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Flexible systems go with the flow.

By viewing manufacturing as more of a continuous process, machine tool builders and users can put their heads together to solve tough production problems. . . flexibly.

Metalworking manufacturing produces discrete parts. The most productive results from manufacturing systems, howevedr, often are realized when engineers view the manufacturing operation not as a chain of separate and discrete functions but rather as more of a continuous process. Modern computer and software technology make possible the flexibility not only to more closely control a manufacturing process, but to change product mix, alter production schedules, and adjust the pace of manufacturing to a degreee that begins to approximate the "flow" of production in a continuous process.

Machine tool builders and users are beginning to understand that this approach requires going beyond standard machining concepts. These builders and users are working together to develop flexible process solutions tailored to meet unique and changing needs. The resulting systems often take the form of automated manufacturing centers created around standard components that have been optimized to expand their process capabilities.

This "systems approach" represents a fundamental shift in the way manufacturing methods are viewed. Rather than seeing a standalone machining center as a static tool to achieve a single, well-defined end, builders and users implementing this approach see the machine as the core of an integrated processing system that includes tool management, material handling, spindle attachments, in-process gaging, and other features.

The task in designing an effective flexible manufacturing system is combining the appropriate type and level of technology into a system that generates a synergistic effect--that is, the combination of technologies to create an impact greater than the sum of the individual technologies.

One of the keys to a successful builder-user partnership is to correctly define the level of technology required to add maximum value to manufacturing processes. Here's how Giddings & Lewis Automation Technology, Fond du Lac, WI, worked with three customers to implement the systems approach to manufacturing and integrate appropriate technologies into their complete manufacturing processes.

Simplifying bearing manufacture

At Morgan Construction Co, Worcester, MA, machining large, thin-wall oil film bearings presented an ongoing problem. Rated to withstand 1.5 million lb of radial force, the precision bearings are fabricated from 4150 steel with hardness of 350 to 400 Brinell. The bearings range from 30" to 50" in diameter and require a concentricity tolerance of [+ or -]0.000 002" (two millionths) between OD and ID faces.

Morgan was unable to consistently achieve the required part accuracies and could not respond quickly enough to changing customer needs and critical delivery times. The company teamed up with Giddings & Lewis to design a new bearing machining process: a flexible manufacturing system (FMS) that integrates three machines with related controls, programming, tooling, and workholding.

The three-machine system consists of a vertical turning center, vertical machining center, and grinder. This combination processes Morgan's complete bearing line, which consists of five families with a wide range of sizes in each family. Special chucks with quick-change jaws allow the VTC and VMC to accommodate all five sub-families.

First, the vertical turning center with Giddings & Lewis NumeriPath 8000 CNC provides simultaneous turning of part ID and OD. The work-piece is then chucked in a vertical machining center, which uses a "2-in-1" spindle to provide both conventional spindle rotation for vertical machining and a right-angle attachment drive for horizontal machining.

Processing operations performed on the VMC include boring, milling, drilling, reaming, and tapping. The 25-hp machine uses a 40-position automatic toolchanger,precision rotary table, tool life monitoring system, in-process gaging system, and automatic tool-tip probing.

A critical processing step includes milling two key pockets in the part ID. These pockets must be machined at 18 deg to the part centerline within a tolerance of [+ or -]0.001". Ability to chuck the workpiece vertically resulted in a 50% reduction in setup time for this operation.

The fully machined workpiece is moved to a grinder for simultaneous ID and OD finishing operations, which produce a #4 microfinish.

Implementation of the flexible system has resulted in reductioin of throughput time from four months to one week, improved accuracy and repeatability, and reduction of work in process. Overall cycle times, including setup and queue times, have been reduced by at least 75%.

The FMS also provides the flexibility to produce a pair of bearings in as little as 40 hours, permitting rapid response to customer needs.

