Maximize Productivity with the Right Workholding Device

2010-01-16 09:22:00

Today’s vises range in configuration from relatively simple single-station models to very elaborate multiple-station designs. Most vises consist of a mounting base or body that is secured to the machine table, a stationary jaw against which part material to be machined is located, a movable jaw and screw mechanism. When tightened, the movable jaw is pushed or drawn forward by the screw mechanism thus clamping the workpiece against the stationary jaw.

Vises are simple, relatively fast and easy to operate. Their advancements were greatly accelerated in the 1960s with the advent of CNC machines when the demand for higher precision parts and greater productivity gave birth to a patented precision machine vise. Early vise designs, when under pressure, deflected so that part alignment was a constant problem. The precision machine vise, with its friction reducing, needle bearing, thrust collar, aligned and held parts more accurately and securely than any previous screw type vise.

Double-station, multiple-station, self-centering, hydraulic, vertical and many other versions were developed out of the basic concept of the original single-station, precision machine vise.

Design and Planning
To address the workholding needs of a particular machining operation, one needs to consider part size, material, machine speed, feedrate and the quantity of parts to be produced. Process planning requires dividing the machining process into steps best suited to the available machines. Smaller machine shops are more likely to plan their workholding around knee mills or VMCs.

Single-station, precision vises made of ductile iron are ideal for precision part clamping on basic machine tools, such as milling machines and machining centers. A machined mold component is locked into position in this photo. Figure courtesy of Kurt Manufacturing.
 

With knee mills, the full range of vise accessories can help with setup reduction, such as quick change jaws, which, in some cases can reduce changing jaw plates to just 5 percent of the previously required time. For more complex machines—HMCs and VMCs—part loading time and setup are an integral element of downtime and need significant attention to maintain high efficiency. Workholding again becomes a central element in maximizing machine uptime.

Following are considerations for maximizing productivity using vises on frequently encountered machining situations:

• Vise selections and their characteristics (number of stations, parts per station, means of actuation, etc.)
• Jaw plate considerations and its effect on part contact and repeatability
• Locating systems for setup reduction and position accuracy
• Workstop systems
• Helpful accessories to make the clamping job easier

Selection
The key factor in choosing a vise for a knee mill is the vise opening, and whether or not a swivel base is needed. Workholding selection for HMCs and VMCs should be based on desired density, clamping station opening size, clamping pressure needed and shape of the part.

High density requires double station vises. These vises have two clamping stations, pushing the workpieces toward the stationary vise jaw block between them. They can be equipped with special carvable jaw plates or carvable jaw blocks.

The next highest workholding density can be achieved with cluster vises where multiple vises are machined into a single body. The advantage of cluster vises is that they remain in exactly the same relationship to each other compared to trying to align multiple vises in a workholding setup.

Highest workholding density is achieved when the movable vise component is a module that can be moved in small increments on a serrated base. The modularity of these systems allows the user to configure the equivalent of custom fixturing with standard off-the shelf components.

Additional workholding options include:

• Self-centering vises are very similar to double-station vises except that they are designed to precisely locate components to their respective centers. They are accurate to within 0.0002 inch repeatability.
• Zero-point workholding systems are designed to integrate with new or existing workholding devices. They provide multiple workholding stations with ultra accurate setup on either HMCs or VMCs, thereby completely eliminating operator setup errors.
• Five-axis clamping systems are designed to take advantage of the five-axis machining capabilities of the latest machining centers.
• Hydraulic actuated vises and high density towers are available for production line clamping applications. Jaw selection is important when choosing a workholding setup. Jaw plates affect part contact and setup repeatability. Many jaw options are available for specific applications.

There are many vise and workholding accessories that make the clamping job easier and more productive—such as speed handles, special vise handles, and a complete array of different workstops, specialty jaw plates and parallel sets.

Summary
As long as machines are needed to machine parts, vises and other workholder types that improve versatility, accuracy and speed of operation will be needed to position and hold materials while the machining operation takes place.
From:http://www.moldmakingtechnology.com

From the Internet, If you believe an article violates your rights or the rights of others, please contact us.