CNC machines are the gold standard in precision manufacturing because of their speed, precision, and ability to hold tight CNC tolerances. The development of CNC machining has facilitated incredible innovations because it allows the design and manufacture of parts with incredibly complex geometry. It’s no wonder that this process is essential to make many products that we use every day. This article aims to teach you everything you need to know about CNC machining: the process, the history, and the future of this marvelous manufacturing technology.
CNC machining has allowed manufacturing to get to where it is today.
What is CNC Machining?
CNC stands for computer numerical control. So, CNC machining is any kind of machining process controlled by a computer. Computerized automation allows parts to be made more quickly, accurately, precisely, and with more complex geometries than those produced via manual machining. CNC also reduces manual machining labor that would otherwise be done by humans. While they aren’t machining each part themselves, people are essential for programming and operating the machines, ensuring that every operation goes smoothly.
How Does CNC Machining Work?
The programs used for CNC machining these days are written with G-code and are usually automatically created by CAM software. CAM, or computer-aided manufacturing software, generates the G-code for a 3D model with given tools and workpiece material. This G-code controls the motion of the tool, the workpiece, and tool changes. It even has commands to turn on or off the coolant and other auxiliary components.
CNC machining can be used for a wide variety of materials, with the most common being aluminum, steel, brass, ABS, Delrin, and nylon. But really, almost any hard material can be CNC machined. We’ll discuss materials more in-depth later on.
The History of CNC Machining
In the early days of machining and manufacturing, everything was done manually. The process was relatively slow and inefficient, but humans (and engineers especially) are driven to improve and progress. And, since automating a process improves its efficiency, productivity, and safety, we’ve arrived where we are today.
One early method of automating the machining process was inspired by cams that played musical boxes. This mechanical form of automation was adopted in the 1870s and used mechanical linkages with cams to transform rotary motion into linear motion. Cams are usually rotating wheels with some kind of geometry – either a key that sticks or an eccentric radius – that strikes a lever during its rotation. This causes actions in the tool or machine to manufacture a part.
Another automation method was tracer control, which used a stylus to trace a template using hydraulics. This could copy templates several feet across. “Record and playback,” a technology pioneered by General Motors in the 1950s, recorded and replicated the movements of a person machining the part.
A lack of accuracy and precision was the main issue with these early automated processes. The control methods weren’t strong enough to make the linear motion necessary to cut through metal. As servomechanisms were developed, they became the solution to this issue because they can execute powerful, controlled movements. Two servos can be attached to produce a synchro — a system that accurately matches one servo’s motion to another. Machinists could measure the output of these synchros to a high level of accuracy and inform further motion of the synchros to create a closed-loop control system.
Once these superior machining controls were in place, punched tape was used to program machines starting in the 1940s and 1950s. The machine could read the coordinates on the punched tape and move to that location, resulting in a form of “plunge-cutting positioning” machining. By attaching the machine’s inputs to the punch card reader, the number of points increased significantly. Previously, the limit was the number of points a person could generate and program by hand. More coordinates meant a smoother, more accurate path of machining!
In the 1950s, this kind of NC (numerical control) machining required five refrigerator-sized cabinets that housed the controllers. As computers became smaller and less expensive, NC machining became more common. These smaller computers were also more powerful and allowed more data processing, which resulted in the phasing out of drafting on paper in the mid-1950s. From that point, CAD (computer-aided design) and CAM (computer-aided manufacturing) continued to become more accessible and more popular. Today, they’re industry standard and the idea of creating a 2D engineering drawing on paper or making a part without CNC machining is preposterous!
Types of CNC Machines
CNC Milling
A CNC mill can produce highly precise and complex parts
CNC milling involves the machine bed, where the workpiece is held securely in place. There is also a cutting tool that spins rapidly. The movement of this tool and machine bed depends on the number of axes of movement your machine has, but for a common 3-axis machine, the bed moves back and forth and left to right, while the tool moves up and down.
CNC Turning
Turning is ideal for round or cylindrical parts that need to be highly precise.
CNC turning is used mostly for parts that are axially symmetric. The workpiece spins rapidly while a cutting tool moves side to side and front to back in the machine. Machining parts using a lathe rather than a mill can be faster and have a lower cost per unit.
