CNC machining is the driving process for almost every manufacturing industry. Even a basic CNC machine setup can transform the entire workspace and exponentially increase production at reduced costs. Therefore, it is imperative to understand ‘what is CNC machining’, its working process, and the many terms and technology that come under this umbrella.
This article will be an all-inclusive guide to the concept of CNC machining. Based on the information presented here, you will be able to easily navigate through the apparently complex world of CNC technology and its various industrial applications.
What is CNC Machining?
The CNC machining process is a type of manufacturing process that uses a programming language to control machine tools for automation. CNC is an abbreviation for Computer Numerical Control. It uses a CNC program containing instructions for the machine. The program is loaded to the machine which interprets each instruction sequentially. The resulting machine movements remove material from the part with the intended tools
Machining in itself is a subtractive manufacturing process that creates a part by removing material from a larger workpiece. It is an old technology traditionally done with manual tools. The combination of Computer Numerical Control to machining provides a high-precision manufacturing process that eliminates the high labor and manual skill requirement of traditional machining. CNC machining generally requires a single person to set up and oversee the operation. They are called a CNC machinist or an operator.
When was CNC Machining Invented?
In 1949, John T. Parsons and Frank L. Sutlens invented the concept of CNC machining working for MIT. The invention of CNC machining came in the bid to find an effective solution for manufacturing helicopter propeller rotary wings as a part of a US Air Force contract.
At this point, CNC technology was in the form of its bare minimum- the Numerical Control (NC), which used punch cards as a movement control mechanism. The setup for numerical control was complex and time-consuming. With the development of computing technology, punch cards were no longer required as the instructions could be created through a machine programming language. In 1958, the development of G-code served as the introduction of computer programming skills into machining.
How Does CNC Machining Work?
The basis of CNC machining is the programming language that contains the instructions. Every CNC machine is designed with an inbuilt computing system called the microcontroller. The microcontroller is designed to understand and interpret every CNC instruction for the machine. The commands in the instructions are then passed to the particular machine parts.
The program is written according to these CNC instructions that the machine understands. Most of the instructions are standard to most CNC machines. Some instructions are machine specific and mentioned in the manufacturer manual. Therefore, the machining process is the result of a two-way communication between the programmer and the CNC machine. The CNC program itself is the communication language.
Machining of simple shapes will have a simpler program. However, complex shapes require sophisticated programming and even many sub-programs.
What are the Main Stages of the CNC Machining Process?
CNC machining process is a multi-step method that mainly requires a programmer and an operator. The various steps involved in CNC machining are:
The first step is to create the blueprints for the required parts. Blueprints are made keeping in mind the features of the part and its applications. Blueprints are made by designers, engineers, or a team of many professionals.
The blueprint is then turned into a digital two or three dimensional model by a Computer Aided Design (CAD) software. The CAD model is a scale design of the part that contains various information such as the dimensions, wall thickness, depth of cavities, etc.
CNC machines do not understand the digital design data of CAD files. Therefore, the CAD files are converted to a Computer Aided Manufacturing (CAM) format. There are many CAM software available for this purpose. This format is readable by the machine.
The machine requires configuration before program execution. The file is transferred to the machine through the dedicated ports on the machine system. The operator also adjusts the various settings of the machine through the system input. The object is mounted on the work table and secured using clamps. All preliminary checks are done at this point.
The operator then executes the program. The machine reads the instructions and begins machine tool movement. The program is stopped once the machining is finished, or the CNC machine tools encounter any error. The operator can also stop the program midway in case of an emergency.
After the program finishes, the operator can remove the workpiece from the table. The operator inspects the workpiece for quality. The workpiece may then be sent for secondary processing as required.
List of Terms Used in CNC Machining
Learning CNC machining terminology is important due to the technical nature of these processes. Here is a some of the terms you will come across in CNC machining processes:
Computer Numerical Control is a type of control system that drives various functions and processes. This drive system is not just limited to machining operations. Computer Numerical Control is responsible for the automation of any type of machine.
