What is CNC Machining? The Ultimate Guide (2022)
Every industrial manufacturing professional and nearly any engineering enthusiast is well-aware of CNC machining. Shaping workpieces with the use of advanced machinery is no wonder. But still, not many have a comprehensive understanding of the entire process.
Let’s briefly review CNC machining one more time and then deepen into its advanced matters like programming. Descriptions of popular manufacturing materials will also be provided in the end.
CNC is the acronym for computer numerical control. The terminology is not self-explanatory, but it simply refers to any process performed by fully automated equipment units – CNC machines.
In other words, CNC machining is a manufacturing process assisted by computerized machinery with little labor involvement. You may have heard of it as subtractive manufacturing. It is basically shaping components from raw workpieces by cutting small chips of material off. All the designs in CNC machining are obtained in such a manner.
Years ago, all the manufacturing operations were done manually. Now, any process, from the roughest to the most intricate, can be performed by specialized machinery.
Some of the equipment units involved in CNC machining are the following:
- Grinding machines.
- Laser cutting machines.
- Plasma cutting machines.
- Electric discharge machines.
- Pick and place machines.
CNC Machining Process Review
All the listed above pieces of machinery operate in accordance with the same working principle. Integrated software dictates their spindles – movable parts that hold cutting tools, change their positions along axes.
In such a manner, the tooling precisely cut tiny bits of materials off workpieces. You will learn more about software and its programming in the next section.
Fundamentals of the CNC Machining
As for the CNC machining process overall, material removal is performed in specific positions. Machinery does not have a computer vision to detect where shaping is needed or how deep material should be cut. Instead, it is guided by coordinates. Back in your school days, you had been taught about X, Y, and Z axes in math classes. The same principle is here.
These axes enable the determination of specific coordinates – distances represented in numbers. The simplest CNC machine has its cutting tools moving in only two directions – X and Y. The most complicated machinery may have spindles moving in eight or even more axes. What does it mean? If necessary, cutting tools can cut materials from every spatial coordinate and at any angle.
Fundamentals of Cutting Tools Usage
Cutting tools for CNC machining are no different from ones for conventional manufacturing. So in case you are familiar with manual machining, you will find the following examples well-known:
- Drill bits
- End mills
- Face mills
- Side and face cutters
- Hollow mills
- Gear cutters
- Thread mills
These are only a few among a wide range of useful tools. Combining them and using them in a proper order helps to create intricate designs.
As for their usage in CNC machining, they are also controlled by integrated software. Any Automated equipment unit may have from one to multiple spindles. These typically accommodate only one cutting tool. But some spindles may have slots for several types of tooling and change them automatically. In case such a feature is not provided, labor changes tooling manually.
The use of correctly chosen cutting tools is the ground for performing particular manufacturing operations. These are outlined further in the text.
CNC Machining Programming
Many may disagree, but the correct CNC machining programming is absolutely the essential step of manufacturing. It is so because the method’s precision requires highly accurate commands to be given.
CNC manufacturing is rather a complex process. It is grounded on creating a digital 3D model first, and then on letting a CNC machine “read” the model and force tooling to shape its design.
CAD stands for Computer-Aided Design. Or simply the modeling of 3D objects in a digital environment. Engineers, architectors, developers, and other specialists widely employ CAD software to construct fully-fledged models.
When it comes to CNC machining, CAD designs are complex digital objects that are constructed with indications of their accurate dimensions. Moreover, they have all the construction elements present. So these are basically the completed, ready-to-use models for further fabrication.
Mechanical engineering is especially demanding the correctness of the materials’ characteristics. Professional CAD software enables users to consider every such nuance while constructing a model. Some popular digital solutions for designing are the following:
- Fusion 360.
- SketchUp Free.
At the end of the day, there is no difference in what software you use. You will end up having a CAD file that does have a finished model. But it cannot be decoded by a CNC machine’s software. That’s why you will need pre-programming then.
You need a CNC machining program or pre-programmed CAD model to have your automated equipment units functioning. Constructing such a program requires the use of two relatively simple coding languages – G-code and M-code.
Both really have nothing to do with languages that app developers use. And they are grounded on a few easy-to-understand principles:
- Writing G-Code
Given the coordinate system, a CNC machine can move its cutting tools along, for example, three axes. An instruction that specifies a type of move, axis, direction, and exact distance should be given to command the machine to move its spindle.
