transfer lines 1

7/27/2019 Transfer Lines 1

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Transfer LinesThe manufacturing systems considered here are

used for high production of parts that requiremultiple processing operations. Each processing

operation is performed at a workstation that is

physically integrated by means of a mechanized

work transport system. Machining is a common

process performed on these production lines.

Automated production lines (fixed automation)

require a significant capital investment and it isgenerally difficult to alter the sequence and content

of the processing operations once the line is built.


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Their application is appropriate under the conditions:

High product demand, quantities.

Stable product design, changes are difficult to cope Long product life, at least several years

Multiple operations on product during mnfg

When these conditions satisfied, aut prdn lines provide

the following benefits:

Low direct labor content.

Low product cost

High production rates Production lead time and WIP are minimized.

Factory floor space is minimized


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FUNDAMENTALS

An automated production lineconsists of multiple

workstations linked together by a work handling systemthat transfers parts. A raw workpart enters one end, and

processing steps are performed sequentially as the part

progresses forward.


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The line may include inspection stations for intermediate

quality checks and Manual stations to perform difficult

or uneconomical operations to automate.

Each station performs a different operation, so that the

sum total complete one unit of work.

Multiple parts are processed simultaneously, one part at

each workstation. The number of parts on the line at any moment is equal

to the number of workstations. If there is buffer storage

b/n stations, there is more than one part/station.

Depending on workpart geometry, a transfer line may

utilize pallet fixtures (palletized transfer line) or simply

index parts from station-to-station (free transfer line).


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System Configurations

The work flow in a transfer line can take:

1. I n-l ine , Consists of sequence of stations in astraight-line arrangement. It is common formachining big workpieces, such as automotiveengine blocks, and transmission cases.


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2. Segmented in-line,

consists of two or

more straight-linetransfer sections,

connected to each

other for reasons of:

Floor space limit forthe line length,

Reorientation of wp

to machine different

surfaces, and

Provision for return of

fixtures for reuse


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3. Rotary configuration, the work parts are attachedto fixtures around the periphery of a circularworktable, and the table is indexed to present the

parts for processing. It is limited to smallerworkparts and fewer workstations; and cannotstore buffer.


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Storage Buffers: is a location (b/n every pair of adjacent stations orb/n line stages containing multiple stations) where parts can betemporarily stored before proceeding to subsequent workstations.The reasons for use of buffers include:

To reduce the effect of station breakdowns.

To provide a bank of parts to supply the line - untended operationbetween refills.

To provide a place to put the output of the line.

To allow for curing time or other required delay.

To smooth cycle time variations.


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Control of the Production L ine

Controlling an automated production line is complexbecause of the sheer number of sequential and simultaneous

activities that must be accomplished during the lineoperation

Control Functions:There are three basic control functions inan automatic transfer machine: Operational/sequence

requirement, Safety requirement, and Quality control. The purpose of Sequence control is to coordinate the

sequence of actions of the transfer system and associatedworkstations. Various activities are done in a split-secondwith accuracy. E.g, the parts must be released from currentstations, transported, located, and clamped into position attheir respective next stations; then workheads must beactuated to begin their feed cycles; and so on.

Sequence control is basic to the operation of an automated

production line.


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Safety monitoring ensures that the line does not

operate in an unsafe condition for both the humanworkers and the equipment itself. sensors must beincorporated beyond those required for sequencecontrol to complete the safety feedback loop and

avoid hazardous operation. example, interlocks toprevent equipment operation when workers areperforming maintenance or other duties.

cutting tools must be monitored for breakage and/or

excessive wear to prevent feeding a defective cutterinto the work.


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In Quality control function, certain quality attributesof the workparts are monitored to detect and possiblyreject defective work units produced on the line. Theinspection devices are incorporated into existingstations or separate inspection stations are included inthe line.

When a defect is encountered, One possible action isto stop production line immediately and remove thedefect with lost production time. An alternative actionis to continue to operate, but to lockout the affectedwork unit from further processing as it proceeds

through the sequence of stations that keeps the lineproducing but requires a more sophisticated level ofcontrol over equipment.


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APPLICATIONS OF PRODUCTION LINES

Automated production lines are applied in

processing operations as well as assembly.

Machining is one of the most common processing

applications. Other processes include sheet metal

forming and cutting, rolling mill operations, spotwelding of automobile bodies, and painting and

plating operations.


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Machining Systems

Many applications of machining on transfer machines,both in-line and rotary configurations are found in theautomotive industry which include: milling, drilling,reaming, etc, and rotational cutting operations.

Recently lines have been designed for ease ofchangeover to allow different but related workparts to

be produced on the same line. They consist of acombination of fixed tooling and CNC machines, sothat the differences in product can be accommodated bythe CNC stations, while the common operations are

performed by the stations with fixed tooling. Thus, atrend in transfer lines in the direction of flexiblemanufacturing systems.


