Nowadays, protection of cutting tools with hard protective covers is a mature technology, widespread in the industrial practice. Covers are put on large batch tools, tools for smaller batches, as well as renewed (grinded) tools. To a certain extent, covers are sometimes put on metal forming tools of smaller dimensions, such as mandrels, dies, knives and insets. The fact that the technology is mature does mean that for the ordinary user it is a standard service – the user orders a cover with the desired properties. However, there is still a lot of room for improvements and new services, offered by the technology of hard protective covers. In addition to the application of new/adapted covers, it can be quite helpful to use analytical technologies, specialised for thin layers.
The first step, starting with the user, is proper preparation of the surface of the tool. The provider of the service of application of covers sets minimum standards regarding the quality of the surface (cleanliness, deburring, texture), and checks the appropriateness of the selection of the basic material and its heat processing. A step further from the bare minimum can be made by performing some additional measures in the preparation, e.g. proper rounding of the cutting edge in the cutting tools, where the selected radius is adapted to the material being processed and the conditions in which the metal will be worked. An open question can be optimisation of the geometry of the tool, perhaps selecting another basic material or additional level of surface finishing, such as plasma nitriding of steel.
Only in the second step do we ask ourselves about the adequacy of the cover used so far. Although nowadays there are a number of nanostructure covers available on the market, there are still plenty of orders of the “good old” TiN, which practically hasn’t changed since the early 1980s. Of course, there is nothing wrong if it serves its purpose in the concrete production application. However, we could ask ourselves whether replacing it with a more contemporary cover could bring advantages in terms of better productivity, durability of the tool, quality of the product and less scrap.
The third step is proper traceability of the optimised tool, monitoring of the condition of the surface and the quality of the product. And, last but not least, the analytics of the product and/or tools in case of a major failure are important. Judging by experience, the best type of analysis is good piece vs. bad piece, where the tool must be compared with the same number of products. The surface can be compared non-destructively, so that the tool can be returned to production after the analysis. However, we can usually acquire far more information if we make a crosscut, ensure proper metallographic preparation and thus enable the analysis of selected properties by depth. As the intervention is destructive, its use is limited to pieces that shall no longer be used.
The instruments necessary for analysis are quite complex (optical microscopy with high magnification, electronic microscopy with chemical microanalysis) and are also rarely seen in large companies. However, a lot of such equipment can be found at institutes and faculties. Such a minor comparative analysis cannot be put into an existing project or pedagogical process; However, we can say from our own experience that they are definitely challenges that simply must be solved. For a company the result is not only a solution to a concrete problem (e.g. cause for excessive wear) but a guideline showing in what way it should improve its technology to avoid such problems in the future.
This leaves us quite far away from the above mentioned standard service, such as application of a cover or routine microscopy; the problem is solved by a whole team. Perhaps the biggest obstacle lies in the fact that companies often don’t know the capacities of research institutions, and the latter don’t know the problems that companies are facing.
doc. dr. Miha Čekada
Jožef Stefan Institute
Head of “Thin layers and surfaces department”
Head of the “Hard Covers Centre”