A CNC machine (Cutter-Numerically Controlled) is a computer numerical control (CNC) machine that utilises an automated system to create or edit the object/ model it is programmed to produce.
Cutter denotes that it cuts material away, reducing its size until reaching the final product. The term ‘Numerically Controlled’ signifies that numbers entered into an electronic computer control the machine’s movements. These numbers represent commands or instructions for movement and tool positioning stored in software programs.
CNC Machine Definition
A CNC machine is essentially a robot with drill heads, saws, routers, etc., attached to move around on different axes guided by sensors and software to perform CNC cutting or a specific task on a material.
NC Machine Definition
NC stands for Numerically Controlled, and it means that the machine moves by being directed with numbers, not coordinates.
An NC machine doesn’t have any controls in its axes, just some cables attached to stepper motors that can be moved in different ways (by hand or using software) via the control panel to make the machine move whatever distance it is directed. This can either be manually set or programmatically calculated.
Open Loop Machines vs. Closed Loop Machines
An open-loop system assumes that no position feedback is available and will move at a fixed rate and stop when the limit switches are tripped. Open-loop systems are generally cheaper, simpler, and slower than closed-loop systems. A typical example is a jack used on most automotive lifts that cycle until it hits a hard stop at full extension.
A closed-loop system detects errors at all times during its motion, making corrections as needed to maintain accuracy. For example, if something is wrong with your printer’s stepper motors or axes, it will cause the print head to drift over time, ruining any prints you might be trying to produce.
How Does CNC Programming Work?
Manufacturing an object on a CNC machine starts with designing the object in either 2 or 3D CAD software (Computer-Aided Design). After creation, the file must be converted to a usable CAD (Computer-Aided Design) file for machining. This can be done manually or with 3rd party software.
When the CAD file is complete, it must be exported/transferred to G-code, the language that CNC machines understand.
CNC Machine Programming Steps
Load your correct cutter into the spindle: You need to ensure that the size and type of bit match what you want to cut out of your material!
Set up your workpiece: Place it on the table beneath where you want the cutter to move, and mark out where your material will be cut.
Set up your toolpath: You can either manually create a path or use a routing function in CAM software to do it for you. It’s good practice to experiment with both.
Run a test cut on some spare material: Ensure that all the correct parameters are correctly set before running production jobs!
Understanding CNC Machine Errors
At times, errors can occur with programming a machine for many reasons:
An error occurs because the computer doesn’t recognize what is happening during machining regarding movement, depth, etc.
Another reason for mistakes is an inconsistency with how actual cuts measure up compared to the information given in the CAD file, and sometimes this can be blamed on a loss of accuracy.
For example: if you use a calliper to measure two inches in from both sides of an object, one side might come out at 1 inch while the other is only 0.9 inches. This could be because there was some distortion due to heat caused by CNC cutting, or it could just be that your measurements were off when measuring the part.
CNC Machine Applications
Industrial Manufacturing: In industries ranging from medical equipment to cookware manufacturing, companies will utilise multi-axis machines capable of performing intricate functions for mass production.
Food & Beverage: Like industrial manufacturing, food & beverage companies need huge quantities of products served quickly with consistency between each item. For example, companies need to produce large volumes of coffee from a consistent source in the coffee industry because consistency is vital in the food & beverage business.
Aerospace: CNC machines are used in the aerospace industry as much as any other. Whether creating moulds and dies or producing custom components, CNC machining can provide necessary tools and parts. Even high-end products like furniture and cars require consistent geometric shapes that lend themselves well to 3D cutting processes.
CNC Machine Types
Sinker Electric Discharge Machines
A Sinker EDM (Electric Discharge Machine) is an electrical discharge machine that uses a shaped electrode as its tooling to remove material from a conductive workpiece. The machine uses a ram to force the electrode into the material, and when current is passed through the electrode, it erodes the material around it, creating a sink in the metal.
This process can even be used on non-conductive materials such as glass and stone.
CNC Drilling Machines
A CNC drilling machine is a high-speed computer-controlled drill that allows for three-axis movement and rotation of a drill bit using its spindle or chuck to cut into practically any material without pre-drilling.
Its purpose is to create holes in objects by moving across their surfaces with precision and speed, allowing for accuracy even in complex designs. These machines will have multiple axes programmed to follow a specific path.
Wire Electric Discharge Machines
Wire EDM is similar in process to Sinker EDM. However, the machine’s function is slightly different. Instead of cutting out material with a shaped electrode, wire EDM uses an electrode constantly fed by spools of wire which frequently cuts away material. The electrode has no contact with the workpiece at all.
It’s only connection is via wiring that follows its axis through guide bearings. This allows for exact cutting and shaping because there are no mechanical limitations involved in the movement of the cutter working against your project piece. This method also lends itself well to hard-to-cut materials like tool steel.
Water Jet Cutters
Like wire EDM, a water jet cutter works by shooting highly pressurised liquid at high speed against a material that erodes it. The liquid is forced out of a nozzle in liquid form by the pressure created when the machine takes in an air source.
This process allows for highly accurate cutting so long as your CAD file’s measurements are precise and you utilise sharp tools explicitly designed for this machining method.
CNC mills are built for large-scale production work where durability and precision will be necessary to get the job done right without spending too much money on thousands of individual parts that may not hold up under stress or testing.
Composed of a heavy-duty base and headstock with a spindle often powered by either induction or brushless DC motors, these machines offer the highest degree of accuracy and repeatability in CNC machining so long as you can afford it.
Like water jet cutters, plasma cutters use high-pressure gas to erode material from your project piece at high speeds. The cutter is fed either air or helium and electricity through its nozzle, rapidly heating the compressed gases into plasma.
This process results in quick cuts that allow metal even down to 1/16″ thickness to be cut cleanly without warping. These tools are handy for stainless steel or carbon fiber materials because they can make cuts so quickly that the material doesn’t have time to warp or shift.
Lathes are machines used for turning, boring, and facing your project piece with precision. Generally speaking, you will want a lathe that may be manually operated or computer-controlled via G-code programming language.
This method of creating parts is best suited if you are making many similar parts over and over again as it allows the machine to complete the same process automatically each time, even if it’s just off by a little bit each time you make another one.
You can take advantage of this common error to help make your finished product fit better against other pieces in its assembly. Lathes are suitable for smaller work requiring fine detail because they offer much control over your project piece while also creating relatively large finished pieces.
CNC machines offer many benefits to people who need to make precision parts time after time, but they also come with a hefty price tag.
If you invest in CNC machinery, you will want to make sure it has the best possible capabilities for creating your type of project pieces and make an informed buying decision based on your needs and the long-term usage requirements for your machine(s).
If you buy tools that can create large quantities quickly, it will be more economical in the long run than if you purchase one that cannot perform these operations.