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WIP Cap Pull Systems 

This eBook gets into the nitty-gritty details of how to implement and continuously improve my favorite Pull Scheduling System! I'll walk you through a sequential process that will help you get a powerful system up and running in no time. This eBook also works as a guide to implementing other work-in-process pull systems such as Capped FIFO Lanes, Drum Buffer Rope (DBR), and Simplified Drum Buffer Rope (S-DBR).
WIP Caps are easy to implement, easy to operate, and provide a level of performance and flexibility that is hard to beat in many applications.
Note - If you are unfamiliar with WIP Cap Pull Systems, please read my Pull Scheduling Systems Overview first. The overview reviews the basics of Pull Systems and helps you understand where they are, and are not, appropriate.

To get this eBook, simply add to your cart and complete the checkout process. The eBook will then be emailed directly to you.

 $29.95 WIP Cap Pull Systems 


The following is a preview from the eBook:

II. Where are WIP Caps Appropriate?

This chapter gets us started on determining where to use WIP Caps and how to establish their initial boundaries.

Where Should WIP Caps be Used (and Not Used)

Appendix A shows a comparison of Pull Methods. This table is a good starting point when you are selecting an appropriate Pull System for a particular application.

I generally look towards WIP Caps first in any application where there is a Product, a Customer, and multiple Resources are necessary to complete a Customer Order. WIP Cap Pull Systems require:

1.       A defined family of products that are routed through the system.

2.       A common Unit of Measure within the system.

3.       An easy method to relay WIP Cap Authorization information from the last Process back to the first Process.

4.       The Lead-Time through the system supports the Customer’s desired Lead-Time.

5.       Some variation in the In-Box quantity at each Process can be tolerated (primarily related to the physical space that the products require).

It is usually desirable (but not absolutely necessary) that:

·         The processes are sequenced such that products follow a FIFO flow between Work Centers.

·         Resources, such as people, machines, space, etc, are dedicated exclusively to the defined family of products in the WIP Cap. 

If one or more of the listed requirements cannot be met, the use of a WIP Cap Pull System is not possible. The following are some examples where WIP Caps may not be used:

·         One or more Processes require choices such as different part numbers, variations, sizes, etc. A typical example is at an Assembly Process.

Figure 3

In Figure 3, there are three Assembly Processes within a WIP Cap. However, the Housing Process is not part of the WIP Cap because there are several different housing part numbers that Assembly needs to choose from depending on the Customer Order. In this case, Assy 1 and Housing are connected by a Supermarket Replenishment Pull System.

·         The customers required Lead-Time limits the number of processes than can be included in the WIP Cap. Let’s say that in the example in Figure 3 that all assemblies use the same housing. However, if each Process in this example takes 1 day, and the customer wants a 3 day Lead-Time, the Housing Process cannot be included in the WIP Cap. The Supermarket between Housing and Assy 1 assures that there is always a supply of Housings, and that the Customer Lead-Time is 3 days.

·         The Unit of Measure changes part way through the Value Stream.


Figure 4

In Figure 4, the Unit of Measure on Customer Orders is “each” whereas Unit of Measure on the Tape Orders is “rolls”. Even though the same rolls are used for all finished part numbers, the WIP Cap cannot extend between Tape 2 and Die Cut because the Unit of Measure changes.

·         The layout of an assembly line does not allow for variable In-Box sizes. This is often the case where the layout has been designed around minimizing material handling for repetitive manufacturing of the same or similarly sized products. In this case, a Capped FIFO Lane is used instead of a WIP Cap. Note – If a little flexibility is designed into the physical layout, a WIP Cap can usually be accommodated.

WIP Caps, and Pull Systems in general, are not just for manufacturing operations. Any system that includes a Product, multiple Resources, and a Customer Order will benefit from the application of a WIP Cap. Some examples where I have seen WIP Caps effectively applied include:

·         Shop floor manufacturing operations.

·         Customer order processing through an office.

·         New product development.

·         Insurance claims processing.

·         Company wide continuous improvement initiatives.

The essence of Lean Manufacturing is to only work on a few things at a time, complete them quickly, then move on to the next thing. WIP Caps force this behavior. They also maximize current Throughput and future improvement by clearly highlighting the current Constraint in any system. The point here is to not limit your thinking on where these systems can be applied.

The following example shows a company wide Value Stream map with a host of WIP Cap Pull Systems.

Figure 5

To get the entire eBook, simply add to your cart and complete the checkout process. The eBook will then be emailed directly to you.

 $29.95 WIP Cap Pull Systems