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Revision as of 08:32, 1 August 2023 by Thumperward (talk | contribs) (WP:NOTMANUAL)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff) Primary programming language used in CNC For other uses, see G-code (disambiguation) and G programming language (disambiguation). "RS-274" redirects here. For the photoplotter format, see Gerber format.| Paradigm | Procedural, imperative |
|---|---|
| Designed by | Massachusetts Institute of Technology |
| Developer | Electronic Industries Association (RS-274), International Organization for Standardization (ISO-6983) |
| First appeared | 1963 (1963) (RS-274) |
| Filename extensions | .gcode, .mpt, .mpf, .nc and several others |
| Major implementations | |
| Numerous; mainly Siemens Sinumerik, FANUC, Haas, Heidenhain, Mazak, Okuma | |
G-code (also RS-274) is the most widely used computer numerical control (CNC) and 3D printing programming language. It is used mainly in computer-aided manufacturing to control automated machine tools, as well as for 3D-printer slicer applications. The G stands for geometry. G-code has many variants.
G-code instructions are provided to a machine controller (industrial computer) that tells the motors where to move, how fast to move, and what path to follow. The two most common situations are that, within a machine tool such as a lathe or mill, a cutting tool is moved according to these instructions through a toolpath cutting away material to leave only the finished workpiece and/or an unfinished workpiece is precisely positioned in any of up to nine axes around the three dimensions relative to a toolpath and, either or both can move relative to each other. The same concept also extends to noncutting tools such as forming or burnishing tools, photoplotting, additive methods such as 3D printing, and measuring instruments.
Background and implementations
The first implementation of a numerical control programming language was developed at the MIT Servomechanisms Laboratory in the 1950s. In the decades that followed, many implementations were developed by numerous organizations, both commercial and noncommercial. Elements of G-code had often been used in these implementations. The first standardized version of G-code used in the United States, RS-274, was published in 1963 by the Electronic Industries Alliance (EIA; then known as Electronic Industries Association). In 1974, EIA approved RS-274-C, which merged RS-273 (variable block for positioning and straight cut) and RS-274-B (variable block for contouring and contouring/positioning). A final revision of RS-274 was approved in 1979, as RS-274-D. In other countries, the standard ISO 6983 (finalized in 1982) is often used, but many European countries use other standards. For example, DIN 66025 is used in Germany, and PN-73M-55256 and PN-93/M-55251 were formerly used in Poland.
Extensions and variations have been added independently by control manufacturers and machine tool manufacturers, and operators of a specific controller must be aware of the differences between each manufacturer's product.
One standardized version of G-code, known as BCL (Binary Cutter Language), is used only on very few machines. Developed at MIT, BCL was developed to control CNC machines in terms of straight lines and arcs.
During the 1970s through 1990s, many CNC machine tool builders attempted to overcome compatibility difficulties by standardizing on machine tool controllers built by Fanuc. Siemens was another market dominator in CNC controls, especially in Europe. In the 2010s, controller differences and incompatibility are not as troublesome because machining operations are usually developed with CAD/CAM applications that can output the appropriate G-code for a specific machine through a software tool called a post-processor (sometimes shortened to just a "post").
Some CNC machines use "conversational" programming, which is a wizard-like programming mode that either hides G-code or completely bypasses the use of G-code. Some popular examples are Okuma's Advanced One Touch (AOT), Southwestern Industries' ProtoTRAK, Mazak's Mazatrol, Hurco's Ultimax and Winmax, Haas' Intuitive Programming System (IPS), and Mori Seiki's CAPS conversational software.
G-code began as a limited language that lacked constructs such as loops, conditional operators, and programmer-declared variables with natural-word-including names (or the expressions in which to use them). It was unable to encode logic but was just a way to "connect the dots" where the programmer figured out many of the dots' locations longhand. The latest implementations of G-code include macro language capabilities somewhat closer to a high-level programming language. Additionally, all primary manufacturers (e.g., Fanuc, Siemens, Heidenhain) provide access to programmable logic controller (PLC) data, such as axis positioning data and tool data, via variables used by NC programs. These constructs make it easier to develop automation applications.
Programming environments
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G-code's programming environments have evolved in parallel with those of general programming—from the earliest environments (e.g., writing a program with a pencil, typing it into a tape puncher) to the latest environments that combine CAD (computer-aided design), CAM (computer-aided manufacturing), and richly featured G-code editors. (G-code editors are analogous to XML editors, using colors and indents semantically to aid the user in ways that basic text editors can't. CAM packages are analogous to IDEs in general programming.)
