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Definition

•The use of mechanized and automated devices to perform various assembly tasks in an assembly line or cell

•Designed to perform fixed sequence of assembly steps on a specific product

Automated Assembly Systems

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When to use Automated Assembly System

•High product demand•Stable product design •A limited number of components in the assembly•Product designed for automated assembly

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•Automated assembly system involve significant capital expenses, but it is generally less than for the automated transfer lines.1. Work units produced on automated assembly system are usually smaller2. Assembly operation do not have the large mechanical force and power requires of processing operation such as machining

•Automated assembly system tends to physically smaller, reduces the cost of system

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Fundamentals of Automated Assembly System

•Performs as sequence of automated assembly operations

1.Combining multiple components into a single entity

2. Single entity can be final product or a subassembly in larger product

3. Assembly is completed progressively

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Subsystem of Automatic Assembly System

• One or more workstation which the assembly steps are completed

• Part feeding devices that deliver the individual components to the workstation

• A work handling system for the assembled entity

1.Automatic Assembly System with 1 workstation, work handling system moves the base part into and out of station

2.Automatic Assembly System with multiple workstation, handling system transfers the partially assembled part between stations.

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AUTOMATED ASSEMBLY SYSTEMS

1. Design for automated assembly2. Types of automated assembly

systems3. Parts feeding devices4. Analysis of multi-station assembly

machines5. Analysis of a single station assembly

machine

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Design for automated assembly

The methods traditionally used for manual assembly are not necessarily the best methods for automated assembly

Ex: The use of a screw, lock washer and a nut to fasten two sheet metal parts1.The position of holes through which the screw must be inserted are different for each screw2.The screw holes between the two sheet metal parts have to be positioned properly for inserting the screw3.The operator must juggle three separate hardware items (screw, lock washer and nut) to perform the fastening operation4.A sense of touch is necessary to make sure that the nut is started properly onto the screw thread

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Design for automated assembly

• The methods traditionally used for manual assembly are not necessarily the best methods for automated assembly

• For assembly automation to be achieved, fastening procedures must be devised and specified during product design that do not require all of these human capabilities

• It is difficult to design assembly machines which have human like capabilities, such as, intelligence, dexterity, manipulating multiple tasks and problems, etc

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Automated AssemblyProduct design principles

1. Reduce the amount of assembly required• Combining functions within the same part• Use plastic molded parts in place of sheet metal parts

2. Use modular design• Design of product should be modular• Each module requiring around 10 to 12 parts to be

assembled on a single assembly system• Subassembly should be designed around a base part to

which other components are added

3. Reduce the number of fasteners required• Design the fastening mechanism using snap fits and

similar features• Design such that several components are fastened

simultaneously rather than each component fastened separately

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Automated AssemblyProduct design principles

4. Reduce the need for multiple components to be handled at once

• separate the operations at different stations rather than to handle and fasten multiple components simultaneously at the same workstation

5. Limit the required directions of access•Ideal situation is to add components vertically from above

6.Maintain high quality in components•Poor quality components cause jams in the feeding and assembly mechanisms

7.Implement hopperability•For ease of feeding and orienting parts

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Types of Automated Assembly Systems

Based on the type of work transfer system:

1.Continuous transfer system2.Synchronous transfer system3.Asynchronous transfer system4.Stationery base part system

Based on physical configuration:

1.Dial type assembly machine2.In-line assembly machine3.Carousel assembly system4.Single-station assembly machine

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Factors that influence type of work transfer system1. The types of operations to be

performed2. The number of stations on the line3. The weight and size of the workparts4. Whether manual stations are

included on the line5. Production rate requirements6. Balancing the various process times

on the line

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Continuous transfer system

• Workparts are moved continuously at constant speed

• Workhead is required to move during processing in order to maintain continuous registration with the workpart

• This may pose inertia problems due to size and weight of the workheads

• Relatively easy to design and fabricate and can achieve high rate of production

• Example: Beverage bottling operations

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Synchronous transfer system

• Workparts are transported with an intermittent or discontinuous motion

• Work stations are fixed in position and the parts are moved between stations and then registered at the proper location for processing

• All workparts are transported at the same time, and hence the name synchronous transfer

• Examples: Progressive dies, mechanised assembly, machining operations, etc

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Asynchronous transfer system• Each part moves independently of other parts

• Referred to as a ‘Power-and-free system’, allows each part to move to the next station when processing at the current station has been completed

• In-process storage of workparts can be incorporated with relative ease

• Can also compensate for line balancing problems

• Disadvantage is that the cycle rates are generally slower than for other types

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Pallet Fixtures

• Workparts are attached to pallet fixtures and the pallets are transferred between stations

• The Pallet fixture is designed so that it can be conveniently moved, located and clamped in position at successive stations.

