Kim Jong Un's visit to China was in no way for the North Koreans to be able to procure nuclear weapons. It was a visit to show that the Un regime was serious about eliminating their nuclear weapons program and to ensure Beijing that the Chinese were safe. The visit was one that had huge ramifications throughout the world because they wanted to see that serious dialogue was being conducted with Kim Jong Un and stressing how important it was for his country to stop the weapons testing that they were conducting.
The visit that Kim Jong Un made to Beijing had nothing to do with procuring any nuclear weapons. It all had to do with Kim Jong Un letting China and the international community know that they were serious about bringing the North Korean nuclear weapons program to a permanent end. The meeting was an effort by North Korea and Un to show the international community that they were serious about becoming a more respected member of the international community.