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Facility Design – An Introduction
R. Lindeke, Ph. D.
IE 3265
Sp. 2006
Facility Layouts:
A Decision that Encompasses:– Placement of ‘Departments’– Placement of Workstations/Machines– Placement of Stockholding points within Factory
or Warehouse– Development of Controlled Traffic Patterns to
generate smooth workflow throughout
Decision Makers:
What is the desired flexibility and required output?
What is the forecast product demand and its growth?
What are the processing requirements? Number of operators Level of flow between work stations and
between work areas How can the design balance
requirements on Workstation loading
Facility Space Available
Signs of a Successful Layout
1. Directed Flow Patterns:1. Straight line or other smooth patterns of
movement
2. Backtracking kept to a minimum
2. Predictable Processing Time
3. Little WIP in Facility
4. Open Floors: allow communication and easy tracking of work & employees
5. Bottleneck operations under control
6. Work Stations close together
Signs of a Successful Layout, cont:
7. Orderly Handling & Storage of Raw Materials and Finished products
8. No extra handling or unnecessary handling of materials
9. Can easily adapt to changing conditions1. Considers demand growth or decline
2. Considers product change over
3. Considers technological change
Workstation Layouts Within a cell:
End to End
Back to Back (poor)
IMPROVED LAYOUTS:
Front to Front
I/O
Circular or U Flow
Standard Layouts
Considering Circular or U-Flow:
Advantages: One operator can tend several machines Common I/O station simplifies material
transfer to/from cell to the rest of the facility
Automation can be tried for several machines
Disadvantages: Limited Queuing space or WIP storage
within cell Requires excellent balance and high
quality to keep flow active between workstations in the cell
Flow Patterns within Process Departments (Job Shops)
Aisle
A. Parallel Flow
Aisle
Aisle
B. Perpendicular Flow
Aisle
Aisle
C. Diagonal Flow
Some Job Shop Ideas:
Flow is in-out of the department not between machines
Traffic patterns must support movement from and to aisles
Diagonal designs often save floor space in 1 way aisle shops
Overall – Flow is a Function of Aisles
As a designer, aisle placement is of primary interest and often marks successful or failed designs!
Aisle Size is a function of Load Size!
Set Aside is controlled by Largest Load Area (Rules of Thumb)
Load Area Aisle Set Aside
< 6 ft2 5 -10% of calc. size
6 – 12 ft2 10 - 20% of calc. size
12 – 18 ft2 20 - 30% of calc. size
> 18 ft2 30 - 40% of calc. size
Aisle Consideration, cont.
Aisle width is controlled by the traffic that flows on it
Type of Traffic Min. Aisle WidthLarge Wheeled Indoor/outdoor Tractors 12’*
Large Forktrucks 11’
Small Forktrucks 9’
Narrow Aisle trucks/AGV’s 6’
Manual Platform Trucks 5’
Personnel 3’
Personnel w/doors 1 side 6’
Personnel w/doors both sides 8’
NOTE: Consider turning radiuses at intersections!
*For each direction
of flow
General Aisle Issues:
Good Aisle Designs … – Avoid curves/jogs/non 90
intersections– Avoid outside wall paths (these
are used for utilities so machine/workstations should back to walls if possible
– Are straight and lead to door ways
– Allow Flow to be controlled by entrances and exits (as it should)
Facility Designs Seeks:
To maximize directed (forward) flow
– Materials move directly from sources to destination without jogging around and by paths that don’t intersect other flows*
Minimize total flow (volume) of all products
Distances minimized, too Minimize cost of flow – expensive
flows should be short while lighter or less critical flows can be longer
*No Backtracks!
An Example:
Flow Straight Thru: A-B-C-D is 250’ Flow w/Backtracking: A-B-C-A-D is 550’ Backtracking is an Economic decision!
