You have already pointed out that 'Normal Conversation' becomes loud.
Therefore, it is not deliberate.
You need to find identify and understand why the noise is there. Is it conversation that is required as a part of the work?
Is it unnecessary conversation and chitchat?
Does it in any way distract from work or cause safety or quality issues?
If it does, then you need to initiate a training that will explain the problem to the workers and show them why they should not talk during their work. You should not initiate disciplinary action when you have not even tried to solve the problem.
If the conversation is a part of the normal discussion at work, or required communication at work, then you need to see who they need to communicate and find ways to separate them or put sound barriers between them. One way is HDPE sheets and curtains. Other way probably is using air curtains. This needs to be studied properly by safety committee or by an industrial engineer. We here on the forum will only be making wild guess work, which is bad if you re taking a decision on that basis.