Week 9 - Project - Master Section Development

Aim:

B PILLAR DESIGN through the objective of this project to develop a Closed Surface Model using Master Sections and to develop attachment features for the Fixation of Parts by the following OEM Design standards and procedures 

Procedure:

Master is the guides for design requirement which shape the component after technical styling of class A surface.

                            

OVERVIEW DESIGN LIFE CYCLE AUTOMOTIVE INDUSTRY 

The Stages of the Design Life Cycle are 

Concept Sketches:

Concept sketches are rough ideas of freehand sketches obtained through the styling team and will be used to prepare the Model. It is usually done through pen and paper and through  the painting software. This is will be used to generate the concept for preparing the model by incorporating various styles and information obtained through the stakeholders

CLASS A Creation:

After finalizing the concept the sketches are usually worked in software’s such as Autodesk Alias to create Class A Surface 

Clay Modeling :

The Class A Surface is concurrently worked by clay modelers to brainstorm and benchmark the styling of the product and later the Concept is validated by bringing up a rough clay model and then it is passed on to the Design team for the preparation of New Product Design (NPD) CAD.

NPD CAD

This where the development of surfaces to parts in CAD kick-off and the Design engineer's involvement is vital in this stage.

The Designers will work on the Input Class A surfaces which are validated by the Feasibility team

The procedure followed in the creation of the plastic New Product Design are 

• Tooling Axis
• B Surface Creation
• C Surface Creation
• Closed Body Creation 
• Draft Analysis

TOOLING AXIS 

The given Class A input is analyzed to envision the part to manufacture and the Tooling axis or Tooling Direction or Die line is the direction that molds pull apart in injection molding. There are two mold pieces names core and cavity. Thus tooling direction determines Mold separation and also becomes vital in developing the plastic product which is drafted to desired nominal angle for feasible clearance and ejection of the final part from the mold.

The Steps Followed in creating Tooling Axis

1. A Reference Point is created along with the Surface zero and a new Axis system is created 
2. The X-direction and Y-direction along Class A was used to create Tooling direction
3. Finally, the Tooling axis is created by bisecting the two lines and it is published. Class A Surface as input using surface operation commands Class B is developed
4. The tooling Axis determines the direction of Class C boundary swept with draft direction.
5. When viewing from tooling direction normal all the parts that are drafted should be visible so it gives a rough idea to determine product manufacturing in Injection molding 

In B Pillar Model there are Two Tooling Directions one on Main tooling and the other on Lifter Side that is used to eject the parts during injection molding 

Lifter Axis is used because the Attachment feature is bounded by closed walls 

CLASS A IMPROVEMENT

Class A Surface is the outer skin of the product which is purely an aesthetic model with no engineering properties involved

The CLASS A Surface has a lot of irregular patches and complexity which are improved using Multi-Section Surfaces and Surface Trims which forms the Improved Class A Input

A Tangential Error Propagation method is used to validate the Surfaces using the Boundary option.

Class A has Flanges which are obtained through Master Sections and developed and compared

Finally, the Class A Improved is used as an input Model and is Published

B Surface creation

• The next step is to design a B surface for the input which is usually the surface where all engineering aspects and support creations are done.
• The B surface Creation is performed using surface operations in CATIA which is an offset from Class A with dimension proportional to the thickness of the part 
• In B Pillar Design  the B surface is offset 2mm from the input which is the thickness of the part 
• The B surface is an extrapolated surface compared to the A surface and forms the bottom skin of the part
• The Offset Surface leads to Surface Degenerations if 

1. The rapid change in curvature or surface continuity
2. Low Radius of CLASS A
3. Conic or Styling Fillets

The Remedy is to Untrim, extrapolate and trim or create surfaces using Multi-Surface Option and Join 

Corrected B Surfaces

In this way, the Patches are corrected along the B Surfaces and the part is Extraploated  with an offset of 2mm from A Surface

C Surface Creation

• The Next step is to from the C surface which is an intermediate surface between A and B and is used to give the closed surface appearance to the design 
• The C Surface is swept using the profile as the boundary line of Class A which is the Guide curve with a subtype along the draft direction.
• The Direction of the sweep is the tooling direction formed earlier
• The draft angle for the sweep operation is provided which is 3 Degree and the surface is swept for length above the thickness of the specified part 
• The C Surfaces must be drafted outwards from the A-Side to avoid the parting Line along the A Surface
• The C surface is refined using smooth Curve options to remove the complexity and patches along the swept surface
• Finally, the Class A and Class C surfaces are joined together and the connexity of surfaces should be less than 0.003mm and the surfaces are merged.

