Workholding's Clever New Concepts: Part II
Don't overlook this path to productivity
By Robert Aronson
"The main trend we have seen is the need for tighter specs or tolerances for location accuracy and ease of loading," explains Mike Casselman, workholding product manager, Kosmek USA (Bridgeview, IL). "The way of locating parts on a fixture in the past was to use dowel pins. The problem with these is workability and accuracy. If the tolerance between the workpiece and pin is too tight, it is very difficult to load the part. If the tolerance is too loose, then the part is not located accurately. This has become more important with the growing popularity of robots in manufacturing."
The Kosmek power datum cylinder replaces dowel pins. This datum cylinder allows enough clearance to permit the operator to load the part easily, without binding on the dowel pins, then expands a tapered collet to locate within 3 µin. (0.0762 µm). Many manufacturers have adopted this system as it gives the best of both worlds, ease of loading and workability, and also a high-accuracy location. "We have also just developed a manual datum pin, which is the same concept except the taper collet is expanded by manual bolt tightening. This cylinder is available in hydraulic or pneumatic models for the food and medical industries," says Casselman.
"We have observed a trend toward better sales of the higher quality and more complex clamps," explains Mark Gordon, president of Fixtureworks (Fraser, MI). "Customers are often willing to spend more to get a product that is more versatile and more specific for their needs.
"Another issue that is not as positive, is that we have encountered a number of people who are in positions of responsibility, but lack practical knowledge. These are often young graduates who understand the design needs of a specific product, but are unaware of the total picture. For example, a designer may build an adequate workholding fixture, but it may not be rigid enough if the workpiece has excess material to remove. This would result in higher loads being exerted on the workpiece, thereby causing workpiece movement and erratic tolerances of the machine surfaces."
At Fixtureworks, one of the best selling products is the One-Touch Swing Clamp, which is used for workpiece holding in medium-to-high production applications. The One-Touch Swing Clamps are simple to apply in many workholding applications and allow for very quick clamping and unclamping.
The 9000 fixturing system from Hirschmann Engineering USA Inc. (Elgin, IL) has a modular zero-point fixturing design for all machine tools. Units can have single or multiple zero-point clampers and workpieces, or pallet-mounted fixtures can be changed quickly. This new system is said to reduce starting times in the 20–25-min range to 2 min.
Simultaneous job loading or workpiece loading is possible during machining. There is said to be no drop in accuracy when transferring jobs from one machine to another.
When the part OD is hard to grip, or cannot be gripped, internal gripping may be your answer, if there is an internal diameter in the 1/8–4" (3.18–102-mm) range. Expanding collets and between-center arbors (mandrels), such as those made by Hardinge Workholding (Elmira, NY), grip the internal diameter of a part for turning, milling, grinding, assembly, inspection, and automation applications.
During chucking operations, parts can be located against the face of the arbor or against a machineable workstop. This provides exact part-length control, as well as improved part consistency. The expanding collet draws the part firmly against the stop, producing an extremely stable part location. Longer parts can be more easily machined due to this added stability. The results are heavier cuts, better surface finishes, and closer tolerances when using a workstop. However, workstops may not be necessary if you are only machining the part OD. Because the part is pulled back against the workstop, short grip lengths can be firmly held.
A built-in safety stop will prevent the collet from overexpanding. Machines with ANSI type-A spindles and machines with collet-ready spindles or collet adapters can use the Hardinge Sure-Grip Expanding Collet System.
No spindle adapters are needed. The one-piece spindle arbor construction and the closing mechanism hold the workpiece extremely rigid for superior surface finishes and concentricity. Hardinge guarantees the Total Indicator Reading (TIR) of the arbor will be within 0.0002" (0.005 mm). With the expanding collet mounted on the arbor, the TIR of the collet and arbor will not exceed 0.0005" (0.013 mm), without the need for adjusting screws.
"Automation is our industry's number one trend," says Tom Stimac, De-Sta-Co product manager, industrial products group (Madison Heights, MI). "Manufacturers that previously used manual clamps for fixturing in welding and assembly environments are beginning to seek out pneumatic clamping technology to speed up processes and improve throughput. Sales for pneumatic clamps are growing at four times the rate of manual clamping systems."
De-Sta-Co is also improving its pneumatic clamping lineup by adding sensing technology. Pneumatic clamps already give machinists the ability to open and close multiple clamping stations from a central point with the push of a button, making the nonproduction time for clamping almost negligible. The company has added magnetic sensing rings to clamp cylinders that communicate with a PLC control board, to determine whether a clamp is open or closed. This further accelerates the process, allowing machinists precise control and an increase in production for manufacturers.
BuiIt-in manual clamping technology is growing in popularity as well. "The next trend in workholding is the automation of processes with manual toggle clamps," explains Stimac. "Manufacturers like GM have long used screws, nuts, and bolts to hold products in place, but when moving and loading/unloading fixtures, there is apt to be movement or vibration. De-Sta-Co has developed patented manualclamping technology that prevents products from moving until a lever is pulled. This added layer of security protects not only the products but the workers as well."
