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Flexible transfer lines machine engine manifolds.

Flexible transfer lines machine engine manifolds

Today, when most manufacturing engineers think of flexible machining systems (FMS), they don't consider transfer machines or lines. After all, transfer lines are not flexible. They've always been used to make one part design in large volumes. Or so it would seem.

When asked to produce a wide variety of intake and exhaust manifolds, most engineers would think in terms of a series of CNC machining centers. These would be strung together by an automatic guided vehicle system (AGVS) carrying palleted fixtures and parts. There are many such systems in use today, and they've been widely publicized.

Granted, this configuration of FMS allows high flexibility. In theory, any part that fits within work-envelope constraints could be run on the machining centers. New, different parts could be made simply by changing tools and loading new control programs.

Further, these FMSs have the advantage of allowing production to continue when one or more machining centers are shut down. The pallets are simply rerouted around the down machines.

In contrast, when a single station goes down in a transfer line, production stops completely. Even so, in many situations such as the one described here, an AGVS/machining center FMS may not be the most cost-effective solution.

Palletized transfer

For this installation, two transfer systems - designed and built by Lamb Technicon, a unit of Litton Industrial Automation, Warren, MI - machine six different auto manifold designs at an average rate of 40/hr. To meet production needs using the AGVS/machining center approach would have required nearly four times more floor space and twice the capital investment.

As the plan-view drawings show, each system is based on a palletized transfer machine. Transfer machines employ proven, reliable technology, and they seldom break down. Even when a shutdown does occur, the high output rate of these machines makes up for any losses.

Each system uses an off-line dial-index machine upstream from the transfer machine to qualify casting workpieces, mill joint faces, and machine manufacturing holes. In addition, the intake manifold system employs an off-line CNC machining center. This performs odd hole operations on some parts.

Both transfer systems use standard CNC milling and machining equipment, but in this case the equipment operates as stations in transfer lines. Parts are mounted on pallet fixtures (photo), which are transported from station to station by a common lift-and-carry transfer bar. This moves pallets into and out of the stations much more quickly than would be possible with an AGVS.

A large measure of efficiency in these systems comes from using multiple spindle heads for machining different combinations of holes. As shown in the photo, these heads are mounted on indexing turrets. This approach allows a series of holes to be completed at one station very quickly.

Successive operations such as drill, countersink, probe, and tap are performed by making multiple passes. The stations can also be used to mount multiple spindle heads with different hole patterns for different part models.

Use of traditional bushing plates on the multiple spindle heads has been eliminated by employing collet-type toolholders and stub-spindle construction. This minimizes tool overhang, thereby avoiding a need for tool guide and support bushings.

The intake manifold system uses two different types of pallets. One is for production of a single part, while the other is for production of two parts. In both cases, parts are loaded and reloaded in each pallet to expose all necessary part surfaces to the cutting tools.

Each of three parts is machined in two positions on the pallets. Only one part is completed during a cycle.

The three exhaust manifolds are all fixtured on a single pallet (photo). Again, each of the three manifolds is loaded and reloaded in two different positions on a pallet. Only one of the three is produced during a machining cycle.

Machining center

As mentioned previously, the exhaust manifold line includes a standard CNC machining center with an automatic tool changer. The indexing, multiple spindle head unit indexes heads on a 45-degree angle. Compared to the traditional indexing head design, where the indexing axis is vertical, this approach reduces the amount of clearance needed for indexing. Thus the distance between stations can be relatively short, minimizing the over-all size of the machines.

In the intake manifold system, which runs two pallets on a randommix basis, the pallets carry metal trip dogs. These are read at each station to identify which parts are present. Reading the dogs also determines whether the station should cycle, which multiple spindle head should be present, or which tools should be in the machining center spindle.

The fixed-sequence configuration of the transfer machines greatly simplifies the control system, especially when compared with controls needed for AGVS/machining center FMSs. In these systems, often it is necessary to fit each pallet with a magnetically coded tag. This records each operation performed on a part, and is read at the machining center so the appropriate machining program can be called up. Eliminating the need for magnetic-tag ID systems reduces initial system costs and maintenance costs.

Changes in holes

Most anticipated design changes for the manifolds are expected to occur in the single holes produced on the CNC machining centers. To accommodate these changes, only modifications in tool selection and programs are required. Even if changes are needed in the mounting-hole patterns made by the multiple-spindle indexing heads, the cost of replacing affected heads will be relatively small. Designing and installing a fully flexible AGVS/machining center FMS to accommodate such changes would cost considerably more.

As a matter of fact, shortly after Lamb Technicon installed the two transfer lines, a radically new design of intake manifold had to be added to production. The shape of this part differed so much from others in the family, that it was necessary to add an auxiliary clamp at each station, and to replace the pallets on the transfer machine. In addition, a change in the center section of a dial-index machine was needed.

Engineering and manufacturing lead-time for production of the new machine components took about six months. Once they were built, however, changeover was made in less than two weeks, during a scheduled plant shutdown for inventory. No machine production time was lost.

So as you can see, transfer machines truly have a place in the world of flexible machining.

PHOTO : Load/unload fixture for three exhaust manifolds.

PHOTO : Three intake manifolds that are completely machined on one of the transfer systems.

PHOTO : Plan-view drawing for transfer line used to machine intake manifolds.

PHOTO : Plan-view drawing for transfer line that produces exhaust manifolds.

PHOTO : Partial view of transfer line for exhaust manifolds.

PHOTO : Multiple spindle heads mounted on turret indexing units.
COPYRIGHT 1989 Nelson Publishing
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Dec 1, 1989
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