Forming a Flanged Hole When Quenching Press-Hardened Steel for Mechanical Fastening
Round 1
Reviewer 1 Report
In the first line of simulation chapter DEFORM 3D is not well written
The material properties used in the FEM modelization are not clear enough. It is necessary to introduce a table with the data used in the model (flow stress, elastic modulus, Poisson's ratio, 99 thermal expansion coefficient, thermal conductivity, heat capacity, and time-temperature transformation (TTT) curve, according to the material temperature and strain rate)
It is also missed the value of the heat transfer coefficient used in the modelization of the process. Is it a constant value? A pressure dependent value?
The temperature values defined for the tools in the modelization are too low. In a production tooling temperatures over 100ºC can be achieved even when refrigeration is applied to the tooling. The results may not reproduce a real experimental test
To my eyes the changes observed in Fig4 b/c/d are negligible. I do not really understand the reasoning about this figure. It makes more sense to compare more different fracture threshold constants. I guess that this is what the authors did to reach a final fracture threshold constant
Concerning Fig5, I would suggest to make a zoom in the cutting area since this is the area that will loose most of the temperature and it is critical area for the subsequent hole flanging. Are the authors sure that the temperature is that area is higher than 640ºC. Another point, in Fig 5a, where are those values taken from? This is not explained
Figure 10 is not clear at all, authors should indicate the burrs and its dimensions
The explanation of the hardness measured in the experimental test is not clear enough. There are different names in the text and in the figure and the reader may get confused. Furthermore these results suggest that the numerical model does not adequately represent the real process because the results in terms of hardness are very different
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript is interesting. The topics of the research work are timely. The authors should consider the following comments before publishing the article.
- The program used in the numerical simulation is DEFORM-3D, not DEFRM-3D (line 92).
- The material model given in Fig. 2 is for a single strain rate of 0.01 1/s. This strain rate is very low. It seems that a punch velocity of 54.1 mm/s would correspond to a much higher strain rate. This can be checked in simulation.
- Has heat transfer been taken into account in the calculations? If so, you need to provide values for the heat transfer coefficients.
- What fracture criterion was used in the numerical simulation? Provide the mathematical formula for this criterion.
- What friction model was used in the simulation? You need to provide the value of the friction factor/coefficient.
- It would be advisable to compare the forming forces from the calculations and experimental studies. This comparison would validate the developed FE model of the piercing process.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors provide an interesting work with good validation for mechanical fastening. A few comments are given below
The introduction should provide details on the materail
Experimental details are missing. The authors should provide in-detail the various parameters and dimensions of the experimental process.
Please correct formatting issues e.g. "strength of 590 MPa or less. [7]"
Simulation details are also missing. Hardening rule? element size ? mesh type ? Material model ? etc etc etc
The authors do not discuss the material integrity after performing the proposed method. Please explain effects on hardness, strength etc.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
No comments
Author Response
We really appreciate your kind review.
Reviewer 2 Report
The authors have responded to my feedback. The responses are satisfactory except for the heat transfer coefficient issue. The authors reported that the value of this coefficient was 2.1 W/m2K. This is a very small value. In the analysis of metal forming processes, the heat transfer coefficient between the tools and the workpiece is assumed to be between 2000 and 20000 W/m2K. The value given by the authors is much smaller than the value of the coefficient describing the heat exchange between the workpiece and the environment. Perhaps the value given was expressed in kW/m2K?
Author Response
As the reviewer commented, we used the wrong unit of heat transfer coefficient in our paper. We changed the unit of the heat transfer coefficient kW/m2K in Chapter 3.1.
