Pad Printing Process: Types of Pad Printing Machines

There are several basic types of pad printing machines. The majority of machines in use around the industry are referred to as vertical machines. These machines can be open or closed. In closed systems doctoring is achieved by either sliding the ink cup back and forth over the cliche' surface, or by sliding the cliche' beneath a stationary ink cup. The illustration below shows a typical vertical machine with an ink cup.


Pressurized Ink CupSome vertical machines can print on any angle using a special pressurized ink cup. Instead of using gravity to flood the cliche', pressurized ink cups use an inflated diaphragm to ensure the image is properly flooded. Pressurized ink cups can be difficult to install and maintain. The illustration to the right shows how a pressurized ink cup works.


Sliding Ink CupClosed vertical machines have also been modified so that their ink cups slide along the X-axis, allowing the printing of wider images. This type of machine is commonly referred to as a "sliding ink cup" machine. The illustration below shows this variation.




By delaying the pad at the end of the print stroke some vertical machines can print 360 degrees around a cylindrical object. The image is transferred as a gear driven nest rolls the part along the length of the pad. The illustration to the right shows how this works.


Without any special pad delays or gear driven nesting fixtures vertical machines can print a maximum of 120 degrees on a cylindrical object. To accomplish this, the pad's set-down point must be top, dead center. The pad is then compressed 60 degrees in each direction from the set-down point.

Horizontal MachineHorizontal pad printers are really just another variation of vertical machines. Horizontal machines flood and doctor like vertical machines, then actuate the pad to print using a horizontal stroke, rather than a vertical one. The illustration on the following page shows a typical horizontal pad printer.

Horizontal machines are typically used only when the part is too large to fit into a vertical machine, or when the image is too large to fit into a pressurized ink cup.

Vertical RotaryRotary pad printing machines are very different from their vertical and horizontal counterparts. Rotary machines have cylindrical cliché’s, usually referred to as "drums". The cliché’s are flooded and doctored as they rotate. The pad also rotates to pick up and transfer the image.

Rotary pad printers can be configured to print vertically or horizontally. Vertical machines can be self-standing for one-up printing, or mounted on automations for tandem or multiple color printing. The illustration below shows a basic vertical rotary design.

Horizontal RotaryHorizontal rotary pad printers are used to print on the vertical sides of parts that are moving along a conveyor. The following illustration is an example of how cassette tapes would be printed on two sides at once using a horizontal rotary pad printer.




Carousel PrinterCarousel machines allow a part to be printed with multiple colors without ever being moved. Ink cups and cliché’s are mounted on a rotary indexing table which turns to locate each individual cliche' under rotating pads for image pickup. The pads then rotate around on a separate carousel, locating over and compressing onto the part to be printed. These machines are typically slower than their multiple color, standard vertical counterparts, and are used only for printing parts too large to fit a standard machine.

Pad printing machines are driven by a number of different means. Most machines are driven by electronically controlled pneumatic systems and are thus referred to as being electro-pneumatic.

Some pneumatic machines are controlled by air-logic instead of electronics. Less expensive than electro-pneumatic machines, these can be more difficult to control, especially if your incoming air pressure isn't well regulated.

Electro-mechanical machines operate under electrical power only. These machines are usually more expensive than electronically controlled pneumatic machines. They can hold tight tolerances, even at high cycle speeds.

Electro-hydraulic machines are the most expensive type. These machines are rare, and are typically used only for large format applications where additional compression is necessary.

Manually operated machines are useful for small format and short run applications. Images are usually limited to less than 16 square inches, and multiple color printing capability is limited. Many manufacturers of manual machines offer trade in allowances when upgrading to semiautomatic equipment.





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