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ASSEMBLY Flashcards

1
Q

What is an ASSEMBLY?

A

Assembly systems are systems which join together components (coming from systems making the parts production or subassemblies) in order to obtain finished products.

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2
Q

What is MANUAL ASSEMBLY SYSTEMS?

A

Manual assembly systems are composed of several stations in which one or more workers executes assembly activities. Stations are linked through a handling system (or transfer system).

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3
Q

What is the main resource in manual assembly systems?

A

The Workforce

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4
Q

WHat is the advantage of the Manual Assembly system?

A

FLEXIBILITY. It depends on the number of the activities of workers.
Workers are versatil and can do several operations

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5
Q

What is the disadvantage of the Manual Assembly System?

A

VARIABILITY OF ASSEMBLY TIME. It also depends on the number of activities of the workers.

It entails a callenge in the balancing of workload

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6
Q

Which are the different configuratons of the ASSEMBLY SYSTEMS?

A
  • Fixed position assembly
  • Assembly Shop and Assembly Cell
  • Assembly Line
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7
Q

What is the Fixed Position Assembly?

A

The product does not move while it is assembled. All the parts are brought to the workstation. All the assembly activities are done within the workstation.

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8
Q

For which kind of products the Fixed Position Assembly is applied?

A

For heavy products, difficult to move. They need to be assembled without being handled.

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9
Q

What is the critical point of the Fixed Position Assembly?

A
  • Material handling system for material feeding: It needs to move more components and different ones (different families)
  • Material handling system for the assembly product.
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10
Q

What is the Assembly Shop?

A

The product to be assembled has to move through different workstations. There is no rigid transport system

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11
Q

What is the Assembly Line?

A

Thw workers are stationary in the workstations and a transfer systems moves the semi-finished assembled product through them, where the parts are added in a sequential way.

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12
Q

Which are the types of transfer?

A
  • Synchronous: Abscence of buffers b/w the workstations
  • Asynchronous: Buffers b/w the workstations
  • Continous: Operators work together with the assembly line while make the operations.
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13
Q

What are the definitions to classify the ASSEMBLY SYSTEMS configurations?

A
  • Variety
  • Repetitiveness
  • Flexibility
  • Volume
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14
Q

What does VARIETY entail?

A

Variety in terms of product tyoes, product families

Variety in opertions done in the workstations

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15
Q

What does REPETITIVENESS entail?

A

Repetion of the operations done by/assigned to the operators in the workstations.
(As opposed to VARIETY)

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16
Q

What does FLEXIBILITY entail?

A

Ability to react to internal or external changes with low effort and costs in terms of time, money, production capacity, etc.
Flexibility entail both assembly operations and material feeding

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17
Q

What does VOLUME entail?

A

Ability of the assembly system to assemble a given range of volumes of assemblies (as opposite to flexibility)

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18
Q

Assembly systems – general features?

A
  • Technology
  • Management
  • Cost structure
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19
Q

Assembly systems – general features - TECHONLOGY?

A
  • Components assembly to make groups, sub-groups and finished products.
  • Operation can be reversible (or irreversible, e.g., welding)
  • Free technology route, with degrees of freedom
  • Low relevance of process technology parameters
  • Process flow is synthetic
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20
Q

Assembly systems – general features - MANAGEMENT?

A

Relevance of management (WIP, Lead Time, delay..)

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21
Q

Assembly systems – general features - COST STRUCTURE?

A
  • Low relevance of fixed assets (“activos”), depending on the customization and utilization
  • A lot of manual operations cause relevance of workforce utilization
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22
Q

By what is the ASSEMBLY SYSTEM composed?

A
  • Workstations

* Handlying systems (belts, rollers, etc) for parts & WIP’s (assembies and sub-assemblies)

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23
Q

What about the assembly tasks ?

A

Do not require specific tools

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24
Q

What about the feeding of material?

A

Assembly needs correct feeding systems:

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25
Q

General features - Three independent axes for classification?

A
  1. Layout configuration
  2. Production mix management
  3. Task organization
  4. Reciprocal movement of assembly, worker and components.
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26
Q

What is the classification according to LAYOUT CONFIGURATION?

A

If it is Fixed Position Assembly or Assembly Shop for instance.

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27
Q

What is the classification according to PRODUCTION MIX MANAGEMENT?

A
  • single model
  • multi model
  • mixed models
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28
Q

What about Single Model and its Pros & Cons?

A

-It is focused on only one product type:
Suitable for high volume od prodcution, linked to high and stable demand

Pros:
- Low management issues
Cons:
- Low flexibility

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29
Q

What about Multi Model?

A

More product-types are assembled on the same system: Bath production

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30
Q

What Multi model entails?

