|Automatic zeropositioning pallet system|
Reducing setup time for workholding is a critical key to increased productivity. This becomes increasingly important as lead times become shorter due to constricted product life cycles, diminished time-to-market considerations and increasing variety and complexity in components.
As a result, shops are looking continuously for workholding innovations that cut setup and changeover times while being rigid and precise, and deliver increased flexibility, efficiency and accuracy.
The best selection of workholding and fixturing devices also can help shops that are trying to cut costs by reducing inventories because they are able to produce parts in volumes that customers want, exactly at the time their customers want them.
As parts become more complex, so do the challenges in choosing the best workholding and fixturing.
Manufacturing complex parts successfully and competitively requires fixturing devices that are flexible, modular and variable.
Fixture flexibility means the workholding devices must be suitable for various cutting conditions. They also must be adaptable to a wide assortment of materials, weights, sizes and configurations, whether they are used on a 3-, 4- or 5-axis machining center.
Fixture modularity means the design principle of the fixture allows the clamping devices to move and be repositioned on the fixture faces in different setups, often within the same job run.
Variability means the fixture can adapt to the particular characteristics of a given machining center for mounting, access to the cutting theater and shuttling, with little or no modification.
To meet the demand for reducing setup and changeover time, while increasing precision and adaptability, several manufacturers recently introduced creative approaches to workholding and fixturing challenges.
Automatic zero-positioning pallet system
The need for increased precision and rapid setup times has resulted in the development of the Centrex Centering System – an automatic zero-positioning pallet system —by Hainbuch America Corp. (www.hainbuchamerica.com).
This compact, simple system uses precision steel ball bearings in a rubber ring in conical positioning elements integrated into the pallet system to produce repeatability of less than 0.003 mm, and level contact. The tapered positioning elements prevent tilting.
The four bushings and positioning cones are ready mounted, allowing the pallets to be fitted to each other with exact repeatability. As a result, changeover times are minimized while the complicated, expensive and close tolerances required for centering tapers are eliminated.
Here is how the system works:
The taper bushing is pressed into the carrier pallet, and the taper mandrel is pressed into the base plate.
If the carrier pallet is positioned onto the base plate, the pallets initially will have no face contact. Under these circumstances the internal and external cones make only indirect point contact through the bearings. If a force is applied to the carrier pallet, the superficial surface of the tapers deforms in its elastic range.
The clearance for the bearings becomes greater, and the taper bushing moves in the direction of the base plate until face contact occurs.
Because the superficial surfaces of the tapers have the same hardness universally, the mandrel always has the tendency to move toward the center of the taper bushing.
A mini, zero-position system in Hainbuch standard pallets allows the changeover of the entire chuck to be performed while retaining process reliability and without alignment.
Users save time, money and space with part-specific equipment. In addition, due to its diversity of applications, this system minimizes setup times and interruptions in production, and individual clamping devices do not need to be adjusted after each changeover. With only two small holes, the Centrex system can be used in any plate connection.
Schunk Inc. (www.schunk.com) said its new Kontec KSM stationary clamping vise with multiple-part clamping increases efficiency in production. The vise’s multiple-part clamping feature is designed to accommodate several workpieces of the same size or several workpieces of different sizes at the same time.
This new system allows operators to reduce setup costs because it clamps parts simply.
It has vertical serrations on the inner side of its clamping rail to allow jaw modules to be positioned quickly and accurately with one hand.
To fix the jaws, one screw has to be turned 180 degrees.
The company said the design is resistant to contamination, so it ensures trouble-free clamping at any time. In addition, Schunk said the clamping method reduces vibrations and increases workpiece stability during the machining process.
Vise jaws, based on the wedge-hook principle, allow safe clamping of workpieces with ideal flow of forces to allow high precision at high chip removal rates.
‘Chaotic’ workholding reduces costs
Through the use of flexible, multipart Triag clamping for complex parts, Profiform AG, of Adligenswil, Switzerland, has completed a 21- hour machining cycle using only one manned shift.
More significant, perhaps, the shop priced out the manufacture of three different order quantities – 3, 300 and 3,000 parts – to China. Being machined in this new way, only the three-part order could be produced at a lower cost, without the shipping cost and time considered. Triag workholding devices are built in the U.S. by Advanced Machine & Engineering (www.ame.com).
The shop, opened in 1987, began with vertical machining centers and simple clamping vises.
In 1992, it invested in 2- and 6-pallet horizontal centers that were equipped with multiple clamping systems. In 2002, it installed its first flexible manufacturing system that allowed it to accomplish its first unmanned production. That made an immediate improvement in the shop’s overall productivity, and helped the owners of the 13-man shop to contain costs.
Currently, the heart of the shop’s flexible manufacturing system is a Mazak PFH 5800, 4-axis HMC, with XYZ movement of 730 mm by 730 mm by 740 mm (28.74 in. by 28.74 in. by 29.13 in.).
A 16-pallet rack, equipped with Tripoxy tombstones up to 960-mm high (37.80 in.), and a 378-position toolchanger are onboard this workhorse.
In what the shop calls its “chaotic” clamp setup, complete subassemblies are partially removed, ready for final assembly. Single large part fixturing and/or the clamping of several small parts simultaneously are done.
Best lube practices pay off
The Society of Tribologists and Lubrication Engineers (www.stle.org) reported research in Great Britain showed that predicted improvements from precise lubrication practices are:
|Cost element||Percent savings|
|Maintenance and repair costs||20|
|Labor for repairs||0.13|
|Utilization and efficiency||0.1|
|New machine purchases||5|
|Energy reduction (friction control)||7.5|
This chaotic clamping setup means the clamping location is changed constantly, and that is done by aTriag Powerclamp system. On a more organized setup, the same part is clamped in all stations on a tombstone.
Profiform machines forged and cast parts, structurals, saw cuts, profiles and parts up to 400 mm by 400 mm by 50 mm (15.75 in. by 15.75 in. by 1.97 in.) in materials that range from aluminum, stainless and tool steels to plastics and composites.
Profiform’s requirements for its clamping system included process safety through rough milling, and the clamping of pressure-sensitive parts; maximum flexibility of the clamping techniques used; maximum clamp density for optimum space use; and short setup times and ease of use.
Triag responded with its modular Powerclamp design. The design includes a base rail that is used as a support unit for the clamping modules, and the company’s Microclamp fixture system for smaller parts. The Microclamp system runs on the same base rail design.
In a typical 21-hour, running production day, only one shift of operators is required, during which all the worker know-how is brought to the task of efficiently scheduling and fixing the workpieces into place on the various stations, then programming the flexible manufacturing system to execute the runs.
As a result, the shop is translating 14 hours of unattended running into a competitive advantage.
Modular CM and vision fixturing
R&R Modular Fixtures from R&R Sales and Engineering (www.cmmfixture.com) have multithreaded holes to locate and elevate parts off the surface for full inspection with touch probe or vision systems.
The fixtures are deisgned for aerospace, appliance, automotive, electronic, industrial and medical applications.
The cast aluminum fixtures range in size from 6 in. by 6 in. to 60 in. by 120 in., making them the largest fixturing base plates available. Base plates are built with NiTuff hard coat anodize to resist scratching and reduce wear.
An alpha-numeric grid pattern on base plates and labeled components are included for easy documentation and to increase accuracy.