New TraCIM-service for 3D-evaluation algorithms in screw thread metrology

Screw threads are machine elements with a wide range of applications, as they are used for sealing as well as for fastening, moving or centring. According to the German Screw Association (Deutscher Schraubenverband e.V.), about 50 companies manufacture screws, nuts and studs in Germany. Apart from the market leader, these are mainly SMEs with a considerable turnover of €3.8 billion in 2019 (StBA). The traceability of screw thread metrology to the SI unit metre is currently realised by 47 DAkkS calibration laboratories accredited for screw threads.

The complex screw hread geometry is described in DIN 2244:2002-05 and dimensional testing is carried out according to the calibration guideline EURAMET/cg-10/v.01 in the conventional point- and line-like manner. Conventional screw thread metrology reaches its limits especially when there are large shape deviations or demanding tolerances have to be met. For this reason, a high-resolution three-dimensional calibration strategy for testing thread standards was developed at PTB. The novel calibration strategy comprises the measurement process, the determination of the measurement uncertainty and the holistic evaluation of the measurement results.

The new software test for the certification of three-dimensional evaluation algorithms for threads (Home | TraCIM (ptb.de)) is based on the above-mentioned holistic evaluation. TraCIM stands for "Traceability in Computationally Intensive Metrology". It is an online service to validate whether an evaluation programme produces expected results within the numerical accuracy specified by the customer. Verificated data sets are available in the TraCIM system as a reference. Users and developers have the option of purchasing a test data set on the website, evaluating it with their algorithm and uploading the results for comparison. If the comparison with the reference data sets is successful, a certificate will be handed over that specifies the accuracy of the tested algorithm. The test covers the evaluation of internal and external screw threads. It includes a total of eight geometry parameters according to DIN 2244:2002-05: the lead of the single flanks P₁ and P₂, screw thread flank angles β and γ, lead of the helix Ph, conicity C, pitch diameter d₂ or D₂ and the total cumulative pitch deviation ΔPh.

Figure 1: Website of the TraCIM service with extended offer "3D Screw Thread Evaluation".