Because clamps are frequently used in harsh application environments, they are subject to contamination from dirt and grinding dust. The accumulation of contaminates reduces the clamp's reliability while increasing maintenance costs and downtime. "To reduce this problem, De-Sta-Co is developing enclosed technology in both manual and pneumatic clamping that will keep all clamps free from impurities. The most exciting product on the horizon is an automated clamp that is completely enclosed, which will greatly increase efficiency, reliability, and production time," he concludes.
"Last year was a record for us in which the company grew over 23%, and this year looks even more promising," says Dave Bishop, president Mitee-Bite Products (Center Ossipee, NH). Their products not only hold small-size aluminum parts, but have clamping systems that produce over 20,000 lb (88,960 N) force.
"Client demands focus on speed of delivery," says Butler. "They need it now, and up and running yesterday." Another trend he reports is that customers are starting to break down their process step-by-step, and are looking for better, more efficient ways to compete in a market that's becoming more advanced every minute.
"To continue its impressive growth, our company needs to expand our market, improve and develop new offerings, provide a better process, and ensure on-time deliveries," concludes Butler. For example, to achieve that goal the company recently added a pallet changer that is also a vacuum chuck that operates on standard shop air. No vacuum pumps are required.
"Any reduction in process or downtime is money found," says David E. Jones, precision workholding manager, Emuge Corp. (West Boylston, MA). "How many parts you can produce in an allotted time is not always the specific answer, however. Everyone knows the basic principle that if you produce 40 components in an hour, but carry a high scrap rate, you need to look at changing the process. You may be better off with a lower components/hour ratio that produces less scrap." This is a simple idea that can pay great dividends, but where can improvements be made on an already lean process is the question. Accuracy, repeatability, rigidity, reliability, and ease of use must all be considered.
"Some of the changes we are beginning to see across the industries we are involved in is the drive towards new materials and new processes for existing components. Companies are asking if the components they have been making for years can be manufactured in a more cost-saving manner. Should they change to a different material or a different process, and what can be gained by doing it a different way?" says Jones.
To meet these new needs, the company can draw from several different clamping systems to supply a device for a specific workpiece or workpiece family. These systems range from System SP clamping sleeves, System SG expanding bushings, System SM diaphragms, System SZ collets, and System SH hydraulics.
When designing a workholding system, considerations include workpiece geometry and material, available clamping surfaces, and machine connection and actuation for the device. The process description must include forces involved in the process, and data all the way down to tooling paths and loading clearances. "Basically, this means that until we are in discussions with a customer, we may not know what our next product will look like, other than that it will use one of our precision clamping systems," he says.
Over the years BIG Kaiser's Unilock (Elk Grove Village, IL) product has helped customers decrease setup time and increase productivity, says the company's Gerard Vacio, product manager, workholding. "Manufacturers have used Unilock products to assist in achieving two primary objectives; decrease the time it takes to convert a manufacturing cell to perform a different process, and reduce the total course of action necessary to complete the total manufacturing plan."
When BIG Kaiser first started offering Unilock, they focused primarily on selling the concept of reducing setup time. Today, BIG Kaiser takes it a step further and demonstrates how they might be able to reduce the number of times someone unclamps a workpiece from a known datum and transfers it to a new datum for another process. For many customers, this has led to improved workpiece quality and streamlined manufacturing because of the "clamp once and cut many" concept.
"BIG Kaiser asked manufacturers to consider modular quick-change clamping systems as a way to increase machine tool utilization, and they responded,” says Vacio. "Now we are asking them to consider quick-change clamping systems as a way to transport a clamped part from one process to another. Since this also eliminates dedicated tooling that will only hold the part for one operation, they are again responding."
The Unilock system from BIG Kaiser uses a ground retention knob to pull fixtures or workpieces into a predefined position. Clamping force is generated by heavy-duty die springs that surpass a pull force of 11,000 lb (48,928 N) and have a repeatable accuracy better than 0.0002" (0.005-mm) TIR.
"Multiaxis machining is a big trend, and it requires space-saving fixturing, so compactness is becoming more and more important in workholding today," explains Fred Gerullis, manager, Swiftsure Engineering, Carr Lane Roemheld Mfg. Co. (Ellisville, MO).
To meet this need, the company now provides very small swing clamps and hinge clamps, which are said to set new standards in miniaturization. Despite their compact dimensions, the new minis meet all the same technical requirements as their bigger brothers. The threaded-body swing clamp has a flange diam of approximately 26 mm, a piston-rod diam of 6 mm, and a clamping stroke of 8 mm. "Joining the clamps are the mini-vises," explains Gerullis. This MC family of vises has mechanical and hydraulic closing features. The available jaw widths are 40, 60, 100, and 125 mm, giving a wide variety of clamping sizes from which to choose for each machining need. These vises are designed especially for multiface machining with a single clamping operation. Their design allows tool access to five out of six workpiece sides. The parts are small, but have a large holding capacity, with clamping forces as high as 7800 lb (34,700 N) on some models, and the vises have excellent rigidity and durability. "We believe these new super-compact workholders provide superior solutions for multiaxis machining," Gerullis concludes.
