Abrasive Water Jet Milling as An Efficient Manufacturing Method for Superalloy Gas Turbine Components

Round 1

Reviewer 1 Report

This paper presents an approach for abrasive water jet milling as an efficient manufacturing method for superalloy gas turbine components. The research has certain application values for practical engineering. However, some issues need to be addressed. The comments are as follows:

(1)     The diameter of the jet nozzle should also have great effect on the machining performance of abrasive water jet milling. Have the authors considered this influence factor?

(2)     Have the authors tried different size of abrasive garnet? Why the abrasive garnet size of 80 is used?

(3)     In this paper, the authors just compare the performance with conventional milling. Actually, there are also many other nontraditional machining methods for gas turbine components such as electrochemical machining, electrical discharge machining et al. The authors should better compare abrasive water jet milling with other nontraditional methods.

(4)     The principle of abrasive water jet milling used in this paper should be described more detailly, and a schematic diagram should be added.

Author Response

(1) and (2):

These two comments are very valid and interesting, which we yet have not investigated but it is intersting for future work. In this work we mainly focused on standard settings recommended by the machine supplier for these two parameters, a text clarifying this has been added to the experimental section, line: 242-245. However, it is an interesting observation made by the reviewer since it may play a crucial role on erosion and consequently the MRR. Therefore, a comment regarding future work has been added to the last sentence of the analysis and discussion section at line: 649-652.

(3)

Yes, we have been exploring such methods in prior work, but our target in this work has been to compare to the traditional machining and we had a feeling that adding such parts may result in the lost focus on the AWJ parts. We have acknowledged this and added a sentence at line: 33-35.

(4)

Very good idea, a schematic illustration of the AWJ process has been added in the experimental section, line 274-275.

Reviewer 2 Report

- Labelling on the diagrams in Figure 4 and 5 too small. Enlarge the figure and/or the labelling.

- The profile examined in chapter 3.4 is not yet a gas turbine component, but only a profile used there. The title and chapter heading therefore promise the reader more than what was actually investigated.

Author Response

(1) Labeling:

Labeling has been increased.

(2) Chapter 3.4

Agree on the comment, the title of the chapter has been changed into: AWJ milling of an example component geometry, see line 501.

Reviewer 3 Report

A brief summary:

The aim of the paper was to investigate the abrasive water jet milling method in terms of its effectiveness and productivity for manufacturing parts from superalloys. Authors presented the experimental tests with main focus on the influence of the input parameters, such as nozzle distance, water jet pressure and traverse speed on the efficiency of the process as well as the accuracy of parts and selected surface roughness parameters.

Broad comments:

A significant achievement and main novelty of the presented work is the analysis of the possibility of adopting the abrasive water jet milling process for the rough machining of superalloys. The subject of the paper is practical and important as it could potentially improve machining crucial parts in aviation industry. The introduction of the paper provides sufficient background. The references are relevant and up to date. The methods and results are presented in a clear way. However, some of the conclusions, where authors state, that the AWJM method is a good alternative to milling need to be changed, because from the results it is plain to see that both the accuracy and the surface quality after AWJM is very poor and there has to be another traditional milling operation (or peening which authors indicated but not investigated) which implies time wasted on re-setup on different machine and thus total efficiency of the process as a whole is bound to be much lower. Authors in some places indicated that, but in some not and it should be made very clear. The references are relevant and up to date. The methods and results are presented in a clear way

Specific comments:

·        Some of the citation is not correct, i.e line 38 or 163.

·        There are quite a few language errors that need to be corrected, i.e line 81 “which prone to distort”, line 108 “This also opens for close loop control” or line 198 “effects … is …” etc.

·        Line 127: “The surface roughness is typically in the range of 4μm to 6μm” Which surface parameter the authors refer to?

·        Line 206: the sentences in that point do not make sense. “AWJM rough milling may offer great possibilities … in the same setup as roughing”.

·        Line 239 “no brand machine built from standard components” authors need to elaborate.

·        Some of the conclusions are obvious i.e. line 316 “lower speed increases the erosion depth” or line 325 “larger distance result in a wider erosion track”.  Were the experiments pertaining single beam passing tests really necessary?

·        Line 364: what are “test coupons”?

