There are many methods. Here are some methods for you. You can search for manufacturers online using the keywords I provided:

1. Silk screen overprinting. Transition colors can also be produced, not just limited to the printing of color blocks, color separation plate making, and then overprinting.

2. Tablet photo. There are many flatbed photo machines on the market now, also called flatbed printers, which can print directly on metal. You can inquire about advertising companies and printing plants nearby that have such equipment.

3. Iron printing equipment. Many cities have iron printing equipment for printing metal packaging. Can be printed directly on metal sheets. However, this method may not be suitable if the quantity is small. It is more cost-effective to choose the above two methods.

Of course, the transfer method can be chosen. Considering the operational feasibility and quality, we do not recommend it. Hope the above answers are helpful to you.