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Paradigm

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Paradigm Shifts in Abrasive Waterjet Technologies

1. Background

The objective of this web page is to make management teams within the waterjet industry aware of the potential to diversify their product portfolios.

1.1 AWJ Paradigm

A paradigm is the way a group/community perceives and thinks about a topic based on a particular version of reality. This means a paradigm has a mental model associated with it. At present the abrasive waterjet community has a single paradigm for generating cutting jets for precision machining – AWJ paradigm.

Initially, industry does not need the mental model associated with a paradigm to represent reality. Rather it needs a model that is a convincing explanation of "how" a technology works so that funding can be obtained for research, product development and exploitation. A mental model that closely represents reality is advantageous for product development and commercial success - but it is not essential.

It is assumed that an AWJ cutting head is a form of jet pump (Hashish 2002). Jet pumps are first and foremost energy dissipaters as their energy efficiency is typically less than twenty five percent. Clearly one does not want a cutting head to act primarily as an energy dissipater. An AWJ cutting head is a unique, two stage, fluid dynamic device (See Section 3.1 in Technology).

A new industry, such as the abrasive waterjet industry, can develop rapidly using a plausible explanation for the process it is exploiting. A research community is, however, in a very different position. It needs to rapidly discover the physical processes industry is exploiting, otherwise it generates more and more research papers that support a flawed mental model of physical processes. In other words, a research community can become trapped into a self-perpetuating process of research projects whose conclusions support a flawed mental model associated with a paradigm. In this situation a research community finds it hard to innovate and it loses the support of industry and research funding organizations.

The abrasive waterjet research Community has been working with a flawed conceptual model for twenty years. In this time it has not discovered new methods of generating abrasive waterjets and as a result has seen the centres of expertise and innovation in abrasive waterjets move to abrasive waterjet manufacturing companies. In addition, research funding for abrasive waterjets has virtually dried up in countries that were the leaders in abrasive waterjet research.

An individual working alone is usually responsible for creating a new mental model that revitalizes a research community. Invariably the individual will not have been deeply involved with the existing paradigm (Gosling 1994) and have little credibility with proponents of the existing mental model or credibility with the companies who will be the ultimate beneficiaries of new technologies. The author found himself in the role of a lone worker without experience of AWJ cutting heads, who needed to understand their fluid dynamics to extend the operation of entrainment cutting heads down to cutting jet diameters of 50microns.

1.2 Paradigm Shifts Needed in Abrasive Waterjet Technologies

Successful technologies evolve through incremental improvements and as a result of paradigm shifts. Incremental improvements are predictable but paradigm shifts may occur many years after the technology for a shift becomes available. Delays in adopting paradigm shifting technologies are often the result of proponents of existing and new technologies having different mental models of the physical processes involved.

Because AWJs are the only abrasive waterjets people have known the capabilities of AWJs are viewed as what is possible. We need to think “outside of the box”; such as - theoretically abrasive waterjets can machine with nanometer diameter jets, so I can at least build an abrasive waterjet system to cut with a 50 micron diameter jet.

Three areas for paradigm shifts are:

1. Improved cutting performance from AWJ cutting heads for general machining. End-users would like higher cutting speeds, lower abrasive use and longer cutting head component lives. These improvements require a paradigm shift that involves changing flow behavior within AWJ cutting heads.
2. Extending capabilities to fine and micro machining to complement and compete with lasers over a much wider range.
3. Enabling abrasive waterjets to operate in dynamic machining mode. It takes several seconds to go through an AWJ cutting cycle - abrasive off, waterjet off, cutting head repositioned, water on, abrasive on. Laser machining systems can achieve beam off, repositioned, beam on in a fraction of a second.

2. Past Attempts at an Abrasive Waterjet Paradigm Shift

In the 80s and 90s attempts were made to develop an abrasive waterjet paradigm shifting technology for general machining using suspension abrasive waterjet technology. It was demonstrated that a 400% improvement in cutting speed was possible. However, these attempts failed because flow circuits and equipment were too complex, user unfriendly and unreliable, with no possibility of overcoming these problems.

Important benefits came out of work on suspension systems, including:

• The knowledge that a substantial improvement in cutting performance is possible
• The realization that jet diameters could be at least 10 and possibly 100 times smaller than those feasible by the AWJ method of abrasive jet generation
• Establishing that suspension jets have commercially viable cutting capabilities when operated at the modest water pressures of 700 bar compared to > 3000 bar for AWJs

The work on suspension jets is an important input to the paradigm shifting technologies on this Web Site.

3. General Machining

The potential user base for AWJs for general machining is over ten times the present user base. In this situation manufactures need to concentrate on selling systems based on existing technologies and on making incremental improvements to their existing products.

Leading abrasive waterjet manufactures have a sufficiently large user base for companies specializing in spares and consumables to enter the market and seriously erode the profitable after-market of leading players. Many “me too” competitors have entered and continue to enter the market, competing for both abrasive waterjet equipment and complete machining systems.

