Advanced Precision Machining

Machine Shop Prototyping Fabrication Methods: Additive (3D Printing) vs. Subtractive (Traditional)

[March 4, 2020] Due in part to manufacturing economic growth, the machine tooling industry is rapidly evolving in concert with better hardware and software applications, more advanced milling and machining equipment, improved process automation, and the integration of additive manufacturing (3D printing) technology. On Advanced Precision Machining’s (APM’s ) Colorado machine shop floor, this is all great news as our business continues to prosper and experience a boom not seen since long before the 2008 Recession. Thanks to hard work on the part of our CNC machinists, a loyal customer base, and increased demand for our high-quality parts, we're currently in the midst of an unprecedented period in our company’s development, and the first quarter of 2020 is truly shaping up to be “one for the books”. That being said, in addition to our ongoing dedication to manufacturing the highest quality precision parts while providing the best customer service experience in the business, keeping up with advancing technology trends is always part of our mission. In this month’s latest blog entry, we'd like to briefly touch upon a topic of particular interest to us and to the future of precision manufacturing operations; that of rapid prototyping and 3D printing’s expanding role in the modern CNC machine shop. 

Given the intricate nature of work to be done on a machined part, and before dedicating man-hours, CNC machine time, and materials, it is oftentimes in the best interest of the customer to begin with a model, or what we refer to as a prototype, of the part to be machined. On APM’s shop floor, our CNC machinists often construct a prototype that acts to serve as both the customer's, and our own model for a check on a part's dimensions, material strength, tolerances, etc., before full-scale production is initiated. Rapid prototyping is also a great platform for testing materials and verifying CNC programs and operations. In short, the methods and techniques involved with creating prototypes are integral to the entire production process of milling and machining precision parts, and prototyping is a key first step to procuring any precision manufacturing work that may follow.

In use on virtually any machine shop floor are two very distinctive prototyping techniques or methods, additive and subtractive, and each is utilized for different applications with their own advantages and disadvantages. Both have revolutionized the manner in which prototypes are manufactured, the technology behind both is rapidly advancing, and incorporating one or the other depending on specific needs can allow CNC machinists to design virtually anything that the mind can conceive. So, in the quest to provide better, faster, more cost-effective ways to produce prototypes and ultimately manufacture precision parts, we’d like to provide readers with a brief overview of additive and subtractive prototyping and present some pros and cons of both technologies.

Additive Manufacturing (AM), also referred to as 3D printing, stereo-lithography, or fused deposition, is a technology that first gained traction in the mid-1990s. It is a great platform for prototype development. Instead of removing material from a part via the subtractive processes used in traditional CNC machining, additive methods involve depositing and joining materials, such as liquid resin, papers, or powders layer upon layer to produce the desired prototype from 3D model data. AM techniques have a lot of inherent potentials that make it a very attractive prototyping alternative, including use in complex inserts and direct rapid tooling processes. Some pros and cons of AM in prototype development include:

[Pros]

  • The CAD driven technology behind AM allows for limitless design options and revisions. Complex features can be previewed first, revised if necessary, and then manufactured into a prototype.
  • AM results in shorter job turnarounds. For small-batch jobs inherent in prototype production, design to final build is a quicker process.
  • Significant costs savings are realized because less raw materials are used.

[Cons]

  • AM may reduce the numbers of qualified CNC machinists needed. 3D printing technology is available to anyone with a printer, raw materials, and the right software.
  • The use of intellectual property rights and piracy is an issue with AM. Blueprints may be easily obtained online for 3D printed prototypes.
  • AM materials can be more expensive than those used by traditional CNC mills, such as bar or billet stock.

Subtractive manufacturing (SM) has been in existence since humans began working with metal. Simply put, it involves the removal of raw material from a blank. Today, this is most efficiently done in a precision machine shop where materials are removed via CNC milling and machining processes involving an array of specialty tools including CNC mills and CNC routers for example. Over the last ten years, subtractive technologies have dramatically improved, with enhanced design and development capabilities. These improvements have allowed for more precise, and more creative prototype designs. Until the advent of AM, SM had been the only tool in use on the CNC machine shop floor to manufacture prototypes, and is utilized by many shops today. Prior to full-scale production runs, SM has some advantages over AM, but also some disadvantages.

[Pros]

  • SM can be faster than AM; even for small batch runs associated with prototyping because of advances in design software.
  • SM techniques do not require outsourcing or investment in new 3D printing equipment.
  • SM requires less finishing work to be done once a prototype has been machined compared to AM.

[Cons]

  • On the startup, or entry level, SM requires more capital investment in precision machining technology than does the cost associated with AM investment.
  • More raw materials are utilized and may be discarded as scrap. Operating costs go up.
  • SM is inherently a longer process, both in design and production, when compared with AM. The result is longer turnaround times.

The process of producing a prototype for a customer will always be a necessary step in the precision machining process. Both prototyping technologies will always require the right combination of machine, manpower, design, setup time and materials costs. There is a case to be made for techniques. The bottom line is that additive manufacturing should not be thought of as a replacement or alternative to the traditional method of subtractive prototyping. Depending on the part to be machined or printed, the material, the schedule, and a host of other factors, both technologies have a spot on the floor of the future CNC machine shop.

Want to learn more about improving machine shop efficiency and productivity, or have a question about your next milling and machining project? Contact the expert CNC machinists at Advanced Precision Machining today. 

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About the Author

Gerry Dillon is a co-founder, current owner and certified CNC machinist at Advanced Precision Machining (APM), a full-service machine shop located in Longmont, Colorado. Before making his home in the United States in 2000, Gerry was born and raised on the emerald isle of Ireland and took an interest in milling and machining from an early age, ranking #1 in the Irish National Apprenticeship Program. In 2005, he and a partner began what’s grown into a leading Colorado machine shop. Gerry brings over 30 years of machining experience to the shop floor, and is certified in all aspects of geometric dimensioning and tolerancing. 

 

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