminium is given as below :

The inner panel is going to be a single part whereas the outer panel can be split into two or three parts .The outer panel is usually a casted part .Aluminium has the advantage of variable thickness and helps to reduce weight but it is expensive to produce parts of aluminium

The various load cases on the door are : 

1.Bend Test 

2.Torsion Test

3.Abuse Test

4.Endurance Test

In order to have good strength it is important to have a y emboss so that there is force distribution done properly.

The following will be part of the backdoor :

1.Backdoor inner

2.Backdoor outer

3.Wiper motor reinforcement 

4.Reinforcements

5.Hemming so that we can apply sealant inside the small volume.

Now we will do some clean up of the given class A surface in order to create a good class B and Class C surface :

We will create a new surface here as well as below in order to remove bad patches of surface :

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We are extending the surfaces as shown below :

We have applied blend corner over here :

Now we will make the tooling direction as shown below :

Now we will design the sealant flange which is used to engage the backdoor on the backside rubber sealant so that the water does not flow in .

We have extracted the surface as shown and offsetteds as below :

Now we have created offsetted curves on the surfaces as shown below , these will be trimmed :

After trimming we get :

Using through curve mesh and bridge curve we get the following :

Now we will create the following :

We have used command such as trim , bridge curve to create the following surface :

We have created the curve as shown :

Now we are using law extension as shown :

After trimming we get the following :

Now we have created the following :

Now we have extracted the surface and used law extension as shown below :

Using the same command we get the following :

We have created an extrusion as shown below :

We have got the following after trimming :

Now we will create the hinge axis as shown below :

The door opening will follow this axis while opening the hinge emboss will have to be created in such a way that it is perpendicular to this circle.

We have created a latch striker emboss as shown below :

We have created the emboss for the wiper motor as well as shown below :

We have created the emboss for the hinge :

We have created the reinforcement for the hinge as shown below :

We have created the gas stay embossment as shown below :

We have created a reinforcement for the gas as shown below :

We have created the following embosses as shown below to create strength in the part :

After sketching we get the following :

Conclusion 

After mirroring we get the following :