Appunti delle lezioni del corso di Production Management (Primo + Secondo Parziale)

Production Management

Production system: is a set of machines and assets that implement, through an industrial

technology, an industrial production process, to make goods.

(è un insieme di macchine e risorse e procedure che attuano il processo industriale di produzione.

Le materie prime vengono convertite in prodotti finali e distribuite ai consumatori)

Industrial technology

Industrial production system is made of:

1. Equipment, machines

2. Personnel, employers FINISHED PRODUCT

3. Service infrastructures

4. Know-how, skills

It uses:

- Energy

- Raw materials

- Information

As inputs in order to create the final product.

A PRODUCTION SYSTEM is the combination between: production process, management

• subsystems (SISTEMA PRODUTTIVO= processi produttivi + sottosistemi di gestione)

A PRODUCTION PROCESS is the transformation of the starting materials (sources) into

• finished products (economic goods)

The SUPPLY CHAIN is made of 3 stages

Idea Market

Analysis

S Market

M D

Source Manufacture Distribution

Stage

We can recognize 3 types of flow:

1. The PHYSICAL FLOW= is the process of transformation of raw materials into Final products.

2. INFORMATION FLOW or PLANNING FLOW. It goes the the opposite site direction and it’s

often recognized as the input of the physical flow. Because it concerns the market analysis and

the development of the idea/design of the future products.

3. CASH FLOW / FINANCIAL FLOW. It doesn’t have specific rules.

MANUFACTURE: is a production system “DISCRETE”, in which each part is produced in a distinct entity.

It consists of many components that have to be put together to make a final product.

es. cars, hamburgers, computers…

Manufacture is in contrast to “continuous goods production” which is the process used to create fluids,

powders etc.

There are differences between manufacturing and assembly.

- Manufacturing: once an item is produced, it is hard to go back to primary materials/components.

So the MANUFACTURING PROCESS IS NOT REVERSIBLE.

- Assembly: After assembly processes is easy to come back to the primary components. It easy to reverse

the process without affecting the nature of the components or materials.

So ASSEMBLY PROCESS IS REVERSIBLE.

WORKSTATION: It is a set of machines and human operators; that perform the same operations

of the same products

The machinery is arranged in a layout. The planning of the layout and of the resource

requirements is the PRODUCTION SYSTEM DESING.

PRODUCTION SYSTEM —> EVALUATION OD THE PERFORMANCES

1. TIME:

- Lead time (LT): Tempo di attraversamento. È il tempo che intercorre tra l’ingresso e l’uscita di

un materiale in un impianto produttivo.

It measures the amount of the time between the initiation and the finishing of the process on

the same unito of material.

Periodo che intercorre tra l’avvio e il completamento di un processo produttivo.

It’s the interval between the initiation and the conclusion of a production system. Measured

by elapsed time (h, min, seconds).

- Cycle time: It’s measured in time/unit. It measures the amount of the time needed to

complete a single step of the production system.

Concept of line Where is the bottleneck?

It is B. Because is the station that asks the largest

amount of time.

Lead time (or throughput time) and lead time —> difference = it is relevant only when taking

about lines.

At first sight the lead time is 12 minutes.

How do you measure cycle time? Is the amount of time between the initiation and the end of a

single step od the process. CT is 5 minutes. (È il tempo tra la produzione di un oggetto e un altro,

cioè quando inizia B e quando finisce).

CT corresponds to the BOTTLENECK —> It’s a rule.

CYCLE TIME —> LEAD TIME —> BOTTLENECK

Ex. Laundry

LT= 30+45+30= 105’

CT= 45’ because if I want to many times the same operations and I want to know what

determines the duration of the whole process. I see that it is the drying step which is

the longest one.

The bottleneck is the 45’ step. CT BOTTLENECK

≡

Bottleneck= within a set of dependent steps, there is one of them that determines the speed of

the whole operation. It limits the speed of the operation.

2. HOW FAST —> THROUGHPUT TIME: jobs/hour parts/minute

It measures the performance of the systems in terms of how fast the production system is. It is

measured by jobs/minute, pieces/hour (CT è il suo reciproco CT= time/unit)

3. WORK IN PROGRESS —> WIP

It’s a measure of how is going the business. WIP= work in progress: are a company’s partially

finished items waiting for completion. It’s a term desorbing partially finished good awaiting

completion.

PRODUCT DEVELOPMENT STAGES

Stage 1 DESIGN —> Stage 2 INDUSTRIALIZATION —> Stage 3 PRODUCTION

The outputs of the design stage are: Engineering drawings and BOM (Bill of Materials).

Then, these outputs are used as inputs for the industrialization stage. Once the industrialization

stage has produced route sheets/ Technological cycles and Assembly/ Processing drawings, the

production can start.

BILL OF MATERIALS= it is a hierarchical and structural list of all the components and raw materials

need to manufacture a finished product.

For each component , a coefficient of use is specified. It is useful to combine the BOM with the

route sheet.

TECHNOLOGICAL CYCLE/ ROUTE

SHEET= it is a list of the operations,

resources and times needed to produce

a component.

