Apple is the world's foremost manufacturer of goods. At one time, this statement had to be caged and qualified with modifiers such as "consumer goods" or "electronic goods," but last quarter, Apple shipped a Boeing 787's weight worth of iPhones every 24 hours. When we add the rest of the product line to the mix, it becomes clear that Apple's supply chain is one of the largest scale production organizations in the world. 

While Boeing is happy to provide tours of their Everett, WA facility, Apple continues to operate with Willy Wonka levels of secrecy. In the manufacturing world, we hear rumors of entire German CNC mill factories being built to supply Apple exclusively, or even occasionally hear that one of our supplier's process experts has been "disappeared" to move to Cupertino or Shenzhen. While we all are massively impressed with the scale of Apple's operations, there is constant intrigue as to exactly how they pull it all off with the level of fit, finish and precision obvious to anyone who has examined their hardware.

This walkthrough is a detailed narration of what we see in Apple's Watch Craftsmanship videos. Of course, we only get to see a mere fraction of the process; I've tried to provide plausible explanations for the likely steps taking place between the processes shown on film, but these are assumptions and are included only to provide a more satisfying and complete narration.

Gold

Gold has always been the wrong metal to make a watch out of; its low yield strength and softness is incompatible with the tremendous amount of abuse an object worn on the wrist receives on a day-to-day basis.  Driven by a history of desire going back millennia, alchemists and metallurgists have alloyed pure gold with nearly every combination of metals on the periodic table in order to overcome these limitations. The standards for 18 karat gold allow for a tremendous amount of leeway in producing innovative alloys (which may be comprised of anything, as long as the final product contains 75%-79.99% of pure gold by weight), and major producers of gold goods have used that flexibility to each create proprietary formulations in an attempt to gain competitive advantage. Rolex built an in-house foundry at their Plan-les-Ouates complex in Geneva to produce all of their precious metals. Hublot has trumpeted their composite ceramic "Magic Gold" as being significantly more durable than anything else available. Recently, Apple patents were uncovered detailing a Metal Matrix Composite process to produce 18kt standard compliance gold with a significant weight reduction and durability increase.

For the Watch Edition however, Apple appears to have eschewed any revolutionary alchemy and instead, applied an innovative work hardening process to create gold that is (claimed to be) significantly harder than the typical 18kt used by other watchmakers. The first portion of the Gold video is carried by the beautiful alloying process and Ive's meditative voice; at the 1m15s mark however, things begin to get interesting.

Work hardening is one of those counterintuitive industrial processes where we take an undesirable aspect of a material and Judo it into a significant improvement. As the gold is cast into ingots, the crystalline lattice structure of the alloy is nearly perfectly aligned. What Apple is about to do is introduce - in a highly controlled and precise manner - defects in that lattice (known in the art as "dislocations"). The effect is to harden the material by giving future impact events or stresses  a limited number of spots on the lattice to start (technical term: nucleate), and if they do start, very little room to propagate. 

You can experiment with this yourself using a metal paperclip- start bending the paperclip back and forth and you'll notice it gets ever so slightly more difficult to bend as you repeat the process. Eventually, you will create so many dislocations in the metal that the part will fracture into two pieces, but for a short period, you will have work hardened that section to a point where some potentially desirable material changes would have taken place. Add a tremendous amount of precision, equipment capable of applying thousands of tonnes of force and replace the paperclip with a US$50k ingot of gold alloy and you're working at Apple.

The process Apple shows begins with the raw cast ingots getting machined with an index cutter face mill to a very precise thickness. Casting is a process that doesn't offer the level of precision Apple needs for the next step and this machining allows them to control the dimensions of the ingot to within 0.01mm.  This level of precision is necessary because any variations in the surface of the ingot would create variations in the hardness across the final part.

The actual squeeze work hardening process likely takes a number of passes through the roller press die Apple shows in the single shot above. It's also sort of boring as it's just a chunk of dull golden metal passing back and forth between two rollers, flattening a few microns with each pass. When the process is complete however, Apple is left with a flattened ingot of gold alloy that has a controlled level of hardness and a precise thickness.

