📚 Inventory Management | 库存管理
Inventory management is a critical function in business operations, concerned with the ordering, storing and controlling of stock to meet customer demand while minimising costs. It directly affects liquidity, profitability and customer satisfaction. Effective systems ensure that a firm holds neither too much stock, which ties up capital and increases storage costs, nor too little, which can lead to stock-outs and lost sales.
库存管理是企业运营中的一项关键职能，涉及订货、储存和控制存货以满足客户需求，同时最大限度地降低成本。它直接影响企业的流动性、盈利能力和客户满意度。有效的库存管理体系确保企业既不会持有过多库存（这会占用资金并增加存储成本），也不会存货过少（这可能导致缺货和销售损失）。
1. What is Inventory? | 什么是库存？
Inventory refers to the stock of raw materials, work-in-progress and finished goods held by a business to enable smooth production and sales. It appears as a current asset on the balance sheet and represents money tied up until items are sold or used.
库存是指企业为保障生产和销售平稳进行而持有的原材料、在制品和成品的存货。它在资产负债表上列为流动资产，代表着在商品出售或使用前被占用的资金。
Inventory can also include consumables and maintenance supplies such as lubricants, packaging materials and stationery. For service businesses, inventory may refer to spare parts or goods for resale.
库存还可以包括消耗品和维护用品，例如润滑油、包装材料和文具。对于服务型企业，库存可能指备件或用于转售的商品。
2. Types of Inventory | 库存的类型
Raw materials are basic inputs bought from suppliers and used in the production process. Without sufficient raw materials, manufacturing may halt and result in idle labour.
原材料是从供应商处购买、用于生产过程的基本投入品。如果没有足够的原材料，生产可能会停滞并导致劳动力闲置。
Work-in-progress (WIP) consists of partially completed goods that are still on the factory floor. High WIP levels can signal bottlenecks and lengthy production cycles.
在制品指仍在车间内处于部分完工状态的商品。在制品水平过高可能表明存在瓶颈和较长的生产周期。
Finished goods are completed products ready for sale to customers. Holding finished goods allows a business to react quickly to unexpected orders but also incurs storage costs.
成品是已完成、可向客户出售的产品。持有成品使企业能够快速响应意外订单，但也会带来存储成本。
Decoupling inventory is stock kept between stages of production to allow independent operation, reducing downtime when one stage experiences a problem.
缓冲库存是在生产各阶段之间持有的存货，使各阶段能够独立运行，从而减少某个环节出现问题时的停机时间。
3. Reasons for Holding Inventory | 持有库存的原因
Meeting customer demand is the primary reason for holding stock. Sufficient finished goods ensure that customer orders can be fulfilled promptly, maintaining reputation and repeat business.
满足客户需求是持有库存的首要原因。充足的成品确保客户订单能够及时交付，维护声誉并保持回头客生意。
Buffer against uncertainty in demand and supply is vital. Firms hold safety stocks to guard against sudden demand spikes or supply disruptions caused by supplier delays, transport issues or natural events.
对供需不确定性进行缓冲至关重要。企业持有安全库存以防范需求突然飙升或由供应商延迟、运输问题或自然事件引起的供应中断。
Economies of scale in purchasing encourage firms to buy in bulk. Ordering larger quantities often reduces the unit purchase price, lowers ordering costs per unit and secures quantity discounts.
采购中的规模经济促使企业批量购买。订购较大数量通常能降低单位采购价格、减少单位订货成本并获得数量折扣。
Seasonal demand creates the need to build up stock well in advance. For example, retailers accumulate festive goods months before the holiday season to meet concentrated peak demand.
季节性需求导致需要提前大量备货。例如，零售商在节假日前数月就开始积累节日商品，以应对集中的需求高峰。
4. Costs Associated with Inventory | 与库存相关的成本
Holding costs, also called carrying costs, include warehousing rent, insurance, security, deterioration, obsolescence and the opportunity cost of capital tied up in stock. These costs typically rise with inventory levels.
持有成本，也称储存成本，包括仓库租金、保险、安保、损耗、陈旧以及占用资金的机会成本。这些成本通常随库存水平上升而增加。
Ordering costs cover the administrative expenses of placing and processing each order, such as delivery charges, inspection and paperwork. More frequent orders increase total ordering costs.
订货成本包含每次下单和处理订单的行政开支，如运输费、检验和文书工作。订货越频繁，总订货成本越高。
Stock-out costs arise when a business cannot fulfil customer orders. These include lost contribution, expediting charges, customer ill-will and potential damage to market share.
缺货成本产生于企业无法履行客户订单时，包括损失的利润贡献、加急费用、客户不满以及潜在的市场份额损害。
Quality costs may be linked to inventory, such as the cost of damage during storage or the risk of perishable items spoiling before sale.
