Conversational programming considered

Tooling & Production, Sep 2001

T&p softwaresolutions &NC machine controls

Advances continue to increase machining efficiencies

The following article is excerpted from the new second edition of Programming of CNC Machines (Industrial Press, New York), by Ken Evans, John Polywka and Stanley Gabrel. The web site for the publisher is http://www .industrilpress.com- The Editors

For many years, the concept of programming the CNC machine tool at the controller was thought of as an ineffident and tedious. When orders of a small lot size were to be produced, the choice was almost always manual machines. Today, this is not the case, largely because of the advances in conversational programming.

Conversational programming is becoming more widely used throughout the industry and is available as standard on many machine tool controllers. Its major advantage is that is gives the machinist the ability to write programs at the machine quickly and easily. Typically, the process includes a sequence of questions the machinist/programmer must answer, sometimes called "question answer format" or "prompting." As these questions are answered, the program is constructed. Most controls with this capability also allow the machinist/programmer to graphically check the toolpath to verify the program. If the program has flaws, the controller will not execute the toolpath and the programmer must remedy the problem. When program errors do occur, an alarm number will show on the screen indicating what the problem is and where, in the program, it occurred. This is obviously a better method of finding errors than actually running a part. Another capability of conversational programming is its feature to perform calculations when programming data are missing from the engineering drawing. The programmer constructs intersection points or tangency points and with this information the controller computes the desired geometry. Feeds and speeds are automatically calculated based on the workpiece material and cutting tool material. The data necessary to do this are stored in the controller memory in the cutting condition parameters.

On the floor Conversational "shopfloor" programming uses the concept of operator prompting combined with a Graphical User Interface (GUI). Questions throughout the programming process prompt the user for information necessary to complete the part program. Icons accessed through the function buttons on the controller identify machining operations, i.e. Point Machining, Line Machining, etc.

Much like CAD/CAM, the process resembles re-creation of the part geometry by constructing the shapes using lines, arcs and points combined with other features.

This information is used in combination with Tool Identification Parameters and Cutting Condition Parameters to generate the tool path code needed to control the machine. The programmer has the added functions of the controlleris ability to calculate for unknown coordinate values and have them automatically inserted into the program where they are needed. In most cases, no calculator is needed for trigonometric calculations. These constructions resemble the formerly popular Automatic Programmed Tool (APT) method of programming. The actual program the machine executes is still a G-code format but the operator may never see the actual code on the display.

This type of programming combined with the ability to call G-Code sub programs has tremendous power. Mazatrol, a conversational programming system offered on all MAZAK machine tools, allows G-Code similar programming within its conversational language in what is called a Manual Programming Process. The acronym used to call this type of program process for Mazatrol is MNP, where MN stand for Manual and P for Programming.

There are many different conversational languages for programming available, and one of the complaints is the lack of standardization between the various machine tool builders. The industry leader in conversational programming has always been Mazak with its Mazatrol language. The focus of this chapter will be centered on this language only. Other languages contain similar techniques that accomplish nearly the same result.

Program creation

What follows are brief descriptions of the programming process for turning centers.

The control must be in the programediting mode and a work number (program number) must be identified. Note: There is no need for the letter address O to precede the program number with Mazatrol programs. Before any programming can take place, the type of program to create either Mazatrol or EIA/ISO must be determined. All Mazak machines use Mazatrol as their standard with EIA/ISO (G-Code) as an optional feature. The turning center programs are made up of these four basic parts: Common Data Process, Machining Process, Sequence Data and End Process.

The information at the head of the program applies to the entire program. The programmer is prompted to answer the following questions for this common data.

What is the material?

The controller is preset with standard materials of carbon steel, alloy steel, cast iron, aluminum and stainless to choose from. This choice affects the automatic calculation of cutting feeds and speeds throughout the program.