The video skips what are most likely a few steps to show us the flattened ingots having been processed into blanks that are just now starting to look like Apple Watch cases. We get a few shots of the case blanks and -interestingly- we see freshly machined surface that change. In the first shot of the blanks, the flats and sides have tool marks and sharp edges, but as we move the the ultrasonic density scanner, those edges have been very precisely chamfered off into bevels. This strikes me as odd; why remove the blank from a CNC mill to do the bulk of machining only to put it into another mill to chamfer the edges? In my mind, it's more likely Apple made a slight process change at the factory while the film crews were shooting.

In the above shot, blanks are placed in an immersion ultrasonic tester. What Apple is looking for is the presence of voids or density variances within the structure of the blank that, under stress, could lead to part failure or surface defects as material is removed in further machining processes. This level of inspection is, to put it mildly, fastidious beyond where most other companies would go (save Rolex). Immersion ultrasonic inspection is typically reserved for highly stressed medical implants and rotating components inside of aircraft engines; not only does this step take time, it also is typically performed by custom built machines of tremendous expense.

With very precise blanks in hand, we move to a CNC mill. In the above shot, we see the Watch held via the center hole while a custom shaped end mill creates the signature full-radius edges. Given that this operation is taking place on high column work holding fixture, I suspect this is a 5 axis mill and further steps in this operation will cut the outside pockets for the button, digital crown and speaker/microphone port on the side of the case.

Apple dispenses with further machining shots of the case to bring us a detail shot of the Digital Crown having the precise, grippy serrations cut. It's hard to tell given the shot, but the crown appears to have already gone through the polishing process; polishing the crown after the serrations are cut would bork up the precise edges and Apple is relying on the sharpness of that edge to make the Digital Crown useable with the tip of one finger. The cutter itself appears to be a custom profile key-set cutter with a meaty center around the arbor to increase rigidity and tool-life.

Apple chooses not to show us the manufacturing of the clasp components, processes that I think would be (in some respects) more interesting than how the watch case is made. Given the complex surfaces of the Modern buckle, this might be the first example of Apple using 3D surface tollbooth in order to machine a component (all Apple products have been created through the very skillful use of relatively simple, precise prismatic 2.5D tool path, with any complex curves being created from stampings).

The manufacturing portion of the Gold video ends with the case being polished by hand. As is shown in other Apple manufacturing videos, the company is expert in using automated polishing techniques across their entire product range, so it's difficult to say if the Edition models are polished fully by hand or if the hand work is simply a final buffing more valuable for letting skilled eyes very closely inspect the final product.

Stainless Steel

Stainless steel is the material used to produce the vast majority of quality watches in the world. Much like with the 18kt gold alloy, Apple is playing it safe and not using some highly proprietary alloy or cutting edge process (such as their tie-up with Liquidmetal). Instead, Apple is working within the confines of the ASM 316L standard - a material more commonly (and incorrectly) known as "Surgical Grade Stainless." Buzzwords aside, 316L stainless is often used in the production of medical instruments and implants, as well as food processing equipment. The reason is simple; 316L does a good job of resisting the seepage of metal particles from the finished component. This makes it the most common stainless alloy used in the watch industry for a similar reason; nickel allergies. Watch manufacturers have decades of experience working with stainless steel to narrow its effects on those with nickel allergy and companies such as Rolex and Omega have tuned their alloys and processes to the point where only the most acute sufferers would notice even mild effects. I suspect a large focus of Apple's metallurgy and process design was on the nickel allergy issue.

Like the Gold video, Stainless opens up with numerous beauty shots directly from the foundry floor as the molten 316L is processed into what foundries call "sticks." The molten metal passes out of the bottom of a crucible (typically located on the top floor of a multi-story foundry) through a valve and into a series of shaping steps that form each stick as the metal's viscosity rises in the transformation back into a solid. This process is very precisely controlled in order to properly form the final stick's grain structure and hardness. Apple is producing the watches in enough volume that they can easily specify the exact alloy composition of the entire crucible of material, as well as define the precise temper, hardness and stick dimensions.

