Manufacturing Systems Types

8/8/2019 Manufacturing Systems Types

1/13

Manufacturing Systems Types

Let us first look at the essential components of Manufacturing Systems:

The process of designing a manufacturing system therefore must engage upon

the design of each of the above four components AND their integration.

Notice that this figure is pretty much consistent with Prof Sohlenius's

architecture of Manufacturing systems, which is partially reproduced in the

following figure. While the following figure implicitly assumes the important

role of the human in each of the modules, I have explicitly placed it separately

in the figure above, partly because it helps in highlighting the importance of

planning the human aspects of the system.


2/13

(source: Lecture notes, Prof Gunnar Sohlenius)

We first look broadly at these four elements, and subsequently, we shall study

each of these aspects in somewhat more detail.

Informal definitions:

Physical Systems refer to all physical aspects of a manufacturing system,including the factories, including the facilities, machines, tools etc., the raw

materials, the material handling systems, the work in process, as well as the

products.

The Operation refers to all aspects of decision structures that determine how

the system functions. For example, does it use a Toyota style pull production,

or does it depend on an MRP II system with forecasts driven production? How

does the plant manager determine the size and sequence of the jobs to be doneon each machine, on each day?

The Information in a manufacturing system refers to all data that will be

accessed by some function/person/decision-maker/software etc., and whose

value may be used deciding upon an action. Examples include design data,


3/13

machine data, tool data, inventory status, process data, vendors, clients,

personnel data and so on. It is likely that for any MS of reasonable complexity,

one will need automated data handling facilities, e.g. a DBMS. I will also

loosely include in this definition, mechanisms that are required for the flow of

information, that is, Information Technology (IT). This includes

communication protocols (such as MAP, TOP, ISO-OSI), etc.

Humans refers to all personnel, vendors, customers, etc. Personnel related

issues include: what is the capability level of available labour, what is the

working culture (1-shift, 2-shift availability), how many do we need to hire for

a given MS, what is the level of training needed, what policies will lead to

better working environment etc. Customers are another essential human

element in the design of MS.

We begin the study with the physical systems. I will use the following

classification of manufacturing systems, which uses the material flow type as

its basis:

Product based: These are manufacturing systems that are designed

specifically for a fixed product (or product type). The underlying

principles are those of interchangeability, and division of labour. These

systems may be highly automated, or human-labour intensive. However,

in every case, they must operate at relatively high throughput rates.

Further divided into:

Continuous production (e.g. chemicals, food processing etc.)

Discrete part production. Further divided into:

Assembly lines

Transfer Lines


4/13

Process-based: these are facilities where machines of the same type are

grouped together physically. Some examples may be seen in job shops,

workshops, prototype makers, tool makers.

Flexible Manufacturing systems may loosely be categorized as highly

automated versions of process-based systems.

Cellular: Cells are formed using GT, and typical cells are small clusters

of a mixed bunch of machines that can handle a particular family of

products. Such layouts are used when the batch sizes of orders are not

large, but throughput times required are lower.

Fixed position: For single units of a large item (e.g. construction project,

MTR line, ship building etc.)

The above are all the physical production systems. In addition, we shall look at

material handling systems, including transportation machines and inventory

handling systems.

Once we have a physical system all installed, we need to worry about theoperational aspects. This includes, among other things, Production Control.

Several important things here include:

Lot sizing;

Scheduling;

Process Planning;

When we design the physical systems, we are concerned with the capability toproduce the designed part. When studying the operational aspects, we are more

concerned with the efficiency at which we are working. Therefore, it is essentialfor us to know our goals, when we make operational decisions. Some typical

descriptors used for Manufacturing Systems include:


5/13

WIP (Work in Process): The number of parts that are currently in the shop

floor, either being worked upon by a machine/operator, or waiting at a buffer or

in a queue.

Production rate: number of finished parts being produced by the system in

unit time.

