23-Ind-A3 Facilities Planning · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Tompkins, White, Bozer & Tanchoco, Facilities Planning (4th ed., Wiley) — facilities design alternatives, material flow planning, activity relationships, machine space determination, material handling systems and the materials handling equation, computerized layout (CRAFT/CORELAP), and tool-crib centralization; Niebel & Freivalds, Niebel’s Methods, Standards, and Work Design (13th ed.) — assembly-line balancing (Ranked Positional Weight technique), balance delay, and production/scrap-allowance planning.
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.
A unit load is a single item, or a number of items arranged or restrained (palletized, containerized, strapped, stretch-wrapped) so that the group can be moved, stored, and stacked as one single unit in one handling operation, by one handling device. It is the physical embodiment of the unit-load principle within the materials handling equation (Question 7(ii)): increase the size of the load handled per operation so that the number of separate handling operations — and therefore handling cost — falls.
Advantages: fewer handling operations/trips are needed to move a given total quantity of material, directly reducing labour and handling-equipment time; mechanized and automated handling (forklifts, powered conveyors, automated storage/retrieval systems) becomes practical, since these devices are built to handle a standard unit load rather than loose, irregular pieces; material is better protected against damage and loss/pilferage while contained in the unit; loading and unloading of trucks and rail cars is faster, reducing dock occupancy time (part (b)); and space utilization improves where unit loads can be stacked or racked to a consistent, known footprint, simplifying storage planning and inventory counting.
Disadvantages: capital is required for load-forming/restraining equipment (pallets, straps, stretch-wrap, containers) and for handling/storage equipment sized to the unit load; the load-forming hardware itself adds dead weight and dead space (tare weight and cube that carry no product), reducing effective payload and increasing shipping cost; flexibility is reduced for small or partial-quantity orders, which may require breaking down a unit load — an added handling step that partly offsets the savings the unit load was meant to provide; and unit-load dimensions must be standardized across the facility (and ideally the supply chain) for the equipment compatibility to actually pay off, which constrains packaging and equipment choices elsewhere in the system.
Because truck bed heights vary (by vehicle type, load weight, and suspension settling as the vehicle is loaded or unloaded) while the dock floor is fixed, several methods compensate for the resulting vertical gap so that material handling equipment (forklifts, pallet jacks, hand trucks) can cross safely between dock and vehicle: (1) Dock levelers — mechanical or hydraulic ramps built into (or mounted at) the dock edge that pivot to bridge and continuously adjust for the gap and slope between the dock floor and the truck bed, including the bed's rise as the truck is unloaded; the most common solution at moderate-to-high-volume docks. (2) Dock boards/plates — portable ramps placed manually across the gap, a simpler and cheaper alternative suited to lower-volume docks or occasional/non-standard vehicles. (3) Dock (scissor) lifts — a powered platform that raises or lowers the entire load (and often the handling equipment) to match a specific truck's bed height, used where the dock must serve vehicles with widely different bed heights (e.g., vans versus highway trailers) that a fixed-height leveler cannot bridge safely. (4) Depressed truck aprons/wells — a building/site design solution that lowers the vehicle parking area itself relative to the dock floor, so a standard trailer's bed naturally lines up with the dock without any moving equipment. (5) Edge-of-dock or air-powered levelers for smaller gaps and lighter-duty applications. The method chosen trades capital cost against the range of vehicle types and volumes the dock must serve.
Powered (live) roller conveyors move unit loads (cartons, pallets, totes) along a fixed path on a series of motor-driven rollers, providing continuous or accumulating (zero-pressure) transport without requiring the load to be self-propelled or manually pushed. Characteristics: fixed path (low routing flexibility once installed); high, consistent throughput for standardized unit loads travelling a repetitive route; capable of accumulation (loads can queue on the conveyor itself, a form of the in-line buffering discussed in Question 3(ii)); relatively high fixed capital cost and floor-space commitment, but low incremental operating cost per unit moved once installed; well suited to point-to-point transport between fixed stations (as in an assembly or process line) rather than to variable, on-demand moves.
A bridge (overhead travelling) crane spans an area on rails mounted high on the building structure or on dedicated runway columns, with a hoist/trolley that travels along the bridge, giving three-axis (bridge travel, trolley travel, hoist lift) coverage of the entire area beneath the crane without consuming any floor space for its own travel path. Characteristics: very high lifting capacity, suited to heavy, bulky loads that floor-level equipment cannot handle economically; covers a large rectangular service area with a single piece of equipment; does not obstruct floor-level traffic or storage since it operates entirely overhead; requires significant building structural capacity (runway beams/columns sized for the crane and maximum load) that must be planned into the building design from the outset, not retrofitted cheaply; and, being a single shared resource over its service area, can become a bottleneck if multiple work areas beneath it compete for crane time simultaneously.
An industrial robot is a reprogrammable, multi-axis manipulator used to perform handling, assembly, welding, painting or other repetitive tasks under program control rather than fixed mechanical linkage. Characteristics: highly flexible/reprogrammable — the same physical robot can be re-tasked for a different product or operation sequence by changing its program and end-effector (tooling), unlike single-purpose fixed automation; capable of high precision and repeatability, and of working continuously (including in hazardous, high-heat, or otherwise unsafe-for-humans environments); higher capital cost and more sophisticated integration/programming/maintenance requirement than either powered conveyors or manual handling; economically justified primarily where volume is high enough and/or the task is hazardous/precision-critical enough to offset the capital and integration cost; commonly used within manufacturing cells (Question 5(i)) for load/unload, assembly and welding operations where its flexibility across the cell's part family is a direct advantage over single-purpose fixed automation.