Two high-level paradigm shifts have been toward:
- abandoning "manual programming" (with nothing but a pencil or text editor and a human mind) for CAM software systems that generate G-code automatically via postprocessors (analogous to the development of visual techniques in general programming)
- abandoning hardcoded constructs for parametric ones (analogous to the difference in general programming between hardcoding a constant into an equation versus declaring it a variable and assigning new values to it at will; and to the object-oriented approach in general).
Macro (parametric) CNC programming uses human-friendly variable names, relational operators, and loop structures, much as general programming does, to capture information and logic with machine-readable semantics. Whereas older manual CNC programming could only describe particular instances of parts in numeric form, macro programming describes abstractions that can easily apply in a wide variety of instances.
The tendency is comparable to a computer programming evolution from low-level programming languages to high-level ones.
STEP-NC reflects the same theme, which can be viewed as yet another step along a path that started with the development of machine tools, jigs and fixtures, and numerical control, which all sought to "build the skill into the tool." Recent developments of G-code and STEP-NC aim to build the information and semantics into the tool. This idea is not new; from the beginning of numerical control, the concept of an end-to-end CAD/CAM environment was the goal of such early technologies as DAC-1 and APT. Those efforts were fine for huge corporations like GM and Boeing. However, small and medium enterprises went through an era of simpler implementations of NC, with relatively primitive "connect-the-dots" G-code and manual programming until CAD/CAM improved and disseminated throughout the industry.
Any machine tool with a great number of axes, spindles, and tool stations is difficult to program well manually. It has been done over the years, but not easily. This challenge has existed for decades in CNC screw machine and rotary transfer programming, and it now also arises with today's newer machining centers called "turn-mills", "mill-turns", "multitasking machines", and "multifunction machines". Now that CAD/CAM systems are widely used, CNC programming (such as with G-code) requires CAD/CAM (as opposed to manual programming) to be practical and competitive in the market segments these classes of machines serve. As Smid says, "Combine all these axes with some additional features, and the amount of knowledge required to succeed is quite overwhelming, to say the least." At the same time, however, programmers still must thoroughly understand the principles of manual programming and must think critically and second-guess some aspects of the software's decisions.
Since about the mid-2000s, it seems "the death of manual programming" (that is, of writing lines of G-code without CAD/CAM assistance) may be approaching. However, it is currently only in some contexts that manual programming is obsolete. Plenty of CAM programming takes place nowadays among people who are rusty on, or incapable of, manual programming—but it is not true that all CNC programming can be done, or done as well or as efficiently, without knowing G-code. Tailoring and refining the CNC program at the machine is an area of practice where it can be easier or more efficient to edit the G-code directly rather than editing the CAM toolpaths and re-post-processing the program.
Making a living cutting parts on computer-controlled machines has been made both easier and harder by CAD/CAM software. Efficiently written G-code can be a challenge for CAM software. Ideally, a CNC machinist should know both manual and CAM programming well so that the benefits of both brute-force CAM and elegant hand programming can be used where needed. Many older machines were built with limited computer memory at a time when memory was very expensive; 32K was considered plenty of room for manual programs whereas modern CAM software can post gigabytes of code. CAM excels at getting a program out quickly that may take up more machine memory and take longer to run. This often makes it quite valuable to machining a low quantity of parts. But a balance must be struck between the time it takes to create a program and the time the program takes to machine a part. It has become easier and faster to make just a few parts on the newer machines with much memory. This has taken its toll on both hand programmers and manual machinists. Given natural turnover into retirement, it is not realistic to expect to maintain a large pool of operators who are highly skilled in manual programming when their commercial environment mostly can no longer provide the countless hours of deep experience it took to build that skill; and yet the loss of this experience base can be appreciated, and there are times when such a pool is sorely missed because some CNC or 3D printing runs still cannot be optimized without such skill.
