In the manufacture of a cars, a large number of metals and their alloys are used, as well as the techniques by which they are processed and the techniques and processes for manufacturing various parts. One of these processes is extrusion.
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections, and to work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms parts with an excellent surface finish. Metal objects made in this way need efficient quench.
Tesla filed a patent: 'System and method for facilitating pulsed spray quench of extruded objects'
Filed date: November 20, 2019
Publication Date: May 21, 2020
Inventor: Ottmann; Jared E .; (Fremont, CA)
This disclosure is generally related to metal treatments. More specifically, this disclosure is related to techniques for quenching extruded metal objects.
Systems and methods for quenching an extrudate using an atomized spray of liquid are described. A system includes a billet die at a proximal end configured to accept a billet and form an extrudate, a quench chamber located adjacent to the billet die for receiving the extrudate and comprising at least one pulsed width modulation (PWM) atomizing spray nozzle and a control module in communication with the at least one PWM atomizing spray nozzle and configured to independently control a liquid pressure, a gas pressure, a spray frequency, a duty cycle and flow rate of each at least one PWM atomizing spray nozzle.
Extruded metal objects, especially aluminum alloy objects, are widely used in construction and automotive industry. The extrusion behavior and mechanical properties of aluminum alloys can be sensitive to the microstructure of the billets after homogenization. Typically, as for the homogenization treatment of 6XXX alloys, a soaking procedure can be used to dissolve the large Si and Mg containing precipitates into the Al matrix. The cooling practice, on the other hand, determines the precipitation behavior of Mg.sub.2 Si, and thus can have a significant influence on the extrusion performance of the billet and the mechanical properties of the final product.
Extruded metal objects, such as 6000 series (i.e. 6XXX) aluminum alloys, often require heat quenching to optimize the homogenization process, which provides higher mechanical properties.
FIG. 1 depicts an Al-Mg.sub.2 Si phase diagram that shows quick cooling of Al - Si - Mg alloys locks Mg.sub.2 Si particles into the aluminum matrix. Such effective heat treatments allow for higher alloy mechanical properties.
In order to obtain effective heat treatments, water is typically used in alloy quench processes in part because of its heat absorption properties during the phase transformation from water into steam. However, conventional quenching techniques that typically employ a high-pressure water spray are subject to the Leidenfrost effect.
The Leidenfrost effect its where a vapor barrier layer over the surface is formed that inhibits heat transfer. As a result, the Leidenfrost effect may prevent effective removal of heat from the hot surface (e.g. alloy quenching).
Embodiments of the present disclosure minimize or overcome the Leidenfrost effect, and thereby improve the quench rate. In particular, the disclosure provides a mechanism for producing atomized water droplets for effective quenching of a metal billed. In other discussion, the water is sprayed in pulses onto the billet which gives time for the vapor barrier to dissipate before the next atomized spray is emitted by the nozzle. These small-sized water droplets evaporate quickly upon contact with the object's hot surface, which minimizes or reduces the Leidenfrost effect and allows for improved quench rate.
FIG. 6 depicts an implemented system 600 for quenching an extrudate with an atomizing spray.
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