For example, the code line may look like this: G00G58X-30.Y-70.Z-5. In this example, “G00” means a rapid, non-cutting move. “G58” is the work coordinates. “X-30” is the command to go -30 mm. from the initial position on the X-axis. “Y-70” is to go -70 mm. on the Y-axis, and “Z-5” is to go -5 mm. on the Z-axis.
You may learn basic G-code commands in the image below.
- Writing M-Code
M-coded commands regulate complementary functions of a CNC machine operating. These are non-related to material cutting specifically but programmed in a similar manner.
M-code is more simple and may look like this” M05; M00; See examples of M-code operations in the image below.
- Carbide Create and Carbide Create Pro.
- Alibre Workshop.
Types of CNC Machining Operations
Once your understanding of the CNC machining process is complete, you may proceed to what exactly you can do with workpieces. Machining operations and CNC centers’ ways of working are numerous. The most popular of them are the following:
- Milling. A rotary cutting tool comes into contact with a material, removing tiny chips from it. Subtypes are end milling, chamfer milling, face milling, boring, tapping, etc.
- Turning. A cylindrical workpiece is being rotated while a fixed cutting tool removes material from it. It is a working principle of CNC turning centers and lathes.
- Routing. A rotary cutting tool removes pieces of material from a workpiece’s surface. It is similar to the milling process performed over softer materials only.
- Drilling. Cutting a hole into a workpiece by using a rotary drill bit.
- Grinding. Removing minor amounts of materials from a workpiece’s surface by using an abrasive wheel.
- Sawing. Cutting a workpiece into parts with a blade.
- Polishing and Brushing. Giving a workpiece a smooth finish by using abrasives.
Advantages of CNC Machining
CNC machining as a subtractive manufacturing method has obvious advantages over additive manufacturing or manual machining. Essential of them are the following:
- High production levels and production rates. CNC machining offers superior production speed compared to any other means of manufacturing. Also, once prepared, equipment units can operate 24/7 with little to no need for technical maintenance.
- Great personnel safety. CNC machining requires little to no labor involvement. Moreover, operators are isolated from the working environment with a protective window.
- Reduced energy consumption and environment-friendliness. Surprisingly, but CNC machining process is not that energy-consuming. And it can be easily scaled without unnecessary energy losses. Also, most CNC machining materials are 100% recyclable.
- High accuracy. CNC machines are considered equipment units with minimal manufacturing errors. It means that they ensure the highest precision possible.
- Superior consistency. CNC machines can reproduce parts that almost do not have discrepancies in their dimensions. There is also no difference in the quality of different batches of components produced.
- Cost-effectiveness. CNC machining requires high initial investments. But in the case of large-scale manufacturing, the final production costs per part fabricated are rather low.
Materials Used in CNC Machining
It is difficult to remember a material that CNC equipment units cannot machine at all. Although the capacities of subtractive machining are nearly unlimited, there are still more or less popular materials to fabricate components from.
Let’s review some popular types of unprocessed materials for CNC machining, their basic characteristics, and potential applications.
- Stainless steel. Corrosion-resistant and highly durable stainless steel also offers a good strength-to-weight ratio. Most industrial equipment units, surgical instruments, and domestic utensils are made from it.
- Brass. It is not as hard as steel but offers even better electrical and thermal conductivity, corrosion resistance, and ductility. Used to fabricate musical instruments, plumbing, decorations, and fittings placed near explosives.
- Aluminum and its alloys. This lightweight but still strong metal offers superior corrosion and chemical resistance. It is widely spread in all industries but is absolutely essential for automotive and aerospace craft.
- Titanium. It is an extremely durable and corrosion-resistant metal. Titanium is one of the common additives to alloys. It is also used in automotive, medicine, jewelry, electronics, and other industries.
- Copper. It is a soft metal that mainly serves as a conductor of heat and electricity. Copper is typically used to produce electrical components like PCBs, wires, etc.
- Plastics. This material consists of semi-synthetic organic compounds and is known for its high versatility. Plastic can have fluctuating strength, durability, transparency, and other properties depending on its type. It is used in nearly every industry and frequently replaced other materials.
- Wood. Surprisingly, wood can also be machined well. Its properties mainly depend on the type and can fluctuate significantly. Wooden parts are widespread in the sports industry and also can serve as decorations.
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