A

Setup times are relevant

CT and Number of workstations depend on the product to be assembled.

31
Q

What Multi model requires?

A
  • Good balancing
  • Good scheduling
  • High inventory because usually demand is not satisfied.
32
Q

What Multi model Pros & Cons?

A

Pros:
*Opportunity to follow the demand
Cons:
* Mandatory to reduce setup time
* Good scheduling
* Difficult to manage the flow of components
* Difficult to manage parallel workstations

33
Q

What is the classification according to TASK ORGANIZATION?

A

It is the classification according to the reciprocal movements:

  • Operator-Assembly:
  • Operator -> Assembly
  • Assembly -> Operator
  • Assembly - Component
  • Assembly -> component
  • component -> Assembly
34
Q

What is the Assembly Cycle?

A

Sequence of operations needed for the assembly

35
Q

Which are the methods to calculate Assembly Times?

A
  1. Work sampling
  2. Standard times
  3. Mtion Time Measurement (MTM)
36
Q

Work sampling method?

A

It consists in the observation of specific assembly operations and in the calculation of the average duration and standard deviation .

A drawback of the method is that it requires the availability of a real assembly station to monitor and collect data.

37
Q

steps of Work Sampling method ?

A

Step 1: Choose and identify the assembly operation to monitor
Step 2: Inform the operator of the work sampling study
Step 3: Divide operation in smaller components (max duration 5-30 secs each)
Step 4: Calculate the required number of repetitions (accuracy)
Step 5: Measure the elapsed time for each work component (precise timing) and store captured data
Step 6: Calculate the average assembly time and its standard deviation

38
Q

Standard Times method?

A

By means of Work Sampling method applied in real assembly systems, the data is collected and stored.

In this way, a data-base is created and used as “standard times”.

39
Q

Motion Time Measurement (MTM)?

A

By means of CAD sofwtare, the motions of the workers and their interaction with the equipment can be simulated.
* MTM is the most used method

40
Q

FIXED POSITION ASSEMBLY – features?

A

The product is assembled in a single site, rather than being moved through a set of assembly stations. Materials (i.e. components), equipment, tools are brought to the site.

41
Q

FIXED POSITION ASSEMBLY - Strengths?

A
  • High flexibility:
  • Mix flexibility (different product-types),
  • Product flexibility (introduction of new products)
  • Expansion flexibility (due to the workstations decoupling, it is possible to add new onesI
  • Low investment
  • Job enlargment, enrichment and rotation for the worker: Every worker performs the entire assembly process.
42
Q

FIXED POSITION ASSEMBLY - Weaknesses?

A
  • Interweave of materials
  • High WIP
  • Large space requirement
  • Worker’s traning may be difficult
  • High cost for workforce
43
Q

ASSEMBLY SHOP?

A

It consists of a series of stations and each station (generally, more than one station) is assigned a phase of the assembly process of a product type.

A mix of different product types can be produced within the assembly shop and its stations.

44
Q

ASSEMBLY SHOP - Strengths?

A
  • The stations (phases) are decoupled by buffers
    The cycle time is not a constraint.
  • The flexibility is high
    Mix, Product and Expansion flexibility
45
Q

ASSEMBLY SHOP - Weakenesses?

A
  • Investment depends on the level of automation of the system
  • It might be difficult to manage the flows of products and components
  • The complexity of production planning and control can cause bottlenecks and idle-times
46
Q

ASSEMBLY CELL?

A

It is a suitable solution for the assembly of a medium range of medium volume products.

47
Q

ASSEMBLY CELL - features?

A
  • In assembly cells the product moves during assembly through a number of stations with some flexibility in its trajectory (slightly different flows for different products)
  • In manual assembly cells, the organization of work is based on team-work following similar rules and organizational solutions adopted for manufacturing cells
  • Normally in an assembly cell, the operator follows the product being assembled, it means that the complete assembly process can be made by the operator together with product testing and quality assurance
  • Operators can be given production responsibilities regarding the cell
48
Q

ASSEMBLY LINE?

A

Each assembly line consists of a series of stations where the product is progressively assembled.

49
Q

ASSEMBLY LINE - features?

A
  • The product is progressively assembled on the assembly line
  • The product flows through the system with the same order
  • Operation are quite repetitive
  • Higher production volumes
  • Cycle Time (CT) is the most relevant parameter
50
Q

ASSEMBLY LINE - strengths?

A
  • Rationalization of material flows
  • Low WIP
  • Limited space requirements
  • Worker’s training may be easy.
  • Low cost of workforce
51
Q

What does it mean “Rationalization of materia’ls flow”?

