Join Veejay Gahir for an in-depth discussion in this video Die-line evaluation, part of Alias Essential Training.
- Let's take a look at another very critical part of designing a plastic part in Alias, and that's to do a Die Line Evaluation. We're gonna take a very simple scenario here, and if you're not familiar with tooling hopefully this will help explain what we're talking about. I wanna go ahead and select this component here, and this essentially is a cupcake. If you can imagine a cupcake sitting in a mold, if I say move and we're gonna pull this cupcake right out in the vertical or in the Z axis, you can see that this cupcake will be removed easily with no damage to sides whatsoever because the angle of the sides is open.
With an open angle we have a great condition to remove this cupcake. Now, this scenario on the right hand side here we have what we call a Die-Locked condition. If I go ahead, select object, and let's say move, as soon as I try to move this in the vertical direction, or in the tooling axis, you can see this cupcake is gonna hit on the sides there. But if I continue to force this out of the mold the whole side down here will be destroyed. That's the terminology that we're gonna use here.
We have an open and we have a die-locked condition. When you're designing a plastic part or any part that's gonna come off with tool in Alias we have to perform this evaluation because when we send this to engineering if it doesn't meet the die-lock or die line evaluation criteria they'll have to either rework it or they're gonna send it back to us to rework. Let's go in to this scenario here which is essentially a mold. If I go into, let's just close this down. I'm gonna go into the diagnostic shading. First thing to do whenever you're gonna perform any of these checks is to make sure that your orientation is correct.
In this case, because we're gonna be looking in this view here the orientation is correct. Let's switch that off and we're gonna go to this icon here which is surface evaluation. We're gonna change the evaluation type to draft angle. Let's go into our true left view and we have set a positive draft angle of 10 degrees. So our tooling engineers come back to us and said "For this particular part and this material "you need 10 degrees draft." Now, remember, draft is the angle of this side wall compared to the vertical axis.
Now, what dictates the angle? It could be a number of things. It could be the type of material that you're using. It could be the shrink ray to that material as it's cooling in the mold. It also could be the type of texture that you want in the side of your cupcake because if you want a very deep texture then you need more draft angle. In this case here I've set 10 degrees. If we look at this scenario on the right hand side everything in red here is die-locked. In other words, if we pull this cupcake out of this tool right now with 10 degrees we would lose all this side here or we would damage the side of the part.
When I design this part, if I was told 10 degrees, I haven't met that engineering criteria. Let's do a really simple exercise. I'm gonna create a line. Just click in space and right mouse button to create a vertical line in Z. Let's switch off CV/Hulls. Let's go back to the line, middle mouse button, rotate, middle mouse button, and we're gonna rotate in the Y axis. We do a CTRL+5. If we look at the rotation we're gonna change this to 10 degrees.
Now that line has rotated 10 degrees, let's go ahead and just move this line over. If I zoom right in here you'll see that where it touches that boundary between the red and blue is exactly 10 degrees. Ideally from an engineering perspective this tool, or this design should follow this line once it reaches that boundary. My surface would come along here to the boundary, and then it should open up like this to ideally meet the tooling criteria. Because it wraps back on itself, all this area in red is gonna be damaged when it comes off the tool.
In some cases you're not even gonna get it off the tool. It's locked in the tool there. This is a very extreme case. Typically we might be only looking at half a degree or a quarter of a degree that could cause a problem here. Let's take this line and move it over to this scenario here. In this scenario the band of red is less than this one, so the tooling condition is not as bad but nevertheless it would still fail. If we move over to this condition here you can see it's better but, again, we still see a band of red. Again, that's not the ideal condition for us.
This is one of the reasons why a design can change later in the stage of the design process. You could start your design with the understanding of 5 degrees. As you move along your design you get to almost releasing it, and things can change at the last moment, and they do. The engineering could come back and say, "Sorry, but we actually need 6 degrees." That can have quite a dramatic effect on the timing of the program because you have to redefine your side surfaces again which could then lead on to redefining your fillets and blends. So the knock on effect can be quite dramatic.
