With CNC lathes saddled with daily multiple workholding changeovers today, quick-change chucks have carved out a growing, albeit modest, share of the workpiece holding market. At least one out of every ten chucks sold in North America today is quick change - some industry watchers predict that within five years this figure will mushroom to 40% of all OEM-installed chucks for CNC machines plus aftermarket.
Not a quick-fix for the high speeds and feeds of computerized machines, quick-change chucks permit setup and changeover times of 1 to 2 min while conventional chucks can demand 20, 30, 40 min or more.
"When manufacturers leapfrog from one job to another, from one part to a second part, you have to change the workholding, which means the chuck jaws," says Cincinnati Milacron's, Cincinnati, OH, George Corwin. "If you use a conventional chuck, you run the parts. When you're done you stop the machine, you go in and do an unfastening procedure where it bolts out. Using the key, take the top jaws off the master jaws. Then you have to go and get another set of top jaws, bolt those on to the new master jaws. Usually you have to do something to the jaw, bore it, or if it's a secondary operation to make it round so it fits the part and gives you the tolerances you need.
"A quick-change chuck allows you to remove the master jaw and the top jaw, very quickly. While your machine is running parts a master jaw and top jaw can be prepared off-line.
Then you put the new master jaw, and top jaw on the chuck and run, keeping the spindle running to make more parts."
In the days before fast CNC lathes, changeover from one job to another was a long process, recalls Sidney Roth, sales vice president for Autoblok Corp, Wheeling, IL. "A master machinist would reset the manual lathe, using manual controls, set his lead screw for a certain feedrate, and set a certain depth of cut.
"CNC lets you program a finished shape and put in a blank hunk of metal and come out with a perfectly finished part in a few minutes. Part production today has jumped by an exponential factor. Setup times are very short because, instead of punching in a whole string of numbers every time you want to change parts, you call up your program from the machine control memory and change it in 15 sec."
Because some high volume production houses using high-speed CNC lathes change workholding three or four times a day, changeovers that require 30 min equal 1 1/2 hr of lost production time per day, per machine. Daily job shop changeovers can be two or three times that number. Under these conditions, a quick-change chuck can:
* Deliver minimal downtime on a job changeover, and
* Establish tremendous accuracy running the same job at different times by changing the jaws in the chuck.
Autoblok Corp, the sister company of SMW of Germany, produces the KNCS quick-change chuck, based upon an SMW design first marketed approximately 20 years ago. The updated KNCS is a short wedge stroke operating off a standard cylinder. Changeover takes under 1 min while delivering excellent accuracy because the top jaws are married to the master jaws permitting one thousandth or better TIR.
The Autoblok RC quick-change chuck uses much larger master jaws for larger, heavier top tooling. It also permits the end user to retain its established inventory of soft jaws. The BH/RM uses palletized top jaws to run part families employing OD or ID gripping.
Cincinnati Milacron now outfits most of its big CNC lathes with quick-change chucks supplied by Pratt Burnerd America, Kalamazoo, MI. "The keys to quick-change chucking are exactly what you would expect - greater speed, saving time and money," says Mr Corwin. "Quick-change chucks are also good for shops running a mix of Japanese, European, and US machines. The OEM-fitted master jaws on any one of those chucks could have a different serration holding the top jaw. By changing the master jaw to fit any one of the unique serrations on the top jaws or soft jaws on a quick change, the need to change the chuck is eliminated."
Quick-change chucks are even valuable in highly specialized, sophisticated job shop operations. Eddie Thomas is the team engineer at Larry Hedrick Motorsports, Statesville, NC. Mr Thomas directs engine development and engine building for the No 41 Kodiak NASCAR racing car. Engine and special parts are turned on two Clausing Colchester 1550 lathes and an Okuma LNC-8 Cadet CNC lathe. To speed setup, Mr Thomas uses Pratt Burnerd three-jaw and six-jaw quick-change chucks with soft jaws. He can bore each set of jaws to the correct size on a lathe. "The chucks have no runout," says Mr Thomas. "They stay true even after disassembly to install collets. And this is very important in critical engine work."
During the past decade manufacturers, particularly in metalturning, experimented with dedicated machines - keeping equipment set up for certain jobs (also called job batching) to reduce downtime and save production costs.
"Then we had a downswing in the economy and manufacturers realized that in order to be profitable you had to be versatile," says Jim Trunk, Advanced Holding Design, Cuyahoga Falls, OH. "That versatility meant throwing out these really new ideas about machine dedication and hatching. They were good concepts, but we discovered you must run many different jobs to be profitable. We no longer had the luxury of dedicating a machine to a specific job for lengthy periods because we still had to reduce downtime."
