Water Jet Cutting Thick Materials
Waterjet cutting systems are much like other shape cutting systems utilizing computer controlled motion and post processing of tool paths, for precision cutting. The versatility of water jet machines make them ideal for cutting a wide range of materials. Water jet machines can cut any known material including composites, laminates, plastics, rubbers, aluminum, and steels including pre-hardened materials.
In thinner materials, abrasive water jet cutting will eliminate the need for machining stock by cutting to print sizes. In thicker materials, abrasive waterjet cutting is ideal for producing shapes near net size, minimizing the need for expensive and time consuming rough mill operations for heavy material removal.
Conventional waterjet cutting systems are the earliest type of waterjet cutting systems. Cutting heads are fixed, positioned or hung in a manner suitable for general shape cutting and for cutting thick materials. Waterjet cutting systems are adjustable to cut at various pressures up to 90,000 psi, with or without abrasive material. High-pressure water moving through the orifice at nearly 3,000 mph provides the necessary energy for cutting soft materials and with the introduction of abrasive can cut materials approaching the hardness of diamond.
As a non-contact process, tolerances can be challenging to consistently maintain, but when cutting thick material, the goal is less about tolerances and more about cutting square/plum and by all means not cutting smaller than final print size. As we know, the waterjet industry recognizes five standard cut qualities (controlled by speed) Q1, Q2, Q3, Q4, and Q5. When cutting thin materials Q3, Q4, and Q5 are typical, however when cutting thick materials Q1, and Q2 are more the norm.
Tips for cutting thick materials include:
Doing a test cut in an unusable area of the material to confirm material is cutting through, to confirm cut speed selected is appropriate, to confirm cutting head is square/plum, that outside corners are sharp, and there is no excessive undercutting on inside corners. Keep in mind that waterjet cutting does not add stress but will relieve existing material stress.
Decide ideal spots to pause program if needed for maintenance issues, abrasive hopper fillings, and shift end. This will not work for every occasion especially when critical maintenance issues arise, yet it’s a good plan in most cases.
Cut speeds for thick materials can get as slow .010” per minute. Be careful not to stall your motion system, the waterjet will cut through anything in its way including the bottom of your table/cut tank.
Typical abrasive grit sizes for cutting thick materials are 36, 50, and 80. Depending on the orifice and nozzle combination being used abrasive flow rates can start at 1.5 lbs per minute and in some cases go as high as 6 lbs per minute. A good rule of thumb is to use as much abrasive as necessary to cut as fast as possible (time is money) being careful not to overflow and waste abrasive.
Regarding lead-in and lead-out paths, lead-ins will nicely engage material top to bottom as long as you don’t cut too fast and cause stream to prematurely deflect. Lead-outs are a different story, they will finish cutting first at the top causing bottom of stream to jump over the unfinished cut area at bottom. Two ways to correct this is to manually slow down or dwell when exiting the material or manually add lines of code to exit part, stop motion, back-track and restart cutting over same lead-out path.
At anytime during the cut, use thin steel banding material as a feeler gauge to confirm cut is penetrating completely through the material.
Photos provided by Cutting Edge Water Jet Service show preparation and cross-sectional abrasive waterjet cutting of thick hardened steel pinion.
Article prepared by Ron Fairchild of Cutting Edge Water Jet Service; South Beloit, Illinois. Ron has over 20 years of experience in hands-on waterjet applications. Cutting Edge Water Jet Service is a job shop provider of water jet services for all industries in the United States. They offer 60,000-psi, 90,000-psi, conventional and dynamic abrasive waterjet cutting using a variety of multi-head waterjet cutting systems.