Tutorial on the Design of a Lean Manufacturing System using PFAST

Heng Huang

Informations

• Publié par: Idru
• Nombre de lectures: 73
• Langue: English

Extrait

Foreword

Implementation of Lean Manufacturing in Custom Forge Shops

Introduction

A custom forge shop, especially one that makes short production runs to supply spares to

defense agencies such as the Defense Logistics Agency (DLA) and Department of

Defense (DOD), must manage a complex and dynamic network of multi-product flows in

their manufacturing facility. This task is made especially more difficult because of the

following characteristics of a typical custom forge shop: process-oriented layout of the

facility, batch-oriented and setup-intensive processes, and large equipment with deep

foundations that cannot be relocated (“monuments”). These constraints severely limit the

efforts of any custom forge shop in its efforts to be cost-effective and on-time, especially

for short production runs. Therefore, like any other jobshop-type manufacturing facility,

a custom forge shop also needs to recognize how their current facility layout

helps/inhibits waste-free flows of products, people, materials, etc. In turn, this would

help them to identify and prioritize the implementation of best practices and tools for

reduction of operating costs and lead times using analysis tools that are suited for

jobshops, and not high-volume assembly line-type facilities. With an effective layout,

material handling system and shopfloor communication system in place, any forge shop

could realize savings from reduced work-in-process inventory, reduced scrap and rework,

reduced production lead times and effective order tracking and progressing.

Trends in the Forging Industry

In the report developed by the Forging Industry Association titled

Forging Industry

Vision of the Future

1

, it is stated that, “to position itself for world leadership in the year

2020, the forging industry has determined that its primary efforts should fall into five

program groups: (1)

production efficiency

, (2) energy efficiency, (3) recycling, (4)

environmental protection, (5)

enterprise issues

……. Through the process of analyzing

the key competitive challenges that will shape its future, the forging industry has

identified specific goals that will have the most profound impact on the competitiveness

of the industry as a whole and on the value of its contribution to the global manufacturing

market by the year 2020. Attaining these strategic targets will assure that the U.S. forging

industry becomes the world leader in customer-focused, efficient and cost effective

supply of superior quality components. These goals include:

•

Tooling--Increase die life by at least 10 times that of current levels. Reduce per-

part die system costs by at least 50%. Produce tooling within 24 hours from time

of order.

•

Energy--Reduce the total forging process energy input by 20% while cutting the

per-piece energy cost by 75%.

1

Available at

www.forgingmagazine.com/misc/vision/

.

(iii)

•

Material utilization--Achieve a minimum overall reduction in raw material

consumption of 15%. Reduce the scrap rate (increase material utilization) by

90%.

•

Productivity--Improve per-employee productivity by 50%. Reduce per-piece labor

costs by 60%. Achieve average forging facility up-times of 90%.

•

Quality--Reduce rejected or returned work to less than 25 parts per million.

Achieve ±6 sigma process control.

•

Environment--Generate no harmful gas combustion products; completely

eliminate aerosol emissions within forging plants; and recycle all fluids necessary

to forging operations …..”

Also, a recent survey of 200 North American mid-sized manufacturers (Manufacturing

Engineering, October 2000, page 22) states that “… some 60% of the companies

surveyed reported that improving plant-floor productivity is the most important issue they

face. Within this group, half are seeking ways to shorten the time needed to implement

workflow process changes …… many who responded to the survey want to improve

workflow processes on the fly, and also want operations people on the shopfloor, not IT

personnel, to implement these real-time solutions that are easy to implement and use”.

Lean Manufacturing in Custom Forge Shops

Lean Manufacturing is “a manufacturing philosophy that shortens the Customer Wait

Time

2

by eliminating waste between the receipt of a customer order and the shipment of

that order to the customer”. Anytime that an order is delayed, the cost of one or more of

the

Seven Types of Wastes

– overproduction, performance of non-standardized work,

queue time, transportation (or material handling) time, inventory (raw material, WIP and

finished goods), unnecessary motions and travel, defective products and underutilized

(workforce) skills – gets added to the cost of producing the order, thereby preventing on-

time delivery to the customer and reduces the profits earned by the supplier. Hence, for

the typical forge shop doing business with the DLA and/or DOD, the adoption of Lean

Manufacturing would minimize the Customer Wait Time for any order.

