Week 9 - Attachment Feature Creation (Ribs & Screw Boss) - Challenge 1

AIM

To create the rib and screw boss for the Drill Handle.

REPORT

1. Creation of tooling axis

• At first we check the class A surface is ok by using the boundary option.
• After that we extract the base surface which identified as the best place for tooling axis to pass through.
• Create a point on the center of that surface.
• Draw a dummy line perpendicular to the surface passing through the point.
• Create a plane parallel to the curve and use intersection option to create the intersection line.
• Indentify the points or place which could cause trouble while moulding.
• Draw a line on both sides as below.
• Now using bisecting line method create a bisecting line passing through the point.
• This line is our tooling axis.

2. Draft analysis on class A

• Open the draft analysis toolbar.
• Click on the compass icon and drag and place the compass on tooling axis.
• Click anywhere on the body to run the analysis/
• From the image we can see that the class A clears the tooling parametrs.

3. Creation of B surface

• To create the B surface, first we offset the class A inside by 2.5mm.
• Check for any patches are formed on the surface, like,,

• Using the boundaries, multi section surfaces and join operation we create the B suface

4. Creation of C surface.

• Identify the sharp corners in the Class A surface.
• Accordingly we create multiple sweeps depending on the number of boundaries.
• Exrapolate al these sweeps.
• Trim them to get the C surface.

5. Final Join

• At first join both the A and C surface.
• Then extrapolate all the sides of class B to a min distance.
• Then using the trim option, we join both B and A+C surfaces.

6. Creation of closed surface.

• Open the part workbench.
• Click on closed surface option.
• Click on the object and the final body is generated.

7. Creation of Ribs

• Extract the top surface of the final body.
  
• Create a point on the center of the surface.
• Create a plane normal to curve
• Create a sketch of the first rib

• Extrude the line from the sketch to 12.5 mm since the rib depth is 5 times the thickness. Also extrude the line downwards of 1mm.
• Apply thickness to this rib which is typically 40% of the nominal wall at the base, i.e 1mm.
• Apply draft to the rib for 0.5 degrees.
• Apply fillets to the rib for 0.25 radius.
• Then union trim the rib to the main body.
• Then create another rib at a particular distance in this case, following the same steps above.

Design rules to follow while creating ribs are:

• Min draft: 0.5mm per side
• Rib thickness-: 0.4*t
• Min thk on tip of rib: 0.75mm
• Max Rib fillet radius: 0.25mm
• Rib height: less than 5* nominal wall thickness
• Rib should be spaced with a height to width ratio: 3:1 or 2:1

8. Creation of Screw boss

The guide lines are:

1. The outside diameter of boss should remain within 2.0 to 2.4 times the outside diameter of the screw or insert.
2. Min draft: 0.5mm on wall of boss
3. Thk: 40% of nominal wall of base
4. Height to dia ratio: 3:1
5. Boss gussets must meet rib guidelines
6. Max fillet radius: 0.25mm

• Create a sketch for the screw boss as shown:

• Pad the sketch for 12.5mm and 1mm inside
• Give draft for 0.5 degrees.
• Create a support for the screw boss following the below sketch.

• Pad it to 7mm and 1mm inside. Also apply thick option.
• Give draft for 0.5degrees.
• Give a chamfer for every edge.
• Union trim this support to the screw boss
• Apply edge fillets.
• Union trim this to the main body.
• Similarly create one more screw boss.

9. Intersect

10. Draft Analysis on Closed Surface

• Draft analysis is done on the finished surface.
• The design clears the draft analysis.

RESULTS

1. ISOMETRIC VIEW

2. FRONT VIEW

3. SIDE VIEW

4. TOP VIEW