Week 9 - Attachment Feature Creation (Ribs & Screw Boss) - Challenge 1
Attachment Feature Creation (Ribs & Screw Boss) :-
To Create the Attachment Features (Ribs & Screw Boss) on A Door Handle through the given Class-A surface by creating tooling direction, the tooling axis for the given Class-A Surface should meet the requirements of the draft angle.
RIBS-
Ribs are indispensable functional structures on many plastic parts. It can effectively improve the rigidity and strength of plastic parts like the H beam. Ribs are generally designed on the non-appearing surface of the plastic part, and its direction is as close as possible to the flow direction of plastic melt filling. Ribs should neither be too long nor too thick, otherwise, it will increase the difficulty of injection moulding, causing problems such as voids and sink marks on the back.
BOSS-
Bosses are common structures on plastic parts in home appliances and interior and exterior of auto-mobiles, mainly for positioning and fastening. The base of bosses often cause sink marks on the back surface of a part, this is because of the large wall thickness. The solution is to core out some material at the base.
- Draft - 0.5 degrees on the walls of boss
- Thickness - Typically 40%* of the nominal wall at the base.
- Height to Diameter Ratio - 3:1
- Radii - 0.25mm maximum radii.
Given below drawings are the referance for ribs and bosses position-
Given Class A Surface-
Class B Surface Creation-
To create class B surface offset the class A with proper direction and distance. Here distance is the thickness of the component. As no given thickness is provided, so we are asuming the thickness value is 3MM. Reasult after offseting-
Perticulerly the marked area of the surface not offseted properly. So we will fill that area and the final surface is class B surface.
Class C Surface Creation-
To create class C surface create boundary using class A surface boundary with 'Boundary' command in 5 parts. And use 'Sweep' command to create a surface that is in 90 deg. angle with class A surface. The reasulyent surface will be the class C surface.
Final Closed Surface-
Class C surface trimmed with class B surface properly and joined with class A.
Solid Body-
Using 'Closed Surface' command of Part Workbench we have to make make the body solid.
RIBS-
As per design standerds we will create a sketch where ribs are needed.
Extrude those line upto the 5 times the base thickness that is 15MM, but we are taking here 12MM. Then using 'thicken' command thicken that part 1.2MM as per design standerd(0.4*Base thickness(3MM)). Then give draft for both wall with nutraf surface(Class B) of minimum 0.5 degree. We can give draft more than that, but tip thickness should not less than 0.75MM. After that give fillet of all surface with fillet value 0.25MM. Now ribs are almost done.
Now we have to check all the design parameters again-
As we can see all design parameters are according to design standerds.
SCREW BOSS-
We are considering a M6 screw to design the screw boss. So we will create a sketch of two 5.5MM inner dia circle. And will 'Pad' those with 3:1 height and base thickness ratio, where thickness of boss wall will be 0.6 times base thickness. Also have to give draft of minimum 0.5 degree with nutral surface of class B. Lastly give fillets of 0.25MM.
Now we will cross check all the dimensions-
Draft Analysis-
Designers of plastic parts and mould tooling manufacturers can use the Draft Analysis tool to check the correct application of draft to the faces of their part. With draft analysis, you can verify draft angles, examine angle changes within a face, as well as locate parting lines, injection, and ejection surfaces in parts.
Tooling Axis-
For this case as no hole is concerned, so we will try to consider the perpendicular axis of that dented curved surface, for creating the tooling axis. So we will analyse bothe perpendicular plane.
Plane1-
In this plane we have created a intersection. And two line have been also created with doubted sutface line. Then we have created a bisecting line with those line.
Plane 2-
For this plane we have created two intersection line with two concerned surfaces. Then cteated two line with angle of 10 degree with those concerned surfaces. After that created another bisecting line with those angled line.
Finally with two bisected line create another bisecting line and that will be the final tooling axis.
Class A Surface draft analysis-
Almost all surface area are clearing draft angle of 3 degree. Some area are clearing draft angle of 1.1 degree.
Solid body draft analysis-
So, from the solid body draft analysis we can see that all surface includong RIBS and SCREW BOSSES are clearing the 0.5 degree draft angle. So this plastic part is manufacturable with B side engineering features in injection process.
Views of final model-
Publication-
Tree Structure of geometrical sets-
