Thanks to recent advancements in 3D printing capabilities, it's becoming easier for manufacturers to utilize additive manufacturing to create parts from various materials, including polymers such as ABS, TPE, and PLA, as well as composites of carbon fiber, nylon, and polycarbonate. Even expensive metals, like titanium, stainless steel, and Inconel, are becoming increasingly common in additive production. There's no doubt that this space will continue to expand and grow in the coming years, but will this make subtractive manufacturing methods, such as CNC machining, obsolete? Absolutely not. In the case of CNC machining, it may be more important for additive manufacturing than you think, as a new process called "hybrid manufacturing" is quickly gaining popularity in the industry. Why is it so important to oversee the manufacturing process? Does CNC have applications in structures within unreachable elements? Does the process itself require specialized skills? We discuss all of this below!
Additive Manufacturing vs Subtractive Manufacturing
Hybrid machining is increasingly replacing machining operations. Before implementing a hybrid production approach, it is important to understand the advantages and disadvantages of each approach. Below is a brief overview of where additive technologies apply, how the part manufacturing process proceeds, and what advantages and disadvantages additive and subtractive production have.
Additive manufacturing - advantages
- Adds layers of material to create parts
- Better for smaller parts
- Slower process, better for small production runs
- Rough surface finish, which requires significant post-processing
- Less precise part tolerances
- Cheaper material costs
- Less material waste
- Complex details are easier to create
Subtractive manufacturing - advantages
- Removes layers of material to create parts
- Faster process, better for large production runs
- Better for larger parts
- More defined surface finish with minimal post-processing required
- Can maintain very precise part tolerances
- Higher material costs
- More material waste
- Complex details may require complex programs and additional capabilities (5 axes)
Using CNC machining to create precise 3D printed parts
It is clear that one of the main differences between additive and subtractive manufacturing is the surface finish and tolerances that can be achieved with each method. In this case, a hybrid approach to additive manufacturing can be very beneficial. When parts come off the printer, they can be quickly transferred to a CNC machine using a program designed to supplement parts. CNC machines will be able to produce 3D printed parts that meet the tight tolerances required in many industries and achieve the desired surface finish. Advanced finishing tools and large-reach tapered tools, such as Harvey tools, allow for easy machining of narrow geometries of 3D printed parts, while very sharp diamond-coated tools and tools for plastic and composite specific materials can create aesthetic, tolerance and ready parts regardless of the material. Large-reach tools facilitate the machining of complex details on hard-to-reach 3D printed parts. By designing this workflow in your workshop, you can spend less time worrying about the accuracy of printed parts, add subtractive operations to reduce material costs, reduce waste, and keep parts within tight tolerances to ensure precision machining excellence.
Using 3D printing to increase CNC machining efficiency
Can't a CNC machine create everything a 3D printer can in less time? By applying both methods and a hybrid approach, production and material costs can be reduced. For example, most parts can be machined using typical subtractive machines, while using additive methods can take a lot of time. You can then return the part using a 3D printer to add complex features to the item, which would require complex programming and hours of planning on a subtractive machine. A typical example is a rotor, where most parts can be machined, but complex ribs and blades can be printed on parts, and then finished on a CNC machine. The ability of additive machines to truly "add" parts can also be a less costly approach to design. Instead of machining the entire part from expensive materials such as Inconel or Titanium, pieces that do not require extreme heat resistance can be cut from cheaper steels, and heat-resistant parts from expensive materials can be added later using additive methods.
Hybrid Manufacturing Machines
As hybrid work methods become increasingly popular, new production machines are becoming more and more sought after. These are "all-in-one" devices that can perform additive and subtractive production in one configuration. Many of these machines offer 3D metal printing and multi-axis machining for working with even the most complex parts. As production and design technology becomes "smarter" thanks to CAM/CAD programs offering generative design and artificial intelligence, these hybrid machines may become the new standard for high-end mechanical workshops operating in advanced manufacturing industries such as aviation, medicine, defense, and mold, tool, and die markets.
How many parts are you producing? Choosing between 3D printing and CNC machining
The number of parts you plan to produce will play a big role in the final decision between 3D printing and CNC machining. Below we break this down into the number of parts, material, and geometry. In addition to our main recommendations, we also consider alternative options: 3D or CNC - depending on the number of parts.
