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| Hybrid flexible assembly > Hybrid Assembly (2/5) |
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| Posted: Jun.17.2006 @ 3:12 pm |
| A company may be already committed to a certain manufacturing system if
there is prvious investment in capital equipment and tooling.
Additionally, the external dimensions, performance or appearance of the
product may be unchangeable. If a product is only part of a much larger
assembly, the effect of changing a critical dimension may have
expensive consequences for the rest of the much larger assembly. The
performance of the re-designed product must be as good as, if not
better than, the original design. The product may be one where visual
appearance plays an important part in it’s acceptability in the market
place. All of these factors place limitations on the engineer being
able to specify the optimum product design and production system for
that design. It is easier to design the most economic assembly system for a product prior to commercial manufacture. In this case, there won’t be an inherited investment in manufacturing equipment or tooling, and the product design won’t have been finalised. If the product is well established, and has been produced for many years, the assembly systems engineer may be limited to a re-design of the assembly system alone. This is because a re-designed product may require expensive design modifications to the tooling used for the manufacture of the product parts. In these situations, a hybrid assembly system is required to meet the product requirements. A hybrid assembly system uses a mixture of methods during assembly of the product. THE COMPONENTS OF A HYBRID FLEXIBLE ASSEMBLY SYSTEM There are six methods of assembly and the simplest form is MANUAL ASSEMBLY. For high volume production, the operatives usually work on an assembly line. Other forms of manual assembly are a single worker assembling a complete product and groups of workers assembling a portion of the product. For a more limited product range, a MANUAL ASSISTED method may be used, whereby workers are assisted by mechanical devices, such as automated parts feeders. The feeders present the parts to the worker in an ordered manner and the assembly time is reduced by eliminating the time taken to separate the parts from bulk random orientation. The reduction in assembly time is the basis for the economic justification of these devices. The third form of assembly uses AUTOMATIC INDEXING assembly machines. These are rotary or in-line systems with a number of workstations. Automatic feeders supply components to workheads and they assemble the part to the fixture or part-built assembly. The workstations are ‘special-purpose’ and are dedicated to the assembly of only one product. Production volumes need to be high for the economic justification of these machines. Component quality must also be high to avoid excessive downtime caused by components jamming, etc. The efficiency of an AUTOMATIC FREE-FLOW assembly machine is less dependent upon component quality. Transfer of work pieces between workstations is non-synchronous. There are small buffer stocks between each workstation and other workstations may operate whilst one is stopped due to a fault caused by, for example, a defective part. The AUTOMATIC PROGRAMMABLE assembly machine has a non-synchronous transfer line and programmable workstations to assemble the parts, which are presented to the workheads by automatic feeders or, in the case of difficult components, part magazines may be used. The workheads execute one, or a number of, operation(s). Different computer programs, for each series of assembly processes, give the flexibility to assemble a variety of product styles on one assembly machine. Robotic assembly is used for the assembly of products with large product variety, required in low volumes. Assembly operations are carried out by a robot which, itself, transfers the completed product onto the next operation. |
| Hybrid flexible assembly > Hybrid Assembly (3/5) |
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| Posted: Jun.16.2006 @ 12:57 pm | Lasted edited: Jul.29.2006 @ 5:33 am |
THE DESIGN OF HYBRID FLEXIBLE ASSEMBLY SYSTEMS
The assembly process has two constituent parts and these are; the
handling of components and the insertion of components. The design
features of a part must be examined to decide if it can be
automatically handled automatically or if it must be handled manually
or placed in magazines. Similarly, the insertion process must be
analysed to decide what type of workhead is required.Various organisations have developed procedures that help the designer to estimate how easy it is to handle and orientate components by assigning a handling code to each part. The maximum feed rate and relative cost of the feeding method can then be estimated from this code. The parts which would require expensive automatic feeders or which could not be fed at the required feed rate can be identified. These parts must then be handled manually or in magazines/pallets. Additionally, certain parts cannot be handled automatically because they have other bad feeding qualities, e.g. they may be flexible or too light. The previously mentioned estimation systems also help the system designer to forecast the relative cost of the workhead required to insert a part into a part-built assembly. Those operations which require a complex path of insertion, or a large