Microforming a Miniature Cup-Shaped Internal Gear Using a Cold Lateral Extrusion Process

Round 1

Reviewer 1 Report

General Evaluation

The paper concerns an interesting study in the area of manufacturing technology of copper micro-gear, focused mainly on the influence of initial grain size on the quality of the formed component. The paper is clearly written and it is within the scope, though it exhibits room for improvement, i.e. concerning mainly the strengthening of its scientific basis and highlighting the innovative aspects of the study which seem that were not strongly presented in the Introduction. More specific comments are following. 

Specific comments

1. Material C1100 corresponds to ETP-Cu alloy. The composition has to be referred and the international relevant alloy specification (e.g. ASTM C11000 or ETP-Cu, CW004A).
2. The Vickers hardness testing procedure and standard have to be included in the section “Materials and Methods”.
3. Equation (2) presenting the feeling factor (FR) has to be more clearly explained together with its terms.
4. Table 1 includes misleading names in the columns (tooth type? spur gear?).
5. In Table 2, the mechanical properties are not suitably shown, e.g. tensile strength (R_m) proof strength (R₂) and elongation at break (A%) are missing.
6. In 2.3 Section, the tool steel type (SKD-11) is necessary to be correlated with international steel designation.
7. HV measurements are inconsistent to soft annealed ETP copper (Table 2). Usual hardness after soft-annealing is ranged within 40-65 HV.
8. The annealed Cu at 900 degC failure condition cannot be stated as brittle, since it presents ~ 15% max strain (Figure 7). Coarse grained copper alloys could lead to lower elongation and strength, presenting lower ductility, due to the effects of micromechanics of dislocation / slip and grain boundary interactions.
9. Please check whether the highest temperature annealed copper exhibits gear teeth failures during forming, as a result of lower ductility. This also could deteriorate the component feeling factor.
10. Figure 11 is confusing; different scale ranges have to be used to make the hardness curves more clear and separable.

Grammar/Language

The grammar/language needs improvement. A final proofreading is also needed to correct minor spelling errors. For example:

1. In the abstract, copper instead of cooper.
2. L114: exponent instead of component.
3. L178, L225-226, L263-264 (11 μm?)

Author Response

Please refer to the attachment (PDF format).

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of the paper entitled "Microforming a miniature cup shaped internal gear using a cold lateral squeezing process".

The paper deals with the problem of  meso-scale small-size forging of  cup with internal gear. The subject is interesting and up-to-date, and correspondingly, so is the paper. Authors investigate the effect of grain size on fillout capabilities of copper in coldwork temperature range, in as-received and annealed condition. The work stays in the convention of micro-forming/forging studies, where grain size effect is focused on. Added value here is consideration of hardening coefficient, thus overall rating of the work is good as long as following deficiencies are amended for:

1) the use of term "microforging"  is not justified here, as the component is relatively "large". The convention is to use this term is dimensions fall bellow 1 mm (or at least one of them) so conventionally negligible effects must be considered. It's safer to use less radical term (see above), or provide justification for using "micro".

2) the term "lateral squeezing" is not common to describe similar processes. Please justify using it, best providing citation after other authors.

3) Introduction needs revision with simultaneous extension of two aspects:

i) review of methods used for shaping this or similar geometries

ii) review the grain size effect related works concerning copper, for reference of grain size used there, for instance.  Grain size effect in microforming is everpresent in literature and it's no use citing dual-phase or magnesium alloys or other materials of different characteristics. Please revise; reducndant references may be removed.

iii) paragraph 53-71 is chaotic, the subjects are mixed and it's hard to follow the thread - please revise.

iv) line 45 "90 um is ideal for forming..." is an abuse. If fact in the work cited speaks of one of three coarse grained materials, and this statement is generally false. 

4) sec. 3.3 need revision:

i) paragr. 212-226 is chaotic - description of own results are mixed with other works with shortcuts, which does not allow to clearly tell them apart. 

ii) what does "elongated material" means? (line 209) - revise the shortcut

5) Conclusions  - are consistent with presented findings, however they need more generalized formulation. In current form they make a good beginning of a summary or abstract to substitute for the present one.

6) abstract is recommended for revision. There are no particular errors to point out, but can sound better. Please follow the advise from p.5)

7) Issues with figures:

i) figure 3: consider changing "basement" to "bolster"

ii) marker in Fig. 8 (on the right) disproportionate versus that on the left and in Fig. 4a)

8) Explain (in methods) if "cold"  refers to room temperature or some heating below recrystallization homologous temperature was used.

Author Response

Dear reviewer

Please refer to the attachment (PDF format).

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised paper addressed most of the review comments satisfactorily.

However, there are some issues to be carefully treated:

1. Concerning Vickers hardness procedure, the applied load should be mentioned (Section 2.5).

2. Also, the annealed copper corresponds to the R220 temper (Tensile Strength = 220-260 MPa), as it is shown in the respective EN 1652 standard. The values of the tensile strength (Rm/TS), as shown in Table 2, are below 260 MPa and hence the hardness measurements (according to the standard) are expected to varied within 40 - 65 HV (or less). Please check and advise

Author Response

Dear reviewer,

The response of reviewer's comment is replied as attachment. 

Thanks for your time.

Author Response File: Author Response.pdf