However, should forge shops adopt the

standard

Lean Manufacturing strategies such as

Manufacturing Cells, Setup Reduction, Process Standardization, Visual Workplace

Design and Pull Scheduling that have been adopted in other sectors of industry,

especially automotive and aerospace OEM’s and their Tier 1/Tier 2 suppliers?

Unquestionably, the OEM’s and their top-tier suppliers have realized major productivity

improvements by implementing the well-known “Toyota Lean” model. However,

custom forge shops that supply the DLA and DOD operate more like jobshops. Hence,

their business model (high product variety and low volumes, or HVLV) is unlike the

business model (low product variety and high volumes, LVHV) of the OEM’s and their

top-tier suppliers.

2

Customer Wait Time = Administrative Lead Time [ALT] + Production Lead Time [PLT]

(iv)

Differences between Toyota Lean and Jobshop Lean (JSLean)

•

Product Variety

: “Toyota Lean” is based on a product family with variations

whereas the HVLV system must be designed for a complicated material flow

network resulting from the large number of dissimilar (100 to 5,000+)

manufacturing routings.

•

Layout

: “Toyota Lean” is based on similar manufacturing routings and Bills Of

Materials for a product family whereas the HVLV system must have a layout

based on multiple dissimilar components or custom product configurations.

•

Demand Volumes

: “Toyota Lean” relies on a high and relatively stable market

demand whereas the HVLV system, being dependent on a broad customer base

for business, may not have the luxury of demand stability.

•

Product Design and Process Engineering

: “Toyota Lean” can enjoy the benefits

of “variant design” because “a car is a car is a car” whereas the HVLV system

often needs to design and manufacture parts and products that have little or no

similarity with past orders.

•

Availability of Internal Resources

: “Toyota Lean” is utilized by companies that

often have the resources to hire full-time engineers or high-profile consulting

companies to implement Lean Manufacturing. Whereas, the typical HVLV

system may not have the engineering talent, technical resources and finances to

finance extensive training and kaizen activities.

•

Flowline vs. Jobshop Scheduling

: “Toyota Lean” can utilize “Takt Time” to

schedule a single U-shaped cell or multi-product assembly line based on a Single

(or Mixed) Model Assembly Line Balancing problem. Whereas, the HVLV

system, unless fully decomposed into independent manufacturing cells, presents a

Jobshop Scheduling problem.

•

Pull vs. Push Scheduling

: “Toyota Lean” can rely on market “pull” to control

inventory buffers using kanban signals. Whereas, the HVLV system, since it

lacks repetitive and stable demand, must use priority-based scheduling of orders

based on their due dates and profit margins for the high product mix, and gate the

release of new orders into a capacity-constrained system.

Assessment of Custom Forge Shops

Tours of several forge shops showed that the typical forging facility is characterized by

batch-oriented processes, large monument-like equipment that cannot be relocated into

cells, a large variety of forgings being produced at any time in the facility and manual

shopfloor communications between machine operators, forklift drivers and plant

managers/supervisors. Figures 1(a)-(d) present an industry-wide assessment of several

custom forge shops. Figure 1(a) shows the flow path of a single forging that is being

produced in at least three different locations. This dispersion of the manufacturing assets,

and the functional (or process village) layout of the facility at each location, results in a

Value Added Ratio (Actual Man Hours/Total Lead Time) of about 10%. Figure 1(b)

presents a comparison of the Administrative Lead Time (ALT) and Production Lead

(v)

Time (PLT) of several forgings supplied to the DLA by a single forge shop. Forgings

that have a high unit price are seen to have the highest lead times in both dimensions,

which is the primary reason for high WIP costs. Figure 1(c) illustrates the existing chaos

in the material flow network at a DOD supplier of forgings. Figure 1(d) illustrates the

existing chaos in the material flow network at a DLA supplier of forgings.