Cost of Added Equipment (replication of A) VS. Cost of added flow movement and traffic patterns (aisle set
aside) for each product that flows along backtrack
50’
50’
50’ 75’25’
A
B C
D
The Technical Jobs of Facilities Design:
Determination of Space requirements:– Workstation space for:
Equipment– Footprint + machine travel + access (load/maintenance) +
shop services (air/electrical/water, etc) Materials –
– consider unit load size + tooling/scrap etc Personnel –
– ingress & egress 30 – 42” for passage between stationary or operating machines
The Technical Jobs of Facilities Design:
Determination of Space requirements (cont.):– Departmental (Cell) Requirements:
(WSreqr + G.Service + M.Handlingreqr) G. Service areas
– offices, records, data, inspection/QC, etc. Material Handling
– inside traffic set asides to move product, tools, raw materials, etc
The Technical Jobs of Facilities Design:
Determination of Space requirements (cont.):– Specifics for Work Centers:
Use a Worksheet (see handout) Lists various resources and their requirements
considering services, physical loading (special needs?) List and sum all areas required Add in Aisle Allowance
– See handout (one for each work center or assembly line)
The Technical Jobs of Facilities Design:
The second job is to effectively provide for minimum flow and cost of flow
Here the designer performs studies of the space requirements and desired travel patterns
– Using Qualitative Tools: SLP (systematic layout planning) based on activity relationship
charts to suggest appropriate layouts Software to optimize the relationships
– Using Quantitative tools: Mileage Charts: area to area distance matrices From -To Charts: Move/Volume/Cost Matrices Appropriate software to compute and optimize the
arrangements
Typical Activity Relationship Chart:
These charts are often called an AEIOUX chart – the letters used to explain relationships that are learned during our facility studies:
Completing the Activities Relationship Chart:
After listing all departments on chart, Conduct Surveys to assess relationships with each department’s staff
Interpret results of surveys as closeness needs – itemize and record closeness requirements to support assessed relationship
Establish the relationships: A – absolutely necessary E – Especially Important I – Important O – “ordinary” closeness okay U – Unimportant X – Undesirable
Allow all concerned parties to review proposed chart for accuracy of closeness settings
Using Activity Relationship Chart to build Designs:
Using Pure SLP ideas we develop a “Meatball” diagram and move departments around to shorten A & E lines while increasing length of X lines
Using Activity Relationship Chart to build Designs
Using Activity Relationship Chart to build Designs
An alternative approach begins with looking at each department as equal sized rectangles listing letter relationship with all departments in the Facility
Receiving: A -; X-; E-B; I-D; O-C,E;
U- F,G
Milling: A -; X-; E-A,D; I-E,F; O-;
U- C,G
Press: A -; X-; E-; I-; O-A,F;
U- B,D,E,G
Sc. Machine: A -; X-; E-B; I-A,E;
O-; U-C,F,G
Plating: A -E; X-; E-G; I-B; O-C;
U- A,D
Shipping: A -; X-; E-F; I-E; O-; U-
A, B, C,D
Assembly: A -F; X-; E-; I-B,D,G; O-A;
U- C
Using Activity Relationship Chart to build Designs
Select template with highest number of A relationships; tied templates selected subject to hierarchy: most E’s, Most I’s, fewest X’s
Here select Plating department (F) Next template chosen should have A relationship w/
1st chosen – any ties broken as above Here Assembly, department E
Next template chosen should have the highest joint relationship with first two chosen
Here is Shipping – G This continues until all departments are chosen
In doing the Design:
F
E
G
B
D
A
C
By This Order:
Place F in Center. Then follow in order keeping Ideas (AEIOUX) of arrangements:
FE
G
BD
AC
A Final Step: now we consider actual departmental areas:
Code Function Area Ft2 # Units (2000 per)
A Receiving 12,000 6
B Milling 8,000 4
C Press 6,000 3
DSc.
