Additive vs subtractive manufacturing – what's the difference?
The two processes defined.
Subtractive manufacturing is the process of beginning with more material than is needed and selectively removing what is not required until the final shape emerges. This process is easily explained by using the marble sculptures of the famous artist Michelangelo as an example. When asked by the Pope how he made his statue of David so beautifully lifelike, he replied “I simply remove everything that doesn't look like David”. This is the basic principal of subtractive manufacturing; start with too much and then remove what you don't need.
Additive manufacturing, on the other hand, is the process of producing objects by adding only what is needed, along with any support material required. The most common way to do this is by placing very thin layers of material on top of one another to stack up and form the final object, like layers of a cake. This process dramatically reduces the time, cost and waste produced from its subtractive competitor, and allows a much more efficient production process.
Their common applications.
Subtractive manufacturing has been the way that almost everything was made, going all the way back to man's earliest tools having been shaped from sticks and stones. From the simple to the inconceivably complex, subtractive manufacturing has been the worldwide standard for bespoke and mass-produced products and tools alike.
Additive manufacturing processes have in the past been too expensive for mass-produced products, but have still found their way into the production process. They have been commonly used for some time now to prototype and test new product designs. For companies like Nike, the production of ‘one of a kind' test products is a highly cost-effective use of additive manufacturing.
R&D, prototyping & testing.
One of the biggest and most immediate advantages of using additive contraction techniques is the ability to create a limited number of ‘test' designs and models. To previously create these beta versions of products would have been a time consuming and costly process. This also greatly reduces the time spent developing new products, not to mention the amount people needed to fabricate a new concept into a working prototype.
Final fabrication and distribution.
For now, short run and individual products are the biggest benefactors of the additive manufacturing process. Each product can be fabricated without the need of building a new assembly line or tooling machines, greatly reducing the cost of these smaller scale productions. Where 3D printers could take the biggest bite from the cost of manufacture and distribution is by consumers printing products themselves. Using additive manufacturing to fabricate their own products at home with 3D printers, the only thing to manufacture and distribute is a 3D CAD file! Delivery of these new digital products would simply require a server where customers could download the file for the product and then replicate at home.
Spare parts and repairs.
With any physical product there will be a need to have a stock pile of spare parts to allow consumers and professionals to repair their products in the event they break or are damaged. The cost of producing, storing and distributing these spare parts can be enormous, but with home manufacturing, spare parts could be downloaded and made at home. The cost is reduced greatly by efficiently supplying spares, as only the parts needed would ever be made.
Shipping and distribution.
Instant, global distribution.
In an ‘on demand' modern world it's not difficult to see the public adopting home manufacturing. The ability to watch movies instantly on your computer or TV with services like Netflix has quickly killed the video store, and additive manufacturing could very well do the same for many of the products we buy every day. For example, tooth brushes could be automatically printed every 3 months, replacing worn out ones without giving it another thought. As the technology becomes more widely adopted, more and more ‘home printing ready' products will start to appear in the market as businesses try to harness the cost saving benefits of distribution through 3D printers.
Universal cost to ‘ship' unlimited quantities of products anywhere in the world.
From Cairo to California, the cost of distributing a digital file is pretty much universal. No matter where you are in the world, digitally distributed products can be downloaded for home manufacture with minimal cost to the creators of the product. For end users also, the cost for large items compared to smaller ones is determined by file size and is generally minimal. Multiple instances of any given product could also be made from a single file to further reduce the cost of distribution.
Permanently and instantly available spare parts.
Nothing inspires us to rush out and make a purchase like when something breaks. Having to wait days or even weeks for a spare part to be ordered, shipped and delivered is a time consuming and often frustrating process. Is the part in stock? Do they still make them? With on demand digital products, spare parts could forever be available for download without the need to store endless spares. If something breaks, simply download and print out the required part.
Reduction in production waste.
By the nature of how it works (using only what is needed), additive manufacturing greatly reduces the waste incurred by traditional tooling methods. When less waste material is produced, not only are less raw materials used but the need to remove, transport and discard waste by-products is reduced to a bare minimum, as too is the carbon footprint.
Eradication of packaging.
If products are delivered via home manufacturing, then the need for packaging for any given product is completely removed. Cardboard and plastic inserts, paper instructions and glossy boxes all would no longer be required in order to deliver products to end users. Along with the products packaging, there would no longer be a need to physically ship anything, and so the freight packaging and boxing would also no longer be needed. While many companies are currently using recycled packaging for their products, the recycling process itself, as well as the physical transporting of the packages, all add to a company's carbon footprint, but could be completely removed by additive manufacturing.
Potential to recycle material at home.
Websites like Kickstarter already have projects to create ‘home recycling' machines to repurpose the materials used by 3D printers, which could make another significant impact on the environment. Imagine using old, no longer required products to make new, better ones! With these proposed machines, the material is shredded and melted down to be reused with fused deposition modeling printers.
If both the general public and companies embrace home fabrication, the global impact that manufacturing causes the environment could be greatly reduced.