Heat treatment plant audit for Nadca 207

One of the things I’ve learned over time is that tool makers or die casters don’t know, or don’t want to know, that they should be auditing their heat treatment suppliers. And if they already know that, which is based on the CQI-27 application, then they don’t know how to do it.

This is understandable, because the field of heat treatment and material engineering is completely outside the scope of their core business. Either the technology of die-casting or the manufacturing of tools for high pressure die-casting (HPDC).

So how to do it? Here is a rough guide. In order for the audit to fulfil its objectives, it must be comprehensively focused on the entire activity of the heat treatment plant.

1. Specification NADCA implementation – the heat treatment plant must prove that there is a document in written or electronic form specifying the implementation of the procedures according to Nadca 207 in the heat treatment plant’s activities, from receiving the order to its delivery, and that all workers of the heat treatment plant who come into contact with orders according to Nadca 207 are with this document introduced.
2. GM specification implementation – the heat treatment shop should demonstrate that it is familiar with the content of the GM specification entitled DC-9999-1, in its latest version, and that it is aware of the content of this specification and the impact on die quality
3. AIAG CQI-27 – The heat treater must demonstrate that it is capable of performing heat treatment in accordance with CQI-27, Table H, Paragraph H1.8 for die casting plants
4. Furnaces Specifications : Dimensions, Charge weight, Pressures etc. – the heat treatment plant must maintain a list of furnaces released for work in the Nadca 207 system and meeting its requirements
5. Furnace inspections temperature conformity, documentation – for each furnace specified above, the heat treater must keep records of the periodic inspection of TUS (Temperature Uniformity Survey) and SAT (System Accuracy Test) according to AMS 2750, now in version F. In case of invalidity of TUS or SAT, the heat treater must have procedures, in written or electronic form, guaranteeing that non-conforming devices will be removed temporarily or permanently from the list of approved devices
6. Measurement of the quenching rates each furnace – each quenching furnace should be able to monitor the temperature of the piece using at least two batch thermocouples, one marked as Ts to measure the surface temperature, one marked as Tc to measure the core temperature. Any quenching process with parts according to Nadca 207 should be evaluated for a cooling rate that should be at least 28 C/min when cooling from the austenitizing temperature to the isothermal hold temperature
7. Isothermal hold – the quenching furnaces for HPDC must allow the application of an isothermal hold to equalize the temperatures in the quenched piece based on the evaluation of the batch thermocouple temperatures Ts and Tc, independently of the shape or size of the quenched part
8. Quenching capability – to determine the cooling capacity of the furnace, it is an advantage if the heat treatment plant has its own test available, performed on a reference piece from H13 steel with dimensions of 400x400x400mm
9. Tempering – the above regarding the application of AMS 2750F also applies to tempering furnaces. To ensure the reproducibility of tempering, each tempering furnace must be equipped with at least one thermocouple Tc, according to which the tempering time is determined, or which is intended to apply the so-called conditional dwell. Tempering or annealing furnaces without a protective atmosphere cannot be allowed into the system.
10. Hardness measurements mobile, availability – the heat treatment plant should have a portable hardness tester available for operative, indicative hardness measurement of large parts
11. Hardness measurements stationary, availability – the heat treatment plant should have a fixed hardness tester for measuring the hardness, with a size corresponding to the dimensions of the hardened parts
12. Calibration of Hardness Testers – all hardness measuring devices must be in a calibrated state, with a record of the last performed calibration, and of its validity until the date
13. Incoming inspection , mold preparation for crack risk minimize – the heat treatment plant must have written procedures for accepting orders, and records of feasibility checks with respect to quenching risks. The heat treatment shop must be able to assess whether the dies have Ts and Tc batch thermocouple holes in accordance with Nadca 207 and DC-9999-1
14. Organization Customer consultation on critical parts and documentation – in the event of a risk condition being detected, the heat treatment plant must have a procedure, in written or electronic form, for notifying the customer of possible risks. Risk parts must be excluded from processing without the written consent of the customer. Written records must be kept of this entire procedure and these records must be archived
15. Process parameter specifications manual/ automatic – the heat treatment plant must have established procedures, in written or electronic form, for determining processing parameters in the form of appropriate technological instructions, and with references to approved furnace programs, and it must be determined which program parameters are fixed for the given material, or which parameters operators can change manually
