Additive vs. Subtractive

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. 


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.


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. 

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