Analysis of Surface Grinding of Thermoplastics Specimens with Inline Measurements

Round 1

Reviewer 1 Report

The manuscript “Analysis of surface grinding of thermoplastics specimens with inline measurements” is very well performed and the results are interesting. This manuscript has the potential to be considered for publication in Journal of Manufacturing and Material Processing after revision.

There are some points to enhance or clarify from your research:

1- The abstract can be improved by highlighting the most significant results obtained in this research.

2- Line 30: give example of other manufacturing processes.

3- Line 31: define Tg, please.

4- Line 83: write as abbreviation of Differential Scanning Calorimetry (DSC), please.

5- Line 86: Please explain how the machining parameters were selected? Include reference or ASTM, please.

6- Line 185: Please explain, how heat generated on the surface by rubbing and plastic deformation can result in power lost during the grinding process?

7- Line 188: complete the sentence before inserting the equation (6).

8- Line 205: Please explain that how the presence of filler can affect plastic deformation and brittleness of tested materials.

9- In Figure 2A and Figure 4A, please write the numbers of x axis similar to the x axis in Figure 2B and Figure 4B.

10- Line 307: please insert DOI for 10^th reference if it is possible.

11- Please include more details about testing condition and information of equipment used for SEM and DSC.

12- Can you please highlight the main objective of current research and explain its novelty compared with similar works, please.

 

 

 

 

 

Author Response

Thanks to the reviewer for his precious suggestions. All modifications were added to the manuscript with the red color. 

1- The abstract can be improved by highlighting the most significant results obtained in this research.

This paper analyzes the surface grinding of unfilled and glass-filled polyamides. The process is performed by varying the workpiece velocities to evaluate applied practical application in the industry while being energy efficient. During the machining, the temperatures, normal forces, tangential forces, and spindle power were collected, and the surface quality was evaluated by a Scanning Electron Microscope (SEM), helping to determine material removal mechanisms and study their behavior under grinding. One of the primary outcomes of the present research was that, differently from most metallic and ceramic materials, polyamides benefited from the material removal rate increase. We had higher quality material removed efficiently. Also, the specific energy of both materials converged to previously demonstrated values, showing once again is highly dependent on the matrix. Moreover, the time-dependent mechanical properties of the material during processing were identified. The fast application of the force at high speed gave less time to respond to the mechanical strain, determining an improvement in the surface quality of the samples. Consequently, the surface quality of the final product improved with a speed increase, leading to low roughness values.  

2- Line 30: give example of other manufacturing processes.

We specify that milling and turning are the other processes.

3- Line 31: define Tg, please.

Tg is the temperature at which polymer changes from a rigid glassy material to a soft one.

4- Line 83: write as abbreviation of Differential Scanning Calorimetry (DSC), please.

The abbreviation DSC was added.

5- Line 86: Please explain how the machining parameters were selected? Include reference or ASTM, please.

The machining parameters were selected after several preliminary testing leading to free-defect specimens. Dimensions of the milled specimens were measured using a digital micrometer with a resolution of 1 µm. 

6- Line 185: Please explain, how heat generated on the surface by rubbing and plastic deformation can result in power lost during the grinding process?

Analyzing the process, three main phases existed. The rubbing phase occurred at small depths with elastic deformations at the surface of the workpiece. Plowing was accomplished by some material plastically deformed with a depth increase. This plastic deformation typically presented itself in the form of upheaval around the leading edge of the grain, and it was most often characterized by the formation of a scratch or groove. Finally, at yet more significant depths, a chip was formed and ejected from the workpiece surface [see 10.1243/09544054jem1520]. 

7- Line 188: complete the sentence before inserting the equation (6).

The sentence was completed.

8- Line 205: Please explain that how the presence of filler can affect plastic deformation and brittleness of tested materials.

Adding the glass fibers to the PA66 matrix improves mechanical properties such as elastic modulus, yield strength, and ultimate tensile strength, drastically reducing the elongation at break (see Table 2).

9- In Figure 2A and Figure 4A, please write the numbers of x axis similar to the x axis in Figure 2B and Figure 4B.

Figures were updated.

10- Line 307: please insert DOI for 10th reference if it is possible.

doi added.

11- Please include more details about testing condition and information of equipment used for SEM and DSC.

