Week 9 - Attachment Feature Creation - Challenge 2

                                  DOG HOUSE AND SCREW BOSS WITH IN COIN HOLDER

OBJECTIVE:

To create the dog house and screw boss in the center console model based on the above design criteria using CATIA.

PROCEDURE:

SCREW BOSS CREATION:

• 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.
• Designing plastic screw bosses is fairly straightforward but there are a few considerstions to ensure a strong connection between parts and mitigate cosmetic defects.
• First i created two circles in the sketch.The inner-circle diameter was assumed to be 5.2mm,the outer circle was arrived by using the design parameter.Thickness of the screw boss should not be higher than 40% of the base.
• we know that the base of the coin holder is 2.5mm.therfore 2.5*0.40=1 mm.there by the diameter of the outer circle =(1*2)+5.2=7.2 mm.
• Height of the screw boss is given by the height to diameter ratio=3:1,thereby the value of height =3*5.2= 15.6mm.
• As per the given design parameters the draft angle and the fillet is provided.The optional edge fillet here is given as 0.25 mm thereby meeting the design parameter

NOTE:

As shown in the above model the screw boss created was strength using the ribs 

DOG HOUSE CREATION:

• The dog house is an engineering feature used in plastic trim design.Doghouse are used as supporting features.Sometimes other engineering features like snap,locaters etc.Mounded on them to increase their strength.Dog house are subjected to draft analysis to prevent breakage of the component during ejection from mould cavity.Dog house and other engineering components are built on B surface.
• First i created a base sketch in a rectangular pattern (with one side made as construction,this was intentionally done inorder avoid plastic defects like flow lines.
• The sketch was then extruded to a height of 12 mm as shown below.Next i used the command "sweep" to get the dog house to draft along the inner direction of 1.5 deg (assumed based on the conventional industrial standards).
• Then to adjust the height and bring it a perfect dog house i used the command surface untrim,offset and trim.As we can observe in the above image,the 3D solid was made out of the surface design using the "thickening command".But still the edges are not proper so i used the command extract,surface untrim of the dog house and made it a complete one using split command.
• The draft angle of the inner side of the dog house for 0.5 deg.The edge fillet for the inner side of the dog house is given a nominal diameter of 1mm.The height of the dog house is given 4mm whereas in the given design parameters it was indicated between (3-6 mm).
• To achieve the C value in the dog house as mentioned in the question,I have made an extract on the inner face of the dog house and an offset for 1mm (0.45*2.5= 1 mm).Edge fillets were done on the inner side of dog house( intersection of a part wall C) for a nominal 0.5mm .This was done to achive a proper draft analysis result.
• The earlier created screw boss was translated to a position above the dog house.Thereby the dog house serving its purpose of strengthing the coin holder and also acts a bridge by joining the screw boss with adjoining part.

DRAFT ANALYSIS:

• The draft analysis is carried out both for the component and the engineering features to ensure the feasibility and avoid the plastic defects after manufacturing.
• This procedure is carried out by creating the tooling direction at first.The bisecting method,where the bisection of the intersection component and the plane is taken.
• The bisecting line of the two opposing walls of the bin along the orgin point yields the tooling direction.
• The draft analysis for the component is pretty much undoable considering the draftless walls in the class A.Hence a maximized tooling direction which clearing the surface is taken into account.The slider direction is provided to clear out the stiffner rear side and the side cut hole profile where it is a undercut.As we can see the draft angle is 0.5 degree which is standard value for the internal features.

TOOLING DIRECTION:

• We will be creating the tooling direction with bisecting method,for that will have to check on Z dirctions.Since here we have a bit difference case because the part is oriented differently. What we have  is that,its not having symmentry one of side. 

CONCLUSION:

Create the dog house and screw boss for the center console coin holder considering the design rules.

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