What's The Best Way To Digitize?

A physical model is some sort of solid object that must be replicated in metal. And a tool maker must figure out how best to capture a dimensional description of that form that is both accurate and detailed enough to eventually enable the creation of a good NC part program.

Article From: 4/1/1997 Modern Machine Shop

Die and mold makers, as well as other manufacturing disciplines, have been working from physical models for a long, long time. For much of that history, a model was an end in itself—as in a pattern—the final definition of 3D geometry. But these days a physical model is more than likely just a beginning. It's some sort of solid object that must be replicated in metal. And a tool maker must figure out how best to capture a dimensional description of that form that is both accurate and detailed enough to eventually enable the creation of a good NC part program.

Shops have a range of ways to go about this task. They can, for instance, use a coordinate measuring machine to scan the surface, capturing a "cloud" of X-Y-Z points. Or, a number of very serviceable retrofit digitizing systems are available that let you scan right on a CNC milling machine. For some shops, however, these options aren't an ideal fit. Tool shops tend not to require the high accuracy inspection capabilities of CNC CMMs, and so have trouble justifying their cost. And while scanning with a spindle-mounted probe on a machine tool is appropriate for occasional use, some shops are uncomfortable to see a machining center spend so much time not making chips.

A good third option for shops that do a lot of digitizing is the dedicated scanning system. This is a machine designed to do nothing but physically gather surface data. While these systems initially were seemingly rather expensive, prices have fallen in the recent past.

A good example of such technology is the Cyclone high speed scanning system from Renishaw, Inc. (Schaumburg, Illinois). Within an X-Y-Z travel range of 23.6 by 19.7 by 15.7 inches, the machine can scan at speeds up to 118 ipm, and data capture rates can go as high as 400 points per second. Perhaps the most critical component of the system, however, is the "Tracecut" software which functions not only to capture data, but also to manipulate the data and then create an NC program or CAD output.

It also provides the means to guide how the scanning program is executed in the first place. A variety of 3D scan patterns are available including zigzag paths of any angle, radial, and manually manipulated pencil mode. Moreover, polygonal boundaries can be established to confine the scan to a specific portion of the model. Several kinds of 2D profile scans can be done as well.

Once a form is captured, the software can create a female form from the male or vice-versa, a mirror-image form, a new scale form, duplicate forms (for multi-impression tools), and can manipulate the data in several other ways as well. It can then proceed to create an NC program to cut the form, employing a range of machining strategies, depending on the user's preference. Or, the scan can be output as a CAD file in an ASCII, DXF or VDA format

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