thrust, require more expensive workheads than for simpler operations. A list of parts (with their associated automated handling codes) and a list of operations (with their allocated automatic insertion codes) can be constructed from the preceding information. If the product parts are listed in order of increasing handling difficulty levels then the most economical method of feeding a part to the workhead can be determined. Parts with low handling difficulty levels are fed by conventional vibratory feeders and, as the difficulty level increases, specially designed feeders/magazines/pallets/manual handling are used. The relationship between the handling difficulty level and the type of feeder to be used depends upon the required return on investment for the equipment. The insertion operations can also be listed in order of insertion difficulty levels to determine the most economical method of insertion of a part into a part-built assembly. Greater difficulty levels can mean that the equipment is more expensive and, for assembly robots, more degrees of freedom are required for an insertion operation. If the difficulty level is too high then it’s necessary to employ manual workers for some operations. When an assembly system is designed for a new product, the cost of parts handling and insertion can be reduced through re-design of the product. It’s usually not viable for an existing product to be re-designed, because of the tooling modification cost in the manufacture of the parts. Inevitably, therefore, the most economical method of assembly is limited to the existing product design, without design efficiency improvements. The assembly handling and insertion codes determine which feeding method and insertion device are most appropriate for each part and operation. The part-built assembly has to be transported to each workstation between operations. This will either be synchronous or non-synchronous motion. Synchronous machines are generally less expensive than non-synchronous types, but they are limited by how many parts can be assembled on one machine. This is due to downtime and the space available. It is desirable to construct a product from as many sub-assemblies as possible to achieve a high overall efficiency of the assembly system. These sub-assemblies should be common to all product styles, within the family of products. The variety can then be created in the final assembly of the product. If this approach is adopted then sub-assemblies will be required at a rate which is enough to justify the use of automatic indexing machines having dedicated workheads. The output from these machines can then be sent to the final assembly line via free transfer lines, to create a buffer stock of sub-assemblies. The buffer stock is necessary to minimise the effect of any indexing machine downtime. |
| Hybrid flexible assembly > Hybrid Assembly (4/5) |
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| Posted: Jun.15.2006 @ 10:01 pm | Lasted edited: Jul.29.2006 @ 5:38 am |
CASE STUDY - THE DESIGN OF A HYBRID FLEXIBLE ASSEMBLY SYSTEM FOR SPEEDOMETERS
The case study describes how a hybrid flexible assembly system was
designed for the assembly of a mechanical drag cup speedometer. This
type of speedometer is the most widely used today and its design has
not changed over the last 50 years. If there is already a heavy
investment in capital equipment for the manufacture of the individual
parts then it is not economical to re-design the product for automatic
assembly.The input shaft of the speedometer carries a permanent magnet. The flexible drive shaft from the engine drives the input shaft, thus setting up a rotating magnetic field. A metallic cup is situated in this field and is continuously connected to the pointer. As the input shaft rotates, a torque is produced at the spindle, which is proportional to the speed of the input shaft. The spindle is free to rotate and yet is restrained by a delicate hairspring. The spring rate is chosen to be linear over the range of the spindle angular deflection, thus providing a pointer movement that is proportional to the input shaft speed. The hairspring returns the pointer to zero when the vehicle is at rest. A series of gears from the input shaft convert the rotation of the flexible drive shaft to a rotation of the odometer wheels. Gear ratios typically vary from 600:1 to 2000:1. There are 25 parts used in the assembly of the speedometer and more than 50 product styles can be obtained by a variation in the design of six parts. These are the dial, second worm gear, third worm gear, odometer sub-assembly, hairspring and pointer sub-assembly. The total annual production volume for all the styles is in excess of one million units. An individual style may be required in volumes between 200 and 200,000 per year. Clearly, these volumes require an assembly system which has flexibility to handle such large demand fluctuations. The speedometer consists of four sub-assemblies and twelve parts. The dial sub-assembly has three parts, the first worm sub-assembly has six parts, the speed cup sub-assembly has two parts and the frame sub-assembly has two parts. Each sub-assembly is a self-contained unit and does not require any holding of the parts for stability between workstations. Synchronous assembly machines are most economical for the high volume assembly of a small number of parts. Each sub-assembly contains six or less parts, making them most suitable for this method of assembly. 