A Distributed Numerical Control (DNC) is a type of control system that connects multiple machines to a central computer system. The computer system can be present remotely to give instructions to each machine. The benefit of DNC system is that operators can oversee the machining even when distant from the machine tool. However, this method works for multiple machines working together.
Computer Aided Design (CAD) is a type of design software that creates two and three-dimensional drawings of the parts to be machined. CAD software is not just limited to machining operations. It is also used for architecture and engineering. Using CAD software requires graphic design or engineering design skills instead of coding.
Computer Aided Manufacturing (CAM) is a software that works as the code generator for CNC machines. It uses the CAD software’s graphical designs and converts them into a coded program. The converted file is a collection of G-code and M-code instructions.
G-code is a type of CNC programming instruction that provides movement based input to the machine tools. For instance, the movement of milling machines in the X, Y, and Z axes to remove material from the workpiece is controlled by the G-code instructions. The G-code tells the cutting tools the precise coordinates where to move, at what speed to move, how to move, and what to do when it reaches there.
M-code is a type of CNC programming instruction that directs the machine-related functions such as the coolant flow, program start, pause, stops, tool changes, etc. M-code encompasses a wide bracket of machine instructions. Therefore, it is also sometimes referred to as Miscellaneous code.
Manufacturing Data Collection (MDC) is a system that collects feedback data from various machine tools. The purpose of MDC is to optimize the manufacturing process and eliminate the bottlenecks in the process. Manufacturers also use MDC to make improvements in their designs.
What are the Different Types of CNC Machines?
CNC machining uses many different types of CNC machines to fit different use cases. CNC machines can be placed into multiple classes based on their operation and design. Here are the different types of CNC machines:
Axis refer to the degree of freedom of movement of the cutting tool. In simple words, a CNC machine axis defines the direction in which the cutting tool can move. For instance, if we say that the cutting tool can move in X axis, it corresponds to the left to right (and right to left) movement of the cutting tool parallel to the work table. Similarly, the Y-axis corresponds to top to bottom (and bottom to top) movement parallel to worktable. The Z-axis movement corresponds to the up and down (and down and up) movement perpendicular to the work table.
A 2-axis CNC machine can work only in two directions- the X-axis and the Z-axis. This is the most basic setup for CNC machining systems. Generally, it is used for simple cutting and turning machines.
A 3-axis CNC machine can move in the X-axis, Y-axis, and Z-axis. These are the most popular CNC machines due to their low cost and high capabilities. 3-axis CNC can work on all machine tools such as milling machines, sawing, turning, etc.
4-axis CNC machining works in the traditional X, Y, and Z axes and additional rotary axes. The rotary axes can be one of A, B, or C axes. A-axis is rotary around the X-axis, B around the Y-axis, and the C-axis around the Z-axis.
A 5-axis CNC machine has three traditional axis and any two of the three rotary axes. 5-axis machines are able to machine complex shapes and internal geometries. However, the price of these machines can be quite high. Therefore, cheaper alternatives like 3+2 CNC machining and 4+1 CNC machining are sometimes used.
A 6-axis CNC machine can move in all six linear and rotary axes. 6-axis CNC machines have an extraordinary improvement in machining speeds and accuracy. 6-axis CNC machines are also a further step forward in terms of the precision of the operations.
There are other types of CNC machines with higher axes, such as the 7-axis, 8-axis, 9-axis, and even 12-axis machining centers. These are made with a combination of different types of multiple axes machines. These machines are generally used in niche applications requiring highly complex designs and extreme precision.
CNC machines can also be classified on the basis of machine orientation. The various types of CNC machines under this classification system are:
In a vertical machining center, the spindle axis of the machine is installed perpendicular to the work table. Vertical machining centers are the most common CNC machines due to the high precision and a simpler setup. These CNC machines also have higher range capabilities for possible design shapes.
