CNC grinders are just the right Rx for helping boost productivity

Tooling & Production, Jun 1998

Thomas Engineering, Hoffman Estates, IL, replaced a fleet of outmoded profile grinders with four CNC cylindrical grinders manufactured by Weldon Machine Tool Inc, York, PA. Today, the same Thomas machinist who once operated a single profile grinder can operate all four Weldon grinders at one time, boosting output per machinist fourfold. In addition, the company's new Weldon grinders provide better quality and repeatability than the profile grinders they replaced.

Thomas Engineering manufactures punches used in tablet press machines to produce, from a powder base, pharmaceutical tablets sold over-thecounter and by prescription. During tablet production, a powder base is inserted into tablet dies.

The punches produced by Thomas are used to compact the powder under great pressure into tablet form. The finished product is stamped out at rates reaching 10,000 tablets per min. The tablets vary in size and geometry but are predominantly oval-shaped with a maximum length of 7/8-.

Thomas' old grinders couldn't consistently produce parts of perfect shape and quality-and even slight variations in shape could cause a punch to wear out prematurely or not mate properly with the dies. In addition, the different punches produced by Thomas all have different orientation angles with respect to the keyway in the grinder, making it difficult to achieve consistent orientation.

Weldon's solution-its model 1632 grinder-allowed Thomas to apply the precision of CNC grinding to its production process and consistently create punches that were exact matches to customer tablet drawings.

Thomas purchased two 1632 grinders in 1993, a 1632 Gold model in 1995 (the Gold is an enhanced version of the original 1632 with a unique shear-damping base design), and yet another 1632 Gold in 1997. Each grinder features a 16"x2"x5" conventional abrasive, aluminum oxide grinding wheel with a 1/4 corner radius, a GE Fanuc 15M CNC control, and Weldon's E-ZPUNCH software. Thomas typically produces its punches from steel grades S-7 and D2 with a Rc of 56 to 60. In the Weldon 1632s, the punches are ground with both the C and X axes operating simultaneously. The CNC control synchronizes the movement of the workhead (the C axis) with the movement of the wheel slide (the X axis) to perform precise nonrounding grinding. Only the working end of the tools are ground, with tolerances of 0.0000" to -0.0005". The surface finish must be 15(mu)" or less, with a concentricity to the barrel of less than 0.001" TIR. A 0.001" to 0.002" back taper is sometimes required as well.

Total stock removal ranges from 0.50" to 0.020" per side. The stock removal rate is 0.0025" per revolution on the rough grind and 0.0005" per revolution on the finish grind. Due to this high level of stock removal and low surface finish that's required on the punches, the grinding wheel must be dressed after production of each part. This is easily accomplished with Weldon's in-process dressing cycle.

"Our 1632 grinders can match punches to dies exactly. That means our customers get perfect compaction during tablet processing and increased life from their punches," says Jeff Simonson, Thomas Engineering's tooling production manager.

For more information from Weldon Machine Tool Inc, York, PA, circle 335; http://www. weldonmachinetool.com