If you are new to CNC Machining, here are three things you should know about machining parts.
According to Foreign Policy:
1. What is CNC Machining?
“CNC machining refers to a manufacturing process to fabricate simple as well as complex CNC machining parts with miniature dimensions by utilizing pre-programmed computer software. The acronym CNC stands for ‘Computer Numerical Control’ and it is basically a subtractive manufacturing process which removes layers of materials from a workpiece by the numerically controlled program.
“Due to its compatibility with a wide variety of materials, CNC machining parts can be made of metals, plastics, wood, glass, foam, composites, and so on. It is an autonomous process that does not require human intervention, thus, it is more accurate, specific, cheap labor cost, and less time-consuming. It is the opposite of the additive manufacturing process (like 3D printing) or mass-replication technique (like injection molding) since it is a subtractive manufacturing method.
2. CNC Machining Material Considerations
“The most important feature which enables them to stand out from its competitors is their suitability to a variety of engineering materials including both plastic (PEEK, PC, PE, PTFE, nylon, etc.) and metal (brass, steel, aluminum, etc.).
“Engineering plastics or polymers are popular because of their high strength, resilience, toughness, lack of conductivity, resistance to corrosion, color, processing, transparency, and low cost. To manufacture high precision plastic parts, CNC machining of plastics is a very strong candidate. It is the most widespread method to manufacture plastic parts with strict tolerance limits and excellent surface finish. Unlike the injection molding process, in plastic CNC machining, molds are not required, hence it moderates the costs and startup times.
“CNC machining of plastics is similar to machining metals however, it requires different cutting speeds, cutting tools, and tool compensation to attain desired surface roughness and tolerances. CNC machined plastics have widespread applications including plastic medical components. Generally, in biomedical devices, they require high precision and geometry. Some examples of such medical devices include anesthetic and therapy components, surgical and dental instruments, catheters, diagnostic devices, cardiac implants, orthopedic, and other implantable devices.
“Properties of metals are different than those of plastics; they are heavy due to the densely packed structure. Metals can outclass almost all material groups in some specific applications where thinness is critical. CNC machining of metals can provide us tight tolerance, mirror-like surface finish, and complex size and shape. You can get your functional metal parts as quickly as one working day by CNC machining services. The precision offered by CNC machining is the best choice for prototyping and rapid production of small and large metal parts. Among the wide variety of metal materials which are compatible with CNC machining services, Aluminum, Stainless Steel, Brass, Copper, Magnesium, Steel Alloy, and Titanium are most popular and most widely used.
CNC milling parts
“The most commonly used method to fabricate almost 80% of the plastic parts is the milling parts. However, it is not only limited to plastic products but also used widely for manufacturing metals such as aluminum, stainless steel, brass, titanium, and so on. It is a subtractive technique that removes plastic or metal from the workpiece by a numerically controlled program. Mostly, the milling machines are categorized by their number of axes. A standard CNC milling machine mostly has three axes X, Y, & Z however, to manufacture parts having complex shapes and size, there are now 5-axis, 6-axis milling machines.
“It is mostly used to fabricate any rotationally symmetrical shape by removing material from the workpiece very rapidly. Turned parts are often adorned with an excellent surface finishing and it often requires no post-processing.
“Typically, a lathe or turning machine is employed for CNC turning parts. It works in a linear motion by feeding the cutting tool along the surface of the rotating workpiece. In doing so, it removes material around the perimeter until the preferred diameter is attained. Some examples of turned parts are cylinder-shaped parts with external and internal structures. By the CNC turning method, almost all kinds of materials can be machined such as all types of steel, aluminum, cast iron, brass, copper, and bronze, along with plastics such as nylon, fiberglass, and PTFE.
3. Tips for Maintaining Tight Tolerances
“Another term to express machining tolerance is dimensional accuracy which implies an acceptable variance in a part or cutting tool. In order to obtain high performing parts with maximum quality, tight tolerances are very critical. Here are some tips for holding tight tolerances while manufacturing CNC machining parts:
To select the perfect tool:
“We have to be very cautious and wise with the choice of tools for tight tolerances. It is to be ensured that for exceptionally tight tolerances, a specific set of tools including separate ones for roughing and finishing should be used. Furthermore, good quality cutting tools can provide more precision than a dull or blunt head cutting tool.
Warm up the spindle:
“A routine warm-up is extremely important for A CNC machine to work at its maximum. It is advised to run the machine for around 15–20 minutes before starting the actual milling procedure. It allows parts of the machine to reach an ideal temperature and will help diminish the effects of thermal expansion during milling.
Effect of the temperature:
“For holding tight tolerances, thermal stabilization is one of the most important things. A slender deviation from the ideal temperature can largely influence the dimensions of the parts in various ways. Therefore, it should always be kept in mind to place the machine in a temperature-controlled environment.
Calibration of equipment:
“Apart from being extremely cautious on all the above points, a desired level accuracy or precision may not be achieved after the machine is used for a longer period of time. It’s time to calibrate the equipment. It is very natural for the machine to loosen up after being used for thousands of hours and it’s unavoidable. However, calibrating, servicing and annual maintenance can keep a fitted leash on the machine precision.
“CNC machining of plastic and metal parts stands out from all other manufacturing processes available in the industry for its diversity, precision, and comparatively faster process. Almost any type of plastic or metal part can be fabricated by the CNC milling or turning process with strict tolerances if the machine is operated and maintained carefully.”