Patent Application
20170304924
A new electrospark deposition (ESD) method and related system are provided in the present invention based on the use of a magnetized electrode, namely magnetic-aided ESD (M-ESD). In particular, the present invention uses an electro-magnetized electrode (anode) or a permanent magnet as a magnetized anode to attract fine coating powders at the tip thereof which acts as a soft brush to coat on intricate surface profiles. Accordingly, the method of the present invention is able to provide a soft contact between the electro-magnetized anode or the permanent magnet anode and the workpiece to be coated or manipulated.
Electrospark-deposit coatings have been recognized to be amongst the most damage-resistant coatings that are suitable for use in harsh environments [Electrospark Deposition for Depot- and Field-Level Component Repair and Replacement of Hard Chromium Plating, Final report Project WP-0202 (page 11), Sep. 7, 2006, Environmental Security Technology Certification Program (ESTCP)]. Unfortunately, similar to all other coating technologies, conventional electrospark deposition (ESD) has its own limitations and problems. One of these is the process's weakness in coping with complex surface geometries and internal surfaces, in particular, those with small features. The limitation arises because ESD normally employs a rigid solid, sizable consumable electrode (
In the US patent application publication 2012/0193329, Liu et al. makes use of powder as a feeding stock, but it does not involve any magnetic devices/forces. The powder simply passes through a “feed channel configured within or at least partially surrounding the electrode for guiding powder” (
A related research paper on the use of loose powder in electrodischarge applications published by Reynaerts et al. [J. Qian, S. Steegen, E. Vander Poorten, D. Reynaerts, H. Van Brussel, EDM texturing of multicrystalline silicon wafer and EFG ribbon for solar cell application, International Journal of Machine Tools & Manufacture 42 (2002) 1657-1664] has described the employment of magnetized metal powder to surface texturing of Si substrates using electrodischarge machining. The aim was to roughen Si wafers and ribbons for solar cell application. In other words, Reynaerts et al. only teaches the electrodischarge technique of using metal powder functions as a thermal erosion process (subtractive) rather than an additive deposition method as in the present invention.
In another related research paper on the subject of using loose powder materials for ESD by Topal{hacek over (a)} et al [Pavel Topal{hacek over (a)}, Laureniu Sl{hacek over (a)}tineanu, Oana Dodun, Margareta Cotea
{hacek over (a)}, and Natalia Pînzaru, Electrospark deposition by using powder materials, Materials and Manufacturing Processes 25 (2010) 932-938]. Topal{hacek over (a)} et al. describes the employment of a relatively high voltage (up to 12 kV) between the electrode and the workpiece to initiate electrical discharges across a relatively large spark gap, without direct contact having been made between the electrodes. Once a discharge plasma channel has formed, the powder for alloying or coating is then fed into the channel (
The present invention employs a magnetized electrode (anode) with ultrasonic vibration or any relative motions (such as rotary). The employment of said ultrasonic vibration or any of the relative motions is necessary to provide an appropriate spark gap between the anode and the workpiece to achieve a stable mode of discharge.
