CNC Machining vs. 3D Printing

3D printing has become the new fad among professionals and hobbyists alike, with new applications and possibilities arising in the science world each passing season. Printing a model as you would print a document is a fascinating prospect for many people both in and out of the manufacturing world.

For specialists within the manufacturing industry, this widespread interest in 3D printing helps draw attention to current manufacturing practices, getting more people interested in the manufacturing industry and the possibilities still on the horizon. However, what exactly does 3D printing have to offer to the manufacturing world?

3D Printing, CNC and the Manufacturing Industry

3D printers are now commonplace in universities, engineering complexes and even homes across the United States. The prospect of having the means to create models and prototypes at the touch of a button is interesting to say the least. In terms of the manufacturing industry, 3D printing boasts the ability to create incredibly complex geometries that other methods are simply incapable of doing. However, this is the beginning and end of 3D printing’s current usefulness to the industry.

While 3D printing’s ability to build from the ground-up is intriguing, the industry stands to gain relatively little from 3D printing when it comes to quality and quantity production. The method certainly makes some designs possible that were previously much more difficult, if not impossible, to produce, but the cost and limitations of the equipment involved in 3D printing tend to be steep. Additionally, the relatively low surface quality of the products produced and the slow production speed of the process mean that 3D printing falls short of the effectiveness expected out of mass manufacturing processes. This is especially true when comparing 3D printing vs. CNC machining.

The more useful cousin of 3D printing, CNC machining has been part of the manufacturing world for much longer. This manufacturing process is highly effective, resulting in larger quantities of higher quality products at much faster speeds than 3D printing is capable of. This isn’t to say that CNC machining is better than 3D printing in every way, but it is certainly a more effective process at producing high-quality products at mass production quantities.

Read on to learn more about what makes CNC and 3D printing so different, the advantages and disadvantages of each and why CNC machining is still king in the manufacturing industry.

The CNC Machining Process

Computer numerical control machining, also known as CNC machining or milling, is a subtractive process, meaning that the process starts with more material than the product needs and cuts away, or “subtracts,” any excess material. This process works by taking a block of solid material, such as metal or wood, and using sharp cutters to remove unnecessary sections, chipping away at the material to create the final product.

Unlike other forms of machining where the machine is controlled manually, CNC machines are controlled by a highly precise computer program. The program is essentially a series of codes designed to control and direct the CNCs cutting tools to create a preprogrammed product. These codes are designed using CAM software, or computer-aided manufacturing software, usually designed by the customer or a consultant. A CAM specialist will input this software code into the CNC machine — though today a person doesn’t necessarily need special training to complete this step as the inputting process has become much simpler.

CNC manufacturing is commonly used throughout the manufacturing industry, and it’s one of the most useful processes for creating complex finished products at low costs.

The Advantages of CNC Machining

CNC machining, though simple enough in concept, offers numerous impressive benefits to the manufacturing world. Some of the key benefits of CNC machining include the following:

• Easy to implement: CNC machining is a process that can be applied to a wide variety of products and materials with little adjustment. In most cases, the only thing that may need to change between projects is the cutting tool used.

Additionally, CNC machines tend to be easier to install and start using vs. 3D printers, primarily because of the machine’s design — CNC machines are becoming increasingly user-friendly, and the prevalence of them within the industry means that finding someone experienced in the use of the machine is rarely a problem.

• Minimize tooling and finishing needs: Because of the extremely precise and accurate nature of CNC machines, the product that comes out of the CNC machine needs minimal tooling to get it ready for shipping. The impressive surface quality of the finished product is due largely to the precision of the method, which all but eliminates unplanned burrs and edges.

At most, the product may need a little bit of tooling and surface finishing to add details and to smooth out any edges. However, the CNC machine completes most of these details during the CNC process.

• High-quality small parts: CNC machines can offer accuracy to 0.001 inch, with tolerances around 0.005 inch, regardless of the material worked with. Though some 3D printers claim to have similar accuracy on paper, in reality, CNC machines are far superior in terms of precision.

Unlike 3D printers, which can produce small parts with surface anomalies due to the nature of the materials they use, CNC machines work with rigid materials that won’t deform under normal conditions, resulting in extremely high-quality small parts.

• Effective with ductile materials: More ductile materials like plastics will tend to move around and bend, or otherwise behave differently than other, more rigid materials. This is especially true in 3D printing, as the process often involves stacking layers of heated plastic.

This can result in beading and other behavior that can alter the surface quality of the finished product. CNC milling gets around all of this by working with a single block of material and simply cutting away the excess. This cutting action allows the material to maintain maximum rigidity while the machine works, minimizing deformations.

• Relatively high speed: Depending on the size and nature of the project, CNC milling machines work relatively quickly. Without the potential error or caution of a human operator, CNC machines work automatically to create the finished product.

