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TRANSFER LINES Flashcards

(48 cards)

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1
Q

What is TRANSFER LINE?

A

It consists if a series of machines where a single product type (or a limited number of product types within the same family) flows.
Resulting in a ROUTING THROUGH THE MACHINES

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2
Q

What does it mean PRODUCT LAYOUT in Tra.Line?

A

Because the TRANSFER LINE is consituted by a series of machines resembling the sequence of operations required by a single product type.

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3
Q

How are the machines grouped in a TRAN.LINE?

A

Machines are grouped according to the processing requirements of a single product (or liited number of products within the same family).

Machines are visited by the products to be manufactured

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4
Q

How the products/parts are moved?

A

They are moved (flowing through the machines) as a single work-piece or small lots of work-pieces.

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5
Q

General features?

A
  • Production flow is serial
  • The TRANSFER LINE is usually a highly automated manufacturing system.
  • The demand of the products must be high & stable
  • The line must be balanced (workload balanced)
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6
Q

Why does the demand have to be high & stable?

A
  • In order to justify the high economical investments regarding to the automation.
  • Because the TRANSFER LINE is focused on one single product-type fabrication, and therefore the production volume must be high to justify the economical investment and installation.
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7
Q

Why is the TRANSFER LINE automated?

A

To be able to meet the high market’s demand by means of a high production capactiy.

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8
Q

What is the drawback of the automated transfer line?

A

The automation tends to be RIGID. Introducing a new machine is quite complicated, requiring a configuration of the whole line.

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9
Q

What are the benefits of a U-Shaped TRANSFER LINE?

A
  • The inlet and outlet area of the products is the same, making the material’s handling easier
  • It is more compacted
  • It is more balanced in temrs of workload
  • Better communication between workers
  • Workers can be focused on different operations
  • Workers can control the quality level easier and more constantly.
  • Reduces the worker’s movement and displacement, saving time.
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10
Q

Strengths?

A
  • Simplest production management (w.r.t JOB SHOP & MANUFACTURING CELLS)
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11
Q

Why is the production managment easier in TRA.LINE?

A

Because it is limited to two aspects:

  1. Batch sizing
  2. Batch sequencing
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12
Q

What is the difference between “batch sizing” & “batch sequencing”?

A

Batch sizing is when a ‘single model’ is applied -> Only one product type is manufactured

Batch sequencing is when ‘a multi-model’ is applied -> Different product-types within the same amily are manufactured.

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13
Q

more strengths?

A
  • High machine utilization
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14
Q

Why is the machine utilization rate high in TR.LINE?

A
  • Production volume is stable & high

- Production of the same type of product (even if ‘multi-model’ is applied)

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15
Q

What is the advantage of having a high machine utilization rate?

A

This leads to a more balanced work-load w.r.t JOB SHOPS and obviously w.r.t MANUFA.CELLS

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16
Q

more strengths?

A
  • Low space requirements

Machines and material’s handling systems are located in the transfer line

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17
Q

more strengths?

A
  • Low need of workforce
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18
Q

why low need of workforce?

A

Because the TRANSFER LINE is highly automated

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19
Q

more strengths?

A
  • Stable quality of products.

Workers can be focused on operations of wuality control since the line is automated.

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20
Q

WEAKNESSES

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A
  • Low flexibility because:
  • Limitation in mix of products (variety of product types)
  • Limitation in Introduction of new products (innovation & customization)
  • Machine flexibility is low
  • No alternative routing cycles
  • Problems related to trial production
  • problems in addition of new machines
21
Q
  • Why is the Machine flexibility low and how does it affect the Expansion flexibility?
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A

Because of the high automation level making the system rigid.
-Adding a new machine entails the configuration of the whole line, leasind to low expansion in technology capacity

22
Q

Why the trial production is a problem?

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A

Because the trial producton occupies the whole line working on the same product-type.

23
Q

more weakeness?

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A
  • High economical investment is needed
    Due to the high automation

*Long time required to start new productions
Due to the long time needed to set the machines, the material’s handling system, reconfigurate and balance the line

  • High risk of obsolescence
    Because the LINE is designed based on the techonology needed for a specfic product-type.
    The lifetime will depend on the product-type’s lifetime
  • High sensitive to breakdowns
    Because the machines are in series, so a high downtime affects the other machines
24
Q

What are the solutions to mitigate the high impact of breadowns in the TRANSFER LINE?

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A

i) buffers b/w workstations, but – due to their (small size) – these are used to limit the effects of limited process variability (e.g. micro-stoppages, for ex. a tool breaking); ii) the installation of redundant machines > when there is a machine breakdown the other machines have still the capacity to produce the demanded production (but this has normally high costs, except in the case that the redundant workstation is featuring a low automation); iii) parallel machines whose nominal capacity is enough to produce the demanded production, while is partially enough in case of a machine breakdown (i.e. production capacity reduction).

