Question 3 of 7: Planning a Materials Handling System

Question 3: Planning a Materials Handling System (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Part (a) — the benefits of planning handling as a system

Materials handling adds no form value whatsoever. Nothing is cut, joined, cured or finished while a part is being moved, and yet in a typical discrete manufacturing plant handling absorbs a quarter to a half of total operating cost and accounts for the great majority of the time a part spends in the works. That asymmetry is precisely why it repays deliberate planning: any cost removed from handling falls straight to the bottom line without touching product specification, and any time removed from handling shortens manufacturing lead time without adding capacity.

The first benefit of treating handling as a system rather than as a sequence of local equipment purchases is reduced handling cost per unit produced. Planning allows the loads to be standardised into unit loads — pallets, tote bins, containers, magazines — so that the number of separate movements collapses and mechanical handling becomes economic. It also allows moves to be combined, back-hauls to be loaded rather than run empty, and handling equipment to be sized to the aggregate flow instead of to the peak of one department.

The second is reduced work-in-process inventory and shorter throughput time. Handling delay is queueing delay; when a planned system fixes the route, the container and the trigger for each move, parts stop waiting for transport and the work-in-process banked at each machine falls. That capital released is real, and in a plant running to a schedule it also improves delivery reliability, because variability in transit time is a major contributor to variability in completion date.

Third is better space utilisation. A planned system decides aisle widths, stacking heights and storage locations together, so it can exploit the cube of the building rather than only its floor. Narrow-aisle trucks, gravity flow racks and overhead conveyors all buy floor area back, and floor area released inside an existing building is by far the cheapest capacity a plant will ever acquire.

Fourth is improved safety and reduced damage. Manual handling is the single largest source of lost-time injury in most manufacturing operations — strains from lifting, crush injuries at truck and pedestrian crossings, falls from stacked material. Under the provincial occupational health and safety regulations that govern Canadian plants, the employer must eliminate or minimise the risk of musculoskeletal injury, and mechanised or containerised handling designed in at the planning stage is an engineering control, which ranks above administrative controls and personal protective equipment in the hierarchy of controls. Planned handling also reduces product damage and scrap, because parts are transported in fixtures that support them rather than being carried loose.

Fifth is improved control and traceability. When loads are standardised and routes are fixed, each move becomes an event that can be recorded — by bar code, by radio-frequency tag, by a signal from an automated guided vehicle system — which is what makes real-time shop-floor control, accurate work-in-process accounting and lot traceability possible. An unplanned handling system produces no data at all.

Finally, planning creates flexibility and a basis for future change. A handling system laid out around a documented flow analysis can be re-routed when the product mix changes; an accumulation of point solutions cannot, because each was justified against a local condition that no longer holds. In practice the discipline of the analysis — flow charts, from-to charts, activity relationship charts — is itself a benefit, because it forces the sequence of operations to be examined and very often eliminates moves altogether. The best handled move is the move that does not have to be made.

Part (b) — direct or indirect cost?

Materials handling labour should ordinarily be treated as an indirect cost, charged to manufacturing overhead and absorbed by products through an overhead rate, rather than as a direct cost booked to individual job orders. The reasoning turns on the two tests that separate the categories: traceability to a cost object, and the practicality of tracing.

Direct costs are those that can be traced to a specific unit or job economically and without arbitrary allocation — the operator who runs the part on the machine, the material that becomes the part. A handling worker, by contrast, typically moves mixed loads for several jobs on one trip, waits, walks empty, and services whichever department calls first. Attributing minutes of that day to individual work orders would require a level of transaction recording whose cost exceeds the value of the resulting accuracy, and would still rest on arbitrary splitting rules. Handling labour is also, in accounting terms, a service to production rather than a component of it: it belongs with inspection, tool crib, maintenance and supervision, all of which are conventionally indirect.

There is a second, more important managerial reason. Because handling adds no value, burying it in the direct labour of each job hides it. Collecting it in a separate overhead account makes the total visible, allows it to be trended, and allows a proposed conveyor or fork truck to be justified against a measured figure. A cost that cannot be seen will not be reduced.

The classification is not absolute, and a complete answer should say so. Where a handling operation is dedicated to one product line and is measurably attributable — a robot loading and unloading a single machining cell, a conveyor serving one assembly line, a driver assigned full time to one product — then its cost is traceable and should be charged direct, and modern activity-based costing deliberately pushes handling out of a general overhead pool and onto the products that actually cause the moves, using cost drivers such as number of moves or number of loads. The correct answer is therefore: indirect by default, because handling serves the plant rather than the job; but direct wherever a specific handling resource is dedicated to a specific product and the tracing costs less than the distortion it removes.

Part (c) — why layout and handling must be determined together

Layout and handling are not two problems in sequence; they are one problem with two sets of decision variables. The reasons for settling them together are:

1. Layout determines the handling work to be done. The load-distance product that a handling system must deliver each week is fixed the moment the departments are placed. No amount of handling equipment can undo a layout that puts two heavily interacting departments at opposite ends of the building; it can only move the material faster or more cheaply.
2. Handling equipment dictates the geometry the layout must provide. Aisle widths, floor loading, column spacing, ceiling height, turning radii, dock heights and clearances are all consequences of the handling choice. Choosing an overhead crane, an automated guided vehicle or a narrow-aisle truck after the building is laid out means either rework or a compromised system.
3. They are jointly, not separately, optimal. The cheapest layout on its own plus the cheapest handling system on its own is generally not the cheapest total. A slightly worse arrangement of departments that permits a simple gravity conveyor may beat the theoretically best arrangement that requires powered trucks.
4. The same input data serve both. Flow analysis, from-to charts, activity relationship charts, route sheets and volume forecasts are collected once and drive both decisions. Doing them separately duplicates the analysis and risks the two being based on different assumptions.
5. Handling cost is the usual objective function of the layout problem. Layout algorithms minimise the sum over department pairs of trips multiplied by distance multiplied by cost per unit distance — and that last factor comes from the handling system. The layout cannot be evaluated until the handling method is at least provisionally chosen.
6. Space is consumed by both. Aisles, staging areas, storage banks and queue space in front of machines are handling requirements that occupy layout space. Ignoring them at the layout stage produces a plan that will not fit once the material actually arrives.
7. Capital is committed once. Buildings, foundations, pits, trenches and overhead structures are expensive to alter later. Deciding handling simultaneously allows the civil work to be provided in the first construction rather than retrofitted.
8. Safety and regulatory compliance are layout-dependent. Segregating pedestrian and vehicle routes, providing clearances at doorways, managing crane travel over work stations and planning emergency egress all have to be designed into the arrangement, not added to it.
9. Future flexibility depends on both. Provision for expansion, for changed product mix and for later automation must be built into the arrangement and the handling infrastructure at the same time if the plant is to be alterable at reasonable cost.

Systematic Layout Planning formalises exactly this joint treatment: the product-quantity analysis and the flow-of-materials analysis feed both the activity relationship diagram and the handling method selection, and the space relationship diagram is drawn only after the handling requirement is known. That is the practising engineer's answer to part (c) — the recognised procedure does not permit the two to be separated.

Final results.