CNC is the abbreviation of computer numerical control, usually using computer control and machine tools to remove the material layer from the blank to produce custom-designed parts. The process is suitable for various materials, including metal, plastic, wood, glass, foam, and composite materials, and is widely used in various industries. Compared with additive manufacturing processes (such as 3D printing) or molding manufacturing processes (such as liquid injection molding), CNC machining usually uses a subtractive manufacturing process. The subtractive process removes layers of material from the workpiece to produce customized shapes and designs, the additive process assembles the layers of material to produce the desired shape, and the forming process deforms and shifts the raw material to produce the desired shape. CNC machining has the characteristics of automation, which can achieve high precision and cost-effectiveness in one-off and mid-batch production. Of course, each type of manufacturing process has its advantages and disadvantages, but this article focuses on the basic knowledge of CNC processing, as well as various components and tools of CNC processing. In addition, this article discusses various operations of CNC machining and proposes alternative methods for CNC machining.
Although CNC machining provides various functions and operations, the basic principles of the process are basically the same. The basic process of CNC machining includes the following stages:
- CAD model design
- Convert CAD files to CNC programs
- Prepare CNC machine tools
- Perform processing operations
Next in detail:
CAD model design
The CNC machining process starts with the CAD design of 2D vector or 3D solid parts internally or created by a CAD/CAM design service company. Computer-aided design (CAD) software enables designers and manufacturers to generate models or renderings of their parts and products, and the necessary technical specifications, such as dimensions and geometric shapes, to produce parts or products.
The design of CNC machining parts is limited by the functions of the CNC machine lathe and tools. For example, most CNC machine tools are cylindrical, so the geometry of the parts that can be produced by the CNC machining process is limited because the tool will form curved corners. In addition, the characteristics of the processed materials, tool design, and machine processing capabilities further limit the design possibilities, such as the smallest part thickness, the largest part size, and the inclusion and complexity of internal cavities and features.
After the CAD design is completed, the designer exports it to a CNC-compatible file format, such as STEP or IGES.
Convert CAD files to CNC programs
The formatted CAD design file is run through a program, usually, computer-aided manufacturing (CAM) software, to extract part geometry and generate digital programming code that will control CNC machine lathe and manipulate tools to produce custom-designed parts.
CNC machine lathes use several programming languages, including G code and M code. The most famous general geometry code in CNC machining programming language (called G code) controls when, where, and how the machine tool moves (for example, when the machine tool is turned on or off, and the speed of the machine tool). The specific position on the workpiece, what path to take, etc., are controlled by auxiliary function codes (called M codes)
The CNC machining process uses software applications to ensure the optimization, precision, and accuracy of custom-designed parts or products. The software applications used include:
CAD: Computer-aided design (CAD) software is a program used to draw and produce 2D vector or 3D solid parts and surface renderings, and necessary technical documents and specifications related to the parts. The design and model generated in the CAD program are usually used by the CAM program to create the necessary machine programs to produce parts through CNC machining methods. CAD software can also be used to determine and define the best part characteristics, evaluate and verify part designs, simulate products without prototypes, and provide design data to manufacturers and workshops.
CAM: Computer-Aided Manufacturing (CAM) software is a program used to extract technical information from a CAD model and generate machine tool programs necessary to run CNC machine tools and manipulating tools to produce custom-designed parts. CAM software enables Wanfuxin CNC machining machines to run without the assistance of an operator and can help automate the evaluation of finished products.
CAE: Computer-Aided Engineering (CAE) software is a program used by engineers in the pre-processing, analysis, and post-processing stages of the development process. CAE software is used as an auxiliary support tool in engineering analysis applications (such as design, simulation, planning, manufacturing, diagnosis, and maintenance) to help evaluate and modify product designs. The types of CAE software available include finite element analysis (FEA), computational fluid dynamics (CFD), and multi-body dynamics (MDB) software.
Prepare CNC machine tools
The main CNC machining lathes are as follows:
- CNC machining drilling equipment
Drilling uses a rotary drill to create cylindrical holes in the workpiece. The design of the drill bit allows scrap metal (ie, chips) to fall off the workpiece. There are several types of drill bits, each of which is used for a specific application. The types of drill bits available include spot drills (used to produce shallow holes or pilot holes), peck drills (used to reduce the number of chips on the workpiece), screwdriver bits (used to produce holes without pilot holes), and chuck reamers (Used to enlarge) previously created holes). Usually, CNC drilling is used in CNC machining and drilling processes, and these drilling machines are specially used to perform drilling operations. However, it can also be operated by a lathe, tapping machine, or milling machine.
- CNC machining milling equipment
Milling uses rotating multipoint cutting tools to shape the workpiece. Milling cutters are horizontal or vertical, including end mills, spiral milling cutters, and chamfer milling cutters. The CNC milling process uses CNC milling machines, which can be oriented horizontally or vertically. The basic milling machine can perform the three-axis motion, while the more advanced models can accommodate more axes. Available milling cutter types include hand milling, flat milling, universal milling, and universal milling machines.
- CNC machining turning equipment
Turning uses single-point cutting tools to remove material from rotating workpieces. The design of the turning tool varies according to the specific application, where the tool can be used for roughing, finishing, facing, tapping, forming, undercutting, parting, and grooving applications. The CNC machining and turning process use CNC lathes, and the available lathe types include turret lathes, engine lathes, and special lathes.
CNC machining lathe model:
CNC machine tools are available in standard models and desktop models. Standard CNC machines are typical industry standard machines that can be designated to perform specific machine operations (such as drilling machines) or perform multiple operations (such as milling machines and lathes). Desktop CNC machine tools are smaller, lighter machine tools, similar to larger similar machines. In general, desktop models can handle softer materials, such as foam and plastic, smaller parts, and are suitable for light to moderate output. Available desktop CNC finishing machine types include plotter-sized laser cutting machines and milling machines, and desktop or desktop lathes.
Various materials can be used in the CNC machining process: metals (such as titanium alloy, aluminum, brass, stainless steel, alloy steel, etc.), plastics (such as PEEK, PTFE, nylon, etc.), wood, foam, and composite materials.
CNC machining materials：
The choice of materials used in CNC machining depends to a large extent on the specific manufacturing application and its specifications. As long as it can withstand the processing process, it can have sufficient hardness, tensile strength, shear strength, chemical resistance, and high-temperature resistance, and most materials can be processed.
The workpiece material and its physical characteristics are used to determine the optimal cutting speed, cutting feed rate, and cutting depth. Measured in surface feet per minute, cutting speed refers to the speed at which the machine tool cuts into the workpiece or removes material from the workpiece. The feed rate (in inches per minute) is a measure of the speed at which the workpiece is fed to the machine tool, and the depth of cut is the depth at which the cutting tool cuts into the workpiece. Usually, the workpiece will first enter the initial stage, which is the roughing stage, and the custom-designed shape and size are processed. Then proceed to the finishing stage, in this stage, the workpiece will experience a slower feed rate and a shallower depth of cut to achieve more precise processing.
Perform processing operations
The CNC machining process uses various CNC machining lathes to produce custom-designed parts or products. The following are the specific steps:
- Turn on the machine, and let each coordinate axis manually returning to the machine origin
- Tool preparation
- Put the tool holder with the clamped tool into the tool magazine manually
- Clean the workbench, install fixtures and workpieces
- Tool setting, confirm and input the parameters of the workpiece coordinate system
- Enter the processing program
- Debug the processing program
- Automatic processing
- Remove the workpiece and inspect it
- Clean up the processing site
- Shut down
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