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Macro Economics, Micro Burrs: Get a Handle on Cost per Part, Set a Target

Jim Lorincz
By Jim Lorincz Contributing Editor, SME Media

The mindset that should accompany decision making about how best to deburr parts should depend on establishing a target for cost per part. That’s the sage advice of LaRoux Gillespie, Dr. Eng, FSME, CMfgE, PE, a past president of SME and author of 13 books on burrs and deburring.

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COFA is Heule’s standard tool solution, which allows for easy deburring of cross bores by removing burrs on the front and back of a drilled through-hole on sloped, even, and uneven surfaces.

Gillespie said that selecting the right deburring approach from the many processes (124) that are available is complicated by the fact that most shops, large and small, may not have as firm a grasp on their deburring cost as they should. Job shops with a high mix of frequently changing part requirements and contract manufacturers running high volumes of the same or similar parts operate at different ends of the manufacturing spectrum. In addition, shops face deburring choices from among mature processes, each with its own strengths and weaknesses that are being challenged to handle newer, tougher part materials along with the more traditional and familiar steels.

Target for Cost per Part

Gillespie, the author of the Economics of Burrs and Deburring, explained that “the most basic question that must be asked in assessing a shop’s deburring requirement is what is the most economical way of achieving the result that I want. What’s my target for deburring cost because I want the cheapest way of achieving it?”

Information about how many parts, their geometries, edge radius requirements, finish, and work materials is needed by both the deburring equipment supplier and the part manufacturer for each to evaluate how effective the deburring solution will be in meeting part quality requirements.

“One of the most common mistakes that companies make is confusing a deburring problem with a surface finishing issue. Drilling, milling, and turning lathes create burrs, more nearly the same today on a day-in and day-out basis because of today’s advanced machining technologies. If the burr is 10 thou thick and tall it’s better to machine it off. Another possibility is machining to place the burr where it is more easily removed. That is both faster and more cost effective,” said Gillespie.

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LaRoux Gillespie, Dr. Eng, FSME, CMfgE, PE, a past president of SME and author of 13 books on burrs and deburring

Every process has side effects, though maybe not hand deburring, said Gillespie. “Electrochemical will leave an oxide on some areas. Electro polishing will take dimensions off the whole part. Vibratory changes dimensions of every external feature, maybe not too much but as much as 0.0001 to 0.002″ [0.0025–0.0508 mm]. If possible, run tests to determine repeatability of the process for radius, for example. Or ask for repeatability of processes from suppliers. The answers will be enlightening, if in fact the studies exist,” said Gillespie.

The following excerpt, “What Machine Shops Need to Know about Deburring,” about choosing a deburring process by size of burr is taken from an extensive interview with Gillespie published by ME in 2017 (https://advancedmanufacturing.org/machine-shops-need-know-deburring/).

“When choosing a deburring process, a shop must address several issues, including the work material, edge radius, stock loss and surface finish. Many questions need to be asked, including how tall and how thick the burr is. Most burrs on precision parts are between 0.001 and 0.003″ (0.025 and 0.0762-mm) thick and can be removed via conventional deburring processes. If a burr is 0.005–0.010″ (0.127–0.254-mm) thick, it will usually need to be machined off. All of these issues factor into choosing a process that meets economic and quality requirements.”

In closing, Gillespie asks shops to determine early on whether the problem is burrs or is it all the features that workers finish (surface finish, nicks, scratches, marking, handling, packaging, cleaning etc.). “Is it a burr problem or a need to reduce the costs of finishing?”

Burrs can be challenging based on any number of factors including size, design, material, and location. Some of the most difficult are found in cross-hole intersections, elbows, and deep recesses in hydraulic components and manifolds for precision applications in aerospace, automotive, oil and gas, and medical industries.

Excellent One Pass Targets

Burrs are produced by upstream processes (most commonly drilling) that are performed by cutting tools that due to wear, produce burrs that change size over time, just as deburring tools can also wear, some by their very nature more than others.

