NC code simulation after postprocessing

Verification after postprocessing examines a different level

CAM first checks the programmed toolpath. After postprocessing, machine- and control-specific NC code is available. It contains axis output, cycles, transformations, tool calls, and other machine functions that are not yet fully visible in the internal CAM toolpath.

NC code simulation therefore processes the posted code with an interpreter and a machine model. It can identify errors introduced during translation for the specific machine. The value of the result, however, depends heavily on how closely the interpreter and model match the real environment.

CAM simulation and NC code simulation check different data

CAM simulation checks the internally calculated motion, stock, and machining sequence. A machine simulation may also represent axes, tool carriers, and collision bodies. Whether it uses the posted NC code or only internal CAM data depends on the system.

NC code simulation reads the postprocessed G-code or NC code. Only then do machine-specific commands, cycles, and transformations become part of the verification. The two types of simulation complement each other because they address different points in the programming chain.

New risks can arise after NC output

The postprocessor selects axis motions, command sequences, and control-specific functions. On five-axis machines, the same tool orientation can be achieved through different rotary-axis positions. Unfavorable output can cause large repositioning moves, axis-limit violations, or problematic retracts.

Work coordinate systems and work-offset commands are also selected and output in the NC code. The actual offset values, however, come from setup, measurement, and data in the control. The simulation and real machine must therefore use the same assumptions about coordinate systems and workholding.

Example of a critical retract

In CAM, a milling operation ends above the workpiece. The postprocessor then generates a retract and a rotary-axis move for the next operation. If the linear motion is output in an unfavorable order, the holder may move toward the fixture.

The original toolpath was collision-free during cutting. The risk appears only in the generated command sequence between operations. NC code simulation can reveal this transition if the machine model and interpreter represent the real execution with sufficient accuracy.

The interpreter determines how the code is executed

A basic G-code viewer often displays only fundamental motion. Control-specific cycles, transformations, and subprograms may be simplified or not evaluated at all. Such a display is not sufficient for complex programs.

Interpreters that match the control and machine project provide more meaningful results. Even then, the supported commands and known deviations must be documented. A simulation is only as accurate as the rules it uses to process the code.

Which errors can be detected

Depending on the system, collisions between the tool, holder, workpiece, workholding, and machine can be detected. Other checks include axis limits, rotary-axis motion, tool changes, unexpected rapid moves, and unsupported commands. Remaining material and cycle time can also be evaluated when the required data are available.

Not every system covers all of these points. Before use, it should therefore be verified which machine functions and control commands are actually evaluated. A long feature list in a data sheet says nothing about how accurately the company's own machine model has been implemented.

Collision-free does not mean the cutting process is stable

A simulation may show a collision-free sequence even though the tool or workpiece vibrates during machining. Chip formation, thermal behavior, wear, and actual clamping force are also often simplified or not represented at all. These influences must be addressed through process expertise and real production data.

NC code simulation reduces known risks but does not replace every check on the machine. How much prove-out can be moved upstream depends on the part, machine, model quality, and process knowledge. The share may be higher for standard parts than for new or unstable machining processes.

Reference programs reveal the actual verification depth

Implementation should use programs whose behavior on the machine is known. They should include straightforward standard cases as well as deliberately critical moves. This shows which errors the system detects and where manual checks still remain necessary.

Metrics can include prove-out time, errors found, machine occupancy, and the number of manual NC changes. Only these data show whether simulation saves time in the company's own process. A convincing demonstration on someone else's demo part does not provide this evidence.

Frequently asked questions about NC code simulation

**What is the difference between CAM simulation and NC code simulation?**
CAM simulation mainly checks internally calculated toolpaths and machining states. NC code simulation processes the posted machine- and control-specific code after the postprocessor.

**Can G-code simulation completely rule out collisions?**
No. The result depends on the interpreter, machine model, tool data, and setup. Differences between the virtual configuration and the real machine can still leave risks undetected.