If security believes that the "dangerous weapon" was left in your luggage because you forgot about or another innocent reason, it's very likely you will be ticketed, the weapon will be confiscated and you will be on your way. You will leave with a ticket to appear at the district court to face criminal charges, but it could have been a lot worse and a lot more serious.
A criminal misdemeanor in Michigan for a dangerous weapon is still a criminal offense and must be taken seriously. Depending on your past history, your present place in life and your future goals, you case could be a candidate for resolution with the prosecutor at the 34th District Court. Wayne County has a specific prosecutor who only handles DTW Airport cases, and he is a reasonable person to work with.
Once we are able to tell your side of the story, and do a number of proactive steps to display your willingness to learn from this lapse in judgment and irresponsible behavior on your past, a path to resolution becomes likely. Common goals for this type of case may be: avoiding jail, opportunity for dismissal of charges, freedom to reside or travel outside of Michigan if you're not a resident of Michigan or even if you are, but travel for work or pleasure.
This type of case is a difficult situation and the facts and circumstances are stacked against you, but there is a reasonable outcome to work towards, and potential outcomes are a lot more favorable than you believe - it all comes down to your willingness to change the perception of your case from day one.