You probably have some idea of how lathes and other metalworking machines work. As technology and computers have improved over the years, a new high-precision computer-controlled manufacturing technique called CNC machining has spawned. CNC machines, or computer numerically controlled machines, are electromechanical devices that can manipulate tools around various axis, usually three or five, with high precision per instruction from a computer program. CNC machining is one of two ways that engineers, machinists, or makers can generate a physical part from a computer design file. The other is 3D printing, also known as additive manufacturing. Like other traditional machining processes, CNC machining is a subtractive process where the material is removed from stock.
History of CNC Machines
The first CNC machines were developed in the 1940s and 50s and relied primarily on a data storage technique known as punched tape. The code to control the machines would be manually punched into a data card and fed into a system that would interpret the data. These early machines were rudimentary, and their functionality was limited. Modern CNC machining technologies rapidly grew as technological capability only accelerated in the late 20th century, which brings us to how modern CNC machines work. As mentioned before, machining is a way to transform a stock piece of material such as aluminum, steel, or titanium into a finished product or part. Before modern computer-aided manufacturing and computer-aided design programs such as Autodesk were around, CNC machines relied on digital instructions specifically referred to as “g code.”
Machinists would manually write the G code to control these machines. When you compare the capabilities of automated CNC machining to manual alternatives like lathes and other machining techniques, you can start to see the benefits. CNC machines run faster, with higher precision and accuracy, while transforming a digital design into a physical part. CNC machines are precise and are measured in thousandths of an inch, referred to as standards. CNC machining can provide tolerances on parts of around +/-0.005 inches. Fine CNC machining can produce tolerances of about +/-0.001 inches in specialized processes like polishing, which can offer up repeatable tolerances as tight as +/-0.00005 inches. For reference, human hair is 0.0069 inches thick.
Types of CNC machines
CNC Milling Machine
CNC mills use rotary cutters to remove material by advancing a cutter into a workpiece. The most basic CNC mills have an X, Y, and Z system, and they run programs that follow letter- and number-based prompts that instruct pieces to move specific distances. A mill’s functions include face milling, tapping, drilling, turning, and shoulder milling.
Lathes (CNC Turning Machine)
Lathes produce precise, high-velocity circular cuts. Lathes are commonly used for complex designs that would be impossible to achieve with a manual machine. The majority of CNC lathes have two axes, X and Z. Some models have more than two axes, allowing them to perform more complex tasks. The material is held on a rotating spindle on a lathe. The non-rotating cutting tool or drill forms the geometry or shape of the part by tracing its perimeters.
Plasma Cutting Machines
A plasma torch is used to cut the material. Plasma cutters are primarily used for metal materials, and they can also be used on other materials. The machine generates heat and speed using compressed air gas and electrical arcs.
Electric Discharge Machines(EDM)
Electrical sparks are used to cut and shape two workpieces using electrodes. As the gap between these electrodes closes, a current flows through, removing a portion of the workpiece. This technique is also known as die sinking, spark machining, spark eroding, burning, or wire erosion. Wire EDM and Sinker EDM are two subtypes.
Water Jet Cutting Machines
Hard materials, such as metal or stone, are cut with high-pressure water jets. Water jets are frequently used when the material cannot withstand high temperatures.
There are some other tools and machines with CNC variants:
CNC routers, 3D printing machine, induction hardening machines, surface grinders, milling machines.
How CNC Machine Works
Now that we have the basics of CNC machining, we can start to dig into the intricacies held within many designs or specific machining processes that require the use of multiple tools to make cuts. A machinist will often build digital tool libraries that interface with the physical CNC machine. These machines, often costing hundreds of thousands of dollars, can automatically switch tooling when directed by their digital instructions, allowing them to become manufacturing workhorses. Basic CNC machining will move one or two axis, referred to as the X-axis and the Y-axis. You’ll often hear the terms “2.5 axis,” “3 axis,” and “5 axis.” A machine can make cuts in three axis, which refers to the degrees of freedom. A machine can make cuts in a 3-axis machine that will move in the X, Y, and z axis.
In contrast, a 5-axis machine can move in these three axis along with two additional rotational axis, as you might be able to imagine the possibilities of production. Five-axis machines are practically endless. Five-axis machines used to be relegated to high-precision work, but as they have become more affordable, they have quickly become standard in many shops. The first is drills. They work by spinning a drill bit and moving a bit into contact with a stationary stock. Next, we have lathes that function like drilling lathes, spinning the block of material against a stationary drill bit or cutter to remove material in a circular or fluid path. The shape capabilities of lathes are more limited than other techniques, but modern technology does allow these machines to create things such as square holes or non-circular shapes. Lastly, the most common CNC machine type is a milling machine. Milling machines use rotary cutting tools to remove material from a stock piece. The function is similar to drills, with their tooling capabilities encompassing much more variety. Almost any material can be used in CNC machines. Different materials have different properties, so machinists and engineers will overcome their unique challenges by altering machining variables like tool selection, rpm feed rate, and coolant flow, among a wide variety of other factors. CNC machined parts are all around you. They hold together and perform vital functions aboard.
