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Least-Touch Moldmaking

 

A systems approach helps toolmaker to cut labor, costs, and leadtime.

 

By James R. Koelsch
Contributing Editor 

 

Anyone who has been following the mold-and-die business knows of the industry's woes over the last decade. As one-of-a-kind products, molds are labor-intensive, a fact that has given shops in low-wage countries like China a huge competitive advantage. The result in a state like Michigan, known for having a large mold-and-die industry, is that roughly a third of these small manufacturers have gone out of business, and about 20,000 people have lost their jobs.

Despite the rough seas, survivors such as Die-Tech and Engineering Inc. (Wyoming, MI) have done more than just ride the storm. A sizeable group has actually thrived. The common thread in their success is a reliance on capital, rather than wages, to be competitive. "This industry has become increasingly more a science than an art," observes Bill Berry, president and cofounder of Die-Tech, a 25,000 ft2 (2323 m2) builder of aluminum, zinc, die cast, and plastic molds for Midwestern automotive, furniture, and appliance manufacturers.

 

Through creative deployments of technology, Die-Tech and its fellow survivors have offset much of the wage advantage by reducing their direct labor and lead times. "We've doubled our size, yet have the same number of polishers," reports Berry. His shop, which employs just over 40 persons, moreover, has organized its technology in a way that can cut manufacturing time by as much as half when schedules permit.

Although many of his colleagues swear by the highspeed machining of hardened steel to reduce setup and polishing, Berry doesn't. "It's a good technology, but it's not without its challenges," he says. "It's analogous to a high-performance racecar. It's very expensive and much more difficult to drive, because you're always trying to come closer to the ragged edge without ever going over it. The cutters are pushing the envelope of what's possible, so you need high-performance tooling with sophisticated coding technologies that have to work just right."

Berry acknowledges that high-speed machining is well worth the effort and expense for large molds that engage the tools in the cut for long periods of time. The moderate-size molds and dies that his company produces, however, use insert tools and have a lot of details. "There is no high-speed machine in the world that can cut them completely," he says. "They always have some detail that will need cutting on an EDM. If I'm going to have to EDM it anyway, why would I high-speed machine and then EDM it?"

Instead, Berry relies on a systems approach built upon production principles that he learned while working for General Motors Corp. years ago. Since establishing his own business back in 1984, he has been deploying advanced technology systematically to enhance the productivity of his engineers and skilled tradesmen. A combination of computerized processes, universal fixtures, robotics, and laser scanning let his staff process pieces of each job in parallel, act upon process feedback, and automate portions of the process.

Data are critical to Berry's approach. By knowing exactly where each point on a surface is or will be in space, he and his staff can generate efficiencies commonly reserved for high-volume manufacturing. This knowledge lets them distribute the process among many people, move physical product throughout the facility, and inspect intermediary steps in the process.

 

Like most toolmakers, Die-Tech receives digital models of the parts that its products will have to make from its customers. Unlike most, though, the design department assigns each job to a team of at least three engineers and experienced toolmakers. The team members then work together using the same solids model in I-DEAS CAD software, originally developed by SDRC, but now available from its new owner Siemens Energy & Automation Inc. (Norcross, GA). CNC programming is done simultaneously on WorkNC (CAM) software from Sescoi USA Inc. (Southfield, MI).

As a design engineer develops a solid model of the tool, a manufacturing engineer does some of the advanced features, designs the electrodes for the EDM work, and begins programming the machines that will cut the graphite electrodes and the mold's various steel components. Meanwhile, a detailer generates the documentation necessary for building the tool and satisfying the customer's demands for documentation. Although the teams typically consist of three people, they can contain more if the size or timetable of a project requires it.

Working from computers linked to an internal network with four terabytes of storage space, the team has access to more than the model of the mold that they are designing. They also have access to a library of the best practices that they and their colleagues have developed and captured over time in templates and setup sheets. Once mold components or electrodes are designed, the CAD system generates drawings for the setup sheets. "All of the setup sheets for machining are exported semiautomatically to Excel, and published for the people working on the shop floor," says Berry.

Dividing the design work among at least three people, and reusing proven practices, are important parts of the overall business strategy at Die-Tech. In as little as a few days after receiving a job, the team can be ready to release the roughing programs for the base and inserts to the shop. The design team then continues its work, completing the details of the design, developing the electrodes used to finish each cavity, and writing the finishing programs while the components are being roughed and heat-treated.

"Just like computers use parallel processing, we're using a parallel-design strategy," notes Berry. "The major, time-consuming roughing operations can be defined and started before the design is completely finished."

Because the close link between design and manufacturing is strategic to Die-Tech's business, Berry has elected to design his products completely in-house, and not to look offshore for cheaper talent. The only exception is the occasional simulation that customers might want in order to study the filling and cooling of the mold or die. For such customers, the design engineer prepares a model of the mold for simulation by the customer or its service bureau, and accommodates any changes suggested by the results.

The manufacturing engineer on the team does not simulate the toolpaths that he develops. "It doesn't add value," explains Berry. "You would use simulation only if you weren't sure whether the program would work." Using best practices on conservative processes generates the confidence that the shop needs in the cutter paths that it receives from the programmer. And because lot sizes are typically one or two, the time saved by conducting time studies and optimizing toolpaths is negligible.

