Before we landed in China, Kaspar and Stefan had been working on creating tooling for our cases. The tooling includes the mold that is placed into the injection molding machine which is used to make each frame of the Leverage case.
The tooling consists of extremely hard stainless steel. A lot of pressure and heat is applied to the tool as molten plastic is pushed through. A strong high quality metal is needed for it to withstand the repeated abuse it endures when thousands of units are produced through the mold. Since the steel for the mold is so hard, it takes quite a long time to shape. This also means that mistakes in the tool also take a long time to correct.
Minute details like part lines and plastic flows need to be taken into account during the design of the tool. As molten plastic flows into the mold it begins to cool. If the plastic cools at different speeds it can leave visible flow lines, so gates have to be placed in the right position. The color and strength of the plastic is also affected by the rate at which it cools. Left too long in the injection molding machine, and you can have a case that is no longer the intended color or it becomes extremely brittle. Daily changes in humidity is also a factor that can affect the consistency of the plastic. Many of the injection molding machines have mechanisms to regulate the moisture of the plastic pellets before they are melted down. Luckily for us, the Kaspar and our factory are experts at determining exactly when the pieces need to be pulled out of the machine.
The tooling is the most expensive part of the creation process, not only for the engineering expertise that’s needed, but for the time and labor that is needed to shape a solid piece of hardened steel. Each undercut and mold cavity also adds to the cost and complexity. For our Leverage case, it took about 4 weeks to create the initial tooling, and then a couple weeks of refinement after that. We also had multiple tools for all the separate metal and plastic pieces.
To form the hard steel into the mold, rough shapes are milled out with a computer controlled arm. The bits seen in the photo below cut the solid steel block and quickly remove metal to start the rough form of the mold. The CNC machining takes out large amounts of metal when compared to the next step of electrical discharge machining (EDM).
The intricate detail work is done with EDM which works by applying an electrical charge to the metal. This results in a spark that knocks microscopic pieces off the steel surface. It’s a slow process, but yields the tight tolerances needed to create a properly fitting Leverage iPhone case.
The above video shows EDM in action. Every time that copper colored piece is lowered, it creates a spark that eats away the steel piece on the bottom. You can’t see the spark in this case, but if you look closely, you can see the smoke that emerges every time the two metal elements get close. The liquid you see flowing is a nonconductive oil that washes away the small metal particles.
Here you can see the final tooling in the injection molding machine.
Once the tooling is done, the pieces are inspected for fit. The needed changes are noted and the tooling goes back to EDM where more material is taken away or if necessary, more material is added to the steel. The mold is usually built so that there is a little extra material since it is easier to take away material than to add it.
When the plastic pieces come out of the machine they are attached to sprues. These attachments are from the channels that the liquid plastic is flows through. You might have seen similar pieces if you’ve ever built a scale model kit. The sprues are removed before assembly.
After the first shots are approved, we do a pilot run that is a small fraction of our order. This small scale production is used to reveal any issues that might arise in the various stages from injection molding to packaging and resolve them before large scale production occurs. Once the pipeline is established, scrap rates and quality control guidelines must be established, but that’s probably best left for another post.
Our metal pieces go through a similar process, but instead of getting coated with a soft touch finish, they are hand polished and sent to get plated. Once all the pieces are properly finished, they are assembled and packaged.
The amount of precision required in just the tooling to build a simple iPhone case is pretty astounding when you really break it down. It really gives one an even greater appreciation for how spectacular devices such as the iPhone really are.
For those looking on more details on manufacturing techniques, I found Manufacturing Processes for Designers to be a great starting guide.