4D High Pressure Gas Quenching - A Leap in Performance vs. Press Quenching
Thermal processing and quenching of steels for hardening is a well-established practice performed by various techniques over the centuries. A common thread has been the unpredictable nature of the size change during the quenching process, which is known as dimensional change or distortion. Material distortion is the undesired trade-off between the development of proper mechanical property and the necessity of rapidly quenching the material from elevated temperatures into a quenching media (i.e. brine, water, polymer, oil, gas, molten salt, etc.). Due to this compromise, users have been attempting to reduce part distortion because once a component is hardened, it becomes very difficult and costly to remove excess material or form the part back into its original shape.
When one looks at the bearing and gearing industries, materials typically are hardened via austenitizing and quenching. Not only do these components require high hardness and wear/corrosion resistance, they also require high dimensional precision to tight tolerances as well as repeatability of results. One of the most common way to reduce material distortion when quenching is a method by which a heated component is placed in a special fixture and a steady force is applied to the component, which allow the part to resist material deformation when the quenching media is applied. This method of quenching is known as “press quenching” and requires specialized equipment, manual or robotic handling, custom die sets and high maintenance as well as being operator dependent to achieve consistent results.
It is well known that machining after heat treatment is one of the most costly and difficult tasks to complete in the entire manufacturing life cycle. This is why an extreme amount of engineering is devoted to the prevention of distortion of a component to ease the post heat treatment machining operations. With the ever prevailing desire to lower the cost of raw materials and still maintain proper mechanical performance, extreme amounts of pressure are applied to the heat treatment process to bring up the quality level of the low cost steel. When using these low quality steels, they are prone to high levels of distortion during the quenching process, such that they distort more than the allowable amount and either become too challenging to hard machine or are not able to be used all together. ~4% of the price for a hardened component is attributed to the removal of post heat treatment material to so that it meets the finished size requirements. When users can control distortion, they lower the overall cost of the component.
This paper will introduce the latest achievements in the advancement of distortion control by way of 4D High Pressure Gas Quenching (HPGQ) versus press quenching. Both processes quench a single part at a time but the 4D HPGQ process does not subject a part to any clamping forces or issues associated with liquid quenching inconsistencies. The 4D HPGQ process results in every single part being heated and quenched identically the same at surprisingly low gas pressures thus producing extremely accurate dimensional variation with highly repeatable results. 4D HPGQ systems are easily integrated into current manufacturing environments and the process is a revolutionary advance in quenching technology, which has been shown to reduce or even eliminate the need for expensive & difficult post hardening manufacturing processes.
Authors: Thomas Hart, SECO/VACUUM and Dr. Maciej Korecki, SECO/WARWICK S.A.
Keywords: Single-piece flow, case hardening, low pressure carburizing, high pressure gas quench, in-line manufacturing, lean manufacturing, mass production, distortion, press quench
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