CNC machining is arguably the most critical manufacturing process of the 21st century. Its functionality drives technological advancement across the globe. It’s a trend keeping up with the growth of technology, and machinists across the planet are changing the world with their CNC machining skills.
In general, CNC machining can be simplified into a 3-step process.
- CAD file is designed
- A CNC technician translates the CAD file into the CNC program
- The CNC program is initiated and the part is machined
Benefits of CNC Machining
CNC machining is suited for applications that require production-grade materials and rapid prototyping of precise plastic and metal parts with excellent surface finishes. CNC machining’s repeatability also enables low-volume manufacture of items. Benefits of CNC machining:
- High-Precision Parts
- Large, Scalable Volumes
- Variety of Shapes, Sizes & Surface Finishes
- Fast Turnaround
- Lower Costs with Greater Efficiencies
Considerations of CNC Machining
A part’s geometry will dictate how it will be positioned on the CNC machine and the amount of setup required. If a part is manually repositioned, it can result in a small positional error and impact the cost of the project and part accuracy.
Machine Tool Stiffness
The tool used to cut the part may vibrate while operating. Tool stiffness may result in loose tolerances.
Temperatures and cutting forces developed during machining may cause the workpiece to vibrate or even cause deformities. The part must have a minimum wall thickness and a maximum aspect ratio of tall features to prevent workpiece stiffness.
CNC machining cutting tools have a cylindrical shape and a flat or rounded end. Tool geometry can restrict the CNC machined parts geometries. The inside vertical corners of the part produced will have a radius, even if a small cutting tool is used.
Workpiece Shape(Geometry Complexibility)
If the cutting tool is unable to reach a surface, it cannot be CNC machined. This limitation on parts requiring hidden internal geometries limits a workpiece’s maximum machining depth.
CNC Machining Materials
CNC machining provides a wide range of materials for CNC prototypes and production components, ranging from solid metals such as stainless steel and titanium to soft metals such as aluminum, copper, and brass, and plastics such as ABS, PC, and PA and more.
CNC Metal Material
Alloy steel contains trace amounts of one or more alloying elements (other than carbon), such as manganese, silicon, nickel, titanium, copper, chromium, and aluminum. Alloying provides it with unique qualities not present in standard carbon steel. Due to its low cost, wide availability, ease of processing, and superior mechanical rates, alloy steel is ideal for industrial applications. In general, alloy steels are more malleable to heat and mechanical treatment than carbon steels.
LEADRP offers a complete Alloy Steel CNC machining service and can produce custom Alloy Steel parts in various shapes and grades, including 4130, 4140, 4340, and more.
CNC Plastics Material
ABS is a plastic material with three main ingredients: acrylonitrile, butadiene, and styrene. Each of these monomers imparts specific properties, making ABS terpolymer with robust features. ABS has good strength, toughness, and resistance to impact and temperature. It is easily molded and gives a high-quality glossy surface finish. This plastic polymer does not have a specific melting point.
LEADRP offers a complete ABS machining service and can produce custom ABS parts in various shapes and grades.
Resources of CNC Machining
If you’re interested in learning more about CNC machine in the crucial trade that it is. One of the best places to do that is through the Titans of CNC academy. This online resource will teach you from the ground up how to design parts in machine them for Free, whether you have acnc machine or not, you can also get Free trials of Autodesk and cam software to play around with. Or if you’re a student, you can get the programs completely Free.
Q: What language is used by CNC machines?
A: CNC machines are primarily programmed using G-code though M-code is also acceptable.
Q: Are CNC and VMC the same?
A: No. A computer controls CNC machines. A VMC is a kind of CNC machine used to cut metal.
Q: What is the difference between PLC and CNC?
A: Programmable Logic Controller (PLC) is sequential while CNC is conditional.
Q: Who invented CNC machining?
A: John T. Parsons
Q: What is the significance of CNC machining?
A: As the process is automated, it increases efficiency, lowers costs and increases accuracy.
Q: What materials can be used in CNC machining?
A: Depending on the application, common materials include stainless steel, copper, brass, aluminum, titanium, foam, polypropylene, ABS, POM, PC, Nylon and more.
Q: What are the five different CNC machines?
A: CNC lathe machine, router machine, milling machine, laser cutting machine and plasma cutting machine.
Q: What is the difference between DNC and CNC?
A: A direct numerical control (DNC) system uses a mainframe computer to operate multiple machines. DNC refers to the networking of more than one CNC machine.
Q: What is an NC machine?
A: Numerical Control (NC) machines receive instructions from a punch card, whereas a CNC machine receives instructions from a computer.
Q: What industries use CNC machining?
A: Aerospace, medical device, photonics, defense, electronics, transportation and more.
Q: What type of finish is produced by CNC machining?
A: Some CNC machines, such as the CNC mill, may leave visible tool marks. Because of this, additional finishing may be required to finish the part.
Q: What are the standard finishes for CNC parts?
A: Bead blast, anodized, chem film, passivation, powder coat, electropolishing, electroless nickel plating, silver plating and gold plating.