Modular fixturing puts JIT into machine maker.
The company traces its origins to the 1880s when it built hot-forging machines to manufacture railroad spikes. Today it has fashioned an economic rebirth through its ability to adopt the techniques of just-in-time manufacturing here and at its subsidiary in Germany.
One key reason for its success: CIM cells that make parts to JIT requirements in a hurry, and in short runs, because of modular tooling. Today, for example, only a few men are needed to build modular fixtures, compared with six to eight men to build the same number of conventional hard fixtures.
As a concept, "modular" defines the header machine itself, its tooling, and the fixtures used in manufacturing the product line. The header's tools are assembled in a package outside the machine and dropped in place in a few minutes to change over to a new production part.
National's products, as well as its production methods, have evolved to meet the needs of its markets. Its first automatic Boltmaker with transfer system was built in 1937. Today, the Formax former is the flagship product, with manufacturing upgraded to cells, families of parts, and modular concepts.
Management has changed, too, especially in machine-tool procure, ment. Gregor Hoch, manager of machining, explains, "In the past, we had to come up with discounted cash-flow justification, a difficult discipline to say the least, Now, we use a more direct procedure. We currentiy base our decisions more on operational factors. The key consideration in this process is production throughput, which results from machine tools that are capable of integrating multiple operations while maintaining consistent part quality. Also, can we keep the new' machine loaded up with the kind of work that will make it pay off?.
"Building our product the way we did 20 years ago didn't let us automate, because we made one piece at a time. But we redesigned our machines so they could be manufactured with today's technology. We even integrated our international operations. FOr example, the computers here in Tiffin download to our computers in Germany, and vice versa, so we don't duplicate programming on both sides of the ocean."
Modular design allows National to make two-, three-, four-, and five-die machines with the same side plate. The center parts, such as the shaft, are changed, but 60% of the parts are of one size all the way through the line. Lots of 20, 30, or 50 pieces are run instead of ones, twos, and threes.
With the new system, 70% of the machined parts are held in modular fixtures, only 30% in hard tools. If there are engineering changes, modular fixturing accommodates' the changes with almost no leadtime. "Even for new parts, we can build new modular fixtures within a few hours. In 1989, we did 30% of our machining on CNC machine tools. Today, that's 60% to 70%, and only 15% of those part numbers involve dedicated fixtures or hard tooling," says Mr Hoch.
Small-lot savvy Originally, when National built a two-die, three-die, or four-die ma- chine, engineers had to order a casting for every configuration. Today, only one side-plate design must be machined, except for the center section, which changes for the number of dies required. Every die station is just a duplicate of the one before. The idea is to minimize the number of tools. Also, the design allows most machining on one side of the plate to avoid multiple setups.
Mr Hoch says he doesn't know of anyone else in the world doing what National's doing with small lot sizes of three or four pieces. "Our product line has more than 200,000 part numbers. Everything new is designed to be machined on our CNC equipment."
None of this is possible without cooperation between design engineers and manufacturing. At National Machinery, manufacturing engineers sit in the middle of the design department. When the designers have a part pretty well set, they can ask how it can be made--what are the limitations out on the plant floor. Then, if necessary, they change the design to make it more manufacturable.
"This is a new era of teamwork that started seven years ago. It has to be this way to pull it off. Any company that doesn't have manufacturing working with design won't survive," Mr Hoch states categorically. What about FMS? Mr Hoch says,
"Make a $5 million FMS and you'll probably do only 24 part numbers, but we have 60,000 item numbers programmed for our two- and three-machine cell groups. Cells are generally more practical than flexible' manufacturing systems. Even our big customers don't talk FMS to us. It's overkill. They're talking about cells." A major portion of the credit for National's ability to meet competition head on goes to a modern CAD/CAM system working in conjunction with machining cells and Halder modular fixturing systems supplied by Flexible Fixturing Systems Inc, East Granby, CT. Components range from T-slotted subplates, clamping angles, and cubes to mounting blocks, locating pins, screws, V-blocks, and up-thrust clamps. Thousands of components are identified by part numbers in well-organized catalogs and computer programs. Once purchased, they reside in drawers or bins in the fixture-building area.
