-> DEF: working stations are organized in groups of similar stations in terms of implemented technology (it gives the name to the department).

-> CHAR:

• Department layout favors local technological competence (areas are technologically homogeneous);
• FLEXIBILITY: it combines the use of general-purpose machines and the specialization of departmental operators;
• Suitable for production on order, manufacturing products differentiated by type, LOW UNIT VOLUMES;
• Management method of batch production;
• 🔺 lead-time and WIP;
• Flows production between departments can be very complicated.
• Each products has is own routining.
• Also named process layout;
• Production departments or functional departmens, each of them had the same technologcal capability.

Outline:

• General features;
• Strengths and Weaknesses;
• Examples;
• System design;

General Features

-> CHAR:

• Create different product specifications;
• Logistics is characterized by high flexibility.
• Labor is divided in departments according to task specialization.
• Workers are skilled on the basis of technological processes involved (creates favourable condition to support knowledge transfer).

-> When a product is introduced in the product portfolio => Production process has to be developed.

-> The technological office is in charge of process development/process planning which mens some activities:

• Defining process plan of the product;
• Looking for the different technological processes involved in the job-shop, identifying how the process plan is released based on the technological capabilities offered by the system.
• This affects the material flows because the functional departments may be potentially different in terms of process plans required by the different types of products.

✔ Strength & …

High Flexibility:

-> Short to Medium-Term:

• Mix
• Volume
• Product (customization)

-> Medium to Long-Term:

• Product (innovation)
• Expansion

Subsequentially:

• Machine flexibility
• Material handling flexibility
• Routing flexibility
• Low impact of breakdowns
• Low obsolescence of the system

A.FLEXIBILITY

-> DEF: ability to change or react with little penalty in time, effort, cost or performance (e.g. quality.

RANGE of possible state space:

• RANGE OF PRODUCT/OPERATIONS that a machine can execute; considering this machine-level, products / operations can be changed within the range with limited cost / time to switch;
• RANGE OF PRODUCT that a plant can execute; considering this plant-level, within the range of technological processes involved in the plant, new products can be launched / introduced with limited cost / time / impact to launch

MANUFACTURING FLEXIBILITY: ability of a manufacturing system to adapt to changes in environmental conditions (market’s demand) and products and processes requirements (variability of their requirements).

-> The request for flexibility is higher with:

• an higher variability of the demand
• the shorter life cycle of products
• the wider range of products that the business aims to offer to the market
• the increased customization of products
• the shorter delivery times to fulfill an order

=> JS shows relevant strenghts in regard to the manufacturing flexibility, both for what concern the short/medium and medium/long term.

DIMENSION of FLEXIBILITY:

• SHORT/MEDIUM TERM:
  • MIX FLEXIBILITY: ability to meet the market’s requirements in terms of variety of products supplied in a certain time

-> Can be measured as «wideness of the range» of products / product types

• VOLUME FLEXIBLITY: ability to deal with variations in the aggregate demand

-> measured in relationship to the variation of the production volume required by the market.

• SHORT/MEDIUM/LONG TERM
  • PRODUCT FLEXIBILITY: ability to meet the demands of the market in terms of product specifications
  • PRODUCT MODIFICATION/CUSTOMIZATION: ability to vary in time the production mix or ability to deal with additions or subctrations over time

-> It become PRODUCT INNOVATION in MT/LT.

• EXPANSION FLEXIBILITY: the ability to easily add technological capacity and production capacity» in the production system

MIX FLEXIBILITY:

-> DEF: wide range of product types + can frequently change the mix over time in terms of relative production volumes (of those product types).

-> POSSIBLE:

• MACHINE FLEXIBILITY: ability to process a variety/range of different parts effectively
• MATERIAL HANDLING FLEXIBILITY: the ability to move different products efficiently for proper positioning and processing through the manufacturing facility
• ROUTEING FLEXIBILITY WITHIN EACH FUNCTIONAL DEPARTMENT: ability to process a given set of parts / products on alternative machines
• ROUTEING FLEXIBILITY THROUGH/BETWEEN FUNCTIONAL DEPARTMENTS: ability to process a given set of parts / products based on alternative technological cycles / process plans

B.LOW IMPACT/VULNERABILITY to BREAKDOWNS

-> Production System (PS) is less vulnerable to a machine breakdown.

-> CHAR:

• Routeing flexibility within & b/w each functional department  are flexibilities that are a lever to reduce the impact of a machine breakdown;
• Decoupling functionality due to inter-operational buffers avoids the possibility of a propagation of a machine breakdown to other machines.

C.LOW OBSOLESCENCE

-> DEF OBSOLESCENCE: depends on

• Market demand could not be requiring the “functions” of equipement, resources and physical assets even if they’re still adequate.
• New technologies are more convenient (more cost-effective).

⚠Ageing is a related issue but is not obsolescence. It’s due to the use of machines and their degradation through time. It’s and endogeneous factor.

-> The PS can easy adequate to the following exogeneous threats:

• Shrinking demand + changes required in function of the production plant.
• Technological development;

-> Thanks to:

• High flexibility;
• Product flexibility;
• Expansion capacity

… & ❌ Weaknesses

-> Limitation in efficiency;

-> Qualitative characteristics of the product can vary for different pieces;

• Need more hours to achieve good quality production  (quality characteristics of products can be different because of the different tollerance guaranteed by different machines)

-> Production management is difficult:

• High WIP
• Lead times are long (because of queues) and characterized by high variability
• Difficulties in estimating delivery lead times
• Low utilization rate of machines
• 🔺 Flexibility <=> 🔻 Production: 🔺working time nominally available is required as inpu in order to achieve the required output.

