7 situations where subtractive manufacturing edges out 3D printing

Situations where subtractive manufacturing edges out 3D printing

A couple of weeks ago, I wrote about the top 9 reasons to adopt 3D printing. But, additive manufacturing is not always a blessing. There are situations where 3DP will not be able to match the advantages of traditional subtractive manufacturing methods.

This is partly due to the fact that 3D printing is not (yet) a mature enough mainstream technology. It cannot meet several challenges that traditional subtractive manufacturing processes use. The other part is the huge learning curve that is involved in starting to use 3D printing. It’s not insurmountable. But it’s not really for the faint hearted.

Huge potential lies ahead for 3D printing.

Don’t get me wrong; I am all for additive manufacturing/3D printing. Wohlers’ Associates, the respected industry analyst reported in April 2016:

the additive manufacturing (AM) industry, consisting of all AM products and services worldwide, grew 25.9% (CAGR) to $5.165 billion in 2015. The CAGR for the previous three years was 31.5%. Over the past 27 years, the CAGR for the industry is an impressive 26.2%.

That is an exciting growth history!

Based on Wohlers Report 2016

Let us examine briefly the reasons why 3D printing is still not a great solution in some situations and how this is changing.

1. Design principles are different for additive and subtractive manufacturing.

3D printing can surmount the shortcomings of subtractive manufacturing. However, this requires designers to see that 3D printing needs a different type of design.

3DP allows designers to try out totally new designs that would not have been possible earlier. If the designer lacks imagination and just tries to print his existing design with a 3D printer, he will not be able to extract all the benefits that 3DP offers.

Traditional manufacturing breaks down designs into small components for manufacturability. Whereas, 3D printing can print multiple sub-assemblies in one go. For example, if you design bricks in traditional manufacturing, you could design entire walls and print them in one go with 3D printing. Designers have to tune in to the new paradigm, which often is not the case.

Image © Stratnel Technologies LLP

2. Production costs with 3D printing are much higher compared to traditional manufacturing.

This is influenced by several factors:

2a. Machine setup complexity

The quality of the print out depends on how well the machine is calibrated. This includes setting parameters for bed leveling, bed temperature, nozzle temperature, Tg of the material used, in fill percentage and several other such factors. The current crop of consumer 3D printers run out of calibration pretty fast and recalibration is a long drawn process. And if you have a mixed lot of products to make, it increases the complexity of calibration by an order of magnitude.

2b. Trial runs and wastage

Every DIY 3D printer knows about how many times he needs to iterate and how much of material gets wasted before a decent print out can emerge.

2c. Material cost

The cost of filaments available today (considering the fact that FDM is still the most commonly used type) is still prohibitive. Especially if you tend to buy filaments in small lots, it is just not possible to meet the costs of a mass produced product. As the saying goes, if you could buy it at Walmart for $5, why would you spend a few weeks of your time and countless reprints in order to eventually get a reasonable reproduction at 3 to 5X of the cost?

2d. Production time

What takes an injection molding tool a few minutes to spit out, could take several hours in a 3D printing tool. This is still a big disadvantage for implementing full scale production with additive manufacturing.

3. Post processing is an extra process step with 3D printing.

Traditional manufacturing can churn out products with little or no finishing required. This is because injection molding has been there for such a long time that most users have figured out how to get finished products without having to baby them. 3D printing has not reached that stage yet. Because of the inherent nature of printing in layers, imperfections are visible quite clearly regardless of the nozzle size used. This means sanding, blowing and painting before the product is ready for shipment.

Source: http://www.slideshare.net/MArifMahmood/finishing-3-d-printed-parts

There have been a few printers recently, the prominent one being Rize One, that claim reduced or no post processing thus greatly improving one of the major drawbacks of 3D printing. Rize One is expected to be commercially available later this year.

4. Repeatability is still not good enough.

3D printing is still not good enough to make products with high repeatability. Jet printing tools have much higher repeatability but the average run of the mill FDM tool printing out plastic parts leaves repeatability much to be desired. So critical applications where repeatability is important are still shying away from 3D printing.

5. 3D printers are still prohibitively expensive.

The situation in the current crop of available 3D printing tools is that if you need reliable high quality repeatable printing, you need to shell out at least a few hundred K $ for a tool. This needs to change. Hopefully with higher demand for such tools and expiry of patents, more players will come in to offer higher quality printers at lower costs.

6. Usability may restrict applications for 3D printing.

If you try printing a spoon with 3D printing, you would realize that the spoon has lots of striations where food particles could go and lodge themselves, leading to bacterial growth. ABS is not BPA free. Several materials such as PLA (Polylactic acid) are not suitable for dishwashing. So 3D printing everyday usable stuff that could be used in homes still has a long way to go.

7. Compelling applications that can drive the usage of mainstream 3D printing are still not there.

The killer use case is still beyond the horizon. There is not yet a revolutionary use case where 3D printing will beat out all other competition for its advantages. There are a few applications in aerospace where weight reduction is a big benefit but none in the mainstream applications so far. It’s a black swan and it’s somewhere out there. It’s more a question of when than if.

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