Mass Finishing

When it makes sense to develop new finishing media

Author: Christoph Cruse, Contributing Editor MFN and general sales manager at Walther Trowal GmbH

 

Introduction:

In this magazine a lot has been written about the equipment that is used for mass finishing applications. Today I would like to tell you a bit more about the importance of the finishing media.

The manufacturers of mass finishing machinery usually offer a wide range of different finishing media that are used for all kinds of applications. However, practically on a daily basis new finishing processes are developed, for which the media “from the catalogue” are not – or no longer – suitable: Frequently, the customers develop new products, use new materials or apply new manufacturing technologies, which require totally different surface finishing solutions. In this respect a good example is additive manufacturing.

Therefore, under certain circumstances it makes a lot of sense to develop new finishing media. But generally, before undertaking such a project, careful considerations must be undertaken including answers to questions such as: When does the development of new media make sense? What are the benefits, and how much does it cost? In short: When do the benefits for the production outweigh the costs for the development? 

 

How is a new media created?

Such media development projects require the consideration of many factors. For example, which material is used, what the geometrical shape should be. Important is also, how well the media fits into the production environment of the user and last-but-not-least, how much the development and production will cost.

Let me illustrate with an actual example, how we approach such development projects. A renowned manufacturer of transmissions needed a new media with a specific geometry for the deburring of toothed gears which followed precisely the shape of the tooth flanks. Because the gears were prone to corrosion, an important technical requirement was that the corrosion protection ingredients in the compound had to be effective on the entire surface area of the work pieces.

None of the standard media available on the market could fulfill these requirements. For this reason, we developed a new media in close cooperation with the customer.

 

The shape has top priority

In this case the challenge was not only to create a new geometrical shape but also to ensure that the compound worked effectively and consistently despite a potentially low pH value of the process water.

In a first step the colleagues in our test lab conducted numerous trials with the customer’s work pieces to determine the optimal media shape. They found that a media with a pyramid shape and a square base provided the best contact area for the tooth flanks of the gears.

… the next priority is the material

Subsequently, wear and process stability were analyzed. In this respect the close cooperation between test lab and chemical lab was extremely helpful: Shortly before this project was started, we had developed a new range of plastic media, called AF. This media creates not only a very smooth surface with a high luster, but it has also excellent wear characteristics.

In addition, the AF media contains a pH buffer that helps prevent a decrease of the pH value in the process water. This is especially advantageous for process water recycling systems. Such a decrease can occur through the carryover of coolants from drilling, grinding and milling operations into the mass finishing process water. The pH buffer ensures that the compounds are always operating within an optimal pH value range. It means also that the acidity of the pH value does not have to be controlled regularly, and no corrective buffer chemicals must be added. Therefore, the dosing of the compound is a lot simpler and requires no special knowledge.

The experience with the new AF media has also shown that it greatly reduces the effect of the hardness of the process water to a minimum. Moreover, the utilized abrasive minerals are more wear resistant and can, therefore, be used for a longer period. Overall, the new media contributes significantly to a higher cost-efficiency of the entire mass finishing operation.

Once the geometrical shape had been defined and the material selected, we created a prototype mold for shaping the new media. This is a complicated process, because the mold with a length of about 2 m must be milled from a solid slab of steel. The prototype mold was then used for making the mold required for volume production.

The results at a glance

This project was a full success: Excellent surface finishes on the work pieces, short cycle times, long-term stable pH value of the process water irrespective of the water hardness, lower personnel costs for compound dosing and control and, finally, overall lower operating costs.

However, one important aspect should always be considered when taking on the development of a new media. Return-on-investment must always have top priority. In other words: Do the benefits of a new media outweigh its development costs?

My recommendation to all interested readers is to contact our experts. They are constantly developing solutions that are based on a combination of equipment technologies, already existing finishing media and compounds….and of course, on decades of experience.