质量成本可能与库存相关，例如存储过程中的损坏成本或易腐品在售出前腐败的风险。
5. Inventory Control Charts | 库存控制图表
An inventory control chart is a visual tool used to monitor stock levels over time. It plots key parameters such as maximum stock level, re-order level, minimum stock level and buffer stock to guide managers in ordering decisions.
库存控制图表是一种用来监控存货水平随时间变化的可视化工具。它标示出最大库存水平、再订货水平、最低库存水平和缓冲库存等关键参数，指导管理者进行订货决策。
Maximum stock level is set to prevent overstocking. It considers available storage space, holding costs and the risk of obsolescence. Stock should not exceed this ceiling.
最大库存水平的设定是为了防止过多库存。它考虑了可用的存储空间、持有成本和陈旧风险。存货不应超过这一上限。
Re-order level triggers a new order when stock falls to that point. It is calculated to ensure new supplies arrive before the buffer stock is reached, accounting for average lead-time demand.
再订货水平是当存货降至该点时触发新订单。它的计算要确保新供应在触及缓冲库存之前到达，同时考虑平均交货期内的需求。
Minimum stock level is a warning line above buffer stock; it signals that emergency action may be required if deliveries are late. Buffer stock is the safety net that absorbs extreme variations in demand and lead time.
最低库存水平是缓冲库存之上的一条预警线；它表示如果交货延迟可能需采取紧急措施。缓冲库存是吸收需求和交货期极端变动的安全网。
6. Buffer Stock, Lead Time and Re-order Level | 缓冲库存、交货期与再订货水平
Buffer stock is the extra inventory kept to mitigate the risk of stock-outs. Its size depends on the volatility of demand, reliability of suppliers and the cost of a stock-out versus the cost of holding the buffer.
缓冲库存是为降低缺货风险而持有的额外存货。其大小取决于需求的波动性、供应商的可靠性以及缺货成本与持有缓冲成本之间的权衡。
Lead time is the period between placing an order and receiving the goods. Longer or unreliable lead times force firms to hold larger buffer stocks and set higher re-order levels.
交货期是下订单到收到货物之间的时间。较长或不稳定的交货期迫使企业持有更多的缓冲库存并设定更高的再订货水平。
e is 3 weeks and buffer stock is 150 units, re-order level is (200 × 3) + 150 = 750 units.
再订货水平 =（每期平均用量 × 平均交货期）+ 缓冲库存。例如，若周用量为200单位，交货期为3周，缓冲库存为150单位，则再订货水平为 (200 × 3) + 150 = 750 单位。
7. Economic Order Quantity (EOQ) | 经济订货批量
Economic Order Quantity is a mathematical model that determines the optimum order size to minimise total inventory costs – the sum of ordering costs and holding costs. The EOQ balances the trade-off: ordering too little increases ordering frequency and costs, while ordering too much raises holding costs.
经济订货批量是一种数学模型，用于确定使总库存成本（订货成本与持有成本之和）最小化的最佳订货量。EOQ 平衡了两难局面：订货太少会增加订货频率和成本，而订货太多则会提高持有成本。
The formula is:
EOQ = √2 × D × O ÷ H
cost per unit per year. The EOQ assumes constant demand, constant lead time and no quantity discounts – limitations that require managerial judgement.
公式为：
EOQ = √2 × D × O ÷ H
其中 D = 年需求量（单位数），O = 每次订货成本，H = 每单位每年的持有成本。EOQ 假设需求恒定、交货期固定且无数量折扣——这些局限性需要管理层做出判断。
Using EOQ can reduce total stock costs significantly. However, businesses must regularly update D, O and H as conditions change, and may need to adjust ordering practices if supplier lead times vary.
使用 EOQ 可以显著减少总存货成本。然而，企业必须随条件变化定期更新 D、O 和 H 值，并且如果供应商交货期波动，可能需要调整订货实践。
8. Just-in-Time (JIT) Inventory Management | 准时制库存管理
Just-in-Time is a lean production approach that aims to receive goods only as they are needed in the production process, thereby eliminating buffer inventory. It originated in Japan and is closely associated with the Toyota Production System.
准时制是一种精益生产方式，旨在仅在需要时才接收生产所需物料，从而消除缓冲库存。它起源于日本，与丰田生产系统密切相关。
Under JIT, raw materials arrive just minutes before they are used, and finished goods are dispatched immediately to customers. This demands exceptional coordination with suppliers, flexible production schedules and a motivated workforce.
在准时制下，原材料在使用前几分钟才送达，成品立即发送给客户。这需要与供应商进行异常紧密的协调、灵活的生产计划和高积极性的劳动力。
Kanban systems – visual signals like cards or electronic messages – are used to trigger replenishment. A two-bin system with a kanban card ensures that when one bin empties, it signals the need for more stock.
