Using a 3D Non-Contact Profilometer for Quality Analysis on Electrical Discharge Machined Metals

EDM or Electrical Discharge Machining is a manufacturing process that can remove material using electrical discharges [1]. Usually, conductive metals are difficult to machine using conventional methods. However, this machining process is generally used with conductive metals.

Precision and accuracy need to be high for EDM, in order to meet acceptable tolerance levels, as is the case with all machining processes. This article highlights the assessment of the quality of the machined metals using a Nanovea 3D non-contact profilometer.

Importance of Profiling Machined Metals

Simple measurement tools, such as rulers or calipers, are no longer able to meet the level of accuracy needed to satisfy tighter tolerance requirements, with the increased preciseness of machining. In such a scenario, high resolution measurement tools must be used. Moreover, in an effort not to cause bottlenecks in the production process, the measurement time of quality control instruments must keep up with the manufacturing speed.

An ideal instrument for quality control will possess high scanning resolution capabilities, along with short measurement time and simple user-friendly analysis tools and software. Here, the short measurement time must include time taken for sample preparation and setup.

The Nanovea 3D line sensor is an ideal instrument for machine metals’ quality control inspections. It can quickly scan and produce high resolution surface scans within seconds, which can then be further analyzed to quantify various different dimensions of a machined part(s). What’s more, it can also measure all types of materials, irrespective of curvature, thus making it ideal for measuring a vast range of surfaces in quality control applications.

Equipment Featured

NANOVEA HS2000

  • High Speed Inspection and Precision Flatness Measure
  • High Speed Precision Flatness Measurement
  • Advanced Automation
  • Customizable Options
  • Rigid and Stable Structure

Measurement Objectives

Using Nanovea’s high-speed line sensor, the inspection of two metallic samples with holes in the form of hexagonal patterns drilled via wire EDM was conducted. To observe the precision and accuracy of the WEDM machining process, the roundness, equivalent diameter, and spacing were then quantified.

Profilometry Results

Measurement Parameters

Table 1

Test Parameter Value
Instrument HS 2000L
Optical Sensor LS2 (1000 µm height range)
Scan size (mm) 40 mm x 20 mm
Step size (µm) 10 µm x 10 µm
Scan time (h:m:s) 00:00:38

Samples Tested

Two metallic samples with hexagonal patterned holes drilled via wire EDM

Two metallic samples with hexagonal patterned holes drilled via wire EDM

Results: Sample A

3D view of scan taken for Sample A

Figure 1. 3D view of scan taken for Sample A

A) Motif analysis of holes B) histogram of equivalent diameter distribution C) histogram of roundness distribution for Sample A

Figure 2. A) Motif analysis of holes B) histogram of equivalent diameter distribution C) histogram of roundness distribution for Sample A

Extracted area of hole with outlying roundness for Sample A

Figure 3. Extracted area of hole with outlying roundness for Sample A

Contour analysis of spacing between holes for Sample A

Figure 4. Contour analysis of spacing between holes for Sample A

Results: Sample B

3D view of scan taken for Sample B

Figure 5. 3D view of scan taken for Sample B

A) Motif analysis of holes B) histogram of equivalent diameter distribution C) histogram of roundness distribution for Sample B

Figure 6. A) Motif analysis of holes B) histogram of equivalent diameter distribution C) histogram of roundness distribution for Sample B

Extracted area on outlier in equivalent diameter for Sample B

Figure 7. Extracted area on outlier in equivalent diameter for Sample B

Contour analysis of spacing between holes for Sample B

Figure 8. Contour analysis of spacing between holes for Sample B

Discussion

Within just 38 seconds, a 40 mm x 20 mm area was scanned, with nanometer level resolution. The results obtained, for Sample A and B, are very similar. In the case of both samples, a hole density of approximately 4.25 holes/cm2 was observed. Below are stated the sample specific details.

On Sample A, the holes had an equivalent diameter of 0.9887 ± 0.0048 mm and roundness of 0.9630 ± 0.0176 (a roundness value of 1 is considered a perfect circle) using a Motifs study. Near the mean of 0.9887 mm, the histograms show that the majority of holes had an equivalent diameter.

Two holes exhibited two standard deviations above the mean. Such holes may not pass quality control requirements, depending on the acceptable tolerances. In the case of roundness, only one hole was significantly different. It is possible to closely inspect the outlier by extracting it and its surrounding area, as depicted in Figure 3. Finally, the average spacing between each hole and its nearest neighbors (3 for hexagonal patterns) is 4.107 ± 0.013 mm.

A Motifs analysis conducted on Sample B showed that the holes on that sample have an equivalent diameter of 0.9842 ± 0.0057 mm and roundness of 0.9630 ± 0.0079. As an outlier, one hole was singled out from the rest – due to its equivalent diameter – as seen in Figure 7. Further, Figure 8 shows the contour analysis and spacing between holes to be 4.107 ± 0.16 mm, which is almost equivalent to Sample A.

Conclusion

The equivalent diameter, roundness, and spacing of samples (which were machined via wire EDM) were quantified. This was done with a view to observe the precision and accuracy of wire EDM machining. Results showed negligible differences between both samples.

A few of the holes from both samples measured fell outside a couple of standard deviation from the mean. These were subsequently singularly inspected by extracting the area that contained the outlying hole of interest from the original scan. Using the analysis software, multiple dimensions were measured on each sample.

Further, this software is capable of creating templates for the quick and automatic generation of results like those seen in this article. Nanovea’s profilometry technology can provide quick and accurate measurements for conducting quality control on machined parts.

References

[1] Jameson, Elman C. Electrical discharge machining. Society of Manufacturing Engineers, 2001.

This information has been sourced, reviewed and adapted from materials provided by Nanovea.

For more information on this source, please visit Nanovea.

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