high mix manufacturing

 

CalAmp, Inc.

  DEHART CONSULTING, INC.'s flow-based manufacturing methods enabled California Amplifier to significantly reduce floor space, manufacturing cycle-time, and overhead staffing requirements, reduce our material costs by nearly 20%, while over tripling California Amplifier's inventory turns to 10+...  


Fred Sturm, President and CEO California Amplifier, Inc.

There are numerous methods of setting priorities in a production environment, too numerous to discuss in total in this paper, but some of the more prevalent methods are discussed below.

First-in, First-out (FIFO)
    One means of determining the priority of authorizing work in queue at a given WC is FIFO.  By this method, the priority of work is determined chronologically by examining the arrival time of the WOs.  The WO that arrived at the earliest time will be the next WO to be authorized for production processing.
 
Due-Date Slack (AKA Critical Ratio)
    Another method of determining the priority of authorizing work in a queue is the difference between the time remaining until its scheduled completion date, the due date, and the time remaining for its Flow Time through the production process. By this method, a WO that is due to complete in five days, for example, and has five days of remaining processing time would have a higher priority than a WO that is due to complete in five days and has three days of remaining processing time.  The logic is that the latter WO has two additional days of slack in its production schedule, while the former WO has no slack and must be processed immediately to complete on time.

Expedite Policies
    Another prioritization method is to assign a higher priority to WOs that are being expedited due to management policy.  This may happen if the customer of the WO has paid an expedite fee, or the WO is a replacement for a previously delivered WO that failed quality or safety standards.  Management may prioritize a customer’s work for a myriad of reasons such as military materials during a time of war. By this method, the expedited WO is always authorized for production ahead of WOs that are not being expedited.

Other Priority-setting Scenarios
    There are other settings in which certain products, or customers, may have higher priority than others.  These priorities may be assigned numerically to WOs, such as a 1- 10 with 1 being the highest priority and 10 being lowest.  In this scenario, WOs for products that are Priority-1 would receive preferential treatment and be authorized ahead of WOs with Priority-5 products.  

    Regardless of the system for setting priorities, for a given WC, the demand-pull system finds the highest-priority WO in its Upstream-Adjacent WCs and applies its Flow Time to Need Time comparison method to determine whether to authorize the WO for production.  If it finds a “tie”, where two or more WOs have identical priorities, it will fall back to FIFO for the subject WOs.

  • DCI Introduces Vortex Demand-Pull Technology +

        Since the early 1980's, the benefits of producing a given production volume throughput with the minimum amount of inventory have been well documented.  Beginning with the Just-in-Time methodologies, using Kanban cards for inventory replenishment, to Demand Flow methodologies,



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  • Vortex Introduction +

        The time-based demand-pull system (“demand-pull system”) technology of the described demand-pull system provides an implementation of demand-pull scheduling for various production operations/systems/factories.  It works in conjunction with a Material Resource Planning (MRP) or Enterprise Resource Planning (ERP) system, which creates production WOs and houses associated data, such as workflows and operational standard hours, to pull work through a factory with results similar to that of POLCA. 



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  • Production Priority-setting Examples +

        There are numerous methods of setting priorities in a production environment, too numerous to discuss in total in this paper, but some of the more prevalent methods are discussed below.



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  • First Authorized - First Processed Work Flow +

        When looking at work flow through a factory from the perspective of minimizing cycle time and honoring demand-pull policies, work should be processed on a first authorized, first processed (FAFP) basis. In other words, once a WO has been authorized within a WC’s queue, it should be pulled into production on a FAFP basis.  Deviating from this policy can result in an increase in the average cycle time, unless batching of WOs will reduce their aggregate cycle times due to machine capacity.  For an example of the latter situation, a machine may be capable of simultaneously processing ten pieces, and if there are two five-piece (or fewer) WOs, they could both be processed at the same time to reduce their aggregate cycle time, improve efficiency and maximize capacity.  