CNC EDM
There are multiple types of electric discharge machining, including wire EDM, sinker EDM, and hole drilling EDM. All of these processes require a workpiece made of conductive material. The tool serves as one electrode and the workpiece acts as the other electrode. Both are submerged in a dielectric liquid and an increase in the voltage between the two creates an electric arc through the fluid. This removes material from the electrodes, resulting in the desired final geometry.
CNC Gear Hobbing
Gears can be produced using multiple CNC methods, including hobbing, EDM, or milling
There are many methods of creating gears. Functional gears can be made out of many different materials. Similarly, gear hobbing can be applied to a wide range of materials, not just metals. Gear hobbing uses a hobbing machine, which is a special type of milling machine that is equipped with a cutting tool called a hob. This hob gradually cuts into the gear blank, forming the keys, or splines, of the gear.
CNC Machines and Their Axes
2-Axis and 3-Axis Machines
3-axis CNC machines are the most common of the CNC machines. The 3 axes refer to linear motion in the X, Y, and Z axes. In milling, the tool spins to do the cutting. CNC lathes often only have two main axes of movement, with the stationary tool moving linearly in X and Y while the workpiece spins.
3-axis mills are usually easier to program and operate than multi-axis machines. However, some operations may be blocked by the geometry of the part or workholding setup. This makes undercuts and internal complex geometry difficult to machine. It is possible to manually reorient the workpiece, but this adds time to the CNC machining operation and could detract from the accuracy of the process.
Even 3-axis CNC machines can make parts with organic or complex geometry
Multi-Axis Machines
Multi-axis CNC machines are anything with more than three axes. When you start adding more axes, you start with rotating the tool head and the machine bed with no human intervention. This saves time by removing manual steps. The easiest way to do this is with indexed CNC machining, where the rotation only occurs in between operations. This is typically called indexed CNC machining with 3 + 2 axes.
To take it to the next level, continuous 5-axis machines can move along the 3 linear axes and at the same time as the machined bed and tool head are also rotating. This allows the machine to handle even more complex geometries. It does come with an increased cost for the specialized machinery and more expert programmers and operators.
Mill-Turning
There are three different methods to mill-turn a part. Overall the process is what it sounds like: a part is machined using some milling and some turning operations.
The first way to mill-turn a part is to first machine a part on the alther, then finish machining on a CNC mill. This requires more work to move the part from machine to machine and set it up multiple times, but it doesn’t require specialized machinery.
The next way to mill-turn a part is to use a live tool lathe. Normally lathe tools are stationary, but with a live tool lathe, tools are (you guessed it) live, or driven. Simply put, the tool moves. In a live tool lathe, special tool holders allow you to mount these live tools into the turret. Then, when the time comes for a live tool operation, that tool is rotated into position and begins spinning. It can then be used to perform the desired operation, whether that is milling a flat or machining a slot.
Finally, a mill-turn machine combines a mill and a lathe in one CNC machine. The difference between this option and a live tool lathe is that there is an upper and lower turret. One has the lathe tools and one holds the mill tools. This can be an advantage because both turrets can be operating at the same time. However, these machines are not as common and may be harder to find, so don’t count on it while designing your parts.
The benefit of combining milling and turning is to take advantage of the speed and cost of turning on a lathe, along with the geometric flexibility of milling. Keep in mind that you may lose some of the efficiency of turning if you are using two different machines, as in the first example.
Beyond 5 Axes
Why stop at 5 axes? Machines with seven, nine, or even twelve axes are out there! A 12-axis machine has two heads (often one vertical and one horizontal) that allow linear motion along the X, Y, and Z axes, as well as rotation around each of those axes. This is the ultimate CNC machine that can double the accuracy while cutting manufacturing time in half!
Benefits of CNC Machining
Rapid prototyping
CNC machining is well-suited to create a low volume of parts. The start-up time is fast. Once you have the CAD model, you can generate a CAM program for the CNC machine and get to work! (Of course, you may also need to develop fixturing, set up tools, and complete a few other tasks before you get started.)
Generally you can get a few CNC parts with a quick turnaround time, which is why CNC machining is so often used in rapid prototyping. Start-up costs are relatively low, since the tools and machines are most likely in use in the machine shop already. Therefore, you can get right down to machining the parts, rather than spending time making a die or mold.
