Door Arm Rest Week 8 Challenge

                                                                 DOOR ARM REST DESIGN

Objective:

The main objective is to design a Door Arm Rest an Automotive Plastic Component using industry principles such as Draft angle, Draft analysis, determining and implementing of Tooling Axis, Side Core Axis, Class A, Class B, Class C surfaces and maintaining the Thickness of the part at 2.5 mm. The component is designed using Surface design and Solid Design techniques in Catia V5 application.

Introduction:

Draft Angle:

• Draft is an angular tapering given at the design stage to every Plastic component that has to be manufactured.
• It is given in the direction of the Mold Movement.
• The draft allows the parts to release easily from the mold without creating friction between the surface of component and the core and cavity plates.
• When a Plastic component cools down inside the mold, the natural tendency of it is to shrink and attach to the core or cavity half.
• The movement of mold opening causes friction on the walls of the component as well as the core/cavity blocks.
• This reduces the life of the mold as well as the component itself.
• The component may also have rough surface finish as well as weak structure due to this method.
• This problem can be solved by giving draft to the component.
• Most applications require minimum draft angles of around 0.5⁰ to 1⁰, however 3⁰ draft angles are widely accepted for cost saving purpose.
• 7⁰ Draft angles are given to textured surfaces like Instrument Panels.
• Minimum possible draft angles are given to screw bosses, ribs and stiffeners due to their critical nature.

Tooling Axis:

• Tooling Axis is the direction in which the mold opens and closes.
• Part Drafts are given along this axis.

Side Core Axis:

• Some features or walls are difficult to clear by the Main tooling axis itself.
• These features may have negative draft angle or are a part of a sub feature which is an important part and cannot be ignored.
• These features need a different tooling direction for clearing the part in the mold.
• This tooling direction is called Side Core Axis which often tends to clear the Sub features or walls at different angle with respect to Main Tooling Axis.

Draft Analysis:

• Draft Analysis is a tool in Catia which identifies the zones which deviates from the specified values of angles along a defined draft direction using colour codes.
• It highlights the region of draft using colours.
• Draft Analysis is the first step performed after receiving the Class A of the component.
• Draft analysis should be passed in order to make the plastic component manufacturable.
• Since it is the factor which decides perfect ejection of part from the Mold.
• Acceptable draft angles are used as range for draft analysis.
• Acceptable ranges are decided before planning to manufacture the product and it may vary from product to product.

Class A Surface:

• In automotive design, a class A surface is any of a set freeform surfaces of high efficiency and quality. It is the visible aesthetic surface of any automotive component.
• Class A surface refers to those surfaces which are visible and abide to the physical meaning, in a product.
• This classification is primarily used in the automotive and increasingly in consumer goods industry.
• It is a requirement where aesthetics has a significant contribution.
• For this reason, the exterior of automobiles is deemed Class A.

Class B Surface:

• Class B surfaces are engineering surfaces which are invisible to the eyes or often on the back side of the Class A surfaces.
• It is mainly the thickness of the component or Class A.
• These surfaces need to be designed as per the Class A surface i.e., the continuity, thickness of the component, functionality etc should be maintained.
• These surfaces include the main engineering features such as Screw bosses, Ribs, Stiffeners and fixations.
• B surfaces also do not contain any aesthetic styling content and textures since it is not visible to eyes.

Class C Surface:

• Class C surfaces are connectors between Class A and Class B surfaces.
• This surface connects both A and B surfaces along or angled to the Tooling Axis.
• It contains the draft as per the design.
• It is basically the thickened surface between both A and B surface.

Design Methodology:

            The design methodology of Door Arm Rest Design is explained through flow charts.

                                           

Description:

Class A (Input):

• After receiving the Class-A surface for the Door Arm Rest check for the connectivity of the surfaces on it.
• Use Boundary operation and disassemble.
• Check for discontinuous Surfaces.
• Any discontinuities do not arise, if the check is over.

Creation of Tooling Axis & Side Core Axis:

• Identify faces which can Potentially create problems while manufacturing.
• Surfaces at angles along a desired Tooling Axis.
• Extract a plain surface and create a point on its center for Axis system creation.
• In this case, Z axis can be a possible Tooling Axis direction.
• The highlighted faces could create a problem in terms of draft analysis along this axis.
• Create a sketch on the XZ plane of the Axis System and use Intersect 3D to plane option to get the sketch.
• The left Wall is at a negative angle with respect to the proposed Tooling Axis.
• The right wall can be cleared using the main axis. So, create a line at an angle greater than the accepted angle for draft analysis passing through the Origin.
• This Line is the Tool Clearing Axis for X.
• Do similar steps for the YZ plane.
• The tooling created here is Y tooling.
• Use Bisecting line option to bisect both the tool clearing axis and pass the bisecting line through the point.
• Now the Main Tooling Axis is created as shown in below image.

