Water jet cutters or waterjets may be still alien to many of us. To me it wasn't known until a few weeks ago, when a telly series on cutting metal and other substances amazed me. Along with high-end cutting machines with razor-sharp cutting technologies, it surprised me when they showed something as liquid as water being used to cut the hardest of substances. Now this is some technology and after this I truly believed in the capacities of engineering and the human mind.
Using water pressure to cut substances, was roughly practiced during the mid 1800's. But the concrete concept of using water pressure as a cutting tool was discovered by Dr. Norman Franz, who was an engineer in forestry, in the year 1950. This was founded as an attempt to find new options to cut trees. He studied the technology of 'ultra high water pressure' (UHP) to be used as a cutting tool. Later to cut high-end solid substances, abrasives were added with the stream of water, which would let them cut even metals, with ease. With advancements today, water jet cutters have been used in many sectors for cutting, drilling and milling. With its benefits being helpful in the industrial sector, a little insight into its work mechanism will be interesting.
Working of a Water Jet Cutter
Waterjet is a tool that uses a high water pressure to erode material. The basic concept of this is derived from nature itself. The natural flow of water erodes rock and soil. So the only difference here is that extreme pressure and acceleration is applied to water. With more research and study on this concept, many types of water jet cutters have come up. Some of the most common ones are:
Pure Water Jet
These use only a super sonic stream of water that erodes the surface and enables cutting. It is most commonly used for cutting soft material, or for material with cracked or rough surfaces. Materials like plastic, wood and aluminum can be cut with pure water jets.
Abrasive Water Jet
In abrasive water jets, along with water there are tiny particles of abrasive mixtures. Some cutters use water with abrasives directly before applying the pressure, while some abrasive cutters have a procedure that mixes particles as the pressurized stream of water escapes the nozzle for cutting. It is the abrasive particles that cut the material, through water pressure. This enables to cut through even hard surfaces like steel and granite.
Water jet cutter has a simple design and mechanism. Let us know how it works.
- In a normal abrasive water jet cutter, a high pressure water pump is connected to the cutter. The pressure in these pumps is very high. It can be anything between 276 MPa to 600 MPa ( Pa is the SI unit for pressure. MPa is an abbreviation of Megapascal unit for pressure. 1 Megapascal = 1,000,000 Pascals).
- Here the water travels through the nozzle and is mixed with the abrasive material like aluminum oxide or garnet. It also has a mixture of other additives and grit.
- The water flows to an extremely narrow nozzle with ultra high pressure. The acceleration and pressure is maintained due to this narrow exit.
- Some water jets come with an orifice (a small hole) of a precious stone. The orifice can have a diameter of 0.010" to 0.015". This gives the water stream intense pressure and acceleration.
- The stream of water that exits this nozzle has a speed of about 900 miles per hour. The distance in between the surface of the material and the nozzle is 3.175mm. This high speed and thin stream of water and abrasive mixture impacts the surface of the material to be cut.
This is the simple mechanism of a water jet cutter. More advanced cutters may have complex techniques. Using a waterjet is a heat free and damage free operation. It cuts almost anything, except for tempered glass and a few other materials. This enables hassle free and finished cutting without harming the materials' inherent structure. None of the properties of the material are affected as there is no use or exchange of heat in this process. It takes less time and energy and is cost-effective. These cutters can make deep cuts of even up to 30 cm.
With so many advantages, waterjets have become the next thing in engineering and cutting technologies. We just learned how a water jet cutter works. I am sure it has left you with more reverence to water and to the brilliance of what we may call - liquid engineering!