Posted November 12, 2020

CNC Machining vs. 3D Printing for Prototyping Components

A CNC milling machine working on metal

Prototyping allows the manufacturing industry to build a physical, functional model of a design. In many instances, a design process may include three to five prototype phases that range from proof-of-concept (POC) and minimum viable product (MVP) to the alpha and beta releases. Because of the differences between the prototype phases, design teams may consider CNC machining vs. 3D printing for prototyping components. Here’s a closer look at the two methods and the advantages CNC machining may offer for prototyping your part.

Understanding the Prototype Phases

Each of the four initial prototyping phases allows teams to test and evaluate form, fit, and function of a model through the use of a technology readiness level scale. After seeing the evaluation results, development and engineering teams can conduct lessons learned meetings to gather feedback and determine the next steps for design and development. 

Those next steps often result in a final prototype phase called the launch-ready release candidate. In that final prototype phase, design teams seek a fully functional and stable product that responds to consumer needs. The figure below shows the prototyping phases for product development.

Prototyping phases for new product development

CNC Machining vs. 3D Printing Depends on Your Prototype Requirements

In some instances, either CNC machining or 3D printing may work for any of the phases when prototyping components. However, the differences between the phases drive the selection of one method over the other. Each offers advantages and value with accompanying costs. 

The selection of CNC machining vs. 3D printing depends on:

  • The type of material needed for the prototype.
  • The number of prototypes required for testing.
  • The shape, detail, and finish requirements of the prototypes. 

All of this has implications for the design and development budget.

While CNC machining produces detailed prototypes with fine finishes, 3D printing offers fast results for low-volume production. The early phases of prototyping may not require the functionality and finish given by CNC machining, making 3D printing a good candidate for the early stages of development. 

Meanwhile, five-axis CNC machining offers the capability to produce parts that have complex geometric shapes while delivering the accuracy required for a beta release or launch-ready release candidate. In contrast, 3D printed parts may have layer lines or require additional work to remove supports. 

In fact, the two processes can complement each other in certain instances. You begin the prototyping process with 3D printing, and then have the prototype machined afterward to refine the finishing.

CNC Machines Offer Versatility

Although both CNC machining and 3D printing rely on data in the form of G-code derived from CAD software, the similarities end with the G-code machine language because of the differences between subtractive and additive technologies. The different CNC machine types listed in the table below are subtractive because each machine uses tools to remove material from a workpiece block.

Machine Type

Description

Commonly Used Materials

Lathe

Manufactures cylindrical objects. Uses a cutting tool to shape a workpiece while material turns on a spindle.

Machinable wax, wood, plastics, aluminum, brass, and stainless steel

Grinder

Uses a rotary wheel to grind or grate material.

Aluminum, stainless steel, copper, brass, steel, titanium, sterling steel, bronze, and graphite

Mill

Creates shapes, slots, holes, notches, grooves, and specialty faces.

Aluminum (6061, 7075), brass, magnesium, AZ31, stainless steel (303 and 316), carbon steel, titanium, rigid foam, carving foam, phenolics, and plastics

Plasma cutter

Uses accelerated jet plasma to cut metals.

Mild steel, stainless steel, carbon steel, alloy steels, copper, bronze, brass, pewter, lead, tin lead, cast iron, and steel

Drill

Drills, reams, counterbores, and tapping in the workpiece.

Hardened steel, aluminum, titanium, composites, brass, copper, bronze, stainless steel, wood, plastics,and phenolics

 

In contrast, 3D printing is an additive technology because the process adds materials to form the final product. Stereolithography (SLA), selective heat sintering (SHS), and selective laser sintering (SLS) use lasers or thermal beams that move horizontally to dissolve different types of materials across a bed. 

Another popular 3D printing method called fused filament fabrication adds layers of extruded materials as a bed lowers to allow more space for the added layers. Along with those processes, 3D printing also includes the capability to form powdered metals through electron beam melting and direct metal laser sintering (DMLS). 3D printing technologies are outlined in the table below.

Process

Description

Commonly Used Materials

Stereolithography (SLA)

Converts liquid thermoset resin into layers via an ultraviolet laser to form a 3D object.