Abbreviations used by programmers and operators
This list is only a selection and, except for a few key terms, mostly avoids duplicating the many abbreviations listed at engineering drawing abbreviations and symbols.
| Abbreviation | Expansion | Corollary info |
|---|---|---|
| APC | automatic pallet changer | See M60. |
| ATC | automatic tool changer | See M06. |
| CAD/CAM | computer-aided design and computer-aided manufacturing | |
| CCW | counterclockwise | See M04. |
| CNC | computerized numerical control | |
| CRC | cutter radius compensation | See also G40, G41, and G42. |
| CS | cutting speed | Referring to cutting speed (surface speed) in surface feet per minute (sfm, sfpm) or meters per minute (m/min). |
| CSS | constant surface speed | See G96 for explanation. |
| CW | clockwise | See M03. |
| DNC | direct numerical control or distributed numerical control | Sometimes referred to as "Drip Feeding" or "Drip Numerical Control" due to the fact that a file can be "drip" fed to a machine, line by line, over a serial protocol such as RS232. DNC allows machines with limited amounts of memory to run larger files. |
| DOC | depth of cut | Refers to how deep (in the Z direction) a given cut will be |
| EOB | end of block | The G-code synonym of end of line (EOL). A control character equating to newline. In many implementations of G-code (as also, more generally, in many programming languages), a semicolon (;) is synonymous with EOB. In some controls (especially older ones) it must be explicitly typed and displayed. Other software treats it as a nonprinting/nondisplaying character, much like word processing apps treat the pilcrow (¶). |
| E-stop | emergency stop | |
| EXT | external | On the operation panel, one of the positions of the mode switch is "external", sometimes abbreviated as "EXT", referring to any external source of data, such as tape or DNC, in contrast to the computer memory that is built into the CNC itself. |
| FIM | full indicator movement | |
| FPM | feet per minute | See SFM. |
| HBM | horizontal boring mill | A type of machine tool that specializes in boring, typically large holes in large workpieces. |
| HMC | horizontal machining center | |
| HSM | high speed machining | Refers to machining at speeds considered high by traditional standards. Usually achieved with special geared-up spindle attachments or with the latest high-rev spindles. On modern machines HSM refers to a cutting strategy with a light, constant chip load and high feed rate, usually at or near the full depth of cut. |
| HSS | high-speed steel | A type of tool steel used to make cutters. Still widely used today (versatile, affordable, capable) although carbide and others continue to erode its share of commercial applications due to their higher rate of material removal. |
| in | inch(es) | |
| IPF | inches per flute | Also known as chip load or IPT. See F address and feed rate. |
| IPM | inches per minute | See F address and feed rate. |
| IPR | inches per revolution | See F address and feed rate. |
| IPT | inches per tooth | Also known as chip load or IPF. See F address and feed rate. |
| MDI | manual data input | A mode of operation in which the operator can type in lines of program (blocks of code) and then execute them by pushing cycle start. |
| MEM | memory | On the operation panel, one of the positions of the mode switch is "memory", sometimes abbreviated as "MEM", referring to the computer memory that is built into the CNC itself, in contrast to any external source of data, such as tape or DNC. |
| MFO | manual feed rate override | The MFO dial or buttons allow the CNC operator or machinist to multiply the programmed feed value by any percentage typically between 10% and 200%. This is to allow fine-tuning of speeds and feeds to minimize chatter, improve surface finish, lengthen tool life, and so on. The SSO and MFO features can be locked out for various reasons, such as for synchronization of speed and feed in threading, or even to prevent "soldiering"/"dogging" by operators. On some newer controls, the synchronization of speed and feed in threading is sophisticated enough that SSO and MFO can be available during threading, which helps with fine-tuning speeds and feeds to reduce chatter on the threads or in repair work involving the picking up of existing threads. |
| mm | millimetre(s) | |
| MPG | manual pulse generator | Referring to the handle (handwheel) (each click of the handle generates one pulse of servo input) |
| NC | numerical control | |
| OSS | oriented spindle stop | See comments at M19. |
| SFM | surface feet per minute | See also speeds and feeds and G96. |
| SFPM | surface feet per minute | See also speeds and feeds and G96. |
| SPT | single-point threading | |
| SSO | spindle speed override | The SSO dial or buttons allow the CNC operator or machinist to multiply the programmed speed value by any percentage typically between 10% and 200%. This is to allow fine-tuning of speeds and feeds to minimize chatter, improve surface finish, lengthen tool life, and so on. The SSO and MFO features can be locked out for various reasons, such as for synchronization of speed and feed in threading, or even to prevent "soldiering"/"dogging" by operators. On some newer controls, the synchronization of speed and feed in threading is sophisticated enough that SSO and MFO can be available during threading, which helps with fine-tuning speeds and feeds to reduce chatter on the threads or in repair work involving the picking up of existing threads. |
| TC or T/C | tool change, tool changer | See M06. |
| TIR | total indicator reading | |
| TPI | threads per inch | |
| USB | Universal Serial Bus | One type of connection for data transfer |
| VMC | vertical machining center | |
| VTL | vertical turret lathe | A type of machine tool that is essentially a lathe with its Z-axis turned vertical, allowing the faceplate to sit like a large turntable. The VTL concept overlaps with the vertical boring mill concept. |
See also
- 3D printing
- Canned cycle
- LinuxCNC - a free CNC software with many resources for G-code documentation
- Drill file
- HP-GL
- STL (file format)
- Slicer (3D printing)
Extended developments
Similar concepts
Concerns during application
- Cutter location, cutter compensation, offset parameters
- Coordinate systems
Industrial robot languages
References
- Karlo Apro (2008). Secrets of 5-Axis Machining. Industrial Press Inc. ISBN 0-8311-3375-9.
