Abrasive water jet machining

1.0 Introduction

Abrasive H2O jet machining ( AWJM ) is a procedure affecting the stuff remotion by the mechanical energy of H2O and scratchy atoms, has a big figure of advantages over other scratchy procedures. It is possible to cut any type of stuff, understate the structural harm of the work piece and no thermic deformation on the work piece with AWJM. Like other jet cutting engineerings, AWJM besides produce kerfs which have some distinguishable characteristics and the quality of the kerf determines the quality of the work. The quality and preciseness of the kerf is determined by different factors like kerf side surface texture, raggedness and curliness, kerf breadth, taper, burr, kerf entryway radius, jet encroaching surface roughening, kerf side micro hardness. The consequence of the above parametric quantities on quality of the kerf in AWJM for different stuffs is discussed in this study.

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2.0 General Kerf Characteristics in Abrasive Water Jet Machining

By and large a kerf is produced with a wider at the entryway of the jet and reduces at the underside which is called a kerf taper. Due to the barrage of the jet, rounding off the top borders of the kerf occurs due to the fictile distortion of the workpiece. The sum of unit of ammunition corners depends on the clip. They are more seeable in ductile stuffs than brickle stuffs. Even burrs may be formed at the underside of the kerf as removed stuff may turn over over the surface.

Two zones are by and large present on the surfaces produced in machining. The upper zone is smooth in nature. This deepness of cut is called while the bottom zone is called striation zone which has curliness as the prevailing characteristic. The curliness is dragged in the backward way due to the slowdown produced in the jet. This backward drag angle depends on the speed used in cutting the work piece. When the scratchy jet cuts on the same jet for more figure of times so it contributes for the deepness of cut. When the force per unit area of the jet is unable to cut the stuff so a big pocket is formed at the underside of the kerf. The cutting procedure in the first zone takes topographic point by cutting wear, in 2nd zone by distortion wear and in the pockets by erosive wear and upward warp of the jet.

The deepness of cut, kerf taper and surface raggedness can be controlled by altering the force per unit area of H2O, mass flow rate of the scratchy atoms, jet crossbeam velocity and distance between the nose and the work surface. Generally among all the above parametric quantities H2O force per unit area and jet crossbeam speed majorly command the deepness of cut and surface raggedness.

Kerf profiles for the Through and Non-Through cuts.

3.0 Case survey on Quality issues in Metallic Coated Sheet Steels

This instance survey is on the kerf features in the AWJM of the metallic coated sheet steels. The experiments were conducted on Zincalume G300 which is the structural steel with a beady surface coated with hot dipped Zn or aluminium metal.

Four major parametric quantities were considered for the survey of the consequence on the quality of the sheet steels. These parametric quantities include jet cross velocity, H2O force per unit area, scratchy flow rate and stand-off distance between the nose and the work piece, where at predetermined maximal stand-off distance, minimal scratchy flow rate and minimal H2O force per unit area, the crossbeam velocity was adjusted at different degrees. Other parametric quantities like nozzle diameter, opening diameter, nozzle length and the size of the abradant are kept changeless. The parametric quantities were selected such that a through cut is obtained in all samples which are easy for comparing. In sheet steels the chief factors which consequence the kerf belongingss are Kerf breadth, kerf taper and kerf surface raggedness and besides burrs which signifier at the jet issue part.

3.1 Experimental Consequences

After executing the AWJM on the metallic sheet steels, general kerf features explained above were observed. From SEM survey two types of burrs like difficult burrs and loose hair line burrs. Hard burrs occurred at the jet issue part of the kerf where the stuff was steadfastly attached, which were removed through a secondary stuff remotion procedure.

Loose hair line burrs were observed at the both the borders of the kerf which occurred due to the remotion of the zinc/aluminium coatings. Merely few sites were found with striations and no hints of micro-cracks and heat affected zones were observed.

At the entryway part of the jet a little part of the stuff was damaged due to the barrage of the scratchy atoms, below which the film editing Markss formed due to two eroding phases were observed. Strias were observed merely in some samples were the H2O force per unit areas were low and the jet crossbeam velocities were higher.In the jet issue part the cut surfaces were more irregular as the stuff was enormously deformed which lead to the formation of the burrs at the underside.

The sheet steels are cut by the encroachment of single scratchy atoms where micromachining and plastic distortion are the chief grounds for stuff removal.The top part is brickle stuff eroding where every bit at the lower part the stuff remotion is by malleable eroding.

