ESAB Knowledge center.
What is post processing software?
May 5, 2013
The Problem with CAD
To cut parts from flat plate using a CNC cutting machine, whether it’s plasma, flame, waterjet, or laser, the CNC has to be programmed with the path of the desired shape or nest of shapes. Most parts are originally designed in a CAD program, such as AutoCAD, Solid Works, CATIA, or some other basic drawing or design package where they are saved in a CAD drawing format. Some of the most popular CAD formats include:
- “DWG” (AutoCAD Drawing format)
- “IGES” (Initial Graphics Exchange Specification)
- “STEP” ("Standard for the Exchange of Product model data")
- “DXF” (Drawing Exchange Format)
But you can’t just take the CAD file and send it to a plasma cutting machine. It has to be interpreted first, so the CNC on the cutting machine can understand it. The problem with these CAD file formats is that:
- They usually contain a lot of information that the CNC cutting machine doesn’t need or would find confusing, such as title blocks, Bills Of Material, dimension lines, borders, welding specifications, etc.
- They usually have multiple layers, some of which are useful to the CNC and some of which the CNC would need to ignore.
- They sometimes have many parts in one file, some of which might need to be cut on the CNC plate cutter, and some might need to be machined, or cast, or sent to an EDM, etc.
- They don’t have all of the information needed by the CNC plasma, or laser, or waterjet machine. Those machines need to be told when to turn the process on and off, how to lead-in & lead-out from the part, how much kerf offset to use, etc. All of that information is referred to as the “process technology”.
Run it through a Post Processor
Somehow the shape of the part needs to be extracted from all of the other information in the CAD file, and then the desired “process technology” applied to it. That is what a “post processor” does, it processes the CAD file “after” (post) the design phase. Post processing software takes the CAD file, strips it down to basic geometry and converts the file from CAD to CNC language.
- Extract the circles, lines and arcs from the CAD file and converts them to lines of code that the CNC can understand, often referred to as “M- and G-Code”.
- Identify which contours are internal cut-outs, or “IDs”, and which are outside cuts, or “ODs”.
- Put the lines of G-Code (Geometry code) in the correct order so that ID cuts and OD cuts are done in the correct direction (clockwise or counter-clockwise), which is necessary for plasma cutting.
- Generate new lines of G-Code to describe the necessary lead-in and lead-out motion, and put those in the appropriate place along each contour.
- Generate new lines of G-Code to perform all necessary tool movement in between cut lines, such as the rapid move from index point to the first ID cut, and moving from the ID cut to the OD cut.
- Add all of the necessary M-Codes (Miscellaneous codes) at just the right point in the sequence to turn various machine and process functions on and off at just the right times.
More advanced post processors will do all of the above automatically, and can also do advanced functions such as adding codes to freeze the height control when crossing a kerf, adding special cutting routines for small holes, adding cutting process automation to the program, and adding codes for beveling the part edges.
Part of a Complete Programming & Nesting System
Post Processing Software can be a stand alone software program, but more often it is part of a much larger programming and nesting software system, which can include modules for Automatic Nesting, Estimation, Job Control, Plate and Remnant Management, and Parts/Data Management.
Automatic Nesting will place parts on a sheet in the best arrangement to increase plate utilization. Automatic Nesting software often includes other capabilities such as Bridge Cutting, Tabbing, and Common Line Cutting to help increase plate utilization.
Estimation software can estimate the time, material, and cost for a job, or for individual parts being cut.
Job Control software will keep track of parts required for a complete “job” or “assembly”.
Plate and Remnant Management software will keep track of plate inventory, plates used or required, which plates are used for which nests, and what remnants are left after nesting which can be used later for additional nesting.
Parts/Data Management software keeps a database of every individual part that you nest, along with all of the data related to that part, including bevel information, grain alignment, material specifications, etc.
Companies can often start out with a basic post processing software and then add on to it as the company grows. But the type of software features mentioned above can be a big investment. And because of the amount of data involved, switching from one software to another is often a long and painful process. So be sure to invest in a software that can grow with your company, instead of a package that you will eventually have to abandon in order to expanded your capabilities.