CNC-machined prototype parts are also high quality. CNC machines can hold tight tolerances and produce quality finishes, meaning that you can use parts for functional testing or to prove out the aesthetic concept.
During prototyping, designs are often still in flux, but CNC programs are easy to change as designs evolve.. Plus, using a CNC machine means there’s no tooling to create or modify. And, you can machine many different types of materials, and create a variety of geometries to compare their properties and performance.
Production
CNC machining is also used to produce final, end-use parts out of a variety of materials. It’s used in production because of its speed and quality. Not only that, parts can be made according to demand, so the risk of overproduction and parts languishing as inventory is low.
A CNC machine’s ability to hold tight tolerances and produce high quality parts is especially critical for assemblies. Assemblies require every piece to be machined precisely, and precision CNC machining can hold tolerances as tight as 0.0002”.
ABS (Acrylonitrile Butadiene Styrene) is a low-cost engineering plastic widely used for pre-injection molding prototypes. CNC machined ABS is a great option for production-like parts, where detail and mechanical properties are important. The colors available for ABS are black and neutral.
ABS has a somewhat matte finish (like lego bricks) and can be painted. ABS can also be powder coated, which gives it more durability while also increasing UV resistance. Certain faces may appear more shiny depending on their geometry and how they are machined. If painting ABS parts, finish will depend on the choice of paint.
Polycarbonate (known also by the abbreviation PC) is one of the most common plastics used in manufacturing. Famous examples of the material are first-generation MacBook laptops, safety goggles, and optical disks.
Polycarbonate is heat-resistant, impact-resistant, flame-retardant, and one of the most recycled plastics in the world.
Polycarbonate has a transparent milky-blue look in its natural state, but is also available in black. Both colors have a glossy finish, and are relatively prone to scratches. Anti-scratch coatings and vapor polishing are available as custom post-processing finishes.
Nylon 6/6 is the most commonly used of the Nylon family of plastics. It has relatively high chemical and heat resistance, and is stiff enough to retain its shape, and tough enough not to permanently deform under load.
Two of the most notable use cases for Nylon are in medical devices and electronics insulation, where it’s often used for screws and spacers on panel mounted circuit boards.
Glass-filled Nylon boasts many useful properties such as high rigidity, strength, hardness, toughness and dimensional stability. This material may be used in assemblies requiring mechanical damping or electrical insulation. Common applications include electrical housings, washers, medical devices and aerospace parts.
Nylon comes in neutral — which has a slightly translucent, milky-white finish — and black colors.
Delrin (generic name: acetal, also known as POM – polyoxymethylene) is a low-friction, high-stiffness material. It’s used in applications ranging from auto parts to musical instruments. With relatively high toughness and minimal elongation under stress, Delrin boasts excellent dimensional accuracy.
Fictiv also offers Delrin AF (13% PTFE-Filled) and Glass-Filled Delrin.
When compared with standard Delrin, Delrin AF has an increased coefficient of friction for applications that require lubrication. With an excellent wear resistance, toughness, strength and dimensional stability, this material is often found in load bearing applications such as bushings, bearings, cams, thrust washers, gaskets and valve seats.
Glass-filled Delrin offers superior stiffness and dimensional stability with a high resistance to creep, or slow deformation under persistent loads. Glass fibers increase impact resistance and fatigue endurance. This material is commonly used for automotive applications, construction, fixturing, and gear manufacturing.
Due to the composition of Delrin and temperatures from machining, it is highly susceptible to warping on large, flat parts or where there are thin walls. Fictiv recommends avoiding thin walls when possible to avoid this warping.
Delrin-150 and Glass-Filled Delrin materials are naturally opaque and white because of Delrin’s crystalline structure, and have a matte finish. Delrin AF is brown.
In high-stress/high-temperature applications, PEEK (polyetheretherketone) is a great lightweight substitute for most soft metals. Additionally, PEEK is resistant to moisture, wear, and chemicals. PEEK is an effective material choice for parts with tight tolerances because it is not as influenced by temperature variation.
Glass-filled PEEK is a high-performance plastic with excellent rigidity, strength and toughness. The addition of glass fibers enhances its ability to maintain dimensional stability even in harsh thermal and chemical environments. This material is often used in aircraft, automotive, medical, chemical, semiconductor and microwave applications.
PEEK comes in an opaque beige color and can be machined to a variety of surface finishes.
