Abstracts and Introductions
Proceedings of the Santa Fe Symposium On Jewelry Manufacturing Technology
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High Frequency Resistance Welding of Gold Alloy Jewelry.
Welding as a final operation is being enhanced by the uses of high frequency welding techniques. The heating to welding temperatures is accomplished with much lower current, the heat is localized, and discoloration of the metal as well as distortion of the part is minimal. For some operations this can eliminate a subsequent soldering process.
The objective of this paper is to contribute some insight to the realitive new technology of high frequency welding and to demonstrate how specific welding techniques can be utilized for the final assembly of gold alloy jewelry. Although, many other materials can be joined utilizing this process, the scope of this material will be limited to presenting a case study of the process and presenting an overview of the fundamentals of resistance welding.
High Frequency Inverter (HFI) resistance welding has made it possible to weld gold alloy jewelry components in the final assembly operations. Historically, resistance welding techniques for gold jewelry have been limited to tack welding operations which require a subsequent soldering procedure. However, due to the improved welding characteristics of HFI technology, some soldering operations are being eliminated. Case in point, Jostens, a leading jewelry manufacturer is currently joining Black Hills Gold leaf products in a final assembly operation using HFI resistance welding techniques. This operation will be presented as the Case Study. The HFI technology will be easier to understand after an overview of the basic resistance welding process.
Resistance Welding Equipment Developments and Applied Welding Techniques
Features of High Frequency Inverter and Linear DC resistance welding power supplies are provided; a revolutionary new weld head is introduced. A guide to identifying important process variables in making a resistance weld is outlined
Repairing Porosity Flaws Using Resistance Welding Techniques
This paper will familiarize the manufacturing jeweler with state-of-the-art Resistance Welding techniques and their application to porosity repair. Resistance welding offers a viable alternative to traditional flame soldering. The reduced heat buildup of resistance welding often eliminates a need to remove stones before repairing porosity flaws.
Porosity flaws adjacent to settings are often the most difficult to repair. Resistance welding techniques offer the manufacturing jeweler the prospect of substantial cost savings in both time and materials.
Porosity repair is the most recent and promising application of resistance welding for jewelry manufacturing. This paper offers the jewelry manufacturer an additional viewpoint on resistance welding’s possible applications.
Welding has been in use within the jewelry industry for many years. Tack welding is possibly the most commonly applied welding technique in jewelry manufacturing today. Tack welding provides time savings and increased output by effectively holding parts in position during soldering operations. Final assembly applications using welding techniques have been far more difficult to implement because welding requires that metals be heated to plastic or melting temperatures while held together under force. Unwanted distortion of metal surfaces is a common result of the process. Avoiding distortion of jewelry surfaces requires innovative techniques that do not appreciably deform surface finish.
Historically, resistance welding has seen limited application in jewelry manufacturing. However, High Frequency Inverter (HFI) and Linear DC (LDC) welding technologies have made possible, and have significantly enhanced jewelry welding applications.
Although resistance welding typically requires metals reach their melting temperatures, short weld times minimize the heat generated allowing stones to be in place during repair. Welding is often complicated for most jewelry manufacturing operations because: it can cause distortion to the parts; it cost more than a torch and people generally don’t understand how it works.
Weldable Silver Alloy
Firestain-resistant silver alloys are currently being produced that have the added benefit of being weldable. Historically, high thermal and electrical conductivity of traditional sterling silver alloys has made them difficult to weld. The topic of welding firestain resistant silver alloys was introduced in 1997. This paper will take a more detailed look at the aspects of welding firestain-resistant silver jewellery with resistance welding equipment.
Small additions of germanium (Ge) to silver greatly improve the welding properties of silver alloys. By comparison, traditional sterling alloys remain one of the most difficult metals to weld. Peter Johns of Middlesex University, in collaboration with Metaleurop S.A. has developed silver alloys which incorporate (Ge) to produce firestain-resistant alloys. Silver Ge alloys represent a breakthrough in welding technology‘s ability to provide new and substantial fabricating capability to jewellery manufacturing. This exclusive innovation will change how designers, engineers, metalsmiths, and even welding equipment manufactures regard the welding sterling silver. Prior to the discovery of Ge silver alloys welding could not come close to the versatility of traditional torch soldering methods. Prepare to forget everything you thought you knew about welding silver; AgGe alloys are radically changing everything.
Weldable Silver Alloy Background
Patented in 1993, Peter Johns‘ silver germanium alloys incorporate small additions of Ge to bring about tremendous contributions to silver‘s firestain resistance(1). Two key factors in its compatibility to welding are decreased conductivity and decreased oxidation. The International Annealed Copper Scale (IACS) is used as a measure of conductivity in metals. On this scale copper is 100% and traditional sterling is 96% conductive. Metals with high conductivity require tremendous amounts of energy, introduced quickly and accurately, to combat rapid heat losses from the weld site, making traditional silver alloys extremely difficult to weld. Johns‘ research determined that 1.1% Ge was the minimum required to maintain firestain resistance. Lower conductivity of these AgGe (Argentium) alloys dramatically improves their welding charactaristics. At 165 vickers hardness, conductivity in a .022 wire was measured at 53.6% IACS, or 3.21 micro ohms per cm and 67.6% IACS, or 2.55 micro ohms per cm in 70 vickers hardness(2). Lower oxidation potiental reduces, if not eliminates, the requirement for inert cover gas.