Approximate Render of Watch Forging Billet

Apple chooses to not show what is likely the most unique and important step in the production of the Watch; cold forging. In production forging, a blank of metal is placed between two extraordinarily hard steel dies that have the bottom and top halves formed into open faced molds. The hammer - a piece of capital equipment roughly the size of a house laid on it's side - slams the dies closed with force measured in tens of thousands of tonnes. Under such pressure, the metal reaches a state called "plastic deformation" and literally bends, compresses and flows into the shaped cavities of the die. For complex, or high-precision forging, multiple dies with successively deeper cavities are used to gradually tease the material into the desired shape.

C*Blade.com Cast v. Machined v. Forging comparison.

Forging produces what's called a "net shape" part; the process is unable to create precision holes, pockets, threads and other features that will require a trip to the CNC mills. What forging does do is create parts of exceptional strength. In the textbook graphic above, we see an illustration of the grain structure for a cast, machined and forged component. We can see the forged variant has an intact grain lattice that is flowing and curving to meet the final shape of the part, leading to tremendous strength. This graphic succinctly illustrates why cold forging is the de-facto standard for creating the strongest metal components possible.

Though we skip the cold forging process (it likely contains a few very proprietary tricks), we start the machining process with 3 raw forgings on custom 5 axis fixtures. Forging is not an extremely high precision process, so one of the challenges in working with a forging is that you're left with limited datum surfaces - something on the part with an accurate surface you can use as a reference for all the precision processes to follow. We can see the part on the right has had some excess forging material machined into a square feature on top of the watch, leading me to think the part will get turned over and held in a fixture by that lip.

We see a few shots of the case in a 5 Axis milling setup with custom work holding, milling out the internal features at odd angles. In this shot, our part is flipped yet again and is being presented to the tool so the pocket for the Digital Crown and button can be milled. Machinists should note that Apple isn't cutting the side button slot with a full-width cutter - the smaller end mill is slower, but produces a far better surface finish by avoiding chip thinning fluctuations.

The machining shots are finished up with one of Apple's favorite processes to show - Coordinate Measuring Machine probing. A CMM machine is sort of similar to a CNC mill in respects to how it moves (X, Y, Z), but are typically built on a granite frame and with air bearings. The "tool" is a ruby tipped touch probe that is programmed to take hyper accurate data point samples across the part and compare them to the original CAD model. They automatically spit out a report that can pass/fail the part, track dimensional changes over a production run and (in the most sophisticated shops) actually feed information back to the milling machines and lathes to compensate for variances.

Second to the CMM probing, Apple's video team also has a serious thing for Apple's automated polishing processes; understandable given that Apple has invested a significant amount of time and money climbing the polishing learning curve. One of the challenges of polishing is that Apple wants to keep crisp edges crisp, and buffing wheels tend to reach into sharp edges. Not only does this munge up and soften the edge in an undesirable way, it also rips the soft buffing wheel to shreds. Looking at this shot, we see Apple has custom molded gray polymer plugs for the lug channels, the strap release button slots and (unseen) the digital crown and side button. This allows the polishing process to have complete access to the case surfaces, without interrupting the desirable crisp edges.

Our case now finished, our video takes a dark turn to quickly show the black variants and mention the "brilliant, diamond like carbon layer." Running with the knowledge that Apple tends to be very precise with their language, the implication is that the process they are using is a Tungsten DLC coating produced in a vapor deposition process. This is a very tough, very thin layer of tungsten that is bonded to the surface of the part in a vacuum chamber, and is the standard blackening process for the vast majority of high-end watches, knives and some mill cutting tools. TDLC has a reputation for being extraordinarily durable, though it has been somewhat surpassed by other, more involved, treatments at this stage.

Finally, we get some quick shots of parts for the Link bracelet and a Milanese band being made. The quick shot of the Milanese getting woven was one of the more interesting as this is a process I've never even begun to explore. I'm very curious as to know if the wire is getting twisted as it enters the weaving tool, or if the wire is pre-twisted and the tool is simply guiding it into position. Given the final polish on the Milanese band, Apple must be using an electropolishing step to clean up the raw wire.