Polyphenylene Sulfide (PPS) is a high-performance engineering plastic with excellent temperature resistance, dimensional stability, and electrical insulation properties. With exceptional mechanical strength, chemical resistance, and flame resistance, PPS is commonly found in high temperature applications such as automotive parts, appliances, electronics, medical devices, and industrial applications.
PPS has an opaque, off-white finish when machined. It has a smooth, matte appearance post machining and its surface finish can be made smoother or coarser depending on need.
Acrylic is also known as PMMA, an abbreviation of its full chemical name, polymethyl methacrylate, as well as by the trade names Plexiglas and Lucite. It’s a scratch-resistant plastic that is often used for tanks, panels, and optical applications. It can be brittle in thinly walled areas, so is not recommended for delicate or complex geometries.
Acrylic is transparent or opaque (black, white, and a variety of colors) in its unfinished state. Clear acrylic will take on a frosted, translucent appearance when machined, though can be polished back to an optically clear state using various finishing methods.
Garolite G-10, otherwise known as phenolic and epoxy-grade industrial laminate, is a composite material with a low coefficient of thermal expansion. Additionally, it does not absorb water and is an excellent insulator, which makes it well-suited for electronics applications.
Garolite G-10 comes in a variety of mostly opaque colors. It’s smooth and has a matte surface when machined.
High-density polyethylene (HDPE) is a slippery plastic that is often machined into plugs and seals. HDPE is moisture-resistant and chemically-resistant, and is an excellent electrical insulator.
HDPE is a naturally opaque white because of its crystalline structure, but is also available dyed black in more limited stock sizes. It has a waxy finish leveraged for low-friction applications.
Polypropylene (PP) resists most solvents and chemicals, so is a widely-used material for laboratory equipment and containers in a variety of applications. PP also offers good fatigue strength, and works well for parts that go through repetitive motions and loads.
Polypropylene is a semi-clear white color by default, but also comes in opaque white.
Commonly known as Teflon (the brand name), PTFE (polytetrafluoroethylene) has high temperature, chemical, and solvent resistance and is also a great insulator. It’s also a slippery plastic, so is a good material for low-friction applications like bearings. PTFE comes in opaque white or black.
Ultra-High-Molecular-Weight Polyethylene (or UHMW) is a hard plastic with a slippery surface, which resists abrasion and wear. Additionally, it has high impact strength and is the optimal material for chute/hopper liners and machine guards.
ULTEM (brand name for PEI, polyetherimide) 1000 is a translucent, amber-colored plastic with excellent durability, strength, stiffness and heat resistance. ULTEM 1000 is superior to Nylon and Delrin in some applications because it has the highest dielectric properties. Common applications include industrial equipment, medical devices and electronics.
When machined, ULTEM is smooth and becomes slightly frosted.
Aluminum is one of the most commonly used metals in the world because of its excellent strength-to-weight ratio, low cost, and recyclability. Untreated aluminum generally has a dull silver/grey finish which varies depending on the texture of the surface. Aluminum can be media-blasted, sanded, and hand-polished to achieve a multitude of finishes.
Many consumer products made with aluminum — like every Apple laptop of the last decade — are anodized, as it provides a variety of color options and adds a consistent, silky finish across the entire part. Chem film or Alodine™ is often used as an alternative protective coating to anodize on aluminum parts, and can be clear or gold in color.
Fictiv offers multiple aluminum alloys:
Our standard alloy on platform is 6061, a versatile and easy-to-machine metal. It is corrosion-resistant, non-magnetic, and heat treatable.
7075 Aluminum is a hard, high strength alternative to 6061 Aluminum. It is often used for parts in high-stress applications, and is also corrosion-resistant, non-magnetic and heat treatable.
7050 Aluminum can be used instead of 7075 when high stress corrosion resistance is necessary (ie. bulkheads and fuselage frames). It is heat treatable and non-magnetic.
2024 Aluminum is not as strong as 7075 Aluminum but is commonly used when a high strength-to-weight ratio is required. It is heat treatable and non-magnetic.
5052 Aluminum is the easiest aluminum to weld and is exceptionally corrosion-resistant against salt spray and saltwater. It’s easy to form, heat treatable, and non-magnetic.
