ManufacturigCase Study

7/25/2019 ManufacturigCase Study

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Click Here to Begin

A Manufacturing Case Study Exercise

Steel Nuggets Inc.


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2 CONTENTS

Introduction .. 3

The Manufacturing Facility .. 4

Overview .. 4Manufacturing the Parts .. 5

The Trim Operation .. 6

Stacking the Products .. 6

The Palletizer .. 7

Pallets .. 7

Conveyors .. 7

Reliability .. 8

Work Patterns .. 8

Exercise 1 Modeling the Factory .. 9Building your Model .. 9

Validating your Model .. 9

Exercise 2 - Experimentation using your Model 10

Exercise 3 - Further Analysis and Experimentation 11

Capital Spend Options .. 12Further Options .. 12

Exercise 4 Advanced Experimentation .. 13Zero Spend Options .. 13

Further Ideas .. 13

Modeling Tips . 14

Experimentation Tips . 18


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3 INTRODUCTION

This case study exercise is designed as an example simulation project conducted in

WITNESS. Students, and others undertaking this exercise, are expected to build a model,

conduct experimentation and try their own ideas for improvement.

The exercise is focused on a manufacturing facility production line that is composed of

machining operations linked by conveyors. At the end of the line goods are stacked and

palletized before being shipped out to customers. A pallet return mechanism is also

included.

The model building process can take between a few hours to a few days dependent onskill and experience. The experimentation exercises could take several days to complete.

The anticipated duration for completion of this case study simulation project including the

model build and all phases of experimentation is between 20 and 35 hours.

This document includes all the information required to build the model and some advice to

guide model structure and experimentation.

Back to Contents Page


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4 THE MANUFACTURING FACILITY

Overview

Steel Nuggets Inc. manufacture three types of part A,B and C and they wish to maximizethe capability of their production facility based in Store Ridge, Texas.

The factory is old and has a number of problems. The manufacture process is not smooth

or streamlined and some of the equipment is unreliable. There are many options for

change, each with a different cost and each with a different potential payback.

Your task is to construct a WITNESS model of the Steel Nuggets Inc. manufacturingfacility, validate your model against the current performance of the factory and then use

the model to analyze the options for improving performance.



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5 THE MANUFACTURING FACILITY

Manufacturing the Parts

Each of the three parts A,B and C being manufactured has a first operation performed on adedicated machine (MakeA, MakeB and MakeC).

These machines are never starved of the raw material (metal blocks) needed to

manufacture the parts. A single part is manufactured on each machine at a time.

The manufacturing times of the parts on these machines are as follows:

MakeA Cycle Time UNIFORM(5,10) minutes

MakeB Cycle Time UNIFORM(5,10) minutes

MakeC Cycle Time UNIFORM(10,20) minutes



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The Trim Operation

The parts are delivered to a Trim operation on three separate

conveyors that can each take 3 parts only. The Trim operation

takes parts from the conveyors in sequence but will not wait

if there is no part present on a particular conveyor it will

continue to the next conveyor in the sequence.

The cycle time for the trim operation (which also processes a

single part at a time) is the same for all parts. It is a samplevalue from a NORMAL Distribution with a mean of 2.7 minutes

and a standard deviation of 0.3 minutes.

Stacking the Products

The Trim operation outputs the part onto another conveyor that delivers the parts to a

stacking operation. The conveyor is long enough to hold 10 parts.

The stacking operation is actually a person who takes the components and stacks them in

three separate feeds to the palletizer depending on part type. Each of A and B take 0.65

minutes to stack but, due to the heavy weight of C, this takes 5.5 minutes.

This results in separate stacks of A, B and C in the feeding mechanism for the palletizer.

THE MANUFACTURING FACILITY



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The Palletizer

When a stack reaches 12 high there is no more room for additional parts of that type untilthe stack is palletized. The palletizer takes the stack and loads it onto a pallet which has

been taken from the Pallet Store. The Palletizer takes anywhere between 3 and 3.5

minutes to complete this operation again this is a UNIFORM distribution.

