GlossaryKind of term: Manufacturing termIGES
What is IGES?
IGES is an older neutral CAD format that often holds loose surfaces rather than a closed solid, and still turns up alongside or instead of STEP.
IGES, the Initial Graphics Exchange Specification, is a neutral exchange format for CAD data dating from the early 1980s, recognisable by .igs or .iges. It can describe curves, surfaces, 2D drawings and, in later versions, solids. Most systems write a model out as a set of loose trimmed surfaces, which the receiving system has to stitch back into a closed solid. The last version, 5.3, dates from 1996; STEP has largely taken over its role.
When does an IGES transfer go wrong?
Whether stitching succeeds depends on the precision with which the source system wrote the surfaces, the tolerance the receiving system uses to join them and the quality of the edges between faces. Where it fails, gaps, overlapping faces or missing patches remain. A model that does not close has no volume: weight and volume cannot be determined, and functions that need a closed solid, such as comparing remaining stock with the finished model, or feature recognition, fail or become unreliable. A CAM system can often still machine the surfaces themselves.
How does IGES work in practice?
Open an IGES file before quoting, and check that it closes into a solid and that units and sizes are right. Repairing or remodelling takes time that lands in programming or preparation time. Asking the customer for a STEP export from the original CAD system is often quicker. If the file holds only lines and arcs, it is a wireframe or a 2D contour, and you need the drawing for the depths.
What is IGES often confused with?
IGES is not STEP: both are neutral formats, but a STEP export usually carries a closed solid, while an IGES export often holds only surfaces.
Frequently asked questions
What do I do with an IGES file that will not close?
Ask for a STEP export from the original CAD system first. Failing that, let your CAD or CAM system stitch the surfaces, then check that the result is a closed solid before you base an estimate on it.
Is IGES still in use?
Less than it was. STEP has become the usual choice, but older CAD systems and archives still send IGES. For shape it works, provided the model closes into a solid and the units are right.