**4.2 AWJ drilling**

Earlier studies have proven that AWJ technology is a viable tool for drilling different materials such as pure commercial aluminum, Al6061, brass, S1030 low-carbon steel, D-3 cold working tool steel, etc. AWJ drilling does not affect microhardness and mechanical properties of the material [48]. Burr-free surfaces can be obtained in AWJ drilling. Drilling at different angles is also quite convenient with AWJ. In AWJ technology drilling can be performed by tilting the cutting head up to 590. Though many types of research are carried out in drilling different materials, no work has been notably reported on drilling of Mg-based materials through AWJ technology. In the present section, experimental investigations are carried out to know the features of holes drilled by AWJ in Mg alloy. Surface roughness and taper of drilled holes are measured and compared with holes drilled by conventional drilling and jig boring.

**71**

**Method**

AWJM

**Hole dia**

**Drilling conditions**

P Mf SOD Time in min

Speed

Feed Time in min

Speed

Feed Time in min

**Table 4.**

*Conditions for drilling holes.*

2.9

2.3

Jig boring

3 1200 rpm

2.5 1100 rpm

Conventional drilling

2.5 1200 rpm

3.5 1100 rpm

**ϕ 3 mm**

**ϕ 5 mm**

**ϕ 10 mm**

300 MPa constant for all holes

425 g/min constant for all holes

1.5 mm constant for all holes

5.4 1000 rpm 0.1 mm/rev: constant for all holes

1.5 1000 rpm 0.1 mm/rev: constant for all holes

1

1

1

1.5 900 rpm

1.5

800 rpm

6 900 rpm

**ϕ 15 mm**

**ϕ 20 mm**

*Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials*

7.9

800 rpm

*DOI: http://dx.doi.org/10.5772/intechopen.85209*


*Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials DOI: http://dx.doi.org/10.5772/intechopen.85209*

> **Table 4.** *Conditions for drilling holes.*

*Magnesium - The Wonder Element for Engineering/Biomedical Applications*

deflected water jet. In cutting AZ91 magnesium alloy, the embedment of spherical abrasive particles and pocket-like structures is observed at the shallow impact angles as shown in **Figure 4**. The surface roughness at RCZ zone is higher than SCZ zones. **Figure 6** shows the 3-D images of SCZ and RCZ generated in optical profiler. The surface roughness of the AZ91 and nanocomposites in the SCZ zones is found between 5–20 μm and 20–40 μm in RCZ at lower traverse speeds. This is due to the increase in the impact of a number of abrasive particles and exposure time. Surface roughness is a function of water pressure because the kinetic energy of water jet increases the velocity of particles which in turn increases the surface quality, and also the influence of abrasive mass flow rate on surface roughness depends mainly on water pressure. However, at higher traverse speeds, an increase in water pressure increases the surface roughness. Hence traverse rate is the most significant

Earlier studies have proven that AWJ technology is a viable tool for drilling different materials such as pure commercial aluminum, Al6061, brass, S1030 low-carbon steel, D-3 cold working tool steel, etc. AWJ drilling does not affect microhardness and mechanical properties of the material [48]. Burr-free surfaces can be obtained in AWJ drilling. Drilling at different angles is also quite convenient with AWJ. In AWJ technology drilling can be performed by tilting the cutting head up to 590. Though many types of research are carried out in drilling different materials, no work has been notably reported on drilling of Mg-based materials through AWJ technology. In the present section, experimental investigations are carried out to know the features of holes drilled by AWJ in Mg alloy. Surface roughness and taper of drilled holes are measured and compared with holes drilled by conventional drilling and jig boring.

parameter in deciding the quality of cut at two zones.

**70**

**Figure 6.**

**Figure 5.**

*Regions of cut surfaces.*

*3-D images of SCZ and RCZ.*

**4.2 AWJ drilling**

Five holes with diameter 3, 5, 10, 15, and 20 mm were drilled in 40 mm thick AZ91 Mg alloy block. Roundness and taper of drilled holes were obtained using profile projector. Drilling time of each hole was also determined and compared. The conditions at which the holes were drilled are given in **Table 4**.

**Table 5** gives actual dimensions of five holes drilled by different methods measured using a profile projector with taper percentage. Diameters of drilled holes were measured in both sides (top and bottom) to know the variations in drilled holes. It can be observed that compared to holes drilled by conventional methods, AWJ-drilled holes were affected by the taper. The taper was comparatively higher in drilling less than 5 mm hole. This is due to hit back of jet from the channel during the drilling process, and this trend will last until full penetration is achieved. Meanwhile, the base hole will be abraded by the perimeter of the jet and thus affects the shape (roundness) and diameter of the hole as shown in **Figure 7**. When compared to other methods, AWJ-created holes are slightly larger than the required size and require comparatively more time to drill holes.

**Figure 8** shows a cross section of holes drilled in AZ91 Mg block using three different methods. The surface roughness of drilled surfaces with diameter 10, 15, 20 mm were measured using contact-type Taylor and Hobson surface roughness measuring instrument by considering 5 mm cutoff length. Measurement was taken in three regions of the depth (top-middle-bottom) of drilled surfaces. The average of three readings in each zone is noted down. **Table 6** gives surface roughness (Ra) of drilled surfaces.


