South Carolina Firm Links New CAM Programming Capability
to Innovative Cutting Tools for Vital 304 Stainless Steel Parts

Joint development efforts in production machining between Pathtrace Systems Inc., Southfield, Michigan, and cutting-tool leader Sandvik are paying off handsomely for a South Carolina machine shop that focuses its business strategy on complicated replacement parts for textile machinery.

“I invest in technology so my customers don’t have to,” says Bart Blackwell, owner and general manager of B & S Machine Tool, Aiken, South Carolina. It’s very simple and given that B & S is located in the heart of the American textile industry, it’s dead-on accurate for his market.

What was once a struggling machine shop is now a bustling business running nine shifts a week. Innovations are coming in as fast as they can be identified. Essentially, B & S is converting what has been a cottage industry, making replacement parts for the machinery used by nearby manufacturers, into a growing business. The company has relied heavily on its skills in reverse engineering and that continues to be a base of the business.

Blackwell bought the 20-person firm late in 2003 and quickly installed two more CNC machine tools. Those were the first significant productivity investments at B & S in many years.

Modernization at B & S focuses on the shop floor. Howard Goman, CAM programmer, machine-tool setup man and CNC operator, is capitalizing on the power of the Pathtrace - Sandvik collaboration to cut his programming time, using:

EdgeCAM from Pathtrace Systems with its Advanced Turning and Solid Machinist modules for complex machining tasks requiring tight integration with solid models from customers’ CAD systems
Coated carbide cutting tools from Sandvik Coromant that have five cutting radii per insert edge rather than one. They were developed for smoother finished surfaces in stainless steel.
• A mid-sized Daewoo turning center with a “C” axis for drilling, tapping and milling.

The benefit of the collaboration is put to the test on one of B & S’s premier contract jobs; governor alignment guides for textile machines. These are not just oddball parts, deemed insignificant in the larger scheme of things: quite the opposite. A reliable supply of these high-quality governor alignment guides is essential to keeping textile machinery running. “These guides are vital to the Aiken area’s infrastructure,” Goman explained. B & S makes replacement parts for a variety of other industries including: automotive, pharmaceutical, fiberglass, building products, paper and golf.

Problem: Overcoming Cost and Productivity Disadvantages
American textile manufacturers have been struggling economically for decades against imports from low-labor-rate parts of the world. Many are also at a significant productivity disadvantage. Machinery in the U.S. is on average about ten years old while much of the Asian machinery is new.

The governor alignment guides manufactured by B & S are about 2 inches in diameter and 1 ¾ inches long, roughly the size of a child’s fist. Each guide has two different tapers with four rounded edges and diameters ranging from about 1 3/8 inch to ¾ of an inch. A 5/8 inch diameter bored and counter-bored hole runs through the part axially. All this is turned and bored on the Daewoo lathe.

There are also two holes in the face of the larger end for extractor screws, drilled parallel to the axis. There are two more holes drilled in the side for steel setscrews that keep the brass guide in place. Also done on the Daewoo, these holes are drilled radially and tapped with the C-axis spindle.

The critical alignment-guide specification is an RMS-32 finish on the outside diameter (OD) tapered surface. They are crucial to the way the guides align the winding machine components, keeping their productivity up. To keep productivity high at B & S, Goman machines every guide surface to finish specs, even a shiny RMS-32s. Several finishing passes are needed.

The stock material is AISI grade 304 stainless steel. It is widely used in textile machinery wear parts because it stands up well to abrasion from fabrics and to chlorine-based dye chemicals. Sixty percent of what Goman machines is 304, well known to machinists for its “gumminess.” As the metal is cut, it tends to stick to the inserts.

“It builds up until it looks like it was welded on to the cutting edges,” he said. “Once that happens, the surface smears.” To deal with this, Goman looked to Sandvik and their Wiper inserts. Wiper inserts are different in that they have two cutting surfaces, or radiuses, on each insert edge instead of the usual one. “As the part is turned,” Goman explained, “the radiuses work together in tandem, to cut and then smooth the surface.” That wiping effect gets rid of the tiny ‘scallops’ that cutting tool cutters always leave in machined metal surfaces. “That’s how we meet the RMS-32 without any secondary finishing.

“Without EdgeCAM, we couldn’t use the inserts very effectively because of the difficulty in keeping the inserts’ two radiuses in contact with the steel at all times,” he pointed out. Goman uses WM and WF CNMG 431 and 432 grade 2015 coated carbides from Sandvik.

The Sandvik Wiper inserts differ significantly from conventional cutting-tool inserts. Instead of a full radius at the nose, the insert has small flats at the tangent contact surface, which is where the surface finish on the component will be achieved in turning. The effect of a Wiper insert's unusual geometry is essentially to give the insert a flatter nose. With the flatter shape, the insert removes more material with the back of the profile: it "wipes" the material. The scallops between passes are smaller because of this effect, and thus the surface finish is improved.