- Number of parts for plastic materials
1-10 – apply 3d
10-100 – apply 3d printing
100-1000 – apply CNC machining
1000+ – injection molding
- Number of parts for metallic materials
1-10 – apply 3d printer
10-100 – apply 3d printer (although CNC can be considered)
100-1000 – apply CNC machining
1000+ – apply CNC machining or casting
Does 3D printing or CNC machining provide better dimensional accuracy?
CNC machining ensures tight tolerances and excellent repeatability. Both very large and very small parts can be precisely machined by CNC. Due to the shape of most cutting tools, internal corners always have a radius, but external surfaces can have sharp edges and can be machined very thinly. Each 3D printing system offers different dimensional accuracies. Industrial machines can produce parts with very small tolerances. If tight clearances are required, critical dimensions can be 3D printed in enlargement, and then subjected to final machining. The minimum wall thickness of a 3D printed part is limited by the size of the effector (depending on the diameter of the nozzle in FDM or the size of the laser spot in SLS). Since parts are produced individually, layer lines are visible, especially on curved surfaces. The maximum size of components is relatively small, as 3D printing usually requires quite strict environmental controls.
Material Comparison: Metal Production vs. Plastic Printing
3D printing and CNC machining work on both metals and plastics, although neither technology handles these materials to the same extent. CNC machining is primarily used for the production of metal parts. The CNC process can also be used to produce parts from thermoplastic materials, acrylics, cork, hard wood, modeling foams, and process waxes.
What are the most popular CNC materials?
Plastics: ABS, nylon, polycarbonate, PEEK
Metal: aluminum, stainless steel, titanium, brass
3D printing is primarily used for producing thermoplastic and thermosetting parts, but metal parts can also be printed using certain techniques. Some 3D printers can produce parts from ceramics, wax, sand, composites, and increasingly, biological materials.
Choosing materials for 3D printing
There is a wide range of materials with significant physical properties. Difficult-to-machine materials (TPU and superalloys) can be 3D printed. Mechanical properties may be worse compared to CNC parts, as they are usually not perfectly isotropic.
Popular materials for 3D printing:
Plastic: Nylon, PLA, ABS, ULTEM, ASA, TPU
Metals: aluminum, stainless steel, titanium, inconel
The best way to manufacture complex parts
The complexity of parts is the main factor to consider when choosing between 3D printing and CNC machining. Both technologies have their design limitations, although the number of geometries that a CNC machine can produce is significantly smaller. CNC machining has several key design constraints, including tool contact and clearance, fixture points, changing the fixture of the machined part, and the inability to machine square corners due to tool geometry. Some geometries are simply impossible to machine with CNC, as the tool does not have access to all surfaces of the part. This also applies to 5-axis systems. Most geometries require the operator to rotate the part so that the tool can access different sides and angles. Changing position requires equipment and labor time. All these factors contribute to the final price of the part. 3D printing can produce parts with very few geometric limitations compared to CNC. For processes such as FDM, support structures may be required, but a small amount of additional machining does not limit the enormous design freedom and complexity that 3D printing provides. In addition, powder bed fusion processes based on polymers, such as SLS and MJF, can produce any organic geometries without support structures. The ability to relatively easily produce very complex geometries is one of the main advantages of 3D printing. CNC machines remove material point by point, although even 5-axis systems may not always be able to reach some surfaces.
3D Printing and CNC Machining Workflow
CNC production is often a labor-intensive process. In the case of CNC, the machine operator must first decide on the choice of tool, spindle speed, cutting path, and any change in the position of the part. He should also manually set the block in the machine, keeping all these factors in mind. It is also necessary to know whether the part is ready after machining or whether one or more stages of final processing are required. All these factors affect the quality of the component and the time of its construction. For 3D printing, the operator first prepares digital files, selects the orientation, and adds supports if necessary. The files then go to the machine, where the printer does all the construction work with little or no human intervention. After printing the parts, they need to be cleaned and subjected to final processing. These last steps are the most labor-intensive parts of the unit production process of 3D printing. The combination of CNC and 3D printing leads to the creation of new production methods and allows for the production of parts even more accurately than before.