A rotary indexing machine for the FRAME SUB-ASSEMBLY is used for the
assembly of two components. There are eight workstations on this
machine to allow for non-value adding operations in addition to the
direct insertion process. The handling difficulty level of the bearing
means that it is presented by a specially designed feeder. It is
impregnated with oil and this doesn’t allow the part to be handled by a
conventional vibratory feeder. The frame cannot be handled by an
automatic feeder because it is large and has no symmetry about any
axis. The complex shape of the frame means that it cannot be magazined
and it is, therefore, palletised. A robot places the frames onto the
machine because they are picked from several hundred pallet locations.
The rotary indexing machine for the SPEED CUP SUB-ASSEMBLY uses a
simple pressing operation to secure the speed cup to the spindle. There
are four workstations for; the assembly of the spindle to the fixture,
the speed cup to the fixture, the pressing of the speed cup onto the
spindle and an output station. Both parts are fed by vibratory bowl
feeders and inserted by dedicated workheads.The FIRST WORM SUB-ASSEMBLY consists of six components, all of which are fed by vibratory bowl feeders. The indexing machine uses ten dedicated workstations to complete the sub-assembly. The first worm shaft is burnished before final assembly. This operation is executed after the rotary indexing machine, on a free-transfer line. Two burnishing stations are used, in parallel, to achieve the cycle time. The free transfer line also provides a buffer stock of completed sub-assemblies before the final assembly line. The rotary indexing machine for the DIAL SUB-ASSEMBLY assembles three parts. Only the pointer stop can be automatically fed and so the dial and label use special feeding methods. Different designs of dials are used to create product variety. However, only the print face and diameter of the dial are variable and the dial is picked from a magazine, on the reverse face, by a dedicated workhead. The label is applied by a conventional labelling device. All sub-assembly indexing machines are linked to the final assembly machine by free-transfer lines, for overall system efficiency. This also creates space for auxiliary operations to be carried out on the sub-assemblies before final assembly. The speed cup sub-assembly is dynamically balanced before final assembly, and this is done with the aid of two robots. The programmability of a robot is required for the 'decision making' operations of this process. Feedback from the balancing machine determines whether the sub-assembly has to be balanced more than once or, in the case of it being excessively out of balance, it is rejected. There are twenty six workstations used for the FINAL ASSEMBLY of the speedometer, making it necessary to use a free-transfer linear machine to allow buffer stocks to be created between each workstation, to maintain high system efficiency. Of the twelve parts used during final assembly; seven parts are handled by conventional vibratory bowl feeders, two parts by multiple vibratory feeders, one part by pallet, one part by manual handling and the remaining part by actual manufacture on the assembly line. The parts which are fed by vibratory feeders are small components with either useable symmetry or definite asymmetry. These are inserted into the part-built assembly by dedicated workheads. |
| Hybrid flexible assembly > Hybrid Assembly (5/5) |
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| Posted: Jun.14.2006 @ 5:49 pm | Lasted edited: Jun.14.2006 @ 10:52 am |
| The two parts to be handled by multiple vibratory feeders are the
second worm gear and the third worm gear. These parts are changed to
produce the various gear ratios used to create different product
styles. The disruption to production, during product changeover, is
minimised by using a group of vibratory feeders which deliver one
particular second or third worm. The pick up point of the workhead is
thus quickly changed to the output of a particular feeder for the
assembly of a different style. The jewel--plate sub-assembly is a large and delicate part which cannot be fed by an automatic feeder. It can, however, be palletised. A robot picks up the jewel-plate sub-assembly from the pallet and inserts it into the part-built assembly. The operation is relatively complex and an operator has been retained at this station to assist the robot when difficulties arise. The hairspring is a delicate part that can’t be handled by an automatic feeder. The insertion process is also difficult because the end of the spring is welded to a stub on the jewel plate. This part is assembled manually by two workers in parallel, because of these difficulties. The second worm gear retaining pin is manufactured from wire and it is most cost effective to manufacture this part on the final assembly line by a guillotining operation. The bending of the pin is carried out simultaneously to the part being inserted and secured. CONCLUSIONS 1) Product re-design for ease of assembly creates worthwhile savings in assembly costs. However, particularly for large products, these cost savings must be offset against the additional tooling modification costs for the manufacture of re-designed components. 