PRODUCTION ACTIVITY CONTROL (PAC) Shop floor control

PLANNING AND CONTROL ACTIVITIES IN MANUFACTURING ENTERPRISE Strategic plan Sales &Operation Plan (aggregated) Master Production Schedule (MPS) Material Requirements Plan Purchasing Control Production Control (PAC) Input /Output Control Detailed Capacity Req. P. Rough-cut Capacity Plan Resource Planning Plan Execution Demand Forcasts Customers Orders Resources

Production Activity Control – PAC Shop Floor Control PAC – the lowest level of production management system in a company PAC - regulates the work flow through the production system Master scheduling (MPS/MRP) is a Planning activity Production Activity Control is an Execution Control activity

Production Activity Control Master Production Scheduling Material Reguirements Planning Capacity Reguirements Planning Manufacturing processes Production Activity Control Scheduling, Dispaching, Monitoring Instructions Planned Orders Data Production Activity Control transfers the data from higher levels of production planning (MPS, MRP, CRP) into manufacturing processes instructions. It also tranforms data from shop floor level into information for higher planning levels.

Production Activity Control Production Activity Control scope, complexity, principles, methods depend on production continuity Production continuity could be: flow shop type (continuous flow) job shop type (intermittent flow, irregular flow) Production control systems: Flow control - for continuous production flow Order control - for intermittent production flow (irregular flow, not continuous production flow)

Intermittent production flow The products are produced based on customer's orders, on a small scale. The flow of production is intermittent (irregular) The large varieties of products are produced The products are different sizes. No continuous flow of the same size. The production system is very flexible The types of intermittent production flows: Project production flows Jobbing production flows Batch production flows Examples: Tailor Goldsmith Furniture to order industry, car to order, ship to order Product to order industry

Continuous production flow The flow of production is continuous. The products are standardized. The products are produced in anticipation of demand, based on demand forecast. Standardized routing sheets and schedules are prepared. The types of a continuous production flows: Mass production flows apparatus (prosess) production flows. Examples: Food industry Fuel industry Cosmetics industry Washing and hygiene industry (soaps, tooth pastes, etc)

Production Activity Control The main elements of PAC Scheduling – to develop detailed schedule based on timely knowledge and data which will ensure that all the production requirements are fulfilled . Dispatching – to implement the schedule taking into account the current status of the production system (orders releasing) Monitoring – to monitor the status of vital components in the system, either with the naked eye or by using technology based methods.

Order Control The goals of Order Control: The objective of Order Control is to optimize the particular order flow through the facility so that production aims are met The goals of Order Control: High percentage of orders completed on time High utilisation of workers and facilities Low work-in-process (WIP) inventory Minimize customer wait time Minimize costs

Job shop scheduling The main Order Control activity is job shop scheduling Scheduling involves assigning due dates to specific jobs (when to start the job, when to finish the job) Job shop scheduling involves: Allocating jobs to specific work centers (loading) Prioritizing all jobs at each work center (sequencing) Release jobs to workcenters (dispaching) Revising priorities as changes occur Monitoring the progress of jobs Job shop scheduling is used to all operations in a factory, hospital, university or office. For service operations, „job” is replaced by patient, customer or whatever flows through the facility. The work center may be a desk, office, room, or skill speciality.

Production Activity Control Job shop control process Start Allocate jobs to work centers (Loading) Prioritize all jobs at work centers (Sequencing) Release jobs to workcenters (Dispaching) Review jobs progress Uncompleted jobs Completed jobs

Scheduling techniques There are two scheduling techniques to assigning due dates to specific jobs: Forward scheduling Backward scheduling Forward scheduling – an approach to scheduling that starts from the present time and schedules each job to start at the earliest possible moment. Advantages: time buffers, Disadvantages: increase work in process inventory Backward scheduling - an approach to scheduling that starts from desired due date and works backward. Advantages: decrease the work in process inventory; Disadvantages: no time buffers. Today Due Date B Forward Scheduling E Backward Scheduling

Shop Loading The allocation of jobs to work centers is called shop loading Loading methods : Infinite loading - It does not take into consideration the limited capacity of the facility. Scheduling with unlimited capacity Finite loading – assigns jobs to work centers without regard to capacity limitations. Scheduling with limited capacity INFINITE LOADING (without regard for capacity) Capacity Time period 6 5 1 2 3 4 under over

Shop loading Finite loading - scheduling with limited capacity – It takes into considaration the limited capacity of each work center. FINITE LOADING (never to exceed capacity) Capacity Time perid 6 5 1 2 3 4

Infinite loading Planned orders to relise emitted by MRP system: 1,2,3,4,5. Completion due date.: Orders1 and 4 – end of period 4. Orders 2,3,5 – end of period 5 Start due date: Order.1 & 2 – beginning of period 1., Order.3 & 4 – b. period 2. Order 5 – b. period 3. 2 1 3 4 5 Order 40 Period 80 Work station load (normal hours) Load calculation: Setup time + (n x tj) E.g. order 1: Setup = 1 h Volume = 100 unites Unit time = 0,4 h Load = 1 + 100 x 0,4 = 41 h

