In good times and bad, shops should constantly be on the lookout for ways to get more production from their existing equipment. Workholding methods frequently offer significant opportunities for improvement: Instead of loading one or two workpieces at a time in a vise or fixture, and then having the machine stand idle every few minutes while the finished parts are unloaded and fresh workpieces are loaded, shops should consider workholding fixtures capable of holding numerous workpieces at a time for machining over extended intervals. Such fixtures enable the machine to run for longer periods without an interruption, permitting the operator to monitor one or two other machines, inspect parts or attend to other duties.
One such workholding system is the Paws system, developed by job shop Paws Workholding. (Clio, Michigan) for its own requirements. It is now available to the metalworking industry at large. The system is intended primarily to hold numerous amounts of small round or multi-sided parts for secondary operations such as milling, drilling, tapping and slotting. Depending on the system selected, parts are held on their ID or OD or are clamped in vises with soft jaws.
The workholding system consists of a hydraulic base plate, a fixture plate, an electric-hydraulic pump and a control valve. (See diagram.) The base plate is available in three sizes (10 inches by 8 inches; 16 inches by 12 inches; and 20 inches by 16 inches) to provide a best fit with the machine on which it will be mounted. The fixture plate (same size as the base plate) bolts to the hydraulic base plate. It weighs 13 pounds and 23 pounds (16 by 12 and 20 by 16 sizes respectively), making it light enough to handle easily. It is also interchangeable with other fixture plates set up for different parts, making for fast changeovers. There are up to 80 points of clamping available every 2 inches on center, and the user selects the points of clamping best suited to his or her needs depending on such considerations as part size, configuration and tool clearance. Parts can be hydraulically clamped by the inside or outside dimension and in a vertical or horizontal orientation.
The electric-hydraulic pump is the power supply to the system. It provides up to 3,000 p.s.i. and is portable. With the standard package, multiple parts are loaded in and removed from the fixture mounted in the machine, which is a big improvement over loading/unloading one, two or several parts at a time. However, the system is also available with an optional accumulator, which enables the system to remain hydraulically charged with the hoses disconnected. With the accumulator, the system can be loaded with parts to be machined and pressurized away from the machine, permitting a pallet-loading arrangement for even greater machine uptime.
Instead of having to secure the parts individually in the fixture plate, the machine operator can secure up to 80 parts with a throw of the control valve lever. Paws uses several methods of workholding, such as ID collets, 5C collets, wedge clamps, swing clamps v-blocks and multiple vises.
"One of the benefits of the system is that it can be added to any make or model CNC machining center," explains John Montague, president of Montague Tool. "With our system, customers can increase the productivity of their existing machines by up to 300 percent. Where a firm is faced with the need to increase production capacity, our system represents a much more economical alternative to buying another machine."
Mr. Montague notes that many companies have been machining small parts one or two at a time for so long that they simply do not think about more productive ways of getting the job done. "Shops continue to make thousands of easy-to-hold parts in the same old inefficient way simply because they are not having an apparent problem," he continues. "A Paws system could greatly increase the productivity of these firms. The resulting effect on the bottom line can be quite dramatic."
"Many of our customers will find that their needs can be satisfied with one of our standard, off-the-shelf configurations," adds John Goodroe, director of sales and marketing for the firm. "However, we also have the capability to custom design fixtures for our customers to handle their workholding needs. The system not only increases a firm's competitive advantage, but it also reduces overhead, cycle time, operator fatigue, setup time and cost."