TECHNICALLY speaking BY DAVE DAVIDSON, DEBURR/FINISH TECH GROUP, AND KATIE MACKAY, MACKAY MANUFACTURING, SPOKANE WASH.

Meeting the Lean Deburring Challenge

L

ean manufacturing and lean process thinking is reshaping the face of American manufacturing. Many companies have adopted “lean thinking” as a way of life. Companies meeting the demands and challenges of the 21st century are those that have adopted lean disciplines and equipped themselves with the agility and adaptability to meet the highmix, low-volume, and just-in-time needs of their customers. Many high-volume parts manufacturing operations continue to see significant portions of their business outsourced overseas. Numerous businesses now find themselves needing the capability to make smaller numbers of more complex and sophisticated components with demanding specifications. These

Figure 1: Lean centrifugal processing: this medical device is manufactured from stainless steel. The image on the left shows edge and surface condition as machined edge and surface condition; the middle image shows surfaces after high-speed centrifugal processing, with tool and machining marks fully blended in, and edge and surface requirements met in a mechanical finishing cycle of less than 10 minutes. The one the right shows the part in its fully configured condition. The lean centrifugal process substantially reduced WIP time and eliminated variables to edge and surface finish. The lean finishing process brought a part-to-part, feature-to-feature, and lot-to-lot uniformity and consistency unattainable with prior methods, and it dropped non-conforming part rates down close to zero.

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companies are now rethinking their deburring and finishing needs. Much of the traditional mass finishing equipment currently available was designed to accommodate large production streams of the same or similar parts. Two primary factors seem to be involved in driving the rethinking of mechanical processing performed in the finishing area of companies that have embarked on a “lean” journey. 1. Batch and queue organizational schemes are giving way to singlepiece, continuous-flow methods of production organization. A need has been identified to replace mechanical edge and surface finishing methods capable of processing large volumes of parts in bulk with moderate-cycle times, with methods that can process the parts intensively and quickly and accommodate the quick changeover and processing needs that high-mix/low-volume manufacturing requires. 2. Many manufacturers have been presented with a need to make smaller lots of much more complex parts have fallen back on hand deburring with bench methods. Although this is a way of quickly handling a suddenly developing problem, it is not a longterm solution. As different operators handle parts, uniformity and quality problems arise, and reject, fall-out, and turn-back rates can become severe. Performing intricate deburring operations by hand can be both time consuming and tedious, and can lead to deburring becoming a significant bottleneck and constraint on the smooth flow of parts.

In the past, high-energy methods such as centrifugal barrel finishing were considered a specialty finishing method, to be utilized when more utilitarian methods, such as barrel and vibratory finishing, could not produce demanding edge and finish requirements within reasonable process cycle times. As the American manufacturing landscape changes, however, and more and more parts require special handling and rigid finish specifications, high-speed centrifugal finishing has become a primary option for meeting the lean deburring challenge. One company that has been successful in bringing lean to deburring and surface finishing operations is MacKay Manufacturing in Spokane, Wash. The company specializes in manufacturing precision and hightolerance components for the medical, electronic, and defense industries. This company has a vigorous lean implementation plan under way that has transformed the way it operates. Like many other companies, MacKay formerly used a combination of hand deburring and vibratory finishing for surface and edge finishing requirements on the many varying parts they manufactured for their customer base. As time went by, and they compared procedures in their deburring area with leaned-out operations in other areas of the plant, the deburring being performed looked less and less lean. Some of the parts involved

Figure 2: One of the important features of centrifugal barrel equipment is the ability to compartmentalize the barrel cavities into processing segments. This assures that critical parts can be processed with the centrifugal process in complete isolation, preventing any chance of parton-part contact.

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Figure 3: Centrifugal processing is also utilized in many industries where developing very refined surface finishes is a requirement. Dental, medical, electronic, and aerospace parts are commonly processed with this method.

were a good deal larger (an 8" × 8" × 12" aluminum frame component, for example) than some of their typical mainstream production items. These posed a severe challenge in that they had intricate geometries not well accessed by their vibratory finishing equipment. Additionally, the parts had small drilled holes that required smaller-sized abrasive media to fully access critical edge and surface finish areas.

Figure 4: An example of the compartmentalization feature of centrifugal finishing that makes certain parts remain isolated from each other during high-speed processing.

Standard vibratory finishing simply did not provide enough motion and force for media movement to accomplish the edge break, radius, and surface finishing objectives, even when run in extended and lengthy process cycle times. In order to meet production schedules, the parts were handed over to the manual deburring area for bench work using, primarily, hand-held tools. The hand deburring operations for these parts required as much as eight hours of direct labor. Whatever

Figure 5: Employing visual aids is an important lean tool in maintaining a standardized work environment.

else you might call this, it is not lean. MacKay was not previously familiar with centrifugal barrel finishing technology, and an opportunity arose to send the problem part to a process laboratory department of a centrifugal barrel finishing equipment manufacturer. This equipment manufacturer, like others, provides a free sample part processing service so that potential end users of the technology are in a position to make a comparative evaluation of this surface finishing methodology with that of other techniques.