6063 Aluminum is more corrosion-resistant and formable than 6061 Aluminum. It’s not ideal for high strength applications, but can be used for exterior railings and decorative trim. 6063 is heat treatable and non-magnetic.
Also known as a jig plate or cast tool, MIC6 is a cast and stress-relieved aluminum alloy that’s great for tight tolerance applications. It’s most commonly used in precision machine tables and tooling. MIC6 is non-magnetic and not heat treatable.
The finish of steel is similar to that of stainless steel, generally shiny in appearance and slightly darker than aluminum alloys. Alloy and carbon steels can be media blasted, or they can be electropolished to a variety of surface finishes. Fictiv offers a variety of steel alloys:
1018 steel is a mild, low carbon steel that is machinable, weldable, and useful where high-strength is not required, such as fixtures and mounting plates. This alloy is magnetic and heat treatable.
4140 alloy steel is generally harder and stronger than carbon steel. Additionally, it provides high impact resistance, fatigue strength, and torsional strength, which makes 4140 a great choice for driveshafts, axles, and torsion bars. This alloy can be hardened using a variety of methods, including cold working, or heating and quenching.
1045 carbon steel is stronger than 1018 steel but is still easy to machine. It’s heat treatable and is often used for bolts, studs, and shafts.
4130 alloy steel is similar to 4140 alloy steel but is easier to weld and has a slightly lower carbon content. It is best suited for gears and other structural applications.
Zinc-galvanized low-carbon Steel has an outer coating of zinc to improve corrosion resistance. It is important to note that the coating is only present in non-machined areas.
A514 alloy steel is a high strength, low alloy steel that is used mainly in structural applications. It’s weldable, heat treatable, and is best suited for supporting heavy loads.
4340 alloy steel is a medium carbon, low alloy steel that is highly useful in environments involving extreme impact, heat, and wear.
Stainless steel is highly resistant to corrosion and rust, so is suitable for parts exposed to the elements for long periods of time. Stainless steel is also fairly malleable and ductile. The finish of stainless steel varies greatly depending on surface roughness, but is generally more shiny than unfinished aluminum alloys, and slightly darker and more silver in color.
Stainless steel can be found in many households in the form of pots and pans
Stainless steel can also be media-blasted, sanded, hand-polished, and powder coated to achieve a multitude of surface finishes.
The 300 series (303, 304, etc.) are austenitic stainless steels named for their crystalline structure and are the most widely produced grades worldwide. Austenitic stainless grades are known for their high corrosion resistance and strength across wide temperature ranges. They are not heat-treatable except by cold working, and are generally non-magnetic.
400 series stainless steels are martensitic in structure and are less common than austenitic grades. Martensitic steels are extremely strong and tough due to higher carbon content, but are more susceptible to corrosion in certain environments. They can be heat-treated to greatly increase their hardness and are magnetic.
17-4 PH Stainless Steel is a high-strength, highly corrosion-resistant material that maintains its durability up to 1100°F. The PH in its name stands for precipitation-hardened, a type of treatment it undergoes to increase yield strength. 17-4 is magnetic and heat treatable to a hardness of Rockwell C50.
Nitronic 60 is an excellent all-purpose material with superior wear and corrosion resistance. It has a yield strength nearly double that of SS 304 and SS 316, as well as superior oxidation resistance. Popular applications include fasteners, valve stems, seats, pins, bushings, bearings, shafts, and rings.
A2 Tool Steel offers excellent wear resistance and toughness. Due to its high compressive strength and dimensional stability, this material is commonly used to make fixtures, tools, tool holders, gauges, and punches.
Similar to other grades of mild steel, tool steel is generally shiny in appearance and slightly darker than aluminum alloys. For corrosion resistance, black oxide can be applied post-machining. To achieve a variety of surface finishes, tool steel parts can also be media blasted or tumbled.
Cast iron is a dependable, wear-resistant material that machines faster than many steel varieties. It’s an ideal material for absorbing vibrations and is commonly used to make gears, bases, pulleys, and bushings.
Compared to steel alloys, cast iron is a darker shade of grey. To achieve a variety of surface finishes, cast iron parts can be media blasted or tumbled.
Cast iron skillets are useful for making beautiful loaves of bread due its heat retention properties
360 Brass is also known as free-machining brass, due to it having the highest amount of lead content of any brass alloy. This excellent machinability comes with minimal tool wear. It’s used for a variety of parts such as gears, lock components, pipe fittings, and ornamental applications.
