October 2005-Cover Story
Package Converts
Mill To Waterjet
Almost every shop has one – an older knee-type mill that sits in the corner of the shop, virtually unused since newer technology has delivered much higher productivity to the process. That old mill might be your ticket to employing a different cutting technology and perhaps opening new markets – convert it to a waterjet.
 The M-Series Ward waterjet is an engineered package that allows easy and temporary conversion of an existing manual or CNC mill to a fully functional waterjet cutting machine. |
An Ohio waterjet manufacturer has expanded the meaning of multi-function machine tools with the introduction of a new package that converts a vertical mill into a waterjet cutter. “The concept is really quite simple,” says Richard Ward, president and founder of WARDJet, Inc. (Kent, OH).
What Ward has done is engineer a unique M-Series waterjet unit that attaches to a mill – placing a waterjet cutting head into the mill’s spindle, securing a cutting table to the mill’s table, powering a high-pressure waterjet pump with shop air, enclosing the entire “water-works” to contain the water and abrasive, while taking full advantage of the mill’s structure, stability and CNC or manual controls.
“In most cases, the bulk of the cost has already been incurred with the purchase of a mill or other CNC machine,” notes Ward.
Traditional waterjets typically use a tank filled with water up to 36” deep to dissipate the excess kinetic energy in the stream generated through the abrasive cutting head. “This energy has tremendous power, enough so that it often cuts deep into the support grates or anything that is under the part being cut,” explains Ward “Furthermore, with the water and abrasive mixture traveling at over 2,000 mph, it is common to have overspray shooting off the part as far as 10’ away. It is these two unavoidable characteristics that have ruled out using just any form of CNC motion system such as a mill, wood router, robot or laser as a waterjet,” admits Ward.
“Taking buckets of abrasive and water and essentially tossing it all over your equipment would not appeal to too many people,” says Ward, whose firm produces a complete spectrum of traditional, stand-alone waterjet machines.
The M-Series waterjet is built to address these specific issues, ensuring that no water or abrasive gets out of the 3D cutting envelope.
To control the excess water and abrasive spray, the system incorporates a flexible enclosure, which contains the water, abrasive and kerf materials, keeping them from the mill’s precision position mechanisms, such as ballscrews.
Dissipating the power of the ~2,000 mph cutting stream within the confines of most traditional knee-type mill designs was a challenge. The traditional waterjet approach to this is to have the stream cut through the part and then shoot into a deep, water-filled tank. The stream-energy remaining after cutting is easily dissipated in these deep, self-contained pools. The dissipation pools also provided a reservoir for spent abrasive particles and the kerf material cut from the part. The traditional knee mill just doesn’t provide sufficient room between the spindle and the table for this normal arrangement.
A design that would fit between the tip of the spindle-mounted cutting head and the table-mounted cutting support had to be developed.
As part of the M-Series’ patented design, Ward engineered a relatively shallow table-mounted tray. Mounted via the mill table’s standard T-slots, the tray incorporates a level grate for part support and mounting and an unusual approach to dissipating the force of the cutting stream. Once through the part, the stream is injected into a layer of ball bearings that absorb the remaining kinetic energy by spinning over each other, explains Ward.
“A grate support system holds the parts to be cut, and the balls fill all the voids. The balls are supported on a double layer of mesh that allows the mixture of abrasive, water, and removed kerf material to drop through onto the floor of the tank. Small streams of water then wash the waste material out of the M-Series for disposal,” he explains.
An integrated jigging and fixturing system allows parts to be placed anywhere on the cutting table and locked into position quickly. An air-pressurized ‘tent’ acts as a water and abrasive cover, keeping everything inside the cutting area. Removable transparent windows allow light and access into the tank for quick loading and unloading of parts.
Setting up the M-Series waterjet is designed to be quickly accomplished. “Simply use a crane or forklift to place the waterjet components on the CNC bed or under the motion system,” says Ward. “If using a mill, the tool holder driven by the spindle is removed and a similar tool holder with the top of the tent and the waterjet cutting head attached, is locked up into the spindle of the mill. So in about the same time it takes to change a tool, it is possible to change the system to operate as a waterjet.”
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The M-Series grate system is a mini version of the proprietary Job Shop Waterjet Grates used on the larger Z, J and R-Series waterjets built by WARDJet. Moving away from the traditional use of slats, the Job Shop Waterjet Grates are made from thin 16-ga. plate and fabricated to form box sections that are flat and rigid. Each joint has eight welds to ensure the strength of the structure. Rotating or reversing the grates can substantially extend their life.
Air-Powered Pump
A key element of the M-Series’ simplicity and adaptability to the shop floor is the intensifier pump that generates the cutting energy.
Most waterjet systems incorporate a very high pressure intensifier pump that is driven by an electric motor. Like most industrial motors, these are often three-phase, 220V units requiring dedicated wiring or circuits.
The M-Series Ward system employs an intensifier pump that is powered by the standard shop air supply. The special pump, an A-20K unit, matches its available pressure and resulting abrasive particle velocity to the scale of the mill-mounted cutting system. This pneumatic pump delivers 20,000 psi to the spindle-mounted cutting head and is described as being small and light enough to be picked-up and carried by hand. Large scale, stand-alone waterjet systems usually employ positive displacement pumps in the 40,000 – 50,000 psi range.
“The idea was to develop a pump that utilized the compressed air common to all job shops to generate the water pressure in the intensifier pump,” says Ward. “So basically the entire M-Series tank combined with the A-WARD pump requires only water from the tap and an air connection.”
 To dissipate the kinetic energy of the abrasive cutting stream, the M-Series employs layers of ball bearings instead of a deep water trough. |
“In about the same time it takes to change the tool, it is possible to change the system to operate as a waterjet.”
“This will revolutionize the way we think, plan, process, and structure everything we do,” believes Buddy Catlette, head of Herman Machine (Tallmadge, OH) He sees being able to use the shop’s existing mill to waterjet cut parts, or use the waterjet as a near-net-shape tool, with the final machining of ultra-high tolerance parts being done on the same mill.
Combination Advantage
“There are many instances where waterjet is a better tool at performing part or all of an operation,” counsels Ward. “In cases where standard two dimensional shapes need to be cut from flat stock, or 3D cutting is required should the mill have 3-axis capacity, waterjets are proving to cut faster and with acceptable accuracies in many materials. Limitations are ultra-high tolerances and situations where the objective of the cut is to not pass all the way through the material.
“It is here that the M-Series offers an incredible advantage,” states Ward. “The same mill used for the waterjet cutting is also used to do the final machining of the near-net-shape parts to final tolerance. The waterjet is also ideal for removing large portions of stock material, and for hogging out material that would otherwise have been made into chips. The solid waste material typically has a higher resale value over chips, again contributing to the bottom line.”
WardJet, Inc.
