CAD-CAM builds die sets faster, easier.
These kinds of design and fabrication problems are currently being solved at Connecticut Spring & Stamping Corp (CSSC), Farmington, CT. Utilizing a CAD/CAM system and solution-oriented applications software from Gerber Systems Technology Inc, (GST), South Windsor, CT, CSSC is replacing tedious, time-consuming tasks with automated, easy-to-use tools.
Recognized as a leader in the design, development, and assembly of progressive stamping dies, CSSC uses their tooling to produce custom precision metal parts and assemblies for companies in the computer, aerospace, railroad, firearm, camera, and toy industries. With a work force of over 500, the company maintains a highly innovative and successful organization.
As Gaston Pelletier, engineering supervisor at CSSC explained, "If a customer wants any close-tolerance metal part, we find a way to design and manufacture it. Our reputation demands this personal service. But, a few years ago, as our metalstamping trade began to grow, a bottleneck evolved within our engineering department. We simply could not produce detailed and verified drawings fast enough to accept new 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 find flaws in the drawing, so revision time also had to be included. Consequently, even with a lead period of 18 weeks, the engineering department couldn't deliver the finished drawings to our toolmakers with adequate time remaining to build and troubleshoot the dies. Furthermore," Pelletier added, "if the toolroom foreman encountered additional design inconsistencies, more precious time would be wasted in redevelopment."
Company management, over the years, has demonstrated foresight and determination to keep pace with the latest technological advancement. This situation was no different. Turning away new tooling jobs was out of the question. Hiring and training more designers, draftsmen, and checkers was not a cost-effective solution. Finding a faster, more accurate way to draw tooling was the only answer.
As Pelletier recalled, "We started investigating CAD/CAM systems early in 1982. Some of the systems we looked at seemed to suit our needs, but they also posed certain problems for us. For example, a few of the companies we benchmarked sold systems that were very complicated to operate. The engineers demonstrating their systems even had trouble displaying basic progressive die-design techniques. Besides," he remarked, "the prices were very high.
"Then we went to Gerber Systems Technology and examined the Autograph CAD/CAM system. Autograph was the logical solution to our productivity problems at a price we felt quite comfortable with."
In July 1982, CSSC purchased their first Autograph system. Roy Bernard, head designer, says, "The system was up and running 4 to 5 hours after installion, and we quickly trained our engineering staff to operate the system. With basic instruction, I believe anyone can learn to draw and design on the system."
Along with the standard Autograph hardware package--which includes a minicomputer, state-of-the-art disk drive with an integrated tape streamer, and high-resolution raster graphic workstation, which supports a large 19" screen--CSSC also purchased a hardcopy graphics printer, 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 and flexibility we need to accept and complete incoming jobs at any rate we choose."
CAD improves layouts
An example of the type of metalstamping work CSSC has accomplished with this system involves the design of a progressive die for producing intricate electrical "shell" connectors. Initially, they receive either a prototype connector or a drawing of the part from a customer, Figure 1. Then, using the system's mechanical design and drafting software, they interactively create a 2-D flat-blank layout of the part by combining lines and curves on the system screen, Figure 2.
Next, the system calculates all of the pertinent dimensions of the connector and, at the direction of the operator, places the appropriate notes, labels, specified tolerances, and other essential details.
Unlike traditional drafting methods, the CAD/CAM system instills confidence that the dimensions are geometrically correct. But to be sure no programming error was made, the system also plots precision overlay charts. These mylar charts contain all of the entities of the part. With the use of an optical comparator, the connector can be projected up to 50 times its actual size. If part specifications fall within the tolerance envelope, the design is approved.
After the connector is completely defined and verified, the tool is graphically developed in three consecutive steps. First, from the mathematics obtained in creating the flat blank, the strip layout is constructed. This design represents the various ways the flat metal stock will be shaped as it progresses from the initial pierce stroke, through pilot, gut, lance, draw, and the other part-forming stations within the power press. Next, the die layout is created. In this design, a flat view of the stamping assembly is displayed and separated into tool blocks (die sections). On these blocks, the numerous clearance, scrap, screw, and dowel holes are carefully positioned, as well as the critical punch and die inserts. In the final design phase, a cross-section view of the entire assembly is developed in the tool layout.
When components are similar, as with many of the shell connectors made by the company, the same basic shape can be modified instead of creating each model from scratch. With family-of-parts design software, the designer simply inputs the changing parametric values, and the system automatically redimensions the new part graphics.
Another important feature is the ability to manipulate layouts visually. By expanding or focusing in on specific design elements, errors that might be missed on the drawing board can be identified and promptly corrected on the screen. Once approved, the three layouts are combined into one comprehensive design that can be drawn to scale on the system's drafting plotter, Figure 3, stored in the data base, or used to generate the numerical control data required to machine the tool blocks.
