Advances in waterjet cutting technology
- September 10, 2002
Shop Metalworking Technology spoke with Joe Bodorkos, regional manager for Flow Waterjet Americas, about recent developments in waterjet cutting.
Bodorkos will be a speaker at Shop Metalworking Technology’s Shop Insights 2012 conference on September 25. To hear his presentation and learn more about waterjet cutting developments, register for the conference at online.
SMT: For those who are considering waterjet technology for the first time, what are the key application factors and what are the key waterjet machine technology factors to consider?
Joe Bodorkos: Generally, people are looking for the most effective and lowest cost method for producing parts that meet already established specifications. In some cases, that means outsourcing when quantities are low or timelines are not critical. In other cases, it means acquiring a technology for in-house manufacturing. For job shops, it means offering a cutting service to almost any other industry and not having all your eggs in one basket.
There are virtually no limits to what waterjets can cut, which is why companies of any size consider the waterjet technology as a viable option. We have customers ranging from small two-person operations cutting artistic glass to multinational corporations such as Boeing cutting the entire fuselage of a Dreamliner 7E7.
One of the greatest advantages waterjet technology brings to the table is that it can cut anything from metals (mild steel, stainless, aluminum, copper, brass, titanium, inconel, etc), stone, glass, plastic, rubber, paper, composites, ceramics, wood, and more—all of this with minimal adjustments (if any) when going from one material to the next. This allows for a quick learning curve when choosing the waterjet technology.
Another key benefit of waterjet cutting is that it does not use heat in the cutting process and does not create a Heat Affected Zone (HAZ). Several other technologies, such as plasma or flame cutting, use heat as part of the cutting process. For some application this is acceptable, such as a base plate that gets painted and anchored to the floor. But for many others, the HAZ is not acceptable and must be machined away. This wastes material and takes additional processing time. If the part was cut with waterjet the first time around, there would be no need to cut the material larger than specified size and depending on final specifications, there may not be any need for additional processing.
Even though there are many considerations and options when looking at waterjets, the two primary items for consideration are the cutting head configuration and the pump.
First, there is the cutting head. There are three considerations. There is conventional waterjet (straight head with three axis ability), articulating head for automatic taper compensation for 2D parts (Flow calls it Dynamic Waterjet), and full five axis articulating head for 3D parts (Flow calls it Dynamic XD; it also compensates for taper in 3D cutting).
The natural process of waterjet cutting with a straight head produces a taper or V-shaped small angle. This means the edge is not truly square or purely vertical as it would be with say a router or CNC machining type process that uses a blade or bit. It has a slight angle to it. The faster you cut and/or thicker the material, the more the taper. \The natural way to reduce taper is to slow down the jet which allows the jet to erode more material and reduces the taper angle. But in slowing down, the cycle time and the cost to produce the part can dramatically increase.
Flow offers a technology called Dynamic Waterjet that articulates the head through small angles (from about 1° to 10° – like a mini five axis). This automatically compensates for the taper through the software. As a user, you just have to enter the material (from drop down list), thickness, and edge finish desired (from 1-100), and the software will take care of the rest.
Extending the capability of automatic taper compensation for 2D parts, Flow’s full five axis can cut 3D parts and automatically compensate for taper in both 2D and 3D parts.
Second, the pump is the heart of the waterjet cutting system. Since the inception of waterjet cutting in the early 1970's, cutting pressures have consistently and steadily increased. The reason is simple: pressure = productivity. Increase the waterjet pressure and the stream moves faster, reduces in diameter, and uses less abrasive (abrasive is the highest cost consumable). Much as the wattage of a CO2 laser increases cut speed, increased water pressure increases cut speed.
Typical pressure options available in the waterjet industry are from 60,000 psi up to and above 90,000 psi. The physics are simple. As the pressure goes up, the stream velocity of the jet increases. This creates a greater cutting power density. With pump pressures at 90,000 psi, the water stream velocities approach four times the speed of sound. As the velocity of the stream is increased, so is the speed of the abrasive particles as they exit the nozzle. The faster velocity of the abrasive particles causes a rapid erosion of the material creating significant increases in cutting speed (up to 50 per cent faster or more) and reductions in the cost to produce the parts.
Ultimately, the customer’s application will define needs and the level of capability of the waterjet system.
SMT: There are have been several developments or advancements in waterjet cutting. Can you briefly explain the benefits of the following:
- Five axis waterjet cutting:
JB: It greatly expands the types of parts that can be cut with waterjet. Complex multi-axis parts can now be processed easily with waterjet. The idea of cutting five axis is not new and has been available for decades (six axis robotic systems). What has held it back has been the complexity of the programming. These parts are becoming more common as the latest 3D CAD systems also make it much easier for the average person to design 3D parts. Customers are now looking for a versatile tool that can take these designs and turn them into parts.
- Multiple cutting heads
JB: While not a recent evolution, multiple cutting heads still offer a cost-effective way to produce more parts in some applications. While the costs per part remain the same with multiple cutting heads (since all consumables are multiplied), the initial investment cost of the equipment increases. If you are producing a large quantity of repetitive parts, use of multiple cutting heads can be explored as a viable option.
- 3D etching (not cutting through the metal):
JB: More opportunities are presenting themselves in this area. This could be as simple as scribing part numbers or bend lines, or producing a “milled” pocket in a proprietary impossible-to-machine material. This is highly specialized and very application dependent, but is being done commercially at this time.
- Energy efficiency:
JB: Like all industries, we continue to examine ways to maximize energy efficiency while not compromising productivity. The greatest advancements are increasing cutting pressure, which greatly reduces the amount of garnet necessary for cutting. Additionally, our newest, most advanced motion system operated on ball bearing (near 99 per cent efficient) greatly reduces friction and resulting in much greater efficiency.
SMT: What key technological advancements do you expect to see in waterjet cutting technology for metal fabricating in the next five years? What needs will these advancements address?
JB: It is often said the best predictor of the future is the past. One can expect to see cutting pressures continue to rise, abrasive consumption continue to be reduced, and programming to become easier. In the realm of producing capital equipment, market acceptance really does revolve around the concept that the end user needs to produce faster parts (increase of pressure), better parts (software and improved motion systems), and cheaper parts (lower abrasive usage, which comprises nearly two thirds of a waterjet’s operating cost) to get ahead of the competition.
SMT: A few years ago, a waterjet machine manufacturer developed a hybrid waterjet/EDM system. The technology did not seem to take off. Do you expect to see a role for "hybrid" waterjet machines or a new version of such machines in the future?
JB: Hybrid machines are viable as long as the investment cost is less than purchasing two different types of machines separately. When looking at an example of why these hybrid machines fail, customers simply aren’t willing to pay $400,000 for a hybrid EDM and waterjet when purchasing them separately may add up to $350,000. When the system is being setup, programmed or is down for preventative maintenance, you don’t have one machine off line, you essentially have two. Customers understand this, so to be viable, you would hypothetically have to produce a hybrid machine for $300,000 to get any traction. Another factor is the fact that waterjet greatest asset is its versatility. Often, by combining this machine with another process, you are adding it to a less versatile technology platform which has great potential for holding back the waterjet. To go back to the EDM example, waterjets are great at cutting large sheets of UHMW. Cutting this material on a hybrid waterjet and EDM would wreak havoc on the filtration system necessary for the EDM portion of the system.