Finite loading 3 Orders planned to execution in week X (one week = 40 hours) Turning [h] Milling [h] Driling [h] 1 8 12 2 4 3 Move time: 2 h. Orders execution sequense (1,3,2) determined with help of critical ratio Machine 1 Day 8h 2 Day 16h 3 Day 24h 4 Day 32h 5 Day 40h Lathe 1 3 2 Mill Drill 1 Load of Lathe [h] 8 2 3 4 5 Day 6 Capacity

Sequencing Gantt Chart - at the same time assign the operations to machines and define the sequence Gantt Chart - based on forward scheduling principles Example: Order Operation 1 [h] Operation 2 Operation3 A Lathe 3 Drill 2 Mill 4 B C D 5 Delay and move time between machines 6 h. Order Completion due date A 24 B 16 C 24 D 16 Machine 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Lathe OrderA Oper1 Order C Oper1 interval Order D Oper 2 Mill Order B Oper 1 Order C Oper 2 Order A Oper 3 Drill Order D Oper 1 Order A Oper2 Order B Oper 2 Order C Oper 3 sequencing sequencing

Sequencing Jobs In Work Centers Priority Rules for Dispatching Jobs Scheduling - provides a basis for assigning jobs to work centers Loading - is a capacity-control technique that highlights overloads and underloads Sequencing - specifies the order in which jobs should be done at each work center. Priority rules - determine the sequence of jobs in process-oriented facilities First Come, First Served - FCFS. Job that enters the work center first has first pririty Shortest processing time (SPT). Job with the shortest processing time is first executed Longest processing time (LPT). Job with the longest processing time is first executed Earliest due date (EDD). Job which is due first should be started first Total slack (S). Job with the least total slack (buffor time) is done first Random selection (RS). Random selected job is first executed . Critical Ratio (CR). Job with the lowest critical ratio is done first

Critical Ratio Due date – Today’s date CR = The critical – ratio (CR) is the rule that considers both due date and processing time . Due date – Today’s date CR = Total processing time remaining The job with the lowest CR is scheduled next. CR = 1 – the order job has time to be completed on time CR < 1 – the order job is delayed (it is already past due) CR > 1 – the order job has time buffer The CR rule is dynamic. The job’s critical ratio will change over time. The critical ratio must be constantly updated

Input-Output Control Many firms have difficulty in scheduling because they overload the production processes. This often occurs because they do not know actual performance in the work centers. Effective scheduling depends on matching the schedule to performance in the work centers. Lack of knowledge about capacity and performance causes increasing in lead times. Input-Output Control is a technique that allows operations personnel to manage facility work flows. If the work is arriving faster than it is being processed, we are overloading the facility and a backlog develops. Overloading causes crowding in the facility, leading to inefficiencies and quality problems. If the work is arriving at a slower rate than jobs are being performed, we are underloading the facility and the work center may run out of work. Underloading the facility results in idle capacity and wasted resources

Input-Output Control Example: (work Past Future Period 1 2 3 4 5 6 Planned Input [h] 50 56 48 Actual Input [h] 54 52 Planned output [h] Actual output [h] Planned load [h] 152 156 154 Actual load [h] 160

PRODUCTION ACTIVITY CONTROL SYSTEM Production Activity Control system modules: SCHEDULING - to develop a plan (schedule) based on current knowledge and data which will ensure all the production requirements are fulfilled DISPACHING - to implement the schedule taking into account the current status of the production system MONITORING – to monitor the status of vital components in the production system during the dispatching activity Devices, machines, production process MASTER PRODUCTION SCHEDULING MATERIAL PRODUCTION SCHEDULING CAPACITY PLANNING Planned orders Data collection Instructions Schedules SCHEDULING MONITORING DISPACHING PAC system

A Production Activity Control System Should Schedule incoming orders without violating capacity constraints of individual work centers Check availability of tools and materials before releasing an order to a department Establish due dates for each job and check progress against need dates and order lead times Check work in progress as jobs move through the shop Provide feedback on plant and production activities Provide work efficiency statistics and monitor operator times for payroll and labor distribution analyses

Order Release Begins Shop Loading Release Order 1 2 3 Gross Requirements Yes Scheduled Receipts 100 Priority & Capacity OK? Available Net Requirements Planned Order Rec. No 100 Hold Release Planned Order Rel.

Johnson’s Rule – Johnson’s Algorithms Used to sequence n jobs through 2 machines in the same order Jobs (n = 3) Saw Drill Job A Job B Job C

Sequencing Jobs on Two Machines Job I Machine 1 Machine 2 Cumulated Lead Time 15 hours Sequence I, II Job II Sequence II, I Machine 1 Machine 2 Cumuleted Lead Time 12 hours The sequance of jobs has impact on total processing time (lead time) of the jobs

Johnson’s rule for sequencing n jobs (orders) on two machines Johnson’s rule can be used to minimize the total processing time by sequencing a group of jobs on two machines . All jobs must followed the same sequence through the two machines Start Select the shortest job time in m1 or m2 List all job times for m1 and m2 Is it in m1? Assign it as early as possible to m1 Assign it as late as possible to m1 Delete the job assigned from the list Are all jobs assigned Stop No Yes

Johnson’s rule for sequencing n jobs on two machines Work processing time for five jobs (in hours) Job Machine 1 (drill) Machine 2 (lathe) 1 5 2 3 6 8 4 10 7 12 2 3 4 7 Initial jobs sequence: 1,2,3,4,5 Optimal jobs sequence: Lead time = 45h 2, 5, 4, 3, 1 Lead time = 35h