CAD-CAM builds die sets faster, easier Essay

Progressive die development has always been an expensive,error-prone process. Valuable time is often wasted redesigning andrebuilding these complex tools. As a result, exhaustive testing andtroubleshooting cycles have retarded progress, increased new productdevelopment costs, and–in many companies–aggravated competitivepressures. These kinds of design and fabrication problems are currently beingsolved at Connecticut Spring & Stamping Corp (CSSC), Farmington, CT.Utilizing a CAD/CAM system and solution-oriented applications softwarefrom Gerber Systems Technology Inc, (GST), South Windsor, CT, CSSC isreplacing tedious, time-consuming tasks with automated, easy-to-usetools. Recognized as a leader in the design, development, and assembly ofprogressive stamping dies, CSSC uses their tooling to produce customprecision metal parts and assemblies for companies in the computer,aerospace, railroad, firearm, camera, and toy industries.

With a workforce of over 500, the company maintains a highly innovative andsuccessful organization. Traditional techniques impede productivity As Gaston Pelletier, engineering supervisor at CSSC explained,”If a customer wants any close-tolerance metal part, we find a wayto design and manufacture it. Our reputation demands this personalservice. But, a few years ago, as our metalstamping trade began togrow, a bottleneck evolved within our engineering department. We simplycould not produce detailed and verified drawings fast enough to acceptnew tooling jobs at this accelerated rate. “To design just one intersection of a strip layout, by hand,might take days. To draw an entire tool assembly, with full detail,usually required weeks. In many cases, the design checker would findflaws in the drawing, so revision time also had to be included.

Consequently, even with a lead period of 18 weeks, the engineeringdepartment couldn’t deliver the finished drawings to our toolmakerswith adequate time remaining to build and troubleshoot the dies.Furthermore,” Pelletier added, “if the toolroom foremanencountered additional design inconsistencies, more precious time wouldbe wasted in redevelopment.” Company management, over the years, has demonstrated foresight anddetermination to keep pace with the latest technological advancement.This situation was no different.

Turning away new tooling jobs was outof the question. Hiring and training more designers, draftsmen, andcheckers was not a cost-effective solution. Finding a faster, moreaccurate way to draw tooling was the only answer. As Pelletier recalled, “We started investigating CAD/CAMsystems early in 1982. Some of the systems we looked at seemed to suitour needs, but they also posed certain problems for us. For example, afew of the companies we benchmarked sold systems that were verycomplicated to operate. The engineers demonstrating their systems evenhad trouble displaying basic progressive die-design techniques.Besides,” he remarked, “the prices were very high.

“Then we went to Gerber Systems Technology and examined theAutograph CAD/CAM system. Autograph was the logical solution to ourproductivity problems at a price we felt quite comfortable with.” In July 1982, CSSC purchased their first Autograph system. RoyBernard, head designer, says, “The system was up and running 4 to 5hours after installion, and we quickly trained our engineering staff tooperate the system. With basic instruction, I believe anyone can learnto draw and design on the system.” Along with the standard Autograph hardware package–which includesa minicomputer, state-of-the-art disk drive with an integrated tapestreamer, and high-resolution raster graphic workstation, which supportsa large 19″ screen–CSSC also purchased a hardcopy graphicsprinter, a paper-tape reader/punch for numerical control applications,and an industry standard, E-size drafting plotter. Bernard says,”The GST system provided our company with the strength andflexibility we need to accept and complete incoming jobs at any rate wechoose.” CAD improves layouts An example of the type of metalstamping work CSSC has accomplishedwith this system involves the design of a progressive die for producingintricate electrical “shell” connectors.

Initially, theyreceive either a prototype connector or a drawing of the part from acustomer, Figure 1. Then, using the system’s mechanical design anddrafting software, they interactively create a 2-D flat-blank layout ofthe part by combining lines and curves on the system screen, Figure 2. Next, the system calculates all of the pertinent dimensions of theconnector and, at the direction of the operator, places the appropriatenotes, labels, specified tolerances, and other essential details. Unlike traditional drafting methods, the CAD/CAM system instillsconfidence that the dimensions are geometrically correct.

But to besure no programming error was made, the system also plots precisionoverlay charts. These mylar charts contain all of the entities of thepart. With the use of an optical comparator, the connector can beprojected up to 50 times its actual size. If part specifications fallwithin the tolerance envelope, the design is approved. After the connector is completely defined and verified, the tool isgraphically developed in three consecutive steps. First, from themathematics obtained in creating the flat blank, the strip layout isconstructed.

This design represents the various ways the flat metalstock will be shaped as it progresses from the initial pierce stroke,through pilot, gut, lance, draw, and the other part-forming stationswithin the power press. Next, the die layout is created. In thisdesign, a flat view of the stamping assembly is displayed and separatedinto tool blocks (die sections). On these blocks, the numerousclearance, scrap, screw, and dowel holes are carefully positioned, aswell as the critical punch and die inserts. In the final design phase,a cross-section view of the entire assembly is developed in the toollayout.

