SAP四种安全库存的设置

安全库存只是一个笼统的说法，本文归纳了SAP 四 种安全库存（时间）的设置，用于增加计划过程中库存数量（时间）的弹性。为何安全库存能增加计划的弹性呢？因为在净需求计算（Net Requirements Calculation）中，Quantity available = Fixed receipts + Stock available for planning - Safety stock - requirements，若可用数量小于零，则报缺料，视为短缺数量（Shortage quantity ）或需求数量（Net requriements），将用于批量计算并得出最终的获取建议。

Safety stock

Safety stock partially available

Dynamic safety stock

Safety time

一、Safety stock

这就是“安全库存”了，安全库存的数量在计划中是不可用的。MRP 中，若物料的数量低于安全库存水平，就会产生计划订单。安全库存在物料主数据MRP2视图设置。

二、Safety stock partially available

如果设置了安全库存，一低于该水平就会产生补货的请求，哪怕只是缺了一点，这增加了计划的工作量。为了弥补这个不足，我们可以在MRP Group 中设置一个百分比，只有安全库存低于该百分比，补货请求方会产生。

三、Dynamic safety stock

动态安全库存就更加厉害了，它根据平均的日需求（Average daily requirements）数量，来确定未来几个时期的安全库存水平（数量等于若干个平均日需求）：最小库存、目标库存、最大库存。若小于最小库存，产生补货请求至目标库存；若大于最大库存，系统将 提示例外信息。若同时设置了安全库存，将累加。该配置称为Range of Coverage Profile ，在MRP2视图分配，配置在IMG: Production - MRP - Planning - MRP Calculation - Define Range of Coverage Profile (Dynamic Safety Stock)。

四、Safety time

前面三种方案都是对安全库存数量上的设置，Safety time则是设置时间上的余量。物料的补货提议时间将提前于实际的需求时间，提前日期在MRP2视图中配置。考虑到物料可能用在产品的不同层次，为了避免重复提 前，可以在MRP2视图的Safety time indicator栏位设置安全时间有效于所有需求还是仅相关需求，或者干脆无效。而考虑到不同时期对安全时间的长度要求不同，可以在后台定义 Period Profile，IMG: Production - MRP - Planning - MRP Calculation - Define Period Profile for Safety Time/Actual Range of Coverage，并在MRP2视图分配给物料。

注意： 百分比是根据MPR 组设置的，在后台：Define Safety Stock Availability。

从我的测试结果来看，系统计算的顺序是：Safety Stock——〉实际需求——〉Dynamic Safety Stock ，然后提前Safety Time的时间来产生相应采购申请

Dynamic Safety stock:

The dynamic safety stock is calculated in the planning run of the order proposal quantity. In the MRP evaluation, MD04 - you can check the parameters used to calculate the dynamic safety stock in the period totals display.To set the dynamic safety stock themaster data settingsrequired are,

动态安全库存是运行于预测需求的计划。当运行MD04时，你可以在区间统计界面看到所有的用于计算动态安全库存的参数。你要设定以下参数才能计算出动态安全库存

1. Maintain MRP view.

1. 维护材料主档的MRP 视图

2. In MRP 2 view enter the coverage profile which in configuration will carry the elements

required as detailed below.

2. 在MRP2视图里，需要设定覆盖组件（coverage profile）

3. Material master- you have MRP type PD.

3. 设定的MRP 类型为PD 。

It is maintained in SPRO under the node->

覆盖组件在后台配置，路径如下

SPRO -Production-Material Requirements Planning-Planning-MRP Calculation-Define Range of Coverage Profile (Dynamic Safety Stock).

.

It is maintained with respect to a plant as the calculation is plant specific.

Calculation-

The dynamic safety stock is calculated using the following formula: average daily requirements * range of coverage

因为计算是基于工厂的，所以配置也是在工厂的基础上进行的。

动态安全库存的计算公式如下：

动态安全库存=每日平均需求*覆盖的区间

The individual parameters are described below:

下面是各个参数的解释

Average daily requirements

每日平均需求

The calculation of the average daily requirements is carried out using the following formula: requirements in the specified periods/number of days in the total period length。You must maintain the following parameters for the calculation of the average daily requirements:

每日平均需求的计算公式如下：

每日平均需求=特定区间内的总需求/此区间内的天数

（天数有不同的计算方法，下面有比较详细的介绍。）

下面的一些参数是在计算每日平均需求中必须的

1. Period indicator

区间指针

You use this indicator to determine the calendar period for which you want to carry out the average daily requirements.

