Week 9 - Attachment Feature Creation - Challenge 2
Aim :
To Create the boss and Dog House for the Centre console coin holder considering the design rules mentioned in the video.
Screw boss :
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. Bosses are typically used to assist in assembly, as a receptacle for a screw or threaded insert or as the locator for a mating pin on another part.
General Guidelines for Bosses:
- Draft - 0.5 degrees on walls of boss
- Thickness - Typically 40%* of the nominal wall at the base.
- Height to Diameter Ratio - 3:1
- Radii - 0.25mm maximum radii.
Step 1 :
The sketch for the screw boss is drawn on the B side surface since screw bosses are B side attachment features. The dia of the dog house is claculated based on the wall thickness of the part body and also based the fastner sizes.
Step 2 :
The sketch for the boss is extruded. The height of the extrusion can be any value but i have followed 5T (T = Wall thickness of part body).
Step 3 :
Profile for the ribs is drawn. which is basically two line intersecting each others at midpoint. the presence of ribs for the boses will improve the strength of the tall boses.
Step 4 :
Now the rib sketche is paded with a thickness of 1mm ( w = 40% of T ). NAd the height of the pad will be determined based on the plastic body thickness ( h =5 * T ) .Then draft angle of 0.5 deg is applied to the rib faces. After drafting fillets are applied to the corners of the ribs with the value of 0.25mm optional radii.
Step 5 :
Draft for the outer surface of the Boss is done with the defined angular value of 0.5 deg. Actually draft should be done befor the rib creation for orderly operations.
Step 6 :
Now the boss created is added to the main plastic part body and the edge fillet is added to the joined porting with radii of 0.25mm. This boss can be copy pasted using Copy - paste special - as result with link and translated to the next point using cordinated translation or poin t to point translation or point translation, here i have translated using co-ordinates.
Dog House :
Dog house is an engineering feature used in plastic trim design. Dog houses are used as supporting feature. Sometimes other engineering features like snaps; locators etc. are mounded on them to increase their strength.
Desgin Guidelines for Dog house :
"C" is where the doghouse contacts the backside of the surface.
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Doghouse wall thickness at the intersection of the part wall ( C ) should be 40% or less than the main wall stock ( T ).
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Height of ( B ) should be between 3.0 – 6.0 mm
Step 7 :
Sketch for the outer faces of the doug house is created and swept along the tooling axis. Basically a square is drawn and one side of the square is converted into construction line and the remaining three sides are extruded.
Step 8 :
The base of the class B surafce is extracted and offsetted to a distance to create the top face of the dog house. This is then trimmed with the side faces to form Dog house. Then the dog house is changed to
Step 9 :
Creating offset for the side faces of 1mm and offsetting the base to 3mm to create Coaring. Coaring is created to reduce the heat sink and other defects at the A sruface where the dog house intersects. From the dog house structure the created surface for coaring is splitted and then added to the part body.
Step 10 :
Now draft for the inner faces of the dog house is created. Fillets at the required faces are given. Draft analysis for the dog house is checked. Draft angle for the inner faces of the dog house is given in the direction of side core movement as 0.5deg.
Step 11 :
Now the translated boss is translated again above the dog house .
Step 12 :
Final draft analysis for the whole body is done and verified that all the faces have the required draft angle.
Final part body with ribs , screwbosses and doghouse are displayed.
The below image shows the proper tree structure followed for various geometrical sets and the requred things are publiched as per the question.