- Xu, Xun (2009). Integrating Advanced Computer-aided Design, Manufacturing, and Numerical Control: Principles and Implementations. Information Science Reference. p. 166. ISBN 9781599047164 – via Google Books.
- Harik, Ramy; Thorsten Wuest (2019). Introduction to Advanced Manufacturing. SAE International. p. 116. ISBN 9780768090963 – via Google Books.
- Evans, John M., Jr. (1976). National Bureau of Standards Information Report (NBSIR) 76-1094 (R): Standards for Computer Aided Manufacturing (PDF). National Bureau of Standards. p. 43.
{{cite book}}: CS1 maint: multiple names: authors list (link) - Schenck, John P. (January 1, 1998). "Understanding common CNC protocols". Wood & Wood Products. 103 (1). Vance Publishing: 43 – via Gale.
- EIA Standard RS-274-D Interchangeable Variable Block Data Format for Positioning, Contouring, and Contouring/Positioning Numerically Controlled Machines, Washington D.C.: Electronic Industries Association, February 1979
- Stark, J.; V. K. Nguyen (2009). "STEP-compliant CNC Systems, Present and Future Directions". In Xu, Xun; Andrew Yeh Ching Nee (eds.). Advanced Design and Manufacturing Based on STEP. Springer London. p. 216. ISBN 9781848827394 – via Google Books.
- Martin., Libicki (1995). Information Technology Standards : Quest for the Common Byte. Burlington: Elsevier Science. p. 321. ISBN 9781483292489. OCLC 895436474.
- "Fanuc macro system variables". Archived from the original on 2014-05-03. Retrieved 2014-06-30.
- MMS editorial staff (2010-12-20), "CAM system simplifies Swiss-type lathe programming", Modern Machine Shop, 83 (8 ): 100–105 Online ahead of print.
- Smid 2008, p. 457.
- Lynch, Mike (2010-01-18), "When programmers should know G code", Modern Machine Shop (online ed.).
- Lynch, Mike (2011-10-19), "Five CNC myths and misconceptions [CNC Tech Talk column, Editor's Commentary]", Modern Machine Shop (online ed.), archived from the original on 2017-05-27, retrieved 2011-11-22.
- Marinac, Dan (15 February 2000). "Tool Path Strategies For High-Speed Machining". www.mmsonline.com. Retrieved 2018-03-06.
- ^ Korn, Derek (2014-05-06), "What is arbitrary speed threading?", Modern Machine Shop.
Bibliography
- Oberg, Erik; Jones, Franklin D.; Horton, Holbrook L.; Ryffel, Henry H. (1996), Green, Robert E.; McCauley, Christopher J. (eds.), Machinery's Handbook (25th ed.), New York: Industrial Press, ISBN 978-0-8311-2575-2, OCLC 473691581.
- Smid, Peter (2008), CNC Programming Handbook (3rd ed.), New York: Industrial Press, ISBN 9780831133474, LCCN 2007045901.
- Smid, Peter (2010), CNC Control Setup for Milling and Turning, New York: Industrial Press, ISBN 978-0831133504, LCCN 2010007023.
- Smid, Peter (2004), Fanuc CNC Custom Macros, Industrial Press, ISBN 978-0831131579.
External links
- CNC G-Code and M-Code Programming
- Kramer, T. R.; Proctor, F. M.; Messina, E. R. (1 Aug 2000), "The NIST RS274NGC Interpreter – Version 3", NIST, NISTIR 6556
- http://museum.mit.edu/150/86 Archived 2016-03-19 at the Wayback Machine Has several links (including history of MIT Servo Lab)
- Complete list of G-code used by most 3D printers
- Fanuc and Haas G-code Reference
- Fanuc and Haas G-code Tutorial
- Haas Milling Manual
- G Code For Lathe & Milling
- M Code for Lathe & Milling