MM 323 MAN SYS 2012 FALL 6 Automated Production Lines PART 1 (1)

8/14/2019 MM 323 MAN SYS 2012 FALL 6 Automated Production Lines PART 1 (1)

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MM 323

MANUFACTURING SYSTEMS

Automated Production (Transfer) Lines

PART 1


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Automated Production Lines

High production of a part type with models (little variation

among models) requiring multiple processing operations

Fixed automation (very difficult to make changes)

Applications: Transfer lines used for machining

Robotic spot welding lines in automotive final assembly

Sheet metal stamping

Electroplating of metals


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When to Use Automated Production Lines? High product demand per product/part type

Requires large production quantities Stable product design

Difficult to change the sequence and content of

processing operations once the line is built

Long product life At least several years

Multiple operations required on product

The total work content is distributed to multiple

workstations. Different operations are assigned to differentworkstations in the line. The specialized and automated

operation is repeated at each station continuously.


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Automated Production Lines provides

Low direct labor content

Low product cost

High production rates

Minimized production lead time and work-in-process.

Minimized factory floor space.


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Automated Production Line

CHARACTERISTICS Automated production lines are fixed-routing manufacturing

systems that consist of multiple workstations linked togetherby a material handling system to transfer parts from one

station to the next

Slowest workstation sets the pace of the line.

Workpart transfer:

Palletized transfer line

Uses pallet fixtures to hold and move workparts between

stations

Free transfer line

Part geometry allows transfer without pallet fixtures


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General configuration of an automated

production line consisting of n automated

workstations that perform processing operations


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An Automated Production Line can have the

following SYSTEM CONFIGURATIONS

In-line - straight line arrangement of workstations

Segmented in-line two or more straight linesegments, usually perpendicular to each other

Rotary (e.g., dial indexing machine)


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Segmented In-Line System Configurations

L-shaped layout

U-shaped layout

Rectangular configuration


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An Example: Two Machining Transfer Lines

with in-line and rectangular system configurations


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Rotary Indexing


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In the ro tary configuration, the workparts are indexed around a circular table or dial. The

workstations are stationary and usually located around the outside periphery of the dial. The

parts ride on the rotating table and are registered or positioned, in turn, at each station for its

processing or assembly operation. This type of equipment is often referred as an indexing

machine ordial index machine.


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The choice between the two CONFIGURATION TYPES depends on the application.

The ROTARY configuration type is commonly limited to smaller workpieces, fewerstations, and has inflexibility in the design (no space for buffer storage capacity). The

number of stations on the dial index machine is more limited due to the size of the dial.

On the other hand, the rotary configuration usually involves a lower-cost piece of

equipment requires less factory floor space.

The IN-LINE configuration type is preferable for larger workpieces, accommodate alarger number of workstations. Also, stations in the in-line configuration can be fabricated

with a built-in storage capability to smooth out the effect of work stoppages at individual

stations and other irregularities.


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THREE Workpart Transfer Typesused in automated production lines

In linearconfigration type:

1) Continuous transfer (motion) not common forautomated systems

2) Synchronous (intermittent) transferall partsmove simultaneously (at the same time)

3) Asynchronous (power-and-free) transferintermittent motion, parts move independently

In Rotary configuration type (indexing mechanisms)

commonly 2)synchronous (intermittent) transfer type

Geneva mechanism

Others


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Workpart Transfer Types

In 1) Continuous transfer, the workparts are moved continuously atconstant speed. This requires the workheads to move during processing in order to

maintain continuous registration with the workpart. Examples of its use are in beveragebottling operations, packaging, manual assembly operations where the human operator can

move with the moving flow line, and relatively simple automatic assembly tasks.

In 2) Synchronous (Intermittent) transfer, the workpieces aretransported with an intermittent or discontinuous motion. The workstations are fixed in

position and the parts are moved between stations and then registered at the proper

locations for processing. All workparts are transported at the same time. Examples ofapplications of the intermittent transfer of workparts can be found in machining operations,

pressworking operations or progressive dies, and mechanized assembly.


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Workpart Transfer Types

3) Asynchronous transfer(power-and-free system) allowseach workpart to move to the next station when processing at the current

station has been completed. Each part moves independently of other

parts. Hence, some parts are being processed on the line at the same

time that others are being transported between stations.