"Where we used to spend weeks manually drawing and verifying new tool designs, we now use the CAD/CAM system to complete all of these steps to our satisfaction in a matter of hours," says Bernard. "This reliable accuracy has totally eliminated the need for full-time checkers, leaving our engineering staff free to concentrate on fresh projects."
From CAD to CAM:
A critical progression
As a result of this improvement in engineering productivity, which includes a 100 percent increase in detailed drawing output, the toolroom and manufacturing areas at CSSC are in full operation 24 hours a day. Barry Sharpe, head of production troubleshooting, explained the company's manufacturing procedures. "After the toolroom foreman receives the progressive die design from the engineering department, he inspects the drawing for flaws. This used to be a long, monotonous process, but with the accuracy we receive from the CAD/CAM system, it's now a simple task.
"Next, we rough out the die sections and corresponding inserts. Then, we heat treat to prepare the metal for cutting with our numerically 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 wire EDMs, the company employs the latest in computerized-programming techniques. Here, NC software functions allow the manufacturing engineer to retrieve the stored data-base geometry of the appropriate die section, previously designed in engineering. Then, with the model displayed on the system screen, he superimposes tool paths on the block to simulate the wire EDM metalcutting procedures. In the CAD/CAM system's interactive mode, the numerical tool path tracks the CRT cursor arm as it is progressively positioned. When operating semiautomatically, the cutter path locks onto and traces the desired entity closest to the cursor's position. It then awaits the operator's next entity definition and cursor location. Postprocessor commands are also added at this level. These functions include wire direction and feed rate, coolant parameters, absolute and incremental coordinate positioning, radii compensation, and other necessary machining functions. The engineer then has an opportunity to window, pan, or zoom in on tool paths to clarify geometric details and achieve greater accuracy.
To prepare the tool-path data for conversion from its graphics format into punched tape, the operator activates the correct system function buttons and transfers the data base to an intermediate APT-like file where it can again be edited before being input to a special, generic postprocessor.
In the postprocessor, the intermediate file is converted into NC data for the suitable machine-tool control unit and wire EDM combination. Here again, the engineer has another chance to edit data prior to final processing. Upon completion, the postprocessed data is used to punch the tape, add a readable leader, and to configure the data to the desired ASCII, EIA, or ISO NC formats. The paper tape is then delivered to and loaded on the wire EDM control unit for cutting the die section to exacting standards, Figure 4.
By using GST's CAM software throughout their NC tape-preparation process, CSSC has realized many impressive results. To complement a reduction in die development cycles, they have also been able to minimize data syntax errors, enforce part-programming standardization, and generally improve product quality.
In the final assembly stages, the die sections undergo additinal sawing, boring, and form grinding. The blocks are then mounted on a die set and various tooling holes are drilled. Next, the inserts are positioned, and the tool is assembled one section at a time, Figure 5. Upon completion, the blocks are lined up, and the assembly is placed in an automatic power press.
At this point, the tool must be proved. Feed, release, and shutheight are set, and the part stock is automatically fed through the press. Block by block, they debug and troubleshoot all of the functions, from the pierce stroke to the final blanking station that stamps out the finished shell connector.
The GST system, which operates 18 hours a day on two shifts, has also provided the company with many important, yet unexpected advantages. As Pelletier commented, "It's hard to break down all of the benefits and cost savings we have received since purchasing the system, because the savings come in so many different and sometimes discrete forms. For instance, when we invite a prospective customer to our plant nowadays, we can display his products on our CAD/CAM system screen. How can we determine the amount of new customers we've received from this type of high-technology presentation? There are also factors such as reductions in scrap material, ease of use, and rapid design revision that we can't put actual dollar amounts on, even though they do save us money. The general feeling is that if we didn't have the system, we wouldn't have been able to withstand the incoming workload, and we would never have seen the production increase we are experiencing today."
Integration: Key to the
CAD/CAM technology has placed the company in a position of high visibility within the metalstamping industry, and the company's management is extremely optimistic about the future.
"Basically," the engineering supervisor stated, "we plan to automate as well as integrate our design and manufacturing operations as much as technology will permit. GST's direct numerical control (DNC) is one viable step available to us right now. DNC will allow us to save time by transmitting machining data directly to our controllers without having to punch tape. Beyond that, it's also conceivable that robotics technology could eventually find a place within our machining and assembly operations. The immediate plan, however, is to install another Autograph system to help ensure our continued success."
Today, more than ever, competition is a vital concern to the management of most businesses. Pelletier clarified his company's stance on this issue. "Competition? In the progressive die industry, if a company doesn't have CAD/CAM facilities, they are no longer our rivals. We can now provide our customers with so many advantages 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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|Title Annotation:||computer-aided design-computer-aided manufacturing|
|Publication:||Tooling & Production|
|Date:||Nov 1, 1984|
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