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

Aim

Create the rib for the Drill Handle considering the design rules mentioned in the video.

INTRODUCTION:

CLASS-A SURFACE: A surface made by the designer which is given as an input to the plastic modeler/ sheet metal designer to work on. It is aesthetic surface and the outer most surface.

CLASS-B SURFACE: A surface below a certain thickness from the class-A surface is class-B surface. This is the surface that contains engineering aspects of a model for example Ribs cutout.

CLASS-C SURFACE: A surface that joins class-A and class-B surfaces together is called as a class-C surface.

Report

A detailed report should be done explaining the draft analysis and the tooling axis creation.

An explanation should be given on the way of creating the tooling axis, particularly the Bisecting method.

Draft Analysis:- Draft is a taper applied to the faces of the part that prevent them from being parallel to the motion of the mold opening. This keeps the part from being damaged due to the scraping as the part is ejected out of the mold, to do that the analysis is done and known as Draft Analysis

Tooling axis: The direction in which the mold or core and cavity opens is called as the tooling axis.

Tooling axis creation

As we can see in 3D the tooling direction should be Y direction we can conclude by seeing that the tooling axis should be in this direction but for surity we need to do a visual inspection from every direction

Visual inspection

As we are seeing the class A surface in X direction but not able to see all the faces

As seeing the class A from z direction but not able to see all the faces

But seeing it from y direction we are able to see all faces thats means the tooling axis will be in y direction

Bisecting Method

The one section surface of the class A was extracted and a point at the centre is created and an axis system was inserted to the point with the current feature is disabled.

Then use the intersection curve command to intesect the class A along YZ direction and get the intersection and draw 2 lines from the curved faces and then use the Bisecting line command to make the Tooling axis and the line appear will be our Tooling Axis

In order to check the correctness off the tooling axis choose tooling axis and select normal to view you didnt able to see the tooling axis by this check we can be sure that the tooling axis is correct

Class A Surface Draft Analysis

Note- Due to the irreguraties in class A surface the Blue region is appear in draft analysis to rectify this issue we need to send an RFI to Class A surface team mentioning that there need to be draft provided and they will rectify this issue and correct and send the new class A surface to work

Creation of Class B:

• Now for Class B creation, we need to offset the class A surface inside by 3 mm and this is going to be our B surface
• Then we use the boundary command to check whether this is a gap or missing surface (mostly fillet created this problem)
• Then we need to make the missing surface either use the blend command, multi section solid or the last option is extract the both surface extrapolate it and then trim them and then join them

Use Multi Section Surface to Fill that region

Creation of Class C:

The outer edges are extracted and then using the sweep (with reference surface) command the class C surface is created and at some egdes use the multisection to creat the surface which is not sweep and then join all the surfaces with the Class A surface

Class A + Class C:

Then both class A and class C surface are joined to get the surface which is going to be trimmed off with class B surface in order to get the closed surface

Class A + Class B + Class C:

After trimming we get the closed surface and then we go to part design and use closed surace to create the plastic part

Draft Analysis for Solid Plastic Part

First the class – A surface is checked before creating the Class –B&C surface and finally the solid body must be analysed. Both can be done by following the below procedures.

By changing the view mode to custom view parameters – Material mode then the feature draft analysis is enabled.

Then the compass was activated and placed with the tooling axis by dragging the red pointer and then locked it.

Then, by selecting the quick analysis mode, the nominal value will be 3 degrees and checked for the component's draft angle.

The green colour area shows that it satisfies the 3-degree draft angle. If not satisfied then by using the Running point tool the area is measured and then altered to get a successful draft for the created tooling direction.

Note: As due to software issue the edges are showing the negative draft but the draft given is correct and after discussion with TSC it was confirmed that there is a software issue thats why it is showing the red region on the side edges and as show in the image there is 3 degree draft given.

B Side Features Creation

Rib Creation

Design Priincipals for Rib Creation

Ribs are thin wall protrusions that extend perpendicularly from a wall or plane. They are usually found in clusters offering support to a plane that would have otherwise been too thick, but can also be stand-alone support for a single wall. They are commonly used to provide additional support and strength to a part. Thickness and location are essential to rib design.

First, the base surface where the rib has to be created is extracted using the Extract command. A positioned sketch is created and the profile for the rib is drawn.

Next, the profile is extruded, to find the height,h=Wall thickness * 5

=2.5*5

= 12.5 mm

Therefore, the height is 12.5 mm

The extruded surface is thickened,

Thickness,w=0.4*t

=0.4 2.5

=1mm

Therefore, the thickness of the rib is 1 mm

• The draft is applied to the sides of the ribs. As per the design rule, the ideal draft angle is 0.5 deg
• Then fillet is applied to the faces of the rib. As per the design rule, the fillet can be 0.25 mm.
• Now copy the whole body and paste special and then translate the other Rib as per the distance

Rib Analysis and the Rib root thickness.

To check for the Rib root thickness, We have to take an Intersection with the XY plane and the Coin holder component. Once we get to the intersection we have to create a tri-tangent circle at the rib area and measure it the thickness will come 1mm and the dia will be around 2mm

Rib Tip radius value must be within 30% greater of the wall thickness

0.03x2.5=0.75mm

The minimum distance between the 2 ribs should be 2XThickness of the part (As shown in the below image)

2*2.5=5mm

CREATING THE SCREW BOSS

Screw Boss features are commonly found in injection molding designs. They are used to aid in the assembly of molded parts by providing a channel for a screw. Their primary use is to strengthen holes or slots in the surface present in the part model.

Design rules consider while creating a screw boss

• Thickness- Typically 40%* of the nominal wall at the base.

• Draft- 0.5 degrees on the walls of boss

• optional radii- 0.25mm maximum radii.

• Height to Diameter Ratio - 3:1

• Boss gussets must meet rib guidlines

• Type of ejection

The construction process of creating the screw boss is explained below:

For thickness, the design rule is as follows,

Thickness,w=0.6*T

=0.6*2.5

=1.5 mm

Therefore, the thickness of the boss can be 1.5 mm per side.

In this case, we have considered the size of the screw boss as M06 so inside radius should be 2.6mm and Thickness of the screw boss is 5.2+1.5+1.5=8.2

• Once the sketch is completed, then it is padded using the Pad'command. The height to diameter ratio can be 3:1(H=5.2*3=15.6)
• The draft is given to the boss. As per the design rule, the draft given for screw boss is 0.5 deg with tooling direction.
• Then fillet is applied to the faces of the rib. As per the design rule, the fillet can be 0.25 mm.
• Now copy the whole body and paste special and then translate the other Rib as per the distance

Screw Boss Analysis

As per the above mentioned design every point is satisfied as shown is the below image

Draft Analysis of the final part with ribs and the screw boss (Engineering Features)

Screenshots of the solid model with the proper color code of the draft angle in various orientations (Isometric, Front, Side, and Top View)

Isometric View

Front Side

Side View

Top View

Tree Structure

Refer to the below-given image to understand the position of the Screw Boss and Ribs

Please find the attached part file for your review