high mix manufacturing

 

Harmonic, Inc.

 DEHART CONSULTING, INC., working hand-in-hand with our factory personnel, redesigned our manufacturing areas and material flows to enable a 250% growth in output with only a 70% increase in floor space. Additionally, the changes were documented, implemented, and provided a clear path for future expansion. 


Mike Yost, Vice President, Operations Harmonic, Inc.

    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.

    In the figure below, for example, WCs #130 and #135 would both be considered UA for WC #145 (refer to this destination WC as WCN), since work from both of these WCs flows into WC #145. In this construct, WO1 can be considered to be a WO that has not yet been authorized (assigned a Pull-Tag) for processing in its WC (WC #135), and that has the highest priority of any WOs in any WCs that are UA to WC #145. In this case, since WO1 is in WC #135, WC #135 can be referred to as WCN-1. The processing Flow Time, the elapsed time necessary to complete processing, for WO1 in WCN-1 plus its transit time from WCN-1 to WCN should be equal to, and certainly not greater than the time required to completely flush the WOs ahead of it through WCN’s queue and first operation.  That is the time that WCN will be ready to begin processing it.

demand pull example

    This timing can be modeled as shown in the figure above. WO1 can be assigned a PT when the sum of the Flow Time of WO1 in WCN-1 (tWO1, n-1) plus its transit time from WCN-1 to WCN (tT,N-1,N) [the sum of these two values is the time it takes WO1 to arrive at the WCN queue, once it is started into WCN-1] is equal to or greater than the remaining Flow, Transit, and Clear times of all the previously-authorized WOs ahead of it and destined for WCN or already in the WCN queue.

    This latter time can be modeled as the time to process the WO with the least remaining Clear Time in WCN's first operation (tR,N) [this is the elapsed time until the next production start will take place at WCN, thus pulling the next WO from the WCN queue] plus ((the sum of the WCN Clear Times of WOs in the WCN queue (QN) and the sum of the WCN Clear Times for all UA WOs already authorized (YN)), divided by the number of capacity units at WCN (CN) [this is the time it will take to process all upstream and queued WOs through WCN, accounting for the fact that some WCs may have the capacity to simultaneously work on multiple WOs and neglecting the transit time between cell pairs]), plus the remaining Clear Time at the WC in which WO1 resides for the WO with the least remaining Clear Time of all WOs that are in the WCN-1 first operation (tR,N-1) [this is the time it will take for the first, currently in-process, UA WO to complete processing at WCN-1’s first operation and  trigger the start of the next WO into WCN-1], plus the quotient of the authorized WCN-1 queue Clear Times (tQ,N-1) and the number of capacity units in WCN-1 (CN-1))  [this is the time required to process all the currently-authorized WCN-1 queue through WCN-1’s first operation and thus the time at which WO1 would be started into the WCN-1 WIP area].

Or when:

equation 1

Where all variables are specified in the Table of Definitions.

Multiplying through by CN and rearranging to simplify:

equation 2

 When this equality is true, then the next WO (WO1) should be authorized (assigned a Pull-tag). This is what the demand-pull system does by continuously monitoring the state of the factory in the context of the parameters of this equation.  Some of these parameters, like the Standard Process Hours that are used to determine the Flow Times that comprise YN, QN, tw01, n-1, and tQ, N-1, come directly from the ERP/MRP system, while other parameters are continuously monitored / calculated by the demand-pull system to complete the algorithm and assign the Pull-Tags as appropriate for the production process.

  • 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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