Week 9 - Attachment Feature Creation - Challenge 2

DESIGN RULES FOR SCREW BOSS AND DOG HOUSE FEATURES:

AIM: to design screw-boss and dog house on the coin holder considering every design rules in the industry.

TOPICS COVERED:

1. Creation of tooling axis

2. Design of screw boss

3. Desgin of dog house

4. Draft analysis report on dog house.

THEORY:

Class-B surface contains all the engineer data required for the model to be completed. This data involves designing of various features. Some of the major features of the B-side are:

1. Ribs

2. Screw boss design

3. Dog house design

SCREW BOSS: they are used for the purpose of mating two parts. They have hole in them which accepts the threaded part of the fasteners such as screws.

GENERAL DESIGN GUIDELINES FOR SCREW BOSS DESIGN:

1. Draft: 5 deg on each walls.

2. Wall thickness: 40% of the nominal wall thickness i.e. 0.4't where t is the wall thickness which is 2.5mm in this case.

3. Height/diameter: 3:1 steel but 2:1 is preferred.

4. Radius of the fillet: minimum 0.25mm.

5. Boss gussets (rib like structure giving strength to the screw boss) must meet ribs guidelines. 6. Avoid merging the screw-boss into wide wall.

DOG HOUSE: primary function of the dog house is to avoid sink marks. But it also helps in other things like if the mating part is to be at a greater distance then we cannot make the height of the screw boss of that greater height, thus we make dog house and mount screw boss on it. Hence it helps in solving the problem of screw boss and also it helps to have perpendicular screw boss.

GENERAL DESIGN GUIDELINES FOR DOG HOUSE DESIGN:

1. Minimum height: Less than 6mm causes steel condition.

2. 3:1 ratio of steel width to height. But 2:1 is preferred.

3. Minimum width: 3:1 ratio of steel width to height. But 2:1 is preferred. 4. Draft: minimum 1.5deg.

5. Sink saver, height= 40% of nominal thickness. Width= 3.0mm-6.0mm. 6. Optimal radius: 25mm

APPROACH:

CREATION OF TOOLING AXIS:

In this model we have made two tooling axis, one for clearing the outside faces of the dog house and other for clearing the inside faces of the dog house. These two axes are in two different directions viz. along z and along y.

Bisecting method for creating the tooling axis:

1. Make an axis system and intersect the model to be analyzed with the required plane of the system. For example is we are confused about the two faces of the model if they have draft or not and those face seems to be vertical then we will intersect the front plane with the model.

2. Once we get the intersection line, we will make lines on the lines which represent those surfaces.

3. Then we will bisect those lines to get one line. 4. This will be the tooling axis for those faces only.

5. Then we will do the similar process for the other two parallel faces which are perpendicular to the earlier faces so that we get two lines which intersect each other.

6. Once we get two lines which are tooling axis for two different pair of faces, we will make a line which bisects these two lines.

7. This new line will be our required tooling axis.

The reason we are using two tooling axis here is that the dog house has an open face. So we will need a side core for the injection molding process. Thus it will need a separate tooling axis. Here we just made a tooling axis perpendicular to the earlier tooling axis which runs along the direction of open face of the dog house.

FOR SCREW BOSS:

1. First make a positioned sketch on the z-x plane for the screw boss.

2. Pad the sketch and we get the cylinder which is initial screw boss structure. 3. Draft both the cylindrical faces it with minimum 0.5 deg draft.

4. Make sure the wall thickness is in accordance with the design standards i.e. 0.4*t.

5. Also while giving height to the pad, give it within the limits. 6. To enhance the strength of the screw boss we make gussets which are rib like structure.

7. First make the sketch of the gussets as shown in the image.

8. Then pad the sketch with thick feature on and ensure that the resulting pad is in the middle. Make sure the thickness is in accordance with the design rules of the ribs i.e. 0.4*t and also the height should not be more than 5*t.