2 ) When assembling a product which has : a) Many parts b) Many variants in the product family c) A large annual production volume d) Many common sub-assemblies a hybrid flexible assembly system is required and it will combine manual, automatic and robotic assembly methods. 3) Sub-assemblies, having a fixed content, are always best assembled on dedicated automatic assembly machines. 4 ) Variable content sub-assemblies are most economically assembled using either a) Assembly robots b) Flexible free-transfer machines 5) Transfer between sub-assembly production units and final assembly need large buffers to de-couple these two activities and reduce downtime. |
| Changes in assembly work > Assembly Evolution (1/7) |
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| Posted: May.23.2006 @ 9:38 am | Lasted edited: Jul.29.2006 @ 5:40 am |
I originally published this article under the title, “Changes in Assembly Work Environments” in the book “Programmable Assembly”, ISBN 0.903608.65.0.
The role of the modern assembly worker is very different now from that
of 3 generations ago. Improvements in parts quality consistency has
eliminated the previously required skill of the apprentice trained
fitter. A new breed of unskilled assembly workers has been created,
through the division of labour, to carry out repetitive and mundane
tasks. However, many companies use assembly automation if it can
be economically justified, and after the product has been re-designed
for automatic assembly.The development of modern assembly techniques is discussed, together with future trends in manual and automatic assembly. Emphasis is given to the changing needs of the people directly involved in these assembly operations. Introduction There has been a rapid increase in living standards in the developed nations throughout the previous century, mostly due to the application of technology to manufacturing. The mass production of goods has made many items available at economic prices. Homemakers now have a multitude of labour saving devices to reduce the amount of time spent on household chores. This has enabled many homemakers to work in factories which produce these goods. Assembly workers can master a simple assembly task and repeat it for more than 1000 times per day; every day. Working with other people on an assembly line can create a sense of cooperation within a joint effort. However, there has been criticism of the assembly line technique. It is argued that the repetitive work is boring and tedious and that workers no longer gain satisfaction from doing their job. Workers never see the finished product and the continual repetition of movements creates boredom. Industrial unrest in high volume manufacturing companies has been associated with the job dissatisfaction of assembly line workers. Manufacturers now realise that the economic benefits of the division of labour have to be judged alongside the sociological and psychological disadvantages. The use of assembly automation during product manufacture eliminates worker dissatisfaction with repetitive work, since most of the mundane tasks are done by machines. Workers are then used to fill magazines/feeders and to maintain the equipment. The reduced labour content often creates a cost reduction in the finished goods. The culmination of this desirable process is an increase in leisure time, through a reduction in the working week. Emphasis must then be placed on how people are to spend their leisure time. This should be the subject of major reform in our training establishments. |
| Changes in assembly work > Assembly Evolution (2/7) |
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| Posted: May.22.2006 @ 9:20 am | Lasted edited: Jul.29.2006 @ 5:50 am |
| Technology Technology is the systematic knowledge of the industrial arts. Industrial engineers have been applying technology to the workplace for over two centuries. Manufacturing systems analysed by method and time studies have been improved by the division of labour, automation and robotics. Large productivity improvements have been achieved by applying technology to manufacturing processes. From the mechanisation of flour production to the robotic assembly of vehicles, process costs have been reduced. The application of technology to the motor industry has resulted in vast increases in productivity. 
