ADDITIVE MANUFACTURING 101
Additive manufacturing is often referred to as 3D printing, but is there a difference?
The short answer is ‘YES’ - even if it is a bit subtle:
Additive manufacturing is a beginning-to-end process of developing and ultimately creating an item using 3D printing technology. The term ‘3D printing’ refers to a more ‘ground-level’ creation.
Still, because in a lot of way each is co-dependent, it’s not unusual to see additive manufacturing and 3D printing intermixed.
FIRST, A NOTE ABOUT 3D PRINTING
Though the technology was pioneered in the 1980’s, the vast breadth of potential applications was only appreciated within this past decade as patents expired, computing technology improved, and various organizations – including NASA -- began to research its value to their operations. Since then, the almost magical capabilities of 3D printers have become widely known.
So what does a 3D printer do?
Short form: A 3D printer creates a desired item incrementally - layer by layer.
Imagine printing a letter or similar document from your computer. The computer sends the code to your regular (2D) printer. The printed words are, of course, flat on the paper. Now imagine refeeding the exact same paper through the exact same printer so that it could print the content of the letter over and over again - one on top of the other. It would essentially ‘layer’ each print on top of the previous. And then you do it again. And again. You would be building ‘upwards’. Imagine the paper was printing with plastic instead of ink. With each layer of print, the words would continue to look the same when viewed from above, but they would also become incrementally taller on the page.
The letter contents would be represented three-dimensionally – height, width and now also depth.
The most common type of 3D printing device currently in use is what is known as a FUSED FILAMENT FABRICATION (FFF) or FDM printer. It functions exactly as it sounds: it deposits molten thermoplastic (or composite) material one layer at a time that fuses together in the desired shape until it is completed.
Thermoplastics are a large group of plastics that are defined by their ability to retain their fundamental physical properties (temperature and chemical resistances, aesthetics, etc.) when melted and allowed to cool. Thermoplastics include Teflon (PTFE), Acrylic, ABS, PVC and nylons. But because of their ability to be melted and formed, they are ideally suited to 3D printing.
FDM printers are also the ones that bear the closest similarity to standard 2D printers. Other methods of 3D printing include:
…and many more!
This incremental layered approach to producing an item is exactly what 3D printing is all about, and it is increasingly pervasive. It is used to create objects smaller than the head of a pin, but also to build houses, car and aircraft components — even castles and bridges!
There are a great number of mechanical and design advantages to 3D printing including the creation of composite parts, enhanced design complexity, and waste reduction.
Breaking down the AM process
If 3D printing presents an almost revolutionary way to create items, it shouldn’t be surprising that the process of designing the items to be printed can be equally revolutionary since it allows a production latitude that has being unavailable prior. The bracket to the right is an excellent example of redesigning a component for similar use, but reduced cost and waste.
While users can always choose to send a file straight to a device and let the device use default print settings, it is usually preferable to include a middle step, rendering and slicing, for a three-step process:
CONCEPTION AND DESIGN
RENDERING AND SLICING
We’ve explained each step below:
1. CONCEPTION AND DESIGN.
The designer’s idea is rendered visually using computer-assisted design (CAD) software. There are a wide number of CAD programs that can create ‘print-compatible’ files with varied levels of complexity, detail and cost.
Entry-level programs like TinkerCAD are a great introduction to design for people who have no modeling experience. These programs are so user-friendly that they are used in elementary schools.
More complex programs like Onshape or Fusion 360 have a learning curve, but allow for greater precision in design -- shaping and texturing, for example.
Some programs are free – including Sketch Up and FreeCAD – while others can be paid for monthly or bought outright.
A number of websites offer downloadable print files. Quality varies.
2. RENDERING AND SLICING.
Step Two in the additive manufacturing process converts the completed computer visualization of the object into a print-compatible file format (typically an .STL or .OBJ file). The computer graphic of the object is then “sliced” and converted into numerical computer code. That code will guide and direct your 3D printer as it creates the physical object.
Slicing software typically allows the user to make a variety of selections that will govern the material used, strength, and quality of the end item.
Choosing correct settings can be tricky to master as each setting will influence quality of the end product. Learners can use default settings recommended by device software, but if finer detail, higher speed, greater strength, supports, or greater adhesion is required, precise slicer settings will be very important.
3. PRODUCTION (PRINTING). Third, the sliced file is sent directly to the 3D printer. The code in that file now directs the 3D printer to physically construct the item layer by layer in accordance with the settings and material you have pre-selected.
Note how streamlined this process is!
‘Direct-to-Device’ production is one of the most powerful aspects of additive manufacturing. The designer can create and immediately upload a file him or herself. There is no down-time and no need to involve another party. In addition, the process requires comparatively little ongoing oversight.
The implications are substantial. Here are some of the benefits that can result:
ALLOWANCE FOR GREATER COMPLEXITY
REDUCED ASSEMBLY (LABOR) REQUIREMENTS
REDUCED LEAD TIMES
REDUCED MANUFACTURING SKILL SET
CONTROL OVER INTELLECTUAL PROPERTY
GREATER FLEXIBILITY TO CUSTOMIZE
REDUCED INVENTORY RELIANCE
NETWORKED DIGITAL PRODUCTION AND INVENTORY
HOW IS THIS DIFFERENT FROM CONVENTIONAL MANUFACTURING?
One of the great artists of the Renaissance, Michelangelo, is reputed to have said:
“Every block of stone has a statue inside it and it is the task of the sculptor to discover it.”
