Week 9 - Attachment Feature Creation - Challenge 2

DESIGN OF SCREW BOSS AND DOG HOUSE IN COIN HOLDER PART

In this report we are going to see the design of screw boss and a dog house in a coin holder part . In the last model we sawed about the rib design and now we are goin to add screw boss and dog house.

DESIGN OF SCREW HOUSE 

Before entering in to the screw boss model, we need to know about the need of screw boss in a plastic component, adavantages and design rules.

Screw boss

It uses in many part designs as a points for attachment and assembly. Most common variety of the cylindrical projections with holes designed to recieve screws, thread inserts or other type of fastening hardware.

DESIGN RULE FOR SCREW BOSS

• DRAFT : The Draft angle for the scree boss is 0.5 degree.
• WALL THICKNESS: The wall thickness is 0.6*T per side of the screw boss. T is the main base thickness of the part.
• HEIGHT TO DIAMETER RATIO: The ratio to height to diameter is 3:1. 
• OPTIMAL RADIUS : The minimum optimal radius value is 0.25mm.

    One of the major concern for designing a screw boss is avoid merging the screw boss with the side wall, they can form thick sections that lead to an plastic defect of sink mark. Position the boss away from the side walls use connnecting rods for support.

DESIGN OF A SCREW BOSS

First create an positioned sketch with the projection as the base of the coin holder as an extract feature and projection point is center of the tooling axis.

Consider creating an M6 screw to a part. So, the diameter of the hole is 5.2mm, the wall thickness for the scree boss is 0.6T. The thickness(T) of the part is 2.5mm. Hence the wall thickness per side is 0.6*2.5= 1.5mm/side. The total thickness is 3mm. The outer dia has the value of 5.2+3=8.2mm.

Check the created sketch as an iso constarianed sketch, and create an body for a pad . The pad has height of 12mm . The height can be calculated by Height/Diameter ratio of 3:1.

Apply the Draft angle to screw dia of 0.5 degree with neutral element as an base extract of coin holder and the filllet radius of 0.25mm.

RIBS FOR SCREW BOSS: For an screw boss the rib support is an much needed one to sustain more load to a screw boss. The design rules are same as we followed in previous rib designs.

The rib height as to be 10mm because the height of the screw boss is 12mm it as to be much lesser height than the screw boss and the thickkness of rib is 1mm as per the rule 40% of the main base thickness of part. Apply the required draft and fillet radius and union trim them to cut the inner portion of the rib inside the screw hole.

To create a Screw boss on the other side, use translation feature. Before translation copy the screw boss part and paste special as a result with link and translate them with the coordinates values of x,y,z.

INTERSECTION VIEW AND DIMENSIONS OF SCREW BOSS

• Draft angle of the screw boss is 0.5 degree
• wall thickness is 0.6T; 0.6*2.5=1.5mm/ side; whole thickness value is 1.5*2= 3mm.Which is 5.2mm inner dia + thickness 3mm = 8.2mm.
• Height of the screw boss is Height to diameter ratio of 3:1; which is H/5.2= 3/1; H= 5.2*3= 15.6mm. We have taken minimum of 12mm.
• Rib height is 10mm
• Minimum radius is 0.25mm.

DESIGN OF DOG HOUSE

The primary function of an Dog house is to avoid the sink mark in the surface  by creating an lesser cross section to avoid the sink mark. The secondary one is to used to reduce the height of the screw boss when we need to create a screw specific height, but according to the design rule we cant create a screw boss , so dog house was used to increase some height and create a screw boss above the dog house surface.

DESIGN RULES AND GUIDELINES 

• The Wall thickness of Dog house intersection(C) should be 40% less than the main wall (T) stock.
• Height(B) should be beyween 3-6mm.
• Minimum height(H) of dog house is 6mm.
• Minimum drafy angle is 1.5 degree.

DESIGN PROCEDURE OF AN DOG HOUSE

Create an postioned sketch by creating a point as refrence of an screw circle and create an sketch. Extract the base of the CLASS A  part offset to 2.5mm for a sketch of Dog House.

Make one side of the dog house box as a construction line to be open on one side. Width as 12mm , we have to give according to the model of the part. The Rib of Screw Boss is 10mm and Dog house be 12mm . 

Sweep the sketch to make easy to give draft angle and height value in a single feature.

Sweep with the draft direction feature angle of 1.5 degree and length of 20mm. 21mm is use to trim when offset the top surface.

Thicken the trim surface to 2mm towards outside direction.

Split the extracted offset surface to cut the extra portion of the dog house.

Draft the inner faces of the Dog house with the pulling direction as line created through Z direction.

Fillet radius as 3mm on outer portions and 1mm to the inner portion of the the dog house.

To design the lesser cross section of the dog house extract the inner section of dog house with no propagation and offset to 1mm outer section. In the lower offse the base extract of 4mm upward to cut the cross section to trim and split them .

Draft the lower cut portion of 1.5 degree with pilling direction of z axis line. 

Translate the screw boos to the Y direction to move upward of the dog house.

Intersection view and Dimensions of Dog House

• Dog House wall thickness at the intersection of wall (C) should be 40% less than main wall thickness(t). T=2.5MM; C=1mm.
• Height of the intersection sholud be 3mm-6mm. Here we used as 4mm.
• Total height of the dog house is totally depends on ur choice. We have given of 22mm

DRAFT ANALYSIS FOR DOG HOUSE AND SCREW BOSS MAIN TOOLING AXIS AND SIDE CORE 

We already created the draft analaysis with the two ribs , In this model we add extra two parts screw boss and a dog house. The screw boos can be cleared throught the main tooling axis but the dog house inner faces can be cleared only through the side core. 

*Draft analysis for Dog House and screw boss

The outer surface of the dog house and screw boss was cleared through the main tooling axis. 

*SIDE CORE TOOLING AXIS

The inner faces of the dog house can be cleared through a separate side core tooling axis. Take a  point direction line feature with the centre point of the main tooling axis as a refrence and directed alog z direction for side core tooling axis. Place the compass to the z direction of the tooling axis to apply the draft analaysis for side core.

GEOMETRICAL SETS TREE STRUCTURE

SKETCH SOLVING STATUS

*Sketch of Screw Boss

*Sketch of Screw Boss Ribs

*Sketch of Dog House

DIFFERENTIAL VIEWS OF MODEL

Front view

Side view

Top view

Isometric view