Method study is concerned with the dissection of a complex operation
into it’s single constituent parts, which are then systematically
analysed. The method study engineer synthesises the complete operation
using components which optimise factors such as symmetry and the rhythm
of movement.
The time study engineer measures the time taken to carry out an
operation. The analysis is carried out in a systematic manner and it
makes this form of study suitable only for simple and repetitive tasks.
Often, time study exposes inefficient operations and these can then be
analysed using method study.It was the use of both method and time studies that led to the wide-scale use of the division of labour and the creation of the assembly line concept. Workers grouped on lines achieve productivity levels many times greater than single operatives making the entire product. Automation has also produced large productivity increases by replacing men with machines. In highly automated manufacturing plants, the operator controls and supervises the process. The main power olders in future societies will not be capitalists or socialists, but people who possess expert technological skills. In this way, power will be passed to the techno-structure. Automation Automation in the manufacturing industries covers a whole range of electrical and mechanical equipment. In the field of automatic assembly, devices are used for automatic feeding and insertion. In addition, work transfer is by conveyor or rotating table. The type of system used for the assembly of a product is dependent upon many factors. The local cost of labour affects the economic justification of using automation to replace that labour. The frequency of design changes and the number of product styles dictate how flexible the equipment needs to be. The market life of the product influences the amortisation period of the capital investment. Finally, the annual product volume determines the required cycle time. In addition to the above economic considerations, another reason for employing automatic assembly may be one of necessity. In certain areas, where labour is scarce, the use of automatic assembly is imperative. Certain operations may be hazardous or they must take place in dangerous working conditions. For example, the handling of toxic chemicals or working in extreme temperature conditions may exclude the use of manual workers. A further reason may be associated with the scheduling of the assembly operations: better control over production can be achieved with automation and product quality will be more consistent. |
| Changes in assembly work > Assembly Evolution (3/7) |
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| Posted: May.21.2006 @ 12:53 pm | Lasted edited: Jul.29.2006 @ 5:51 am |
| The assembly operation consists of the two basic activities of handling
and insertion. If a product is to be assembled automatically then
thought has to be given to the economics of these activities. The
automatic feeding of simple parts is usually carried out using a
vibratory bowl feeder. Components in bulk random orientation are placed
into the feeder and the parts are presented to the workhead in an
ordered manner. Difficult parts may be fed by special feeders, hoppers
or by magazines. The insertion process is defined as being the action
where one part is assembled to another part, or group of parts. High
speed operations, where the same parts are inserted for long periods of
time, are normally effected by standard pick-and place units. Difficult
operations, involving the assembly of a number of different parts with
different operations may require assembly robots. The flexibility
of the robot is created by using computer programs to control the robot
arm movements. The difference between a robot and a pick-and-place is
that the path of the robot arm is not restricted by mechanical means,
whereas pick-and-place units rely upon mechanical stops to determine
the path they follow. Division of labour 
The division of labour is the process whereby one complex operation is
broken down into a number of simpler tasks. These single tasks are
carried out using a series of people, each doing one task. In this
manner, a complex task performed by one worker is replaced by a number
of workers operating in series. This allows operations to be carried
out simultaneously, instead of the single operator having to complete
one task before commencing another, different task. Unskilled workers
can then be used to carry out these simple operations and they soon
