Lean String Theory

Before the widespread use of computers the location of warehouses, stores, franchises were often settled by using a ‘string map’. Pins were stuck in the map at customer’s locations, and string, usually thread or fishing line, looped over them, the weight on the end of each line being proportional to that customer’s deliveries. The ends of the string were knotted together. Where the knot settled was the center of pull (not gravity).

 

 

 

 

EVOP – Evolutionary Operations

Evolutionary Operation: A Statistical Method for Process Improvement (Wiley Classics Library)

 

Evolutionary Operations, first described by George E. P. Box and Norman R. Draper in in their book Evolutionary Operations – A statistical method for process improvement, New York: John Wiley and Sons, 1969.

EVOP is Continuous Improvement + Design of Experiments.

Basic idea is to replace the routine  operation of a process by continuous and systematic plan of slight adjustments of the control variables.  The effects of the adjustments are then evaluated just as with DOE.  The process is then shifted in the desired direction of improvement.  In many product and service processes it is impossible or very expensive to do DOE, especially where trials can be disruptive or the process owner would let you have the necessary time, materials, labor to run your experiments.  So rather than running experimental production runs you use actual production by shifting off the base point left, right, up, down all within "spec".

 

 

  Continue reading EVOP – Evolutionary Operations    

Cheat Sheet – Material Handling Equipment & Aisle Widths

Material Handling Equipment and aisle widths:

 

Type

Clear Height

Area to store 1,000 pallets

Aisle width

Counter-Balanced Truck

22′

10,000 sqft

144"

Narrow Aisle Reach

32′

6,270 sqft

90"

Very Narrow Aisle Swing-Reach

32′

5,480 sqft

66"

VNA Double Deep

32′

5,120 sqft

66"

Narrow Aisle Deep- Reach

32′

5,120 sqft

92"

VNA Swing-Reach

40′

3,420 sqft

66"

VNA High Reach Rail Guided

65′

2,020 sqft

56"

 

Fixed Repeating Schedule – Product Family Turnover Rate

Here’s another example for “sizing the wheel” for a mixed model fixed repeating schedule.

Given:

  1. Changeover Time = 100 minutes
  2. Available Production Time = 2 shifts * 7 hrs/shift * 60 min/hr = 840 min/day

and

Product Daily Demand (pcs) Cycle Time (min.) Load (min.)
A 80 5 400
B 40 4 160
C 20 4 80
D 10 6 60
700

Now some math:

  1. Total Load = 700 min.
  2. Time Available for Changeovers = 840 min/day – 700 min/day = 140 min/day
  3. Changeover Time for group = 100 min * 4 products = 400 min/family
  4. Changeovers per day = 140 min/day / 400 min/family = 0.35 group/day or a Replenishment Time of 2.85 days/family

So the fixed repeating wheel will turn once in 2.86 days.  Production run sizes as follows:

Product Daily Demand * Replen Time Cycle Time (min) Load (min)
A 229 5 1145
B 114 4 456
C 57 4 228
D 29 6 174
2003

Plus 4 changeovers of 100 min each = 2403 min = 2.86 days.

When it comes time to run product A, run 2.86 days worth. Got it?

Would be nice if we could run just one piece.  But until we can make the 100 minute changeover go away we’re stuck running a batch of some size.

 

 

 

Cheat Sheet – Stock Storage Types

 An example from a recent warehouse layout project; analysis leading up to a facility block (zone) layout.

 

Pallets per Item

No. of Items

Total No. of Pallets

Average No. of Pallets per Item

Floor Stack

Double Deep, Drive In

Push Back

Single Deep

Case Deep

Flow Rack

Shelves

Bin Drawers

>100

2

350

175

x

x

x

o

o

 

 

 

51 to 100

18

1,100

61

x

x

x

o

o

 

 

 

21 to 50

40

1,000

25

x

x

x

x

o

 

 

 

11 to 20

160

2,200

14

o

o

x

x

o

 

 

 

6 to 10

330

2,300

7

o

o

x

x

x

 

 

 

2 to 5

500

1,600

3

 

 

o

 

x

 

 

 

0.5 to 1

750

750

1

 

 

 

 

x

x

 

 

0.25 to 0.49

900

270

0.3

 

 

 

 

o

x

x

 

0.001 to 0.25

1,100

65

0.06

 

 

 

 

 

x

x

o

< 0.001

200

0.10

0.0005

 

 

 

 

 

 

o

x

 

X=preferred, O=workable but not preferred