Full Pallets are placed in the dispatch system where they are taken to the customer and

the pallet is then returned. The whole process of delivery takes between five hours and

eleven hours randomly again a UNIFORM distribution. When the pallet returns it is placedin the pallet store for re-use. There is no restriction on how many pallets can be delivered

at once.

The Pallets

The pallets used are expensive custom items (due to the need to keep the parts

particularly rigid in transport). The company currently owns just 12 pallets.

Conveyors

All conveyors in this facility are of the accumulating type in WITNESS terms they are

queuing conveyors all parts will roll up to the queue of parts at the front. The time for all

conveyors to cycle one part position is 0.5 Minutes.




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Reliability

Not all the machinery in the factory is 100% reliable!

The Trim machine breaks down every 100 to 200 minutes (UNIFORM distribution) and

takes 20 to 25 minutes to repair (UNIFORM distribution)

The Palletizer breaks down every 10 to 20 operations (UNIFORM distribution) and takes

between 1 and 4 hours to repair.

The Trim and the Palletizer machines are repaired by the same person who prioritizes

work on a first come first served basis.

The other machines and the conveyors do not break down.

Work Patterns

The factory is run 24 hours a day, 7 days a week. Each position involving people is

manned for the entire duration of production.




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Building your Model

Using the information provided, build a WITNESS model of the current facility.

You can use the sample models for guidance, but you are free to design your model in any

style you see fit.

Validating your Model

Once you have built your model, validate its accuracy against the currently observed

output at the factory.

The current production output at the factory averages 2546 parts per week.

Note: You will notice that this model has some variation in it. You will need to determine

how long a model run is needed before the production settles down to give an accurateaverage figure.

EXERCISE 1



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Experimentation using your Model

The manager of the factory thinks that performance is not good enough and has noted anumber of things that he thinks may be improved. The key performance metric for the

factory is the number parts produced per week, however running costs are also important.

There is also limited amount of funding available for improvement.

The manager is currently convinced that although the pallets are expensive, the factory

simply does not have enough! At certain times he has observed that the palletization

machine is ready to input but there are no pallets available, so he has concluded output

will increase if he either:

a) Adds additional pallets into the system

b) Invests in a faster delivery service: This would reduce the transport time for

delivery by 10% - and therefore enable pallets to be returned more quickly.

The factory manager wants you to evaluate implementing each of these options and report

back on the increased average number of parts per week which can be produced.

Produce a clearly labeled table of results for the number of scenarios that you think fit.

Include details of how long the model was run to achieve the demonstrated results and

explain in a short paragraph how the run time was determined. In the results table clearly

include both experimentation parameters and the key results achieved. You may even

include graphical representation of results.

EXERCISE 2



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Further Analysis & Experimentation

The manager of the factory is delighted with your analysis in Exercise 2 and decides togive you much greater responsibility for improving the factory.

Finance have determined that each additional part that can be produced per week will

increase revenue by $5.

Overall there is a limit on spend of $50,000 in the next year. All capital costs need to be

depreciated over just one year as this industry changes rapidly. Therefore all costs areincurred over the year being planned.

Using the available improvement options listed on the next page; identify and produce a

report that indicates how best to invest the improvement budget. Include a clear table of

the result you have found together with your recommendations.

EXERCISE 3



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Capital Spend Options:

New Pallets Each new Pallet costs $2,000 The new faster delivery service costs $6,500

Adding capacity to any of the conveyors. There is enough space in the factory for

1 additional space on each conveyor. For each conveyor this costs $3,000

Further Options

Hiring extra people (stackers or maintenance people) - the cost over the year for each

new person/position (i.e. at a position 24 hours a day) would be $30,000

Improving the reliability of the trim machine through a better maintenance program

(intervals between breakdowns up by 10%) costs $2,500 per year

Improving the repair times of the palletizer machine by 20% through the use of hired

advanced repair tools costs $3,500

From these options alone identify and report on the best use of the investment money.