360 Brass has a shiny yellow finish that varies depending on surface roughness. It can be hand-polished to increase its sheen (like a trumpet or saxophone), or media blasted for a matte texture.
932 Bearing Bronze is a high strength alloy with good wear and corrosion resistance due to its tin, iron, and zinc content. It’s most commonly used for bearings, bushings, and thrust washers. 932 Bronze is not heat treatable.
932 Bronze has a shiny reddish-brown finish (slightly darker than copper), which will vary slightly based on the specified surface finish. It can be polished or media-blasted to change its cosmetic appearance.
Bronze is often used for statues, but can also be used to make electronics, pipes, bearings, and gears, depending on the alloy.
101 and 110 copper alloys offer excellent thermal and electrical conductivity, which make them natural choices for bus bars, wire connectors, and other electrical applications. While 101 (also known as super-conductive copper) offers higher conductivity due to its purity (99.99% copper), 110 is generally easier to machine and thus more cost-effective.
Copper has a shiny reddish-orange finish, which varies slightly based on the surface finish method. Copper can be media-blasted and polished to achieve many different cosmetic finishes.
Titanium Grade 5 is the strongest titanium alloy with good corrosion resistance and the ability to be welded. Titanium may be selected over other materials such as steel due to its relatively lightweight and ability to withstand both high and subzero temperatures. Common applications include aerospace fasteners, turbine blades, engine components, sports equipment, and marine applications.
Titanium is similar to most grades of stainless steel in terms of overall appearance. Titanium can be media blasted or tumbled to achieve a multitude of surface finishes, and a light, protective coating may be applied using passivation.
Chromate conversion coating, more commonly known as chem film or its brand name Alodine™, is a chemical coating that passivates and protects aluminum from corrosion. It’s also used as a base layer before priming and painting parts. The standard most commonly specified in engineering applications is MIL-DTL-5541F, which refers specifically to the coating of aluminum alloys.
This protective layer is much thinner than an anodizing layer, and while both are created by immersion of parts into a bath, Chem film or Alodine™ is a simple chemical coating and its application process does not use electrical current.
Chem film or Alodine™ is more prone to scratches, wear, and cosmetic damage than anodizing. The coating’s most common color is an iridescent greenish-gold, and so may be used for cosmetic purposes. However, its unique color comes from hexavalent chromium, which is toxic. So, for RoHS compliance needs, there are clear versions of the coating available as well.
Anodizing is an electrolytic passivation process that grows the natural oxide layer on aluminum parts for protection from wear and corrosion, as well as for cosmetic effects. It’s a conversion coating, similar to Chem film or Alodine™, so the surface of the aluminum recedes dimensionally before the protective oxide layer is built up. After the process is complete, the oxide layer is integral to the aluminum substrate below, which means it won’t chip or flake.
The name anodizing comes from the fact that the treated part forms an anode (positive electrode) in an electrical circuit. During this process, the part to be anodized is hung on a conductive rack and submerged in an electrolytic solution, where a direct current of electricity is introduced. While the acidity of the solution dissolves the oxide layer of the part, the electric current releases oxygen at its surface, which builds up a protective layer of aluminum oxide. By balancing dissolve rate with build-up rate, the oxide layer forms with nanopores, allowing continued growth of the coating beyond what is naturally possible.
There are a few main types of anodizing. Type II, or sulfuric acid anodizing, leaves a film that can be .0001″-.001″ thick. This is the most commonly used type. Type III, Hard Anodize, is much thicker and denser and provides better wear resistance. Type III anodize with PTFE is enhanced with PTFE. This adds a dry lubrication quality to the abrasion resistance of standard Type III hard anodize. These options all have different properties, thicknesses, and color options so you want to choose the right one for your application.
Nonstick pans often have a Teflon (PTFE) coating
Those nanopores are perfect pathways for corrosion, so the final steps of the anodizing process seal the nanopores. Just before sealing, however, they can be filled with other corrosion inhibitors or colored dyes for cosmetic purposes. Once sealed, the coating will be 0.0002-0.0012” in thickness, in accordance with the common engineering spec MIL-A-8625 Type II.