25
Steps of Design of a transfer line (single-model) ?
1. Define the technological routings and the operations for the single product-type 2. Based on the technological routings/operations, identify all the machines types needed (specialized or general purpose machines) 2. 1 Balance the line based on the given Cycle Time (CT) 3. Calculate the Theoretical Production Capacity TPC = 3600/CT [pieces / hour] CT -> Cycle Time of the line [seconds / piece].. Maximum working time (of the bottleneck machine)
26
What does it mean 'Balance the line' ?
It means to allocate the operations to the work-stations / machines. Specialized machines are more constraining than the general purpose machines
27
The other Steps of Design of a transfer line (single-model) ?
4. Calculate the Actual Production capacity (APC) APC = TPC * A * (1 – SR) [pieces/hour] where A = line availability (0 < A < 1) SR = scrap rate (0 <= SR < 1) 5. Compare the actual production capacity and the demand. If necessary, modify the line and go back to step 2
28
Why teh Actual Production Capacity (APC) is lower than the Theoretical Production capacity (TCP) ?
Because of two reasons: 1. scraps: Products which do not meet the wuality requirements. 2. Failures /breakdowns: Leading to machine downtime producitng a a line downtime as well. The Availability is computed by means of the multiplication of each machine Availability since the machines are in series
29
(2) Steps for: Machine identification and line balancing ?
2. 1. Define the operations and their sequence 2. 2. Get the required Cycle Time (CT) 2. 3.Compute the Theoretical minimum number of workstations 2. 4. Allocate the workstations 2. 5. Balance the line (allocate the operations to the workstations) 2. 5.1 compute the efficiency of the solution 2. 6. Assign the personnel (if any)
30
(2.1) Define the operations and their sequence
- Breakdown and identification of the fabrication cycle. The cycle is composed by elementary (basic) operations (tasks) - Definition of precedence diagram - Calculation of (determistic) time for each operation total work content (sum of operation times)
31
What are the two ways to define the operations sequence?
- Precedences tables - Hoffman's matrix Both allow to get the precedence diagram
32
What does the sequence of operations entail?
Constraints in term of operations. These constrains can be represented by diagrams or tables.
33
(2.2) Get the required cycle time
CYCLE TIME: It is the reciprocal of the production capacity (rate) required (units/h, i.e., the production volume to be processed in a given time); usually expressed in seconds/unit (or minutes/unit) in such production systems
34
What is the CYCLE TIME?
It is the maximum time allowed at each workstation to complete its set of operations on a work-piece (unit)
35
What is the cycle time with MORE THAN ONE WORKSTATION?
CYCLE TIME OF THE SYSTEM = longest processing time in a workstation.
36
What is the cycle time with ONLY ONE WORKSTATION?
CYCLE TIME OF THE SYSTEM = the total processing time of operations.
37
(2.3) minimum number of workstations?
N_min = Total work time / Cycle Time N_min => theoretical minimum (lower bound) number of stations required
38
(2.4) Allocate the operations to workstations ?
Allocation of operations to the workstations: using the precedence diagram and the associated operation times Tk, the operations are allocated to individual stations so that the sum of operations at each station does not exceed the work station time Ts (that is always ≤ CT).
39
(2.5) Line balancing ?
Line Balancing is the process of assigning tasks to workstations in such a way that the workstations have approximately equal time requirements. Goal is The example is used in order to illustrate the line balancing problem: this is a typical decision problem at design stage of a manufacturing line, such as is the case for a transfer line.
40
What are the other goals of the Line Balancing?
To minimize idle ("inactividad") time along the line, which leads to high utilization of equipment and labor. NOTE: Perfect balance is often impossible to achieve
41
What are the objectives of LINE Balancing and Assigning tasks to workstations ?
* Minimize - Number of workstations/machines - Production costs Minimize the Cycle Time (CT) * Maximize - Profits - Efficiency
42
Models for Linear Balancing?
* Linear programming (Optimal) | * Maximum Fixed Utilization Rate (heurist)
43
what are the types of Maximum fixed utilization rate (heuristic) ?
* Simple method, without priority rules (i.e the fisrt available operation in assigned) * With local priority rules for assgning priorities: - MaxDur (Longest processing time) - MaxNFol (largest number of immediately following tasks/operations) * With global priority rules: - MaxFol (largest number of following tasks/operations) - Ranked Positional Weighting
44
Which other different approaches (using the same rule) can be adopted ?
- "Task Oriented": | - "Station Oriented"
45
On what is "Task Oriented" focused ?
When the remaining idle time ("tiempo de inactividad") is not sufficient to assign the i-th operation, a new workstation is opened It is simpler but less efficient
46
On what is "Station Oriented" focused ?
When the remaining idle time ("tiempo de inactividad") is not sufficient to assign the i-th operation, instead of opening a new workstation, other available operaitons are considered to fill-up.
47
Steps for "Fixed utilization"?
1. Draw the precedence graph (assembly graph) 2. Calculate the total tasks’ time T (sum of all tasks’ times) It can be defined as total work content or, equivalently, total time 3. Calculate the cycle time CT CT = available time / demand 4. Calculate the minimum number of stations K*: K* = T/(CT ∙ α) 5. Assign tasks to stations, respecting the constraints (CT, precedence relationships, etc.) If there is more than one task available to be assigned, use a rule to prioritise tasks
48
What about α?
For each operator, the following constraint has to be verified UR ≤ α α is the maximum value of the utilization rate (0 < α ≤ 1)

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