Production Activity Control Chapter 5

MPC System with PAC (VBW, figure 5.1)

PAC Framework PAC concerns execution of material plans, aided by use of shop-floor computers, EDI, and the Internet. Usual linkage is to MRP system. Shop-floor and vendor activities begin when an order is released. Feedback: status information and warning signals. JIT may limit the need for most PAC activities. Primary PAC objective is managing material flows (JIT, material velocity); other objectives may include efficient use of capacity.

PAC Responsibilities Execution Control Scheduling Dispatching Work order progress – move tickets Labor efficiency – labor tickets Quality – scrap/rework tickets Shop status – machine/tool tickets

Planning for Shop Order Release Review planned orders Material availability Order quantity and due date Routing and tooling availability Capacity data and labor standards Verify lead times Authorization for release creates an open shop order (scheduled receipt)

Planned Lead Time Job order – setup time and run time Work center – queue time Material handling – wait time and move time Longer lead time leads to more jobs in the system, which leads to longer queue and more work-in-process inventory

Scheduling Focus Scheduling individual jobs – need dates, release dates, processing times, priority adjustments, performance measures, etc. Scheduling the shop – work-in-process, average lead time, labor efficiency, machine utilization, percent early/late, etc.

PAC Techniques Basic shop-floor concepts: Essential inputs—routing and lead time data (see figure 5.3) Queue/wait times often accounts for 80%+ of total lead time. Operations setback chart—based on each part’s lead times. Work center schedules—based on various elements of lead-time elements

PAC Techniques Gantt charts (or bar charts) – Figure 5.4 Show a schedule based on lead time assumptions (maybe omit queue, wait, and move times) Often shown on a schedule board. Primary problem—updating. Computer systems can bring updating into real-time and to the shop floor.

PAC Techniques Priority sequencing rules: which job to run next (usually determined as the current job is being completed). Earliest operation due date. Earliest part due date. Order slack (based on all part data). Slack per operation (all part data). Critical ratio (time/work). Shortest operation time. PAC creates a dispatch list that shows the priority sequence for the work center.

PAC Techniques Finite loading system—detailed schedule for each work center based on work center capacity and other scheduled jobs. (Will only schedule work up to w/c capacity.) May conduct a simulation of each w/c for the planning horizon May consider jobs coming from upstream w/c as well as the current queue Matching parts may have inconsistent due date

PAC Techniques Finite Loading (continued) Vertical versus horizontal loading: Vertical—scheduling w/c job by job. Horizontal—scheduling jobs (by priority) across all w/c’s. Front versus back scheduling: Front—load an order as soon as w/c capacity was available. Back—load a job backward from its due date. Optimized Production Technology (OPT) approach may be used.

PAC Techniques Vendor scheduling and follow-up Similar to SFC system, but customer demands are managed by the vendor with its MPC system. Schedule and priority changes must be sent to the vendor, but may be contractual limits to the amount of change allowed.

PAC Techniques Lead time management. All elements except setup and run times (which may only be 10-20% of total lead time) can be compressed with a good PAC system. Lead time and WIP are directly related. Some WIP may be needed to ensure capacity utilization—but not too much. System queue times are often over-stated.

Dispatch System Create and maintain an open shop order for each scheduled receipt. Maintain a dispatch list. Basis for priority control Identify required resources, work units, work contents Perform status and audit reports Open order status Exception reports

Schedule Adjustments Reschedule order release Reschedule due date Vary lost size Relocate labor Alternative equipment or routing Overlap operations (move portion of lot) Lot splitting

PAC Database Relation to MPC system (see figure 5.9.) Open shop orders with due dates. Routing files. Standard operations (run) time estimates. Move, wait, and queue time data. Work center information. Data acquisition and feedback Automate WIP data collection (bar coding). Decentralized computer systems. Base scheduling on real-time transactions Integrate other systems (quality, maintenance, CAD/CAM/CIM).

Concluding Principles PAC system design must be in concert with the firm’s needs. The chop-floor control system should support users and first-line supervisors, not supplant them. Vendor capacities should be planned and scheduled with as much diligence as are internal capacities. Lead times are to be managed.

Concluding Principles Organizational goals and incentives must be congruent with good PAC practice. Discretion and decision-making responsibilities in PAC practice need to be carefully defined for both shop and vendors. PAC performance should be defined and monitored. Feedback from PAC should provide early warning and status information to other PAC modules.

Concluding Principles Automated reading systems and and distributed computers should facilitate data acquisition and shop-floor decision making. Database design and integrity must be assessed for PAC systems to be effective. The ongoing evolution in PAC systems as firms increasingly adopt world class manufacturing methods is reduced detail, smaller databases, and simpler systems.

Chapter 5 Assignments Problems 5.2 and 5.12 Due Tuesday, November 12