Leading players can maintain market share through the quality of their products, their ability to meet demands for sophisticated machining systems and through their marketing and sales capabilities. Given these factors it is not surprising that there is little pressure from major abrasive waterjet manufacturing companies for a paradigm shift in the way abrasive waterjets are generated.

AWJ cutting performance has more than doubled over the past fifteen years through incremental increases in pump pressures and by optimizing cutting head parameters. Concurrent with improvements in cutting performance, the cost of cutting parts has reduced through:

• Improved reliability of pumps and cutting heads
• The use of multiple cutting heads on cutting tables
• The development of productive software for programming and control
• Automation for loading and unloading materials to reduce dead time.

Other developments, such as dynamic control of cutting heads to eliminate edge taper, have allowed abrasive waterjets to produce parts to a higher quality. However, until abrasive jet cutting capabilities are significantly improved, further reductions in cut part costs and improvements in quality will be modest.

Further increases in pump pressures are occurring but will be difficult to justify for the wider market because of reliability and costs issues. There is also the problem of cutting nozzle life, with arguments being made to restrict water pressures to under 4000 bar to minimize overall operating costs. It is known that cutting performance can be improved by reducing the ratio of cutting nozzle bore to waterjet orifice diameter but again nozzle life suffers.

Given that improved cutting performance is dependent on having a satisfactory nozzle life, and that no new nozzle materials are likely in the foreseeable future, the available options are:

• To improve fluid dynamic conditions in cutting heads to reduce wear in nozzle bores when operating with higher water pressures and/or reduced ratios of cutting nozzle bore to waterjet orifice diameter. The improved AWJ (IAWJ) mode of abrasive waterjet generation aims to achieve lower nozzle wear rates by improving the flow processes within cutting heads.
• To intensify the momentum transfer process in cutting nozzle bores so that nozzle lengths can be reduced sufficiently for it to be practical to make nozzles from industrial diamond. The SAW method of abrasive waterjet generation aims to achieve this by carrying abrasive to a cutting nozzle in steam and condensing the steam so that momentum is transferred to abrasive in a water/abrasive environment.

Over the past ten years the wall plug efficiency of abrasive waterjets has improved by a percentage point to 3% or so energy transfer to abrasive particles. Over the same period laser wall plug efficiencies, have in some cases, risen from 3% to over 10% of energy transfer to cutting beams. In the same period the cutting capabilities of lasers have been extended to encompass materials and material thickness that were considered the preserve of abrasive waterjets. New types of lasers will continue to enter the market and further erode the competitiveness of abrasive waterjets.

Paradigm shifts for general machining will involve new cutting heads and modified abrasive feed equipment, without affecting the major capital item in cutting systems - the pump. This means it should be cost effective to upgrade existing cutting tables with new cutting heads and to adapt existing abrasive feed systems.

4. Fine Machining (FAWs)

AWJ cutting heads in their basic form do not function well below jet diameters of about 400 microns because air entrainment is insufficient to carry abrasive particles to a cutting head. AWJs can operate down to jet diameters of 300 microns by inducing additional airflow to a cutting head using auxiliary suction. Below 300 microns particle agglomeration and attachment to passage walls, caused by electrostatic forces and/or moisture, become particularly troublesome.

To achieve jet diameters below 300 microns it is necessary to change the abrasive carrier medium from air to water. Abrasive particles are statically suspended in water rather than dynamically suspended in an airflow.

Abrasive waterjets generated by entraining abrasive/water mixtures into a high velocity waterjet were used for on site cutting and under developed for general machining until they were replaced, in the early 1980s, by the then paradigm shifting technology of AWJs. AWJs were more effective, much simpler and easier to operate and more reliable than systems using abrasive/water mixtures.

Past problems with cutting systems based on entraining abrasive/water mixtures can be minimized by limiting maximum cutting jet diameters to 300 microns or so (FAWs). With jet diameters less than 300 microns:

• The abrasive consumption per hour is sufficiently small for pre-prepared, stabilized abrasive mixtures to be used, thereby overcoming serious problems experienced in the past with abrasive mixture preparation and use
• It is economic to make wear parts for cutting heads from industrial diamond.

FAWs represent a paradigm shift in the capabilities of abrasive waterjets. However, there is a need to overcome misconceptions as to their suitability for precision machining. It is particularly important that AWJ manufactures see FAWs as an added capability to AWJ cutting tables.

A FAW cutting head can be powered by an AWJ's intensifier pump and have an exchangeable container of abrasive mounted alongside a cutting head. A one kilogram disposable plastic container could hold abrasive mixture for over an hour of cutting. It will, therefore, be relatively easy to add a FAW to an AWJ cutting table designed for multiple cutting heads.

Misconceptions about entraining abrasive/water mixtures into a high velocity waterjet include:

• The energy available to transfer to abrasive particles is significantly reduced by the mass of carrier water that has to be accelerated compared to accelerating air in an AWJ cutting head.
• Friction losses are much greater than in AWJ nozzles because of the high density of water relative to air.

In practice these disadvantages can be minimized and compensated for by other factors. In particular:

The general exploitation of FAWs requires ultra high pressure pumps that have water flows that are 5 to 20% of the flows from the smallest pumps used for AWJs. Relative to AWJ pumps, the development cost of a pump for FAWs will be considerably lower, thereby reducing the investment for a company seeking to start an abrasive waterjet manufacturing business.