#### **Table 5.**

*Dimensions and taper percentage of drilled holes.*

**Figure 7.** *Roundness of holes produced by AWJ.*

**73**

*Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials*

**Measurement zone Conventional Jig boring AWJ** Top (0–13 mm) 2.65 μm 0.93 μm 3.96 μm Middle (14–26 mm) 3.99 μm 1.48 μm 4.47 μm Bottom (26–40 mm) 4.30 μm 1.57 μm 5.09 μm

From **Table 6**, it can be observed that the surface roughness of AWJ-drilled holes is more than the other two methods in all the regions. Surface roughness increases with increase in depth. This is due to loss of jet energy and a decrease in cutability of the abrasive particles at higher depths and thus deteriorates the surface quality. However comparable results can be achieved by AWJ technology when compared to conventional drilling. Despite few drawbacks, AWJ drilling offers several advantages over other methods. No burrs are observed in the AWJ-drilled surfaces, unlike conventional methods. Adhesion of the material to the drill bit, especially in drilling less than 5 mm diameter holes, is observed in both conventional methods as shown in **Figure 9**. Formation of FBU increases heat generation during drilling. This tendency of the Mg-based materials to adhere to the drill bits is a serious problem. Formation of FBU is completely absent in AWJ drilling since there is no direct contact between tool

and work. Therefore risk-free drilling is possible through AWJ technology.

The versatility of AWJ technology makes it suitable for cutting almost all engineering materials. Besides cutting and drilling of materials as discussed in the previous section, AWJ technology has been successfully implemented to perform some of the essential machining operations such as turning, milling, finishing, and piercing. Several investigations are carried out on these machining operations with promising results. Thus AWJ technology has become a potential machine tool for modern machining industries. This section highlights the suitability of AWJ in turning and milling operations based on past studies. Research possibilities in AWJ

In AWJ turning, workpiece is rotated while the jet is traversed parallel to the axis of workpiece to produce the required shape. Research efforts on AWJT were started by Hashish during 1987; since then several experimental investigations on different machining operations were made to produce near net shape parts with faster material

**5. Other alternative operations with AWJ**

technology are also discussed.

**5.1 AWJ turning**

*DOI: http://dx.doi.org/10.5772/intechopen.85209*

*Ra of drilled surfaces measured in different depths.*

**Table 6.**

**Figure 9.**

*Adhesion of material to the drill bit.*

**Figure 8.** *Cross section of drilled holes.*

*Abrasive Water Jet Cutting: A Risk-Free Technology for Machining Mg-Based Materials DOI: http://dx.doi.org/10.5772/intechopen.85209*


**Table 6.**

*Magnesium - The Wonder Element for Engineering/Biomedical Applications*

conditions at which the holes were drilled are given in **Table 4**.

size and require comparatively more time to drill holes.

**Φ at top Φ at** 

*Dimensions and taper percentage of drilled holes.*

*Roundness of holes produced by AWJ.*

**bottom**

Five holes with diameter 3, 5, 10, 15, and 20 mm were drilled in 40 mm thick AZ91 Mg alloy block. Roundness and taper of drilled holes were obtained using profile projector. Drilling time of each hole was also determined and compared. The

**Table 5** gives actual dimensions of five holes drilled by different methods measured using a profile projector with taper percentage. Diameters of drilled holes were measured in both sides (top and bottom) to know the variations in drilled holes. It can be observed that compared to holes drilled by conventional methods, AWJ-drilled holes were affected by the taper. The taper was comparatively higher in drilling less than 5 mm hole. This is due to hit back of jet from the channel during the drilling process, and this trend will last until full penetration is achieved. Meanwhile, the base hole will be abraded by the perimeter of the jet and thus affects the shape (roundness) and diameter of the hole as shown in **Figure 7**. When compared to other methods, AWJ-created holes are slightly larger than the required

**Figure 8** shows a cross section of holes drilled in AZ91 Mg block using three different methods. The surface roughness of drilled surfaces with diameter 10, 15, 20 mm were measured using contact-type Taylor and Hobson surface roughness measuring instrument by considering 5 mm cutoff length. Measurement was taken in three regions of the depth (top-middle-bottom) of drilled surfaces. The average of three readings in each zone is noted down. **Table 6** gives surface roughness (Ra) of drilled surfaces.

**Desired Φ Conventional Taper % Jig boring Taper % AWJ Taper %**

**Φ at top Φ at** 

2.5 2.384 2.451 0.17 2.375 2.435 0.15 3.526 2.321 3.012 5.129 4.955 0.44 4.930 5.071 0.35 5.841 5.263 1.445 9.960 9.981 0.05 10.013 10.069 0.13 10.555 10.161 0.985 14.796 15.133 0.84 14.790 15.196 1.09 15.375 15.021 0.885 19.549 20.211 1.66 19.867 20.207 0.85 20.355 20.100 0.637

**bottom**

**Φ at top Φ at** 

**bottom**

**72**

**Figure 8.**

*Cross section of drilled holes.*

**Table 5.**

**Figure 7.**

*Ra of drilled surfaces measured in different depths.*

#### **Figure 9.** *Adhesion of material to the drill bit.*

From **Table 6**, it can be observed that the surface roughness of AWJ-drilled holes is more than the other two methods in all the regions. Surface roughness increases with increase in depth. This is due to loss of jet energy and a decrease in cutability of the abrasive particles at higher depths and thus deteriorates the surface quality. However comparable results can be achieved by AWJ technology when compared to conventional drilling. Despite few drawbacks, AWJ drilling offers several advantages over other methods. No burrs are observed in the AWJ-drilled surfaces, unlike conventional methods. Adhesion of the material to the drill bit, especially in drilling less than 5 mm diameter holes, is observed in both conventional methods as shown in **Figure 9**. Formation of FBU increases heat generation during drilling. This tendency of the Mg-based materials to adhere to the drill bits is a serious problem. Formation of FBU is completely absent in AWJ drilling since there is no direct contact between tool and work. Therefore risk-free drilling is possible through AWJ technology.
