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Programming options benefit mold maker.

Programming options benefit mold maker

Using the appropriate program for a particular part is important to effectively produce a variety of complex molds, dies, patterns, and core boxes. Taking advantage of current technology, we use CNC, digitizing, and CAD/CAM programming, or a combination of them. Each programming option benefits us in the production of specialized mold cavities for blow molders, injection molders, vacuum formers, and detailed patterns and core boxes for foundries.

Although we use the programming options separately to produce shapes, on some parts we can use all three to shorten production time. We might program the cavity with CAD/CAM, the core with CNC, and make a partial model to digitize a complex shutoff. Three programmers can work on their portions of the mold simultaneously, reducing completion time.

Digitizing programs

The simplest method is digitizing. A Numerex coordinate measuring machine with hand-held stylus and specialized rapid-scan software electronically records from 2 to 65 points/sec (pps).

While digitizing demands the least amount of programming skills, a particular job often requires a skilled model and pattern maker. With the stylus, the operator manually traces a path on the model, digitizing a complete range of X, Y, and Z data; no product drawing is necessary. He is not limited to digitizing within a certain envelope, but can trace his path in any and all directions, jumping to and from specific parts of the model at will. Recording the program

points in a separate PC memory, the operator can program detailed cutting action on rounded shapes, parting lines, and shutoffs.

Digitizing also lends itself to investment dies with complex parting lines, mold cavities, and lightening out of evaporative-foam tooling. Parting lines, for example, are often blended shapes--so the maker develops them as he goes along. In a complex investment die where pieces have to fit together, it's easier to make a wood model, fit the pieces together with the detail required, digitize, and machine.

The CMM operator first digitizes with the largest stylus practical to remove the maximum amount of stock in the least amount of time. Then he digitizes in smaller increments to bring the finished tooling within close tolerances. During digitizing he collects as many points as possible, and uses the software to sort and remove unnecessary points to improve straight-line machining and reduce machining time. The operator adds all machining parameters to the program, including machine language G codes, tooling changes, feeds and speeds, and shrinkage factors. He is then ready to run DNC.

Digitizing is also well-suited to free-flowing forms such as those used in blow molding, where the forms may not need mathematical definition. For lost-foam molds, it is easier and safer to pour the male plug from the already-machined cavity, digitize it with a certain sized stylus, then remove stock from the back of the cavity with a smaller-diameter end mill, ensuring a constant wall thickness within the confines of the tool size.

CNC programming

In the early 1980s, we began producing patterns for a foundry that casts replaceable wear parts for the pulp and paper industry. To automate and speed production of complex patterns, we bought a Bridgeport CNC mill with a Boss 5 control. But our customer quickly recognized its potential and began designing more complex refiner plates. We soon outgrew the Bridgeport capability.

In 1982 we bought the first of five CNC vertical milling machines with an Israeli-made Sharnoa Tiger computer control. While other controls at the time required one line for each point in the program, the Sharnoa was a welcome change. The control is based on an algebraic equation format that gives programmers the capability to machine a hemisphere--possibly having millions of points--with just seven lines of information.

With algebraic programming we were able to program complex shapes that were difficult to do on other machines without computer assistance. Because the 16-bit control is softwired, it continually upgrades its software. When we recently added our fifth Sharnoa, we were one of the first in the country to use the Tiger 5 CNC 32-bit processor.

Adding the new control was only a first step in expanding our capability. During the past eight years we've developed and refined a variety of programs for machining specialized patterns for the pulp and paper industry.

These patterns are made in aluminum or brass, with each unit forming one segment of a circle. The foundry casts them in stainless-steel alloys and assembles them in circular sets for the end user.

These patterns are difficult to program because they contain complex geometric designs. The plates usually include a series of parallel bars and nonparallel grooves of increasing depth, converging on a point other than the origin of the circle. Often the plate contains as many as three different zones from ID to OD, each with a different geometric configuration.

Machining the actual pattern from the program stored in the Sharnoa memory may take from 20 to 70 hours. Because the operator does not constantly have to watch the CNC machine, he can handle other jobs at the same time. We often machine patterns at night and on weekends because machines can run untended.

3-D CAD/CAM programming

In early 1989 we broadened our programming capability by adding an Apollo computer with Deltacam DUCT software, an advanced computer-imaging system that speeds the modeling of complex surface shapes. DUCT (Design Using Computer Techniques) is a 3-D system designed for heavily contoured and blended surfaces.

With the Sharnoas we define the shapes to be produced in geometric equations, but with DUCT we can use the computer's specialized spline and surface functions to blend areas that are difficult to describe geometrically.

Unlike wireframe CAD/CAM systems, the software uses 2-D or 3-D part-section data to model 3-D surface shapes. We can model a complex cavity, create a tool path, analyze it, and test it on the screen. It's so powerful we can generate actual wall thicknesses, core patterns, and milling paths, then produce the exact part needed.

Open or closed sections of the part to be modeled are positioned relative to each other within a 3-D space by using curved or straight lines, defined by at least two points, each with X, Y, and Z coordinates. Every section of the part must have the same number of points, each fixed in relation to the coordinates. When the number of sections and positioning points are equal, the program automatically blends between the sections to create an optimally smooth surface.

The programmer models the various surfaces of the desired part to its nominal dimensions and true position in the 3-D space. He then uses DUCT's blending power to mold the individual surfaces into the completely modeled part. Using the visualization mode, the programmer can call up a detailed, colored, and shaded image of the actual part. Because exterior and interior surfaces are shaded in different colors, blend quality, surface integrity, discontinuities, and other critical aspects are quickly evident.

PHOTO : Using a Sharnoa CNC vertical milling machine, a machinist cuts a complex refiner-plate pattern into a high-density carbon block. The finished carbon piece will be an EDM electrode used to cut the reverse shape into aluminum, creating the pattern needed to produce an investment casting that will look exactly like the carbon shape.

PHOTO : This stainless steel manifold (sample part hand held) is made by investment casting (lost wax process) using a Metals Unlimited pattern. The complicated 22-piece pattern was first made of wood to verify fit before machining the aluminum pattern. The complex dark shape (left in photo above) is the actual wax lost during casting.

PHOTO : Products such as this aluminum pattern feature geometry so complicated that Metals Unlimited believes it may be the only company in the world producing such complexity on CNC equipment.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Author:James, Ray; Opgenorth, Jim
Publication:Tooling & Production
Date:Jul 1, 1991
Words:1294
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