Attachment Feature Creation - DOGHOUSE

OBJECTIVE: To create the Door Trim Plastic Component from the given Class A Surface & then create two dog houses as attachment features for it while following the issued Design Guidelines.

 

KEYSHOT RENDERINGS OF THE FINAL FILES:

 

Use case of Dog-House in any Plastic Component: The dog-house is an engineering feature used in the plastic trim design that is used as a supporting feature. Sometimes other engineering features like snaps; locators etc. are mounted on them to increase their strength. Usually, this engineering component is built on the B-surface and is subjected to draft analysis to prevent breakage of the component during ejection from the mould cavity.

Wall Thickness: Thick sections waste material and are simply uneconomic. So solid shapes that would do the job well in wood or metal must be transformed to a 'shell' form in plastics. This is done by hollowing out or 'coring' thick parts so you are left with a component which regardless of complexity is composed essentially of relatively thin walls joined by curves, angles, corners, ribs, steps and offsets. As far as possible, all these walls should be the same thickness. The Wall thickness guide range is 0.75 mm to 3mm for reinforced materials and 0.5 mm to 5 mm for unreinforced materials.

 

Fillet Radius: Properly designed corners will make a big difference to the quality, strength and dimensional accuracy of a moulding. But there is another benefit too. Smooth curved corners help plastic flow in the mould by reducing pressure drops in the cavity and minimising flow-front break-up. Internal radii should be at least 0.5 and preferably 0.6 to 0.75 times the wall thickness.

 

Draft Angle: Tooling must be cleared for easy ejection of the component, from the core cavity. In order to clear tooling certain value of draft is given to the component. A minimum of 1-3deg is provided on all plastic components.

DESIGN GUIDELINES FOR DOGHOUSE IN THIS CHALLENGE:

•  Doghouse wall thickness at the intersection of the part wall ( C ) should be 40% or less than the main wall stock ( T ). 

• The height of  ( B ) should be between 3.0 – 6.0 mm 

• The draft angle with respect to the Main Tooling Axis should be 3 degrees & the Side Core Axis should be 1.5 degrees. 

 

Examples of Doghouses with Screw Boss, Locator & Snap Head respectively:

        

 

 

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.

 

Since the direction is the most important factor while creating the Main Tooling Axis, we'll just pick any vertex at the extremity of the Class A Surface or Use the Inertia Method to find out the Center of Gravity and use that point to create a line along the required direction for the Main Tooling Axis. We have to perform a draft analysis on the Class A Surface to crosscheck if feasible to be the Main Tooling Axis or not.

 

The steps for creating the Main Tooling Axis are shown below:

This method may not work for every component but it was considered to be used for this component.

We'll click on the 'Measure Inertia' icon from the 'Measure Toolbar' as shown below:

 

We'll select our Class A Surface that will open up the 'Measure Inertia' dialogue box as shown below:

After that, we'll click on the 'Create Geometry' option in our Measure Inertia Window that'll open up the 'Creation of Geometry' window. 

There we'll choose 'Non-Associative Geometry' and then click on 'Center of Gravity' to create the required C.G point as shown below:

 

Now, using the 'Line-Definition' command while choosing our Line-Type as 'Point-Direction' we'll create a line along the X-Axis as shown below:

 

DRAFT ANALYSIS FOR THE CLASS A SURFACE USING THE MAIN TOOLING AXIS FROM THE FIRST METHOD:

Now, We will perform a Draft Analysis on the Class A Surface itself using the Main Tooling Axis created using the First Method:

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'.

Upon careful inspection, we found some regions that are not clearing the Draft Angle as shown below:

 

If this project needed to be created in a real industrial environment then we have to contact the Class A Surface Designer and ask them to fix these regions but since this is just a challenge we're going to proceed with it anyway.

It is evident from the above image that the Draft-Analysis on our Class A Surface was successful for the degree of 3 degrees. 

Hence, we can see that the Draft Analysis was successful along the Main Tooling Axis.

 

PROCEDURE TO CREATE THE CLASS B SURFACE:

We'll start the procedure by creating an offset for the entire Class A Surface at a distance of 2.5mm as that is the desired thickness for our final plastic component.
As this is a complex surface hence the offset will fail to offset every element according to our necessity. It'll select some sub-elements that belong to the filleted regions by themselves that we have to remove to get the rest of the surface that is offset.

This warning will be shown when we'll try to offset the Class A Surface.

These 'Sub-Elements' will get selected by themselves to be removed if we want to obtain the rest of the offsetted surface.

Now, we're going to fix these patches by recreating these sub-elements using various tools such as Extract, Offset, Untrim, Extrapolate, Multi-Sections Surface, Trim, etc.

Class B Surface after 2.5mm Offset:

Fixed Class B Surface:

 

PROCEDURE TO CREATE THE CLASS C SURFACE:

We'll create the Class C Surface with respect to the Class A Surface and provide draft angles to those surfaces that are parallel to the Main Tooling Axis. Surfaces at the bottom won't be needing any draft angle as they'll get cleared by the core itself. To create the Class C Surface we have to use various commands such as Sweep with Reference Surface and With Draft-Direction depending upon the necessity and at places where it'll be difficult for us to create a surface using Sweep, we'll use Multi-Sections Surface to create those surfaces. The draft angle will be 3 degrees. 