Parallel processing is not a concept used just by design. Manufacturing uses it too. Just as the solid CAD model allows the design department to split the design work among several people, a workholding system from Erowa Technology Inc. (Arlington Heights, IL) allows the shop to distribute manufacturing among a variety of operations. With it, the shop can move the work among the operations without ever letting go of it and losing the reference points.

The system has two pieces, a precision-machined pallet and a standard receiver mounted permanently on each machine. After fixing a workpiece to a pallet, a worker either puts the pallet directly into the receiver or stages it for a robot to load. For machines tended by a robot, the robot's controller then takes over, telling the robot which pallet to load into machining centers from Sharnoa Technologies Inc. (Westland, MI), and EDM units from Charmilles Technologies Corp. (Lincolnshire, IL). Each pallet slides into the interface and locks into position with a position accuracy that's within microns.

"By palletizing our work, we can move it from machine to machine with very little setup time and a high degree of flexibility," says Berry. "We can rough it on a machine built for that task. We can semifinish on another machine that is a little faster, lighter-duty machine, but precise. If we want to do some finishing operations, we can put it on a high-speed machine designed to take lighter cuts." Prestaging the work reduces the time that the operators need to interact with their jobs to the point that three operators can run nine CNC machines on each shift.

Although the pallets help to automate the production and inspection of certain steel molds, they really shine in production of graphite electrodes. As the graphite blanks come off the saw, a worker clamps them onto the pallets and puts them in queue for machining. Afterward, the machined electrodes go to a CMM from Brown & Sharpe Inc. (North Kingstown, RI) for laser inspection. When they return to the smart, robotic magazine for use in EDM, the robot changes the electrodes automatically, putting the correct electrodes in the cavities being finished.

This parallel-processing strategy is much faster than having a high-performance machine cut a hardened block completely from scratch. "I would have to wait a day or two longer for the design to be completed before I could begin cutting," says Berry. "Meanwhile, I would have this big dragster waiting at the starting line with its engine revved up, waiting for the engineering to be done." The process he is using can rough and heat-treat the job before the high-performance machine even gets a chance to start.

In-process inspection is another benefit of parallel processing. When the electrodes arrive at the CMM, the operator inserts the pallets into the Erowa interface on it. The machine then makes millions of measurements at 19,200 points/sec with a laser scanner from Metris North America Inc. (Rochester Hills, MI). Using Metris' Focus software, an inspector compares this point cloud of the electrode to the CAD drawing of the mold cavity.

Just as the pallet interface solved one set of problems preventing CMMs from being practical as in-process feedback devices, the scanner solved another set. It allows the machine to move in broad sweeps, rather than going from point to point. Consequently, the programs are both easier to write and faster to execute than their touch-probe counterparts.

"It used to cost a few thousand dollars to take 60 or so points," notes Berry. "Now, a few dollars worth of data contains a million measurements. Without the laser scanner, there was really no cost-effective way to apply inprocess inspection to the production of molds."

The inspector now can collect enough points to check entire surfaces, not just a few points. To do so, he imports both the point cloud and the necessary parameters from the setup sheet to orient the cloud in space. The comparison, therefore, checks more than just the dimensions of the electrode. It also verifies the correctness of the information on the setup sheet, and serves as a kind of simulation of the electrode in the EDM.

Such simulations are valid because electroerosion is a highly predictable process. As long as the electrodes and setup parameters are correct, an EDM will produce a perfect surface. "We have reduced the dimensional errors in production of our molds to basically equipment-level tolerances, which normally exceed the requirements of customers," says Berry.

One reason is that the simulation can uncover subtle errors that often defy detection. For example, one found that an electrode would burn a post in one location in a two-cavity mold perfectly, but its identical twin would not in a second location. The solution to the puzzle was that the electrodes were fine, but one of the parameters on the setup sheet contained a set of transposed numerals.

"Nobody would have noticed it," says Berry. "If we had burned it lights-out at night, we wouldn't have noticed it until the next day, when we would have tried to insert the core pin." Not only did the simulation save a $10,000 insert, but it also prevented the delay associated with making a new one.

Not only does inspecting the electrodes give workers feedback on the process, but it also gives them a way to measure small holes, cavities, ribs, and other difficult-toreach features. Because the electrodes are mirror images of the features that they produce, features hidden within a hole or recess are now on the outside and in the open without any obstructions hindering access to them. Even 1-mm radii are easy to measure this way.

The process feedback is a strategic element in Die-Tech's process. It provides the means to build its products right the first time, rather than relying on rework based on post-process inspection and trials. The goal now is to build as many molds and dies as possible that will produce perfect parts without the customary tweaking afterward. "We are working towards 100% dimensional approval of our tools on the first shot," says Berry. "We can't afford having tools sent out the door come back for anything other than customer-paid engineering changes."

Budgets and schedules no longer contain the funds and time for the series of tweaks that were conventional practice in the past. And these tight budgets and schedules are only going to get tighter. Survival will continue to depend on how well toolmakers learn to compete with capital and develop systems approaches for least-touch manufacturing.

 

This article was first published in the November 2007 edition of Manufacturing Engineering magazine. 


Published Date : 11/1/2007

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