Frequently Asked Questions

CNC Machining vs Direct Metal Laser Sintering (DMLS)

The most obvious difference between these processes is that CNC machining is a subtractive method and Direct Metal Laser Sintering (DMLS) is additive. (For the sake of this article we will refer to DMLS from EOS, however the vast majority of the information applies to all the powder bed metal sintering options). 

DMLS titaniumAdditive or Subtractive?

So, faced with additive or subtractive, how does one decide? Parameters such as time, material, geometry, and design, all impact that decision, as they all have implications on cost, which is usually the deciding factor if other issues are equal.

Size?

Starting with geometry, the first issue to tackle is size. The vast majority of DMLS machines that are available have a 250 x 250 mm bed size, whilst the build height (z) can vary from 215 to 325 depending on machine age. Newer machines can accommodate larger builds, but access and availability can be limited leading to longer lead-times and higher costs.

Size can eliminate additive (powder bed) options altogether, but even if it can be built bear in mind that cost rises with part size. The larger the part (especially in height), the greater the build time, and hence, the greater the cost.

Increasing the material volume has the same effect albeit to a smaller extent. Hence producing a part that has 10mm wall sections will take longer and cost more than a similar part with 2mm wall sections. Dropping the wall section further to say 0.5mm can make the geometry impossible for CNC whilst DMLS can still achieve it.

CNC machiningComplexity?

This leads us to complexity, where both systems can produce a 25mm cube; CNC will deliver it faster and more cost effectively. Now as we start adding complexity and the solid cube morphs towards a complicated manifold, with multiple set ups required to machine each face, DMLS comes into its own.

This can be driven to extremes by removing any thick sections and replacing them with lattice structures. This totally rules out a CNC approach, leaving DMLS as the only option.

DMLS TitaniumThus at this point a general rule would be smaller complex parts are likely to be more cost effective as DMLS whereas simpler or larger parts will be cheaper as CNC machined items.

Increasing complexity whilst suiting DMLS does have limitations. The process requires supports and these (usually) have to be removed post build. Support removal brings with it a cost and thus part orientation and part design are key to achieving a cost effective part.

Surface Finish?

Surface finish will be another difference between the two options. Features such as seal grooves are likely to require post machining, threads may require cleaning up, critical bores may require boring out if roundness is critical. So studying the interfaces and defining exactly what is required is important for a DMLS part. In most cases this is not an additional cost with CNC machining.

CNC machined in aluminiumMaterial Selection?

Material selection is important on two counts, firstly it affects build speed, and secondly it can affect availability of machine capacity.

For DMLS different materials will build at different speeds and thus the situation arises whereby a Titanium part can be cheaper to produce than an aluminium part! Choosing ‘popular’ materials will also increase the probability of a quick turnaround, builds can stretch into days, so being the only person wanting a particular material can result in extended lead-times. DMLS can process some specialty materials that are otherwise challenging to machine, such as Inconels, Hastalloy and Cobalt Chrome.DMLS

Quantities?

The implications of quantities on relative costing are more difficult to summarise. With CNC, complexity brings programming time. A larger batch size allows this to be amortised more effectively, thus reducing the part cost. With DMLS the effect of quantity is really linked to the ability to pack the platform. A small thumb sized part can be built by the hundred, whereas a larger part might only be able to fit 4 to a platform. Thus as a rule of thumb, the smaller the part the more likely it is that DMLS can offer a cost effective solution, so long as any post machining is negligible.

Design for the Process

Whilst there is a general awareness of designing for CNC, to really extract the benefits of DMLS the component should be designed for the process. Making the design suitable is likely to have the biggest single effect on the cost competitiveness of an additive solution.

If you are unsure how to proceed, Plunkett Associates can offer an unbiased view of both options to find you the best solution, whether you are driven by cost or a performance factor. However please note the common misconception is that DMLS is just like Stereolithography (SLA), but in metal, could not be further from the truth, to make it work for you requires you to address its strengths and weaknesses.

