Solidworks Plastics Features: Evaluation Tools

Evaluation tools are some of the most important functions in any CAD program. This becomes especially true as you get into more complex processes and more complex parts or assemblies.

For working with plastic parts, many of these tools are important, but the Draft Analysis is probably the most important.

Draft Analysis

Draft analysis is probably the most valuable tool Solidworks has in the plastics toolbox. It works in a few ways that have important differences. Default mode is as shown. The coloring is temporary.

Direction of Pull can be established with an axis, edge, plane or planar face. Or you could use the Adjustment Triad, shown below, when you don’t have physical or reference geometry to establish direction of pull.

The Draft Angle entry box lets you establish the minimum acceptable draft angle. Any draft angle less than this number will be displayed as “Requires Draft”. In this case, the yellow faces actually have 0 draft, but they could have 2.5 deg. On a part like this with interior and exterior walls, that’s a problem.

The coloration method used in these images is called Gourad shading. This ignores lighting, and just gives you a flat color. Plus, it can vary the coloration across a single surface in a way that normal face colors in Solidworks can’t.

Face Classification does a couple of things. First, it actually changes the face color of the model faces, and it allows you to keep the colors on the model after you exit the command. This is more useful than you might think. If you are adding split lines and draft to the model, it is often a big help to have the faces colored according to draft. If you don’t work this way, at least try it.

Second, it gives you a total of faces within each classification, and allows you to turn on or off faces from the different classifications.

The Straddle Faces classification is also added. This indicates any face that straddles the parting line. Gourad shading can just change the color on a single face across the parting line, but this is using face shading, which can’t do that, so SW added a classification. Straddled faces usually need to be split at the parting line.

Face Classification also adds the Find Steep Faces option which in turn adds two face classifications: one for steep faces in each direction.

Thickness Analysis

Thickness analysis is an important tool to run in plastic parts. It can also be used for castings, and I suppose even sheet metal parts, although the sheet metal process should keep the thickness constant. Thickness can effect how your mold fills, if you have sink marks or voids in the finished parts, or a number of other things. It allows you to check for thick and thin areas.

The PropertyManager interface is a little wonky. It has a toggle for Show Thick/Thin Regions, but if you set it to Thick regions, it will show both thick and thin. If you set it to Thin, it will only show thin. I would recommend leaving this on Show Thick Regions and leave it there unless you’re in a big hurry and only need to see thin areas.

The idea is to set up the thinnest acceptable thickness and the thickest acceptable thickness in the value entry boxes.

You want to take some care selecting these numbers. Generally they will come from a combination of the material you are molding with, the cooling configuration in your mold, machine temperature and pressure settings, injection and vent locations, as well as other factors. If you’re not familiar with all of this, you might want to have the molder help you select reasonable high and low limits. You don’t want to drive your design using unrealistic thickness values.

The “Treat Corners As Zero Thickness” will add a lot of complexity to the calculation. The calculation can take a minute or two, it is not instantaneous. This setting will prefer filleted corners over sharp corners.

The shading here is again the Gourad shading, so it can show a gradient on faces, and the shading is not kept when you exit the PropertyManager.

As we’re fond of saying in the CAD industry when dealing with analysis, “Green is good, Red is bad”. And so it is. If you get light gray areas, those are also bad, they would be too thin. So our design to the right still needs a little work.

Thickness analysis is one of the most useful evaluation tools for working with plastic parts.

Undercut Analysis

Undercut analysis is specifically for plastic parts. As the name implies, it is meant to help you find all of the faces that are undercut from a given direction of pull. Unfortunately in my experience, this tool is always wrong. Here’s a sample.

We saw this part in the draft analysis, so we know there are no undercuts in the part. In this image, I’ve turned off all of the “No Undercut” faces. So whatever is shown should be undercut faces.

The truth is that the “Direction 1 Undercut” is only undercut from Direction 2, and Direction 2 Undercut faces are only undercut from Direction 1. This is as it should be, but it shouldn’t be displayed like this.

If this tool shows you an Occluded Undercut, well, that’s different. It identifies those fine, but there are none on this part. In fact, this part has no undercuts whatsoever, so all of the faces should be in the No Undercut classification.

So Matt’s advice is to not waste your time on this tool unless you want to pull a prank on someone.

Deviation Analysis

Deviation analysis is useful when you are doing highly curvy models where you have to have nice smooth transitions between faces, and you can’t appear to have any edges or dents in the part. The idea is that Deviation Analysis measures how far from perfect the face normals are at a shared edge. The goal is of course to get the normals parallel.

The first thing you should do is to set the tangent edge display to phantom (Tools/Options/Display). This lets you know visually if your edges are in the ballpark. I’m not sure just “how” tangent faces must be to display the tangent edge font, but it’s a first level check.

To use Deviation analysis, start the command and select an edge or set of edges and press the Calculate button. It will show you a series of colored arrows on the edges you are analyzing. The colors represent angles shown in the scale. The max, min and average deviation are shown. This means the maximum departure from tangent between the faces on either side of the edge. Different applications have different requirements, but the numbers shown to the right are generally pretty good.

Depending on the manufacturing process, certain types of deviation can be minimized by those processes. For example, an outside edge might get polished out with bead blasting, sanding or polishing. But it’s never good for your model to start out with flaws, so you should strive to get it as good as possible. Deviation Analysis is a great tool to help you check, but also remember that it only gives you real numbers to quantify tangency, it doesn’t say anything about curvature continuity.

Zebra Stripes

Zebra stripes is another tool for highly curvy models. Here’s a screen shot of zebra stripes being turned on in addition to deviation analysis. You can see that the deviation analysis is good, but the zebra stripes is not.

If you click the green check in the propertymanager, the stripes display can stay on as you work with the part. Just click on the Zebra Stripes icon in the CommandManager again to turn it off.

Zebra stripes are meant to help you visualize curvature continuity issues on your part. If the stripe touches itself across an edge, that’s a tangent edge. If the stripe is tangent to itself across an edge, then the curvature is equal on both sides of the edge.

It is like making your part completely reflective, and putting it in a room with black and white stripes painted on it. Reflections are a great way to help visualize the quality of your surfaces, in CAD and in the real world.

You can control the width, number, and smoothness of the stripes from the sliders in the propertymanager. You can also use the Environment drop down to supply your own image instead of the stripes.

Curvature

Curvature display is another tool for complex shaped parts. It colors the surface according to the local curvature. So as the curvature changes, so does the color. As you hover over the part, the cursor will give you the local curvature. Remember that curvature is the inverse of radius (c=1/r).

You can combine Curvature and Zebra Stripes (and Deviation Analysis), but that gets to be a lot of information on the screen at one time.

The Curvature function does not have a PropertyManager. You set up the colors at Tools/Options/Document Properties/Model Display/Curvature. Here the bigger numbers denote the smaller radius. You can see the small red faces on the slots in the part shown.

You can reset the colors to fit the range of your model, or leave it as it is.