Firstly, the pieces were cleaned and mounted after processing on an Evo MA25 Scanning Electronic Microscope (Carl Zeiss AG, Oberkochen, Germany) to examine the ground surface and systematically appraise the surface quality and possible factors of defects. The ground surface was coated with gold to reveal the initial microstructure without polishing it to alter the surface quality. The surface images were taken with 20 kV using an NTS BSD detector to identify backscattered electrons under very low angles and a maximum magnification of 500x. 

DSC analysis was performed on small samples (5 mg) with a DSC 403 F3 Pegasus (Netzsch-Gerätebau GmbH, Selb, Germany), equipped with a silver furnace, performing a thermal cycle from −50 to 340 °C at a rate of 20 °C/min and N2 condition. 

12- Can you please highlight the main objective of current research and explain its novelty compared with similar works, please.

The main objective of the present research is to use the recently emerged High-Efficiency Deep Grinding (HEDG) to machine Glass Fiber Reinforced Plastics. HEDG is a grinding process undertaken at high wheel speed, relatively large depth of cut, and moderately high work speed. HEDG requires a high power input and consequently needs a well-designed process to secure the workpiece surface integrity, low temperature, and reduced wear of the grinding wheel.

Reviewer 2 Report

This paper aims to evaluate the resulting surface properties of natural and glass fiber-filled polyamides (PA66 and PA66GF30) after the surface grinding process was performed by varying the workpiece velocities to determine whether this process can be applied practically in the industry while being energy efficient. 

The experimental methods and detection methods used in this paper are reasonable and the data are credible, but there are still some problems.

1、The paper only compares the monitoring results of force，roughness，energy caused by the feed rate, and the experimental samples are not comprehensive enough, such as the grinding wheel speed, X/Y axis speed, and the amount of cutting tools. At the same time, the author did not analyze the limit experiment results.

2、The discussion of the force, roughness, and energy monitoring results is not deep enough. Only the trend of changes in monitoring results was analyzed, and the reasons for the changes were not sufficiently explained.

3、The paper is not theoretical enough, like a test report rather than a scientific paper

Author Response

Thanks to the reviewer for his precious suggestions. All modifications were added to the manuscript with the red color.

1- The paper only compares the monitoring results of force, roughness, energy caused by the feed rate, and the experimental samples are not comprehensive enough, such as the grinding wheel speed, X/Y axis speed, and the amount of cutting tools. At the same time, the author did not analyze the limit experiment results.

The same authors did the variation of the parameters mentioned above in previous papers (10.1016/j.promfg.2020.04.279 and 10.3390/ma14175041). For this reason, the present paper only focuses on the variation of the infeed speed.

2- The discussion of the force, roughness, and energy monitoring results is not deep enough. Only the trend of changes in monitoring results was analyzed, and the reasons for the changes were not sufficiently explained.

Adding the glass fibers to the PA66 matrix improves mechanical properties such as elastic modulus, yield strength, and ultimate tensile strength, drastically reducing the elongation at break (Table 2). Consequently, a lower cutting force was required to grind the material, as reported in previous research [10.3390/ma14175041].

 

3- The paper is not theoretical enough, like a test report rather than a scientific paper

The article reports the experimental activities of grinding natural and glass-filled polyamides to use the recently emerged High-Efficiency Deep Grinding (HEDG). HEDG is a grinding process undertaken at high wheel speed, relatively large depth of cut, and moderately high work speed. HEDG requires a high power input and consequently needs a well-designed process to secure the grinding wheel's work-piece surface integrity, low temperature, and reduced wear. The fundamental issue is to acquire sufficient data before creating a numerical-theoretical model of this process for thermoplastics. This article aims to collect this data, giving an excellent theoretical background of the physical phenomena.

Reviewer 3 Report

This paper analyzes the surface grinding of unfilled and glass-filled polyamides. The process is performed by varying the workpiece velocities to evaluate applied practical application in the industry while being energy efficient. The temperatures, normal forces, tangential forces, and spindle power were collected, and the surface quality was evaluated by SEM. The results are not resonable in understanding the material removal mechanism of polyamide. These research results lack of theoretical significance and application values. I have few critical comments that are aimed to help the authors improve the quality and impact of this manuscript.

1. As mentioned in the manuscript, the Peclet number was applied to evaluate the heat transfer process of grinding. The Peclet is always used in fluid mechanics and please clarify why it is reasonable in this situation.

