Carbon DLS Accuracy for Engineering Materials

The Carbon DLS™ process has accuracy and repeatability capabilities that depend on resin and part geometry. General Accuracy is described as a constant offset plus a ratio, for example, ±70 μm +1 μm per mm dimension size. General Accuracy is what you could expect when first printing any given geometry. After a part has been optimized for production, some of the sources of variation are removed. The remaining variation is cited as Production Repeatability.

Previously, we gave very conservative high-level guidance around our tolerances. We now offer more granular guidance based on several years’ worth of CT scans and field data on both general first-print accuracy and production accuracy following process optimization. The following figures are a summary of the updated guidelines, followed by a deeper dive into the data itself.

Accuracy Definitions

Two numbers describe the general accuracy capabilities of the Carbon DLS process: 1) the constant offset and 2) the dimensionally-dependent μm per mm. The constant offset is determined by the stack-up of variation sources that affect what we call “local offset accuracy.” This is measured with a test part that has both horizontal and vertical struts (below). Excess curing of the vertical and horizontal struts is called “overcure” and “cure-thru,” respectively.

The second number that describes accuracy is a factor that is multiplied by the length of the dimensional span. In this way, larger spans are expected to have larger deviations from nominal dimensions compared to smaller spans. These values are meant to include inaccuracies due to uniform part shrinkage and warpage (i.e., non-uniform shrinkage). The values are determined from a series of stair-step test parts with different wall thicknesses. The percentage we report is determined by subtracting the shrinkage of the 3-mm wall thickness part from that of the 1-mm part.

Sources of Variation That Affect Local Offset Accuracy

• Lot-to-lot variation in resin characteristics
• Printer-to-printer light engine peak wavelength
• Build area variation across the printer
• Temperature variation during printing
• Print speed variation
• Resin pot life age
• Variation in lab environment

Accuracy Data

3D as It’s Meant to Be

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