Attachment Feature Creation (Ribs & Screw Boss)

OBJECTIVE: To create the Door Handle Plastic Component from the given Class A Surface & then create attachment features such as Ribs and Screw Bosses for it while following the issued Design Guidelines. 

 

KEYSHOT RENDERING OF THE FINAL FILE:

 

Use case of Rib in any Plastic Component: Ribs provide economic stiffness and strength in moulded parts without increasing overall wall thickness. 

They also facilitate the followings:

1. Locating & arresting components of an assembly,

2. Providing alignments in mating parts,

3. Acting as stops or guides for mechanisms. 

 

If we don't use these ribs then we've to increase the thickness of the component which will lead to added cost, weight and plastic defects due to the increased thickness. 

Thick ribs are the leading cause of sink mark defect that turns into cosmetic problems on the opposite surface of the wall to which they're attached.

The material, thickness of the rib, surface texture, colour, proximity to a gate, etc are some of the factors to determine the severity of the sink.

Highly glossy, critical surfaces may require thinner ribs, placing ribs opposite character marks or steps can hide rib-read-through.

Thin-walled parts(<1.5mm) can often tolerate ribs that are thicker than the percentage in these guidelines. On parts with wall thicknesses that are 1.0mm or less, the rib thickness should be equal to the wall thickness. Rib thickness also directly affects mould ability. Very thin ribs can be difficult to fill because of flow hesitation, thin ribs near the gate can sometimes be more difficult to fill than those further away.

Flow entering the thin ribs hesitates and freezes while the thicker wall sections fill. Ribs usually project from the main wall in the mould-opening direction and are formed in blind holes in the mould steel. To facilitate part ejection from the mould, ribs generally require at least one-half degree of draft per side. More than 1* of draft per side can lead to an excessive reduction in rib thickness that can lead to filling issues in the case of taller ribs. 

Generally, taller ribs provide greater support but to avoid mould filling, venting and ejection issues standard rules of thumb limit the height to approximately 5 times the base thickness of the component as the top section of the tall ribs may become too thin to fill easily.

Additionally, very tall ribs are prone to buckling under load. If we encounter one of these conditions, we can consider designing two or more shorter, thinner ribs to provide the same support with improved mould ability. We have to maintain enough space between ribs for adequate mould cooling. For shorter ribs, we have to provide a spacing distance that is at least two times the wall thickness.

 

DESIGN GUIDELINES FOR RIBS IN THIS CHALLENGE:

1. Draft-Angle of 0.5 degrees on each side.

2. Base-Thickness for the Rib = 0.4 times(40% approx) the Thickness of the Plastic Component

3. Minimum Thickness at the Rib's tip should be greater than 0.75mm.

4. Optional Rib's fillet radius can be taken as 0.25mm while not violating the base thickness condition.

 

Use case of Screw Boss in any Plastic Component: Bosses find use in many part designs as points for attachment and assembly. The most common variety consists of cylindrical projections with holes designed to receive screws, threaded inserts, or other types of fastening hardware. As a rule of thumb, the outside diameter of bosses should remain within 2 to 2.4 times the outside diameter of the screw or insert.

Avoid bosses that merge into the sidewalls because they can form thick sections that lead to sinking. Instead, position the bosses away from the sidewalls and if needed use connecting ribs for support. Bosses that merge into the sidewalls can lead to the formation of thick sections that can lead to sinking. Instead, position the sidewalls away from the sidewalls and if needed, use connecting ribs for support. Consider using open boss designs for bosses near sidewalls. 

Normally, the boss hole should extend up to the base wall level, even if the full wall is not needed for assembly. Shallower holes can leave thick sections, resulting in sinks or voids. Deeper holes reduce the base wall thickness, leading to filling problems, knit lines, or surface blemishes. The goal is to maintain a uniform thickness of the attachment wall because of the required draft, tall bosses- those greater than 5 times their outside diameter can create a filling problem at their top or thick section at their base.

 

DESIGN GUIDELINES FOR SCREW BOSSES IN THIS CHALLENGE:

1. Base Thickness = 0.6*Thickness of the Plastic Component.

2. Optional Fillet Radius = 0.25mm

3. Draft Angle = 0.5mm

4. Height to Diameter Ratio = 3:1 or 2:1 

 

First, we will begin by checking the State of Connectivity for the Class A Surface and ensure that there are no gaps between the surfaces as all the surfaces should be joined well together with each other and shouldn't consist of any discontinuities between them.