During this transition period the AHD chuck with many multiple-grip and quick-change options began building its customer base. "We saw a lot of manufacturers and job shops change chucks a lot," says Mr Trunk. "They would add a machine mainly dedicated to running bar stock using a collet chuck, then run to a two-jaw or three-jaw chuck running shapes, or castings, with a two-jaw or three-jaw chuck - that requires a long changeover."
The AHD chuck features solid collets and an expanding-mandrel unit for ID chucking. The Multi-grip quick-change chucking option includes a two- or three-jaw assembly to hold rectangles, squares, castings, forgings, or special shapes. When switching jobs, Multi-grip eliminates reboring or remachining soft or top jaws or changing the chuck itself.
Two AHD customers - Biomet, and Zimmer, Warsaw, IN - make medical devices including artificial joints, hip replacements, and prostheses. Specialty small-lot machining changes part styles constantly demanding multiple changeovers without changing the entire chuck.
"These companies did not start out with quick-change devices, they established their product lines and workholding methods, then switched to quick-change chucks," explains Mr Trunk. "When medical device manufacturers establish instrument pricing there is a certain amount of work and cost that goes into every part. Once tooling and machining becomes more efficient, a higher profit margin is established."
Also committed to the elimination of any unnecessary reboring or remachining of chuck jaws is Northfield Precision Instrument Corp, Island Park, NY, designers and manufacturers of quick-change jaw blanks in aluminum and steel, and quick-change hardened/ground inserts. "Our niche is precision and repeatability with guaranteed accuracy ranging from 0.0001[inches] to 0.000 010[inches]," says Northfield workholding designer and chief engineer Paul DeFeo. "We make a quick-change system that eliminates the need to bore jaws or true your chuck. Our jaws don't snap on and off (manual screws require less than 2 min to insert or remove), but they do repeat to 0.000 050[inches] or better."
One example is a manufacturer making a family of parts in slightly different sizes. Stepped top jaws can't be used so Northfield makes a set of top jaws that will hold inserts of different sizes. "You can change the inserts in less than 1 min and they actually repeat better (less than 0.0001[inches] TIR) than changing top jaws," explains Mr DeFeo.
"Most decide whether quick-change chucks are worth it by conducting a time study," explains Paul Dillon, senior product applications specialist at Huron Machine Products Inc, Fort Lauderdale, FL, a manufacturer of quick-change chucks to OEMs including Mazak, Hitachi, and Mori Seiki. "A job or production shop will look at its machine or machine groups, determine setup costs, then the savings to be developed over any time period with a quick-change chuck."
Many Huron quick change customers are manufacturers that run several different parts and switched to quick change to lower inventory costs. "The old formula to manufacture parts economically dictated you make long-runs and stock leftovers in inventory." explains Mr Dillon. "With a quick-change chuck system, you lower the total number of parts manufactured each time to meet orders only, and still maintain the lower long-run cost saving. You lower your inventories because you can respond to your customers quicker."
Also suited for JIT is the Ultimate CNC Chuck from SMW Systems Inc, Santa Fe Springs, CA, offering normal quick-change features that can also be retrofitted to existing CNC lathes equipped with a short-stroke cylinder. Both the cylinder and draw bar are used in the new installation, reducing installation cost, and equally important, using the short stroke cylinder to produce full range jaw clamping stroke.
This chuck also features master jaws so the buyer can use his current inventory of top jaws, including both wide and narrow jaw designs. SMW also offers Ultimate CNC chucks in a "matched chuck" option. These chucks are selectively assembled so that the jaw mounting accuracy between chucks allows complete chuck-to-chuck jaw interchangeability. Remounted soft jaws also repeat within 0.0002[inches], eliminating the need to rebore them.
Worth a second look?
"I would love to get more people thinking about the quick-change chuck because it is the most overlooked item on the machine," laments B J Lillibridge, marketing director of Pratt Burnerd. The company manufactures and supplies conventional and quick-change chucks to metal-working machinery users and OEMs alike.
"Quick-change chucks have been in existence for some time, but when they first came out they were expensive, and I think it turned off a lot of people," says Mr Lillibridge. "Since then the cost has come down considerably, especially with designs that use standard top tooling.
Potential quick change customers who look at what the market has to offer today may be pleasantly surprised, believes Brian Lane of Buck Chuck, Logansport, IN, a manufacturer of quick-change chuck systems and top jaws. "The quick-change chuck manufacturers have had a lot of experience and have settled in on products they are comfortable making, and those products are standardized.
"The concepts have hardened; the customer now knows he can get replacements and parts when he needs them."
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|Author:||Davisson, John F.|
|Publication:||Tooling & Production|
|Date:||Dec 1, 1995|
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