It’s important to select operating parameters and tools that maximize performance in deburring based on the degree and size of the burr found on the entrance and exit of a drilled hole, which is dependent on the material and sharpness of the drill. The back sides of holes are particularly difficult as they are frequently inaccessible with conventional deburring tools and parts have to be removed from the machine and deburred by hand.

Cogsdill Tool Products Inc. (Camden, SC) offers tools for deburring that allow the user to easily deburr the front and back of the holes in a single pass. “On a daily basis, our customers face the challenge of deburring both sides of a hole [entry and exit] which our tools can do in one pass, eliminating hand deburring,” said Don Aycock, vice president sales and marketing.

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Cogsdill’s mechanical hole-deburring tools remove burrs on both sides (entry and exit) of drilled holes in one pass. The Burr-Off’s “clothes pin” design is ideal for automated, high-production ferrous metals applications. Burraway features an inexpensive replaceable cutting blade that adjusts to control the amount of edge break.

Cogsdill has customers in a variety of industries, including aerospace, automotive, oil and gas, food processing, firearms, and general machine shops. “If it’s metal and has holes drilled in it, we deburr it,” said Aycock. Materials include ferrous and nonferrous metals: steel, aluminum, cast iron, brass, bronze, stainless steels, titanium, and aerospace alloys, among others.

Among the most challenging deburring applications for Cogsdill’s customers are small-diameter holes, holes that exit at an angle, and cross holes. “Some of the challenges facing our customers in these industries are having to hand deburr parts, which is very time-consuming, or deal with internal burrs in very intricate parts and materials that are harder than Rc 45, as well as composites.” Typical applications include clevises, tubular components, transmission parts, hydraulic parts, airbag canisters, wing skins, bulkheads, sheetmetal, framework, monocoque fabrications, pipe and tubing, and circuit boards, said Aycock.

With the demand for deburring smaller and smaller holes increasing, Cogsdill has introduced a new line of one-pass micro-deburring tools. The new Micro Burraway series of tools will deburr both sides of a hole in one pass in holes ranging from 0.040 to 0.092″ (1.00–2.33 mm). “Applications ranging from medical parts to automotive parts, electronics, and everything in between are driving the sizes of holes smaller and smaller,” said Aycock. “Materials can include aluminum, steel, stainless steel, titanium and even composites. These holes need to be deburred on both sides as well,” said Aycock. The Micro Burraway line features replaceable cartridges that include the arbor and blade, and a holder which accommodates the different cartridge sizes.

Deburring Intersecting Holes

Deburring a perpendicular hole through a flat plate is one thing; deburring a hole that intersects a bore or internally deburring a 90° elbow made of aerospace alloy is another, said Stanley Kroll, sales manager, J.W. Done Corp. (Hayward, CA). His company’s Orbitool was developed to deal with these challenging internal pathways, whether made by a CNC mill, drill, or lathe. The Orbitool itself comprises a flexible shaft topped by a carbide sphere surrounded by a radial disk.

“The easiest way to describe the path we need to take with the Orbitool from a CNC standpoint is that it’s a thread milling routine created by helical interpolation,” said Kroll. “The Orbitool, which can be used manually as well as through the more efficient CNC application, isn’t rotating when it is moved into the cross hole on center. It is offset to one side of the cross hole so that the protective disk contacts the wall of the hole and the flexible shaft bends, creating cutting pressure. The CNC program then rotates the tool and feeds it via helical interpolation past the intersection of the hole and the bore,” said Kroll.

As the Orbitool feeds down it finds the edges of the intersection and begins removing material with the carbide burr at the intersection as soon as it moves beyond the end of the wall of the hole. When the hole edge ends inside an elbow, the protective disk rides the wall and cutting doesn’t occur. Metal removal rate to create the radius is controlled by adjusting four of the Orbitool’s parameters: length of the tool shaft, tool rpm, feed rate and pitch of the thread created by helical interpolation.

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Orbitool was developed to deburr holes that intersect with bores or to internally deburr a 90° elbow.

Programming for the Orbitool is relatively simple, according to Kroll. It is a basic thread milling routine with a Z-axis interpolation.”We just come into the hole, preload and push it against the wall and choose the distance that the tool will travel, start to finish. The edge looks like a Pringle chip and we never have to tell the tool what the edge looks like.”