Black oxide is a conversion coating (similar to Chem film or Alodine™) that’s used on steel and stainless steel. It’s used mainly for cosmetic purposes and for mild corrosion resistance, with black oxide impregnated with oil providing the highest amount of protection. Black oxide is formed in a process similar to anodizing, where parts are dipped into hot baths of chemicals to convert the surface of the material into magnetite, which creates the black color. Black oxide does not have a significant dimensional impact, therefore masking parts is not necessary. This process is slower than anodizing because it’s labor-intensive and the baths take longer to come to the correct temperature.
Electroless nickel plating (ENP or NiP) is a reaction that deposits a nickel-phosphorus alloy onto the surface of a metal. It uses a purely chemical reaction to induce plating and does not leverage electricity. Though this process takes much longer than electroplating, it achieves more uniform thickness over even the most complex surfaces because it doesn’t rely on varying electric fields. It also provides superior wear and corrosion resistance. The standard specification for ENP in North America is MIL-C-26074E, with various grades specifying thicknesses from 0.0003-0.002”.
Electropolishing is an electrochemical process used to improve the surface finish of a part by removing material to level microscopic peaks and valleys. This process can polish, passivate, and deburr parts. It’s the inverse of plating processes, as the part acts as the anode in the reaction. As the current passes through the part (anode), the surface is oxidized and dissolved in the solution to the cathode.
Electropolishing is useful for polishing irregular parts with hard-to-reach surfaces. Additionally, only a small amount of material is removed, so tolerances aren’t greatly affected by this process.
Fictiv offers electropolishing for stainless steel parts only.
Media blasting uses a pressurized jet of abrasive media to apply a matte, uniform finish to parts. The most common media used are varying sizes of glass beads or sand, though for other levels of abrasion, plastic beads are also used.
This process can also hide machine marks and remove small flaws in parts prior to anodizing or other plating processes.
Nickel plating is an electroplating process for metal parts. This plating provides corrosion and wear resistance, as well as a decorative finish. Once parts are cleaned of debris, they’re submerged into an electrolyte solution. A nickel anode is then dissolved into the solution and deposited onto the part, which acts as the cathode in the reaction.
Passivation is a chemical reaction that increases metals’ resistance to corrosion and other environmental factors. Passivation creates a micro-coating by oxidizing the surface of the material, then converting the oxidation to a metaphosphate. This surface is then sealed into the part using either a manganese or zinc compound. Passivation can be used on steel and stainless steel.
Powder coating is a process in which a dry powder paint (either a thermoplastic or thermoset polymer) is applied to a metal surface using electrostatic application. Unlike traditional liquid paint, powder coating does not need a solvent to keep the binder and filler of the paint in liquid suspension. This allows for the application of thicker coatings without running or sagging, and the coatings are also more scratch and corrosion resistant as a result.
This bicycle has a steel frame that is powder-coated to add corrosion resistance and a pop of color.
The powder coating process starts off by electrically grounding the part to be coated, which gives it a net negative charge. After grounding, the paint is sprayed at the part using a corona gun, which applies a positive charge to the powder. The polarization of the two components causes the powder to stick to the metal.
After the powder has reached a specified thickness on the part, it’s cured into a polymeric film using elevated temperatures (~200°C), in a convection oven. Thermosetting polymers will crosslink during the curing process to improve performance, but thermoplastic varieties simply flow while heated to form the final coating.
Powder coating results in a thicker coating than other finishing processes, so it is important to mask critical surfaces.
Tumbling is a finishing process used to clean, deburr, and slightly smooth smaller parts. Tumbling uses a horizontal drum filled with an abrasive substance, such as sand or ceramic chips. The drum rotates slowly, causing the media to abrade the parts, breaking any sharp edges and smoothing the surface.
Zinc plating, which is also known as galvanization, is applied to steel to prevent the surface from oxidizing or corroding. This process works by coating the part in flux and then dipping it into molten zinc. The molten zinc forms a bond with the steel and creates a protective surface layer.
Clear zinc plating gives the part a light blue appearance. Black zinc plating will result in a black color and a similar appearance to black Type II anodizing.
Applications and Industries of CNC Machining
Consumer Electronics
Many components of consumer products are manufactured using CNC machining because its speed allows the development cycle to keep up with market demand. Enclosures of some laptops are commonly made this way, as are many small components in cell phones. Many companies also produce circuit boards on CNC machines.