16. Documentation of the data – the heat treatment plant must demonstrate a method of documenting process data, i.e. keeping records of the process, in relation to the processed parts in the process. In the case when several parts are processed in one batch according to Nadca 207, then either each part of the batch must be checked for cooling rate, or the heat treatment company must demonstrate that the two batch thermocouples Ts and Tc were inserted into the largest body in the furnace, and that it was for this largest part, the required cooling rate of 28 C/min was achieved, so that it is possible to infer that the other, smaller parts were cooled at the same rate or faster
17. Archiving of data – the heat treatment plant must have a procedure, in written or electronic form, for archiving data from processes and from ERP systems so that full traceability of the processing can be demonstrated at any time during the guaranteed archiving period. The minimum period of archiving should be 2 years, which is the period for which the heat treatment company is liable for hidden defects according to the Civil Code
18. Employees , qualification matrix – the heat treatment plant must keep a list of employees, their roles, and for each role have a qualification matrix with regard to the required practice, experience, education and necessary training. For each designated training, a record must be kept in the employee’s personnel file, including the period of validity until the date
19. Risk Management / Emergency water supply etc. – the heat treatment plant must have a guideline, in written or electronic form, to cover risks during heat treatment, especially with regard to power outages, cooling water, etc. For all risks, a procedure for the behaviour of employees should be established in such a way that there is no irreversible damage to the customer’s material and appropriate technical measures should also be prepared, such as backup sources or nitrogen pumps ensuring the supply of water to the furnaces during a power failure
20. Documentation new hardening in case the failure to achieve results – the heat treatment facility should have procedures in place, in written or electronic form, in the event that adequate impact strength values on the test coupon are not achieved after quenching and tempering, including a procedure for soft annealing and re-hardening the dies
21. Documentation the hardness is not reached – the heat treatment shop should have developed procedures, in written or electronic form, in case the required hardness is not achieved after quenching and tempering. Especially if the resulting hardness is higher than desired, and especially if the resulting hardness is lower than desired
22. Documentation in case of cracks, failures – in the event of defects in the work, in the form of cracks or other damage to the hardened parts, the heat treatment shop must have a procedure, in written or electronic form, for the documentation of these defects, their analysis, and for the subsequent resolution of complaints from the customer
23. Measures in case of deviations or Continuous Improvement Process (CIP) – the heat treatment plant should have established procedures, in written or electronic form, for evaluating deviations from normal behaviour, and key measurable indicators of the quality system that allow the heat treatment to be evaluated, including its continuous improvement
24. Process descriptions heat treatment process – the heat treatment plant must ensure the management of heat treatment values, primarily in the form of technological instructions and routings, ensuring that the materials supplied by the customer will be processed according to Nadca 207 parameters
25. Master Data temperatures , austenitize temperarures, holding times etc. – the processing technological parameters must fully correspond to the wording of Nadca 207 and must be fixed enough to prevent deviations from the required values during the processing of the parts

What to say in conclusion? It is a complex, continuous process, focused on strict compliance with the rules according to various specifications and standards, with the aim of ensuring continuous improvement of both the heat treatment process and, above all, the trust between the heat treater plant and the customer. It doesn’t matter if it is a relation to a tool shop or a relation to a die-casting plant.

A heat treatment plant can become a provisional source based on the input test of the quenching capability of its furnaces according to DC-9999-1. However, in order to become an approved source, it must go through a testing period (see table), but above all a customer audit according to the above, the result of which must be OK.

Why is that so? Because we work in a system where a number of parameters are affected by variable physical properties of both steel and equipment. And since the success rate is determined by variables that we can only partially influence, it is necessary to narrow their range of deviations. Only then we can consider the results so reliable that we can deal with other problems affecting the life of the tool.

So, I wish everyone the best of luck in this effort and let´s go up into e-mobility.

August 31, 2022

Jiří Stanislav