这一指针用于决定计算每日平均需求的日历区间

Here you can enter the following:

有如下几种设定

weeks (W) 周

months (M) 月

periods according to the planned calendar (K) 根据计划日历决定

2. Type of period length

区间天数的计算方法

You use this indicator to determine the length of the individual periods in detail.

用于决定计算区间天数的方法

Here you can enter the following:

如下几种设定可以用作计算

workdays 工作日

calendar days 日历日

standard days 标准日

If you set standard days as the period length, you must enter the number of days per period in the "NO. standard days" field.

如果设定了标准日作为区间天数，必须要设定每个区间包含多少标准日。

3. Number of periods

区间数

Here, you define the number of periods you use to calculate the average daily requirements. 在这里要设定用于计算每日平均需求的区间数。

Determining the range of coverage

定义覆盖区间

You can determine the range of coverage for a maximum of three periods and you can maintain different coverage for each period.

To do this, you must define the ranges of coverage and the periods in the screen section entitled, "Determine range of coverage".

可以为三个时间范围设置不同的覆盖区间

You also have the option of limiting the range of coverage in each of the three periods by entering a minimum and a maximum range of coverage. The system checks whether the actual range of coverage ( available quantity / average daily requirements) lies below the minimum range of coverage or above the maximum range of coverage. If this is the case, the dynamic safety stock level is recalculated using the information for the target range of coverage.

也可以为不同的时间范围设置覆盖区间的范围。填入最小和最大区间即可。系统会检查实际覆盖区间（可用数量/每日平均需求）是否小于最小或大于最大。如果是这样的，动态安全库存会用目标区间来重新计算。

以下有两个例子：

Example – 1

例一

Coverage profile - 001, with following settings assign in material master - MRP2 view, Period type = M（月）

No of period =2 （区间数）

Type of length = 3 （标准日）and days/period = 20(每个区间包含20个标准日).

Range of coverage for first period (target) = 3（目标覆盖区间）, no of periods= 2 （区间数） Lets us say requirements areas below –

需求如下

12.11.2007 - 1000

19.11.2007 – 2000

No of days = 2*20 = 40（天数）

average Daily requirement = (1000+2000)/40 = 3000/40 = 75 （每日平均需求）

Safety stock requirement = 75*3(target) = 225.（动态安全库存）

Run MRP, result is as below

运行MRP ，结果如下

12.11.2007 - pl order qty- 1225 available qty - 1225

12.11.2007 - VSF 1000- available qty - 225

19.11.2007 - pl order qty - 2000 balance - 2225

19.11.2007 - VSF 2000- available qty - 225.

Example - 2

例二

Coverage profile - 002, with following settings, assign in material master - MRP2 view Period = M（月）

No of period = 1（区间数）

Type period= 1 （工作日）i.e. working days as per factory calendar, please check your factory calendar. it is taking form no of days of factory calendar, remove the days which already passed, then remove holidays.（根据工厂日历计算。从总天数中减去已过的天数和假日） Example - In factory calendar -

工作日举例

2,3,9,10,16,17,23,24,30 are holiday. i,e 9 days in 30 days are holidays,

2,3,9,10,16,17,23,24,30是假日。一共9天

First, today is le us say 8th, hence from 30 days remove 7 days, ( as it is already passed), hence left with 23 days.

今天是8号，所以要从30天里减去过去的7天，剩下23天

Holidays applicable are, 9,10,16,17,23,24,30 i.e. 7 days i.e. from 23 days I need to remove 7 days hence the working days are only 16 days.

假日中，2,3已经过去，还剩7天。要再减去7天，剩下16天。

range of coverage = target 7,(目标覆盖区间)

no of period = 1.（区间数）

now my requirement is 3000 in that month

当月需求一共3000

daily average consumption is 3000/16 = 187.5（每日平均需求）

safety stock = 187.5*7 = 1313.（动态安全库存）

MRP 结果

12.11.2007 - pl order - 1 qty 2313 available qty - 2313

12.11.2007 - VSF 1000- available qty - 1313

19.11.2007 - pl order - 2000 available qty - 3313

19.11.2007 - VSF 2000- available qty - 1313.