Water Jet Machining: Prinsip, Aplikasi, dan Manfaat
Water Jet Machining (WJM), also known as water jet cutting, is a non-traditional machining process that uses high-velocity jet of water to remove materials from workpiece’s surface.
Water jets are used in this process, which acts as device in form of water saw. Water is rapidly raised and focused on target workpiece in this process.
It is capable of using abrasive particles mixed in water jet materials and some metals at high velocity and pressure. Some processes use no abrasive at all, and these are known as pure water jet machining processes.
This machining process uses water pressure ranging from 200 MPa to 400 MPa. Pressure varies depending on workpiece from which material is to be extracted. This process is similar to natural phenomenon of water erosion.
It is primarily used to remove materials from non-metallic and soft workpieces such as plastics, rubber, and glass. In this process, high-velocity water jet is used to remove materials from workpiece. Basic principles of this process are that water jet’s kinetic energy must be converted into pressure energy in order for it to remove material from workpiece.
When water jet collides with workpiece with kinetic energy, kinetic energy is converted into pressure energy. This pressurized energy will cause stress on workpiece, and as result, tension material will begin to move away from workpiece.
Working Principle of Water Jet Machining
Working principle of water jet machining is based on water erosion. Material is expelled when high-velocity jet of water strikes surface. Soft materials are machined using pure water jets. To cut hard materials, however, some abrasive particles are mixed with water for machining, which is known as AWJM (Abrasive Water Jet Machining).
Parts of Water Jet Machining
Key element in water jet machining (WJM) is a water jet.
1. Reservoir
A water reservoir is used for storing water that will be used during machining process. Reservoir is generally located somewhat above entire setup.
This is done to ensure continuous and uninterrupted flow of water.
2. Hydraulic pump
Hydraulic pump is powered from 30- kilowatt (kW) electric motor and supplies oil at pressures as high as 117 bars in order to drive reciprocating plunger pump termed an intensifier. Hydraulic pump offers complete flexibility for water jet cutting and cleaning applications. It also supports single or multiple cutting stations for increased machining productivity.
3. Hydraulic intensifier
Intensifier accepts water at low pressure (typically 4 bar) and expels it, through accumulator, at higher pressures upto 3000 to 4000 bar. Intensifier converts energy from low-pressure hydraulic fluid into ultrahigh-pressure water. Hydraulic system provides fluid power to reciprocating piston in intensifier center section.
4. Accumulator
Accumulator maintains continuous flow of high-pressure water and eliminates pressure fluctuations. It relies on compressibility of water (12 percent at 3800 bar) in order to maintain uniform discharge pressure and water jet velocity, when intensifier piston changes direction.
5. High pressure tubing
High-pressure tubing transports pressurized water to cutting head. Typical tube diameters are 6 to 14 mm. Equipment allows for flexible movement of cutting head. Cutting action is controlled either manually or through remote-control valve specially designed for this purpose.
6. Nozzle
In water jet machining, it is device that converts pressure energy of water into kinetic energy. Nozzle in this case converts pressure of water jet into high-velocity beam of water jet. To prevent erosion, nozzle tip is made of ruby or diamond.
7. Control valve
This control valve regulates both pressure and flow of water and directs it to flow regulator. Pressure energies will be converted into kinetic energy at this point.
8. Flow regulator
Flow regulator regulates flow of water coming from control valve. After adjusting flow regulator, water will pass through nozzle, converting high pressure of water into high-velocity water.
9. Catcher
Catcher acts as reservoir for collecting machining debris entrained in water jet. Moreover, it reduces noise levels (105 decibels (dB)) associated with reduction in velocity of water jet from Mach 3 to subsonic levels.
Working of Water Jet Machining
First, a pump is used to transfer water at high rate. Water enters intensifier at low pressure and is transferred to accumulator at high pressure of about 3800 bar. Accumulator is device that temporarily stores high-pressure water.
The accumulator’s high-pressure water is transferred to control valve, which controls direction of water. Control valve converts water pressure energy to kinetic energy, converting high-pressure water to high-velocity water, which is then sent to flow regulator.
Flow regulator regulates flow rate of water and directs it to nozzle. Kinetic energy of water increases significantly in nozzle, and nozzle produces high-velocity water.
Water then exits hole and is directed toward workpiece. When water jet reaches workpiece, kinetic energy is converted back to pressure energy, and workpiece is under full pressure.
This pressure from water jet will cause some fractures on part of workpiece where water jet bike is located, as well as some cracks in surface of workpiece, and as water jet continues to strike surface of workpiece for extended period of time. Crack will deepen, and material will be removed from workpiece.
Extracted material is carried away by water. After material is removed, water that cuts material is collected for later use. Parts of chips cut using this process will be present in material in this water. This water will be sent for further purification, or it can be reassembled through entire jet machining process.
Advantages and Disadvantage of Water Jet Machining
Advantages
It has multidirectional cutting capacity.
No heat is produced.
Cuts can be started at any location without need for predrilled holes.
Wetting of workpiece material is minimal.
There is no deflection to rest of workpiece.
Burr produced is minimal.
Tool does not wear and, therefore, does not need sharpening.
Process is environmentally safe.
Hazardous airborne dust contamination and waste disposal problems common when using other cleaning methods are eliminated.
There is multiple head processing. Simple fixturing eliminates costly and complicated tooling, which reduces turnaround time and lowers cost.
Grinding and polishing are eliminated, reducing secondary operation costs.
Narrow kerf allows tight nesting when multiple parts are cut from single blank.
It is ideal for roughing out material for near net shape.
It is ideal for laser reflective materials such as copper and aluminum.
It allows for more accurate cutting of soft material.
