Inside an ink cartridge factory

There are some fascinating industrial processes behind the technology we use every day. This week, I took the opportunity to tour HP's inkjet cartridge factory near Dublin in Ireland, which manufactures most of the integrated (combined ink tank and print head) HP ink cartridges used in Europe. Here's how it works.


Zone 1

Zone 1 is the first part of the "dry loop", where the ink cartridges are assembled before filling. Here we see foam-packed tri-colour cartridges on their way to having their lids fitted.
The empty ink cartridge bodies move along an automated production line to be packed with a dense foam, manufacturered by a third party. The foam will later hold the ink, a little like the wadding that holds the fuel in in a Zippo lighter. The foam's specific density means that the ink reaches the print head at the correct rate though capillary action.

Black cartridges have just a single chamber into which a piece of foam is forced. Tri-colour cartridges have three chambers containing three separate pieces of foam. Before the foam goes in, a filter is inserted. This sits between the foam and the print head to prevent large solid particles from getting through and clogging the head. Tri-colour cartridges have additional seals to prevent the different colours bleeding into each other from adjacent chambers.

A 2D matrix is laser etched on to the cartridge so it can be tracked through every stage of the production process. Finally, a lid is joined to each cartridge. The lids contain either one (for black cartridges) or three (for tri-colour cartridges) filling valves which will later be used to inject the ink. The lid is attached using an ultra-sonic welding process. A lid is placed on a cartridge and held in position. A high-frequency vibration is then applied to the interface between the two parts, exciting the molecules at the join until they melt together.


Zone 2
The cartridge bodies are conveyed to Zone 2, the second part of the dry loop, the print head is joined to the cartridge. The processes carried out here are slower and more delicate than those in Zone 1, so HP's factory has two separate Zone 2 stations, which each run at half the speed of Zone 1, to handle its output.

The only function of this zone is to attach the print head, which shoots the ink out on to the page, and the flex circuit that allows the printer to communicate with the cartridge. These are manufactured in a clean room elsewhere in the same factory complex. Each print head contains microscopic channels that allow ink to flow from the cartridge to a reservoir and from there into the print head's ink firing chamber. The surface of the print head is covered by a palladium orifice sheet which contains the tiny holes through which ink is fired on to the page.

In Zone 2, each cartridge is coated with adhesive in the area where the print head and flex are to be located. The print head and flex, which are already joined together, are adhered to the cartridge. The alignment of the head and of the contacts on each flex are checked using a camera by an automated system. This ensures that they are correctly positioned to within a few microns.


Zone 3
In Zone 3, also called the wet loop, fully assembled cartridges are fed into a machine that can fill four cartridges every six seconds. A vacuum is then applied to remove the air from the filled cartridges. This forces the ink into position at the bottom of the cartridge and helps to keep it fresh. As the ink in the cartridge is used, the cartridge will take on air through the filling valves. A label is applied over the valves. Grooves in the plastic lid are designed to optimise the passage of air into the cartridge when required.

Each cartridge is sent through a printer which prints a test pattern to ensure that everything functions correctly. The print head is then cleaned and sealed with a strip of tape before being sent to packaging.


Packaging and Testing

A print head is checked for microscopic imperfections.
The final stage of the production line is a packaging machine that puts each cartridge into the foil wrapper that is familiar to HP inkjet users across the world. The cartridges are later shipped to an external factory to be boxed.

At every stage of the assembly process, the cartridges go through an electrical contact test to ensure their functionality. At the end, a random sampling of cartridges is taken to be fully checked by humans, rather than machines.

These randomly selected cartridges (also called "pens" in HP's internal terminology) are tested to see if they can withstand being bumped around during shipping and handling, have their functionality tested in high altitude conditions, or are simply printed to end of life (EOL) - the point at which they run out. An autopsy area means that spent and failed cartridges can be dismantled and checked.

Print heads are tested in front of slow-motion micro video equipment which allows the directionality and dynamics of their ink release system to be checked at a microscopic level.

Once a batch of cartriges has been packaged, checked and confirmed as functional, they'll soon be boxed and on their way to shops across Europe. Within two years - the cartridges carry an expiry date - almost all will have found use in an HP printer.