What is CNC Machining?


The term CNC stands for 'computer numerical control', and the CNC machining definition is that it is a subtractive manufacturing process that typically employs computerized controls and machine tools to remove layers of material from a stock piece—known as the blank or workpiece—and produces a custom-designed part. This process is suitable for a wide range of materials, including metals, plastics, wood, glass, foam, and composites, and finds application in a variety of industries, such as large CNC machining, machining of parts and prototypes for telecommunications, and CNC machining aerospace parts, which require tighter tolerances than other industries. Note there is a difference between the CNC machining definition and the CNC machine definition- one is a process and the other is a machine. A CNC machine (sometimes incorrectly referred to as a C and C machine) is a programmable machine that is capable of autonomously performing the operations of CNC machining.






Subtractive manufacturing processes, such as CNC machining, are often presented in contrast to additive manufacturing processes, such as 3D printing, or formative manufacturing processes, such as liquid injection molding. While subtractive processes remove layers of material from the workpiece to produce custom shapes and designs, additive processes assemble layers of material to produce the desired form and formative processes deform and displace stock material into the desired shape. The automated nature of CNC machining enables the production of high precision and high accuracy, simple parts and cost-effectiveness when fulfilling one-off and medium-volume production runs. However, while CNC machining demonstrates certain advantages over other manufacturing processes, the degree of complexity and intricacy attainable for part design and the cost-effectiveness of producing complex parts is limited.






While each type of manufacturing process has its advantages and disadvantages, this article focuses on the CNC machining process, outlining the basics of the process, and the various components and tooling of the CNC press machine. Additionally, this article explores various mechanical CNC machining operations and presents alternatives to the CNC machining process.






Overview of CNC Machining Process


Evolving from the numerical control (NC) machining process which utilized punched tape cards, CNC machining is a manufacturing process which utilizes computerized controls to operate and manipulate machine and cutting tools to shape stock material—e.g., metal, plastic, wood, foam, composite, etc.—into custom parts and designs. While the CNC machining process offers various capabilities and operations, the fundamental principles of the process remain largely the same throughout all of them. The basic CNC machining process includes the following stages:






1. Designing the CAD model


2. Converting the CAD file to a CNC program


3. Preparing the CNC machine


4. Executing the machining operation






Hydraulic mechanism


Hydraulic cutters, including swing arm cutting press, utilize a hydraulic mechanism to close the scissors’ hardened steel blades. Oil under high pressure (around 700 bar) is pumped to the movement mechanism to deliver enough power to cut even the hardest materials. The hydraulic cylinders of some cutters are filled through an external pump, while others have an electric pump with a battery integrated in the scissors’ handle. Each type has its advantages and disadvantages. Read on to find the type of hydraulic cutter that is most suited for your job.






Mobile hydraulic cutters


Holmatro’s mobile hydraulic cutters are specially designed to be used on site. Examples include the dismantling of buildings, cleaning up of industrial cables, and the remediation of gas stations. For those kind of purposes, mobile cutters are made with easy handling and portability in mind. The electric and fuel-driven mechanisms in Holmatro’s mobile cutters are lightweight and compact. The brand also offers models with batteries, which are specially designed to work in hard to reach places. The durable yet lightweight aluminum construction of most mobile cutters makes them easy to handle and carry around.






Stationary hydraulic scissors


In contrast to mobile cutters, stationary cutters are made for continuous use on a fixed worksite. These hydraulic cutter machines are often used in production processes, and in the recycling of cars and household appliances. Because of this, stationary cutters are developed for maximum durability and frequent use. The machines are largely made from high-grade steel, which results in a higher weight. Thanks to a so-called balancer, however, the weight does not rest directly on the user and a great ease of use is maintained.






Automatic Travelling Head Cutting Press






Where high speed output with predictable accuracy and material yields are needed, move up to a GCT automatic travelling head press.






Cutting jobs and patterns are pre-programmed into the machine’s computer or this can be carried out off-line and information sent down to the machine.






Thus, the operator has no more to do than load the material and cutting tool and gather the cut pieces as they emerge from the machine – the machine dictates the speed, accuracy and material yield.






In all cases, the cutting tool, such as swing arm cutting press, is loaded onto the machine’s cutting head which, on 3 axis models, can be rotated to obtain the best fit or interlock of cutting patterns. Cutting can be onto a polypropylene cutting board for easily fed material but the most versatile model uses a moving cutting and feeding belt. This acts both as a cutting barrier and as a conveyor to carry the cut components away from the cutting area.






For work which is exclusively in sheet form a version is available with a powered, mobile, feed table – very popular in the envelope industry.