·        The conclusions that imply that AWJM has similar MRR as traditional milling, not taking into account the necessity of further machining after AWJM, i.e: line 369. This is a serious flaw and should be carefully addressed.

·        Line 459: “for the SS of 0.2 mm, which has an almost flat sidewall” – Not according to the figure 13, where one can see a huge undercut at the bottom

·        Line 480: Figure 17 should be Figure 16.

·        Line 590: “Another advantage is … the ability to change direction and generate very small radii” – in theory it is true, but in practice small radii need sharp change in direction of linear axes which necessitate either lower traverse speed (which will result in more material removed and thus lowering the accuracy) or very sharp turn which induce high load on the axes and will result in following error in servodrive.

·        Table 9 is titled “results” and contains hardly any results, no accuracy, no surface roughness etc. but some comments from literature. The whole chapter 4 seems to be repetitive and not giving much new insight or imput.

·        Last sentence of conclusions imply again that the AWJM followed by a traditional milling is the most preferable, whereas authors hadn’t even compared efficiency of AWJM + milling to traditional milling. Thus the main conclusion of the article seem to be unfounded and misleading.

Author Response

(1) Citations:

We interpret this as wrong to entitle et al. when it was only one author and adjusted accordingly at several locations in the introduction. Please advise if we misunderstood this comment.

(2) Language corrections:

Agree, the manuscript has been adjusted accordingly on several locations throughout the manuscript.

(3) Surface roughness:

We refer to the Arithmetic mean height of the surface, this clarification has been added to the text at line:129

(4) Line 206:

Agree, the sentence has been deleted.

(5) Line 239:

This machine was built by in-house using standard AWJ components, text has been adjusted with this information. However, we regret to inform that we do not have any further information of the machine since the company does not exist anymore. In fact, the company founder, who built the machine has unfortunately passed away and we do not have any access to the machine to give further information. This is the reason that we wanted to evaluate the single track erosion with this machine to study if it is comparable to standard machines.  

(6) Single track tests:

Yes, the results may be obvious, but the actual magnitudes of the erosion depth track width shown in the result figures are not. It was further of interest to compare the non-branded and the standard AWJ machines in this perspective to verify that we got the same single track erosion characteristics as expected. A comment on this was added to the text at line: 251-252. Further, from our point of view, we definitely see the single track evaluation as the foundation of this study. This investigation has set the premises for the specific machine influence on specific parameters on the resulting erosion characteristics. We the have used this input for selection of suitable settings for the further study of different sidesteps.

(7) Line 364:

We have rephrased this into samples, the same mentioned in the experimental section. The same material has been used for these test expect the test on the large ring. 

(8) MRR:

Yes, we agree, this is a fair comment if we compare AWJ milling to traditional finish milling. We have added this as comments into the text, see line: 15-16, 375-378 and also in chapter 4 at line: 632-633.

(9) Sidewall geometry:

This text refers to the sidewall created from the changing of direction which is mentioned and clarified in text at line 435-437 and in further explained by red arrows in Figure 14. The text at Line 459 was superfluous and removed.

(10) Figure 16/17:

Yes, figure numbering has been adjusted. 

(11) Small radii:

Good comment, in this work we mainly wanted to show the MRR and this was a result was more of a note rather than a clear conclusion. However, we believe that it could be possible to evaluate this further in a detailed study. We have added a comment on this in the analysis part, see line: 554-556 and 592-593.

(12) Table 9 and Chapter 4:

The Table labeling has been changed into: Comparison between rough AWJM milling and conventional milling, line 637.

We agree to some extent on of this comment, but Chapter 4 is the key that summarise the results and set it in relation to traditional milling, which has been the aim of this work. We have adjusted the chapter and removed the repetitive parts.

(13) Conclusion:

Yes, we agree and have changed the conclusion respectively to: AWJM for rough milling subsequently followed by a traditional finish milling is a viable concept for further exploring of manufacturing of gas turbine components. See line: 671-673.

Thank you for all good and useful comments, we really appriciate your time and effort spent on this. We think that the adjustments based on your comments has made the manuscript much better and clearer. 

Round 2

Reviewer 3 Report

The responses and changes in the articles are satisfactory.