Join Thom Tremblay for an in-depth discussion in this video Applying draft, part of Fusion 360: Designing for Plastics.
- [Instructor] Faces that lie along the axis of mold separation must include a shallow angle called draft to make sure that the still hot part is not distorted, or remains stuck in the mold cavity. I'd like to turn on the origin planes, and take a look at the Z axis represented in blue. This would be the direction of our mold separation, if we were to make an injection molded part out of this design. Looking at it, there would be different surfaces, on different sides of the void, that the plastic is injected into.
For example, the holes would be developed by a body that sat on the cavity side, or this side of the model, the A side. The same would be true for this opening. The geometry for this web support, and the ribs, would be developed on the B side. You need to keep this in mind when adding draft to phases. I'll start out first, by addressing the draft issues around this frame, that support the LCD panel.
I'll start the draft tool, select the back face as the draft plane. And then, select the faces around the outside of the frame, as those that will have draft applied to them. Looking more closely, there's a curved manipulator I can use to change that draft angle. You can see in this case, it's a very dramatic angle that I've added, but in reality two degrees should be just fine.
So it will kick the bottom edge of these faces outward, two degrees. And, that will work well for the core side. However, this opening will be developed from the other side. So, I'll start the draft tool again, selecting the same face, and then choosing the inside faces. But, for these faces, instead of the bottom edge tipping in, it would tip out because in the mold this edge would be the one that's at the bottom of the feature, defining it.
So, I'll tip this angle back out, and we'll make that minus two degrees. Let's go ahead and add draft to the grill. This will be a fairly complex feature, but the selection options in Fusion 360 should help me out. I'll start the draft tool again, this time selecting the back face. And, then for the model faces, I'll reorient the model, so that I'm looking at the front.
I'll check my selection options to make sure that selection filters has select through, turned on. And, I'll take a slight angle at my view, and use a window select, from left to right, to grab all the faces in that space. I'll set my draft angle to two, and then now it looks like it just made this edge thicker. What I'd prefer to do, is go ahead and have this edge be thinner than the back edge.
So, I'll use flip direction to change the angle of the draft, rather than a negative value. I'll click okay, and add draft to 52 faces, all at once. For the bosses in the holes, I'll a take different approach. I'll go ahead and use draft for the holes, themselves, making them larger to the outside, just like the grill.
But, for the boss features, I'll go back to the extrusion that created them, double click, edit it, and we see that when we extrude, we always have the option of adding a taper angle. This is just another way of saying draft. So, for this, I'll add a two degree angle, that will kick the bottom edge out, say okay, and have the model update, including the ribs that will update to accommodate this new geometry.
Now the faces are prepared for ejection from the mold. In the next step, we'll add the final details.