Reduced tool costs, increased productivity, improved precision and extended maintenance intervals – these are objectives which top the priority list of manufacturing companies today. The service life and production reliability of metalforming and cutting tools such as indexable inserts, drill bits and milling cutters are key parameters for performance optimisation and hence, safeguarding the user's competitive edge.

In order to minimise wear, tools are often surface-coated with a hard material such as titanium, aluminium, zirconium, or diamond-like carbon (DLC). The coatings are deposited in the micron gauge range by means of a PVD, PACVD or CVD process. On a cutting tool, a hard material coating ensures a longer service life while reducing the formation of built-up edges. In the case of punching and metalforming dies, it can reduce unwanted effects such as abrasive wear and cold welding.

A Ready-to-coat Surface Standard Is Essential

For the hard layer to deliver its beneficial effects, it is critical that the coating material is perfectly matched to the application and that the tool itself has a proper surface finish. Any particulate or film-forming residue is bound to degrade the coating-to-substrate adhesion.

"In order to attain an adequate level of cleanliness in a cost-efficient and process-reliable manner, one must consider the entire toolmaking process. Otherwise, contaminants will be carried over through the manufacturing chain and can then be removed only through an intense effort at the final cleaning stage, or not at all," comments Volker Lehmann, managing director of UCM AG.

When Is Cleaning To Be Performed?

Tools such as indexable inserts, which are often made of hard metals, are ground upon leaving the sintering furnace. Grinding commonly involves the use of machining fluids, the residue of which must then be removed. "This is typically done with the aid of hydrocarbons, i.e., solvents which effectively remove non-polar contaminants such as oils while exhibiting a good material compatibility," Mr Lehmann explains.

Tools such as indexable inserts, which are often made of hard metals, are ground upon leaving the sintering furnace. Grinding commonly involves the use of machining fluids, the residue of which must then be removed. "This is typically done with the aid of hydrocarbons, i.e., solvents which effectively remove non-polar contaminants such as oils while exhibiting a good material compatibility," Mr Lehmann explains.

If the indexable inserts are polished as well, this operation must be followed by another cleaning step. This should be performed directly after the polishing cycle to prevent polishing paste residue from drying into a difficult to remove film on the part surface. The preferred solution here is a multi-chamber system in which intermediate cleaning is performed with an aqueous medium.

This has the advantage that parts can be run through the cleaning system immediately in a single layer so that the polishing paste will be fully removed without residue. A common subsequent step before coating is alumina blasting, i.e., surface finishing of the product using a fine-grained aluminium oxide.

Complete Development Of The Cleaning Process

Next, the parts move on to the final cleaning stage which takes place in multi-chamber systems with the aid of ultrasound. The objective of this cleaning step, on the one hand, is to remove all residue from the part and to dry each product to a stain-free finish. On the other hand, an aqueous cleaning process must always be designed to minimise the so-called cobalt leaching effect, i.e., the dissolution of cobalt from the hard metal.

Next, the parts move on to the final cleaning stage which takes place in multi-chamber systems with the aid of ultrasound. The objective of this cleaning step, on the one hand, is to remove all residue from the part and to dry each product to a stain-free finish. On the other hand, an aqueous cleaning process must always be designed to minimise the so-called cobalt leaching effect, i.e., the dissolution of cobalt from the hard metal.

At the equipment engineering level, a consistently high level of part cleanliness is ensured by the four-sided overflow developed by UCM. The cleaning or rinsing fluid enters each tank from below, then rises up and flows out over the rim on all sides. As a result, a permanent flow is generated in the tanks which ensure an intense treatment of each part.

At the same time, removed residue and particles are discharged from the tanks and filtered immediately so that no re-contamination will take place when the parts are lifted out or transferred. In order to obtain a stain-free surface, moisture is blown off the part before the actual drying cycle commences.

Thus, proper cleaning after each processing step is a key contributor to an optimised coating quality and can provide a competitive advantage to toolmakers and coating contractors.

Photo Credits: Dürr Ecoclean