It could be argued that a paradigm shift is needed in the abrasive supply chain for FAW technology to become a reality. A high level of quality control, from initial abrasive preparation through to abrasive mixture flowing into a cutting head is required, particularly for FAW cutting jet diameters less than 100 microns. Abrasive supply chain requirements for small diameter FAWs are similar to those for micro abrasive waterjets (MAWs) and are discussed in Section 6.

5. Micro Machining (MAWs)

It is not generally known that abrasive waterjets are capable of micro machining, so MAWs could be seen as a paradigm shifting technology looking for a market. However, MAWs will compete with and complement micro machining lasers in a similar way that AWJs complement and compete with general machining lasers. A market for MAWs is, therefore, already identified in micro machining laser job shops which can use MAWs to extend the services on offer.

In order to minimize technical risks and to achieve good reliability, water pressures for MAWs need to be limited to about 700 bar. At 700 bar the cutting jet energy density is equivalent to that of an AWJ operating at about 3000 bar.

Water flow rates for cutting jets less than 50 microns in diameter are under 2.5 litres per hour, making it practical to use pneumatically driven intensifier or direct driven plunger pumps to generate 700 bar water pressure. By utilizing materials and sealing technologies developed for AWJ pumps, MAW pumps will achieve considerably longer lives than AWJ pumps. Also capital costs for a MAW pump are a fraction of an AWJ pump.

Machining cycle times reduce as feature size decreases. If it takes 1 second to machine a unit feature with a 1 mm diameter tool, a 100 micron diameter tool would be expected to produce a unit feature in 0.1 seconds. Technologies to allow FAWs and MAWs to machine multiple features per second have been developed.

The business model for MAWs is likely to represent a paradigm shift with manufacturers of MAWs taking control over the abrasive supply, rather than the situation with AWJs where numerous suppliers compete to supply abrasive. It will be essential for MAW manufacturers to provide abrasive in order to ensure adequate quality control over abrasive and to obtain an appropriate financial return for the investment in bring the technology to market. The paradigm shift associated with abrasive supply is discussed in the next Section.

MAWs can be built as desktop systems with a particular attraction for small businesses and the hobby market. Ease of use, reliability and serviceability will be critical for these markets along with good presentational design.

6. Paradigm Shift in Abrasive Supply

The commercial success of AWJs owes much to the use of garnet abrasive in a size range that is free flowing, relatively low cost, easy to prepare and handle, and available from many suppliers. Paradigm shifting abrasive waterjets for general machining will continue to use such abrasive, with abrasive waterjet manufacturers having no influence over the supply of the major consumable - abrasive.

In comparison to AWJs, the commercial success of MAWs, and of FAWs with jet diameters less than 150 microns or so, will depend on manufactures of these systems controlling the abrasive supply. The level of quality control needed over maximum abrasive and contaminant particle size is outside the experience of most abrasive suppliers, but well within the capability of abrasive waterjet system manufactures to implement or sub-contract.

By providing abrasive mixtures in proprietary form FAW and MAW system manufacturers will have a major business opportunity. Abrasive consumption of a MAW is only a percent or so of an AWJ but the price per unit weight of this abrasive, in packaged form, could be ten or more times that of abrasive for AWJs.

In the case of MAWs, it is likely that abrasive will be sold in plastic proprietary cartridges that are quite sophisticated in design. The abrasive/water/additive mixture is also likely to be proprietary. Although supplying quality assured abrasive mixtures in pre-packaged form is a business opportunity it requires appropriate investment as two paradigm shifts are involved - one in the method of abrasive waterjet generation and the other in the abrasive supply chain. In this situation a strong intellectual property position is needed to reduce the risks in commercializing the technology.

7. Paradigm Shifts in Abrasive Waterjet Businesses

The abrasive waterjet industry is currently a single product industry in terms of abrasive waterjet generation. With the rapidly growing market for AWJ systems, being a single product industry is not a problem. However, the cyclic nature of the machine tool market means that relatively soon the abrasive waterjet industry will find it has over capacity, with all the attendant financial problems for individual companies. This situation has been played out in many industries and is a fact of business life.

To mitigate the effects of market downturns, forward planning companies seek to diversify their product portfolio, with the expectation that market downturns are out of phase across different market sectors. An example of this is the laser machine tool industry where companies evolved from a single product – one cutting beam generation method – to companies providing a range of products – several cutting beam generation methods.

The laser research community played an important role in driving the development of new laser beam generating methods and in the creation of start-up companies to exploit new laser technologies. To diversify their product portfolios major laser companies were able to acquire new products by buying start up companies and/or using the research community for product development. The situation in the waterjet industry is very different from that of the laser industry, as no new methods of abrasive waterjet generation have come out of the research community. Also there are no innovative small companies that major abrasive waterjet companies can buy to acquire new products.

8. References

Gosling, W. (1994) "Helmsmen and Heroes - Control Theory as a Key to Past and Future" Weidenfeld and Nicolson, London, UK.