As a result, a CNC machine can produce a product in a very short amount of time. They also take less time than a 3D printer because cutting away material doesn’t take as long as adding material layer by layer. CNC machines can also be used all day and all night year round if need be, provided they are regularly cleaned and maintained.

• Product integrity: The reductive nature of CNC milling also means that the initial material is not heated and reformed. In other words, the bonds between the material’s molecules remain intact and are not altered by heat or the introduction of foreign materials.

This means the material retains its strength and other key qualities in the final product. That feature is especially important for products where the strength, ductility or electrochemical properties of the final product are important.

• Wide variety of materials: CNC mills can work with a wide variety of materials, including metals, woods, thermoplastics, acrylic, modeling foams and waxes. Though the attachments and cutting tools on the CNC machine may need to be switched out to work with different materials, the machine itself can work with any of these materials effectively.
• Price independent of size and volume: Much of the cost of 3D printing depends on the volume of material that needs to be solidified. For CNC milling, the price doesn’t rely on the end volume. Regardless of the final volume of the product, the process takes about the same amount of work. Additionally, higher quantity projects will tend to be lower in cost.

All of these qualities mean CNC machining is much quicker and more versatile than many other manufacturing methods, especially 3D printing. Additionally, the high production speed, consistent product quality and volume-independent pricing associated with CNC machining make it an ideal method for mass producing products of a variety of sizes.

The Disadvantages of CNC Machining

While CNC milling poses numerous advantages over other manufacturing methods, it is far from flawless. When compared to 3D printing, CNC milling does pose some minor disadvantages, including the following:

• Waste and mess: Because CNC machining involves cutting away material, the material removed from the finished part ends up becoming waste. Not only does this waste increase the cost of materials going into the production process, but this waste can also cause other problems.

If the CNC isn’t fully enclosed, the shards and pieces can go everywhere, resulting in a mess that can interfere with the processes of other machines if not handled correctly. This excess material can sometimes be reused, as in the case of some metals, but more often than not, it is written off and disposed of as waste.

• Noise: Depending on the material it is working with, a CNC machine can produce a great deal of noise. Harder materials will tend to be much noisier to work with than more ductile materials. The amount of noise production also depends on the size of the tool in the CNC machine.

Large-diameter tools designed to quickly remove large portions of metal or wood can produce much more noise than smaller tools. The level of noise produced by the machine can greatly affect the vibrations produced by the machine, as well as the conditions within a manufacturing facility.

• Vibrations: As well as being loud, CNC machines can vibrate quite a bit depending on the product and material they are working with. Generally speaking, the louder the CNC machine, the more vibrations it will release. This can be especially problematic if the CNC machine is located in close proximity to other equipment, as these vibrations can cause damage to measuring tools and interrupt manual processes.
• Design restrictions: CNC machines are capable of quite a lot, but they are limited in what they can produce. With any subtractive method, you can only remove what you can reach, and CNC milling is no exception. If your part has complex internal geometries that a CNC drill simply can’t reach, you may need to alter your design to accommodate the machine.

With the exception of design restrictions, these disadvantages have no bearing on the quality and effectiveness of the final product, which is why CNC milling is still vastly superior to 3D printing for quantity manufacturing purposes.

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The 3D Printing Process

3D printing is a catchall term for a variety of different methods, including selective laser sintering (SLS), stereolithography (SLA) and others. The similarity between these methods, however, is that they build up products from scratch. This additive process is the polar opposite of subtractive manufacturing, involving the “addition” of material in layers, producing the final product from the ground up. This results in a vastly different product with a different set of attributes.

While this manufacturing process is particularly useful for rough prototyping and one-off products, it is not nearly as useful as CNC machining for quantity manufacturing.

The Advantages of 3D Printing

3D printing is the new technological fad for a reason. It sports some incredible capabilities and functions, producing products in a novel and interesting way. Some of the key benefits of this process include the following:

• Reduced waste: Because of its additive process, 3D printing uses no more material than is necessary to produce a product. As a result, minimal material is wasted during the 3D printing process. The only waste produced occurs when a mistake happens in the printing process and the product must be scrapped, or when the product has to be post processed with grinding and sanding. Both of these situations result in a minimal amount of waste compared to other production methods.

• Less noise: 3D printers tend to create very little noise, with desktop versions creating pieces with only a bit of a rattle or whirring sound. This minimal sound production is much improved over other processes, like CNC, that can produce noise loud enough to cause hearing loss.
• Reduced vibrations: 3D printers rarely let off vibrations unless there is a problem with the printer itself. This reduces the effect the printer has on surrounding equipment, and it means people can work in close proximity to the printer without the machine affecting their work.
• Minimal design restrictions: If you can model the design in CAD, you can 3D print the product. Unlike CNC machining where you are limited by what the tools can reach, 3D printing can build anything from the ground up. This includes complex internal geometries that would otherwise be impossible with a CNC machine.
• Short lead times: 3D printers require very little manual input. You can simply upload your design to the printer and press the start button to get it moving. This is especially useful if you are using the 3D printing method to get a prototype for your design and need to see it as soon as possible.
• Fewer production preparations: Overall, 3D printing requires much less preparation than CNC milling. While 3D printing does require a little bit of programming, object orientation and the addition of structural support where needed, this preparation is a far cry from the preparation needed for a CNC milling procedure.