Using Sweep Command with Draft Direction to create the C Surface:

   

Using Multi-Section Surface where it is necessary:

 

Final Class C Surface:

 

Finally, we'll join the Class A & Class C Surface together as shown below:

Then, we'll create an intersection with the Class B Surface and check if it is feasible to trim with each other. After inspecting the intersection, we noticed that the Class B Surface was not intersecting with the Joined surface of Class A & C and hence we extrapolated the Class B Surface as shown below:

After this we trimmed the extrapolated Class B Surface with the joined surface of Class A & C as shown below:

 

To check whether this body is closed or not we'll use the Boundary Command on it as shown below:

From the above image, we can see that the final closed body doesn't have any boundaries, and hence our final closed body is obtained successfully.

Finally, we'll go to the Part Workbench and use the option 'Closed Surface' from the 'Surface-based Features' toolbar to convert the final trimmed body into a solid body as shown below:

 

PROCEDURE TO CREATE THE DOGHOUSE:

Reference Image provided for the construction of two doghouses:

It is just a reference image and doesn't exactly adhere to all the design rules but we have to take the reference image into account to create these doghouses on our plastic component.

 

First, we'll begin by creating the sketch for the doghouse as shown below:

From the sketch, we can see that the width of the doghouse is more than 12mm which is one of the design rules. We cannot go below that value.

Then, we'll use the Sweep Command with the Draft Direction to provide a draft angle of 3 degrees with respect to the Main Tooling Axis as shown below:

   

From the above image, we can see that 1.5 degrees draft angle is provided to the sweep surface.

After this, we're going to use the Multi-Sections Surface command to create the top face of the doghouse as shown below and join it with the sweep surface:

Now we're going to move on to the Part Workbench and use the Thick Surface command from the Surface-based Features toolbar to thicken the surfaces by 2mm as shown below:

Then we're going to provide a draft angle of 1.5 degrees to all the adjacent faces as shown below using the Draft Command in the Part Workbench:

After this, we're going to remove the material from the lower section of the doghouse for coring and to do that we going to use create a base surface of the doghouse using the Multi-Section Surface command and then offset it by 4mm. Then, we used the Multi-extract command to extract the inner faces of the doghouse and trim it as shown below:

Now, according to the design rule, the thickness of the coring section's wall should be 40% value of our part's thickness and 40% of 2.5 is 1mm and our current wall thickness of the doghouse is 1.685mm. Hence, we're going to offset this trimmed surface by 0.685mm and extrapolate it so that we can use the Split Command from the Park Workbench to remove material from the doghouse as shown below:

After that, we'll provide a draft angle of 1.5 degrees to the newly formed surface made using the coring operation as shown below:

Finally, we're going to provide all the necessary edge fillets on the required surfaces following the design rules as shown below:

Hence, our doghouse is finally complete and we'll make the second house following the same design rules. 

Now, we'll perform a draft analysis operation on our doghouse to make sure that is clearing along the required tooling axes as shown below:

 

DRAFT ANALYSIS WITH RESPECT TO THE MAIN TOOLING AXIS:

First, we'll place the compass on the Main Tooling Axis as shown below:

Then, we'll set the value to 1.45 degrees as the required draft angle was 1.5degrees and inspect it as shown below:

We're only needed to clear the outer surfaces of the doghouse using the Main Tooling Axis and from the above image, we can clearly see that is achieved here.

 

DRAFT ANALYSIS WITH RESPECT TO THE SIDE CORE AXIS:

Now, the inner section of the doghouse is needed to clear along the side core axis and hence now we'll place the compass on the Side Core Axis and perform the draft analysis as shown below:

From the above image, we can see that the draft analysis was successful and hence our doghouse will get cleared along both the Main Tooling Axis as well as the Side Core Axis.

 

Now, using Boolean Operations, we're going to assemble these doghouses with our main plastic component and create the final part as shown below:

 

DRAFT ANALYSIS ON THE FINAL PLASTIC COMPONENT WITH ATTACHMENT FEATURES:

 

From the above images, we can clearly see that the draft analysis was successful and every necessary surface is clearing the draft angle. 

 

3D VIEWS OF THE FINAL PART WITH PROPER COLOR CODE OF THE DRAFT ANGLE IN VARIOUS ORIENTATIONS:

1. FRONT VIEW:

 

2. TOP VIEW:

 

3. ISOMETRIC VIEW:

 

 

TREE STRUCTURE:

1. CLASS A SURFACE:

 

2. MAIN TOOLING AXIS:

 

3. CLASS B SURFACE:

      

   

 

 

4. CLASS C SURFACE ELEMENTS:

      

      

      

   

 

5. FINAL JOIN AND TRIM OPERATIONS:

 

6. DOG HOUSE CREATION:

 

 

8. PART BODY AND DRAFT ANALYSIS:

 

 

9. PUBLICATIONS:

 

THANK YOU :)