Aluminum

It would be hard to argue that Apple isn't the world's foremost expert on the volume production of high-precision, high-finish aluminum components.  It is with no surprise that Apple is using the basic iPhone production blueprint, with some new tricks we haven't seen before, to create the high-volume Sport variant of the Watch.

From the original unibody MacBooks, Apple has been using aluminum in enough volume to dictate alloys of their own specification and held to their exacting tolerances. My belief is that they aren't really attempting to create a "better" aluminum alloy — the commercial industry has spent decades creating standard alloys that are optimized for common desirable properties - Apple likely optimizes for their specific manufacturing process. With the Watch, Apple has upgraded from 6000 series alloy compositions (using magnesium and silicon) to a custom 7000 series alloy that relies on zinc. The closest commercial equivalents would be the 6061 aluminum alloy (the world's most common manufacturing material) and 7075 aluminum - the comparison between the two tracks very precisely with Jonny Ive's language about having "custom designed a new alloy that it 60% stronger, but just as light."

Let us take a moment to revel in what must be the most stunning video of the smelting process ever committed to film. We see a forklift drive past the crucible furnace, and molten aluminum pouring beautifully into an open, multi cavity mold to produce cylindrical ingots. From there, Ive uses some marketing speak to outline the process of tempering - a heating and cooling control process that aligns the molecular structure of the metal in the proper orientation.

Apple has always leveraged the extrusion process to create machined components of staggering complexity, and they have always done their best work on the small parts that often go unappreciated (see: the Apple TV remote and Magic Trackpad). The Sport Watch is no different - we see two sticks of aluminum being squeezed out of the extruder with the long radius edges of the case already formed, but (and this is impressive) a nearly impeccable surface finish. Cut from the extruded stick, we see a Sport Watch blank take a quick trip back under the remorseless ruby tipped probe of a CMM machine and it's off to CNC milling.

Besides slightly modified work holding (to hold the extruded blank vice the forged blank) and slightly different cutting tools, the machining process for all 3 materials of the Watch are roughly the same. We do get to see one process that should have any manufacturing nerd a bit hot-n-bothered:

Another process Apple leads the world at is laser machining. We'll see it twice in the Aluminum video, but the above picture is extraordinarily impressive. Machining tends to leave a little lip on the edge of metal, known as a burr. Often just 0.05mm thick, burrs are razor sharp and are the bane of a machinists existence. They can be milled off in the machine using very tiny tools, or removed by hand, or knocked down in tumbling, sanding or other processes - all of which are present tradeoffs.

Apple is doing something utterly unique in this 5 seconds of video - they are using a laser to clean up any burrs or finishing defects from machining. You can see the laser quickly outline the lip of an inside pocket, and come in for a more intense second pass on the floor of that pocket. I would consider this (quite long) blog post a success if the engineer or designer who thought that trick up reads this and knows that this is an astonishingly brilliant trick they cooked up. Bravo!

Though I design aluminum parts, I long ago gave up even attempting to craft them to Apple's finishing standards. No company in the world is finishing and anodizing to Apple's level and part of their secret is every perfectly bead blasted Apple surface starts off as a perfectly polished surface. To compete with Apple, one either needs to invest in equipment with prices equivalent to a CNC machine (6 axis robotic arms with custom end actuators - i.e. hands - to hold your parts), or pay staggering sums of money to have an expert hand polish your parts and accept the fact that the best you will ever get is a reject rate of 10%.

Here we see the Sport Watch fixed in a polishing assembly in a similar way to the Stainless Watch from earlier. Both the lugs have custom plugs to protect the edges, but unlike the Stainless, we can see the side button and digital crown features are unprotected. The reason is simple- the radius on this edge of the Sport are never machined as they get produced perfectly in the extrusion process, again speaking very high volumes of Apple's core ability to extrude aluminum to the world's highest standards.

