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1、附录ATheory of ConstraintAn output of a system that identifies the need for and the type of action to be taken to correct a current or potential problem. Examples of action messages in an MRP system include release order, reschedule in, reschedule out, and cancel. In constraint management, the use of
2、nonconstraint resources to make parts or products above the level needed to support the system constraint(s). The result is excessive work-in-process inventories or finished goods inventories, or both. In contrast, the term utilization is used to describe the situation in which nonconstraint resourc
3、e(s) usage is synchronized to support the needs of the constraint.1) The classification of quantities of items that have been assigned to specific orders but have not yet been released from the stockroom to production. It is an uncashed stockroom requisition. 2) A process used to distribute material
4、 in short supply.2) A routing, usually less preferred than the primary routing, but resulting in an identical item. Alternate routings may be maintained in the computer or off-line via manual methods, but the computer software must be able to accept alternate routings for specific jobs.The percentag
5、e of time that a worker or machine is capable of working. The formula is Availability = (S - B)*100% / SWhere S is the scheduled time and B is the downtime. The volume/mix of throughput on which financial budgets were set and overhead/burden absorption rates established.In the theory of constraints,
6、 a process in which all expediting in a shop is driven by what is scheduled to be in the buffers. By expediting this material into the buffers, the system helps avoid idleness at the constraint and missed customer due dates. In addition, the causes of items missing from the buffer are identified, an
7、d the frequency of occurrence is used to prioritize improvement activities.A material of value produced as a residual of or incidental to the production process. The ratio of by-product to primary product is usually predictable. By-products may be recycled, sold as is, or used for other purposes. Th
8、e capability of a system or resource to produce a quantity of output in a particular time period. The process of measuring production output and comparing it with the capacity plan, determining if the variance exceeds preestablished limits, and taking corrective action to get back on plan if the lim
9、its are exceeded. Inventory decision making exercised at each stocking location for SKUs at that location.An amount of inventory kept between entities in a manufacturing or distribution network to create independence between processes or entities. The objective of decoupling inventory is to disconne
10、ct the rate of use from the rate of supply of the item.The locations in the product structure or distribution network where inventory is placed to create independence between processes or entities. Selection of decoupling points is a strategic decision that determines customer lead times and invento
11、ry investment. See: control points.A work center that is designated to produce a single item or a limited number of similar items. Equipment that is dedicated may be special composite part.equipment or may be grouped general-purpose equipment committed to a In the theory of constraints, the generali
12、zed process used to manage resources to maximize throughput. The drum is the rate or pace of protection against uncertainty so that the system can maximize throughput. production set by the systems constraint. The buffers establish the The rope is a communication process from the constraint to the g
13、ating support the constraint. operation that checks or limits material released into the system to Products whose customer specifications require unique engineering design, significant customization, or new purchased materials. Each customer order results in a unique set of part numbers, bills of ma
14、terial, and routings. A situation where the output capabilities at a nonconstraint resource exceed the amount of productive and protective capacity required to achieve a given level of throughput at the constraint.A method of inventory valuation for accounting purposes. The accounting assumption is
15、that the oldest inventory is the first to be used, but there is no necessary relationship with the actual physical movement of specific items.of range and time, to external or internal changes. Six different 1) The ability of the manufacturing system to respond quickly, in terms categories of flexib
16、ility can be considered: mix flexibility, design changeover flexibility, modification flexibility, volume flexibility, rerouting flexibility, and material flexibility. In addition, flexibility involves concerns of product flexibility. Flexibility can be useful in coping with various types of uncerta
17、inty. 2) The ability during periods of increasing or diminishing volume.of a supply chain to mitigate, or neutralize, the risks of demand forecast uncertainty, and transit time plus customs-clearance time uncertainty variability, supply continuity variability, cycle time plus lead-time A procedure f
18、or building process train schedules that starts with the first stage and proceeds sequentially through the process structure until the last stage is scheduled.A work center that performs the first operation of a particular routing sequence.The capacity generally not used in a system of linked resour
19、ces. From a capacity and excess capacity. The branch of accounting dealing with valuing inventory. Inventory may be recorded or valued using either a perpetual or a periodic system. A perpetual inventory record is updated frequently or in real time, while a periodic inventory record is counted or me
20、asured at fixed time intervals, e.g., every two weeks or monthly. Inventory valuation methods of LIFO, FIFO, or average costs are used with either recording system.Inventory used to protect the throughput of an operation or the schedule against the negative effects caused by delays in delivery, qual
21、ity problems, delivery of incorrect quantity, and so on.The dollars that are in all levels of inventory.A statement of a companys goals and approach to the management of inventories.Coordinating the lot sizing and order release decision for related items and treating them as a family of items. The o
22、bjective is to achieve lower costs because of ordering, setup, shipping, and quantity discount economies. This term applies equally to joint ordering and to composite part fabrication scheduling. A method of inventory valuation for accounting purposes. The accounting relationship with the actual phy
23、sical movement of specific items. The process of, or techniques used in, determining lot size.Dividing a lot into two or more sublots and simultaneously processing each sublot on identical facilities as separate lots, usually to compress lead time or to expedite a small quantity. A number that ident
24、ifies the lowest level in any bill of material at which a particular component appears. Net requirements for a given component are not calculated until all the gross requirements have been calculated down to that level. Low-level codes are normally calculated and maintained automatically by the comp
25、uter software.A production area consisting of one or more machines that can be scheduling.considered as one unit for capacity requirements planning and detailed The amount of time, in hours, that a machine is actually running. Machine hours, rather than labor hours, may be used for planning capacity