9. Give draft to the gussets i.e. minimum 0.5deg.

10. Union-trim it with the screw boss and add/assemble it to the main model.

11. Give minimum edge fillet to it i.e. 0.25mm.

IMAGES (IN ORDER OF THE STEPS MENTIONED ABOVE)

1.

2. 

3.

4. 

FOR DOG HOUSE:

We made a ditto screw boss for the dog house:

1. Copy the existing screw boss.

2. Paste special in the main part file.

3. Translate it to the desired position.

For making dog house we follow the given steps:

1. Make a rectangle to enclose the screw boss in it but make sure it is open from one side.

2. Sweep it with tooling axis as the pulling direction and give minimum draft of 1.5deg inwards.

3. Enclose it from the top by using the off-set of extract of the base of class-A surface. The offset distance determines the height of the

dog house, so give it according to the design rules.

4. Go to part design and thicken the surface. Thickness should be according to the design rules.

5. The inward face of the dog house should the drafted too, so give them a draft of 0.5deg.

6. After this we have to design the sink saver at the bottom of the dog house:

7. Use the same extract of class-A, and offset it at the height of 3mm-6mm. 8. Extract the inside faces of the dog house and offset it outwards at 0.4't. This is the width of the sink saver denoted as "C" in the

FOR DOG HOUSE:

We made a ditto screw boss for the dog house:

1. Copy the existing screw boss.

2. Paste special in the main part file.

3. Translate it to the desired position.

For making dog house we follow the given steps:

1. Make a rectangle to enclose the screw boss in it but make sure it is open from one side.

2. Sweep it with tooling axis as the pulling direction and give minimum draft of 1.5deg inwards.

3. Enclose it from the top by using the off-set of extract of the base of class-A surface. The offset distance determines the height of the

dog house, so give it according to the design rules.

4. Go to part design and thicken the surface. Thickness should be according to the design rules.

5. The inward face of the dog house should the drafted too, so give them a draft of 0.5deg.

6. After this we have to design the sink saver at the bottom of the dog house:

7. Use the same extract of class-A, and offset it at the height of 3mm-6mm.

8. Extract the inside faces of the dog house and offset it outwards at 0.4't. This is the width of the sink saver denoted as "C" in the

9. Trim them togeth

10. Go to the part design and split it with the model.

11. After that we will fillet the entire model of the dog house and add it to the main body.

12. Later we mount the screw boss on the dog house by translating it.

IMAGES (IN ORDER OF THE STEPS MENTIONED ABOVE)

DRAFT ANALYSIS OF THE DOG HOUSE:

Draft analysis is done to prevent breakage of the component while ejection from the mould cavity. It tells us which faces will clear according to the tooling axis chosen by us. Following steps are followed to do the draft analysis:

1. Go to insert-analysis

2. Choose the compass and place it along the main tooling axis first.

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3. Lock it and click on the component. We will see colors on the component. 4. As we cannot run two draft analysis on the same component, use the compass for the side core tooling axis.

5. Lock it and click on the inner face. We will see colors on it.

6. We should get the desired faces in green color.

What are these colors?

To understand the color code first we have to know the color scale. This option pops-up a small window where we can give three different colors to three different values of. These values are nothing but the draft values that we can change. For example if we give 0.5deg value in green, Odeg in blue and the last as red:

1. The surfaces which are in green color means that the draft value it has is more than 0.5deg and it will not create problem.

2. The surfaces in blue have the draft value between Odeg to 0.5deg (in this example).

3. The surfaces in red have the draft value in negative.

Now if we are getting inside surfaces in red for the main tooling axis. This result is correct as we know that those faces will not clear this axis and has a different axis for that. But if we expected any outer surface in green but it is either in blue or red then either we have to give draft or we have to modify our tooling axis. Basically the idea here is that the component will create problem while ejection. Hence the component should be in green.

1. The outer faces using the main tooling axis cleared the test.

the faces were in green.

2. The inner faces had a small patch of surfaces (shown below) in red. This meant the draft had to be given on those. After correcting all the faces were in green.

FINAL COMPONENT