The Wiper inserts worked just fine when B & S turned the horizontal and vertical faces. But there were problems turning the tapered surfaces of these conical parts. “When we cut the tapers, and the shoulders between them, one of the two Wiper radiuses would lose contact with the surface,” Goman noted. “That was just enough to give us a finish that was smeared rather than cut.” With an RMS-32 spec, that was completely unacceptable. There were two potential fixes, neither of which appealed to Goman and B & S.

One was in manual programming, inserting feedrate changes one line at a time to the G-code generated by the software to slow the feedrate as the cutter approached any tapered or rounded surface. The programmer would have had to insert the feedrate changes at each appropriate place in the program.

“I would have had to find each instance where a horizontal surface or a vertical face changed to a taper and slow the feed rate way down, maybe by 40% to 50%,” Goman explained. “Then I would have to find the code where the cut returned to the horizontal or vertical and tell the program to go back to the feedrate for the overall job.” That is usually 0.012-inch per revolution (IPR).

Since each of these parts have tapered and rounded surfaces, eight feedrate changes are needed. “To change the feedrates manually,” he explained, “I would have to search through a minimum of 500 lines of code in every program.” That would be tedious and time-wasting but worse, “it opens up an opportunity for error, the human factor,” he noted. Moreover, the eight feedrate changes were needed in each of several roughing and finishing passes. “If you fat-fingered something or misplaced a decimal point, boom, gone, the workpiece is scrap.”

Goman sets up and operates two CNC machine tools and writes their programs at a shop-floor desk in between them. Programming errors are hard enough to avoid in a nice, quiet engineering office, which has far fewer distractions.

The second surface-finish alternative involved a secondary operation—hand-finishing or polishing. But secondaries are slow, disruptive, and can be unreliable so B & S avoids them. To Goman and B & S, hand finishing just introduces another potential for human error and another possibility that the part would be scrapped. It would be no different than manually inserting feedrates in CAM programs.

B & S strives to prevent any kind of production error. A cornerstone of its business is an uncompromising zero-defects policy. It is prominent in B & S advertisements and on its Web site at www.bsmachinetool.com. “Zero defects applies internally as well, which means getting it right not just the first time but every time,” Blackwell said.

The textile machine guide jobs have two other uncompromising specs:

• Customers don’t do incoming inspection. “The parts go straight from our machine tools to the customer’s factory floor,” Goman said. “They have to be right because we better not shut them down!”
• Customers demand ongoing price cuts, just as if B & S were in the automotive industry. The piece-part prices B & S gets this year will be less than last year, and will be less again next year.

Solution: Automatic Feedrate Adjustment
Innovators that they are, B & S quickly recognized the value of the Sandvik Wiper inserts.
Making the insert Wipers work properly requires automatically adjusting the feedrates (inches per revolution or IPR) while holding the cutting speed constant in surface feet per minute (SFM). Constant SFM is the key to machining flawless surfaces these customers demand.

In version 9.5, released early in 2005, EdgeCAM added direct support for the range of Sandvik Wiper inserts. No longer do programmers have to insert code to manually slow down feedrates on tapered and rounded surfaces. The Wiper support in EdgeCAM will automatically vary the feedrate values as recommended by Sandvik cutting data. The EdgeCAM toolpath also accurately reflects the unique form of the Wiper inserts, avoiding potential accuracy errors caused by assuming a single radius on the insert.

“Getting and using EdgeCAM was the technology jump for us,” Goman said. “The Sandvik Wiper inserts were a bonus on top of that.”

Sandvik Coromant’s patented wiper technology makes use of five radii to “build” the nose radius of the insert. The main cutting radius is situated at the point of the insert. Behind this radius on either side is the wiper radius itself, which is blended into the main cutting radius by using another radius called the blending radius. The blending radius serves no purpose machining but reduces tool pressure by eliminating the need to use a flat as the wiper.

As the insert enters the material, the main cutting radius cuts in the same fashion as a standard nose radius. This cutting action produces feed lines that are equal to the feed rate programmed. These feed lines have peaks and valleys, or “scallops,” that can be measured using a profilometer. The trailing wiper radius removes them as it passes, which leads to better surface finish and / or the ability to use higher feedrates and maintain a surface finish.

[The wiper nose radius on CNMG and WNMG inserts conform to the ANSI / ISO standards for nose radii. As a result, a standard CNMG or WNMG insert can be replaced by a wiper without changes to the program. However, TNMG and DNMG inserts have a smaller point angle (60 and 55 degrees, respectively). Due to the smaller point angle, the build up of the radii that constitute the wiper nose radius will not allow the ANSI / ISO standard nose radii, and as a result are designated DNMX and TNMX inserts. When a standard TNMG or DNMG insert is replaced by a wiper insert changes have to be made in the program to maintain the correct work piece dimensions.]