Resin

Selective heat sintering (SHS)

Uses a thermal printhead to harden layers of powder.

Thermoplastic

Selective laser sintering (SLS)

Fuses powdered materials via a laser according to 3D CAD specifications.

Nylon or polyamide

Electron beam melting

Melts material in a vacuum according to the CAD model using a high-power, precise electron beam controlled by electromagnetic coils. 

Powdered titanium, cobalt-chrome

Fused filament fabrication

Extrusion process that deposits layers of melted material.

Thermoplastics

Direct metal laser sintering (DMLS)

Uses a laser to create a metal part defined by a 3D CAD model.

Finely powdered metal alloys or pure metals, including steels, aluminum, titanium, and nickel

 

Overall, CNC machining offers added versatility over 3D printing. CNC operators can respond to complex design shapes and cuts with multiple types of bits. The capabilities to shape, drill, grind, and turn materials to precise specifications allow design teams to broaden their creativity and address market demands with prototypes. As such, a collaborative team of designers and engineers can respond to a manufacturer’s call for a fully functional prototype quickly and without errors.

There is also a significant difference in materials used by CNC machining and 3D printing when producing prototypes. While the 3D SLS, SHS, and SLA methods use resin, thermoplastic, nylon, or polyamide to produce parts, the DMLS and electron beam methods work with powdered metals. Yet, limitations exist. 

Objects printed through stereolithography typically do not have the strength that functional prototypes need to resist deformation under load. While DMLS and electron beam methods produce metal prototypes, the smaller bed sizes eliminate the possibility of producing larger-size objects. For platforms that permit printing larger-size objects, the 3D printing processes require more build and lead time, and higher costs.

CNC machines work with a wide range of materials, including wood, plastic, composites, rigid and carving foam, phenolics, and metals. In contrast to the rougher surface finish seen with selective laser sintering or fused deposition modeling, CNC machining also produces finishes that do not require the additional post-machining seen with 3D printing. The capability to produce prototypes from different materials allows CNC machining to match manufacturer requirements for durability and functionality.

CNC Machining Combines Precision, Lower Costs, and Quantity

The advantages of CNC technologies also become apparent through the operation and capabilities of CNC equipment. A CNC machine consists of a controller within its command function that reads the G-code and interprets the dimensions and shape of the design. Computer numerical control establishes the sequence for machining steps as well as the dimensions for an object.

Because the controller also interfaces with CAM software, it receives the exact design data required for producing and finishing an object. Because of the connection with CAD and CAM software, the controller directs the CNC drive/motion system to move either the cutting tools or the workpiece.

As the table below shows, the combination of movement across different axes and the option to automatically select from different types of cutting tools allows CNC machining to reproduce complex designs.

CNC Machine Type

Axis Amount

Capability

Lathe

2

Tool moves in two directions.

Drill

2.5

Tool moves to a position on the X and Y axes, stops, and then moves across the Z axis.

Mill, Drill

3

Simultaneously moves the tool to a position on the X, Y, and Z axes.

Mill

4

Simultaneously moves the tool to a position on the X, Y, and Z axes while adding rotation on the A or B axis around the X axis.

Cutter, Mill, Drill

3 + 2

Simultaneously moves the tool to a position on the X, Y, and Z axes while the A- and B-axes maintain a fixed position for the workpiece.

Mill

5

Simultaneously moves the tool to a position on the X, Y and Z planes while rotating on the A and B axis around the X axis.

 

As a result, CNC machining offers reliability and the identical production of parts. Prototype machining of larger quantities of complex prototype designs occurs automatically at a lower cost than seen with 3D printing. With one CNC programmed machine controlling many operations, CNC machining can produce many identical, error-free prototypes for testing by separate user groups.

Plethora is the leader in precision CNC machining for the prototyping and production of components. To learn more about the advantages of CNC machining vs. 3D printing, contact our experts today by calling 415-726-2256. Or, get started on your project by uploading your design files to Quote My Part.

Quote My Part

the-plethora-team

The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: CNC machining, Prototyping

Comments