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Abrasive Waterjet Machining
Introduction to Waterjet
 Fastest growing machining process
 One of the most versatile machining processes
 Compliments other technologies such as milling, laser, EDM, plasma and routers
 True cold cutting process – no HAZ, mechanical stresses or operator and environmental hazards
 Not limited to machining – food industry applications
History
 Dr. Franz in 1950’s first studied UHP water cutting for forestry and wood cutting (pure WJ)
 1979 Dr. Mohamed Hashish added abrasive particles to increase cutting force and ability to cut hard materials including steel, glass and concrete (abrasive WJ)
 First commercial use was in automotive industry to cut glass in 1983
 Soon after, adopted by aerospace industry for cutting high-strength materials like Inconel, stainless steel and titanium as well as composites like carbon fiber
Pure WJ Cutting
 Pure cuts soft materials – corrugated cardboard, disposable diapers, tissue papers, automotive interiors
 Very thin stream (0.004-0.010 dia)
 Extremely detailed geometry
 Very little material loss due to cutting
 Can cut thick, soft, light materials like fiberglass insulation up to 24” thick or thin, fragile materials
 Very low cutting forces and simple fixturing
 Water jet erodes work at kerf line into small particles
Pure WJ Cutting cont.
 Water inlet pressure between 20k-60k psi
 Forced through hole in jewel 0.007-0.020” dia
 Sapphires, Rubies with 50-100 hour life
 Diamond with 800-2,000 hour life, but they are pricey
Abrasive WJ Cutting
 Used to cut much harder materials
 Water is not used directly to cut material as in Pure, instead water is used to accelerate abrasive particles which do the cutting
 80-mesh garnet (sandpaper) is typically used though 50 and 120-mesh is also used
 Standoff distance between mixing tube and workpart is typically 0.010-0.200 – important to keep to a minimum to keep a good surface finish
Abrasive WJ Cutting cont.
 Evolution of mixing tube technology
 Standard Tungsten Carbide lasts 4-6 hours (not used much anymore)
 Premium Composite Carbide lasts 100-150 hours
 Consumables include water, abrasive, orifice and mixing tube
Tolerances
 Typically +/- 0.005 inch
 Machines usually have repeatability of 0.001 inch
 Comparatively traditional machining centers can hold tolerances 0f 0.0001 inch with similar repeatability
 WJ tolerance range is good for many applications where critical tolerances are not crucial to workpart design
 Setup
 When is it Practical?
Advantages
Disadvantages
 Waterjets vs. Lasers
 Waterjets vs. EDM
 Waterjets vs. Plasma
 Waterjets vs. Other Processes
Future of Waterjet
 Drilling wells
 Drilling for oil
 Radial tunnels
Practical Applications
 Edge finishing
 Radiusing
 De-burring
 Polishing
Conclusion
 Relatively new technology has caught on quickly and is replacing century-old methods for manufacturing
 Used not only in typical machining applications, but food and soft-goods industries
 As material and pump technology advances faster cutting rates, longer component life and tighter tolerances will be achievable
 Paves the way for new machining processes that embrace simplicity and have a small environmental impact

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KEYWORDS: Abrasive waterjet, machining, depth, tolerance, model, integrity
The waterjet technology appears to be the most convenient for composite part cutting. Indeed,
it leads to low induced force and temperature on the material which is particularly adequate
for machining. However, the use of the abrasive waterjet technology (AWJT) requires a great
control of the machining parameters in order to avoid delamination. Different research
programs already aimed the confrontation between AWJT and composites [1, 2]. But they
generally concern one or two materials and deal more with the machining process than with
the composite specificities.
This study intends to specify the range of application of the AWJT for blind machining of
long-fiber polymer-matrix composites, and to page link the result to the structure of the material
(matrix, reinforcement and manufacturing process). For this reason, the study concerns eight
composite materials frequently used in industry. This includes:
- Carbon / epoxy Hexply UD T700 268 M21 34 % (autoclave) 20 plies quasi-isotropic
- Carbon / epoxy Hexply UD T700 268 M21 34 % (oven) 20 plies quasi-isotropic
- Carbon 3K / epoxy DBF (RTM) 20 plies plain weave
- Glass / epoxy HexFIT (autoclave) [0°/90°]4
- Glass / epoxy HexFIT (oven) [0°/90°]4
- Glass / phenol HexPLY 260 (oven) 8H 30 plies crowfoot satin
- Glass 20860 / epoxy DBF (RTM) 20 plies plain weave
- Glass 7781 / epoxy DBF (RTM) 20 plies
Within the first stage of the work, we studied the influence of the AWJT parameters (Pressure
(P), in-feed speed (V), abrasive mass flow rate (Da), and standoff distance (s)) and the
material manufacturing process on the average machining depth (h) and the machining
quality. Three materials (the M21T700 and the two HexFIT) were machined during this first
step. The jet scanned the sample with several adjacent passes. A mask (stencil) was used to
limit the area of the machined surface to the desired shape (Fig. 1). Those tests were
developed to respect the Doehlert experimental design, leading to forty-one machining
operations per sample.
For the analysis, the pockets were divided into two groups: a first one contains the unsuitable
pockets which involved delamination or excessive striation. Those samples were used to
define the AWJT range of application for composite machining. The second group of pockets
contains the clean samples. For each of them, twenty-one depth measurements were obtained
using a 3D feeler in order to inform about the average depth and the tolerance. At the end,
those values were used to identify a penetration forecasting model (equation (1)) which
matches the common literature. The five constants were identified from the experimental
design results.
machining settings is presented. It appears that the evolution of depth versus machining
parameters is similar is similar for each material. Furthermore, the relative deviation between
the depths obtained for the three materials is almost constant. This observation leads to only
use one parameter (a0) to define the material (this is named workability [3]) for scan
machining average depth forecasting models.
Besides, the AWJT range of application differs from a material to another one: several
materials (like the HexFITs) delaminate more easily than the others (like the M21T700).
Concerning the technology, the ratio between the abrasive mass flow rate and the hydraulic
energy (pressure) in one hand, and the in-feed speed in the other hand, appear to highly
control the material integrity. Their limit values also directly depend on the material
characteristics. The materials and their manufacturing process (autoclave, oven, RTM…) also
influence the pocket roughness and tolerance as far as they imply a size and a distribution of
the heterogeneities (porosity, reinforcement mesh sizes…)
Machining tolerance and roughness models are being developed in order to complete the
reachable results forecasting. The set of materials that is presented above is being machined in
order to follow a five hundred point experimental design. Many samples will be equipped
with Bragg network (optical fibbers) then mechanically tested to follow the material reactions
before, during and after the waterjet machining operation.