Now, Apple literally blasts their perfectly polished surface in an automated glass bead blast line. The rotating, multi-aperture nozzle heads are designed to hit every surface of the case from every possible angle, leaving a perfectly even texture across each watch.

Formed, machined, laser deburred, polished and bead blasted, the Sport Watches are placed in custom racks for the anodizing process. If you will recall from earlier, some industrial processes are counterintuitive insofar as they take an undesirable issue with a material and flip it into a positive. Anodizing is another one of these processes. Just as steel parts can react with air to oxidize (creating rust), aluminum also oxidizes to form an uneven, chalky white film. The anodizing process uses electricity and chemistry to create a thick, precise layer of this aluminum oxide on the surface of the part.

While rust on steel is a terrible and corrosive thing, oxidized aluminum actually brings tremendous benefits to the table as it is essentially a very hard ceramic. A controlled, even layer of this oxide actually makes a finished aluminum part very durable and resistant to scratches. Furthermore, that layer builds up in a convenient honeycomb structure that (for a short period of time) can be coaxed into holding colored dyes in nearly any shade imaginable.  

Again, Apple is likely anodizing more metal than any other organization on the planet, and we get a glimpse of a highly optimized set of racks with Sport cases in it. Most anodizing racks are general purpose affairs with clips or hooks that both hold the part and make the positive electrical contact. Apple is using custom formed and plastic dipped racks that very (very) densely hold parts. It's yet another detail that anyone in manufacturing is likely to look at and think "Wow, I wish we had the volume/budget to pull that trick off."

Before leaving the factory floor to go back to flying Watch land (it's right off of Jonny's white room), Apple gives us a peak at one final bit of manufacturing trickery. Where the Steel and Gold Digital Crowns receive their serrations on milling lathes, the Sport's serrations are laser machined. One notes that the crown appears to be bead blasted, though it's hard to say if it has been anodized yet or if that is the final step. An index chuck spins the crown so each cut is perfectly tangent to the axis of the laser. I suspect both the gold and stainless crowns are machined because the reflectivity of the polished surface wouldn't be compatible with the laser.

Some Final Notes

One of the more interesting things one notes in the videos is that the internal structure of the gold Edition models seems to include a pocket feature not present on the Watch or Sport. It is hard to say if this exists to stiffen the Edition or if Apple is removing a bit of the dense gold alloy in order to reduce the weight of these models.

There have also been rumors of a 6 pin port hidden under the top strap lug channel, used for burn in and diagnostics. It remains to be seen if this port will exist on the shipping Watches, or if Apple will delete these ports on production units. In the Aluminum video, we see finished Sport watches laid out with the ports clearly shown, but it is just as likely that these videos were shot months ago during production line setup with prototype watches.

I do have a theory that the port may remain on the Sport models because I suspect the "movement" on the Sport is installed in the case permanently with adhesive. As such, it stands to reason Apple might maintain a diagnostics capability to troubleshoot issues at the Apple Store before simply trashing the defective unit and handing the customer a new one. With the Watch and Edition lines, it would make more sense to simply pull the movement out and replace it (something that can be quite easily performed with most mechanical watches; it's taking the movement itself apart that requires the skill of a watchmaker).

Jonny Ive often speaks of care. It is an odd word to use as it doesn't imply the traditional notion of "craftsmanship" in the classic, handmade sense. Nor does it imply quality or precision in the way a Japanese car manufacturer or German machine tool maker would. "Care" implies a respect for the raw materials and end result, with little concern about what it takes to link those two ends of the production chain together, and we see that highlighted with the Watch. Apple could very easily have forgone forging to create stainless steel cases, just like everyone else. Hardening gold alloy with cold working could have been eliminated, putting them on par with the rest of the industry. Nobody will see or feel the inside pocket for the microphone on the Sport, yet it has been laser finished to perfection.

I see these videos and I see a process that could only have been created by a team looking to execute on a level far beyond what was necessary or what will be noticed. This isn't a supply chain, it is a ritual Apple is performing to bring themselves up to the standards necessary to compete against companies with centuries of experience.