-> Difficult to calculate production capacity. Depends on:

• Mix of jobs that have to be manufactured
• Technological characteristics of jobs
• Complexity of pieces to be manufactured (too complex only if is a long term product, difficult to have a good prevision).
• Possibilities to use alternative routings
• Number of machines and their state
• Lot sizes
• Ability to schedule jobs

• Difficult management (Scheduling product routining is a combinatorial problem and complexity 🔺 <=> 🔺pieces or typers)
• On-line control and scheduling is required to cope different unexpected events.

-> 🔺 WIP (avoid machines standby) <=> 🔺 LT (every time an order requires an operations, it meets a relevant number of orders already waiting).

Rough design of a JS

1.Production Mix Definition:

1. Identify all the product types:

-> We identify product types:

1. Based on analogies with past experiences, similar plants / productions + Fostering future scenarios for potential production mix;
2. A sensitivity analysis can be useful in order to cope with uncertainty: due to uncertainty, a set of «credible» scenarios can be proven as a range to see how design decisions are changing/robust.

1. Estimate yearly demand for each product type;
2. Define the lot sizes for each product type:

-> this definition affects the trade-off b/w set-up costs and stock holding costs; during production management, the lot size is in fact a relevant variable as well, exactly due to such cost trade-off.

2.Routing definition:

• Define the main routing for each product type
• If possible, define alternative routings

3.Machine identification:

-> On the basis of routings, it is possible to identify all the machine types that are necessary to manufacture the production mix.

4.Math:

-> For each product type, calculate the total time of the operations that have to be done on the same type of machine: T_ij;

• Consider the time for processing cycle on a work piece (the cycle include auxiliary movements -position of piece-)
• Does NOT include the set-up time (time needed to prepare the machine for next processing cycle).

-> Calculate the yearly workload NHi for each type of machine i:

5.Calculate the number of hours available for each machine-type i

• WHi(s) =yearly working time available (depending on the number of shifts per day)
• SE = scheduling efficiency         (0 < SE  £ 1)

⚠scheduling system is not capable to fully utilize machines with production orders, which finally corresponds to unefficient schedules => in the model, time losses caused by unefficient schedules are estimated by the SE (correspondent to time losses due to scheduling efficiency).

6.Calculate the number of machines of type i necessary to manufacture the production mix, given the yearly demand:

7.The number that has been obtained must be rounded up or down depending on

• Machine-type cost
• Possibility to outsource the production of some product-types
• Possibility to use alternative routings for some  product-types

📌Why Rounding Down:

• Coefficients are only estimates (based on past averages, experiences…, similar plants) +
• Coefficients can be improved during operations (thanks, e.g., to better preventive maintenance policies);

💡If the machine-type cost is high, it is wise to reduce =>

• Outsourcing (i.e. moving workloads to suppliers) or
• Planning alternative routings (i.e. moving workloads to other machine-types, less utilized or any how at least cost of the machine-type)

8.Evaluate the number of shifts/day, computing the yearly costs adopting 1, 2 or 3 shifts/day:

-> CAPEXs are splitted during the facility / machine life time > splitted cost can be then comparable (so, summed up) with costs representing OPEX.

=> Two possible way to evaluate the system deisgn under economical convenience:

1. Same shifts(turni)/day for all departmensts vs
2. Optimal shift for each department.

-> This choiche minimizes the cost function expressed in the above formula but we have to consides ather costs:

• cost of higher WIP & required space for stock holding;
• other extra-costs induced bythe different shift operations

Example

Some Definitions:

SCRAP RATE SR: percentage of materials out of tolerance (not achieved the target quality); the material cannot be restored or repaired (reworked), hence it is discarded. More general, we can consider also the possibility to rework the material (which causes time loss, as well)

TRIAL RATE TR: percentage of time, when the machine could theoretically be used, since the technical conditions required for its use are fulfilled, but the time is dedicated to trial production (subtracted as time loss). In fact, some external reasons (i.e. external to the machine) leads to non utilization: in this case, the machine is not utilized because it is used for technical tests for trial production / pre-series; therefore, this time is not planned for production, thus leading to time losses for trials (i.e. subtraction of these time losses from the time that can be theoretically used)

AVAILABILITY: percentage of up time (intervals), when the machine is required for production and actually available to work (w/o trials), with respect to the total time (up time + down time); down time intervals regard the overall failure and maintenance downtime. In this case, the loss is caused by some technical conditions & requirements (preventive maintenance planned in the production shift > hence impacting on the required production time) + malfunctions / anomalies / failures (by definition, impacting)

HUMAN COEFFICIENT HC: percentage of up time, when the machine is required and actually available to work & the operator is available to carry out its required tasks. Sometimes, in fact, the operator cannot be present because he/she is carrying out tasks in other machines; as auxiliary resource to carry out tasks related to the operations of the machine (load/unload work-pieces, clamp them etc.), sometimes he / she is busy when required (in other machines); this leads to the occurence of some time losses on the machine under concern, which is then waiting for the worker; in other words (alias), the machine is waiting in a stand-by time, caused by the organization of human task allocations to machines leading to the occurrence of the problem of man-machine interference (this theory will be considered later on during the course)