A horizontal machining center is a CNC Machine that has its spindle axis parallel to the work table. A horizontal machining center provides a smooth finish to the surfaces. Therefore, this orientation is a popular choice when conducting surface machining operations. The chip evacuation is easier in a horizontal machining center than vertical orientation.
A universal machining center is a combination of horizontal and vertical orientations. This configuration is possible only in five and higher axes CNC machining. This configuration can machine multiple sides of the workpiece simultaneously.
What are the Most Popular CNC Machining Operations?
It is important to know about the different types of CNC machining processes to understand the basics of what is CNC machining. Here is a discussion of the most popular CNC machining processes:
CNC drilling is a type of machining process that uses a drill bit to create holes in the workpiece. CNC drilling benches are the most common types of CNC machines as they are used in combination with all other equipment and processes. The diameter of the holes created by CNC drills is limited. Therefore, these machines are generally used in hole punching for screws or aesthetic reasons.
CNC milling uses a stationary workpiece against a high speed rotating cutting tool to machine parts. CNC mills come in multiple axes options to suit various requirements. The rotating cutting tool comes in many shape and size variations. Therefore, there are different types of CNC mills such as end milling, face milling, slab milling machines, etc.
CNC turning is a type of machining process that uses a stationary cutting tool and a rotary workpiece. The workpiece is brought closer to the stationary cutting tools which symmetrically remove material. Turning machines are usually applied for machining of cylindrical parts. For instance, machining of turbine cylindrical holes is done with turning and drilling machines.
CNC routing is the method where a cutting tool moves across the workpiece through its thickness to pierce the workpiece and dividing it into subparts. The cutting action of CNC routers is accomplished due to friction between the workpiece and the cutting tools. It is sometimes also known as the CNC cutting process.
CNC grinding is a surface finishing process where abrasive wheels are rubbed against a workpiece to remove a minimal amount of material. CNC grinders come in varying roughness levels, so an adjustable amount of material can be removed. The resulting finished product has a smoother surface. CNC grinders can also remove the physical defects of other manufacturing operations, such as welding.
Other Types of CNC Machining Operations
Besides the techniques mentioned above, many other CNC machine tools are in common practice. Some of these are:
CNC broaching uses a specialized toothed cutting tool to remove material from a workpiece. The cutting tool itself is called a broach. There are two variations of broaching- linear and rotary. Broaching is generally used to create keyways and profiles into a workpiece.
CNC plasma cutting is a type of metal cutting process where an ionized gas is accelerated at a high velocity and it melts and removes the workpiece material at the predetermined location. The plasma jet also blows away the molten metal resulting in a clean cut. However, this method is very limited in terms of compatible materials and the maximum cutting thickness.
CNC laser cutting is a type of material cutting process that uses an amplified light beam to remove material from the workpiece. Laser cutters work on most materials and are not limited to metals. The thickness of the laser cutting beam can be reduced to a microscopic level leading to extremely low kerfs and high precision
CNC waterjet cutting is a type of cutting process that uses the force generated by ultra high water pressure to remove material from a workpiece. Water jets can cut material of any thickness and type. Unlike other cutting processes, water jets are a cold-cutting method that doesn’t leave any burn marks.
CNC honing is a type of surface machining process that creates a precision face on a workpiece by using abrasive grinding wheels or stones. The grinder used in this process is called a honing stone.
CNC lapping is a type of surface machining process that uses an abrasive paste instead of stones or wheels. The paste consists of a mixture of abrasive particles in oil. A lapping machine can remove minute amounts of material from workpieces to increase their dimensional accuracy.
CNC flame cutting is a type of material cutting process that uses oxy-fuel gas to melt and remove workpiece material. The direction and magnitude of the cutting head can be controlled with a computer numerical control machine. CNC flame cutting is not as preferrable as water jets or laser cutters due to the low quality of results obtainable.
