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Emerald Group Publishing Limited
Copyright © 1998, MCB UP Limited
New stainless alloys help increase throughput
New stainless alloys help increase throughput
Keywords Carpenters, Machine tools, Stainless steel
American Micro Products, Inc., contract manufacturer of high precision machined components, has gained a significant competitive advantage by upgrading to premium grade, free-machining stainless steels for a growing number of the parts it makes (Plate1).
Plate 1 Variety of small parts that have been made from Carpenter's project 7000® stainless steels Types 303 and 304
The Cincinnati, Ohio, job shop, with several high-volume parts of different configuration, already has enjoyed up to 40 per cent increase in throughput, 50 per cent reduction in cycle time, up to ten times longer tool life, better finishes and the ability to machine more complex parts it is claimed.
American Micro had been using Project 70® stainless steels Type 303 and 304 from Carpenter Technology Corp., Reading, PA. These alloys are well known in the metalworking industry for their improved free-machining characteristics.
Management found, however, that its job conditions were just right to capitalize on the advantages offered by Carpenter's new Project 7000® stainless steel series. These newer steels have been designed to improve on the results obtained with the Project 70 grades.
The shop was running large volumes of small diameter stock, producing up to a half million each of several key parts. It had machines that could be run at higher speeds. Parts were fairly complex and short enough to keep material weight low. Finally, it was a high technology plant that routinely tracks costs.
Productivity gains and quality improvements were impressive when the company tried Carpenter Project 7000 stainless Type 304 for jiggle pins that were used in the thermostats of diesel engines. The shop manufactures about a quarter of a million of these pins per year.
The pins, varying slightly in size and complexity, are turned on a single-spindle Swiss automatic screw machine. A typical pin is 0.188in. diameter and 0.500in. to 0.750in. long with a spherical ball on the end.
With the switch to the Project 7000 stainless grade, the shop has halved its cycle time from 56 to 28 seconds per part, improving yield per shift proportionately. The company estimated it has increased throughput from 25 per cent to 40 per cent, depending on the pin.
While the shop operates multiple shifts, it runs the machine involved just one shift daily. Before switching to stainless, the shop had to sharpen its tools three to four times per shift. Using Project 7000 stainless Type 304, tools now need sharpening only twice a week. This translates to seven to ten times longer tool life.
The shop also has been able to achieve a surface finish on the ball of 24 RA sometimes lower than 16 RA simply by turning, thus eliminating the cost of subsequent grinding.
American Micro has experienced similar benefits in the manufacture of small cylinders for miniature pneumatic valves. This part, 0.75in. long and less than 0.25in. in diameter, is drilled and turned on a multi-spindle Swiss automatic using Carpenter Project 7000 stainless Type 303 (Plates 2 and 3). Annual part production is approximately 500,000.
Plate 2 Closeup of a single-spindle automatic turning outside diameters of a production run of stainless steel jiggle pins
A tiny drill makes a 0.086in.-diameter hole, 0.625in. deep down the centre of the cylinder. The upgraded stainless allowed enough increase in drilling rpm to boost throughput from nine to 11 parts per minute. Feeds were not increased because tool rigidity was of paramount importance in this type of micro manufacturing.
Plate 3 Forming operations are performed, using this multi-spindle Swiss automatic, on a long run of small retaining buttons
In addition, tool life was tripled. Whereas the shop used to change drills every 5,000 pieces when machining Project 70 stainless Type 303, it was able to manufacture 15,000 parts before drill change was necessary when using the Project 7000 alloy equivalent.
Managers documented more benefits when they switched to Project 7000 stainless Type 303 for the manufacture of buttons that were used in diesel engines. The company produces about a half million of them annually on a multi-spindle Swiss automatic.
Drilling and forming of several diameters are performed on parts that are 7Ž16in. OD by 5Ž16in. long. A 0.132" diameter hole is drilled down the center, holding a drill tolerance of +0.000/0.002in.
Using the improved stainless steel, the shop has increased part throughput by 30 per cent, and more than tripled drill life. While the shop originally had to change drills every 20 hours, it was able to run 60 to 80 hours before a drill change was needed, after switching to the Project 7000 stainless alloy.
American Micro has been using the Carpenter Project 7000 stainless alloys for a growing variety of parts which have included critical products such as bushings for aerospace applications and clevis used to hold surgical instruments.
"We have used the Project 7000 stainless steels also on a lot of shorter runs of 5,000 to 10,000 parts", reported Gary Heineman, American Micro sales manager, "and have seen a typical increase of 30 per cent in throughput".
"In general", he said, "we have found that the more complex the part and the more machining is required, the greater the benefits to be offered by these stainless grades".
Heineman noted that the new Project 7000 stainless Type 304 has helped his company not only to retain its jiggle pin business, but also to strengthen relations with its customer. He attributes this stronger bond to the shop's ability to improve throughput and quality, while holding down costs.
"Now that we have seen the value of these new stainless steels", he observed, "we are in a position to expand our horizons and more aggressively price new jobs".
Carpenter's Project 70 stainless and Project 7000 stainless steels are both described as stainless alloys offering significantly improved machinability characteristics over their generic counterparts. Project 70 stainless steels have been machined at speeds up to 15 per cent higher than standard stainless steels, with improved finishes and longer tool life.
Project 7000 stainless steels have been turned at speeds 50 per cent or even higher than conventional stainless grades. The Project 7000 stainless steels meet standard industry specifications, and are patented.
For additional information, contact Carpenter on +1 800 654 6543.