Present-day computer numerical control (CNC) machines follow a set of protocols based on the older numerical control (NC) system first developed in the mid-twentieth century. With the advent of NC machines, the metalworking industry began relying on the use of paper punch-tape applications (or “G-Codes”) to program instructions used for manufacturing components. This continued for several decades, until the late 1960’s, when more advanced CNC programs became the industry standard.
Numerical Control Use Prior to 1949
Although conventional NC programming became common in the metalworking industry in the 1950’s, a rudimentary form of the punch-card system was already in development in the nineteenth century, when it was used to control textile looms and player pianos under a similar, although greatly simplified, principle.
In 1949, a numerically operated toolmaker’s lathe introduced the process of numbered tape-controlled machining, but manufacturer response to the new technology was ambivalent. After World War II, the U.S. Air Force sought a method for adding greater component design precision to existing fabrication methods. This led John Parsons, the president of Parsons Works of Traverse City, Michigan, to develop a by-the-numbers manufacturing technique involving servo controls. The servo control system was driven by positional data input into a computing device. The new method sped up manual processes and increased machining precision.
From 1949 to 1964
From 1949 to 1952, Parsons worked with the Massachusetts Institute of Technology to create an experimental machine capable of numerically controlled contour milling. At the time, the electronics industry hadn’t yet created support systems to help integrate the new machines, and it was impractical to mass-produce Parson’s technology. However, in 1952, a three-axis numerically driven milling demonstration was successfully completed before members of the military, the aerospace industry, the machining industry, and the media. By 1964, over 35,000 numerically controlled machines were in use nationwide.
Punch Tape to Software Programs
Originally, NC punch tape cards were created with a typewriter-like machine known as the “flexowriter.” Punch cards were fed into a large control unit adjacent to the machinery and imprinted with a programming sequence called G-Code, named after the company that developed it, Gerber Scientific Instruments.
NC machines were the industry standard until the late-1960s, when the first computer numerical controlled (CNC) machines were introduced. CNC technology followed the same principles set by the original numerical protocol system, but replaced the punch and paper method with more advanced computer software programs. This new programming technology quickly replaced NC machining as the industrial standard. CNC was also the foundation for subsequent processes, such as computer-aided design (CAD) and computer-aided manufacturing (CAM). While conceptually similar to the machining punch card system created in 1952, CAD/CAM provides today’s manufacturers with greater flexibility in their operations.
Numerically controlled machines of the 1950s and 60s employed vacuum tubes and mechanical relays as their primary controller sets. At that time, the controllers were “point A to point B” locators that functioned along two axes. Today’s high-density integrated circuits, however, are capable of creating three-dimensional shapes in a vast range of designs and dimensions. Modern controllers can also communicate with the user and store and analyze program data.
Sophisticated CNC machinery can automatically monitor the quality of the work being performed, and relay its findings to other segments of the machining process, such as the loading and unloading phase. If the controller notices a defect or deviation from intended product design, it can sometimes make a correction in real-time by replacing dull tools or notifying the manufacturer about any problems. This level of automation highlights the key difference between the two conceptually similar programming methods: while NC controllers must function within the parameters of direct, simple tasks, CNC programming enables machinery to analyze data and adapt to changing circumstances.
Advantages of CNC Machining
Since computer-controlled machining has evolved over the course of several decades, its current iteration is more advanced in terms of precision, automation, and production speed than any of its earlier forms, including NC programming. Some of the benefits provided by the most recent type of CNC machining include:
• Complex and intricately shaped part fabrication can be performed with greater accuracy and faster turnover rates.
• Quality control and equipment inspection systems can be semi- or fully automated.
• Shorter CNC machine set-up and integration times result in greater productivity.
• In some cases, computer-controlled networks can reduce the number of machines required for a particular project.
• CNC programs can be modified, making them adaptable to a wide range of machining tasks.
• There is less need for prolonged machining trial runs under CNC programs.