How Are Micro-Small Characters Printed on Models?

[maihama eki]

How do manufacturers print the super small characters, numbers, symbols, etc. on models?

 

I am consistently amazed at the small size and relative clarity of the printing.  The are often printed on curved or non-flat surfaces on multiple sides of the model.

 

I grabbed a Tomytec bus that I just received and took a poor photo of the characters on one of the windows.  This window is about 8 x 8 mm.  The characters are only about 250 um high.

 

[kvp]

It's called pad printing and it's a pretty simple process:

-design the graphics

-print it onto transparent film

-light it to a photsensitive metal plate (and shrink it in the process)

-develop and etch the plate to generate a printing stamp

-ink the plate

-take the ink with a rubber pad

-stamp the pad onto the model to transfer the ink

 

The last 3 steps are the mass production part, repeated for each color. Curved surfaces could be done with an appropiately curved rubber pad. The resolution is just a question of ink particle size as the photo etching technology is the same that is used for computer chips and could produce really tiny transistors nowdays.

 

ps: Actually there is a newer, slightly faster, but less mass production friendly way, UV cured 3D inkjet printing. With this technology, the paint is sprayed directly onto the model from the 3D inkjet heads and cured with UV light. From the larger model makers at least Fleischmann used this technology on some smaller batches, but the resolution is still far away from pad printing. On the other hand, 3D inkjet printing allows custom text, like different car numbers for each car to be produced without any added cost.

[maihama eki]

Thank you for the explanation.

 

Maybe a simple process, but not really something the home hobbyist is likely to do.

[kvp]

1 hour ago, maihama eki said:

Thank you for the explanation.

Maybe a simple process, but not really something the home hobbyist is likely to do.

Yes, getting a 3D inket is an option though as it doesn't need the photo lab and there is no tooling cost. There are hobbyst grade 3D inket heads for hobby CNC machines, so if someone already has a changable head (cnc/printer/laser) machine at home, it's possible to add a 3D inkjet head for printing directly onto the models. Lower resolution, but it even allows color photos without the complexity of dithering, matching and aligning multiple color passes.