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  • Demand-Based Production from a Flow-Time Versus Need-Time Perspective +

        From a flow-time perspective, Work Orders should arrive in a Work Center's queue at precisely the time when they are needed to be worked on.  This minimizes both production cycle-time and inventory investment. The desired time for the next WO to arrive for processing is when the currently-authorized work in a WC and its upstream-adjacent (UA) WCs has been started into the WC and cleared the first operation in the WCs routing. This assumes that demand exists for the WO at the next downstream work cell.



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  • Examples of the Vortex Authorization Process +

        The examples set forth in the table below illustrate the WO authorization process resulting from the pull-test in different circumstances.  In all the examples, a set of WCs such as shown in the following Figure is used.  There are two WCs (WC 130 and WC 135) that feed into a third WC (WC 145) and the downstream WC (WC 145) is presumed to be healthy (reference the discussion of Work Center Performance Testing) so that the pull-testing for this WC is active. 



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  • Calculating Flow Time in a Work Center +

    Using Standard Labor/Machine Processing Hours
         In the case where all units in a WO are processed as a discrete set, the Flow Time of a WO in a WC is equal to the Standard Process Hours of the WO.



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  • Demand-Based Production from a Work-Volume Perspective +

    When looking at authorizing work in upstream stages of production, the traditional Kanban system establishes quantity buffers, or queues, at each WC. Then when the buffer quantity hits a minimum value (the Queue Policy), the Kanban card is returned to its originating WC for replenishment. 



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  • Table of Definitions +
    The following is a Table of Definitions for the articles describing the Vortex technology.

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  • An Optimum Queue Policy +
  • An Automated Demand-Pull System Embodiment +

        The Figures below illustrate an embodiment of the demand-pull system, which can be implemented using a software system with a database.  In this embodiment, a .NET service bus and MSSQL database running on a networked Microsoft Windows server are connected via the local area network (LAN) to individual clients in the various WCs. 



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  • Comparison of Time-Based Demand-Pull versus POLCA +

    POLCA (Paired Overlapping Loops of Cards with Authorization) is a prior art system to produce solutions to the application addressed herein, that is, demand-based shop floor control in a high mix, or high variety, production environment. 



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  • Vortex Shop Floor Control for Discrete Manufacturing +

    Is your manufacturing environment order-driven? Do you Engineer-to-Order or Customize-to-Order? Do your spaghetti diagrams look more like a network than continuous flow? If you struggle with production cycle-times that are too long and inventories that are too high, we have a solution!


    Introducing Vortex, a Shop Floor Control system designed to minimize your production cycle time and reduce inventory. Vortex works to pull production through your factory exactly when it’s needed! It predicts when a work center will be in need of more work, identifies the highest priority batch in all upstream work centers, and then authorizes the batch to be started just at the right time for it to reach the work center exactly when it is needed.


    Upstream work is only released if there is downstream demand, thus implementing one of the basic tenets of Lean Manufacturing – demand-pull production – in the high-variety, order-driven factory.


    Sounds simple, right?  In theory, yes.  However, if you’re talking dozens of work centers, dozens of different work flows and varying batches of sizes and flow times – predicting the time at which more work than is currently authorized for production will be needed can very quickly get complicated – the real-time calculations piling up pretty fast.

     
    Vortex streamlines the thousands of computations with a patent-pending algorithm, which works not only to synthesize all the math, but also integrate those solutions directly into your production system.


    Vortex’s modern, standards-based API is compatible with most ERP and Shop Floor Control systems.  The fully featured API allows your ERP and other internal systems to always stay up-to-date with the status of work on the shop floor. Vortex relies on your existing ERP system to create Work Orders according to your existing planning policies and inject them into the system through the API.  From there, Vortex handles the Starts into each work center based on demand-pull policies – minimizing both cycle-time and Work-in-Process inventories.  


    Check out our demo based on the following 5 products with individual work flows through 10 work centers. To view the demo, please click the link on this page - or drop us a line and we will take you for the tour.



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