 

Our Class A Surface:

There are two methods to inspect the State of Connectivity for the Class A Surface:

1. Using the 'Join' Command' from the 'Operations Toolbar': 

First, we'll click on 'Join Command' and select our Class A Surface. Then, we have to ensure that the 'Check Connexity' option is marked as shown in the images below. It will check for any gaps that may be present between our surfaces. Then, we'll click on the 'Preview' button and if it doesn't show any 'Connexity Error' on our surface then it means our surface is well-connected and there are no discontinuities between it.

In our case, there are no 'Connexity Errors' for the given Class A Surface. 

In case there is a 'Connexity Error', we can fix it by increasing the 'Merging-Distance' and then performing a join operation between those surfaces.  

 

2. Using the 'Boundary' Command' from the Operations Toolbar: 

In this case, we have to click on the 'Boundary' command and then select the Class-A Surface. After that, we'll click on the 'Preview' button to highlight all the boundaries that are on the Class-A surface and check if there are any internal boundaries other than the outer edge boundaries. 

In our case, there is only one boundary present on the Class-A Surface which is the Outer-Edge Boundary and hence we can conclude that all the surfaces are well connected.

 

PROCEDURE TO CREATE THE MAIN TOOLING AXIS:

We'll view the Class A Surface from different axes to find out the optimal axis along which we can create our Tooling Axis:

View from the X-Axis:

From the above image, we can see that not much surface area is exposed along this axis and hence this cannot be the direction along which we can create our Main Tooling Axis:

 

View from the Z-axis:

From the above image, we can see that not much area is exposed along this direction as well and hence this as well cannot be the direction along which we can create our Main Tooling Axis.

 

View from the Y-axis:

From the above image, we can see that the maximum surface area is exposed along this axis and hence we have to construct our Main Tooling Axis along this direction.

 

Now, we'll create a plane such that it will allow us to create an intersection as shown below using which we can create our Main Tooling Axis:

After that, we'll create two lines on the edges of the component and use those two lines to create a bisecting line as shown below:

 

DRAFT ANALYSIS ON THE CLASS A SURFACE:

Next, We will perform a Draft Analysis on the Class A Surface itself:

Before starting with a Draft Analysis Operation, we will go to the 'Customize View Parameters' option under the 'View Toolbar'. Then we will enter the 'Customize View Mode' where we will go under the 'Mesh' option and select 'Material' and press 'OK'.

To start the Draft Analysis in the 'Generative Surface Design Workbench', we will go to 'Insert' and then look for the option called 'Analysis'. Once found, we will go under that and click on 'Feature Draft Analysis. This will open the 'Draft Analysis' Dialogue box. There, we will ensure that under 'Mode'  we have selected 'Quick Analysis', under 'Display' we will select 'Show or Hide the Color Scale' and then select '3 Degrees' as the permissible draft angle. Then, under 'Direction' we will choose the icon with the symbol of the compass on it which stands for 'Use the Compass to define the new current draft direction'.

 

PROCEDURE TO CREATE THE CLASS B SURFACE:

First, we'll offset the Class A Surface by 2.5mm as shown below:

It won't be able to successfully offset each and every section of the Class A Surface.

This warning will be shown to us when we'll try to offset it.

From the above image, we can see the surface that will be removed from the offsetted surface.

We will reconstruct that surface using a command known as Multi-Section Surface as shown below:

Final Class B Surface:

 

 

PROCEDURE TO CREATE THE CLASS C SURFACE:

We'll use Sweep Command with Draft Direction & Reference Surface depending upon our needs and construct our Class C Surface as shown below:

 

After this, we'll join our Class A Surface with the Class C Surface as shown below:

CLASS A + CLASS C:

 

Now, before trimming this joined surface with the Class B Surface we'll create an intersection between them to check whether the Trim-Operation is feasible to perform or not because if they're not intersecting properly then we cannot trim them with each other.

After inspecting the intersection we noticed that they were not intersecting with each other properly and there was some extrapolation needed in the Class B Surface.

Extrapolated Class B Surface:

 

Now, we'll trim them with each other as shown below:

This is a completely closed body as there are no boundaries present on it. If we want to verify it, we can use the boundary command on it and if it gives us the error shown below that means we're correct. 

 

Finally, we'll go to the Part Workbench and use the Closed Surface command from the Surface-based Features Toolbar to create our solid door handle plastic component as shown below:

 

PROCEDURE TO CREATE RIBS FOR THE DOOR HANDLE USING DESIGN RULES:

First, we'll create a point and a projection point that can be used to create a sketch as shown below:

After this, we'll use the Extrude Command in the Surface Workbench to Extrude these lines for 12.5mm with respect to the Main Tooling Axis. The reason we're deciding the height as 12.5mm is that the thickness of our plastic component is 2.5mm and according to the given design rules for ribs, we can make the height of our ribs up to 5 times the value of the thickness of the component. 