A
  • Material flows are really rationale because each workstation is fed with just its pertinent components.
  • besides, the product being assembled is moved along the line and the finished product is taken from just one specific point (the end point of the line).
52
Q

ASSEMBLY LINE - weaknesses?

A
  • Low flexibility
  • Long time to start new production
  • Repetitive work
  • Line balancing may be difficult.
53
Q

On what does the ASSEMBLY LINE categorization depend?

A

On the way the material handling system works

54
Q

Which are the ASSEMBLY LINE categories?

A
  • Paced

* Un-paced

55
Q

What is the ‘“Paced” Assembly Line ?

A

Typically a common Cycle Time (CT) is given which restricts process times at all stations.

(is constrained: always synchronous)

56
Q

Which are the two ways at which the material can be transported in “Paced” Assembly Line?

A
  • Intermittent transport:
    workpiece comes to a full stop at every station, but is automatically transferred as soon as a given time span is elapsed.

-Continuous transport:
Advancing material handling which forces the operator to finish their activities before the work-piece reaches the end of the workstation.

57
Q

What is the ‘“Un-Paced” Assembly Line ?

A

Workpieces are transferred whenever the required operations are completed, rather than being bound to a given time span.

(unconstrained)

58
Q

Which are the two ways at which the material can be transported in “Un-Paced” Assembly Line?

A
  • Synchronous:
    All stations wait for the slowest one to finish its operations before workpieces are transferred at the same time.
  • Asynchronous:
    Each station decides when to transfer the workpiece.
59
Q

“machine-Paced -> Intermittent” ASSEMBLY LINE ?

A

The movement of pieces is paced by a timer and given by the cycle time of the line

60
Q

“Machine-Paced -> Intermittent” ASSEMBLY LINE - strengths?

A

Cycle time and production capacity are perfectly controlled

61
Q

“Machine-Paced -> Intermittent” ASSEMBLY LINE - weakeness?

A

Probability of no completion (at the line stations) and problems of unfinished pieces

62
Q

“Operator-Paced -> Intermittent” ASSEMBLY LINE ?

A

The movement of pieces is paced by the operators: the material handling system moves only after all operators have given their approval

63
Q

“Operator-Paced-> Intermittent” ASSEMBLY LINE - strengths?

A

No problem of unfinished pieces

64
Q

“Operator-Paced-> Intermittent” ASSEMBLY LINE - weakeness?

A

Cycle time is variable and it is determined by the slowest operator

65
Q

The two cases for “Continuous flow paced” ASSEMBLY LINES?

A

Case 1: operators can’t stop the line
*Strengths
Cycle time and production capacity are perfectly controlled
*Weaknesses
Probability of no completion (at the line stations) and problems of unfinished pieces
—————————

Case 2: operators can stop the line
 *Strengths 
No problem of unfinished pieces
 *Weaknesses 
Cycle time and production capacity are not perfectly controlled
66
Q

‘“Un-Paced” Assembly Line - strengths?

A
  • No problem of unfinished pieces

* Cycle time can be exceeded, but only occasionally (i.e. problems of blocking and starvation)

67
Q

‘“Un-Paced” Assembly Line - weaknesses?

A
  • Cycle time and production capacity are not perfectly controlled
68
Q

aspects to consider in the Design of a manual assembly line ?

A
  • Definition of the balancing constraints
  • Evaluation of the time of each assembly operation
  • Calculation of the cycle time

The design consists of Assembly Line Balancing (ALB)

69
Q

Which are the Balancing constraints?

A

*Cycle time
*Precedence relationships among operations
*Incompatibility between operations that cannot be
assigned to the same station
*Opportunity or necessity to assign some operations to
the same station
*Constraints related to space
*Constraints related to workers
*Constraints related to the material feeding

70
Q

Which are the ojectives of Balancing?

A
  • Technical objectives

* Economical objectives

71
Q

Which are the Technical objectives related to Balancing?

A
  • Minimizing the number of stations, given the cycle time
  • Minimizing the cycle time, given the number of stations
  • Minimizing the total idle time

-Minimizing the probability of no completion
in a machine-paced line, or
in a continuous flow line, in case the operator can’t stop the line
-Minimizing the probability that the times of operations in one or more stations exceeds CT
in an operator-paced line, or
in a continuous flow line, in case the operator can stop the line

72
Q

Which are the Economical objectives related to Balancing?

A

Minimizing the total expected cost (TEC)
TEC = LC + E_CUT
LC = line cost (equipment cost + operators cost)
E_CUT = expected cost of unfinished operations (i.e. tasks

73
Q

LINE BALANCING method: Probability of no-completion ?

A

For each task the following constraint has to be satisfied:

Pk ≤ P*

where:
Pk = probability of no-completion of task k
P* = maximum probability of no-completion

production (4 decks)

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