It cuts through very thick material such as 383 mm in titanium and 307 mm in Inconel.
Disadvantages / Limitations
It is not suitable for mass production because of high maintenance requirements.
Initial cost is very high.
Very thick materials can’t be machined by this process.
It is used for cutting softer materials, but AWJM CAN cut harder material for limited thickness.
Applications of Water Jet Machining
WJM is used on metals, paper, cloth, leather, rubber, plastics, food, and ceramics. It is versatile and cost-effective cutting process that can be used as alternative to traditional machining methods. It completely eliminates heat-affected zones, toxic fumes, recast layers, work hardening, and thermal stresses.
It is most flexible and effective cleaning solution available for variety of industrial needs. In general cut surface has sandblast appearance. Moreover, harder materials exhibit better edge finish. Typical surface finishes ranges from 1.6 µm root mean square (RMS) to very coarse depending on application.
Tolerances are in range of ±25 µm on thin material. Both produced surface roughness and tolerance depend on machining speed.
Applications of WJM are :-
Water jet machining is used to cut, shape, and streamline operations in variety of industries, including mining, automotive, and aerospace.
Rubber, textiles, plastics, foam, leather, composites, tiles, stone glasses, food, metal/paper, and other materials are commonly mechanized by water jets (WJM or AWJM).
WJM is typically used to cut soft and easily machined materials such as thin sheets and foil, wood, nonferrous metal alloys, textiles, honeycomb, plastics, polymers, leather pieces, frozen, and so on.
AWJM is frequently used to machine materials that are difficult to machine. It is used to machine thick plates made of steel, aluminum, and other commercial materials, reinforced plastics, metal matrix and ceramic matrix composites, layered composites, stone, glass, and so on.
Aside from machining process, high-pressure water jets are used to remove residual stresses in paint removal, surgery, cleaning, peeing, and other applications. Drilling, pocket milling, turning, and reaming can also be done with AWJM.
Some Questions Related to Water Jet Machining
What products are made by water jet cutting?
Waterjet cutting allows businesses to create wide range of parts and products. Interlocking hardware (bolts, gears, etc.), automotive parts, electrical components, big assembly line items, and design prototypes are just few of products they manufacture with water jet cutting. Waterjet cutting can also be used by artists to make geometrically accurate and/or intricate artworks.
Is water jet cutting sustainable?
Waterjet cutting is environmentally favourable process by nature. Waterjet cutting, unlike traditional mechanical cutting systems, does not require cooling or lubricating oils. This eliminates need to dispose of chemically affected chips. Waterjet, unlike thermal techniques like plasma or laser, produces no harmful fumes during cutting process.
Garnet abrasive is non-toxic and inert, and because very little metal is removed during cutting process, very little actual metal is wasted. This keeps environmental impact quite minimal.
How precise is a waterjet cutter?
Flow waterjets may produce products with extremely tight tolerances; some systems can achieve tolerances as low as 0.001″. (0.025 mm). Part tolerances for water jet machining typically range from 0.003″ to 0.005″ of inch. For materials thicker than 1 inch, machines will create parts with tolerances ranging from 0.005 to 0.100 inch (0.12 to 2.5 mm).
Because of variances in technology, such as control, and machine structure, tolerances vary widely by manufacturer.
How much pressure does a water jet cutter have?
Waterjet cutting pressures typically range from 50,000 to 60,000 PSI. Many newer systems are pressured to 90,000 pounds per square inch. Water is then discharged through small orifice machined into diamond or saphire, normally between 5 and 15 thousandths of inch in diameter. Water stream that results is supersonic, meaning it travels faster than speed of sound. Fortunately, flow rate is relatively low, at roughly 1/2 gallon per minute.
What are some safety issues regarding water jet cutting?
Water jet penetrating skin, getting hit by flying debris, and being exposed to noise are all common hazards and concerns associated with water jet machining. Working in confined areas, fall hazards, respiratory and eye dangers, electric shock, and potential exposure to dangerous substances are all risks linked with high-pressure water jetting.
Multiple Choice Questions on Water Jet Machining
Q. What is key element of water jet machining for material removal? a) Tool Holder b) Work piece c) Water jet d) Power source Answer: c Explanation: Water jet is one, which is used to cut work piece and to remove material.
Q. Which of following is not part of machining system of Water jet machining? a) Transducer b) Accumulator c) Jet cutting nozzle d) Hydraulic pump Answer: a Explanation: Transducer is not part of Water jet machining and other components come under WJM.
Q. What is velocity of water jet stream in water jet machining? a) 100 m/sec b) 300 m/sec c) 700 m/sec d) 900 m/sec Answer: d Explanation: Velocity of water jet stream used in Water jet machining is about 900 m/sec.
Q. Which type of materials cannot be machined using Abrasive jet machining? a) Soft materials b) Hard materials c) Difficult to machine materials d) None of mentioned Answer: a Explanation: Soft materials such as candy bars, thin softwood etc.., cannot be machined using AJM.
Frequently Asked Questions
Water jet machining is also called as
Water Jet Machining (WJM) also called water jet cutting. It is defined as, non-traditional machining process in which high-velocity jet of water is used to remove materials from surface of workpiece. WJM can be used to cut softer materials like plastic, rubber or wood.
How is material removed abrasive Jet Machining
In abrasive jet machining, focused stream of abrasive particles, carried by high pressure air or gas is made to impinge on work surface through nozzle and work material is removed by erosion by high velocity abrasive particles.
Where is water jet machining applicable
WJM process has been applied successfully for different machining operations such as cutting, drilling, deburring and wire stripping, etc. It has also been applied in field of surface engineering such as surface treatment, cleaning, texturing and finishing, etc.
What industries use waterjet cutters?
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