The leading supplier of cutting edge technology

Measuring the surface profile of a recessed valve seat - non contact surface metrology for Engineering applications

Rousant Sherwood manufacture precision recessed valve seats in monolithic components where the profile of the seat is critical to its performance. However, measurement of the profile is difficult to achieve with traditional metrology tools when the seat is deep inside the cavity of the part. Until now the only method open to them was to section the component and then using an imaging tool to get a sample end profile of the valve seat. This is a slow and resource intensive operation and only allows sampling of part of the valve seat, furthermore the process of sectioning the component and polishing it to examine the end profile leads to distortions in the sample. A new approach was called for.

For this metrology application the Zygo NewView 6300 non-contact surface optical profiler was used with a Super Long Working Distance Objective having a working distance of 40mm. This allows the tool to measure the complete profile of the valve seat deep inside the cavity of the part in seconds. The results shown below are example measurements of recessed valve seats measured with the Zygo NewView 6300. To summarise, the key advantages of this approach are:

  • Fast Non contact measurement, over 300, 000 data points in seconds
  • Measurement deep inside the part where conventional tools would not have access
  • Automation of the measurement process once the part has been placed in the fixture the operator need only press the measure button to perform a complete measurment that can be passed to the SPC (statistical process control) system
  • Obviates the time and resource in sectioning and polishing components
  • Provides an accurate and faithful surface profile measurement that can include a host of surface parameters such as Ra, rms, PV etc including 2D slices taken from the 3D topography

Figure 1 is taken from a measurement of a complete valve seat, and Figure 2 shows the results from measuring the profile of a valve seat that has been sectioned conventionally to allow access to the end profile.

Figure 1

Figure 1

In the above screenshot (Figure 1) the results of measuring a complete valve seat are displayed. The height profile of the valve seat is colour coded for clarity - pink indicating maximum surface height and blue indicating lowest. The top left image shows the positioning of a circular snap line around the top of the valve seat and this is displayed as a 2D profile below the image, showing the 12 micron variation in height of the valve seat along the top surface. The results display a number of measurement parameters for this application including Ra, PV and rms as well as the dimensions of the part. This measurement was taken in a few seconds.


Figure 2

Figure 2

In the above screenshot (Figure 2)the end profile of a conventionally sectioned component has been measured. To show the distortion from the sectioning and polishing process. The sample surface profile appears “peakier” at the end when compared to the profile further along the sample, this is made clearer by the pink height colour information fading away as the profile becomes closer to its original form before sectioning.

These measurements were taken from test parts manufactured by
precision engineering company Rousant Sherwood: www.rousantsherwood.com