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System Design Considerations

In the use aut prdn lines and related systems, the design

of the system is turned over to a machine tool builder.The customer develops specifications that includedrawings of the part and the required production rate ofthe line that will produce them.

Machine tool builders are invited to submit proposals.Each proposal is based on the machinery componentscomprising the builder's product line as well as theingenuity of the engineer preparing the proposed line. It

consists of standard workheads, spindles, feed units,drive motor, transfer mechanisms, bases, and otherstandard components, all synthesized into a specialconfigurations to match the requirements of thecustomer's particular part.


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An alternative approach in designing an

automated line is to use standard machine

tools and to connect them with standard or

special material handling devices. The

material handling hardware serves as the

transfer system that moves work betweenthe standard machines. The term link-line is

sometimes used in connection with this type

of construction.


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Assembly systems

Most manufactured products consist of multiplecomponents joined together by assembly

processes.Manual Assembly lines: consists of a sequence ofworkstation where assembly tasks are performed

by human workers. Products are assembled as they

move along the line. base part is launched on thebeginning of the line and workers add componentsthat progressively build the product. The reasonfor manual lines to be productive is:

Specialization of labor

Interchangeable parts Work principle in material handling - smooth

flow, minimum distance

Line pacing


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There are two basic ways of Work transport system:

1. In manual methods the problem is starving andblocking. To mitigate these problems storage buffersare used between stations.

2. Mechanized work transportsystems are:

Continuous transport at constant velocity. Works are

fixed on conveyer and workers walk with the productor units are removed for convenience

Synchronous transport: all work units are movedsimultaneously b/n stations with quick, discontinuous

motion and positioned at their respective positions. Asynchronous transport: work units leave a station

when the assigned task has been completed and theworker releases the unit independently. Small queues

are permitted in front of each station.


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Coping with product variety

Manual assembly lines can be designed to deal with

differences in assembled product. There are threetypes of lines.

1. Single model line produces many units of oneproduct; every work is identical

2. Batch model line produces each model in batches.Workstations are set up to produce the requiredquantity of first model, and then reconfigured to

produce the next model.

3. Mixed model line produces more than one model butnot in batch mode. while one model is being workedon at one station, a different model is being made atthe next station.


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Automated Assembly Systems

Automated assembly refers to the use of mechanized

and automated devices to perform the various assemblytasks in a line or cell. Although the manual assemblymethods will be used for many years into the future,there are significant opportunities for productivity gains

in the use of automated methods. Aut assembly sys are usually included in the category

of fixed automation. It is considered when the followingconditions exist:

High product demand. Stable product design.

The assembly with limited number of components,

The product is designed for automated assembly ,


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FUNDAMENTALS

An automated assembly system performs a sequence of

automated assembly operations to combine multiplecomponents into a single entity. The single entity can bea final product or a subassembly in a larger product. Inmany cases, the assembled entity consists of a base part

to which other components are attached. Thecomponents are joined one at time (usually), so theassembly is completed progressively.

A typical automated assembly system consists of the

following subsystems: One or more workstations

Parts feeding devices that deliver components to theworkstations, and

A work handling system for the assembled entity.


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System Configurations

The principal configurations Automated assembly

systems are: (a) in-line, (b) dial-type, (c) carousel, and(d) single station.

The in-l ine assembly machine, consists of a series ofautomatic workstations located along an in-line

transfer system. Synchronous and asynchronoustransfer systems are the common means oftransporting base parts.

In the dial-type machine, base parts are loaded onto

fixtures or nests attached to the circular dial.Components are added and/or joined to the base part atthe various workstations located around the peripheryof the dial. The dial-indexing machine operates with asynchronous or intermittent motion.


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The carousel assemblysystemrepresents a hybridbetween the circular of the dial and the straight

work flow of the in-line system. The carouselconfiguration can be operated with continuous,synchronous, or asynchronous transfermechanisms .

In the single station assembly machine,operations are performed on a base part at a singlelocation. The operating cycle involves the

placement of the base part at a stationary position,

addition of components to the base, and removalof the completed assembly from the station ; I eprinted circuit boards.


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Parts Delivery at Workstations

The parts delivery system typically consists of the

following hardware: Hopper is the container into which the

components are loaded at the workstation in bulkand randomly.


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Selector and/or orientorestablishes the orientation ofthe components for the workhead. selectoracts as afilter, permitting only parts in the correct orientation to

pass through. An orientorallows properly oriented partsto pass through, and reorients parts that are not properlyoriented initially.

Feed track. is used to move components from hopperand feeder to the assembly workhead, maintaining

proper orientation of the parts during the transfer. Thereare two feed tracks: gravity in which the hopper and

parts feeder are located at an elevation and the force of

gravity is used to deliver the components; and poweredthat uses vibratory action, air pressure, or other means toforce the parts to travel along the feed track toward theassembly workhead.


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