  • “Plunkett Associates have excellent breadth of experience, work with high quality partners and have a flexibility that we have found enables challenges to be met successfully, cost effectively and in a timely manner.”
    Nick Skaer, CEO, Orthox Ltd
  • Plunkett associates always find a solution. Whatever we need to prototype, they have a great grasp on the technologies available, costs and lead-times so we get the right solution tailored to the project needs. Have always delivered and never let us down.
    Naim Audio
  • “I can’t recommend Tim and his team highly enough. We ended up with a design which can be produced and assembled quickly, efficiently and reliably, in volumes that make sense”
    Simon Leggett, Director, Olivewood Technology
  • "Tim's experience, expertise and supplier base have been fundamental to us getting this project off the ground."
    Sam Pearce, Jelly Products Ltd
  • “We were really surprised at how quickly they turned round such a high quality prototype and the parts certainly proved their worth. They were of high enough quality to provide a fantastic visual representation and to undergo rigorous testing."
    Stuart Wilson, Design Director, TRT Lighting
  • “Accuracy, finish and delivery all first class.”
    Andrew Peters, JMDA Ltd
  • “We use Plunkett Associates because we want someone we can trust, that knows what they’re talking about, has all the contacts, will provide reliable advice and feedback and will get the right result for us.”
    Jim Copestick. Design Manager, Thorlux Lighting
  • “We always know exactly what we’re getting and we know we won’t be let down on quality, price or lead times.”
    Mark Williams, Research and Development Director, Johnson Safety Products
  • “Plunkett Associates truly offer a complete turnkey solution with Speed, Effectiveness and Precision.”
    David Harden, Director, Enica Ltd
  • “Kirintec were thrilled with Plunketts. They made a complex process simple and we were just amazed at the lead times achieved. Plus, every single deadline was met without any drama.”
    Penny While, Marketing Director, Kirintec
  • “Thanks to Plunkett Associates flexible, bespoke and cost effective service I was able to produce the objects that I had originally had in mind.”
    Simon Ryder, Artist
  • To create such a consistent quality finish in chrome was an amazing achievement and the prototypes really gave our stand the wow factor.
    James Clark, Group Commercial Director, The Airdri Group
  • Interestingly, people who look at it in its own right with little knowledge of what it does, just like it! It’s tactile and it looks good…
    Tim Collings, Operations Director, Troika Systems Ltd
  • "With their simple to understand language, willingness to go the extra mile and approachability, Plunkett Associates were a great partner for our company. We couldn’t be happier with the results of our project. (A working prototype that they got right first time, by the way). Thank you!"
    Carolina Ballon-Forrester, Director, Kittyrama Ltd
  • Plunkett Associates worked on the design and production of titanium frames for an artificial heart valve where precision and consistency was paramount. Communications were efficient and productive with concepts readily incorporated into the final design, and suggestions for improvements all highly appropriate. The quality of the end product was ideal and I have no doubt that I will use the advice and expertise of Plunkett Associates again.
    David Wheatley, Wheatley Research Ltd
  • “Thanks for the present that arrived this morning, as promised. Parts look first class, as always.”
    Jon Todd, Design Manager, PHS Group
  • “Plunkett Associates have a fantastic supply chain, work with all sorts of production processes and will always do their utmost to solve a problem.”
    Naim Audio
  • “ Plunketts developed a solution that met our precision requirements at a cost significantly lower than alternative manufacturing approaches we had investigated”
    Nick Skaer, CEO, Orthox Ltd
  • “Doing business with you has been an absolute pleasure. You have made my goals a reality. You have been patient, helpful and above all, responsive. Best service that I have experienced in ages. I consider Plunkett Associates to be an integral part of my business plan moving forward.”
    Jet Cooper, Sculptor
Related Processes

CNC Machining

The benefits of CNC parts include substantial flexibility in material choice, high accuracy and repeatability.

more info

Direct Metal Laser Sintering (DMLS)

DMLS (or Laser Cusing) is an additive process, suitable for prototyping & manufacturing of metal parts with highly complex or feature rich designs.

more info

Read more expert articles in our FAQ section where we discuss topics on materials, methods and products.