become efficient at the particular task.Assembly systems An assembly method can be classified into one of six types, and most systems may contain a number of different methods. The traditional form of assembly is manual and, for high volume production, the workers are arranged on an assembly line. Other forms of manual assembly include a single worker assembling a complete product and groups of workers assembling a portion of the product. When the range of products is more limited, a manual assisted method can be used, whereby workers are assisted by mechanical devices, such as parts feeders. The feeders present the parts to the assembly worker in an ordered manner. The assembly time is reduced by eliminating the time taken to separate the parts from bulk random orientation. The third form of assembly uses automatic indexing assembly machines. A rotary or in-line machine has a number of workstations with automatic feeders which supply components to workheads for assembly of the part to the fixture, or part-built assembly. The workstations are 'special-purpose' and are dedicated to the assembly of one product only. Production volumes need to be high for the economic justification of these machines. Component quality must also be high to avoid excessive workstation downtime, caused by jamming, etc. |
| Changes in assembly work > Assembly Evolution (4/7) |
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| Posted: May.20.2006 @ 5:37 pm | Lasted edited: Jul.29.2006 @ 5:55 am |
| The efficiency of an automatic free-flow assembly machine is less
dependent on parts quality. The transfer of work pieces between each
workstation is non-synchronous. Small buffer stocks are held between
each workstation and the other workstations still operate even if one
is stopped because of a fault, e.g. a defective part jammed in the
escapement mechanism. The programmable automatic assembly machine has a non-synchronous transfer line with a series of programmable or robotic workstations to assemble components. Parts are presented to the workheads by automatic feeders or, in the case of difficult components, magazines may be used. The workheads can execute one or a number of operations. Flexibility is acheived by using different programs for each product to be assembled. The final type of assembly system is robotic assembly and it is used for the assembly of products manufactured in low production volumes. This method can also be used when there is large product variety. Work transfer is not by conveyor, as all the assembly operations are carried out by a single robot. Transfer of the completed sub-assembly onto the next operation may also be done by the same robot. The direct labour content in assembly is reduced in the progression from manual assembly to robotic assembly. However, the complexity of the equipment increases as workers are replaced by machines. Indirect labour also increases for the maintenance and computer control of the equipment. Economic aspects The application of technology to manufacturing is used to increase productivity and the selection of a system for the economic assembly of a product depends upon a number of factors. The final selection must take into account the following: 
- Market life of product - influences the decision of the company on
investing in capital equipment. Products with short market lives are
usually assembled manually.- Variations in demand - Automatic assembly machines are designed to operate with fixed cycle times. Low demand leads to increasing stock levels or the machine has to be stopped. Both of these actions are expensive. Flexibility to assemble different types of products is needed if there are large demand variations. This flexibility can only be provided by manual assembly or programmable machines. - Parts quality- Automatic assembly machines are intolerant of defective parts and they can cause a station to breakdown. Whilst inter-station buffers will reduce the effect on efficiency, manual assembly is necessary for products that use low quality parts. - Number of products - to be assembled by a system determines how flexible it needs to be. Different products manufactured in high volumes can be assembled using programmable workheads. Smaller volumes require manual assembly. - Major design changes - Products subject to frequent design changes need flexible assembly systems, in a similar way to systems used to assemble a variety of products. |
| Changes in assembly work > Assembly Evolution (5/7) |
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| Posted: May.19.2006 @ 12:57 pm | Lasted edited: Jul.29.2006 @ 5:56 am |
 - Company investment potential - Assembly system selection is
influenced by the company's policy towards investing in automation.