It is not our intention to take anything away from what the architects of the Toyota

Production System have achieved. However, it must be recognized that the typical

HVLV manufacturer operates in a Make-To-Order business environment. These

jobshop-type manufacturers do not have an extensive suite of well-documented, easy-to-

use and thoroughly validated methods and tools to support their implementation of Lean

Manufacturing. Clearly, there is a need for new concepts and analysis tools specifically

suited for custom forge shops to implement Lean Manufacturing in a manner that suits

their business model and manufacturing environments. They are ill-advised to implement

several elements of the Toyota Production System that are primarily suited only for

assembly facilities!

Key Challenges for Jobshops seeking to Implement Lean Manufacturing

The how-to books on design and operation of “Lean” jobshops are significantly fewer in

number than those written for Lean Manufacturing for assembly line-type facilities. Here

is a sample of challenging issues in the JSLEAN arena that lack effective solutions:

ƒ

How does a jobshop segment its product mix into categories such as “Runners”,

“Repeaters” and “Strangers”? Are computer-oriented methods, such as Product-

Quantity-Routing-Revenue (P-Q-R-$) Analysis, Group Technology and Product-

Process Matrix Clustering, capable of analyzing a large database of anywhere

between 500 to 5000+ routings?

ƒ

How does a jobshop identify and implement not just a

single

“pilot” cell, but

all

potential cells for different families of parts that may exist in its large product

mix? What does it do about the “cats and dogs” in its product portfolio? Could

it implement virtual (dynamic and reconfigurable) cells for a portion of its

product mix?

ƒ

How does a jobshop develop a self-motivated workforce knowledgeable in

Industrial Engineering skills who seek to eliminate

muda

in a wide variety of

administrative and production processes

on a daily basis

?

ƒ

How does a jobshop adopt, or adapt, the concepts and models of Lean Thinking

when:

o

demand forecasts are unreliable or non-existent?

o

suppliers may not be prepared to deliver JIT?

o

equipment must be multi-function,

and not right-sized

, to compensate for

a small multi-skilled workforce?

o

customers could be here today but gone tomorrow?

o

drawings, route sheets, inspection plans, gauges, tools, etc. for past (or

new) orders need to be retrieved (or developed from scratch) on a routine

basis?

(vi)

400'

Location 3 Facility

Inspect

Saw Trim

Grind

Cleanup

Etch

Press 8

Press 3

Straighten

Age

Heat Treat

Penetrant

Cleanup

100'

200'

100'

100'

100'

Stockroom

Final Inspect

Shipping

Inspect

Machine Shop

~

~

~

~

1500'

~

~

~

~

Location 1 Facility

Outside

Processor

25 Miles

~~

~~

1

2

3

9

13

34

40

35

36

37

41

42

38

39

23

22

24

15

5

11

16

6

12

17

7

19

30

18

27

28

26

21

32

33

4

8

10

14

20

25

29

31

260.4

2760

0

500

1000

1500

2000

2500

3000

Hours

Actual Man Hours

Total Lead Time

0

2

4

6

8

Etch

Inspect

Shipping

Press

Cleanup

SawTrim

Grind

Outside

Processor

Straighten

Penetrant

Age

HeatTreat

Machine

Shop

Stockroom

Operation

Frequencyof

Occurance

Figure 1(a) Enterprise Flow Map for a Forging

0

100

200

300

400

500

600

700

0

50

100

150

200

ALT (Administrative Lead Time)

PLT(ProductionLeadTime)

Low Unit P ric e P arts

M edium Unit P rice P arts

High Unit P ric e P arts

A verage LT

Figure 1(b) Comparison of Forgings based on Unit Price, ALT and PLT

(vii)

Figure 1(c) Material Flow Network at a DOD Supplier

Figure 1(d) Material Flow Network at a DLA Supplier

(viii)

ƒ

How does a jobshop define and distill its “core manufacturing competencies”

into a guidebook that its sales staff could use to accept, evaluate or reject new

orders based on past cost/benefit performance measures?

ƒ

How does a jobshop implement Finite Capacity Scheduling without purchasing

expensive software, since Theory Of Constraints and Drum-Buffer-Rope

scheduling have been known to succeed in such facilities?

ƒ

How does a jobshop layout its facility to achieve flow and be flexible to changes

in product mix, demand and manufacturing technology?