• Another advantage of pallet fixtures is that they can be designed to be used for a variety of similar parts

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Dial type assembly machine

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Dial type assembly machine

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Dial type assembly machine

• Base parts are loaded onto fixtures that are attached to a circular dial

• Components are added and/or fastened at various workstations located around the periphery of the dial

• The dial indexing machine is the most common system in this category

• It operates with a synchronous or intermittent motion

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In-line assembly machine

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In-line assembly machine

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In-line assembly machine

• Consists of a series of automatic workstations located along an in-line transfer system

• Continuous, synchronous or asynchronous transfer systems can be used with the in-line configuration

• For synchronous transfer of work between stations, the ideal cycle time equals the operation time at the slowest station plus the transfer time between stations

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Carousel assembly system

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Carousel assembly system

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Carousel assembly system

• It represents a hybrid between the dial assembly system and In-line system

• It can be operated with continuous, synchronous or asynchronous transfer mechanisms

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Single-station assembly machine

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Single-station assembly machine

• Assembly operations are performed at a single location

• First, a base part is placed at the workstation where components are added to the base

• Components are delivered to the station by feeding mechanisms

• One or more workheads perform the various assembly and fastening operations

• Typically uses robotic assembly

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•Once all the components have been assembled onto the base part, the base part leaves the system.

•Inherently slower than the other three system configurations, as only one base part is processed at a time.

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Parts Delivery at Workstations

•Parts delivery to workstations depends upon specific pieces of delivery equipment, particularly associated with automatic assembly. These pieces of equipment are connected together to create the parts delivery system. The following hardware for parts delivery consists of:

•Hopper—a container into which components are loaded at the workstation, and which passes components to the parts feeder

•Parts feeder—a mechanism used for removing components from the hopper, and passing them to the feed track; the parts feeder is often connected to the hopper to form one unit

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•Selector and/or orientor—devices found on the feedtrack that establish the proper orientation of the components for the assembly workhead: a selector is a filter device that only-correctly oriented parts to pass; while an orientor re-orients parts that are not properly oriented initially on the feed track

•Feed track—the pathway along which the components pass from the hopper and parts feeder to the assembly workhead, whilst maintaining proper orientation of the parts via selectors/orientors along the way; it generally operates by gravity, though powered feed tracks (operated by vibratory action or air pressure) may also be encountered

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•Escapement and placement devices—devices used to remove components from the feedtrack (escapement), and to place them at the workstation for the assembly operation (placement); there are a number of different device designs to accomplish this

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The general arrangement of Part Delivery System

Hardware elements used to delivery parts to workstations

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The hopper and parts feeder device are often combined, as shown schematically and pictorially

Hopper and parts feeder

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Typical selector and orientor devices

(a) Selector and (b) orientor devices used upon the feedtrack

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Escapement and placement devices

Horizontal placement device

Device used on dial-type assembly machines: parts move via horizontal delivery into vacant nests on the dial, as they appear, from the feed track; meanwhile the circular motion of the dial table means that the nests are revolved away from the feed track, permitting the next component in the feed track to move into the next vacant nest, and so forth.

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Vertical placement device

Device used on dial-type assembly machines: here, the parts feeder is arranged vertically above the dial table, so that when the table turns, to reveal an empty nest, the component can fall by gravity from the feed track into the empty nest. Successive parts fall by gravity to take up their position at the mouth of the feed track in turn.

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Escapement device

This device is actuated by the top of the carrier contacting the lower surface of the rivet-shaped part, causing its upper surface to press against the spring blade, which releases the part so that it falls into the work carrier nest. The work carriers are moved horizontally to cause the release of the part, and—after the first part has escaped—the work carrier and released part move off, to be replaced by the next work carrier, and so forth.

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Pick-and-place mechanism (1)

This mechanism uses a pick-and-place unit with a horizontal arm that may be extended and retracted as necessary, so that parts may be removed from the feed track, and placed into work carriers.

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Pick-and-place mechanism (2)

This mechanism uses a pick-and-place unit with a revolving arm, so that parts may be removed from the feed track, and placed into work carriers.