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Computer-aided NC programming - coming slow but sure.

Computer-aided NC programming-- coming slow but sure

More than 50 percent of US metal-working companies use manual methods to prepare programs for their CNC equipment, i.e., direct-data generation, storage, and editing at a machine-tool controller, or a tape-preparation system that permits off-line programming and editing. More progressive shops, though, have made the transition to computer-assisted programming--either by using a time-sharing service, which is accessed by one or more in-house terminals, or by using a resident computer-based programming system.

A recent unpublished survey of shops that have made the jump to a computer assist indicates that 60 percent use time-sharing systems, 30 percent use stand-alone systems, and 10 percent use main-frame-based systems. A small portion meet their needs by subcontracting programming to service bureaus.

Studies comparing programming methods, however, indicate that lowest recurring costs, fastest turnaround time, and highest return on investment are only possible when using a stand-alone system (see chart and Figure 1).

The ideal system

Every potential user has his own set of criteria to judge the benefits that stand-alone computer-aided programming systems offer. There is, however, a universal set of capabilities and characteristics that should be considered. These can, for purposes of conducting an organized evaluation, be grouped as impact on present operation, productivity improvement features, and growth capabilities.

No system has all that's needed (or desired) by everyone. But, if there were, it might have the following characteristics:

Impact on operation. The system would be easy to operate, using a widely recognized command language conforming to an industry standard (such as ANSI X3J5). The system must be easily integrated into the organization and be compatible with present programming procedures and equipment.

All previously generated programs written in other languages (e.g., APT and COMPACT II) could then be loaded into the system and used or modified as required for future applications. And, of course, the system must be totally vendor independent; i.e., have a universal postprocessing program for self-generation of all machine links.

Further, the system vendor should have a well-organized dependable customer service and support organization that provides operator training, and software and hardware maintenance and problem solving. Detailed, well-written user manuals and equipment/software documentation must also be provided.

Productivity improvement features. The system should include a highly interactive graphics terminal that provides a real-time display of both part geometry and tool paths as they are generated. It would use multipurpose, flexible operating system software for executing different tasks simultaneously (e.g., editing one program while plotting geometry for another).

On-line error checking for syntax and logic is desirable, as is validating punched tapes. Sophisticated calculation aids would be available as a program is generated, and the system must also provide automatic point-to-point definition of tool paths using interpolation routines.

The programming software would include a complete set of geometric manipulation routines (rotation, translation, mirroring, replication etc) and permit hierarchical programming using embedded, predefined, parameter-driven macro routines and logical computation techniques (if, then, or statements). It also would accommodate insertion of canned cycles (roughing, threading, pocketing, drilling etc) and standard tool commands.

Routines for performing family-of-parts programming, file editing, and machine-time calculations are desirable. And a library of data describing standard tools, machines, and setups might be maintained in the system. Finally, the system should be configured to accept design geometry from CAD/CAM systems and communicate NC command files to a variety of machine controllers.

Growth capabilities. The system would be constructed using a building-block approach, thereby permitting users to incrementally expand it as the work load grows. Concurrently usable, multiple workstations could be added to the system, along with memory and storage capacity, and other peripherals.

The system should have the flexibility to be networked to remotely located CAD/CAM systems. Programming capabilities initially would be for 2 1/2 axis machining, but could be expanded to deal with additional axes and different metalworking technologies.

Most of it's here already

With the advent of 16-bit and 32-bit microprocessors, high-resolution color-graphics terminals, low-cost CMOS memory devices, and mass magnetic storage at ridiculously low prices, the tools are in place to approach the ideal system at reasonable cost. For example, here's sampling of what's available:

Hewlett-Packard Inc, Palo Alto, CA, has a single workstation (the NC 36) that incorporates all NC programming features in a single package. Its software capabilities cover a spectrum of machine-tool technologies including milling, drilling, flame cutting, and EDM. It also offers a generalized postprocessor program for user generation of machine links. For more information, circle E61.

Manufacturing Data Systems Inc, Ann Arbor, MI, is well known for its COMPACT II NC programming language. The firm also makes a broad line of systems, including terminals designed to be used with their time-sharing service. The company's latest effort, NC Graphics, is a high-end system incorporating interactive color-graphics terminals supported by a DEC 32-bit VAX super-minicomputer. Major emphasis is also put on CAD interfaces. For more information, circle E62.

Numeric Micro Inc, Dallas, TX, incorporates a high-resolution color-graphics display in its system for 3-D plotting, along with a standard array of features that include an alphanumeric workstation, plotters, printers, tape punchers/readers, and comprehensive communication capabilities. For more information, circle E63.

Numeridex Inc, Wheeling, IL, markets products ranging from simple tape-preparation systems of single-user and multi-user computer-based programming systems with interactive graphics, Figure 2. Offered are both a conversational, color-graphics-oriented programming language (Numeripower) and a new ANSI-standard COMPACT-like program for driving three-axis machines (Numeripower III). The firm also has universal link-generation software that eliminates purchasing machine-unique postprocessors. For more information, circle E64.

Weber NC Systems Inc, Brookfield, WI, has recently established a software interface between its NC program and AM Bruning's computer-aided drafting system, EasyDraf2. Both programs use the same graphics hardware, and part geometry generated on the CAD system can be transmitted directly to the NC software for tape preparation. For more information, circle E65.

Don't drop the ball

Managers of shops that do most of their NC programming in-house have, at one time or another, examined the value of making the transition to computer-aided techniques. Some go to great lengths to perform a detailed analysis, including "bench marking' a variety of available systems against existing in-house capabilities (see January '83 Tooling & Production, p 65). The performance data is then converted to estimated savings (or losses) compared with manual programming and used to calculate ROI.

If the payback isn't high enough or fast enough, most managers lose interest. Unfortunately, many factors that have a direct impact on profitability, but are difficult to quantify, include part yield, schedule responsiveness, flexibility, and image of the company as perceived by customers.

If you take the time and assign dollar values to these items, the cost benefits of computer-assisted programming quickly become obvious. Ignore them and the competition will spank your bottom line in short order.

Table: Comparing programming procedures

Photo: 1. Graph shows comparitive recurring costs of NC-programming techniques.

Photo: 2. This stand-alone system from Numeridex Inc, provides a real-time display of both part geometry and tool paths as they are generated.
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Title Annotation:numerical control
Author:Marks, Leonard
Publication:Tooling & Production
Date:Jan 1, 1984
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