Electrical Discharge Machining (EDM) is a type of metal cutting operation that uses the high temperature generated by high-frequency electrical pulses. The pulses are generated due to a high voltage between electrical electrodes and the workpieces. EDM cutting has high precision. However, it is only limited to metals with a low thickness.
What are Some Common Applications of CNC Machining?
The CNC machining process is used in virtually every sector of manufacturing. Applications of common CNC machining operations are:
What are the Advantages of CNC Machining Over Traditional Manual Machining Methods?
CNC machining is a big step up over manual machining processes. Some of the benefits that these processes are:
How Much Does CNC Machining Cost?
CNC machining generally costs between $30 per hour to $120 per hour. The exact cost of the process is highly variable, depending on several factors. Some of these factors that can affect the cost of CNC machining are:
What Materials Can Undergo CNC Machining?
CNC machining processes work on virtually any solid material. Even the hard to machine materials and delicate materials are machinable with CNC systems. Popular materials that undergo CNC machining include:
Are There Any Limitations to CNC Machining?
There are certain limitations to CNC machining, such as:
CNC machines are susceptible to certain problems like every other machinery. Some common CNC machine problems are:
Design Tips for CNC Machining
The following tips can help you in improving your CNC machine designs:
How Long Does CNC Machining Typically Take?
CNC machining can take anywhere from a few seconds to many hours. The duration depends on the type of machining process, the part complexity, and the scale of operations. When calculating the machining duration, consider the time it takes to set up and load the part.
Is CNC Machining Hard?
CNC machining is not hard or difficult to learn. It does have a learning curve associated with it that requires proper research and training on the equipment. This is why the skill and experience of CNC machinists play a major role in the final part outcome.
What is the Environmental Impact of CNC Machining?
Most CNC machines have a low environmental impact due to their highly efficient nature and lower rejections in the manufacturing processes. In most cases, the removed parts can be recycled as scrap material. In some instances, such as machining plastic parts, CNC processes can harm the environment.
How Do CNC Machines Compare to Alternative Technologies?
CNC machines have a lot of advantages over alternative manufacturing processes. Here is a brief comparison of CNC machines vs. alternative technologies:
3D Printing: CNC machines have significantly better precision than 3D printing processes. Additionally, 3D printing generates a lot of toxic fumes due to the melting of plastic material. The same materials can work with a CNC milling machine with quite high-quality results.
Injection Molding: Injection molding is time-consuming due to a long lead for manufacturing molds. Additionally, it has poor precision. CNC manufacturing turns out to be faster with more accuracy.
Die Casting: Die casting process is also time consuming as it requires the molten metal to cool off. Additionally, the accuracy is quite poor after cooling the molten material. CNC machining operation eliminates all of these concerns.
What Role Does CNC Machining Play in Modern Manufacturing?
CNC machining is the bedrock of modern manufacturing processes. Modern manufacturing requires mass production numbers along with high consistency. Therefore, CNC machines are integrated into the assembly lines of all manufacturing sectors. Most of the consumer products today use CNC machining processes directly or indirectly.
What are the Future Trends in CNC Machining?
The future of CNC machining is quickly adapting to Industry 4.0. CNC machines are becoming a part of a wider network where CNC machinists can use them remotely with intelligent systems. The data from CNC machines is collected and optimized based on the manufacturer and consumer demands.
The scale of manufacturing is also becoming smaller. CNC machines can even work on small parts such as semiconductor wafers. The degree of automation is also increasing. CNC machines are being installed on robotic arms on the assembly line to provide machinability of all parts simultaneously without loading requirements.
Endnotes
With the above information, you now have more than a clear understanding of what is CNC machining. Even after decades of existence, CNC machining is still a vastly growing sector. You can go through the range of CNC machining technologies available if you are looking for a machine to handle the requirements of your next manufacturing project.
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