During August of 2021 Bowers Group reached out to the National Physical Laboratory (NPL) for assistance with our measurement program after an internal conversation about optimising the measurement process of the setting ring gauges. We discussed with the NPL on using a measuring technique to work within the bounds of our process as determined by the ISO standard (K2) (B7). The following is a discussion of the mathematics provided and surrounding context around the finer details of systems in place of manufacture, calibration and collaboration with important parties Almost all of the communication throughout this project was over email what can cause some difficulty in explaining complicated problems. Therefore it was important to ensure clear standardised language was used with regards to technical discussion to avoid confusion, conflict or non-resolution. (K8)

Manufacture of the Setting Ring Gauge

Setting rings are manufactured to an incredible degree of precision using a S121 Universal cylindrical grinder. This machine has a number of complicated technology’s to achieve sub micron accuracy in optimal conditions. The internal grinding process is as displayed below (K6)

Each ring is secured to the magnetic chuck and ground individually as part of a batch before calibration. Batch flow is needed due to the chemical blacking process being provided by an external supplier which are sent out in bulk (K19)

Above is the drawing of the setting ring master sheet showing the tolerances for various rings with things such as parallelism, uniformity and nominal diameter (K14) (S6) This data was used to construct the pinning values for the rotational analysis further on in the report (S1)

For the manufacturing of the ring gauge we use the specific grade of steel hardened to a 61-63 Rockwell ‘C’ meaning that the gauge is hardwearing (K18)

How are the rings measured

Bowers XT setting rings are measured using a 6 point calibration using highly accurate linear measuring machine

The ring is measured for diameter at 3 points of the ring (top, middle and bottom) and then rotated 90 degrees to take a further 3 measurements to construct roundness, parallelism and mean size

Due to the 6point nature of the calibration its determined that there is an optimal measuring site of the position of the calibration to begin to ensure that the closest to optimal values are measured theoretically improving the quality of calibration. As the laser marking process sets the angle meaning the calibration is true and accurate (Plain setting rings are specified in BS 4064:1966) (K5) (K20)

Missed Calibration!

This can be a problem during the manufacturing stage as although a ring may be conformant to the standard it end up being rejected for rework/scrap because we cannot determine the correct location to measure the form of the ring.

The 8 Wastes of a missed calibration

Under the scope of the missed calibration there are a number of wastes to breakdown from this

Defects

Because of the calibration stage being rather expensive in terms of time (The Trimos machine is a slow process) defects at the final stage of checks can be costly, A pre check would be an excellent way to avoid investing time in a defected part

Overproduction

Due to the specific rejection rate of a calibrated ring being rather high overproduction is required due to the possible variability of the variability of pass rate variablity^2 leading to excess stock should a batch be excellent therefore actually reducing the principle gain from said good batching

Waiting

Due to the slow speed of the Trimos there is a large wait to determine the actual correctness of the ring which could be further alleviated by the speed of the Rondcom pre check. Furthermore the ring must temperature soak in the lab for at least 24 hours causing a huge time waste of up to 48 hours for a ring rework.

Unused Talent

There are a number of skilled operators who can operate the calibration machine is limited and those same individuals are working in other areas of the calibration system. This talent is taken away from other important systems to be implemented such as in-process inspection of manufactured parts.

Transportation

Bad rings are wasted through sending out for the blacking process can end up ultimately wasted meaning a cost in transport from going to an external supplier.

Inventory

Excess material is required to buffer out inaccuracies and errors in manufacturing what is not fixed through remanufacturing or in process testing and intervention.

Motion

Due to the placement of the Rondcom machine being next to the S121 grinder the pre inspection can be performed in the same room as opposed to when a reject ring is sent from the lab and then back to the grinding machine.

Extra-Processing

The further work required for a remanufacturing operation is costly and certainly eats into the profit margins through higher variance (K3)(S7)(K12)(S2)

Using another measuring machine (Rondcom NEX 200SD) we can measure the form of a ring gauge before sending to the linear measuring machine to determine the best angle to construct a good measuring face

From this we can export the raw rotary measurement data to get a trace form measurement of the Rondcom (S4)

(K9)(S5)

The combination of roundness traces and an accurate diameter measurements opens up the possibility of providing accurate calibration features at potentially many angles, e.g., every degree. For this kind of approach to be practical value, it would probably be necessary to take a further two traces close to a single trace in order to determine how sensitive the diameter is to changes in height about the trace.

Once the measurement process has been completed its possible to do the following

  1. Define a cross hairs feature only for one height, e.g., one that is close to mid-height for the ring gauge, or one for which the trace has least form error. From Figures 1 and 2, it would seem that the first trace would be a poorer choice than either of the other two.
  2. Define a compromise cross hairs feature according to some goodness of-fit criterion.
  3. Define a cross hairs feature for each trace, at potentially different angles.

Once the crosshairs are defined at each point over $1…3600$ then we get a series of measurement values to be calculated at those fixed points and perform a best match fit to the dimensional tolerances required within the specification

The above mathematics and calculations were provided from the M4R NPL collaboration project through the research funding available for middle sized businesses (B2) (B6) This mathematics was written to research level standardised and required significant personal development to understand and operate inside (B4)

During the manufacturing process the crosshairs feature matching can reduce the rejection rate of the rings under the precise calibration Trimos machine, due to the accuracy of the machine calibration is a slow and arduous process meaning a best fit calibration pre check will improve that speed

The outcomes of a missed calibration

A missed calibration can arise due to a number of reasons related to the manufacture of a setting ring gauge. Although not all setting rings are completely scrap due to the crosshair features having an optimal alignment position (A square is round in the right place) there are a number of reasons why the ring may have missed a calibration and this can be evaluated in a RCA

Root Cause Analysis

(K1) (S3)

(K16)

Sustainability

The increase of environmental efficiency is important for a number of factors going forward in the business. l. In today’s world, there’s a growing awareness about climate change and other environmental issues, and businesses are expected to play their part in addressing these challenges. By using resources more efficiently, minimizing waste, and investing in renewable energy sources, companies can reduce their environmental impact and contribute to a more sustainable future. and we seek to follow the new ISO standards going forward. (K17) (K23) (S9)

Industry 4.0

Although the simple nature of the artefact IR4.0 is relevant due to the application being involved with “big data” where the factory can operated in data driven development to improve the manufacturing process downstream in a smart feedback optimised system to further encourage efficiency gains in this section of bowers group manufacturing. (K4) Advanced manufacturing systems are ideally part of an in process deep data analysis requiring a conium of data, although this process does not perfectly align with those principles it can be recognised as a considerable advancement in the production line of Ring gauge manufacturing at Bowers Metrology. (B3)