What are CNC machines and how do they work?

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CNC machines are used extensively in manufacturing facilities. CNC stands for Computer Numerical Control. It is a manufacturing process that involves the use of a computer to control machining tools. Complex machinery such as lathes, grinders, routers, mills, etc. can be controlled using the CNC process.

Software from a computer can accurately control the position, velocity, and feed rates of the machine. Three-dimensional cutting can also be done easily using a CNC machine. The CNC process can be used with metal as well as plastic products for machining.

A CNC machine moves along the x and y-axis, using stepper and servo motors for moving accurately along the two axes. Advanced models can move along the z-axis as well. Depending on the requirement of a machining job, there could be a single machine or multiple machines used together. You may even notice different types of CNC machines at different facilities.

Sometimes, a job might need a cutter, sometimes a driller. If multiple machines are used simultaneously in one setup, then the product gets transferred from one machine to another via robotic hands or at times physically. Every machine in the combined setup will carry out a particular function. The whole combined setup would be controlled by a single software/code.

CNC process

The first step to machine an item using a CNC machine is to create a CAD drawing. The CAD drawing will have the exact design and details on how to machine a part. Once the drawing with the design is created, it gets converted into G-code. G-code is the language that the CNC machine understands.

After that, the G-code program gets loaded onto the machine and a test run is made to check if everything is working as per the design created. This test run is also known as “cutting air”. The test run is very important because a mistake in the design or the code could lead to a scrapped part or damaged CNC machine. Once everything is verified and approved, the CNC machine along with the software can machine large quantities of products with very little human involvement.

There are two types of CNC machining systems, open and closed loop. An open loop system can only allow the flow of signals in one direction. The flow of the signal is from the controller, which holds the software, to the motor on the machine. There is no feedback capability.

A closed loop system, on the other hand, allows for two-way communication. The controller can send signals to the motor on how to move, and the motor can then send feedback to the controller. If there is any error or deviation from the intended path of motion, corrective action can be taken by the controller instantly. For most industrial works, a closed loop system is recommended. A closed loop system ensures consistency and accuracy. If the speed and force requirements for an application are not very high, then an open loop system can be used.

Advantages of CNC machines

The biggest advantage of using a CNC machine is that it is more accurate than manual machining. Because of the use of computer and automation, human error is practically eliminated resulting in an accuracy tolerance of up to 0.001.

Secondly, the CNC machining process can be repeated with a high degree of accuracy. So, if a large volume of units is being manufactured, then a CNC machine can repeatedly work unit after unit in an identical manner, something which is not possible with manual machining. Jobs with a high-accuracy requirement will benefit from a CNC machine.

Thirdly, because of the computerized nature of the CNC machine, complex shapes and dimensions can be processed. A higher level of such complexity will be almost impossible to achieve using manual methods. Whether you have a simple design or a complex three-dimensional shape, a CNC machine can work all shapes and designs.

Additionally, CNC machines have a leg up over conventional machining in the area of production rate. As CNC machines use an automated process, the speed of machining is a lot faster than what we see in conventional processes. A shorter production time can mean lower cost of manufacturing.

CNC machines are also very reliable. They can work for long hours, on weekdays and weekends. They only need to stop for maintenance and repair work. This kind of longevity is not possible with conventional and manual machining processes.

Operating a CNC machine requires an operator who is at a safe distance from sharp tools and equipment. Operators of conventional drills, punches, and lathes work in direct contact with the equipment which increases the chance of a mishap or injury. Hence, CNC machines are a safer option from a health-safety point of view than conventional machining processes.

Lastly, CNC machines are cost-effective as they require relatively simple and inexpensive maintenance. One mainly has to do some light cleaning and regularly change the cutting tools and parts. This basic maintenance can be done in-house and does not normally require any professional service.

FAQs

What to look for in a CNC machine?

First of all, you need to have a clear idea of your application. You must know what kind of quality and precision levels you need. You must also know how long you plan to use the CNC machining. Price is also important because everybody has a budget. But, the price is secondary because if your requirements for precision and quality are critical, then you will automatically rule out many models. After all, if your new CNC machine does the job as you intended it to do, you may not ever remember the price after a few days.

What types of materials can be machined using CNC process?

You can use CNC machines on plastic, polypropylene, steel, aluminum, titanium, bronze, brass, wood, inconel and monel.

Do I need to buy additional software when purchasing a CNC machine?

The answer to most people is no. Most modern CNC machines come with pretty good software already installed. This default software will cover most manufacturing and designing situations that you will encounter. However, after using the machine initially, if you do find the need to get software for something specific, then the best place to start would be the company that made your CNC machine. Most good companies tend to have contacts with software providers. You can explain your requirements to the CNC company and they will point you in the right direction.

Can I directly run a CAD file on my CNC machine?

No. You cannot run a CAD file directly on a CNC machine. The CNC machine will not understand CAD. What you have to do is convert the CAD file into a G-Code. There are programs which do this conversion. If you run a search, you will find several inexpensive programs that will fit your purpose. The G-Code file is basically a text file with numbers and letters. It has all the vector information from the CAD file.

Can I use my CNC machine in metric mode?

Yes, you can use your CNC machine in inch or metric mode. There is a way to toggle between the systems by modifying the G-Code. If you insert a “g21” at the beginning of a line of code, then that tells the machine that you want to use millimeters. Similarly, if you use g20, then that will denote inches.

Can a photo be converted into G-Code for use in a CNC machine?

Yes, there are programs which convert a photo file into G-Code. One example of a program that does this conversion is DeskArt. It looks at the dark and light shades on a photo and estimates depth levels to reproduce the contours on your machined product.

Is a CNC machine better than 3D printing?

The answer to this question depends on the application. You need to look at the material being machined and the complexity/design of the part in question. It is true that 3D printing can create complex parts with intricate designs. It can do so because it uses a bottom-up approach.

However, 3D printing has its limits when it comes to the type of materials that it can be used with. A CNC machine can be used with a lot of materials and metals, and it might be a better option for certain metal-based parts. So, one type of process is not better than the other. Rather, you have to holistically look at the application in question and then take a call accordingly.

Is a conventional machining process cheaper than CNC machining?

Surprisingly, conventional machining is more cost effective when running small productions batches. If the number of units is low, then a CNC process will end up being more expensive than conventional processes. CNC machines are most effective when a large volume is to be machined and the parts are identical.

What are some of the machining jobs that a CNC machine can do?

A CNC machine can accurately and effectively carry out the following:

Bore, Contour, Weld, Turn, Thread, Texture, Tap, Stamp, Shape, Shear, Punch, Mill, Lathe, Knurl, Groove, Grind, Face, Engrave, Drill.