OpenSpecEngineering

Scores a facility layout by how much material handling it causes. For each path that material travels between two departments, enter how many loads move along it and how far each load goes. The page gives the load–distance score, the total flow and the average distance a load travels. Run it once for each layout you are weighing: the layout with the lower score moves the same material less far. Facility planners and industrial engineers use it to compare block layouts before moving equipment [1], [2].

Equations

LD = Σ f_ij · d_ij     F = Σ f_ij     d̄ = LD / F

f_ij is the flow from department i to department j: the number of loads (trips, pallets, carts) moved in a period. d_ij is the distance one load travels on that path. The sums run over every path you enter, up to six. LD is the load–distance score, F the total flow and d̄ the flow-weighted average distance per load [1].

Any units work, as long as every path uses the same ones. The score is in loads times distance, for example load·m per week.

Limits and common mistakes

• Measure distance the way loads really move. In a building with aisles, that is usually the rectilinear distance between department centers (along x plus along y), not a straight line [2].
• Use the same flows for every layout you compare. Only the distances should change.
• Count loads, not parts, if a load is a pallet of parts. A path with heavy or awkward loads can be weighted by entering a higher flow, such as an equivalent number of trips.
• Enter each direction once. If loads go both ways between two departments, either add the two flows on one path or enter two paths.
• The score only covers handling. Noise, safety, shared utilities and room to grow also decide a layout.

Worked example

A small plant moves material between five pairs of departments each week. Receiving to machining: 150 loads over 30 m. Machining to assembly: 90 over 20 m. Machining to paint: 40 over 45 m. Paint to assembly: 40 over 25 m. Assembly to shipping: 120 over 35 m. What is the score of this layout?

1. Choose Number of Flow Paths 5.
2. For paths 1 to 5, enter the flow and distance pairs 150 and 30, 90 and 20, 40 and 45, 40 and 25, and 120 and 35.
3. Press Solve. The Solution shows: Load–distance score Σ f·d: 13,300 load·distance
   Total flow: 440 loads/period
   Flow-weighted average distance: 30.2273 distance/load

Check by hand. 4,500 + 1,800 + 1,800 + 1,000 + 4,200 = 13,300 load·m a week, and 13,300 / 440 = 30.2 m per load. Receiving to machining and assembly to shipping make up about two thirds of the score, so a new layout should shorten those two paths first.