Between programming the machine, setting up the machine for the product, preparing the material, setting the dimensions and deciding how to fix the material to the workstation, CNC milling takes much longer to set up than a 3D printing process by far.

• Price independent of complexity or batch size: Regardless of the complexity of the part or the number of parts needing to be produced, the price of each part remains essentially the same, depending largely on the materials used to create the product. This is a major advantage when it comes to producing prototypes or particularly complex parts.

These qualities make 3D printing an ideal manufacturing method for one-off products. Short lead times and the ability to create complex custom parts make this new process especially useful for constructing prototypes and small-scale models.

The Disadvantages of 3D Printing

While the possibilities 3D printing offers are exciting, the reality is that it is a relatively ineffective process for any quantity manufacturing purposes. This is due to some of 3D printing’s limitations, including:

• Limited workable materials: Though efforts are currently underway to expand the number of materials 3D printers can work with, current manufacturing models are sorely limited. The most common materials for 3D printers include thermoplastics and resins.

Additionally, 3D printers designed to handle one material usually cannot work with another — for example, a printer designed to work with thermoplastics cannot then switch to using resins, and vice versa. This greatly limits the capabilities of 3D printers and those working with them.

• Reduced accuracy and precision: Though some 3D printers promise much in accuracy and precision, they often fail to hit the mark. Much of this has to do with the nature of the materials 3D printers work with and how they work with them.

Thermoplastics and resins are often laid down in layers while they are still “wet”, meaning that they’ll need to solidify. Before these layers solidify, the material can bead, overflow or otherwise behave differently than expected or wanted. As a result, the surface of the final product may be very rough, requiring additional processing before it is ready for shipping.

• Slow production speed: The additive nature of 3D printing can take much longer than other methods. This is mostly because the product is built layer by layer, and most 3D printers are designed to slow down around complex areas to ensure maximum accuracy. As a result, each layer can take minutes to complete, meaning that the process can be excruciatingly slow.

Usually, a product that would take a CNC machine under an hour to make takes a 3D printer several. This slow speed dramatically reduces the number of products a 3D printer can feasibly make over the course of a day, making it an inefficient production method for mass-produced products.

• Reduced product integrity: Though useful in creating complex models, the layer-by-layer approach to manufacturing products is not nearly as structurally sound as the subtractive process. By adding material in layers, 3D printing produces lines between the layers where the material didn’t bond quite as well at a molecular level. When placed under stress, this material will then break along those lines, usually with the application of less force than it would take to break material that was formed as a solid piece.

The Bottom Line of CNC Machines vs. 3D Printers

It is true that 3D printing offers incredible opportunities and possibilities for numerous industries, especially in the cases of precision technology and prototyping. When someone needs a single highly customized part, 3D printing can do the job effectively. Many people in the 3D printing world share a vision of consumers owning their own small 3D printers in their homes, printing small, custom-made products on a daily basis to cut out the middleman.

Although this vision is an interesting take on the potential future of 3D printing, and is certainly within the realm of possibility, 3D printing is unlikely to ever replace CNC machining. Why? Because 3D printing is extremely inefficient at mass producing products. Mass-produced products created with CNC milling are much cheaper than their personally printed counterparts, and the quality and integrity of CNC milled products are vastly superior vs. those of 3D printed products.

In short, while 3D printing is an excellent method for one-off products like prototypes and extremely small-scale custom products, CNC milling is by far the best choice for manufacturing large quantities of quality products of all sizes and materials.

CNC Machining and Summit Steel

If you are looking for a fabrication specialist experienced in the use of CNC machines, Summit Steel can help.

Since 1992, Summit Steel & Manufacturing, Inc. has offered superior metal manufacturing and fabrication services to customers across the East Coast. We serve companies in a variety of industries, from consumer products to military and defense equipment. With our wide range of manufacturing capabilities, we can provide our customers with services of all kinds, all from a single source.

We provide only the best in service, offering you such benefits as:

• Quick turnaround times: We are highly experienced in production orders ranging from medium to large in size and can promise you’ll get your finished product back in record time. Our short lead times and fast service is even better when you get all of your manufacturing processes from Summit Steel, keeping it all under one roof.
• High-quality products: Our primary focus is on providing the best quality to our customers. We pride ourselves on our excellent workmanship and our maintenance of our ISO 9001-2008 certification, as well as our broad range of experience working with companies from a variety of industries.
• Decreased costs: We do things right the first time, which is why we offer the best products at competitive prices. By reducing lead times, guaranteeing high quality with each part and sourcing all of our services in-house, we can offer a cost-effective manufacturing service to all of our customers.