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17 May 2017

Walter Trowal drag finisher draws on fairground ride to deliver superior finishes

Walter Trowal drag finisher M-TMD Walter Trowal drag finisher draws on fairground ride to deliver superior finishes
Walter Trowal’s new drag finisher line M-TMD is for processing high value parts requiring perfect surface finishes. Workpieces are mounted on rotating satellite stations and undergo multiple overlapping, pre-programmed, rotational movements. This rotational variation produces optimum finishing results.

Typical part examples include: medical engineering items, such as hip and knee implants requiring a high gloss polish; aerospace industry turbine blades and other components; automotive industry turbochargers vanes.

In standard drag finishers, parts are mounted to rotating work stations and ‘dragged’ through the grinding or polishing media. This movement creates a high processing intensity and produces excellent results on many parts. In the new machines, the work stations consist of multi-spindle heads with each spindle holding one work piece. In addition to the carousel and workstation rotation, each spindle has its own rotational movement. So spindles move in a circle within two larger circles formed by the carousel and workstation rotation. This is similar to the movement of the cabins in ‘Octopus’ rides that can be found at any amusement park.

The drag finisher M-TMD 4 is equipped with four multi-spindle heads (work stations) that each have three spindles. In the M-TMD 6, up to 18 workpieces can be processed at the same time.

The independently adjustable rotational speed and rotational direction of the spindle heads and spindles creates a wide range of different movement patterns. In addition, the spindle heads can be tilted in different angles. This allows adjusting the flow characteristics to the specific shape of the various work pieces. Using the PLC unit, multi-stage processing programs can easily be implemented.

During the finishing process, the work bowl vibrates to deliver the optimum mixing of the grinding or polishing media. This guarantees a high degree of process consistency. The media fines and undersize media, along with the metal fines from the workpieces, are continuously discharged from the machine - another contribution towards process stability and consistency.

The new Trowal machines can be operated in wet or dry processing mode. For surface grinding and smoothing, as well as for certain polishing operations, compound plus water are used. In the case of targeted edge radiusing with tolerances of a few micron - for example, hard metal drill bits and milling heads - a dry process with special grinding granulate is utilised. Dry processing with organic polishing media and paste is also suitable for high gloss polishing.

Multiple finishing steps, from pre-grinding all the way to the final polishing stage, can take place in one single machine, without the need to remove and remount the work pieces to the work stations: One work bowl filled with a certain finishing media can be easily and quickly removed with a pallet truck and replaced with a bowl containing another media.

The first unit of the new machine generation has been installed in the Walther Trowal test lab in Haan/Germany and is available for processing trials with customer workpieces.

Says Christoph Cruse, general sales manager at Walther Trowal, foresees a big demand at those customers who produce high precision, high value components: “With our new equipment line, we address precision component manufacturers, who want perfect surface finishes, and where any blemishes like scratches could require scrapping a part. We also target manufacturers demanding tolerances of just a few microns. For these workpieces, the M-TMD drag finishers with their optimum flow characteristics open entirely new possibilities.”

Andrew Allcock

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