EXERCISE 3 IMPROVEMENT OPTIONS



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Zero Spend Options

Often in models such as this one there are options that will cost nothing and yet willimprove the situation. These often include ways that production can be controlled

differently. For example a different priority of selection of work on to a machine, or tasks

for a person carried out in a different priority order. People can even be called away from

one task to complete another if it arises read about Labor pre-emption in the help text to

explore this option.

The manager would like to know are there any options here that would improve the basescenario with no spend at all?

Identify and evaluate any improvement options that will not result in additional cost for

Steel Nuggets Inc. Report back on any improvements you have found.

Further Ideas

Identify whether you think there might be any additional ways that production could be

improved through the spending of more money.

List any ideas that you have that could have an effect, regardless of the cost implication.

EXERCISE 4



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The following topics are designed to help you locate further information if need assistance

with modeling particular areas of layout and logic.

Basic Model Building

The help section within WITNESS covers many of the things that you will need be aware

of to build this model including the four basic elements; machines, parts, conveyors and

labor.

Think of elements as your building blocks that have different properties and have different

purposes they do not necessary have to represent what they are called.

Modeling Labor

Even though there is a labor element in WITNESS, it does not mean that this needs to be

used every time a person is involved in a task. Sometimes a simpler alternative is to modelthe person as a machine element, staying in a particular location and processing parts just

like a machine.

In this model there is a need for a labor element in one area of the model and there is also

a place where it is simpler to model the person as a machine.

MODELING TIPS



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Attributes and Variables

There are a number of places in this model where attributes can be used effectively. Thevalues for the attributes can be set inActions on Create on the dialog and then the

attribute names can be used in other element dialog fields for example, within the cycle

time of a machine expression.

Variables provide a good place for storing information. There are many uses including the

ability for a value to dictate which logic is chosen in a section of a model for example

which buffer a machine is currently inputting from or outputting to.

Conveyors

All the conveyors in this model are Queuing type and the simplest way to model this type

of conveyor is to select Indexed Queuing from the type drop down box on the Conveyor

detail dialog and then enter how many parts can queue on the conveyor in the Length in

Parts field.

MODELING TIPS



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Delay Buffers

There are a number of places in this model where delay buffers can be used effectively. Abuffer can have either a maximum or a minimum delay defined (or both). After the

minimum delay a machine (or other element input) rule is allowed to pull the part out of

the buffer. After a maximum delay the output rule on the buffer is run (just once it will

not block and retry).

This is a simple way to model the time for an activity which can accept other parts in to

the activity at the same time as others are being processed.

An example of this might be a delay for parts to cool down after being cooked, or a

transportation delay where a delivery mechanism is not being limited by other resources

(such as vehicles).

Breakdowns

All machine element detail dialogs contain a tab where breakdowns can be defined.

MODELING TIPS



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Limited Part Arrivals

Where there is a fixed number of a particular part in a model, for example pallets, the partdetail dialog offers a field called maximum arrivals which can be set to stop too many

entering the model.

Rules

A number of different rules are useful in this model. One model that contains a SEQUENCErule is Bells.mod accessible from the start page sample models option. In this model

the Assembly machine uses a SEQUENCE input rule.

MODELING TIPS



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18

Make sure that you look at the report tables and charts produced by WITNESS carefully in

your evaluation of each scenario. These are accessed by right clicking on a WITNESS

element and selecting the Statistics option.

In this model the machine reports are especially useful. Right clicking on the Simulation

folder of the WITNESS element tree (View -> Element Tree) and clicking on Statistics will

display the reports on all elements within the model (using the >> and


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Experimentation in the WITNESS Workbooks

Many of the examples in the two Learning WITNESS books accessed from the WITNESSStart Page include conducting experimentation and interpreting the reports. Time spent

studying these examples will increase your model analysis skills.

Speed to Answers

To get some idea of which improvements are worth making it is often a good idea to try anumber of shorter model runs which can be accomplished more quickly. This will help

determine which are the obvious good ideas and the poor ideas. The longer runs to

determine the more accurate answers then need only be carried out for the better

solutions.

EXPERIMENTATION TIPS


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ManufacturigCase Study