The department head should show the qualities such as listening skills, better understanding, maturity and leadership too. First, he should give a chance to each of them to explain the pros and cons of the Machines supplied by american vendor as well as of swissmade ones.
The Department head listens to the points put-up by both of the person. Then, he should make a cost and productivity analysis based on the data provided by both of the team leaders. Moreover, he should also research himself about the American supplied machines and Swissmade machines unbaised.
Then, definitely he should be reach at a point where he can decide between the one between American supplied machines and Swiss made machines. But by chance he can't reach at a decision, he should show his research and analysis to both the team leaders. The team leaders should able to decide the choice based on the head's analysis on both the machines.