Week 8 - Challenge 5 - Core & Cavity Design

CONSTRUCTION of CORE and CAVITY BLOCKS and DRAFT ANALYSIS

Draft analysis technique is used to analyze whether our part model created in CAD is manufacturable or not. The part should get easily removed from the mould or die. No part can be ejected from the tool if it is having straight 90 degree angle from its base surface. A small draft angle is provided to each and every area of the component and we are providing a direction in which components should eject in order to easily remove the component from the tool.

Draft Angle is the amount of taper given to the molded parts perpendicular to the parting line. As the plastic cools it shrinks and sticks to the mould surface and therefore need draft angle while ejecting, and to avoid damage. Normal draft angle is 3 degree. Increasing draft value will increase manufacturing cost.

TOOLING AXIS

In order to perform analysis, we need to create tooling axis and in order to do that we need to check class A surface first. We need to check whether all the surfaces are closed or not using boundary option. Once inspection is complete, we need to create separate geometrical set for tooling axis. We need to choose the axis in such a way that all the pockets, holes, sections etc. should get covered. For example, once inspection is completed, we concluded that Z axis is the tooling axis. Now we extract the base surface from class A. We then create a point at the centre of the extracted surface and place an axis system at that point.

Now create a sketch using intersection. Draw two lines using point-point option. Then create bisecting line using previous two lines.

Now we do one more sketch on XZ plane. Since we dont have any inclined lines we just create a line at the point at an angle of 4 degree from the surface.

Now we usee both the lines and create bisecting line. This is our TOOLING AXIS.

Class B surface creation

Now the top surface and walls of class A is extracted using extract option. Then surfaces are untrimmed to get original surfaces. Then these faces are extrapolated to form intersection between them. An offset of 2.5mm is given and all the surfaces are trimmed togather to form B surface. Required edge fillets are given to B surface.

Class C surface creation

Here the outer boundry of class A surface is extracted first and then sweep command is used to create the surface with draft angle of 3 degree and direction along tooling axis. Now the class A surface & class C surface are joined togather with thickness value of 0.003mm. Finally all the surfaces A,B & C are trimmed togather to form a closed surface.

Now we go to part workbench and select closed surface option to close it and form solid component.

DRAFT ANALYSIS

Now we need to check whether material mode of class A surface is in customize view parameters. Now go to Insert – Analysis - Feature draft analysis. Select the compass mode and drag the compass to the tooling axis of surface or part. Now select the surface to activate the surface and lock it using lock button. You can also do analysis during running point and move mouse all over the surface to check degree and draft angle. You can do analysis on full scale mode or quick scale mode. The color change shows change in draft angle.

PARTING SURFACE design

Now extract the boundary of class A surface and extrapolate it. Trim it with class C surface.

Now trim the above surface with B surface to get required parting surface.

CORE and CAVITY BLOCK design

Now draw a rectangle sketch in XY plane and make sure it is within the parting surface. Now extrude the sketch on both the sides to create the core side and trim it with parting surface.

Now extract the top boundary of the extrude and use fill option to fill it. Now join the surfaces and use close surface option in part workbench to close it and form a solid core block.

Now to create cavity block repeat the same steps as done for core block. Extrude from the same rectangular sketch in opposite direction and trim with parting surface. Extract outer lower boundary of extrude and use fill option. then close the surface and form solid cavity block.

Now to make parting line the join between Class A & C surface is trimmed with parting surface. Now an intersection between the trimmed surface is taken which is our parting line.

The orange is core block and green is cavity block . The red dotted line is parting line.