A machinist builds the first modular workholding tool for a new part on the shop floor. He constructs the fixture on a pallet that travels on a railguided vehicle directly to the machining cell targeted for the job.
But the tool builder doesn't work alone. Working on the shop floor lets the machine-tool operator help decide how that part is going to run. He may say, "You can't hang a part out like that; there's no way we can hold tolerance." Of course machine-tool setup personnel and process planners have their say, too, and so does the programmer: "You're running the tool right through a damp!" "I can't handle a tool that long in that area." "We need a clamp here, and a block there to support this area." "But you can't put a clamp there, because I need that space for a through--hole." Etc,
The tool-construction team uses a Polaroid camera to photograph the completed fixture or perhaps make a pencil sketch of it. Then, someone lists the Halder components used. When the fixture is acceptable, the team goes to the CAD/CAM room and puts the results on the screen. Thus, the computer system is ready to facilitate any engineering changes or corrections after the first run.
The second time around
Once the fixture design has been proved and locked into computer memory, it's easy to set up a second run of the same part. By this time, the photographs and sketches are tossed because now the information is in the electronic file on disk drives. The original documentation is replaced by a computer-generated assembly print, available from a plotter or a CRT display on a shop floor computer. This will include a list of fixturing components by part number.
For review, engineers call up programs on computer screens to check fixturing, CNC programs, etc. They can see if there are any problems such as interference between the tool path and the fixture. Also, the CAM-system operator can assign cutting tools. The system creates a tooling list for every part, and this list can assist tool presetting.
The CAD/CAM system also contains guidelines for tool engineering. National uses metric tools and parts, as well as inch sizes, and the guidelines help avoid complexity. They include a standard list of drill, tap, and reamer sizes to keep engineers from picking odd-size drills or taps. The firm even uses standard-size milling cutters to ensure uniform radii for milling.
The entire list of Halder components was put on a special computer file. Fixture builders don't have to detail the blocks, clamps, etc. Components are already detailed in 2D and 3D views, so that a CAM programmer can build up a fixture on the scope by simply calling out components he wants from the detail file. The program overlays the drawings on a grid in any desired position.
When an order clears the cell, operators tear down the fixture to make the components available for the next setup. They wash and clean each element and inspect it to make sure it has not been damaged. The firm runs dozens of part numbers through the cells every day, so it's necessary to use the components over again (if only 15 or 20 setups were involved, it would be practical to keep the modular fixtures intact and store them like ordinary hard tooling).
The sound of music
National built its own two.pallet system/or quick exchange of fixtures. Getting things on track was a big factor. Gregor Hoch tells T&P, "Everybody else we looked at had a gear-driven vehicle running on a raised track. But we wanted our track to be at floor level so it would be user-friendly. We wanted our operators to move freely from machine to machine without the hazard of tripping over the track. We wanted fewer people running more machines, and a raised track would cause too much interference.
"We respect the vehicle, and it respects us. We won't run in front of it deliberately, but, if we do, its sensors will stop it before it hurts us.
"Suddenly, we hear loud music. The vehicle has started to move, and. when it does, an on-board portable tape player turns on to warn passersby to look out for the vehicle."
Mr Hoch says, "Every week, a different operator brings in his favorite tape to play on the vehicle's boom box. To make it even more user friendly, we put an elevator on the unit to raise the table to a convenient work height and to the proper level to slide the pallet onto the machine tool."
Infrared eyes and a safety bumper on the vehicle detect the presence of anyone in danger of collision with the vehicle. Control communication is via infrared transmission, and the battery-operated vehicle has an onboard Allen-Bradley PLC-5 processor to take it through its routine. A special terminal directs the vehicles to specific machine tools, and each vehicle carries everything needed to complete the machining: fixture, work sheet, workpiece, and special tools and instructions.
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|Title Annotation:||just-in-time manufacturing; National Machinery|
|Author:||Miller, Paul C.|
|Publication:||Tooling & Production|
|Date:||May 1, 1992|
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