ƒ

How does a jobshop train its material handlers to perform shopfloor scheduling

and order progressing functions, similar to the “whirligig beetles”

(“mizusumashi”s) who are employed in the Toyota Production System?

ƒ

How does a jobshop adopt real-time inventory tracking technology utilized in

warehouses and distribution centers to achieve pseudo-JIT operations?

ƒ

How does a jobshop develop a partnership with its suppliers in order to better

estimate and control supplier delivery schedules?

Design For “Lean Flow”

Forge shops that pursue military/government contracts have a critical need to be flexible

to respond to significant changes in product mix changes in order to be able to quote

short lead times and profit from short run orders. A poorly-designed facility layout and

complex material flows resulting from a diverse product mix are primary reasons for high

manufacturing lead times for delivery of mission-critical parts to the DLA and DOD.

In

just about any manufacturing facility

, empirical evidence suggests that, of the

Seven

Types of Wastes

(overproduction, overprocessing, queuing delays, transportation time,

work-in-process inventory, unnecessary motions and travel by operators, scrap and

rework), 95% of the production lead time of an order is dominated by two types of waste:

Queuing at each workcenter

and

Transportation between workcenters

. These dominant

wastes can be eliminated or reduced by design and operation of custom forge shops based

on the principles of “Lean Flow” to design

any

facility layout:

•

Principle #1: Minimize production flows,

•

Principle #2: Maximize directed paths for production flows,

•

Principle #3: Minimize the cost of production flows.

For example, the Toyota Production System (TPS) is a classic example of how the above

principles apply to an assembly facility. Principle #1 is embodied in flattened product

Bills Of Materials that have minimum number of components and product Bills of

Routings that contain manufacturing routings with the least number of operations on

different machines. Principle #2 is embodied in POUS (Point-Of-Use-Storage) focused

factories and assembly line-type material flow routes. Principle #3 is embodied in U-

shaped cells with one-piece flow, kanban-based WIP control and Pull-based production

scheduling.

Ideally, the forging equipment in a forge shop should be located in some type of work

cell composed of heating, forging and trimming capabilities. Unfortunately, these

machines have significant foundations that make it economically infeasible to relocate

(ix)

them. However, the support equipment in a forge shop, such as induction heating, flash

trimming and machining, is easier to relocate, as are other support operations such as

material storage, tool and die storage/repair, material cutting (shear and saw), shot

blasting, and magnetic particle inspection. Further, the machine shop that is attached to a

custom forge shop, is ideally suited for implementation of both manufacturing cells

and/or layout modules (which are partial cells). Therefore, the foundation for our

strategy for the implementation of Jobshop Lean in custom forge shops is:

(1)

grouping of the equipment for these support operations into layout modules, and

locating these modules in close proximity to the forging machines,

(2)

scheduling the monuments such as heat treatment and plating to coordinate with the

production schedules of the layout modules.

Conversion of the current facility layout of

any

custom forge shop into a Cellular or

Modular configuration is

the

prerequisite

and

foundation for them to improve delivery

performance, reduce work in process inventory levels and eliminate scrap by

implementing JobshopLean.

Group Technology and Cellular Manufacturing: Foundations for Implementation

of Jobshop Lean (JSLean) in Custom Forge Shops

Naturally, the first question that will be asked is, “How do we implement the proposed

JSLean strategy?” The answer is: Through the integration of Group Technology (GT) to

decompose a product mix into part families and Cellular Manufacturing (CM) to design a

flexible facility layout.

Group Technology (GT)

seeks to identify and group together

similar parts to take advantage of their similarities in manufacturing and design. GT has

been practiced around the world for many years as part of good engineering practice and

scientific management. Originally, GT was defined as “a method of manufacturing piece

parts by the classification of these parts into groups and subsequently applying to each

group similar technological operations” (Mitrofanov, 1966). A modern definition of GT

is “the realization that many problems are similar, and that by grouping them, a single

solution can be found to a set of problems, thus saving time and effort” (Shunk, 1987).