SEM graphs of the kerf profiles

3.2 Effect of Process Parameters on Different Kerf Characteristics

3.2.1 Kerf Geometry

Kerf geometry plays an of import in finding the work quality as the kerf produced has some taper angle, which is wider at the top and narrow at the underside. Kerf taper is represented by the relation? =tan ( ( Wt-Wb ) /h ) , where Wt is the top kerf breadth and Wb is the bottom breadth of the kerf and H is the deepness of the cut.

The experimental consequences were plotted on graphs which revealed the relation between the kerf geometry and the procedure parametric quantities. Both the top and bottom kerf breadths increased with addition in the H2O force per unit area as the higher kinetic energy would hold cut a wider slot. The impact of H2O force per unit area reduced on the kerf top breadth with its addition from 290 MPa to 340 MPa which implies that the scratchy H2O jets become less effectual when the cross a threshold value. The threshold value depends on the other procedure parametric quantities. A consequence similar to above instance was seen in the kerf taper angle i.e the taper angle reduced with an addition in H2O force per unit area as the top kerf breadth became about changeless and bottom kerf breadth increased steadily with an addition in H2O force per unit area.

Graphs demoing the consequence of H2O force per unit area on kerf geometry

An addition draw distance between the jet nose and the work piece resulted in an addition in the kerf top and bottom breadths but, the top breadth increased quickly compared to the bottom breadth. The cause of the above phenomenon might be due to the variegation of the jet with an addition in the base off distance. As the top breadth increased at a faster rate compared to the bottom breadth, the kerf taper besides increased with an addition in the stand-off distance.

Graphs demoing the consequence of stand-off distance on the kerf geometry

The experimental consequences on the consequence of jet crossbeam velocity on the kerf geometry revealed that, it showed a negative impact on the kerf breadths where as it acted straight relative to the kerf taper angle. The negative impact was observed due to the fact that the faster crossbeam velocities allow less atoms to cut the stuff ensuing in a narrow kerf and the kerf taper increases as the bottom part is exposed for a really less clip compared to the top part.

Graphs demoing consequence of jet crossbeam velocity on the kerf geometry

From all the above secret plans, the consequence of scratchy mass flowrate had no proper consequence on the kerf geometry within the selected scopes of flowrates.

3.2.2 Surface Roughness

Surface raggedness is an of import factor in finding the quality of the kerf. Here in our instance as the thickeness of the sheet steels are really less the opportunities of formation of surface striations are really less, so merely surface raggedness was studied in this instance.

Due to the addition in the crossbeam speed the surface raggedness increased as the surface raggedness as the addition in traverse velocity leads decreases the figure of atoms encroaching the stuff. This lead to improper film editing of the workpiece, which resulted in the addition of surface raggedness.

It was observed that an addition in H2O force per unit area upto a certain value resulted in the drum sander surfaces. But a farther addition in the H2O force per unit area increased the surface raggedness. This phenomenon is due to the construct of strength zones in the H2O jet. When the velocity of the jet is increased upto a certain extent, the effectual zone becomes wider ensuing more effectual cut of the stuff which leads to smooth surfaces. If the H2O jet still increases so the outer part of the H2O jet attains good strength ensuing in irregular surfaces. An addition in the scratchy atom flow rate resulted in the lessening of the surface raggedness, as the figure of atoms encroaching the kerf surface additions. The surface raggedness was observed to be increasing with the addition in the stand-off distance as the H2O jet diverges cutting work piece irregularly.

3.2.3 Burr Formation

As discussed earlier chiefly difficult burrs and loose hair line burrs were found were observed on the jet issue protions of the kerf. Number of burrs were high at low H2O force per unit areas likely due to the axial rotation over of the french friess at the bottom part of the kerf. Besides low jet crossbeam velocity resulted in addition of the burr tallness as the slow crossbeam velocity allows the thorough film editing of the atoms and the addition in the draw distance caused an addition in the burr height due to the decrease in the power of the jet.

4.0 Case Study on Quality Issues in Alumina Ceramicss

Alumina ceramics are being used in many industrial applications. As they are brittle the AWJM of the aluminum oxide ceramics is by the cleft extension and so by

In ceramic stuffs the kerf taper is broad at the entry zone of the jet, while the width lessenings with the addition in the thickness of the workpiece due to the lessening in the cutting efficiency of the jet ensuing from the atom atomization and the energy soaking up by the stuff. The entryway breadth can be mentioned as the opposite of the crossbeam velocity. If the scratchy flow rate is increased so it can be observed that the kerf breadth additions.

Experimental consequences showed that kerf taper angle is relative to the crossbeam velocity, reciprocally relative to coerce and scratchy flow rate. With the lessening in cutting efficiency of the fluid, it can non cut the stuff wholly which leads to the formation of the done hole. Hence it can be concluded that rate of lessening in deepness of cut lessenings with the increasing crossbeam velocity.

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