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The ancient origins of moulds
The very first moulds date back to ancient times, with examples found from as early as the Bronze Age. Despite such ancient beginnings, they are still vital to modern manufacturing. If anything, they have become more important as industry strives to meet the ever-growing demand for products in today’s world. An almost endless number of products compared to ancient times.
The reasons for making moulds, however, are still essentially the same: they enable us to work with materials such as metals that would otherwise be impossible to process and they let us do it on a massive scale, producing the same identical result quickly and consistently.
Nowadays the art of high-performance mould making is still a work in progress. In our business, moulds are, without a doubt, one of the most important tools we have to produce exquisitely crafted metal and acetate glasses, from the simplest to the most elaborate models.
Callipers and an old worksheet, written by hand and signed by Giovanni Franzoia.
Taking quality to new heights
Evolution continues today. Given the vital role of moulding in manufacturing, technical departments throughout the world are constantly striving to make them more efficient. Because a single mould can produce such large numbers of pieces, there are many reasons for wanting to improve them, as they raise quality standards and save time and money.
Up to a couple of years ago, moulds were made in an almost artisan manner and often had flaws, which meant the finishing processes took longer to achieve the desired result. Today, however, numerical control machines are used to make them and the result is more refined.
In this article Andrea Scopel, head of our Technical Department, presents examples of old and new moulds, illustrating their characteristics to help us understand the differences between them: «This is a cutting mould» he explains, taking a mould used by D.F. a while ago. «All the part removed by roughing is now done by CNC work centres or wire electro-erosion, whereas in the past it would have been milled manually.»
Worn electrodes; electricity going through the electrode causes it to oxidize and go dark
«Numerical control machines are now used to produce copper electrodes that faithfully reproduce the shape of the part you want to coin or cut. Electro-erosion uses continuous electrical discharges to remove the metal and create an exact negative replica.»
«Electrodes can be reused to make other moulds. In fact, when a mould had been used repeatedly, it can sometimes break. So it can be handy to have your original electrode to repair it. Over time, however, the electric current wears the electrode down and it gets smaller. The black bit you can see is caused by electricity going through it, oxidising it.»
The new way of making moulds to thermoform acetate
Let’s take a look at the differences between moulds used to thermoform acetate past and present: «In the past the process took a lot longer. You started with a 3D drawing of the temple and made an electrode by milling a piece of copper at the CNC machine. Next you had to make the cavities by cutting out tempered plates. Tempering was yet another process that added time and increased costs. Plus, the part was very rough after electro-erosion. Polishing also took longer because the surface was rough and had a number of flaws, so you had to add this time to electro-erosion, which was already slow. It could take as long as 4 or 5 hours of electro-erosion to make a mould. Add to that the hours at the CNC machine to make the electrode and polishing. Sometimes it took a whole day to make a mould.»
Moulds obtained using the new method
«Things are a lot different today. Thanks to the new method, we don’t need electrodes because we produce the shape directly on the solid plate. We still make the three-dimensional drawing of the temple but now we use CAM to make the plate that is then sent to the CNC and basically in a couple of hours we have the negative impression of the temple. Next the milling machine cuts directly into the plate, so the shape is complete when we remove it. We don’t need to make an electrode and, by skipping electro-erosion, the new method saves us time. The mould is already semi-finished when it comes out, so polishing is quicker.»
«We still use electrodes to obtain certain details, like small engravings (because the diameter of the milling machine doesn’t reach), raw edges, undercuts or other geometric details or to process very hard materials. In cases like these, an electrode is made to create details like these on the mould that would otherwise be complicated to obtain: combining the two methods means these details are reproduced more effectively and efficiently.»