Throughput time: the time that a part spends in the system from the moment it

is released from the inventory to the time it leaves the system.

Usually, we would like to make operational plans that are "good". That means

we should know what we mean by "good", especially since often, different

desirable objectives tend to be conflicting [which is what gave rise to teh

famous saying: Good, Cheap, Fast. Pick any two.] Here are some definitionsand some typical objectives:

Assume that jobs coming into the system are identified as Ji.

Due date, Di: date when the job is expected to be completed.

Completion time, Ci: time at which Ji is completed.

Flow time, Fi: length of time Ji is in the shop.

Lateness, Li = ( Ci - Di).

Tardiness, Ti = max( 0, Li).

Typical objectives include: minimize average flow time, minimize number of

tardy jobs, minimize average tardiness, minimize the makespan (makespan =time to complete all the jobs), minimize the maximum tardiness etc.

Once we define our goals, we can test out which operational method (heuristic)

gives us the best performance in order to achieve our goal(s). We can do so by

actually testing our operation plans on the shop floor, or we may study their


6/13

perfomance using models. A good designer will model his MS before

implementing it: it is almost always cheaper to do so!

Therefore, we shall take a brief look at methods used to model manufacturingsystems: in particular, simple mathematical models, and simulation.

Why are operational performance tests important to MS Design ?

- since they can give a good estimate of potential bottlenecks, and also be used

to refine designs before implementation.

In the Human part, we will look at two important aspects:

What the are conditions under which the workers perform the best? How

can this information be used to design the work pattern of workers, andworking system of manufacturing systems (team oriented systems)?

Why is the customer an important part of the operations of the MS ?

What implications does this participation of the customer have on the

operation and organisation of the MS.

Before you can decide on a manufacturing system that will work for

your manufacturing plant, you need to understand the differencesbetween the manufacturing systems. To understand the differences

between the four types of manufacturing systems you will need to

understand what each type of system is and how it works. By knowing

how the systems work, you will be able to choose the system that

works best for your manufacturing plant.


7/13

Here is a look at the four types of manufacturing systems:

Number one: Custom manufacturing

Custom manufacturing is the oldest type of manufacturing system in

the world because it goes back to when products were first made.

Custom manufacturing is where one person has the skill that is needed

to make a certain product. A great example of this type of

manufacturing is a shoemaker or a candle maker; it used to be that

only one person was required to make these customized products.

Custom manufacturing is still used today but rather than just one

person making the product that is required, we have machines that

will do the jobs for us. If people are doing the manufacturing, you aregoing to need more than one person to make the specialized product

so you can keep up with the higher demands.

Number two: Intermittent manufacturing

Although intermittent manufacturing is not as old as custom

manufacturing, it is still an older style of manufacturing. This system

of manufacturing was created for the times when custom

manufacturing could not meet the demands of the customers.Intermittent manufacturing is where more than one of the same

product is being made. This type of manufacturing is actually used

worldwide and it is a great way to make more than one product in a

short amount of time, as long as the product is the same product. This

type of manufacturing won't work on multiple products. A great

example of this type of manufacturing is making five pairs of the same

shoe rather than one custom pair of shoes.

Number three: Continuous manufacturing

Continuous manufacturing is a newer style of manufacturing. It was

created because product demand has to be too much for intermittent

manufacturing to handle. Continuous manufacturing is the type of

manufacturing system that uses an assembly line to manufacture


8/13

products. This system is usually used when more than one product is

being made and it takes more than two people working together to

actually make the product. In this type of manufacturing system the

product moves from one station to the next and each person at each

station has a specific job that they need to do in

the manufacturing process. This type of manufacturing system is

great if you are producing a product that requires you to complete

many steps before it can be considered a finished product, but the

drawback to this type of manufacturing system is that it can be

expensive to run.