Hence, 2.5*5 = 12.5mm

We'll also provide a second limit of 1mm so that the extruded surface doesn't have any gaps from the surface of the component.

Now, we'll go to the Part Workbench and use the thicken command to make the extruded surface thick by 0.5mm on each side as shown below:

The thickness of the Rib is 1mm because according to the design rule we're supposed to create the rib with 40% thickness of the plastic component and since the thickness of our plastic component was 2.5mm hence 40% of 2.5mm is 1mm. 

Now, we're going to provide the draft of 0.5 degrees on each side of our rib in accordance with the design rules as shown below: 

After applying the draft angle on both ribs we'll use the measure tool to measure the distance between two edges at the upper section of the rib that was supposed to be higher than 0.75mm so that molten plastic can flow in it easily to eventually fill it properly. 

From the above image, we can see that the distance between two edges after applying the draft angle is 0.782mm which satisfies our design conditions.

Now, we're going to perform a Boolean Operation known as Union Trim to get rid of sections of ribs that are protruding outside of our components shown below:

Now, we'll apply the fillet values at each and every face of our ribs for a value of 0.25 according to our design rules as shown below:

Hence our ribs are made for this component following all the necessary design rules.

 

RIB'S ANALYSIS VIA INTERSECTION: 

The rib's root thickness is lower than 40% of the thickness of the component and hence it won't cause a sink mark for the rib and hence the rib is feasible to manufacture.

 

PROCEDURE TO CREATE SCREW BOSSES FOR THE DOOR HANDLE USING DESIGN RULES:

 First, we'll begin by creating the sketch for the Screw Bosses. We'll consider the Inner Hole's diameter as 3.5mm.

Hence, to calculate the outside diameter we have to calculate 60% of 3.5 and multiply it by 2 and then add it to the value of the inner diameter as shown below:

Outer Diameter: ((3.5*0.6)*2 + 3.5)mm = 7.7mm

 

After this, we'll use the Pad Command in the Part Workbench to extrude these two bosses to a certain height. 

To find out the height up to which can extrude it, we have to use the Height-Diameter ratio stated in the design rules that instructs us to use either 3:1 or 2:1. We'll use 2:1 for now. Here, the diameter's value is of the outer diameter and hence the height will be 7.7*2mm = 15.4mm

We'll provide the second limit of 1mm so that there won't be any possible gap between the extruded section and the plastic component. 

 After that, we'll apply a draft angle of 0.5 degrees on both bosses according to the design rules as shown below:

Finally, we'll apply a fillet value of 0.25 on each and every edge of the bosses as shown below:

Finally, both our ribs and bosses are ready for the plastic component and using boolean operations we'll add it to the main body.

 

BOSS'S ANALYSIS VIA INTERSECTION:

 

DRAFT ANALYSIS ON THE FINAL BODY:

Finally, we'll perform the Draft Analysis for the Final Part in the Part Workbench:

We'll click on the 'Draft Analysis' under the 'Analysis' Toolbar in the Part Workbench.

Then, we'll click on the Compass Symbol under 'Direction' which stands for 'Use the Compass to define the new current draft direction'.

We'll drag and place the compass on the Main Tooling-Axis.

Then, we'll select 'Show or Hide the Color Scale' under 'Display' and define our Draft-Angle as 3-Degrees. After that, we'll click on the surface of the Final Part to show the results as shown below:

 

 

In the Draft-Analysis,

Green Colour stands for regions where the Draft Angle is more than 3 degrees,

Blue Colour stands for regions where the Draft-Angle is between 0-3 degrees, &

Red Colour  stands for regions where the Draft Angle is lower than 0 degrees

INVERSING THE DRAFT DIRECTION:

 

For the Draft Analysis of our attachments, we'll enter 0.45 degrees as our value on our colour scale to see if they're clearing the needed draft angle or not as shown below:

 

3D VIEWS OF THE FINAL PART IN VARIOUS ORIENTATIONS:

1. FRONT VIEW:

 

 

2. TOP VIEW:

 

3. SIDE VIEW:

 

4. ISOMETRIC VIEW:

 

TREE STRUCTURE:

1. CLASS  A SURFACE: 

 

2. MAIN TOOLING AXIS:

 

3. CLASS B SURFACE:

   

 

4. CLASS C SURFACE:

 

   

   

   

 

5. FINAL JOIN & TRIM OPERATIONS:

 

6. DESIGN OF RIBS:

 

7. DESIGN OF SCREW BOSSES:

 

8. PART WORKBENCH:

 

 

9. PUBLICATIONS:

 

 

THE REQUIRED CATPART IS ATTACHED WITH THE REPORT IN A ZIP FILE.