The Orbitool was originally developed for aerospace components made from materials like Inconel, Nitronic steels, and exotic metals, so it can handle the toughest materials for aerospace, oil and gas, and medical applications. Typical applications now include hydraulic fittings and manifolds for medical, aerospace, energy, and general engineering, or wherever it’s difficult-to-reach drilled and blind holes. CNC applications are readily accomplished on manifolds that are produced by milling and elbow or cross-section holes produced by CNC lathes.

Automated Deburring

Burrs can be challenging based on any number of factors, including size, design, material and location. Some of the most difficult are found in cross hole intersections, elbows, and deep recesses in hydraulic components, manifolds, and for precision applications in aerospace, automotive, oil and gas, and medical industries.

“Manifolds, fluid components, uneven surfaces, and cross holes are the most challenging machined parts for deburring,” said Lynn Bissell, sales and marketing coordinator for Heule Precision Tools (Cincinnati). “And new, difficult-to-deburr materials like composites, exotics, as well as stacked materials with multiple materials layered on top of each other, require different feeds and speeds but make up the same bore.”

New complex or delicate part designs that are now possible with CAD can create designs that have impractical implications for machining the parts. They can add additional machining costs unnecessarily by arbitrarily deciding an angle, tolerance, or size that is difficult or impossible to machine, said Bissell. They may also involve challenges such as thin-walled material or holding specific edge break sizes.

Heule provides automated deburring solutions for high-volume manufacturers in aerospace, defense, automotive, medical, energy, heavy construction, and agriculture, as well as precision machining companies who do work across all of these industries. “Our tools are designed to deburr a part on both the front and back of a hole in one pass, so they eliminate time-consuming processes like manual deburring or having to remove a workpiece and turn it over to deburr the back of a hole,” Bissell said. “This deburring solution is referred to as back bore deburring or back bore machining, as opposed to standard deburring tools that are designed to only deburr the front of the hole, resulting in the need to remove the part and turn it over to deburr the other side.”

Heule tools are used for a range of materials: steel, iron, aluminum, nickel, brass, titanium, alloys, and exotics, among others, with composites being a newer, more challenging material. There are two major challenges to machining composites: one is to cut the fibers neatly without fraying; the other is that the abrasiveness of the material leads to heavy wear on the cutting edge of the tool blade. Heule worked with an aircraft manufacturer to develop a cost-effective solution, a tool with a long blade life that would also deburr the bore neatly.

Shaving a Few Seconds off Cycle Time Adds Up

“Our tools address many challenging areas for our customers,” said Bissell. “For some, it is a solution that reduces the cycle time that is necessary to machine a part. Because our customers are producing a high volume of parts, shaving off a few seconds to several minutes per part results in large time gains. These customers may be facing increased numbers of parts they need to produce, so gaining the ability to produce the parts quicker allows them to satisfy their production demands while also cutting their costs, she added.

“The quality and consistency of parts are issues that many customers face on a daily basis. For some of our customers, the quality of the part is very important to the integrity of the end product, and they want a part that contributes to making that product last and perform well,” said Bissell. “Our tools provide more consistent deburred bores compared to other methods, so they increase the integrity of the product while also eliminating the cost of scrapped parts that don’t pass quality inspections.”

Heule tools lend themselves to automation and are designed for challenging automotive applications, for example. For a manufacturer of V-8 crankshafts that consist of a main bore that breaks out into seven different surfaces, some of which are angled/irregular cast surfaces, Heule provided a tool solution that reached all of the large exit burrs on the part. The tool was a special C12 COFA with a 20° M blade and S spring. The COFA tool has a cutting blade that can pivot and deburr all of the flat and angled/irregular surfaces by entering through the main bore to reach the seven different bores.

“The automated nature of our tools also eliminates the subjectivity of standards by different machine operators who have to decide when a burr is too big and needs to be manually deburred. The traditional ‘fingernail test’ will differ with different machine operators [of which there are many on high-volume jobs] and result in inconsistent parts, some of which may contain burrs that could cause the product to fail,” Bissell concluded.

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