Conventional forms of production are likewise largely “subtractive”. The designer starts with a raw material and pares it down until left with the desired item. Of course this is true with sculpting, but it is also true of other conventional production processes. For example, furniture-making requires trees. Once harvested, those trees will be delimbed, debarked, sawed and resawed, planed. Before the carpenter ever begins to put a chair together, that wood has already gone through a series of ‘subtractive’ processes. Even with the help of the many machines involved, we have a laborious, time-consuming and expensive process.
Methods of subtractive manufacturing include casting, molding, joining, machining, and forming.
The video link to the left offers a look at a Computer Numerical Control (CNC) milling machine. It shows the CNC mill in various stages of milling different items. Notice that during all stages, the milling machine is subtracting filings or shavings from the stock material. A lot of waste is created.
Who wins in this match-up?
You might expect we are going to tell you that the winner is additive manufacturing?
Not necessarily. Each has advantages.
Let’s have a look at both processes. We’ll compare additive manufacturing with more traditional forms of production in a real-life contest and reach a better appreciation for the circumstances where each is more effective.
CASE STUDY ROUND ONE - THE SIMPLE GEAR
Let’s assume your organization needs to produce a simple gear to replace an existing one. Perhaps you need one like this one to the left. This is a 45-tooth gear and it measures 8mm x 6.25mm (3.15” x 0.25”). And it cannot be purchased outright from a supplier.
CONTESTANT: Conventional Manufacturing
You could ask a conventional manufacturer to reproduce the gear for you. This simple gear is too complex to cut out accurately by hand, and the size variables alone make off-the-shelf dies impractical.
They might use laser-cutting to cut a sheet of high-density polyethylene (HDPE) and create your gear. They inform you that there will be a one-time set up fee of $105.00, plus the cost of the plastic ($0.50). They also charge $1.00 per cutting inch. Including the octagonal shape in the center, this will come up to roughly 11 inches, or $11.00. The total cost of one gear using conventional subtractive methods will be $116.50 plus applicable taxes.
Because the setup time for the production of more than one gear will not change much, if you needed two gears, the cost would be $105.00 + (2 x $11.50) = $128.00. Averaged out between two gears your cost will be $64.00 per gear. So the unit cost goes down. For three gears, $46.50. For ten gears, $22.50 per unit. For 100 gears, $12.55 per unit, and so on.
Depending on how many gears you expect to need, a mold might be fabricated in order to further cut costs.
Your gear is a small component, but it does have some finer details, so the estimated cost for a mold would place it at approximately $1,500. However, once the mold is in place your cost, including material, cooling and labor, now drops down to $0.50 per gear. In order to justify the capital cost of the mold over laser-cutting, you will need to produce at minimum 125 to compare with laser cutting. However, if you need 1,500 gears, having a mold produced would be the economical choice. Your unit cost will now be $1.50 -- and less with every gear produced.
Of course costs may vary from supplier to supplier, and from region to region, but the basic principle remains the same. It both cases, the average cost per gear goes down as the number of gears goes up.
CONTESTANT: Additive Manufacturing
You decide to produce this same gear using your 3D printer. Your costs will be very different from traditional manufacturing.
Production of this same gear requires precisely 8.55 grams of material and will take one hour to produce. Perhaps you decide to use HDPE filament which you purchased at a cost of $35/1,000 g, or $0.035/g. Of course as a business-owner you will want to take into account the electricity used and the operating time of the machine into account. You calculate that these operating costs increase your unit cost by an extra $0.30/gram, for a total of $0.335/g, multiplied by 8.55 g of material. Your cost is $2.86 per unit.
Note that the cost for additive manufacturing is flat. It does not reduce with volume unless the producer chooses to discount. If you need 10 gears instead of just the one, it will take 10 hours and the cost will be $2.86 x 10 = $28.60. If you need 100, it will take 100 hours and the cost will be $286.00.
A cost equilibrium is reached between Additive Manufacturing and Conventional Manufacturing when the cost of producing a part using either method is the same.
CASE STUDY ROUND TWO - THE HELICAL GEAR
CONTESTANT: Conventional Manufacturing
For conventional manufacturing methods, an inverse cost relationship exists with regards to the complexity of the item being produced. The more complex the item, the more costly it will be to make.
There are a few different reasons for this, starting with availability of machines to produce simpler items. For example the flat gear above can be cut by a laser cutter or a water jet cutter. In fact, because it is a polymer gear, probably various smaller cutters could work.
What if your organization required a helical gear instead? There are good reasons for such a choice. Helical gears have slanted teeth. They reduce noise and vibration, and are stronger.
However, using conventional methods, helical gears also prove a bit trickier to produce. They cannot simply be cut out of a flat sheet of plastic or nylon with a laser cutter. Instead they must be carefully machined out of a thicker chunk of plastic using special processes such as hobbing or milling. Producing only one gear can be cost-prohibitive -- $500 for machine set-up and charges for machine down-time from other projects are not unusual.
Creation of a mold to allow for mass production of helical gears similarly requires more time and higher capital costs than for our first gear. More attention must be paid to the mold to ensure proper dimensions and uniform cooling time, especially when using polymers.
CONTESTANT: Additive Manufacturing
What about producing a helical gear using additive manufacturing? Well, complexity of the gear really isn’t as big a concern.
The same helical gear can be produced - layer by layer - using the exact same costing method discussed above (material weight x material weight cost).
Again, as with the quantity/cost graph, the complexity/cost bar continues to be relatively flat for additive manufacturing. Occasionally, it can be helpful to print very complex items more slowly. And occasionally, use of temporary support materials is needed with extremely complex designs. However, the complexity of an item often has little bearing on the over-all cost.
Unless your business can justify the cost of a mold, additive manufacturing will offer the cheaper, faster process and the best per-unit production cost. If the item has a complex design? This will be all the more true.
What about your business? Could additive manufacturing improve your production? We’d love to talk to you about that.