Let's take a look at this last scenario here. In this one here I've got a mold that's set at 10 degrees on the side angles. If I go back to the cupcake, let's take this, and I'm gonna assign it to this layer. Let's go ahead grab this edge and let's just move it over here like this and let's go back into evaluation. Right now we're set at 10 degrees, and you can see that this surface here is kind of patchy. It's kind of red and blue. That's because the side surface here is exactly at 10 degrees.
When you're at 10 degrees it kind of gives you kind of a mottled or checkered effect to show you that you're exactly at 10 degrees. It's not a bad thing but that's the effect of the graphics here. If I move this line over you'll see that that side wall is exactly at 10 degrees, and that's the ideal situation for what I would want. Tooling engineer specified 10 degrees, and that's what I've given you here. If he comes back and says, "Sorry, I need 11 degrees," you can see we've got a problem now. We have a die-lock condition. If he comes back and says, "We need 9 degrees," that's fine.
It may be that we don't have to change that side wall at all. I wanna go ahead in the top view, and let's set up a new layer and let's create a sphere. Let's open this up. Shade, orientation is fine. We're gonna do another surface evaluation here. I'm gonna go to the left view, and in this case I'm gonna set the angle at 0 degrees. That should go exactly where that central isopod is.
Now, if you prefer to have the red on the top or the blue on the bottom all you simply have to do is go into the Z axis and just put a minus in there like that. It just flips the two. It just depends on what color you want to see there. One other option that we do have here is we have a positive tolerance. In other words we have a draft angle tolerance. We're gonna leave it at 0 here so it's easier to see. If we set the tolerance at, let's say, 10 degrees, and I'm gonna set the draft angle here, let's say at 10 degrees as well, you'll notice that we have a band of blue.
Let's go ahead, go back into this layer. I'm gonna move this over and let's just grab our line again and assign it to our new layer, and let's just hide that layer. Let's move this over like this. In reality when we're creating a tool it's very difficult to create a tool with an exact clean line like you see here. When the tooling engineer is gonna be creating this tool there's a tolerance that's allowed on the split line or the opening part of this tool.
In other words we're not gonna get a cupcake that has a completely crisp edge as you see here. The edge will vary a little bit between this band of sky blue here. Now, the tolerance again, that's something that the tooling engineer can specify to you, if he says, "I want 10 degrees "but I'll give you a tolerance angle of 1," you know that within this band here your surface edge is allowed to vary. That's just what tolerance means there. Again, don't ignore it. Keep an eye on that and just at least ask the question, "What's the tolerance on my split line?" Because if the tolerance is very tight, if it's like half a degree, then you've got to be a little bit more careful how you create your part.
If it's a very loose tolerance, if it's like 5 degrees, then you know that your edge can vary anywhere between that blue line. We'll make that 0. Again, first thing is just to make sure that you check your surface normals. I'm gonna go back to this cupcake layer and I'm gonna change the orientation of this to show you what effect it can have. We'll go to orientation. We're gonna say set surface orientation, and I wanna change the orientation like that and go back to our evaluation.
You can see that the colors are jumbled up now. It's not incorrect, it's just according to the surface normals this is the evaluation that Alias provides you. If you were evaluating this part it just looks a little bit confusing and you could say, "I'm not sure why this is red and blue "and everything else is red." It really is back to the orientation. You have to just go back, surface edit, set surface orientation like that, and then the evaluation should be correct.
Let's go back, make that Z like that and there we are.
- Manipulating views and entities
- Working with layers
- Creating curves
- Sweeping, extruding, revolving, offsetting, and blending surfaces
- Modifying geometry
- Moving, scaling, flipping, and rotating objects
- Trimming curves and surfaces
- Creating copies of objects
- Aligning, combining, and splitting objects
- Analyzing geometry
- Shading models