Flexible diesel machining

Flexibility in large-part processing also was the goal of a high-volume diesel engine manufacturer. Having earlier experience producing in-line engine blockson a transfer line, the company wanted instead to maintain flexibility in processing its new V-6, V-8, V-10, and V-12 engine blocks. The largest of these blocks is 40" long with a 6" bore. The system also had to machine the blocks to German tolerances for accuracy.

The manufacturer and Gidding & Lewis developed a process for machining the entire family of engine blocks on a flexible manufacturing system rather than a traditional transfer line. The FMS, which consists of five machines, a material handling system, controls, programming, tooling, and fixturing, can convert the blocks from raw castings to finished blocks ready for the wash tank in seven to eight hours.

The engine blocks are processed across five horizontal machining centers, each with NumeriPath 8000 CNC. A cell management controller, which integrates systems management software, and a Digital Equipment Corporation (DEC) Micro VAX computer direct all aspects of FMS operation, including:

* Machining operations,

* Verification of correct part fixturing and loading.

* Selection of machining center best suited to process each part,

* Monitoring of machining cycles,

* Determination of future tool needs based on production schedule,

* Verification of tool availability,

* On-line tallying of tool life,

* Dynamic display of line information, including system status,

* Status of all parts in the system,

* Running report of cycle times, interruptions, and malfunctions.

The five machining centers are arranged in two groups to provide both shared and unique processing capabilities. In one group, machines are configured to perform facing operations. In the second group, machines are arranged to use a large, special tool to mill the "cheeks" on main bearings. Individual machines have 120-tool capacity toolchangers.

An important goal of the FMS was to reduce the number of individual setups and fixturings required for the family of engine blocks. The solution was a set of five fixtures designed to accommodate all four block sizes. Because only length varies between the blocks, the different sizes are fixtured simply by moving selected clamp locations. All fixture clamps are hydraulically actuated to minimize operator intervention.

Aircraft production takes off

A major aerospace manufacturer needed machining flexibility to process a family of four sizes of aircraft wing flaptracks. The solution was a four-machine FMS that reduced overall cycle time by 200 hours. The new process replaced sixteen standalone machines previously needed to drill, ream, countersink, and bore numerous holes in the 4340 steel flaptracks, which are as long as 18 ft and weigh up to 750 lb.

The FMS consists of four horizontal machining centers. Each 25-hp machine has virtually unlimited X-axis travel, allowing precision hole positioning without re-fixturing. Other technologies include automatic toolchangers with 96-tool capacity, on-line part probing, adaptive control with horsepower monitoring, and through-spindle coolant.

The four-machine system is laid out as two facing pairs separated by a staging area. Between each pair of machines is a common worktable. The arrangement permits simultaneous machining of both sides of the workpiece.

Two factors were critical in the design of fixturing for this system. The first was the desire to avoid distortion from heat processing, which led to the decision to machine the flaptracks after heat treating. The second was the fact that the 80 holes produced in the flaptracks had to match precisely in size and alignment with holes in mating "failsafe" bars machined on the second pair of machining centers.

The solution was a modular fixturing system that accommodates the four sizes of flaptracks by modifying selected clamp elementss. Depending on flaptrack length, between 30 and 40 hydraulic/mechanical clamps are located to miss "live" machining areas in each of the four regions.

To eliminate flaptrack wall deflection during machining operations which can exert up to 3000 lb of force, the fixture incorporates an expandable T-bar that presses against the inner workpiece walls. The support mechanism ensures accurate part "set" and proper hole location.

A unique aspect of this system is the ability to communicate with the host computer from within an NC program via a serial link. Using data from the serial link, the customer developed three proprietary subsystems: one that automatically monitors tool wear and detects dull tools, an in-process gaging system to precisely measure diameters of reamed holes for statistical process control, and a system to precisely locate holes machined in wing flaptracks with mating holesin failsafe bars.

For more information from Giddings & Lewis Automation Technology, circle 286.
COPYRIGHT 1992 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:metalworking manufacturing systems
Publication:Tooling & Production
Date:Sep 1, 1992
Previous Article:High-speed machining enters the Iron Age.
Next Article:Flexible gaging for flexible manufacturing.

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