2. In line 148-152, the author stated the heat transfer mechanism at high and low speed. But I think there is not enough data to get this conclusion. Please make it mor clear for this part.

3. For Section 3.2, the force and energy were discussed and some equation were listed in the manuscript. But I don’t think the relationship between the force and processing parameters are clearly stated. Please state the why the forces of PA66 AND pa66gf30 are different from each other.

4. For Eq.6, please clarify the meaning of this equation and why it is efficient to evaluate the so-called specific energy.

5. In line 206-208,the author indicated the PA66GF30 were more brittle, but the material mechanical property was not discussed in this work. I think the mechanical properties of the two materials should be added.

6. The written English in the whole part needs to improve, as well as grammatical errors need to be addressed.

 

Author Response

Thanks to the reviewer for his precious suggestions. All modifications were added to the manuscript with the red color.

1. As mentioned in the manuscript, the Peclet number was applied to evaluate the heat transfer process of grinding. The Peclet is always used in fluid mechanics, and please clarify why it is reasonable in this situation.

A Peclet number is a similarity number, characterizing the cutting regime's relative influence on the workpiece material's thermal properties. For Pe greater than 10, the heat source (the cutting tool) moves over the workpiece faster than the velocity of thermal wave propagation. The thermal energy generated in cutting due to the plastic deformation of the work material and friction at the tool-chip interface did not affect the work material ahead of the tool. On the contrary, for Pe less than 10, the thermal energy due to the plastic deformation and friction makes an essential contribution to the process of plastic deformation during cutting, affecting the mechanical properties of the work material [see 10.1007/978-1-84996-450-0_1]. 

2. In line 148-152, the author stated the heat transfer mechanism at high and low speed. But I think there is not enough data to get this conclusion. Please make it more clear for this part.

The contact time t_c was equal to l_g/v_w defined as the time the tool was in contact with the workpiece. Its value ranged between 0.211 and 0.632 s for a contact length lg of 6.32 mm. As the speed increased, less heat was transferred to the samples because of a reduction in the contact time. The thermal data shows no variation, as reported in 10.3390/ma14175041.

3. For Section 3.2, the force and energy were discussed and some equation were listed in the manuscript. But I don’t think the relationship between the force and processing parameters are clearly stated. Please state the why the forces of PA66 AND pa66gf30 are different from each other.

Adding the glass fibers to the PA66 matrix improves mechanical properties such as elastic modulus, yield strength, and ultimate tensile strength, drastically reducing the elongation at break (Table 2). Consequently, a lower cutting force was required to grind the material, as reported in previous research [10.3390/ma14175041]. 

4. For Eq.6, please clarify the meaning of this equation and why it is efficient to evaluate the so-called specific energy.

The knowledge of specific energy was essential in grinding because it influenced the surface integrity of machined components in ductile materials. The specific grinding energy was a helpful process parameter to control ductility since the specific grinding energy was accompanied by a transition from ductile-regime to brittle-regime [10.1016/j.jclepro.2015.12.106]. 

5. In line 206-208, the author indicated the PA66GF30 were more brittle, but the material mechanical property was not discussed in this work. I think the mechanical properties of the two materials should be added.

Adding the glass fibers to the PA66 matrix improves mechanical properties such as elastic modulus, yield strength, and ultimate tensile strength, drastically reducing the elongation at break (see Table 2).

6. The written English in the whole part needs to improve, as well as grammatical errors need to be addressed.

The revised version of the manuscript was proof corrected by a native English lecturer. 

Reviewer 4 Report

In this work, the authors focussed on grinding of natural and glass-fiber filled polyamides. The proces analysis was studied by measurement of temperature, forces and spindle power. The results were also evaluated in terms of roughness measurements. 

This study is timely and suitable for JMMP. The experiemntal procedure is well described and results are presented properly. The conclusions also support the observations.

 

I recommend accepting this paper as it is.

Author Response

Thanks to the Reviewer for his comments

Round 2

Reviewer 1 Report

Thanks for revision. 

Author Response

Thanks to the reviewer

Reviewer 2 Report

 Accept in present form

Author Response

Thanks to the reviewer

Reviewer 3 Report

Please state that why grinding is used to cut the polymers intead of the other methods.

Author Response

Thanks to the reviewer for his precious suggestions. All modifications were added to the manuscript with the red color. 

The surface improvement by grinding is essential concerning other machining processes, especially when PMCs parts are realized with Additive Manufacturing.