If you want to improve your production process you have to reduce the set up time.

Technology diagram: it is a method/ set of symbols used to describe graphically a technology

routing, it is a set of datas/ information that describes the sequence of operations required to do

a production process. Wait/ buffer due to technology

Inspection / Quality check reasons

Operate Transfer

Deliver triangle. STORE.

Storage/ waiting/ buffer stage

due to management reasons

LINEAR FLOW •

RM Finished good Synthetic Flow

• Analytic Flow

• Continuos Flow

• Discontinuos Flow

Process operations

LEAD TIME= It’s the amount of time between the initiation and the finishing of a process.

Measured in elapsed time (h, s, min). There are several types of lead time.

‣ MLT= Manufacture Lead Time= acceptance of the order and delivery of product.

can be divided into 2:

- Processing time

- Waiting time: (<— Loss)

➡ Breakdowns

➡ Production maturation (<— wait due to technological causes)

➡ Set up

‣ TLT= Total Lead time= also known as Costumer Lead Time

Date of Actual

issue of the delivery date

order

‣ PLT= Production Lead Time

Date when Actual

production delivery date

starts

‣ RDLT= Requested Delivery Lead Time

Issue of Requested

the date by the

order client

‣ DLT= time between: when the product is ready to be sold and actual delivery date.

If DLT < MLT ( <— I need CODP)

MCE= Manufacturing Cycle Efficiency= Production time/MLT= job shop 5% and lines 98%

∼ ∼

It calculates the % of the time spent in manufacturing a product with value added activities.

MCE = Value added time (processing time) / MLT

MLT = Process time + Inspection + Transport + Queue

Ex.

Wait time= 2d

Process time= 10d MCE = 10/ 10+2+3+1= 62,5%

Inspection= 2d

Queue= 3d

Moving= 1d

VALUE ADDED ACTIVITIES: VALUE ADDED ACTIVITIES:

-

Processing time Inspection time

• -

Service time Transfer time

• - Wait/ idea time

- Queue

- -

Increase the worth of a product Unnecessary from the costumer point of

- The costumer is happy to pay it view

- Increases the time spent on a product

- Can be reduced without affecting the

selling price of the product

The process flow chart is useful to distinguish value added from non-value added activities.

Process Operation Movement Inspection Delay / Wait Storage

description

Proc. 1

Proc. 2

Proc. 3

Proc. 4

… Value added Non value added

‣ TTM = time to market: time between the initiation of the production and the time/moment

when the finished product is put into the market.

M D Market

S

Workload sizing approach

It is a widely used method to do a first approximation of the size of a production system. Comes

from the assessment of the workload.

Disadvantages: strong simplification ‘cause it considers the production system as a static thing.

the design of the production system is made referencing to a conventional period of 1 year.

• The system is sized with respect to a production target, which is referred to the conventional

• period of 1 year. CONVENTIONAL = 1 YEAR <— Production

OPERATING target

PERIOD

It need resources H = Annual required capacity (hours) for a

Ri

process/machine.

H = Available Hours/year for a resource.

Ai This is the workload needed to produce a

This is the theoretical annual availability certain production target.

for each resource. It takes into account

inefficiency factors, so is reduced. Resource’s availability

N = H / H

i Ri Ai

Number of a resources Workload of a resource

needed N = [ ] /

umber Hours/year

[ ]

Hours/year

There are other methods, that carry out in a more precise way, the planning of a production

system’s capacity.

- Experimental methods —> Based on discrete model simulation. They realize a computer model

of production system and they emulate the production running.

Classification MANUFACTURING

FABRICATION ASSEMBLY

Job shops Assembly shop

Fixed position

Manufacturing cell Assembly cell

Transfer line Assembly line (manual)

Linear Paced

Rotary Unpaced

FABRICATION

We can describe it’s features considering 3 aspects:

1. Technology:

Not Reversible

• Not fixed technology route —> variants and flexibility are allowed

• Not particular relevance to process parameters

• Product technology parameters are relevant

•

2. Management:

Relevance of management parameters: WIP, synchronization, lead time, delays…

• There are multiple resources that can be used in flexible ways

•

3. Cost:

Relevance of fixed assets

• Labour intensity depends on the level of automation of the machinery

•

- Job shop

It is a manufacturing system with different types of machines, grouped and organized in works

enters, called shops or departments.

Different type of machines The same types are grouped into departments/shop

In the shops there are machines/resources with the same nature/ skills involved/ technological

process.

Dept 4 Dept 1

Painting All the departments are organized and

Assembly built according to their technologies

Dept 3 Dept 2

Characteristics of Job Shops:

1. Each product has its own technological cycle that defines a route through several types of

machines.

2. Processing can be flexible, cause a product can be processed by more than 1 machine, so its

route can be modified.

3. Physical flows are interwoven complex flows.

4. There are many alternative cycles.

5. Items can be made in batch or unitary production.

6. Products pass a lot of time waiting or queuing (low efficience).

7. Space used for warehousing.

8. Many products (grande varietà) and low volume (pochi).

9. High Flexibility

Flexibility means:

Elasticity in terms of quantity of items available for the client. Being able to satisfy costumer’s

mixing preferences. Being able to accomodate the costumer’s demand by changing the mix of

the order. Having a small frozen period. Low TTM (time to market).