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Figure 6: MacKay, like many other companies that have undergone a lean transformation, makes wide use of highly visual status boards, to make certain that anyone involved in a given operation is constantly updated on the status of work in progress and is immediately alerted to problems or obstructions to flow.

The test specimen part that was beta tested using the centrifugal method was processed in a centrifugal barrel machine with a resinbonded abrasive media for 10 minutes. The small media and intensive centrifugal action accessed areas not reached using vibratory processes and reduced the six to eight hours of hand deburring required to less than 10 minutes. (Total WIP time was reduced from an average of eight hours to a total of 20 minutes.) This process reduction alone provided

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Figure 7: Titanium shims, shown here after centrifugal finishing, presented a significant deburring challenge that interrupted product flow because of the need to spend considerable time hand deburring, which now has been largely eliminated.

sufficient cost justification for MacKay to acquire the machine, which it did. The company purchased a four-barrel compartment, 120-liter capacity machine that could process the larger components in segmented barrel compartments, and smaller parts in bulk. Many companies undergoing a lean transformation develop a horizontal and organizational learning capability not usually seen in more vertically oriented business organizations, and this is the case at MacKay Manufacturing. Applying lessons learned from other applications and drawing appropriate analogies is an important part of a vibrant lean culture. This willingness to experiment, to utilize trial and error and learn by doing is a part of lean culture that traces its roots back to TWI methods adopted by American industry during World War II. This TWI psychology and culture of flexibility and effectiveness was largely responsible for the dramatic improvements in manufacturing productivity that made the successful outcome of that conflict possible from an American perspective. Effective lean cultures strengthen organizational learning by making the best possible utilization of horizontal and collaborative group problem solving and process development. As company employees and managers became more and more familiar with centrifugal barrel technology capabilities, ideation for making use of this processing capa-

bility came from many different areas of the plant. MacKay has developed a significant knowledge base, specific to its own needs, that has magnified and amplified the effectiveness of the new technology deployment. Many parts that were once outsourced for various finishing needs are now part of a more integrated part flow within the plant. Like other organizations applying lean principles, the conventional cost-accounting wisdom of outsourcing is being challenged and coming into question because of contraindications when viewed from a continuous-flow perspective. One area of current exploration and developmental inquiry at MacKay is processing parts with centrifugal methods to improve part performance and service life. While often an overlooked and not well understood facet of high-energy finishing, it has been observed that parts processed with these kinds of methods often exhibit dramatic improvements in metal fatigue prevention, wear resistance, and in-service performance. In an example of applying lean thinking to analogous situations, MacKay’s CNC production supervisor, Gregg Meyer, arranged to have carbide tools used in a very demanding stainless steel application to be processed using the centrifugal method with a view toward improving tool life. Brand-new tools were processed with the method, and it was found that the modified tooling had an increased service life of up to four times that of new tooling normally used in the application (800 vs. 200 minutes of run time). Similar experimentation on other tooling involved in demanding and severe applications is also underway. As a result of this kind of lean organizational input, the centrifugal barrel finishing cell has become a solar plexus of part flow within the plant. Far from being a constraint or bottleneck, the quick changeover and cycle time processing has contributed to improved flow—from deburring and surface finishing operations to final assembly and packaging. MacKay Manufacturing has also www.metalfinishing.com

TECHNICALLY speaking benefited from overall improvements in edge and surface finish quality. Although cycle times are much lower than would be the case with traditional mass finishing processes, centrifugal processing produces edge and surface finishes of exceptional quality, especially when compared with hand deburr operations. When adopted, this kind of technology often produces a quantum leap in finish standardization, as much of the variability introduced by manual or single pointof-contact methods is removed. This leap in consistency, uniformity and quality is so dramatic that surface and edge quality can become a signature or hallmark that distinguishes a company’s products from that of its competitors, and such is the case at MacKay Manufacturing.

SUMMARY This study is an interesting example

of how lean thinking and acculturation, when mated with appropriate technology deployment, can have a synergistic, positive effect on production and manufacturing operations. An effective lean culture can magnify and build on technology improvements, and surpass in effectiveness the reasoning and cost justification used to rationalize the original deployment. Centrifugal finishing is an especially useful tool in a lean manufacturing environment. To a degree not possible with manual methods, edge and surface finish expectations and outcomes become standardized. Because the forces at work affect all parts the same way and to the same degree, part-to-part and lot-to-lot variations are minimized if not eliminated. Processing is flexible and versatile; at MacKay’s installation it is possible for the equipment to simultaneously process four different sets of part types. This type of high-forceload media processing develops

unique part attributes that cannot be duplicated by manual methods. All part surfaces processed with this method are isotropic, plateaued, have negative or neutrally skewed surface profiles, and have substantial fatigue and fracture resistance from the beneficial compressive stresses developed. These kinds of surface characteristics can substantially contribute to enhanced “lean” performance of the parts when placed into service by the end user, but that is a subject for another article.

ABOUT THE AUTHORS David A. Davidson is the 2009 Chair, Deburring/Surface Conditioning Technical Group, Society of Manufacturing Engineers, Spokane, Wash. He has written extensively on the subject of mass finishing, particularly vibratory finishing. He may be reached at [email protected]. Katie MacKay is the Deburring Operations Manager for MacKay Manufacturing, Spokane Wash.

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