Water knife: water knife, that is, using water as a knife, this technology originated in the United States. Used in aerospace military industry. It is favored because cold cutting will not change the physical and chemical properties of materials. With the continuous improvement of technology, pomegranate sand is mixed into high-pressure water, which greatly improves the cutting speed and thickness of water jet. Now water knives have been widely used in ceramics, stone, glass, metal, composite materials and many other industries. In China, the maximum pressure of water jet has reached 420mpa. Some technologically advanced companies have perfected 3-axis and 4-axis water knives, and 5-axis water knives are becoming more and more mature. As a new technology and new product, water jet has not been paid attention to by the media because it is a mechanical product, not as strong as the technical mystery and sense of science and technology of electronic products. Until 20 1 1, water jet expert Ji Xingang creatively found another way to make water jet smaller and safer, which changed the situation that water jet could not be used in dangerous areas.