Machines12,000 6
E Assembly 8,000 4
F Plating 12,000 6
G Shipping 12,000 6
Leads to the following Proposed Layout:
When equal sizes are replaced with scaled sizes we develop these layouts:
Obviously, many variants would be possible (no X’s and few A and E’s)
We determine appropriate layout only after quantitative analysis is applied to the proposed arrangements
Addressing the Quantitative Approaches:
Mileage Charts: showing Distances between Departments– Distances measures “Euclidian-wise” using
computed straight lines between department centroids
– Distances measure “Recti-linear” were department to department distances are computed by moving horizontally and vertically along expected aisle routes
Mileage Chart Format
A B C D E
A XXX 100 200 300 400
B 100(?) XXX 100 200 300
C 200 100 XXX 100 200
D 300 200 100 XXX 100
E 400 300 200 100 XXX
BackTracks:
From-To Charts
Charts, based on Routings, that show each relevant part’s movement through the proposed facility
Format is similar to Mileage chart but are rarely symmetrical or fully populated
More expensive travel can be handled with increased Volumes or have other special handling costs attached
Examining Quantitative Design
We begin with a Qualitatively designed facility (one that meets perceived activity relationships)
To keep it simple, lets look at a Flow–thru facility:
A B C D E
General Flow Direction
Consider that each of the departments
(A to E) are 100 units square
Representative Products are selected for study:
These might be “group seeds” or “large volume” products or in other ways represent how the product will move thru the facility
Lets explore 3: (Pr 1, Pr 2 and Pr 3)
Product Prod. Quantity Routing
Pr1 30 A-C-B-D-E
Pr2 12 A-B-D-E
Pr3 7 A-C-D-B-E
Mileage Chart:
A B C D E
A XXX 100 200 300 400
B 100 XXX 100 200 300
C 200 100 XXX 100 200
D 300 200 100 XXX 100
E 400 300 200 100 XXX
From To Chart (based on Routing)
A B C D E
A XXX Pr2 12Pr 1 30 +
Pr 3 2*7 = 30 +14 = 44
0 0
B 0 XXX 0Pr 1 30 + Pr2 12 = 42
Pr 3 2*7 = 14
C 0 Pr 1 30 XXXPr 3 2*7 = 14
0
D 0Pr 3 2*7 = 14
0 XXXPr 1 30 + Pr2 12 = 42
E 0 0 0 0 XXX
Pr 3 is heavier and costlier to move – we double volume to make it equivalent to Pr 1 & Pr 2
From To Issues
The filled cells below the diagonal represent moves against the general directed flow of the original facility design ( they – may (should) – cost more than moves above the line for the same distances)
Cells Close to the diagonal are short distance moves while cells remote from the diagonal are long distance moves
The number of moves (not filled cells!) must equal the total of each move in the routing sheets for the products
Costing Transport in the Layout:
For comparison: all forward moves cost $1/unit vol/unit distance All Backtrack move cost $1.25/unit vol/unit distance
Costs A B C D E
A xxx 1 1 1 1
B 1.25 xxx 1 1 1
C 1.25 1.25 xxx 1 1
D 1.25 1.25 1.25 xxx 1
E 1.25 1.25 1.25 1.25 xxx
Layout Total Transport Cost
Form: M*F*C “cell products” Sum each cell of resultant matrix it is the facility
transportation cost (for comparison)
Can we do Better?
Lets Swap Departments B & C
This will change our Mileage and Cost Matrices as well as arrangements in From/To Matrix
A C B D E
General Flow Direction
New Mileage Chart:
A C B D E
A XXX 100 200 300 400
C 100 XXX 100 200 300
B 200 100 XXX 100 200
D 300 200 100 XXX 100
E 400 300 200 100 XXX
New From-To Chart
A C B D E
A XXXPr 1 30 +
Pr 3 2*7 = 30 +14 = 44
Pr2 12 0 0
C 0 XXX Pr 1 30 Pr 3 2*7 = 14
0
B 0 0 XXXPr 1 30 + Pr2 12 = 42
Pr 3 2*7 = 14
D 0 0Pr 3 2*7 = 14
XXXPr 1 30 + Pr2 12 = 42
E 0 0 0 0 XXX
New Cost Matrix:
Costs A C B D E
A xxx 1 1 1 1
C 1.25 xxx 1 1 1
B 1.25 1.25 xxx 1 1
D 1.25 1.25 1.25 xxx 1
E 1.25 1.25 1.25 1.25 xxx
New Transportation Costs:
Examining these results:
Swapping 2 departments lead to a reduction in cost of:– $9900 or about 28% of the original cost
Can we improve further?– Not with this fundamental design – Can we redesign the general footprint?– Then we can keep looking!
New Fundamental Design:
And applying a Euclidean Concept of distances!
Distance from A to B is: (1002+1002).5 = 142 units Distance A to E is: (2002+1002).5 = 224 units Typically, with Euclidean distances, were would not consider
transport cost differences in either direction – this facility shape doesn’t favor general directions of flow!
A
B
C D
E
Mileage Chart (now)
A C B D E
A XXX 100 142 200 224
C 100 XXX 100 100 142
B 142 100 XXX 142 100
D 200 100 142 XXX 100
E 224 142 100 100 XXX
Transportation Cost Picture:
A further savings of $1000 – as manager we decide if the new configuration design is worth the savings gained!