To ensure accurate fixturing of a part, Hainbuch (Milwaukee) has introduced a zero-positioning pallet system with repeatability of less than 0.003 mm. The company's patented Centrex solution reduces downtime between setups by an average of 25 min per setup. The baseplate is made from cast mineral that is scratch, bulge, and temperature-resistant. Lightweight for ease of handling, it offers vibration dampening and eliminates the oxidation that can occur with steel plates.
The complete package contains bushings and positioning cones mounted in the carrier plate. The bushings and positioning cones are mounted so the pallets can be fitted to each other with exact repeatability.
Here is how it works:
- The tapered bushing is pressed into the carrier pallet, and the tapered mandrel is pressed into the baseplate.
- If the carrier pallet is positioned onto the baseplate, then initially the pallets have no face contact. Under these circumstances, the internal and external cones make only indirect point contact through the bearings. If a force is now applied to the carrier pallet, the surface of the tapers deforms in the elastic range.
- The clearance for the bearings thereby becomes greater, and the tapered bushing can move in the direction of the baseplate until face contact occurs.
- As the surfaces of the tapers have the same hardness everywhere, the mandrel always has the tendency to move towards the center of the tapered bushing.
Through the use of two Centrex units, the carrier pallet is exactly aligned between two defined points. The Centrex interface system eliminates the alignment process on Hainbuch mandrels, chucks, and other devices as well.
But finding new designs isn't the only issue. "Our main problem right now is keeping up with orders, both from the OEM and aftermarket," says Bill Graham, Kitagawa-North Tech Inc. (Schaumburg, IL). "We are experiencing significant sales in both the OEM and aftermarket. Often the demand is so great that early delivery outweighs everything else." This growing market has caused the company to utilize more lean procedures in both their delivery and manufacturing operations.
Another trend for Kitagawa is a growing repair and rebuild market. This began during the last recession when companies that had eliminated their own repair facilities needed work done. However, the demand for these services has continued and become a major growth market for both standard and custom equipment.
The company has also increased the testing of all custom-engineered solutions because of the need to have the workholding running productively out of the box. Customers are also demanding the ability to cut deeper and faster under heavier load. "The overall goal is to squeeze every second you can out of the production time," explains Graham. "Customers know that if you can't get throughput, it's leaving the country." This need has seen an increased use of near-net-shape parts as well as forgings and castings for products that only require finish machining.
"As far as product changes, our new BB218, 18" [457-mm] chuck now has a 6.5" [165 mm] through hole, so it's possible to work with larger parts with a small machine envelope," Graham concludes.
"We are seeing more automation in the workholding/fixturing area, and we are responding with more hydraulic products," says Greg Arnold, Jergens Inc. (Cleveland). "We also see more small parts with smaller runs, which fits right into our new offering of production machineable-jaw vises."
Recently the company launched a hydraulic version of their 4" (102 mm) production (machineable-jaw) vise, and will launch a 6" (152-mm) version soon. Jergens is also in the process of introducing another Hydraulic Swing Cylinder Clamp.
The hydraulic version features a compact design that incorporates an internal hydraulic slide assembly. The company's hydraulic swing cylinder is similar to some of the competitors, but it has a new and improved internal piston design that the company believes will extend piston life and enable smoother operation.
If you want to know what customers want, ask them. That's just what Chick Workholding Solutions Inc., (Warrendale, PA) is doing to develop the design of a vise specifically for CNC machines. "Chick will only release the final version of the CNC vise when it is satisfied that the market truly has the optimal solution for its needs," says the company's Christopher Whitlach. Meanwhile, Chick continues to solicit advice via their Web site and trade shows. So far the prototype has undergone five major reworks.
The CNC vise reportedly creates a new category of workholding, as a single-station vise designed specifically with attributes that are intended to make it the most efficient single-station vise available for a CNC machine.
To reduce the setup times typically encountered with a traditional vise, the Chick CNC vise features a QwikSlide, which rapidly positions the vise for various size parts. Additionally, a QwikChange jaw system makes it possible to switch from hard jaws to selflocating machinable jaws in seconds.
The manual vise has a longer base than a traditional vise, because modern CNC machines feature wider tables than old manual mills. This gives the CNC Vise more travel than traditional vises, allowing for a wider variety of part sizes to be held. The unit is completely sealed.
The vise mounts using toe clamps, and has an internal hex that eliminates constriction points, especially on CNC pallet changers.
Lubrication is sometimes forgotten. "Total sealing is offered in our newest line of chucks," explains Sidney Roth, president, SMW Autoblok (Wheeling, IL). One of the main advantages of this feature is that it minimizes lubrication frequency. "We have found that lack of lubrication is one of the main reasons for early chuck failure, and our sealed design will minimize this problem."
SMW's latest design is a diaphragm DFR-ABS chuck which is designed for quick change and rapid setup. Jaws can be changed in two minutes or less. This design is accurate to 4 µin. (0.1016 µm) and designed for hard-turning gears. It has been particularly successful with the ring gears needed for the new sevenspeed automatic transmissions.
This article was first published in the May 2007 edition of Manufacturing Engineering magazine.