Asynchronous transfer systems offer the opportunity for greater

flexibility than do the other two systems, and this flexibility can be a great

advantage in certain circumstances: a) In-process storage of workparts

can be incorporated into the asynchronous systems with relative ease. b)

Power-and-free systems can also compensate for line balancing

problems where there are significant differences in process times

between stations.

Asynchronous transfers are often used where there are one or more

manually operated stations and cycle-time variations would be a problem

on either the continuous or synchronous transport systems. Larger

workparts can be handled on the asynchronous systems. A disadvantage

of the power-and-free systems is that the cycle rates are generally slower

than for the other types.


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Worpart Transfer MECHANISMSThere are various types of transfer mechanisms used to

move parts between stations. These mechanisms can be

grouped into two types: those used to provide linear travel forin-line machines, and those used to provide rotary motion for

dial indexing machines.

In Linear transfer mechanisms:

A) WALKING BEAM SYSTEMSB) POWERED ROLLER CONVEYOR SYSTEM

C) CHAIN-DRIVE CONVEYOR SYSTEM

In Rotary transfer mechanisms:

D) RACK AND PINION

E) RATCHET AND PAWL

F) GENEVA MECHANISM

G) CAM MECHANISMS


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A) WALKING BEAM MECHANISMWith the walking beam transfer mechanism, the warkparts are lifted up from their

workstation locations by a transfer bar and moved one position ahead, to the next

station. The transfer bar then lowers the parts into nests, which position them moreaccurately for processing.


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A) Walking Beam Mechanism---can only provide linear synchronous transfer (motion)


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C) CHAIN-DRIVE CONVEYOR SYSTEM Either a chain or a flexible steel belt is used to transport the work carriers. The chain

is driven by pulleys in either an "over-and-under" configuration, in which the pulleys

turn about a horizontal axis, or an "around-the-corner" configuration, in which the

pulleys rotate about a vertical axis.

This general type of transfer system can be used forcontinuous, synchronous

(intermittent), or asynchronous movement of workparts. In the asynchronous

motion, the workparts are pulled by friction or ride on an oil film along a track with the

chain orbelt providing the movement. It is necessary to provide some sort of final

location for the workparts when they arrive at their respective stations.


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C) CHAIN-DRIVE CONVEYOR SYSTEMSide view of chain or steel belt-driven conveyor (over and undertype) for linear transfer using work carriers


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ROTARY TRANSFER MECHANISMSD) RACK AND PINION This drive mechanism converts a linear motion into a rotational motion. It is

simple but is not considered especially suited to the high-speed operation ofindexing machines. It uses a piston to drive the rack, which causes the pinion

gear and attached indexing table to rotate. A clutch or other device is used to

provide rotation in the desired direction.


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ROTARY TRANSFER MECHANISMS

E) RATCHET AND PAWL

This drive mechanism converts a linear motion into a rotational motion. It issimple but somewhat unreliable, owing to wear and sticking of several of the

components.


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EXAMPLE FOR Geneva Mechanism

Let us examine the operation of a six-slotted Geneva mechanism. Suppose

that the driver rotates at 6 rpm. Determine the cycle time of the indexing

machine, the process time, and the time spent each cycle in indexing the tableto the next work position.

Note that:

indexing angle=180- (360/n) [proportional to indexing time]

dwell angle= 360-(indexing angle)) [proportional to processing time]

Solut ion:

As indicated above, for a six-slotted Geneva mechanism, the driver spends

120 (=180-(360/6)) of its rotation to index the table, and the remaining 240

(360-120) of rotation correspond to dwell of the table. At 6 rev/min, the cycle

time of the indexing machine is 10s. The portion of this cycle time devoted to

processing (dwell of the indexing table) is 240/360 = 0.667. This corresponds to

6.67 s. The indexing time is 120/360 = 0.333 x 10 s = 3.33 s.


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G) Cam Mechanism for Rotary Transfer Type (Indexing)-- can only provide synchronous intermittent motion

Cam mechanisms provide probably the most accurate and reliable method of

indexing the dial. They are in widespread use in industry despite the fact that the cost

is relatively high compared to alternative mechanisms. The cam can be designed to

give a variety of velocity and dwell characteristics.

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MM 323 MAN SYS 2012 FALL 6 Automated Production Lines PART 1 (1)