C Surface merged with Class A 

Closed Body Creation

• The merged surface is then trimmed with a B surface to form the closed surface.
• The Closed surface is then validated to find the irregularities along the edges and imperfections along the edges were then corrected using operation like extrapolate and surface trim 
• This Closed surface is the outer skin and finally, the part is formed by Closed Surface in part design workbench 
• The final part is measured to validate the uniform thickness of the part, especially along the filleted edges.
• The Uniform Thickness ensures that the part Created doesn't form Sink Mark and Flow Lines along with Class A

ATTACHMENT FEATURES

The Attachment features are the Fixation and Location features that Fix the components The Common Attachment features used in B Pillar Are

1. Doghouse with 4 Way Locator
2. Ribs

DOGHOUSE

Using the Master Section the Doghouse is created and then part modeled using the Thickness option

• The 4 Way Locator is Formed above the Dog House which locates the B pillar towards the Mating Surfaces
• The Dog House Design Rules are
• The Thickness of the Connecting surface towards the B Side should be 40% off the main thickness
• The Walls are drafted with Min 0.5 Degrees along the Main Tooling Direction

                                                                

• The Attachment feature created needs a separate tooling axis to clear the part Hence a Lifter Axis is used 
• The Surfaces that are cleared along the Lifter axis are also given a Minimal Draft
• The Height of the attachment walls should be a minimum of 3 mm.
• This avoids the plastic defects on the B Side and maintains the texture of the A Side.

                                                                 

The Dog House with four Way Locator are shown below

          

Four-Way Locators are Tapered along the Edges to create an entry point for locators and the Locator Walls are drafted along the Main Tooling Direction.

The Walls are a minimum of above 0.4  times of the total Thickness to avoid shot incapacity during plastic product creations and the apex walls are ensured to enough for creation of parts.

RIBS

Ribs provide stiffness to the parts and can be to impart toughness without increasing the part thickness and are locators and provide alignment to the mating parts

The Design Rules for two way and four-way fixtures are 

• Rib Wall Thickness should be 0.4 times of Thickness of the part
• The Drafted walls of the rib should be within 0.5 degrees
• The top height of the rib should be at least  0.70 mm thick to allow the molten plastic to reach the top to avoid Short Shot
• The Thickness of the Rib, Fillet Radius, Draft, and rib root thickness are measured and are within the design specifications 

                                        

In B Pillar The Ribs are 50mm apart on both Sides

• Thus B Pillar Cover is Surface Development is completed and attachment features are added.
• It should be noted that the fixation of bolt locators always follows the 3-2-1 Taylor Principle.
• Translational Movements along X, Y,Z-Axis  ( Positive and Negative)
• Rotational Movement along X,Y,Z-Axis ( Clockwise and Anticlockwise)
• The Improvement in Given B Pillar could be an addition of another Dog House at an extreme end to satisfy Taylor's principle and Thermal Stakes are provide that arrests all degrees of freedom and completely fits the B Pillar Part

DRAFT ANALYSIS

The finished part is then analyzed to detect if the drafted part will be easily removed from the injection molding.

Draft Analysis option in CATIA is enabled through Insert> Analysis> Feature Draft Analysis

The Draft Analysis Icon has 

1. Mode
2. Display 
3. Direction

Mode:

This is the color code that specifies the color to part based on the draft angles and is two types

• Quick Analysis
• Full Analysis

The Color code specifications for B Pillar DRAFT ANALYSIS

 Display:

The various display modes are 

• Show/hide the Color scale
• Running point Analysis
• Highlight Representations
• Light Effect

The display options are used to refine the analysis and results

DIRECTION:

This is one of the important tools which 

• Compass Definition: This is used to pan the compass to the die line or tool direction. 
• Lock Direction: This option locks the compass at the specified position
• Invert Draft Analysis: which is used to invert the axis system and used to analyze  the negative tooling direction

Draft Analysis Procedure

• The part created has to be changed to the material mode in the display frame
• Then by enabling compass definition the axis system in pan along the direction of the part and aligned in line with the tooling direction
• Lock Direction is applied that fixes the compass and then the mode dialog box is formed by snapping at any point on the part 
• The Color Codes are classified and Draft Angle are applied
• Then the Running point analysis is used to hover around the part to analyze the permissible draft angles and the analysis is saved

The Analysis  is provided below

DRAFT REPORT

The Draft Report for B Pillar Model is shown Below

                      

                              

The B Side Surface Analysis is Shown Below

                                        

                                                                   

All The C Side Surfaces are drafted and are below 2.9 degree

          

The Lifter Axis Draft Analysis are shown below

         

RESULT

• The Green color is drafted walls above 3 degree
• The Blue color is drafted walls from 0-3 degree
• The red surfaces are negative degree

• The analysis shows the drafted walls  are above the par of 3 degree which is permissible to manufacture in the injection modeling
• The Running point analysis hovered along the drafted walls shows parts are above 3 and will be easily cleared from ejection.
• The Areas in Negative Tooling that falls short of the permissible design Rules are shown
• These surface are corrected using Surface Operations and generally, in OEM Class A Improvement requires prior approval from the Styling team and the draft report and analysis is used to get approval  

• The Tree Structure is Classified and the important features are published and the operations are renamed and classified into geometric subsets shown below.        

• The 2D Sketch created for this operation is positioned sketches projected through a point and all geometries are fully constrained 

          

CONCLUSION

Thus a Tooling Axis is created and an open aesthetic Class A Surface is developed into a closed surface with all plastic design rules and a final part body is created out of it in CATIA Surface Work Bench. The design is then validated with Master Section and understood the use of Master Section Development in Product Design through the development of the B Pillar Cover used in the Car Interiors.