Intended learning outcomes: Explain discrete order picking and batch picking. Describe sequential picking and zone picking. Differentiate between decentralized goods preparation and centralized goods preparation.
Order picking, or simply picking, is the issuance of items from stocking locations for delivery. Items are issued according to a particular picking strategy.
The picking strategy is the type of order picking chosen.
The order picking process typically includes making goods available in storage units, picking the required quantities of goods, consolidating the goods according to the picking sequence, transporting the result to shipping, and return of part-picked storage units to storage.
Order picking facilities find implementation mainly in the distribution of finished goods and in the shipping of spare parts, but they are also needed internally for supplying assembly or production. There are four picking strategies, depending on the type of stocking system and the replenishment techniques employed, as shown in Figure 15.4.1.1:
Fig. 15.4.1.1 Picking strategies. (Following [RKW-Ha]).
- In discrete order picking, orders are picked one after the other. The required accompanying document is a delivery note with the positions sorted in an optimal picking sequence. This optimal sequence is the shortest driving route through the warehouse. Accordingly, the specific sorting of the items of the delivery note is called a picking list (see also Section 15.2.1).
- Batch picking pools a number of orders and sorts the positions of all the corresponding items of the delivery notes together in an optimal sequence. The resulting picking list then permits all the products for delivery to be picked up in one trip through the warehouse. The individual shipments are then put together following the single, completed trip in a special secondary warehouse, in an order picking store, or in a commission stock. This procedure makes high-performance order picking possible, but it entails higher costs than discrete order picking, as both higher capital and operating costs result. Only where the range of products is very large and there is a high volume of orders with few positions, such as in mail-order businesses, is batch picking a cost-effective solution.
There are further picking strategies dependent on both the size of the warehouse and the product structure:
- Sequential picking: A trip is made through the warehouse for each single order or batch of orders in its entirety.
- Zone picking, or parallel picking: The warehouse is segmented into a number of picking zones, and the single order or batch of orders is split into partial orders picked in parallel. In a further operation in a separate area of the warehouse, all partial orders are then placed together. This makes sense for very large warehouses to shorten the routes of individual pickers. There is also segmentation of the warehouse according to product, such as segmentation into different temperature zones for refrigerated and frozen goods or separate areas for flammable or hazardous chemicals or for products that should not be stored together in proximity.
Other distinguishing criteria are the type of storage and the movement of the picker:[note 1513]
- In decentralized goods preparation, the goods are stored at constant locations, and the picker moves from one picking position to the next (called routing “people to the product”). The picker then moves the picked goods to an order consolidation area. Depending on the warehouse layout, the picker moves back and forth, or — in the case of multilevel storage with platforms that can be elevated and lowered or mezzanines with materials elevators — back and forth and up and down. This very common picking method is relatively simple to realize.
- In centralized goods preparation, goods are conveyed from storage to a permanent picking station, or kitting area (called routing “product to the people”). Conveyor belts, rack operation equipment, or stacking cranes move the goods. An important decision criterion for this type of goods storage is the issue of how to handle part-picked storage units from which items have been picked for an order. Part-picked pallets of product, for example, can remain at the pick station, but for space reasons, they often must be transported back to storage or to a special storage area. Control units of modern picking systems decide on the frequency of demand for the item (for example, using an ABC classification). Frequently demanded goods remain at the pick station, while other goods return to storage until needed.
Picking can range from manual to fully automated, depending on warehouse layout and type of picking system. Automation is possible for retrieving storage units, transporting them back to storage, dividing storage units (multiple-unit cartons or pallets) for single item picking, and finally, transporting the commissioned unit. Automation does not always require the use of robots. Separating single items can be accomplished by “automatic moving” rather than by gripping robots, whereby goods are lifted from a carton flow channel or caused to slide out of the channel.
Fully automated picking is a special case that is typically found in the pharmaceuticals industry and in mail-order businesses. For order consolidation, picking robots, automated conveyors, and other technical devices replace people entirely. This is only possible, however, if the items to be picked have similar dimensions (geometry) and are stable in shape (stiffness). In addition, the goods must be stored in precise arrangements, meaning that items must be stored in predetermined and dedicated storage locations and particular orientations to allow retrieval by automated equipment. Full automation is cost effective, however, only with high turnover and steady load of the facility.
For optimum processing of order picking, increasingly complex IT-supported control systems are being implemented. Warehouse management systems collate orders, create picking lists, calculate optimum picking routes, control and monitor traffic in the picking system (for example, the movements of picking robots), and, finally, document completion of the order. Modern systems also shorten retrieval times and retrieval routes by calculating the optimum design for the warehouse (that is, minimization of routes and replenishment efforts, with good utilization of floor space) and, when capacity is available, automatically trigger restocking of piles for faster goods retrieval.
The picking process ends when the item quantities have been consolidated to fulfill the order. The goods, usually not yet packaged, must now be prepared for shipment by the packaging department. Exceptions, however, are “pick and pack” operations, where goods are packaged during the picking process. If picking is incomplete, that is, not all the positions on a delivery note can actually be issued — whether foreseeable from the start or due to errors in inventory information — then the remaining positions of the order waiting for delivery can be split and put on a separate backorder.[note 1514]
Order picking should choose an analogous procedure for putting accompanying materials together for contract work, that is, external operations. The delivery of accompanying materials is a legally binding event, just as true sales orders are. The only difference is that no invoicing results from this, since the accompanying materials ultimately remain the property of the company and are only temporarily “loaned out.”
Course section 15.4: Subsections and their intended learning outcomes
15.4 Distribution Control
Intended learning outcomes: Explain order picking, packaging, load building, and transportation to receiver.
15.4.1 Order Picking
Intended learning outcomes: Explain discrete order picking and batch picking. Describe sequential picking and zone picking. Differentiate between decentralized goods preparation and centralized goods preparation.
15.4.2 Packaging
Intended learning outcomes: Present a conceptual framework to handle the diverse functions and requirements of packaging.
15.4.2b Load Building
Intended learning outcomes: Explain load building. Identify the levels of aggregation in load building.
15.4.3 Transportation to Receiver
Intended learning outcomes: Describe the selection of the mode of transport. Explain the transport chain from supplier to receiver and various kinds of organizing transshipment points.
15.4.3b Transport Routing and Scheduling
Intended learning outcomes: Present routing and scheduling and the optimization of loading space.
