What is shop control?
Shop control is the means by which shop activities are coordinated to complete jobs. Shop control can be actively managed in real time using a shop control system such as DBA or it can be done manually.
Manual shop control is complicated
Shop control occurs whether it is actively managed by software or done manually. Manual shop control is not easy because of the inherent complexity involved in coordinating numerous job sequences among multiple work centers and subcontractors.
Manual shop control encourages “job chains”
Because manual shop control is so complex, MRP is often bypassed in favor of using BOM explosions to manually create “job chains”, which are used as a means for determining the order in which multi-level jobs are to be performed out on the shop floor. Each job chain typically has a one-to-one relationship with a sales order.
Job chains encourage expediting
Job chains encourage the use of expediting to meet sales order required dates. Expediting degrades shop throughput because it favors one set of jobs at the expense of other sets of jobs, which then require expediting as well in an endless cycle.
Job chains create excessive jobs and longer times to shipment
Not only do job chains encourage expediting, they also create an excessive number of fragmented jobs with inefficient run sizes that complicate the master schedule. Job chains also preclude the option of making selected sell items and components to stock to eliminate or significantly shorten times to shipment.
Manual shop control is overly reliant on key personnel
Because manual shop control is expediting-intensive, it is overly reliant on key persons who are adept at “getting orders out the door.” This leaves the system vulnerable to late shipments when key persons are sick or on vacation or leave the company.
Backflushing material causes inventory problems
Without formal shop control, job components are typically deducted from inventory after the fact at time of job receipt. This is referred to as “backflushing”, which causes the following problems:
•On hand quantities are never fully reliable, which complicates stock counts and erodes user confidence in the system.
•Backflushing perpetuates BOM errors because they are rarely detected when components are issued well after their actual use. BOM errors are a major source of inventory problems.
•Backflushing is not compatible with multiple locations and thus discourages their use, even though location control facilitates stock issuing and picking and reduces inventory errors.
Lags in labor updating cause timing issues
Without formal shop control, job labor is typically updated in batches well after job sequences are actually finished. Lags in labor updating pose timing issues. If a job is finished but labor is not updated, delaying job receipt may adversely affect dependent jobs and sales orders. If the job receipt is made without labor updating, the item’s inventory cost will be understated. We recommend Standard Hours completions for most items.
It is difficult to identify bottlenecks
When a work center gets overloaded, it can create a bottleneck that adversely affects shop throughput. Machine and worker resources should be deployed when possible to alleviate bottlenecks and optimize shop workflow. In a manual shop control environment, bottlenecks can be difficult to detect, especially in the early stages when preventive action can be taken.
Active shop control is easier and far more effective
An active shop control system is much easier to use and far more effective than manual shop control.
•Instead of using multi-level job chains that correspond to individual sales orders, MRP generates jobs that reflect the aggregate demand among interdependent sell items and subassemblies. This results in fewer jobs with more efficient run sizes that simplify the master schedule.
•Eliminating job chains encourages making selected sell items and subassemblies to stock to eliminate or reduce times to shipment.
•The job release process automatically determines the correct order in which to start multi-level jobs, based on material availability. Jobs are automatically prioritized in work center queues relative to required dates and thus there is no need for manual expediting and all the time it consumes.
•Shop control is incorporated into standard processes and, unlike expediting environments, is not reliant on key persons to be effective.
•Material is issued to jobs in real time so that on hand quantities are reliable, which facilitates stock counts and maintains user confidence in the system.
•Labor is updated as job sequences are finished so that there are never timing issues when finished items are received that can delay dependent jobs or sales orders or understate finished item costs.
•Work centers in early stage bottleneck condition can easily be detected so that machine and worker resources can be deployed where needed to optimize shop workflow.
