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Thanks to recent advances in 3D printing capabilities, it is becoming increasingly easy for manufacturers to use additive manufacturing to create parts from various materials, including polymers such as ABS, TPE, and PLA, carbon fiber, nylon, and polycarbonate composites. Even expensive metals such as titanium, stainless steel, and Inconel are becoming more common in additive manufacturing. There is 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, the talk here is that it may be more critical to incremental manufacturing than you think, as a new process called „hybrid manufacturing” is rapidly gaining popularity in the industry. Why is it so essential to ensure the manufacturing process? Is CNC applicable to structures inside unreachable parts? Does the process itself require specialized skills? We write about all this below!

Additive manufacturing vs. subtractive manufacturing

Hybrid machining is increasingly replacing machining. Before implementing a hybrid manufacturing approach, it is important to understand the advantages and disadvantages of each approach. Here is a brief overview of where incremental technologies are applicable, how the part manufacturing process works, and the advantages and disadvantages of additive and subtractive manufacturing.

Additive manufacturing – advantages

  • Adds layers of material to create a part
  • Better for smaller parts
  • Slower process, better for small production runs
  • Rough surface finish, which requires significant post-operative finishing
  • Less precise part tolerances
  • Cheaper material costs
  • Less material waste
  • Complex details are easier to create

Subtractive manufacturing – advantages

  • Removes layers of material to form parts
  • Faster process, better for large production runs
  • Better for larger parts
  • More defined surface finish with minimal post-processing required
  • Is able to maintain very precise part tolerances
  • More expensive material costs
  • More material waste
  • Complex details may require intricate programs and additional capabilities (5 axes)

Using CNC machining to create precision 3D printed parts

One of the main differences between additive and subtractive manufacturing is the surface finish and tolerances that can be achieved by 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 to complete the part. CNC machines can produce 3D printed parts that meet the tight tolerances required in many industries and achieve the desired surface finish. Advanced finishing tools and long-reach taper tools, such as Harvey tools, make it easy to machine the narrow geometries of 3D printed parts, while ultra-sharp diamond-coated tools and material-specific tools for plastics and composites can create aesthetically pleasing, tolerant and finished parts regardless of material. Long-reach tools make machine complex details on hard-to-reach 3D printed parts easier. By designing this workflow into your shop, 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 for precision machining excellence.

Using 3D printing to increase CNC machining productivity

Can’t a CNC machine create everything a 3D printer can in less time? By using both methods and a hybrid approach, manufacturing and material costs can be reduced. For example, most parts can be machined using typical subtractive machines, while using additive methods can take a long time. You can then return the piece using a 3D printer to add complex features to the part that 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 into the part and then finished on a CNC machine. The ability of additive machines to truly „add” parts can also provide a less costly approach to design. Instead of machining an entire part from expensive materials such as Inconel or Titanium, pieces that do not require extreme heat resistance can be cut from less expensive steels. Heat-resistant parts from expensive materials can be added later using additive methods.

Hybrid production machines

As hybrid working methods become increasingly popular, new production machines are increasingly in demand. All-in-one equipment can perform additive and subtractive manufacturing in a single configuration. Many of these machines offer 3D metal printing and multi-axis machining to work with even the most complex parts. As manufacturing and design technology becomes „smarter” with CAM/CAD software offering generative design and artificial intelligence, these hybrid machines could become the new standard for high-end machine shops working in advanced manufacturing industries such as aerospace, medical, defense, and markets for molds, tools and dies.

How many parts do you produce? Choosing between 3D printing and CNC machining

The number of parts you plan to produce will play a big role in deciding between 3D printing and CNC machining. Below, we break this down into several parts, material and geometry. In addition to our main recommendations, we also include 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+ – use injection molding

Number of parts for metal materials

  • 1-10 – apply 3d printer
  • 10-100 – use 3d printer (although CNC can be considered)
  • 100-1000 – use CNC machining
  • 1000+ – use CNC machining or casting

Does 3D printing or CNC machining provide better dimensional accuracy?

CNC machining provides tight tolerances and excellent repeatability. CNC can precisely machine both very large and very small parts. Because of the shape of most cutting tools, the inside corners always have a radius, but the outside surfaces can have sharp edges and can be machined very thin. Each 3D printing system offers different dimensional accuracies. Industrial machines can produce parts with very tight tolerances. If tight clearances are required, the critical dimensions can be 3D printed to magnification and then machined in post-processing. 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 the parts are produced one at a time, layer lines are visible, especially on curved surfaces. The maximum size of parts is relatively small, as 3D printing usually requires fairly strict environmental controls.

Materials comparison: metal fabrication vs. plastic printing

3D printing and CNC machining work on metals and plastics, although both technologies handle these materials equally. CNC machining is mainly used to produce metal parts. You can also use the CNC process to make parts from thermoplastics, acrylics, cork and hardwood, 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 to produce thermoplastic and thermoset parts, but metal parts can also be printed using some 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 important physical properties. Materials that are difficult to work with (TPU and superalloys) can be 3D printed. Mechanical properties can be inferior compared to CNC parts, as they are usually not perfectly isotropic.

Popular materials for 3D printing:

  • Plastics: Nylon, PLA, ABS, ULTEM, ASA, TPU
  • Metals: aluminum, stainless steel, titanium, Inconel

The best way to produce complex parts

The part’s complexity is the main factor when choosing between 3D printing and CNC machining. Both technologies have design limitations, although the number of geometries a CNC machine can produce is much smaller. CNC machining has several key design limitations, including tool contact and clearance, clamping points, changing workpiece fixtures, and the inability to machine square corners due to tool geometry. Some geometries are impossible to machine with CNC because the tool cannot access all surfaces of the part. This also applies to 5-axis systems. Most geometries require the operator to rotate the part so the tool can access different sides and angles. Repositioning requires equipment and labor time. All of these factors add up to the final price of the part. 3D printing can produce parts with very few geometric constraints compared to CNC. Support structures may be required with processes such as FDM, but the little additional machining does not limit the tremendous design freedom and complexity that 3D printing provides. In addition, polymer-based powder bed fusion processes such as SLS and MJF can produce any organic geometry without support structures. The ability to produce very complex geometries with relative ease 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 manufacturing is often a labor-intensive process. With CNC, the machine operator must first decide on tool selection, spindle speed, cutting path, and possible part repositioning. He should also manually position the block in the machine, keeping all these factors in mind. Knowing if the part is ready after machining or if one or more finishing steps are required is also necessary. All these factors affect the quality of the component and its build time. For 3D printing, the operator will prepare the digital files, choose the orientation, and add support if necessary. The files then go to the machine, where the printer has done all the construction work with little or no human intervention. Once the parts are printed, they need to be cleaned and post-processed. These last steps are the most labor-intensive parts of the 3D printing unit production process. Combining CNC and printing three leads to new production methods and allows components to be produced more accurately.