GlossaryKind of term: Manufacturing termPostprocessor
What is a postprocessor?
A postprocessor converts the toolpaths from CAM into an NC program for one specific control and machine configuration.
What CAM outputs is machine-independent: the toolpaths or CL (cutter location) data. The postprocessor translates them into code with the right G and M codes, cycles, tool changes, work offsets, and the program header and end. Machines with the same control and the same kinematics can share a postprocessor; a different axis layout or option often needs its own version.
What does a postprocessor handle?
For 3-axis work the postprocessor mostly translates codes and formats. For 4- and 5-axis work it also handles kinematics: the order and position of the rotary axes, their limits, the choice between two possible axis solutions, and whether the code uses the control's tool centre point control (TCP) or the postprocessor computes machine coordinates itself, in which case the program depends on tool length and pivot distance. It also settles details that cost or save time: retracts at rapid or at feed, the use of canned cycles, how arcs are written out. A postprocessor error usually does not show in a simulation of the CAM toolpaths, because that shows the paths before posting; finding it needs a simulation of the NC code with a machine model, or a controlled first run.
How does a postprocessor work in practice?
A new machine or a different control needs a postprocessor that has been proven on real parts; until then, prove-out takes extra time. The same goes for a repeat order that moves to another machine: post again, prove out again. A badly tuned postprocessor, with needless stops or retracts at feed, makes the cycle time on that machine longer than it needs to be. The cost of the postprocessor itself usually sits in machine costs or overhead, not in the piece price; that is a choice in how you build up cost.
What is a postprocessor often confused with?
A postprocessor is not the NC program: the program is the output, the postprocessor produces it. Nor is it the control: the control sits on the machine and executes the code, the postprocessor belongs to CAM and writes it.
Frequently asked questions
My new machine has a different control. What does that mean for existing programs?
Existing programs have to go through a postprocessor for that control again and then be proved out. The CAM project usually stays usable; the posted code does not, as it stands. Allow extra programming and setup time on the first orders for that machine.
Does the postprocessor belong in a part's cost?
Usually not as a line of its own: it is an investment per machine that comes back through machine costs or overhead. What does count per part is the consequence: posting again and proving out, as programming time and setup time.
Can I use the postprocessor of another machine?
Only if control, kinematics and options match. Small differences, such as another tool changer, axis limit or cycle option, can cause errors or collisions. Test a borrowed postprocessor with a simulation of the NC code and a controlled first run.