in Vol. 16 - November Issue - Year 2015
"Surf Finishing" - Targeted Surface Finishing Of High Value Parts
Photo 1: Surf Finisher equipped with two robots
Photo 2: While the robot is immersing the work pieces into the media bed, the work bowl is rotating at a speed of up to 80 RPM
Photo 3: The robot holds the finished work pieces into a cleaning station where residual media pieces still adhering to their surface are removed with a mix of air, water and compound
Photo 4: The Surf Finisher is completely enclosed with a protective cabin
Photo 5: Deburring and polishing of gear components
Photo 6: Hip stem polished to Ra = 0.04 μm (1.6 μin)
Photo 7: Surface grinding and smoothing of turbine vanes
Photo 8: Surface grinding and smoothing of aluminum fan wheels
Mass finishing is a highly dynamic technology that is constantly evolving and adapting itself to the requirements of modern manufacturing. While in the past most customers were simply looking for the deburring of mass produced parts in batch or continuous machines like vibratory or centrifugal disk finishing systems, today's customers frequently request the targeted surface finishing of complex, high value components. Drag finishing was no doubt a breakthrough allowing the processing of delicate work pieces that are never touching each other throughout the finishing process. With the "Surf Finishing" concept, a leading supplier of surface finishing equipment has taken this approach to a totally new level: Now the parts can be manipulated during the process, allowing the targeted finishing of specific surface areas. This technology has opened a completely new field of applications for the precise finishing of high value components.
Work pieces that are "surfing" in a bed of finishing media
The heart of the Surf Finisher consists of a work bowl filled with grinding or polishing media and one or several 6-axis robots (photo 1). While the work bowl rotates at a preset speed, each robot is immersing one single or multiple work pieces into the media bed. The rotary movement of the work bowl causes the media to flow around the work pieces creating a "surfing" effect with a very high pressure between the work pieces and the media. And, of course, such high pressures generally translate into achieving excellent finishes in surprisingly short cycle times (photo 2).
But that is not all: While in conventional mass finishing systems the work pieces typically receive an all-around surface finish, during the surf finishing process, the robots are guiding the work pieces through the media at pre-programmed tilting and/or rotary movements, thus providing a higher or lower exposure of specific surface areas to the media flow. This allows the targeted finishing of clearly defined areas on the work pieces.
From aggressive grinding to mirror image polishing
Surf finishing is an exceptionally flexible technology that can be utilized for a broad range of applications. Depending on the media choice, process type (wet or dry), rotary speed of the work bowl and the rotary speed and immersion angle of the work pieces, the surf finishing applications can reach from aggressive deburring & edge breaking, over intensive surface grinding, up to high gloss polishing with Ra values of < 0.04 µm (1.6 µin). Above all, as already mentioned, these results can be achieved on specially selected surface areas of the work pieces without the work pieces ever touching each other.
Abundant technical features
To make them suitable for such a wide range of applications, the Surf Finishers are equipped with many technical features:
Surf Finishers come in different sizes. The largest work bowl has a diameter of 1,800 mm (71") providing ample space for use with multiple robots and the treatment of relatively large work pieces.
The intensity of the finishing process is largely determined by the rotary speed of the work bowl, which can be as high as 80 RPM. This translates into a linear speed of up to 7 m/sec (23 ft/sec), providing ample pressure between the work pieces and the media.
For wet finishing process - with the continuous addition of water and compound - the Surf Finishers are equipped with a special extraction pump that reliably removes the process water contaminated with media and metal fines from the work bowl. And, of course, for fine grinding applications, these machines can also be run with "high water level" for cushioning the impact of the media on the work pieces.
Undersize media classification is also taken care of by pneumatically removing media from the work bowl in by-pass mode and classifying it offline, before returning it into the system.
The Surf Finishers are also equipped with cleaning stations, where residual media pieces still adhering to the finished work pieces are removed with a mix of air, water and compound (photo 3).
Last, but not least, for safety reasons and noise suppression the whole system is enclosed with a protective cabin (photo 4).
The robots make the difference
Robotic technology represents an integral part of the Surf Finishing systems, with the robots playing a dual role.
(1) Equipped with specially engineered work piece clamping systems, the robots are utilized for a variety of material handling functions: They pick up the raw work pieces, immerse them into the media bed of the rotating work bowl, bring the finished work pieces to the cleaning station and, finally, deposit the finished and cleaned work pieces onto special receptacles or transport systems, from where they are transferred to the next manufacturing station.
(2) An equally important function of the robots is the pre-programmed movement of the work pieces through the media bed to expose certain surface areas to the media flow and thus allow the targeted finishing of special surface areas on the work pieces. Such movements can be the tilting of the work pieces at different angles as well as a rotary or stationary movement of the work pieces through the media.
Depending on the size of the work bowl and work pieces, up to three robots can be utilized with a single Surf Finisher.
Numerous applications - from milling tools to large turbine components
Surf Finishers are universal finishing systems that can be utilized for a variety of high value precision parts from such diverse industries as aerospace, automotive, machine tools, orthopedic implants, land-based turbines and even the building industry, to name just a few.
And there is a wide spectrum of finishing applications covering deburring & edge breaking, surface grinding and mirror image polishing.
Here are just a few examples:
Deburring of milling tools, surface grinding of turbine blades and vanes, grinding and polishing of bathroom fixtures, grinding and polishing of orthopedic implants, cleaning and polishing of dies, deburring and polishing of gear components, even components as special as camshafts sleeves (photos 5 - 8).
Modern industrial manufacturing is characterized by stringent surface finishing requirements and increasing demand for automated manufacturing processes. Competitive pressure calls for just-in-time production with special, fully automatic manufacturing cells integrated into the overall production process. This poses significant challenges for the suppliers of mass finishing equipment. No doubt, the Surf Finisher, offering complete automation, total process flexibility and absolutely repeatable finishing results, is meeting these challenges head-on.
by Eugen Holzknecht
Contributing Editor MFN and
Rösler Oberflächentechnik GmbH
Author: Eugen Holzknecht