Number four: Flexible manufacturing

Flexible manufacturing is the newest manufacturing system that is

being used by manufacturingcompanies. This type of manufacturing

system uses machines that are controlled by computers. This type of

manufacturing produces a product just like intermittent manufacturing

and is continuous like continuous manufacturing, but the thing about

this type of manufacturing system is that it cuts out having to hire

people for an assembly line. Not to mention that it is also a great way

to always make the product faster, which is a great way to keep up

with the customers' demands.The only way to determine which manufacturing system will work best

for your manufacturingcompany is to know what your company

needs and choose the manufacturing system that works best.

FLEXIBLE MANUFACTURING SYSTEMS (FMS)

Introduction

In the middle of the 1960s, market competition became more intense.

During 1960 to 1970 costwas the primary concern. Laterquality became a

priority. As the market became more and more complex,speed ofdelivery became something customer also needed.
http://www.businessknowledgesource.com/manufacturing/differences_between_manufacturing_systems_029549.htmlhttp://www.businessknowledgesource.com/manufacturing/differences_between_manufacturing_systems_029549.htmlhttp://www.businessknowledgesource.com/manufacturing/differences_between_manufacturing_systems_029549.htmlhttp://www.businessknowledgesource.com/manufacturing/differences_between_manufacturing_systems_029549.htmlhttp://www.businessknowledgesource.com/manufacturing/differences_between_manufacturing_systems_029549.htmlhttp://www.businessknowledgesource.com/manufacturing/differences_between_manufacturing_systems_029549.html


9/13

A new strategy was formulated: Customizability. The companies have to adaptto the environment in which they operate, to be moreflexible in their operations

and to satisfy different market segments (customizability).

Thus the innovation of FMS became related to the effort of gaining competitive

advantage.

First of all, FMS is a manufacturing technology.

Secondly, FMS is a philosophy. "System" is the key word. Philosophically,

FMS incorporates a system view of manufacturing. The buzz word for todays

manufacturer is "agility". An agile manufacturer is one who is the fastest to the

market, operates with the lowest total cost and has the greatest ability to

"delight" its customers. FMS is simply one way that manufacturers are able to

achieve this agility.

An MIT study on competitiveness pointed out that American companies spent

twice as much on product innovation as they did on process innovation.

Germans and Japanese did just the opposite.

In studying FMS, we need to keep in mind what Peter Drucker said: "We must

become managers of technology not merely users of technology".

Since FMS is a technology, well adjusted to the environmental needs, we have

to manage it successfully.

1. Flexibility concept. Different approaches

Today flexibility means to produce reasonably priced customized products of

high quality that can be quickly delivered to customers.

Different approaches to flexibility and their meanings are shown Table 1.

Table 1

Approach Flexibility meaning


10/13

Manufacturing The capability of producing different parts without major

retooling

A measure of how fast the company converts its process (es)from making an old line of products to produce a new product

The ability to change a production schedule, to modify a part,or to handle multiple parts

Operational The ability to efficiently produce highly customized and

unique products

Customer The ability to exploit various dimension of speed of delivery

Strategic The ability of a company to offer a wide variety of products to

its customers

Capacity The ability to rapidly increase or decrease production levels or

to shift capacity quickly from one product or service to another

So, what is flexibility in manufacturing?

While variations abound in what specifically constitutes flexibility, there is a general

consensus about the core elements. There are three levels of manufacturing flexibility.

(a) Basic flexibilities

Machine flexibility - the ease with which a machine can process variousoperations

Material handling flexibility - a measure of the ease with which different part

types can be transported and properly positioned at the various machine tools in asystem

Operation flexibility - a measure of the ease with which alternative operation

sequences can be used for processing a part type

(b) System flexibilities

Volume flexibility - a measure of a systems capability to be operated profitably atdifferent volumes of the existing part types

Expansion flexibility - the ability to build a system and expand it incrementally

Routing flexibility - a measure of the alternative paths that a part can effectively

follow through a system for a given process plan


11/13

Process flexibility - a measure of the volume of the set of part types that a system

can produce without incurring any setup

Product flexibility - the volume of the set of part types that can be manufacturedin a system with minor setup