The governor alignment guides are cut on a Daewoo Puma 230-MB, a midrange turning center with a 12-inch swing, a 22-inch Z travel, a “C” axis, and a Fanuc 18i-T CNC. The machine is set up for collets for small diameter work, and the machine has a 4-foot bar feeder. It also has a programmable tailstock. B & S also has a Milltronics milling machine and a new Haas VF3 Vertical Mill. They too are programmed with EdgeCAM.

Results: Far Exceeding Expectations
“The combination of EdgeCAM and the Sandvik Wipers greatly exceeded our expectations,” Goman said. “All we originally expected from the Wiper inserts was doubling the feed rates on tapered surfaces to about twelve-thousandths of an inch instead of six –thousandths.” Going to a 0.012 IPR feedrate from 0.006 “would work out to maybe a 5% or 10% savings in time. That was all. We didn’t even expect surface finish to improve.”

What actually happened was dramatically better:

• Running overall jobs two, three and even four times faster, partly by stepping up the depth of cut to 0.125 IPR per side from 0.080, which is about 50% more.
• Doubling key machining speeds to 900 SFM in the tapers from 425.
• Faster programming, up to 20 minutes per program on repetitive jobs.
• Halving the consumables cost. Each lot of 50 guides is run with just two Wiper inserts, one for the outside diameters (ODs) and one for the bored through-holes.
• More than halving the number of machining passes, saving several minutes machining times per part, and yielding better surface finishes.

B & S programs many of its parts directly from solid models provided by its customers in EdgeCAM. “EdgeCAM has done such a great job on their associativity that we never have to touch up the information from the customer,” Goman said. Just as with secondary operations in finishing, “we never want to touch the customer’s geometry, either.”

EdgeCAM helps Goman in two other ways:

• Getting frequent engineering changes into the toolpaths. “I just reload the file, open it, click Accept All Changes [a menu pick], hit Update Toolpaths [an on-screen button], click on OK [in a pop-up dialog box] and I’m done. EdgeCAM regenerates the tool paths automatically,” he added. “Basically, I just hit the Return key a lot.”
• Demonstrating that the changes were made and the parts meet the dimensional specs. “EdgeCAM lets us compare the part as machined, based on the CAM program that generated it, with the CAD geometry that we imported. It’s very good for validating the B & S Zero Defects policy to customers.”

Benefits: Finding the Best Mix of Innovations
All these gains help B & S lower costs, which answers a never-ending demand from customers, as noted. The ability of B & S to boost productivity means it can pass part of the savings along to its customers. They share the benefits of any B & S innovations. In turn, they can be a little more competitive.

Taking on this kind of difficult work highlights another B & S business strategy. Blackwell actively seeks contracts for complicated replacement parts from demanding customers. Such work often overwhelms machine shops not staffed and equipped for it. Preferring less troublesome work and smaller profits, few shops will bid for these jobs. All things being equal, difficult jobs yield better margins.

“My plan,” Blackwell said, “is to extend our customer base beyond the Aiken area by expanding the contract manufacturing side of our business. At the same time, we will not let that jeopardize the industrial maintenance and repair support business. That has been our bread and butter for over 20 years. Successes like this make me very optimistic about the future of B & S.”

Blackwell has owned B & S since December 2003; he had been its general manager and co-owner since late 1998. He came well prepared. Prior to joining B & S, he spent five years as the general manager of a medical equipment manufacturer. Before that, he was a manufacturing consultant supporting Department of Defense process improvement initiatives at Army arsenals, Air Force deports and Naval shipyards.

The B & S success shows how contract machining shops and American manufacturing firms—even those under fierce competitive pressure—can take advantage of technology gains by forming virtual partnerships. For essentially this is what B & S has done with its 24-hour standby service.

“This business is becoming increasingly competitive and in order to survive you must be able to take advantage of the available technologies to reduce costs and increase throughput,” Blackwell summarized. “We can only be successful if our customers are successful. We must support them by delivering components faster and less expensively than before.

“We achieve this by continuing to upgrade our equipment, utilizing the best tooling available, and optimizing the tooling and equipment’s performance with applications like EdgeCAM,” he added. “We will continue to leverage the latest technologies to grow this business.”

On a deeper level, B & S is addressing the real opportunity of globalization: searching the globe for the best mix of technology and business methods. B & S and the textile companies— quintessentially American firms in their outlooks—are meeting global challenges with global solutions. Pathtrace is based in Reading, England. Sandvik is a Swedish company. Daewoo is Korean. Its CNC provider, Fujitsu Fanuc, is Japanese. To put this in further perspective, the U.S. is the largest or second-largest market for each of them.