tool
For machining centers, cutting tool holder is the connection between the cutting tool and the machine spindle. For lathes, the tool holder is mounted in the turret.
What is often called ‘speeds and feeds’ is only part of overall cutting conditions. Cutting conditions are influenced by many fixed factors, such as material being machined, its shape and condition, machine capabilities, etc. They are also influenced by conditions that are with the power of CNC programmer - for example, tooling selection, setup method, depth of cut, width of cut, and spindle speeds and cutting feedrates.
Part program can be developed by several methods:
▪Manual programming
▪Macro programming
▪Computer programming
▪Conversational programming
Manual programming means manual calculations and manual writing of the program. A computer is often used, but only as a text editor or a toolpath simulator. In manual programming, the computer does not generate the program code.
Enhanced methods of manual programming use so called macros, such a Fanuc Custom Macro B. In simple terms, a macro is a type of a subprogram, but it can handle features that no subprogram can. Those features include variable data, conditional testing (IF), iteration (WHILE), arithmetic, algebraic and trigonometric calculations, and many other features.
In a true computer program development, a special software is used to generate complete program. Typical software used for such purpose includes Mastercam®, Edgecam®, and many others.
Programming directly at the machine control is called conversation programming. Generally, lathe programming can benefit from conversational programming a little more than programs for milling.
Regardless of how the program is developed, it has to be written in such a format that the controls system of the CNC machine ‘understands’ it. Part programs generated manually or by software should have the same format (some minor inconsistencies should be expected).
A program that contains even a single error is not desirable. One of the programmer’s responsibilities is to check the completed program before it is used. There are several ways of verifying the program. One proven method is to use a toolpath simulator software, such as NCPlot®, another is to employ a fairly extensive variety of manual checks.
Simulation software varies quite a bit in features and cost. Price of the software by itself does not necessarily reflect its quality and features. Most simulation software lack support for some high end control features, such as coordinate rotation, polar coordinates and macros. Before purchasing software that simulates the toolpath, make sure to do some research.
Numerous manual checks can also be used to find program errors. Even a brief scan of the program may reveal some obvious errors. If you know what you are looking for, the program check is that much faster. Many errors in the program happen at the beginning of the program. Errors in the middle of a program are of a different kind. An experienced operator will discover an error before it does any damage.
The final part program is the result of many small, progressive steps, some quite straightforward, others more complex. The program can be generated by a CAM software or it can be written completely manually. In any case, the programmer had to go through certain steps that required calculations, for example, as well as other steps. Documenting these calculations or processes can prove to be very valuable if the program has be modified for any reasons. Program modification can range from a simple error correction to an engineering change.
It is an unpleasant reality, that many CNC programs, regardless of how they were developed, lack any background information that can help the machine operator. At best, the part program may include some basic data regarding the setup and even some special instructions.What is often missing are details of individual steps. The operator needs to know what fixture has been used, how the part is oriented, what tools have been selected, and where the part X0Y0Z0 is located.
Program transfer includes several methods of making the program available for machining. Commonly, this process is called Program Loading. There are different methods of loading program - the most common is to store it in the memory of the CNC unit. Other methods include DNC (processing the program from an external computer), or a program stored on a flash drive.
Once the drawing and program reach the machine shop, it is up to the CNC operator to continue with actual production. Production cannot start right away, and certain workflow is followed at the machine as well:
▪Evaluate the part program
▪Check supplied material
▪Prepare required tools
▪Setup and register tools
▪Setup part in a fixture
▪Load program
▪Set various offsets
▪Run first part
▪Optimize program if necessary
▪Run production
▪Inspect frequently
Evaluating a part program serves the purpose of knowing what it will do and how it will do it. Careful evaluation provides means of organizing the part setup, too1 preparation, and relates activities in an efficient manner. Program evaluation is typically combined with the drawing and material provided.
Ideally, any material used for CNC work should be qualified as acceptable. Qualified material guarantees consistency in size, shape and condition from one blank piece to another. Unfortunately, this ‘ideal’ condition does not always exist, for different reasons.