When components are similar, as with many of the shell connectorsmade by the company, the same basic shape can be modified instead ofcreating each model from scratch. With family-of-parts design software,the designer simply inputs the changing parametric values, and thesystem automatically redimensions the new part graphics. Another important feature is the ability to manipulate layoutsvisually. By expanding or focusing in on specific design elements,errors that might be missed on the drawing board can be identified andpromptly corrected on the screen. Once approved, the three layouts arecombined into one comprehensive design that can be drawn to scale on thesystem’s drafting plotter, Figure 3, stored in the data base, orused to generate the numerical control data required to machine the toolblocks. “Where we used to spend weeks manually drawing and verifyingnew tool designs, we now use the CAD/CAM system to complete all of thesesteps to our satisfaction in a matter of hours,” says Bernard.”This reliable accuracy has totally eliminated the need forfull-time checkers, leaving our engineering staff free to concentrate onfresh projects.

” From CAD to CAM: A critical progression As a result of this improvement in engineering productivity, whichincludes a 100 percent increase in detailed drawing output, the toolroomand manufacturing areas at CSSC are in full operation 24 hours a day.Barry Sharpe, head of production troubleshooting, explained thecompany’s manufacturing procedures. “After the toolroomforeman receives the progressive die design from the engineeringdepartment, he inspects the drawing for flaws. This used to be a long,monotonous process, but with the accuracy we receive from the CAD/CAMsystem, it’s now a simple task. “Next, we rough out the die sections and correspondinginserts. Then, we heat treat to prepare the metal for cutting with ournumerically controlled wire electrical discharge machine (wire EDM).This is another area where CAD/CAM saves us time,” he stated.

For generating the paper-tape data needed to control their two wireEDMs, the company employs the latest in computerized-programmingtechniques. Here, NC software functions allow the manufacturingengineer to retrieve the stored data-base geometry of the appropriatedie section, previously designed in engineering. Then, with the modeldisplayed on the system screen, he superimposes tool paths on the blockto simulate the wire EDM metalcutting procedures.

In the CAD/CAMsystem’s interactive mode, the numerical tool path tracks the CRT cursor arm as it is progressively positioned. When operatingsemiautomatically, the cutter path locks onto and traces the desiredentity closest to the cursor’s position. It then awaits theoperator’s next entity definition and cursor location.Postprocessor commands are also added at this level. These functionsinclude wire direction and feed rate, coolant parameters, absolute andincremental coordinate positioning, radii compensation, and othernecessary machining functions. The engineer then has an opportunity towindow, pan, or zoom in on tool paths to clarify geometric details andachieve greater accuracy.

To prepare the tool-path data for conversion from its graphicsformat into punched tape, the operator activates the correct systemfunction buttons and transfers the data base to an intermediate APT-likefile where it can again be edited before being input to a special,generic postprocessor. In the postprocessor, the intermediate file is converted into NCdata for the suitable machine-tool control unit and wire EDMcombination. Here again, the engineer has another chance to edit dataprior to final processing. Upon completion, the postprocessed data isused to punch the tape, add a readable leader, and to configure the datato the desired ASCII, EIA, or ISO NC formats. The paper tape is thendelivered to and loaded on the wire EDM control unit for cutting the diesection to exacting standards, Figure 4.

By using GST’s CAM software throughout their NCtape-preparation process, CSSC has realized many impressive results. Tocomplement a reduction in die development cycles, they have also beenable to minimize data syntax errors, enforce part-programmingstandardization, and generally improve product quality. In the final assembly stages, the die sections undergo additinalsawing, boring, and form grinding. The blocks are then mounted on a dieset and various tooling holes are drilled.

Next, the inserts arepositioned, and the tool is assembled one section at a time, Figure 5.Upon completion, the blocks are lined up, and the assembly is placed inan automatic power press. At this point, the tool must be proved. Feed, release, andshutheight are set, and the part stock is automatically fed through thepress. Block by block, they debug and troubleshoot all of thefunctions, from the pierce stroke to the final blanking station thatstamps out the finished shell connector. The GST system, which operates 18 hours a day on two shifts, hasalso provided the company with many important, yet unexpectedadvantages. As Pelletier commented, “It’s hard to break downall of the benefits and cost savings we have received since purchasingthe system, because the savings come in so many different and sometimesdiscrete forms. For instance, when we invite a prospective customer toour plant nowadays, we can display his products on our CAD/CAM systemscreen.

How can we determine the amount of new customers we’vereceived from this type of high-technology presentation? There are alsofactors such as reductions in scrap material, ease of use, and rapiddesign revision that we can’t put actual dollar amounts on, eventhough they do save us money. The general feeling is that if wedidn’t have the system, we wouldn’t have been able towithstand the incoming workload, and we would never have seen theproduction increase we are experiencing today.” Integration: Key to the competitive edge CAD/CAM technology has placed the company in a position of highvisibility within the metalstamping industry, and the company’smanagement is extremely optimistic about the future. “Basically,” the engineering supervisor stated, “weplan to automate as well as integrate our design and manufacturingoperations as much as technology will permit. GST’s directnumerical control (DNC) is one viable step available to us right now.DNC will allow us to save time by transmitting machining data directlyto our controllers without having to punch tape. Beyond that, it’salso conceivable that robotics technology could eventually find a placewithin our machining and assembly operations.

The immediate plan,however, is to install another Autograph system to help ensure ourcontinued success.” Today, more than ever, competition is a vital concern to themanagement of most businesses. Pelletier clarified his company’sstance on this issue. “Competition? In the progressive dieindustry, if a company doesn’t have CAD/CAM facilities, they are nolonger our rivals.

We can now provide our customers with so manyadvantages and services that we far outstrip our, so-called,competitors,” he said. For more information from Gerber Systems Technology Inc, circle E9.

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