If the company requires a payback period of less than one year then it
is unlikely that any form of automated assembly system can be
economically justified.- Annual production volume – This determines the cycle time of the system and automatic systems must run continuously to be justified. If the annual volume is low then the product must be assembled manually. - Number of parts – This dictates whether the product should be assembled in a series of simple operations or in a single, complex operation. Automatic indexing machines cannot be used for the assembly of more than 8 parts on a single machine. The downtime caused by defective parts rapidly increases for every part above this value. Free-flow transfer should be used for products containing a large number of parts. Social aspects The application of technology to the assembly environment has sociological and psychological effects. The economic advantages of certain assembly systems can produce serious social disadvantages. These social effects are not limited to the confines of the factory and they affect the whole of society. Assembly line work can provide jobs for people challenged with limited abilities. They can soon acquire a skill for a specific task and take pride in doing a job that may seem uninteresting to other people. Working with others on an assembly line often brings a worthwhile feeling of cooperation in producing goods required by society. Some people enjoy the fact that they can start a job and, with minimal training, soon be earning a bonus on piece-rate assembly lines. A highly specialised assembly task, requiring little dexterity, gives this opportunity. The correct candidate can be selected for an assembly line job by using aptitude and vocational tests. There is scope for job rotation and managers can circulate workers so that they don’t have to do the same operation for long periods. Job rotation also gives the manager with a labour force able to do many operations. This is beneficial to the company when there is a high rate of absenteeism. The assembly line workers soon adopt a rhythm of working, as they do not have to set aside one tool to pick up another. 
Many assembly line workers don’t want to use mental effort and choose
not to accept responsibility in a job. They prefer to execute a task
that allows them to simultaneously talk with their colleagues and
listen to music. The workers are also able to take advantage of the
reduced selling price of goods assembled by the flow-line method,
available in high street stores. They can buy goods that would normally
be outside their budget, were it not for the division of labour. Low
priced home appliances like washing machines and vacuum cleaners reduce
the amount of time required to do work around the household. Homemakers
find that they are more available to work on an assembly line, earn
money and to gain companionship in a work environment. |
| Changes in assembly work > Assembly Evolution (6/7) |
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| Posted: May.18.2006 @ 11:46 pm |
| The social advantages of assembly line work must be considered
alongside the often serious psychological disadvantages. There can be a
loss of job satisfaction when the worker is not involved in all of the
assembly processes that lead to the finished product. The job is
repetitive and some workers are unable to take much pride in the task
itself, as they don’t have the opportunity of seeing how important
their operation is to the successful completion of the product. Boring
work may suppress the creative ability of the worker and their time out
of work may be spent so passively that life goals may disappear. The
effect of carrying out monotonous work is often excessive fatigue. With
the decline in individual craftsmanship, many unskilled operatives have
no opportunity to display their creative talent at work. Goods built on
an assembly line lack the variety that can be created by craftsmen.
This dull product uniformity can have an adverse effect on some workers
who see the same product every 20 seconds or 1350 times a day. Assembly lines are usually installed in factories with a large workforce. Each group within the factory is dependent upon the other for the manufacture of the product. Strike action by one group of workers may affect the production of the whole factory. The assembly worker output is effective only during the time spent doing tasks. The cycle time is fixed by the conveyor speed and so it is the periods of time spent off the job that reduce the output. These psychological problems often cause the assembly worker to create avoidable delays in which they try to gain control of the rate of work. The social effects of automation are different from those of the division of labour. Many of the simple operations carried out by assembly workers can be substituted with automatic workstations. By replacing workers with automation, these repetitive tasks are executed by machines. The displaced workers are then available to carry out other, less tedious, tasks like supervision and inspection. The automatic assembly machines must be fully utilised to be economically justified. Dedicated automatic assembly machines are less flexible than manual assembly lines. The products must be assembled in large batch sizes. Overproduction and under-consumption lead to inefficiency. Severe demand fluctuations and gross lack of demand can’t be accommodated with assembly automation. Behavioural scientists say that technology can be applied to assembly without employing automation. They believe in job enlargement/enrichment and argue that the division of labour has been taken too far, to produce boring and repetitive assembly line jobs. Job enlargement increases the number of tasks completed by a single operator and this is intended to give more interest and variety to the job. The same grade of worker does more complex operations. The net effect of job enlargement is a reduction in the number of operators per assembly line, an increase the cycle time and more flexibility, but an overall increase in assembly costs. |
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