TPT May 2022
AR T I C L E
To further enhance the mill operator’s awareness of the HF welding process, we have a visual indication of HF welding parameters – power (kW) and frequency (kHz), as well as important new tool such as an external LED stack light.
Cpk measures the centering of the process and the variation of the process relative to the process specification.
Shandong Province Sifang Technical Development Group
Green process window – indicating the process is centered and well within user defined
weld heat input process limits.
Yellow process window – indicates that the process is approaching variation limits. This indicates that the process is not centred but you remain within acceptable upper and lower control limits.
A high Cpk number means high statistical process reliability. In general, the higher the Cpk the better. A Cpk value less than 1 is considered poor and indicates the process is not capable and will produce product out of specification. A value between 1.00-1.33 is considered barely capable or fair and a value in the range 1.34 – 2.0 is considered capable or good. For a Six Sigma processes the Cpk needs to be 2 or greater and the process is considered excellent. We will use a truck loaded with pipe driving into a tunnel to more simply illustrate the concept of Cpk. The truck driver on the left with the red coloured tunnel is unsteady. The truck often scrapes the walls of the tunnel. This represents a process that is not capable. Vehicle damage can be minimised by reducing driving variation and keeping the truck within the tunnel limits.
Red process window – indicates process is outside of process specification limit and could result in product quality issues.
In today’s competitive tube and pipe industry, the priority is to deliver the same high-quality product, from the very first tube to the very last, every mill run. The path to a better HF weld involves the use of process control tools and precise weld heat input control to deliver the highest quality product with the highest level of repeatability to the end customer. References 1. M Nallen “A Path To A Better High Frequency Weld”, TPT March 2022, p68 2. https://www.twi-global.com/technical-knowledge/faqs/faq-what is-the-difference-between-heat-input-and-arc-energy 3. Ahmed, M Z; Ataya, S; El-Sayed Seleman, M; Mahdy, A M A; Alsaleh, N A; Ahmed, E – Heat Input and Mechanical Properties Investigation of Friction Stir Welded AA5083/AA5754 and AA5083/AA7020. Metals 2021, 11, 68 4. L D Frame, O Tupalo, T Ignatowski, M Nallen – “Aspects of precise heat input control for high frequency welding.” You can request the article at http://thermatool.com/hct 5. John L Hradesky “Productivity & quality improvement: a practical guide to implementing statistical process control.”
In the middle picture, the truck driver is better than before, but he often gets too close to the tunnel walls. The truck is likely to be damaged unless the driving variation is reduced. This process is barely capable. Entering the green tunnel is the driver who never scrapes the sides. The truck enters the tunnel in the centre with little variation. This truck is unlikely to ever take damage, even if the truck moves slightly to either side. This process is capable. Thermatool applied the same process control techniques to a new version of HAZControl™ Technology software to help tube producers control their HF welding process. This software tool is used to visualise the HF welding process against defined process limits. After saving the recipe that establishes the optimal result, the upper and lower limits of the process are set (if necessary, they can be changed by the user).
Thermatool Corp – USA firstname.lastname@example.org www.thermatool.com
Made with FlippingBook - Online catalogs