Typically in a simulation program, the user designs CAD solids that collectively represent the CNC machine being used to cut the mold. The user also specifies how the solids move and interact, mirroring the operation of the actual machine. Tool, workpiece and spindle attachment locations are defined via user coordinate system (UCS) points consisting of an origin and three vectors (X, Y and Z) that determine a position and orientation in three-dimensional space.

Once the user loads a machine design file, a postprocessor file, and CAM part file into the machine control, he or she can select the machine simulation mode and view the machining process on a virtual mill. Potential collisions and other erroneous movements can be detected and the program adjusted long before code is sent to the real CNC machining center. If a collision is detected, the simulation pauses and a dialog box appears with information on the specific components involved. Test cuts or dry runs become unnecessary.
The solids representing machine com-ponents can be modeled from scratch, or imported from CAD solid libraries. One simulation package, for example, permits definition of machine components using either the software’s own solid modeling option or solid model data imported from other CAD programs. Each solid represents a particular part of the machine, and each “movable part” of the machine is imported as an independent solid. That is necessary because presenting two machine tables or components as one solid will cause problems when one component must move independently of the other.

The user can determine exactly which machine components to add to the model, including turrets, heads, spindles, tool shanks, tool changers, rotary tables, axis slides, clamps and fixtures. Simulations of auxiliary machine functions like parts catchers and bar feeders also are possible. It is recommended; however, to keep the machine model as simple as possible. Only the necessary details should be included. Modeling every chamfer, fillet and tiny detail is only going to slow the simulation down. Once the machine simulation data are saved, they can be used with any other part program run on that machine tool.

Some machine simulations are designed to run outside the CAM program after the program is completed and saved, while others permit viewing and editing during the programming process, speeding turnaround time. Still another machine simulation module complements the software’s feature-recognition capabilities and ease of use, as well as its existing 2-D and 3-D cutting simulations, and can be used on basic two-axis mills, lathes, and mill/turn centers as well as multi-axis milling machines.

In addition to alerting users to the possibility of collisions, simulation software provides an accurate determination of cycle time. And, like the fast forward feature on a video player, simulation views aren’t restricted to running at real-time machining speeds.