(c) Aggregate flexibilities

Program flexibility - the ability of a system to run for reasonably long periods

without external intervention

Production flexibility - the volume of the set of part types that a system can

produce without major investment in capital equipment

Market flexibility - the ability of a system to efficiently adapt to changing marketconditions

2. Seeking benefits on flexibility

Todays manufacturing strategy is to seek benefits from flexibility. This is only feasible

when a production system is under complete control of FMS technology. Having in mindtheProcess- Product Matrix you may realize that for an industry it is possible to reach

for high flexibility by making innovative technical and organizational efforts. See the

Volvos process structure that makes cars on movable pallets, rather than an assembly

line. The process gains in flexibility. Also, the Volvo system has more flexibility becauseit uses multi-skill operators who are not paced by a mechanical line.

So we may search for benefits from flexibility on moving to the job shop structures.

Actually, the need is forflexible processes to permit rapid low cost switching from one

product line to another. This is possible withflexible workers whose multiple skills woulddevelop the ability to switch easily from one kind of task to another.

As main resources, flexible processes and flexible workers would createflexible plants as

plants which can adapt to changes in real time, using movable equipment, knockdown

walls and easily accessible and re-routable utilities.

3. FMS- an example of technology and an alternative layout

The idea of an FMS was proposed in England (1960s) under the name "System 24", a

flexible machining system that could operate without human operators 24 hours a day

under computer control. From the beginning the emphasis was on automation rather thanthe "reorganization of workflow".


12/13

Early FMSs were large and very complex, consisting of dozens of Computer Numerical

Controlled machines (CNC) and sophisticate material handling systems. They were very

automated, very expensive and controlled by incredibly complex software. There wereonly a limited number of industries that could afford investing in a traditional FMS as

described above.

Currently, the trend in FMS is toward small versions of the traditional FMS, called

flexible manufacturing cells (FMC).

Today two or more CNC machines are considered aflexible celland two ore more cells

are considered a flexible manufacturing system.

Thus, a Flexible Manufacturing System (FMS) consists of several machine tools along

with part and tool handling devices such as robots, arranged so that it can handle anyfamily of parts for which it has been designed and developed.

Different FMSs levels are:

Flexible Manufacturing Module (FMM). Example : a NC machine, a pallet changer and a

part buffer;

Flexible Manufacturing (Assembly) Cell(F(M/A)C). Example : Four FMMs and anAGV(automated guided vehicle);

Flexible Manufacturing Group (FMG). Example : Two FMCs, a FMM and two AGVs

which will transport parts from a Part Loading area, through machines, to a PartUnloading Area;

Flexible Production Systems (FPS). Example : A FMG and a FAC, two AGVs, an

Automated Tool Storage, and an Automated Part/assembly Storage;

Flexible Manufacturing Line (FML). Example : multiple stations in a line layout and

AGVs.

4. Advantages and disadvantages of FMSs implementation

Advantages

Faster, lower- cost changes from one part to another which will improve capital

utilization


13/13

Lower direct labor cost, due to the reduction in number of workers

Reduced inventory, due to the planning and programming precision

Consistent and better quality, due to the automated control

Lower cost/unit of output, due to the greater productivity using the same number

of workers

Savings from the indirect labor, from reduced errors, rework, repairs and rejects

Disadvantages

Limited ability to adapt to changes in product or product mix (ex. machines are of

limited capacity and the tooling necessary for products, even of the same family,

is not always feasible in a given FMS)

Substantial pre-planning activity

Expensive, costing millions of dollars

Technological problems of exact component positioning and precise timingnecessary to process a component

Sophisticated manufacturing systems

FMSs complexity and cost are reasons for their slow acceptance by industry. In most of

the cases FMCs are favored.

Manufacturing Systems Types

Documents

Transcript of Manufacturing Systems Types