Generative Shape Design of Door Arm Rest

OBJECTIVE

Conduct a Draft Analysis for the Door Arm Rest Model by determining the appropriate Tooling Axis and check if all the features are above the Nominal Draft angle (3 degrees).

PROCEDURE

STEP 1: CHECK CONNECTIVITY

We have to ensure that the Class A Surface is connected as one single profile. We can do that with 2 options:

Visually	Using the Join option. This option is efficient but not effective.
Manually	Extracting the Boundary of the Class A surface. This option confirms better.

STEP 2: FIND THE TOOLING AXIS

• Tooling Axis is the direction in which the Mold(Core-Cavity) travels perpendicular to the parting surface/line.
• Place the component on each plane (XY/YZ/ZX) and find the desirable tooling direction.

[Note: The plausible tooling axis is perpendicular to a Hole or large flat surface so look for those features when selecting.]

• So we need to create a midpoint on the plane perpendicular to the tooling axis.

Holes	Use Multiple extracts to get the Boundary and define a midpoint using the "Curve/Circle" option.
Flat Surfaces	Extract the surface and then create a mid-point using the "On Surface" option.

• Now, introduce an Axis system at the Midpoint. This will act as a reference coordinate system.

STEP 3: EXTRACT THE BOUNDARY FOR BISECTING THE TOOLING AXIS

• Intersect the respective plane with respect to the component.
• We get a First Angle projection of the component with respect to the direction of view.
• Analyze if each profile will pass the tooling.

• Note:
  • Perpendicular lines always pass the draft analysis.
  • Check the Fillet radius.
  • Manually check for the Parallel(almost parallel) lines to ensure they have a positive draft angle.

STEP 4: DRAW THE TOOLING/DRAFTING AXIS

• Extend the almost parallel lines by drawing lines with a Point-Point definition.
• Bisect the lines with respect to the center point to get the "Dummy Tooling Axis"
• We can view the Tooling from 2 different planes (Front and Side view) so repeat the above procedure for the other plane.
• Finally, Bisect both the "Dummy Tooling Axis" with respect to the center point to get the Final Tooling Axis.
• Publish the tooling axis and the Class A surface so it becomes easy to access during future operations.

• Due to the complexity of the part, it needs a Side Core/ Lifter along with the main Core.
• Therefore, we have introduced a Side tooling using the bisecting method as well.

STEP 5: DRAFT ANALYSIS FOR CLASS A

Insert > Analysis > Feature Draft Analysis

Note: Ensure you have the Material view mode ON.

• Define the Draft direction using the "Compass" option.
  • Drag the Axis system representation close to the model and align it along the tooling axis.
• "Lock" the Draft direction.
• Set the Colour scale

Colour	Description	Value
Green	Core Side	Above 3 degrees
Blue	Parting Line	0 degrees
Red	Cavity Side	Below 0 degrees

Method 1: Manual Selection	Method 2: Visual Selection
Analyze each feature manually. Place the Arrow icon on each feature to check if it passes the minimum draft angle. We can distinguish each feature's angle using the colour scale.	Directly choosing the plane (XY/YZ/ZX), that would pose fewer problems for tooling. This also ensures that the features (fillets) are captured on that plane. Analyze the entire geometry at one go.

Method 2 is more efficient as it gives us an overall result of the draft analysis without manually picking any feature.

STEP 5: B SURFACE CREATION

Note: Depending on the geometry, the extraction and offset of the fillets might generate non-uniform thickness. So it is advisable to extract only the flat surfaces and then apply fillets at the end of Class B formation.

Perform the following operations in the order:

EXTRACT	Choose the respective A surface and extract with no propagation option.
UNTRIM	The extracted surface will possess the specific trimmed. Untrim to get the basic geometry.
EXTRAPOLATE	The surfaces have to overlap each other in order to facilitate trimming therefore extrapolate it up to the required dimension.
TRIM	Trim the surfaces according to the required geometry.
OFFSET	Now, Offset the Trimmed geometry by the value of the thickness of the component. This Offset is our B Surface.
FILLET	Extract the Fillet surface from Class A. Untrim to get the basic Geometric shape. Measure the uniform radius of the surface. Apply Fillet to the respective edges to get the desired finish.

Extracted, Untrimmed and Extrapolated surfaces	Trimmed B surface with Fillet

Note: The fillet radius of the Class B offset is altered to maintain the uniform thickness throughout the geometry.

Offset direction	Fillet Radius
Inward	Initial Radius - Thickness
Outward	initial Radius + Thickness

STEP 6: C SURFACE CREATION

C surface is the part of the geometry that connects Class A with B surface.

Rules to be followed. for C surface creation:

• A minimum draft of 3 degrees should be provided to facilitate the Ejection of the Molded component.
• The parting line should be on the B surface. This means that the draft should sweep outwards, from the C surface.

Perform the following operations in the order:

MULTIPLE EXTRACT	Extract only the Boundary by Tangential selection.
CURVE SMOOTH	We need minimum Parting lines as possibles, so smoothen the extracted boundary.
SWEEP	The C surface is swept with the Line option along the Drafting Angle Direction. Guide Curve: Select the Smoothened Curve Draft Direction: Select the Tooling Axis Draft Angle: 3 Degrees
MULTI-SECTIONS SURFACE	In places like Fillets where the Sweep option doesn't work, we can fill in the gap using MSS. Choose the Sections. Then choose the Guide Curve along which we can drag the profile.
EXTRAPOLATE	The Sweeps at the edges need to overlap in
JOIN	For our future reference, we can Join all the C surface sweeps as one single entity.

STEP 7: CLOSED SURFACE

• First Trim/Join Class A with Class C.
• Then Trim with Class B and keep the respective surfaces.

Surfaces to Trim	Closed Surface

STEP 9: SOLID BODY

• Switch to Part Workbench.
• Define the part body.
• Select the closed surface trim to fill it with volume.
• Now we have a solid body with a certain volume and density (depending on the material we give).

STEP 10: FINAL DRAFT ANALYSIS

All the 3 class surfaces must pass in this analysis.

Insert > Analysis > Feature Draft Analysis

Note: Ensure you have the Material view mode ON.

• Define the Draft direction using the "Compass" option.
  • Drag the Axis system representation close to the model and align it along the tooling axis.
• "Lock" the Draft direction.
• Set the Colour scale

Colour	Description	Value
Green	Core Side	Above 3 degrees
Blue	Parting Line	0 degrees
Red	Cavity Side	Below 0 degrees

• Place the Analysis Tool (Arrow Icon) anywhere on the model and review the colours on the feature.
• If any feature (especially C surface) is showing Blue/Red then choose the same option again (It will switch to Analysis under Running point) and place on the respective feature to review the deviation of the sweep angle from the Tooling Axis.

Some surfaces failing for the Main tooling:	The failed surfaces are passed by the Side tooling:

RESULT

We get the following Desirable Outcome:

Green	Class A and C Has a Projection, falls into the Core side.
Red	Class B. Has a depression, falls into the Cavity side.

• Since we have done the Initial Analysis for Class A, the only area for drafting error might occur in Class C.
• If Class C shows Red/Blue in colour, then the draft given is not right and we have to edit the sweep angle to get the draft above 3 degrees.
• Rectify the error until we get the Desired output and submit the final model.