By: Tommy Y Ta, Date: 02/13/2018

• Computer numerical control (CNC) machines is a manufacturing process that automates machine tools using pre-programmed code for machine control commands. Motion is generated using servo or stepper motors to provide precise and accurate movements, allowing for more complex shapes to be manufactured. The CNC machine provides a more cheaper and precise cut than manual machines, and can be used to repeatedly manufacture the same part over and over again. In modern CNC machines, the part is dimensioned using computer-aided design (CAD) software, and then translated into g-code using computer-aided manufacturing (CAM). The code is then loaded into the machine and test run by the operator to ensure no problems arise, a technique referred to as “cutting air,” before the cutting of the actual part begin.
• https://www.youtube.com/watch?v=5FU_VlkQ63k

• The first NC Machine was developed by John Parsens as a way to create stiffened aircraft skins. Using an IBM 602A multiplier to calculate airfoil coordinates, Parsens was able to use punched cards as data templates.
• Parsens’ work led the U.S Air Force to request MIT to develop their own NC Machine, using servos to control movement. Early development of NC machines used punched tape, fed into the machines as readable code. Punched tape were largely used during the mid-twentieth century to store large amounts of data in the form of procedures for cutting specific parts using an NC machine. This was a widely used method as early computers had very little memory to store massive codes.

• CNC machines can be used in all sorts of designs in all types of industries, from automobile to aerospace companies requiring precise cuts. CNC machines allow industries to get their desired parts to be almost exactly as the one designed in CAD software. There are also a variety of CNC machines as well, and the table below lists several important CNC machine types.

CNC Machines	Description	Image
Milling Machine	Most widely used device in the CNC family. These machines use rotating cylindrical cutting tools, and move along 3-5 axis to create a variety of shapes, slots, and holes. This makes this machine much more versatile than using a hand drill or saw.
Lathe Machines	A device that autonomously rotates a workpiece about an axis to perform various operations of cutting, sanding, or drilling, to name just a few. CNC Lathe Machines replace traditional engine lathes in ease-of-use, accuracy, and less labor intensive.
Plasma Cutting Machine	A device for autonomously cutting metals using compressed air blown at high speeds. The gas creates an electric arc at the surface, turning the gas to plasma. This tool is often used for quickly cutting through sheet metals, metal plates, straps, etc. It can also be used to remove defective welds, as well as cutting small shapes from steel plates.	https://www.youtube.com/watch?v=w92SSzBQGpE
Electric Discharge Machines (EDM)	EDM, often referred to as spark machining or spark eroding, is a manufacturing process where a desired shape is produced using electrical discharges (sparks). The material is removed from the workpiece by the two discharging electrodes, separated by a dielectric liquid. EDM allows for incredibly complex shapes to be made with ease.	EDM Machining: https://www.youtube.com/watch?v=L1D5DLWWMp8 Wire EDM: https://www.youtube.com/watch?v=pBueWfzb7P0
Multi Spindle Machine	A type of screw machine that carries multiple spindles that can cut multiple workpieces in a highly efficient manner. CNC multi spindle machines are commonly used in industries of mass production, and provides productivity, energy efficiency, and space savings.	https://www.youtube.com/watch?v=GcddvL4ZteI
Water Jet Cutting Machine	Also known as waterjet, this tool cuts material using water at high velocity and pressure. This technique is often used on materials that are sensitive to high temperatures generated from other methods of cutting. Mining and aerospace industries are one of many to use this method.	https://www.youtube.com/watch?v=PCsoC3i7JYc

• As aforementioned in the table descriptions above, the CNC machine operates autonomously once the code has been dialed in by the operator, so no further involvement is needed until the material is completed. This is in contrast to manual machines, in which the operator require the use of levers to move the workpiece in the right position for cutting.
• Tolerances will vary from machine shop to machine shop due to the quality of CNC machines, but the common range of tolerances are 0.001” to 0.005”.
• Despite the many advantages of using a CNC machine, crashes are also common. These crashes can include:
  • Machine moving in a way that is harmful to the tools.
  • CNC machines losing their sense of absolute position. If the workpiece were to be positioned incorrectly, the coordinates in which to cut the part will now be off.
  • The motor on the tool will “slip in place” if the drive system is weaker than the machine structural integrity.

• Using CAD software, begin by dimensioning the part to be manufactured. CAD design creates the specification for the product as a 3D model. Once the design is complete, detailing is produced on CAD drawing. This will decide the manufacturing requirements of the part. Path planning is then generated via CAM software to provide a blueprint of movements for how the CNC machine should create the part. Finally, the blueprint is converted into G-code that the CNC machine can use to execute the process.
• Mechanical Engineers are needed to design the part using the CAD/CAM system, and once completed, only one operator is needed to implement the code into the CNC machine to execute the process. He/she will then watch for any crashes that could potentially occur.

• Home CNC Machines can range from $600 to $4000
• Industrial CNC Machines can range from $25,000 to $150,000.
• According to Xometry, a machining service company, a typical cost for CNC machining a simple L-bracket using aluminum 2024  is $98.86 for one piece. If ordered in a quantity of 100, each part will cost $10.20 for a grand total of $1020.00. Note that Xometry delivers high end parts with tight tolerances. It is possible to machine the same part at a cheaper price if tight tolerances are not needed.