26、 for scheduling, and for allocating costs.The accumulation by workstation, machine, or machine group of the hours generated from the scheduling of operations for released orders by time period. Machine loading differs from capacity requirements planning in that it does not use the planned orders fro
27、m MRP but operates solely from released orders. It may be of limited value because of its limited visibility of resources.A document, group of documents, or schedule conveying authority for the job order, manufacturing authorization, production order, production manufacture of specified parts or pro
28、ducts in specified quantities. A technique that schedules materials before processors . This technique facilitates the efficient use of materials. MDS MRP systems use material-dominated scheduling logic.A type of order point replenishment system where the min is the order point, and the max is the o
29、rder up to inventory level. The order quantity is variable and is the result of the max minus available and on-order inventory. An order is recommended when the sum of the available and on-order inventory is at or below the min.A procedure used in some process industries for building process train s
30、chedules that start at an initial stage and work toward the terminal process stages. This procedure is effective for scheduling where several bottleneck stages may exist. Detailed scheduling is done at each bottleneck stage.A technique for short-term planning of actual jobs to be run in each work ce
31、nter based upon capacity and priorities. The result is a set of projected completion times for the operations and simulated queue levels for facilities. A set of procedures for determining the lot size and other parameters related to an order. A lot-sizing technique under which the lot size is equal
32、 to the net requirements for a given number of periods, e.g. weeks into the future. The number of periods to order is variable, each order size equalizing the holding costs and the ordering costs for the interval.An inventory record keeping system where each transaction in and out is recorded and a
33、new balance is computed.A bill-of-material coding and structuring technique used primarily for is set to zero and the order quantity to lot-for-lot. A phantom bill of transient subassemblies. For the transient item, lead time material represents an item that is physically built, but rarely stocked,
34、before being used in the next step or level of manufacturing. This permits MRP logic to drive requirements straight through the phantom item to its components, but the MRP system usually retains its ability to net against any occasional inventories of the item. This technique also facilitates the us
35、e of common bills of material for engineering and manufacturing. The standard hours of work required by the planned production orders. A generalized method for planning equipment usage and material requirements that uses the process structure to guide scheduling calculations. It is used in flow envi
36、ronments common in process industries.Production that adds value by mixing, separating, forming, and/or performing chemical reactions. It may be done in either batch or continuous mode. A technique that schedules equipment before materials. This technique facilitates scheduling equipment in economic
37、 run lengths and the use of low-cost production sequences. This scheduling method is used in some process -industries. Equipment that performs a basic manufacturing step, such as mixing or packaging, is are combined into process trains. Inventories decouple the scheduling of called a process unit. P
38、rocess units are combined into stages, and stages sequential stages within a process train.In the theory of constraints: The maximum of the output capabilities of a resource or the market demand for that output capacity.for a given time period. In the theory of constraints: A given amount of extra c
39、apacity at nonconstraints above the system constraints capacity, used to protect against statistical fluctuation. Protective capacity provides nonconstraints with the ability to catch up to protect throughput and due date performance. A price reduction allowance determined by the quantity or value o
40、f a purchase.The amount of time a job waits at a work center before setup or work is performed on the job. Queue time is one element of total manufacturing lead time. Increases in queue time result in direct increases to manufacturing lead time and work-in-process inventories.The process of changing
41、 order or operation due dates, usually as a result of their being out of phase with when they are needed. Reprocessing to salvage a defective item or part.In the theory of constraints: The planned amount by which the available capacity exceeds current productive capacity. This capacity provides prot
42、ection from planned activities, such as resource contention, and preventive maintenance and unplanned activities, such as resource breakdown, poor quality, rework, or lateness. Safety capacity plus productive capacity plus excess capacity is equal to 100% of capacity. fluctuations in lead time so th
43、at an order can be completed before its An element of time added to normal lead time to protect against will plan both order release and order completion for earlier dates than real need date. When used, the MRP system, in offsetting for lead time, it would otherwise. The standard hours of work requ
44、ired by scheduled receipts, i.e., open production orders.Material outside of specifications and possessing characteristics that make rework impractical.Products that have been stored uncompleted awaiting final operations that adapt them to different uses or customer specifications. The time required
45、 for a specific machine, resource, work center, process, or line to convert from the production of the last good piece of item A to the first good piece of item B. Reductions of actual quantities of items in stock, in process, or in transit. The loss may be caused by scrap, theft, deterioration, eva
46、poration, etc.In a min-max inventory system, the equivalent of the maximum. The target inventory is equal to the order point plus a variable order quantity. It is often called an order-up-to inventory level and is used in a periodic review system. The maximum output capability, allowing no adjustmen
47、ts for preventive maintenance, unplanned downtime, shutdown, etc.The amount of good or acceptable material available after the completion of a process. Usually computed as the final amount divided by the initial amount converted to a decimal or percentage. In manufacturing planning and control syste
48、ms, yield is usually related to specific routing steps or to the parent item to determine how many units should be scheduled to produce a specific number of finished goods. For example, if 50 units of a product are required by a customer and a yield of 70% is expected then 72 units should be started
49、 in the manufacturing process. A management philosophy developed by Dr. Eliyahu M. Goldratt that can be viewed as three separate but interrelated areas-logistics, performance measurement, and logical thinking. Logistics include drum-buffer-rope scheduling, buffer management, and VAT analysis. Performance measurement includes throughput, inventory and operating expense, and the five focusing steps. Thinking process tools are important in identif