Accordingly, in the first aspect of the present invention, it is provided a system comprising an anode, which can be an electromagnet or being a permanent magnet. Said system also comprises a cathode which is the workpiece to be manipulated. Said system further comprises a source of shielding gas to protect the processing area and the coating powder from being oxidized. Said system additionally comprises an ultrasonic generator exerting ultrasonic vibration to the magnetized anode. Alternatively, a rotary or a transverse device or the like (collectively called a relative motion generator) can be employed for exerting the relative motion to the anode. In one embodiment, the anode is an electromagnet or a permanent magnet with a type of loose ferromagnetic metal powder or a mixture of different coating powders comprising non-ferromagnetic (e.g. ceramic) and ferromagnetic powders surrounding the tip of the anode. When the system is in operation, the anode is electro-magnetized or magnetized, thereby adhering the coating powders on the surface of the end of the electromagnetized or magnetized anode that is to be in contact with the workpiece, which behaving like a soft brush. The coating powders adhered on the surface of the end of the electro-magnetized or magnetized anode conform to the surface profile of the workpiece when the electro-magnetized or magnetized anode and the workpiece (the cathode) are brought together. The way of which the present system to process a workpiece is different from the conventional ESD in that the conventional ESD employs a rigid non-magnetized solid anode electrode and requires a direct contact force to be exerted on the solid anode, whereas the present invention does not require the exertion of direct contact force on the anode but simply a “soft” contact between the powders on the anode and the workpiece is sufficient. By the present invention, intricate surface profiles including internal walls of a workpiece (e.g., flat and non-flat surfaces of a non-straight channel-like hollow structure) can also be coated with the coating materials, which is not possible to be achieved by the conventional ESD because of the requirement of a rigid solid anode rod and it is a line-of-sight process. In operation, the working principle of the present system is that the spark breaks down when the “soft” contact between the powders on the anode and the workpiece is broken as a result of the ultrasonic vibration generated by said generator. Alternatively, the breaking of contact can also be achieved by means of a device which provides the relative motion between the anode and the workpiece. A micro-gap is momentarily created in which spark plasma is produced, with the size controlled by the amplitude of the vibration of the anode (i.e. the gap size is increased by the vertical displacement of the ultrasonically activated anode away from the workpiece). Electrospark discharging ends when the pressure of the plasma collapses, leading to expel of small molten droplets of the coating powders from the anode and deposition thereof onto the workpiece surface. By moving the workpiece on a movable working table or by means of moving the anode with the above steps repeated, a coated surface is generated.
In the second aspect of the present invention, a method for coating based on magnetic-aided electrospark deposition is provided. The method comprises fixing the anode of the present system to a movement drive system, magnetizing the anode by an electromagnet or configuring said anode as a permanent magnet such that coating powders are adhered onto a tip of the anode where it is in contact with a workpiece which is the cathode of the system and placing the workpiece on the movable working table, setting an ultrasonic vibration amplitude of ultrasonic vibration generated by the ultrasonic generator, switching on the ultrasonic generator to exert ultrasonic vibration to the anode, switching on a power supply which is connected to said anode and cathode to create a spark at the micro-gap, discharging the coating powders which is adhered onto the tip of the anode to a surface of the workpiece when the size of the micro-gap is increased by the vertical displacement of the anode away from the workpiece such that plasma pressure of the spark is decreased, and moving the workpiece on the movable working table and/or by moving the anode such that the above steps are repeated to deposit the coating materials onto the remaining surface of the workpiece. As an alternative, said ultrasonic generator can be replaced by a motion device or the like to exert a relative movement between the anode and the workpiece such that the size of the micro-gap between the anode and the workpiece is increased. Alternatively, the relative movement can be introduced by moving the workpiece. The degree and extent of the relative motion should be set before it is switched on to ensure the motion exerted to the anode will be sufficient for the coating powders to discharge when the plasma pressure of the spark is decreased.
References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a voltage range of “about 0.1V to about 5V” should be interpreted to include not only the explicitly recited voltage of about 0.1V to about 5V, but also the individual voltage (e.g., 1V, 2V, 3V, and 4V) and the sub-ranges (e.g., 0.1V to 0.5V, 1.1V to 2.2V, and 3.3V to 4.4V) within the indicated range.
As described herein, the terms “a” or “an” are used to include one or more than one and the term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.
In the methods or processes described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E, and that the sequence still falls within the literal scope of the claimed method. A given step or sub-set of steps can also be repeated.
Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting method will fall within the literal scope of the claimed method.
The present invention is not to be limited in scope by any of the following descriptions. The following examples or embodiments are presented for exemplification only:
In
During the M-ESD method, as a result of electrospark actions, the coating powder will be consumed and continuously deposited onto the workpiece. The coating powders can be replenished by using either an external powder carrier to supply powder to the tip of the anode or an external feeder to lay powder on the surface of the workpiece. It is noted that any steps depicted in
The present invention is useful in various surface engineering applications in the fields of aeronautical (e.g. restoration and repair of damaged aircraft turbine blades), nuclear reactors, military engineering, and in medical industries. As compared to conventional ESD, the present invention can address complicated surface geometries and internal surfaces while the cost can be significantly lowered by using inexpensive components and simplified method steps.
The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.
The embodiments are chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.
