In the processing of eyewear metal components, hydraulic forming causes plastic deformation of the material, and hardness may change accordingly. This article uses a cupronickel product as an example to compare hardness records before the first hydraulic pressing, after the first hydraulic pressing, and after a second pressing and edge trimming. The test force for this test was 500 gf, and the average was taken after 5 measurements; the instrument type, measurement point locations at each stage, and raw readings still need to be verified.
Before the first hydraulic pressing, the average hardness measured on the cylindrical cupronickel material after wire drawing was HV141.39 (Figure 1). This value falls within the half-hard 1/2H range (HV130–160) used in the article. Figure 1 only shows the material appearance; the hardness value before wire drawing was not included in this record; the above range also needs to be confirmed based on the specific material grade and product standard.
Figure 1 Appearance of cylindrical cupronickel material
After the first hydraulic pressing, the average hardness of the workpiece was HV215.56, an increase of 74.17 HV compared with before hydraulic pressing. The hardness increase of this part is consistent with the phenomenon of cold work hardening. The appearance of the workpiece after the first hydraulic pressing is shown in Figure 2.
After the second pressing and edge trimming, the average hardness was HV215.07, a decrease of 0.49 HV compared with after the first hydraulic pressing. The average values after both processings are within the 190–220 HV range used in the article; the correspondence between this range and the SH grade needs to be confirmed in conjunction with material standards. Due to the lack of readings for each measurement point and information on measurement fluctuation, the effect of the second processing on hardness cannot be judged solely based on the 0.49 HV difference. The appearance of the secondary processed part is shown in Figure 3.
Figure 2 (left) Workpiece after the first hydraulic pressing Figure 3 (right) Appearance of the secondary processed part
For this part, the hardness after the first hydraulic pressing was higher than before hydraulic pressing, and the average value after the second edge trimming was close to the value after the first hydraulic pressing. Since the actual deformation amount and measurement point data are not listed, this record cannot infer a general relationship between deformation amount and hardness change. For microscopic Vickers hardness testing, please refer to article 004 "Application of Microscopic Vickers Hardness Testing in Eyewear Manufacturing"; the testing method actually used in this article still needs to be confirmed based on instrument records. If you would like to learn more or supplement on-site data, please contact us. Thank you for reading.