BMFS 3373

CNC TECHNOLOGYLecture 11

Modern Developments in the Process of CNC Programming

In the past: Programming was done manually, written in word address and tailored

to specific controller. Trigonometry was one of the fundamental knowledge in calculating the

tool path. The CNC machine needed to be halted during the program key-in

process into the MCU. Program verification was a must, that leads to machining and

inspecting a test part first before a full run.

And that soon changes with the coming of the digital age.

Modern Developments in the Process of CNC Programming

Using off-line computer to write and store part program, it creates an optimum condition when running a part program.

Modern Developments in the Process of CNC Programming

Introduction of Computer Aided Programming Languages:The CNC controller can only function with word address codes with

specific format acceptable to that specified controller. Trigonometric computation is also required.

A computer aided programming language tries to address some of these issues by allowing the program to be written using English-like command.

Furthemore, a program known as postprocessor allows the translation of this computer aided programming languages to word address program for all suits of controller.

The most popular computer aided programming language in use today is Automatically Programmed Tool (APT)

Modern Developments in the Process of CNC Programming

APT is short for Automatically Programmed Tools. It was the first and still is the most powerful computer programming language.

APT can used to program the machining of complex surfaces on four- and five-axis machining centers, though it was originally restricted to run on large mainframe computers.

Advances in microprocessor technology have allowed it to be available on workstations and personal computers.

Modern Developments in the Process of CNC Programming

An Introduction to CAD/CAM

CAD/CAM stands for Computer-Aided Design and Computer-Aided Manufacturing.

CAD/CAM approach is superior to the technique of using computer aided programming language in preparing a part program

Some of the advantages of using CAD/CAM are: The system can be used to check the program off-line. Resulting tool paths

can be graphically displayed on the computer screen, and the user can zoom in and view the tool paths at various orientations. The system can generate real-time material removal simulations and flag tool breakthrough or part violation problems.

Time and cost of machining the part can be quickly determined. The system can determine optimum tooling, speeds, and feeds for the

material selected.

An Introduction to CAD/CAM

The element comprising a CAD/CAM approach in creating a part program is as followed:

A CAM file is created. The CAD model is sent to the CAM file for machining. The portion of the model to be machined is identified by the

operator. The start point for the machining is also input. The tool to be used is identified. Tool speeds and feeds are input. A postprocessor file for a particular CNC machine controller is

recalled from the computer’s memory. The CAM file is retrieved and post-processed into a word address

program file acceptable to the machine controller. The word address program can then be played back for editing.

Upon playback the computer can display all resulting tool paths. The tool paths can be zoomed, viewed or simulated at any angle.

An Introduction to CAD/CAM

The CAD/CAM approach to part programming

EndChapter 11