That all depends on how hard you want the finished product. Generally
any work hardening is just incidental to to the burnishing/polishing.
Vibratory tumblers aren’t typically used to work harden items, but if
an item were left in for an extended period of time it might get
harder than if left in for a hour or less. I don’t know of any
diffinitive studies done to determine then amount of hardening done
in a vibratory tumbler.
2. I live in Sigapore now, where electric current is 220V, but I
plan to come back to the US in a couple of years. Is it possible to
use tumbler and ultrasonic cleaner made for 110V with 220V (with a
transformer/adaptor perhaps)? I don't want to burn expensive
Step down transformers (220 to 110) are generally available for use
with incompatible voltages. Just be sure the current (amps) carrying
ability of the transformer is great enough to supply the device
connected to it.
The other consideration is the frequency of the power. The US uses 60
cycle power. Many other countries use 50 cycle power. A device (motors
etc) designed to run on 60 cycle power may run slower & warmer on 50
Without knowing the type of power supply used in an electronic
device, it’s impossible to determine what effect 50 cycle power will
have. It’s best to ask the manufacturer if 60 cycle electronic
equipment can be used with 50 cycle power.