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Have you ever looked in a jewelry store window and wondered at the patience of the goldsmiths responsible for crafting gold chains? Every link perfect, thousands of links in all sizes and patterns, right down to the finest sub-millimeter gauge of wire. As you might have suspected, handmade chain is now the realm of the custom jeweler. Most chains today are made by machine.  And the true craft is in the design and manufacture of the machine that will make perfect chain from precious metal all day, every day.

Such a machine, or rather range of machines, is designed and built by Sisma. Based in the community of Schio in northern Italy, close to the traditional Italian goldsmithing center of Vicenza, Sisma design and manufacture a comprehensive range of machines for the production of precious metal chains of all descriptions. The privately held company is about to celebrate 40 prosperous years of operation.

Whatever your fascination with machines, there is something rather special about a machine that can tie knots. When you consider the complexity of the chains that Sisma machines can produce – every link  perfect and made at blinding speed, this equipment is right up there with the best of them.

Most of Sisma’s jewelry machines make a variety of different types of chain from gold and silver wire. The smallest wire gauge used is 0.12 mm (less than a hairs’ breadth) which is an incredibly thin piece of gold wire used to make the very finest gold chain. Other machines such as the diamond ice lathe and pin and link form/fixers, provide automated and semi-automated finishing operations for manufacturing jewelry around the world.

Sisma manufactures more than 30 different kinds of jewelry machines from its factory and ships over 800 machines every year. All machines are designed entirely with CADKEY. To perform consistently and reliably at high production rates these machines are built to very high precision. Computer-aided design and manufacturing was introduced at Sisma in 1986. CADKEY has been the principal CAD system in use since 1993.

Sisma design uses CADKEY to design machine parts and assemblies.

Over 300 instruments are used to check and monitor the precision and operation of machines during and after manufacture. The management and calibration of the measuring instruments alone is a significant role in the success of the business. The heart and soul of a chain-making machine are the jaws that grip and manipulate the wire and the cams that actuate the movements. The hardened steel jaws are precision cut with EDM machines. The EDM tools are made on high precision Swiss CNC equipment installed specifically for this purpose. The cams are precision ground on a multi-pallet Hauser CNC grinder (see movie). VisiCAM is used to create tool paths from CADKEY drawings.

High-speed milling of cams for Sisma machines.

There are 80 PCs throughout the organization and while only a few are involved in design activities, all are networked and have access to the custom in-house QA system that is fundamental to the business.

Networked PCs have online access to the company’s 25,000+ CADKEY drawings. Each PC is equipped with CADKEY viewer to access drawings to check details and produce hardcopy output if required. The company employs 120 people (40 in production) and more than 30 sub-contractors. Staff development is a high priority within Sisma, with up to 8% of work-time spent on on-going staff training. Says technical director Arfeo Canaglia, "It is very important that everyone is doing the same thing and using the same tools". A high importance is also put on understanding the operations and needs of other departments, such as, marketing, design, production and service. This also makes up a good proportion of the training time.

The 12-person Sisma design department creates new machine designs and is also responsible for prototype construction. Both 3D and 2D documents are used in the design process. Machine design time can be as little as 200 hours or as many as 7000 hours. An important reason for using 3D is fast, accurate access to mass, centre of gravity and other derived engineering data essential for balancing machine components for high speed and high performance operation.

All electrical and electronic design is conducted in-house. Out-sourced subcontractors complete the specialized electronic component development and production using OrCAD and ECAD software.

Traditional-style 2D annotated drawings are still a vital part of the company information store. They are used in manufacturing and are the only way that surface finishes and tolerances can be communicated to the production people.

Perhaps surprisingly, no kinematic or FEA design tools are used in Sisma’s design office. I say perhaps because I got the feeling that the Sisma team know these machines inside out. I suspect that they could easily design a high-speed precision machine with a burnt stick and a sheet of butcher’s paper! But seriously, it goes to illustrate that at Sisma, figuring the complexities of each machine and its workings is the domain of real people. CAD is used as an aid to tedious calculation and as a documentation system that integrates very well with the company’s internal communication and quality assurance system.

In addition to jewelry machines, Sisma has also begun to design and manufacture large flat-bed knitting machines. 

Unocad's Ivano Ambrosini and Sisma technical director Arfeo Canaglia inspect the precision bed of a Sisma knitting machine. Unocad is the Italian distributor of CADKEY and maintains a close relationship with Sisma.

Knitting machines now account for 15% of Sisma’s business and this share continues to grow. Knitting machines are also very complex and require precision manufacturing for a reliable and high performance working life. This area of design and manufacture complements the machinery business and draws on Sisma’s strengths of high quality, high precision machine manufacturing.

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