CAM Adapts Feed Rates To Wiper Inserts

Like many other businesses today, textile manufacturers compete against imports from countries with low labor costs. To remain economically viable, companies constantly invest in technology. At B & S Machine Tool (Aiken, South Carolina), a shop that specializes in producing complicated replacement parts for textile machinery, modernization begins on the shop floor.

Located in the heart of the American textile industry, B & S aims to convert what has been a cottage industry—making replacement parts for the machinery used by nearby manufacturers—into a growing business. Bart Blackwell, owner and general manager, purchased the 20-person firm late in 2003 and installed two additional CNC machine tools.

"I invest in technology so my customers don't have to," says Mr. Blackwell.

Recently, the company was able to accomplish one of its premier contract jobs—namely its governor alignment guides for textile machines—by incorporating the use of EdgeCam Advanced Turning and Solid Machinist modules from Pathtrace Systems Inc. (Southfield, Michigan) and wiper inserts from Sandvik Coromant (Fair Lawn, New Jersey). The company also enlisted the help of a mid-sized turning center from Daewoo Machine Tools (West Caldwell, New Jersey).

The company's governor alignment guides are about 2 inches in diameter and 1 3/4 inches in length. Each guide has two different tapers with four rounded edges and diameters ranging from about 1 3/8 inch to 3/4 inch. A 5/8 inch diameter bored and counterbored hole runs axially through the part. The turning and boring are performed on a Daewoo lathe.

There are also two holes in the face of the larger end for extractor screws, drilled parallel to the axis. Two additional holes are drilled in the side for steel setscrews that keep the brass guide in place. Using the same lathe, these holes are drilled radially and tapped with the C-axis spindle.

The critical alignment-guide specification is an RMS-32 finish on the OD tapered surface. This specification is crucial to how the guides align the winding machine components, maximizing productivity. In an effort to maximize productivity at the company, Mr. Goman machines each guide surface to finish specs, including shiny RMS-32s for which several finishing passes are needed.

The stock material is AISI-grade 304 stainless steel. Commonly used in textile machinery wear parts, the material is resistant to abrasion from fabrics and chlorine-based dye chemicals. As the metal is cut, the steel tends to stick to the inserts.

To address this, Mr. Goman evaluated Sandvik's wiper inserts, which have two cutting surfaces, or radii, on each insert edge. "As the part is turned, the radii work together in tandem to cut and smooth the surface," he says. "That wiping effect eliminates the ‘scallops' that cutters usually leave in machined metal surfaces. This is precisely how we can meet the RMS-32 without secondary finishing.

"Without EdgeCam, we couldn't use the inserts effectively because of the difficulty in keeping their two radii in contact with the steel at all times," Mr. Goman points out.

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 intended effect of a wiper insert's custom geometry is to give the insert a flatter nose. According to the manufacturer, the flatter shape enables the insert to remove more material with the back of the profile. Therefore, the insert "wipes" the material. As a result of this effect, the scallops between passes are said to be smaller, and thus the surface finish is improved.

When the company turned the horizontal and vertical faces, the inserts worked correctly. However, turning the tapered surfaces of these conical parts proved to be problematic.

"When we cut the tapers and the shoulders between them, one of the wiper radii would lose contact with the surface," notes Mr. Goman. "That yielded a finish that was smeared rather than cut. With an RMS-32 spec, that was not acceptable. There were two potential solutions, neither of which was appealing."

One course of action would entail inserting feed rate changes one line at a time to the G-code generated by the software. The goal would be to slow the feed rate as the cutter approached any tapered or rounded surface.

"To apply this method, I would need to find each instance where a horizontal surface or a vertical face changed to a taper," explains Mr. Goman. "I would have to decrease the feed rate by about 40 percent to 50 percent for the overall job."

Because each of these parts has tapered and rounded surfaces, eight feed rate changes are necessary. Changing the feed rates manually involves searching through a minimum of 500 lines of code in each program.

"In addition to being tedious and time-consuming, this would offer opportunity for error," notes Mr. Goman. "Moreover, the eight feed rate changes are needed in each of several roughing and finishing passes. If the programmer misplaces a decimal point, the workpiece is scrap."

Released this year, EdgeCam's Version 9.5 features direct support for Sandvik's wiper inserts. This eliminates the programmer's task of having to insert code to manually decrease feed rates on tapered and rounded surfaces. The program automatically varies the feed rate values as recommended by Sandvik cutting data. The tool path also reflects the custom form of the wiper inserts, which, according to the manufacturer, reduces potential accuracy errors that are caused by assuming a single radius on the insert.

The wiper technology incorporates 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. It is blended into the main cutting radius by using a blending radius. This reduces tool pressure by eliminating the need to use a flat as the wiper.

As the insert enters the material, its main cutting radius cuts in the same manner as a standard nose radius. The cutting action produces feed lines that are equal to the feed rate being programmed. These feed lines have peaks and valleys (also called "scallops") that can be measured using a profilometer. The trailing wiper radius removes the scallops as it passes. As a result, improved surface finishes and high feed rates are possible, the company says.

The governor alignment guides are cut on a Daewoo Puma 230-MB, a turning center with a 12-inch swing, a 22-inch Z travel, a C axis and a Fanuc 18i-T CNC. Useful for collets for small diameter work, the machine has a 4-foot bar feeder and a programmable tailstock.

"The combination of using the CAM software and the cutting tools exceeded our expectations," says Mr. Goman. "We originally expected the inserts to increase the feed rates on tapered surfaces 0.012 ipr to 0.006 ipr, which would represent a 5 percent or 10 percent time savings," he explains. "Improving the surface finish was an unexpected bonus."

The actual results the B & S experienced were better than the company had anticipated. Of the two jobs that were executed, the depth of cut was increased from 0.080 ipr to 0.125 ipr per side. Machining speeds were increased from 425 sfm to 900 sfm. Results also included a programming time reduction of as much as 20 minutes per program on repetitive jobs and a reduction in consumables costs by as much as 50 percent. Each lot of 50 guides is run with two wiper inserts, one for the ODs and one for the bored through-holes. The number of machining passes was reduced by 50 percent, a savings of several minutes of machining for each part. According to the company, this yielded better surface finishes.

"We stay viable in the marketplace by continuing to upgrade our equipment, using the best tooling available and optimizing the tooling and equipment's performance with applications like EdgeCam," Mr. Gorman adds. "We will continue to leverage the latest technologies to grow this business."