Constructing 3D models with FDM technology has different challenges. One challenge that faces designers are Start/Stop lines, or seam lines. Insight, the STL setup software that comes with Fortus 250mc and larger units, can edit these seam lines using a feature called Seam Control. This feature allows you to change and control the location of seam lines. Note: Catalyst software, used on FDM desktop units, cannot edit seam lines.
Below is an example of a simple boss extrusion, with a seam line running down both the boss and the base of the printed part. Traditionally, we remove the seam line with a metal file and/or sand paper. For one, or two, it is fun to dig up the Ye Old file and whisk that line away. But what if you had to build two-thousand of these parts? Fun suddenly escapes us. Not long ago, I faced a similar problem with the seam line interfering with a mating component, causing the two components to bind.
My solution was to edit the part model in order to tuck the seam line into the model, so it couldn’t interfere with the mating component. The first step was to use SOLIDWORKS to make a sketch of a circle on the top face of the boss. The center of this circle was on the boss edge and a cut extrude was created to the top surface of the base. I made the diameter of the circle equal to twice the slice height. For example, a .010” slice height would require a .020” cut diameter. After these adjustments to my CAD model, I exported a new STL file to be used in our Insight processing software.
From Insight, I used Seam Control, found under the Toolpaths menu. Seam Control is turned on as indicated by the white and grey arrows. This shows where the seam line will build if left unaltered. The default placement method is set to Automatic, however we want to select Align.
When Align is selected, Reference point dialog boxes light up and the crosshair at the origin is visible. Start by selecting the lines of the Boss as shown below.
From left to right, the first box is X and the second is Y. To figure X; I use the following formula: Center major OD edge to center of key + ½ major OD - Slice Height. For X example: Major OD= 1.020/2+.392-.01=.892
To figure Y; Major OD/2. For example 1.02/2 = .510
Enter the values and click okay. Then click out of Seam Control so you don’t accidentally click and change the work just done.
Seam Control is now complete. The desired results are functional right off the printer. The seam line is tucked away and the mating component will not bind. If the base does not have a key cut, the seam will protrude as always.
Holes are not treated differently. Repeat the steps above. Overall, the function is there and the goal not to file and/or sand a thousand seam lines is achieved. I will continue to work on the aesthetics of this process and see if the seam can completely hidden.