看板系统——即卡片或电子信息等可视化信号——用于触发补货。带有看板卡的双箱系统确保当一个箱子空出时，发出需要更多存货的信号。
9. Advantages and Disadvantages of JIT | 准时制的优缺点
Advantages include lower holding costs, reduced waste from obsolete stock, faster response to market changes and improved quality focus. With minimal inventory, problems such as defective materials are quickly exposed and corrected.
优点包括较低的持有成本、减少陈旧库存带来的浪费、对市场变化的更快响应以及提高的质量关注度。在存货极少的情况下，诸如次品材料等问题会迅速暴露并得到纠正。
Disadvantages centre on vulnerability to supply disruptions. A strike, natural disaster or transport failure can instantly halt production. JIT also demands reliable suppliers and high-level workflow coordination, which can increase initial investment and training costs.
缺点集中于对供应中断的脆弱性。罢工、自然灾害或运输故障可能瞬间导致停产。准时制还要求可靠的供应商和高水平的工作流协调，这可能增加初始投资和培训成本。
JIT may reduce the ability to handle sudden demand surges and can strain relationships with suppliers if frequent, small orders raise their costs. Bulk discounts are often lost.
准时制可能降低处理突发需求激增的能力，并且如果频繁的小批量订单增加了供应商的成本，可能会损害与供应商的关系。批量折扣通常也会丧失。
10. Factors Influencing Inventory Management Decisions | 影响库存管理决策的因素
Demand predictability is a key factor. Stable demand allows for precise re-order levels and lower buffer stocks, while volatile demand requires higher safety stock.
需求的可预测性是一个关键因素。稳定的需求允许精确的再订货水平和较低的缓冲库存，而波动的需求则需要更高的安全库存。
Reliability of supply chains affects how much buffer is needed. Businesses with trusted local suppliers can hold less stock than those relying on distant, unpredictable sources.
供应链的可靠性影响需要多少缓冲。拥有值得信赖的本地供应商的企业，可以比依赖遥远且不可预测来源的企业持有更少的库存。
Cost of stock-outs must be weighed against holding costs. A hospital must carry far higher safety stock of life-saving drugs than a clothing store carries backup T-shirts.
缺货成本必须与持有成本权衡。医院对救命药品所必须持有的安全库存，要比服装店对备用T恤的准备要高得多。
Type of product also matters. Perishable goods, fashionable items and technologically sensitive components require tighter control and faster turnover to avoid obsolescence and spoilage.
产品类型也很重要。易腐品、时尚商品和技术敏感部件需要更严格的控制和更快的周转，以避免过时和腐败。
11. Impact of Poor Inventory Management | 库存管理不善的影响
Excess inventory ties up working capital, reduces liquidity and increases holding costs. It may lead to write-offs if stock becomes obsolete, damaging profitability and wasting resources.
过多库存会占用营运资金、降低流动性并增加持有成本。若库存变得过时，可能导致注销，从而损害盈利能力并浪费资源。
Insufficient inventory leads to stock-outs, lost sales and dissatisfied customers. In business-to-business markets, repeated stock-outs can permanently damage reputation and cause buyers to switch to competitors.
存货不足会导致缺货、销售损失和客户不满。在企业对企业市场中，反复的缺货可能永久损害声誉，并导致买家转向竞争对手。
Poor inventory control can result in inaccurate stock records, theft and pilferage. Without reliable data, managers may make irrational ordering decisions, creating a vicious cycle of over- and under-stocking.
库存控制不力可能导致库存记录不准确、失窃和盗窃。没有可靠数据，管理者可能做出不合理的订货决策，形成过度库存和库存不足的恶性循环。
12. Evaluating Inventory Performance | 库存绩效评估
Inventory turnover ratio measures how many times stock is sold and replaced over a period. A high turnover indicates efficient inventory management and strong sales, while a low turnover suggests overstocking or slow-moving items.
存货周转率衡量在一段时期内库存被售出和替换的次数。高周转率表明库存管理高效且销售强劲，而低周转率则意味着过度库存或滞销品。
Stock-out rate measures the frequency and duration of shortages. Reducing this rate must be balanced against the rising cost of carrying additional safety stock.
缺货率衡量短缺发生的频率和持续时间。降低该比率必须与增加安全库存所带来的上升成本相平衡。
Order fill rate tracks the percentage of customer orders fulfilled from existing stock without backordering. It is a direct measure of service level and is vital for customer retention.
订单满足率追踪从现有库存（无需延期交货）即完成的客户订单百分比。它是服务水平的直接衡量指标，对留住客户至关重要。
Managers should continually review key performance indicators and adapt inventory policies to align with corporate objectives, such as maximising return on capital employed or achieving a target delivery lead time.
管理者应持续审视关键绩效指标，并调整库存策略以配合企业目标，例如最大化已动用资本回报率或达到目标交付提前期。
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