Adding high speed electric spindle systems to its Boston Digital vertical machining centers has helped Sohn Manufacturing improve accuracy and productivity in precision operations. The company uses a variety of spindles made by the Precise Corporation (Racine, Wisconsin) to expand the capabilities of several machines from Boston Digital for performing precision operations and producing small parts faster and more accurately.
Sohn Manufacturing, Inc. manufactures a broad line of products related to the paper converting and labeling field and markets them worldwide. One division manufactures rotary flexographic label printing machines; another supplies flexographic printing plates and related graphic arts; still others produce rotary die cutting machinery and dies, supply papers and custom inks. The firm's SMI Division manufactures various medical devices.
The company traces its roots back to the 1950s and has been using Boston Digital machines in its plant since about 1974. This was not long after President Wallace J. Beaudry took over management of the company in 1972 and marks the beginning of an expansion that has taken the firm from its original 11 employees to approximately 200 today.
In producing the machinery, dies and other products, Sohn performs a wide variety of machining operations, many of which require a high degree of precision and repeatability. Mr. Beaudry explains that Boston Digital's machining centers are used for everything from drilling fine holes down to 0.015-inch diameter, to grinding carbide tooling and performing precision slotting operations.
Early on, the company had equipped some of the machines with auxiliary air turbine spindles, but these proved unsatisfactory. Mr. Beaudry says, "The air spindles did not give the torque we needed under load. They had a tendency to stall easily and didn't maintain the speed to give the surface feet per minute we needed."
Now all Bostomatic machines are configured mechanically and electrically to easily accommodate a Precise high speed electric spindle system as an auxiliary spindle. By mounting it to a premachined pad on the side of the main head, it is easily changed and does not disturb the main spindle. Because the mount is rigid and in a fixed location, it is said to be easy to program the spindle into the machine's operating cycle. In addition, Boston Digital offers automatic toolchangers to further increase the productivity of these spindles.
The company has several different spindle models available, so the operator can select the one that will provide the correct power, capacity, and speed for the application. For the smallest diameter holes, a 0.67-hp Precise SC 1060-OA spindle provides speeds up to 160,000 rpm, to achieve optimum surface speeds. Most recent additions to the spindles used for this purpose is a Precise SC 80. This 2.4 hp spindle is capable of infinitely variable speeds from 10,000 to 40,000 rpm and is liquid-cooled.
Repeatability is essential for the precision machinery made at Sohn, to assure parts interchangeability in the field. For precision drilling of holes as small as 0.015-inch, Mr. Beaudry likes the rigidity and close-tolerance runout of the Precise spindle design in conjunction with the Boston Digital machine. "Because its so solid and rigid, we can go back to the same hole when we're drilling multi-sized holes with a tolerance of less than ±0.0005-inch on location," he explains. The air spindles"...were nowhere near as rigid and their runout was worse," he adds.
Liquid cooling is another plus for the electric spindles. The air spindles used compressed air cooling and their tolerance would change with the ambient temperature. The Precise spindles feature a refrigerated liquid cooling system that circulates internally to hold a stable temperature throughout the automatic cycle, Mr. Beaudry notes.
On many of Sohn's BostoMatics, the spindles were installed during production of the machines at Boston Digital. This provides the benefit of fully-integrated CNC and the ability to service the Precise spindles with automatic tool-changers. Other BostoMatics were outfitted with spindles at Sohn, a task made easier by the fact that the BostoMatics are built to easily accept Precise spindle retrofits, both in terms of machine castings and electrical considerations. Both approaches have worked for the company, and Mr. Beaudry says that the important thing is to determine the right spindle for each application.
He says they are used for everything from machining aluminum and copper through various grades of tool steel, as well as for grinding on carbide, using special grinding tools that Sohn makes in-house. Tooling size varies from 0.015-inch diameter drills to 3/4-inch diameter abrasives and slotting saws. Mr. Beaudry adds that the spindles are also excellent for machining plastic parts, because of their low tool pressure. MMS