Automotive
CNC machining is widely used by automotive companies because the program and setup can be easily changed for custom car parts and low-volume runs. Some of the most common components of cars that are CNC machined include cylinder heads (which are parts of the cylinder block) and acrylic parts for interior and exterior lighting.
Robotics
The high dimensional accuracy of CNC machining comes into play with robotics; robots need to be accurate in their movements and positioning. CNC machining is also effective for manufacturing gears, which are critical components in robots. While robots themselves are becoming more and more common in manufacturing, they have to be made somehow as well! CNC machining is used to make the end effector parts that pick up and interact with components. Custom jigs and fixtures used along with robotics are also CNC machined.
Automation with robots occurs in all corners of the universe.
Aerospace
The end products of aerospace manufacturing, such as airplanes, don’t have room for error. The accuracy and precision of CNC machining make it capable of producing parts that do not fail, which is essential for resulting in safe aircraft. Some aerospace and aeronautical parts that are CNC machined include components that go into jet turbines, such as turbine exhaust struts, stator assemblies, which go into aircraft engines, and titanium shroud sets, which are also components in jet engines.
Medical
Have I mentioned precision and accuracy yet? Precision machining is essential for medical devices, and CNC machining is here for it. Because these are often custom or low-volume parts, CNC machining is a good choice. With medical devices, the material choice is more limited because the material has to be safe and approved for human contact, sometimes in the long term. Materials like titanium, cobalt-chrome, stainless steels, and PEEK are used for temporary or permanent implants because they meet these criteria. Medical implants, like knee implants or hip replacements, are CNC machined. Other machined parts include medical equipment such as catheters, stents, components in MRI machines, and instruments such as forceps or clamps.
Given the production advantages and wide range of materials and finishes provided by CNC machining, the technology has proven useful in a variety of fields. Fictiv, in particular, has worked with companies in the consumer electronics, automotive, robotics, aerospace, and medical device industries.
The Future of CNC Machining
Industry
Digital manufacturing/transformation is making CNC machining more accessible than ever before. Anyone can upload a model and get an instant quote, then receive their parts in less than a week. It is not just for start-ups, hobbyists, and personal projects, either! Large companies can take advantage of on-demand manufacturing to get the benefits of supply chain agility and inventory management.
IoT
The Internet of Things has increased the communication between machines during different stages of manufacturing. These smart devices create a lot more manufacturing data and by applying machine learning techniques, companies can speed up the process of identifying and addressing issues. The IoT enables “smart machines” that can take measurements and perform process qualification in the CNC machining process.
New CNC Technology
CNC machines have been around for years, but the technology has continued to advance. Multi-axis machines are one such innovation that has made CNC machining more efficient. And, their use will only increase. as improvements to technology make 5-axis machines, in particular, more financially accessible.
CAD and CAM software also continues to improve. These technologies are becoming more affordable and therefore available to a wider range of people. More intuitive and user-friendly software will also increase efficiency and accuracy, shortening design cycles.
Research is constantly being conducted to increase the speed of CNC machine operations such as milling, drilling, tapping, deburring, and chamfering. People are addressing this in a variety of ways, from machine capabilities to materials and the geometry of cutting tools.
Universal fixturing via vacuum fixturing is also becoming increasingly common because vacuum fixturing is easily adaptable to many different parts and geometries. It eliminates the need to machine a fixture before you can make the actual part! Also, vacuum fixturing allows more flexibility in machining, since fixtures are only in contact with the bottom of the workpiece — there’s no vise or clamp to get in the way of the machining process.
Jobs
There’s an assumption that CNC machining and automation in manufacturing will eliminate many jobs. If you don’t need someone to machine the part, what will they do? And while the number of roles requiring manual machining skills has been reduced, many new jobs have been created. There is still a need for people who are skilled at programming CNC machines, operating them, and doing maintenance. With automation, the robots doing the manufacturing also need maintenance, updates, and upgrades. The CNC machines may be doing the work of machinists, but a human touch is still necessary to bring it all together and make your final parts.
CNC machining remains a versatile, dependable process. Its ability to be used with many different materials throughout the product development cycle has helped it stand the test of time in manufacturing. As industries develop, they will continue to require CNC manufacturing.
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