This definition captures the true essence of GT that the population of entities or activities

in a manufacturing system, or sub-system, can be replaced by a smaller number of

families. However, the most general definition of GT is that “it is a manufacturing

philosophy which identifies and exploits the underlying proximity of parts and

manufacturing processes” (Ham, 1985). Part families are at the core of best practices,

such as Variety Reduction, Standardization, Design For Flow, Flexibility, Agility and

Reconfigurability, which are essential for

“supercharging”

the implementation of Lean

Thinking in high-variety low-volume manufacturing facilities.

Cellular Manufacturing

(CM)

is an application of the GT concept

specifically

for factory reconfiguration and

layout design. Cellular Manufacturing Systems (CMS) have been erroneously promoted

as the

only

layout alternative to replace the process layouts that are widely observed in

job shops. This is because process layouts give a jobshop owner a false sense of mix and

volume flexibility. Whereas, cellular layouts give a jobshop owner limited operational

benefits of flow line production only for certain segments of his/her total product mix and

customer base. CM involves processing a collection of similar parts on a dedicated group

of machines or manufacturing processes. A

Manufacturing Cell

can be defined as “an

(x)

independent group of functionally dissimilar machines, located together on the floor,

dedicated to the manufacture of a family of similar parts”. A

Part Family

can be defined

as “a collection of parts which are similar either because of geometric shape and size or

because similar processing steps are required to manufacture them”. Usually, in a

Cellular Manufacturing System (CMS), it is preferable that a cell be dedicated to a single

part family, that each part family be produced completely within its cell, and that the

different cells have minimum interaction with each other.

Jobshops are complex high-variety low-volume manufacturing facilities where the

changes in product mix, volume, customer base, workforce skills, process technology,

etc. are significant. A complete reorganization of a typical jobshop into a Cellular Layout

may be ill-advised due to the inherent inflexibility of manufacturing cells to adapt to

changes in their product mix, demand volumes and capacity requirements (machine and

labor) to meet production schedules.

Hybrid Cellular Layouts

, unlike the traditional

network of manufacturing cells in a Cellular Layout, provide an effective foundation for

jobshops to configure their shopfloors differently from the typical assembly facility.

These layouts integrate the flexibility of a Process Layout with the order flow tracking

and control of a Cellular Layout. They are designed based on the principles of Design

For Flow to achieve waste-free, and therefore high-velocity, flows of orders in a Make-

To-Order (MTO) realm without necessitating repeated shopfloor reconfiguration.

About this Book

This book describes the architecture, program outputs and variety of

potential

industrial

applications of PFAST (Production Flow Analysis and Simplification Toolkit). In

particular, it focuses on how to use the PFAST software for design of flexible facility

layouts that serve as the foundation for effective implementation of JSLEAN best

practices in jobshops.

PFAST (Production Flow Analysis and Simplification Toolkit)

is a software tool that has automated the manual methods of Production Flow Analysis

(PFA) for material flow analysis, part family formation, design of manufacturing cells,

and factory layout. In a typical application, Production Flow Analysis (PFA) is

implemented in four stages – Factory Flow Analysis (

FFA

), Group Analysis (

GA

), Line

Analysis (

LA

) and Tooling Analysis (

TA

). Each stage in PFA seeks to eliminate delays in

production flows and operational wastes in a progressively smaller area of the factory. In

Factory Flow Analysis (FFA)

, the flows between shops (or buildings) on the factory site

are evaluated to eliminate wastes due to transportation, communication delays, use of

large containers to store WIP and use of bulk-handling material handling equipment to

move the large containers over large distances. In

Group Analysis (GA)

, the flows

between machines in

each

shop within the factory are evaluated to implement

manufacturing cells to produce families of parts with identical (or similar) routings. In

Line Analysis

(

LA

), the flows between machines in

each

cell are evaluated. A layout for

the cell is designed for efficient inter-machine material handling, multi-machine tending

by individual operators and minimum wasted motions by operators. In

Tooling Analysis

(

TA

), the flows at

each

machine in a cell are evaluated to optimize the workstation layout

for ergonomics of machine operation and rapid execution of setup activities, such as

machine loading/unloading, tool changes, fixture changes, tool kitting and storage, parts

(xi)

(xii)

inspection and cleanup. To date, PFAST has been used successfully to implement

JSLean in machining, pipe fabrication, forging, woodworking, cable manufacturing,

electronic assembly and welding jobshops.