10. General purpose machinery.

11. Operators are highly skilled (in their department’s operations) and work for one department.

12. There is fixed layout of the process. Machine and equipments of the same type are arranged

in the same shop.

13. High material handling.

14. High lead time.

15. Unorganized material flow.

When is useful to adopt job shop?

1. High variety of products or parts to be processed

2. Volume low —> Few final products (low quantity)

3. The production mix can change with the passing time. This flexibility is not allowed in

industrial plant for the process production of cement, powders, liquids, etc…

Little’s law = WIP / LT

(throughput rate)

WIP= n° of items being worked on by the jobs

LT= it’s the time an item spent in the production system. It is the period between the initiation and

the completion of the process.

= n°/time

If you want to speed up the process you have to reduce LT and reduce WIP.

Job Shop Pro and Cons

Pro:

- Flexibility

- General Purpose machines

- Alternative cycles

Cons:

- Difficult to keep products flow under high control

- High WIP

- High throughput time

- Low machines saturation

- Not regular quality level

- Difficult to manage production (the management of the flow it’s a mess)

- Difficult to foresee bottlenecks

- High dependence of performance in the mix of product to ne manufactured.

- Manufacturing cell

It’s a group of machines (cell) of different types that completely fabricates (and sometimes

assembly) a range of similar products. Families of products

Cell Manifactures or parts

Cell are based on the group technology model.

Pros

- Shorter lead time than Job Shops

- Lower WIP

- More customer-oriented

- Setup reduction

- Production in batches

- Higher saturation

- Better utilization of space than Job shops

Cons

- high implementation costs

- Imbalanced workloads among cells

- Difficult to manage changes in mix

- Difficult to gain fully autonomous cells

Workload sizing approach —> basic common aspects.

The production system is designed and sized by referencing to a conventional operating period of

one year and to a production target.

The workload (=required working time) can be calculated also considering the presence of setups

and inefficiencies.

H = Annual required capacity (workload of the resource)

Ri

H = Annual availability hours per each resource (machines) and this value is reduced in order to

Ai

take into account inefficiency factors (strikes, maintenance) (Availability of the resource)

N = H / H = number of resources needed for each type “i”

i Ri Ai

So the workload sizing approach is a basic design method there are more precise methods

(detailed design) such as the simulation, the experimental method = model based on the

simulation of discrete events. MANUFACTURING

FABRICATION ASSEMBLY

Job shops Assembly shop

Fixed position

Manufacturing cell Assembly cell

Transfer line Assembly line (manual)

Linear Paced

Rotary Interm.

Contin.

Unpaced

Async.

Sync.

General features of fabrication:

Not reversible transformations

• Not fixed technology route, possibility to change/ flexibility

• Relevance of product technology parameters, management parameters

• Flexible utilization of resources

•

Costs:

- Relevance of fixed assets

- Labour intensity depending from automation and machines characteristics.

Job Shop

Ex.

Production of parts (mechanical) for: car industry, machine industry, aircraft industry. Machine

shop, production of mechanical parts, gear manufacture.

Manufacturing system with different types of machines.

• Able to process high variety of products.

• Machines are organized in work centers (departments or shops) and work centers include

• machines of the same type. Important: machines technologically similar are grouped together in

the same shop.

Each product has its own technological cycle —> has its own route through several machines.

• Processing flexibility. ✓

• Several alternative cycles are possible ✓

• Sometimes unitary or batch production

• ✕

A lot of space used for warehousing

• ✕

Many stages of queuing and waiting (low efficient)

•

Many different products and low quality

Operators are very skilled only in their departments operations

• ✕

High lead time

• Messy material flow

•

When to use Job Shops:

- High variety of products or parts.

- Production volume is low

- The production mix can change with the passing of time

General-purpose machines —> able to produce a vary flexible mix of products ✓

• ✕

High WIP, high throughput time

• ✕

Uneven quality level

• ✕

Difficult to force bottleneck

•

Manufacturing Cell —> Group Technology

Group of machines (called cell) of different types (this is the difference between job shops and a

manufacturing cell) that completely fabricates and often assembly, a range of similar products or

parts (families of products).

Flows from one cell to another one are not allowed

• Machines are grouped according to the families manufactured.

• Fewer variety than job shops —> Higher production volume.

• Batch production.

• Reduced set up time. ✓

• Flexible routing, flexible process, skills grouped. ✓

• The manufacturing cell combines the

Low WIP, low lead time, predictable, visible. ✓ advantages of job shops and transfer lines.

• Cells are more customer oriented and easy to control. ✓

• Better utilization of space and higher saturation of machines than job shops. ✓

•

Layouts Not for good work can be Improved

Workers can cooperate divided in an uneven way layout

U-Shape:

Reduce space occupied

• May reduce employees’s movements

• Improve communication

• Reduce n° of workers

• Facilitate inspection

•

Group Technology

The principles of this method, that can change the layout of “classical” factories is:

- Realizing together simi