Back to FAQs
  • “Plunkett Associates have excellent breadth of experience, work with high quality partners and have a flexibility that we have found enables challenges to be met successfully, cost effectively and in a timely manner.”
    Nick Skaer, CEO, Orthox Ltd
    Nick Skaer, CEO, Orthox Ltd
  • Plunkett associates always find a solution. Whatever we need to prototype, they have a great grasp on the technologies available, costs and lead-times so we get the right solution tailored to the project needs. Have always delivered and never let us down.
    Naim Audio
    Naim Audio
  • “I can’t recommend Tim and his team highly enough. We ended up with a design which can be produced and assembled quickly, efficiently and reliably, in volumes that make sense”
    Simon Leggett, Director, Olivewood Technology
    Simon Leggett, Director,  Olivewood Technology
  • "Tim's experience, expertise and supplier base have been fundamental to us getting this project off the ground."
    Sam Pearce, Jelly Products Ltd
    Sam Pearce, Jelly Products Ltd
  • “We were really surprised at how quickly they turned round such a high quality prototype and the parts certainly proved their worth. They were of high enough quality to provide a fantastic visual representation and to undergo rigorous testing."
    Stuart Wilson, Design Director, TRT Lighting
    Stuart Wilson, Design Director, TRT Lighting
  • “Accuracy, finish and delivery all first class.”
    Andrew Peters, JMDA Ltd
    Andrew Peters, JMDA Ltd
  • “We use Plunkett Associates because we want someone we can trust, that knows what they’re talking about, has all the contacts, will provide reliable advice and feedback and will get the right result for us.”
    Jim Copestick. Design Manager, Thorlux Lighting
    Jim Copestick. Design Manager, Thorlux Lighting
  • “We always know exactly what we’re getting and we know we won’t be let down on quality, price or lead times.”
    Mark Williams, Research and Development Director, Johnson Safety Products
    Mark Williams, Research and Development Director, Johnson Safety Products
  • “Plunkett Associates truly offer a complete turnkey solution with Speed, Effectiveness and Precision.”
    David Harden, Director, Enica Ltd
    David Harden, Director, Enica Ltd
  • “Kirintec were thrilled with Plunketts. They made a complex process simple and we were just amazed at the lead times achieved. Plus, every single deadline was met without any drama.”
    Penny While, Marketing Director, Kirintec
    Penny While, Marketing Director, Kirintec
  • “Thanks to Plunkett Associates flexible, bespoke and cost effective service I was able to produce the objects that I had originally had in mind.”
    Simon Ryder, Artist
    Simon Ryder, Artist
  • To create such a consistent quality finish in chrome was an amazing achievement and the prototypes really gave our stand the wow factor.
    James Clark, Group Commercial Director, The Airdri Group
    James Clark, Group Commercial Director, The Airdri Group
  • Interestingly, people who look at it in its own right with little knowledge of what it does, just like it! It’s tactile and it looks good…
    Tim Collings, Operations Director, Troika Systems Ltd
    Tim Collings, Operations Director, Troika Systems Ltd
  • "With their simple to understand language, willingness to go the extra mile and approachability, Plunkett Associates were a great partner for our company. We couldn’t be happier with the results of our project. (A working prototype that they got right first time, by the way). Thank you!"
    Carolina Ballon-Forrester, Director, Kittyrama Ltd
    Carolina Ballon-Forrester, Director, Kittyrama Ltd
  • Plunkett Associates worked on the design and production of titanium frames for an artificial heart valve where precision and consistency was paramount. Communications were efficient and productive with concepts readily incorporated into the final design, and suggestions for improvements all highly appropriate. The quality of the end product was ideal and I have no doubt that I will use the advice and expertise of Plunkett Associates again.
    David Wheatley, Wheatley Research Ltd
    David Wheatley, Wheatley Research Ltd
  • “Thanks for the present that arrived this morning, as promised. Parts look first class, as always.”
    Jon Todd, Design Manager, PHS Group
    Jon Todd, Design Manager, PHS Group
  • “Plunkett Associates have a fantastic supply chain, work with all sorts of production processes and will always do their utmost to solve a problem.”
    Naim Audio
    Naim Audio
  • “ Plunketts developed a solution that met our precision requirements at a cost significantly lower than alternative manufacturing approaches we had investigated”
    Nick Skaer, CEO, Orthox Ltd
    Nick Skaer, CEO, Orthox Ltd
  • “Doing business with you has been an absolute pleasure. You have made my goals a reality. You have been patient, helpful and above all, responsive. Best service that I have experienced in ages. I consider Plunkett Associates to be an integral part of my business plan moving forward.”
    Jet Cooper, Sculptor
    Jet Cooper, Sculptor