Tooling Axis:

Side Core Axis:

Draft Analysis on Class A along all Clearing Directions:

• Change View Mode Customization to Material mode.
• Clicking on Insert Tab, selecting Analysis and then select Feature draft analysis and drag the compass to the tooling axis.
• The input Class A also has walls having negative angle to the tooling axis.
• This can be an issue while manufacturing the component as it would be very difficult to draw from the molds.
• So, this design needs to consider various side tooling options.
• To clear the Bin wall a Side Tooling along Y can be considered as a possibility.
• Create a line along Y axis through a point on the bin surface.
• Perform draft analysis through this axis.
• If clearance not achieved, orient the compass as per requirement.
• When Clearance is achieved that is when the green range occurs on the required Bin Wall, Lock the compass orientation.
• Now Change the line direction to the compass direction.
• The created Side core Tooling Axis is shown in below image.

Draft Analysis 1:

Draft Analysis 2:

Creation of Class B Surface:

• Extract the Class A Surfaces for example the Door Arm Rest surface.
• Untrim it to obtain a continuous surface.
• Extrapolate the obtained surface to a value such that it passes the class A door rest arm surface.
• Offset the surface to value of 2.5 mm on B side which is downwards in this case.
• Perform similar operations for all the surfaces and obtain the offset and trim it with the Base to Obtain Bin on Class B side surface.
• Similar operations to be performed on the Arm rest face and the Walls.
• Use Similar options for the Side Walls and Upper Surface.
• Use Extrapolate option only on required direction to obtain the surface trims.
• Use fillets, so as to maintain wall thickness to 2.5mm.
• Create Fillets while maintaining the part thickness of 2.5 mm between the class A and Class B surfaces.
• The Value of Fillet is given by the equation (B surface fillet = A surface fillet +/- Thickness of the part).
• The sign + or – must be decided, so as to maintain the part thickness which in this case is 2.5 mm.
• To create a connecting surface for the Class B surface, create a point on the Class A surface and create another point on the same surface with respect to mid-point of blend surface and create Point to Point line with respect to created points.
• Then use multiple extract command to extract the center line which passes though the existing created centre point and use smooth curve command to the extracted line.
• Then use sweep command to create surface for before created lines.
• Offset the surface for 2.5 mm downwards.
• Perform similar above operations to create Class B surface.
• The Class B Surface is shown in below image.

Creation of Class C Surface:

• For creating Class C Surface, the commands were used like Multiple Extract, Curve Smooth, Sweep, Extract, Multi-section Surface and Join.
• Here, Multiple Extract command used to extract the boundary of Class A surface.
• Curve Smooth command used to make a multiple curve into single smooth curve.
• Then using sweep command to form surface which could join the Class A and Class B surface.
• Clicking on the Sweep option, the dialog box appears in that select profile type as type 2, subtype as with reference surface, Guide curve as Curve Smooth, reference as Class A surface, Angle as 90⁰, Length as 4 mm and click Ok to perform the operation.
• The above same procedure was followed to create the Class C surface.
• Once the Class C surfaces created and then join the multiple surfaces into single surface.
• The Class C surface is shown in below image.

 Final Trim:

• Trimming the Class B surface and Class C surface to get output trim.
• Again, trim command is used to trim with sweep to get patched surface to cover the hole gap.
• Then, joining before created trim surface with Class A surface.
• Continuing the same process to get closed surface to develop solid Part Body.
• Final Trimmed surface is shown in below image.

Creation of Closed Part Body:

• Switch to Part Design Workbench and use Closed Surface option to create a Solid Part from the final obtained surfaces.
• The part created is the required Door Arm Rest Component designed from a Class A.
• The Closed Part Body is shown in below image.

Draft Analysis on Closed Part Body:

• Change View Mode Customization to Material mode.
• Clicking on Insert Tab, selecting Analysis and then select Feature draft analysis and drag the compass to the tooling axis and lock the compass position.
• Then click on the closed part body, to check the part whether its clearing all required faces on respective Tooling Axis that as created.

Draft Analysis on Closed Part Body 1:

Draft Analysis on Closed Part Body 2:

Standard Views:

Front View:

Back View:

Right Side View:

Left Side View:

Top View:

Bottom View:

Isometric View:

Final Assembly View:

Conclusion:

            Successfully created the design of automotive plastic component – Door Arm Rest from Class A surface by developing Tooling Axis, Class B surface, Class C surface, Closed Part Body and Draft Analysis using Catia V5 application.