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 and
rebuilding these complex tools. As a result, exhaustive testing and
troubleshooting cycles have retarded progress, increased new product
development costs, and–in many companies–aggravated competitive
pressures.



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.



Traditional techniques



impede productivity



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



competitive edge



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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