2 Drum – Buffer – Rope (DBR) DBR is the TOC concept of production scheduling.Drum:Comes from a story in Eli Goldratt’s book “The goal”.Q: In a production facility, who sets the pace of the output?Ans.: The weakest link!
3 Drum – Buffer – Rope (DBR) In a group of scouts on a journey, the slowest boy is referred to as the Drum.Dictates the pace for the entire group.
4 Drum – Buffer – Rope (DBR) On the shop floor, bottleneck sets the pace.What if there are no bottlenecks on the shop floor?Ans.: Market demand is the drum!Once the drum is identified, the maximum pace can be determined.
5 Drum – Buffer – Rope (DBR) Concepts If the drum is a physical constrained resource, overall planning depends on the capabilities of the resource.That is, planning around the drum/bottleneck.Difference with MRP:MPS (Master Production Schedule) is created first!In TOC, MPS is the result of bottleneck planning.If drum is the market, MPS is generated from demand without considering capacity vs. load!
6 Drum – Buffer – Rope (DBR) Buffer: represents a protection for the drum.Ensures the drum never runs out of work.Can contain raw material to feed the drum.Can also contain ‘time’.Means providing enough time for the drum to finish its tasks.All resources that prepare input must be given enough time (including waiting and moving time) to overcome any delays.
7 Drum – Buffer – Rope (DBR) Difference between Buffer and Lead Time:Lead time* here applies to a single production step.Time Buffer covers area between Raw Materials to the Drum.If no bottleneck exists, it spans between Raw Materials and Shipping.Lead Time*- The total amount of time between the recognition of a required task, operation or process and its completion. Elements of lead time can include order entry, material accumulation, machine setup, queue, processing, move and other activities.
8 Drum – Buffer – Rope (DBR) Implements the buffer.A procedure to release materials only when the schedule dictates to do so.Prevents early release of materialbefore it is due.Prevents accumulation of WIP.Materials
9 DBR Summary Once found, the constraint becomes the DRUM. Constraint should always be protected by a BUFFER.ROPES link constraint to control points for release of raw materials into the factory.
10 DBR SummaryGive upstream (non-constraint) operations extra protective capacity to allow for surge capacity to feed the buffer in front of the constraint.Execute downstream operations asap to avoid any delays in the output of the constraint.In theory, flow of constrained parts should never stop until they reach the customer.
11 Analysis If decisions are made such that the organization can: Increase overall ThroughputDecrease overall InventoryDecrease overall Operating Expensethen,Decisions will be good for the business in general.
13 Are the Organization’s Operations Moving Towards the Goal? Three operational measurements:Throughput (TP)The rate at which the system makes money through sales;TP = Selling Price – Cost of Raw MaterialsExcludes labor operating expense.
14 Are the Organization’s Operations Moving Towards the Goal? Three operational measurements:InventoryThe money the system spends on things it intends to sell.Includes:Conventional inventory.Land.Vehicles, plant, equipment.Excludes:WIP Labor added.
15 Are the Organization’s Operations Moving Towards the Goal? Three operational measurements:Operating Expense†Moneys spent by the system turning Inventory into throughput.Includes moneys poured into a system to keep it operational.Heat, power, scrap materials, depreciation.† Those expenses in to the normal operation of the business, excluding interest expense and one-time charges. The actual expense a company incurs while maintaining a business. Also referred to as Overhead.
16 How to Compute Results for the Organization? Net Profit (NP)NP = Throughput – Operating ExpenseReturn on Investment (ROI)ROI= (Throughput – Operating Expense)InventoryProductivity (P)P = Throughput / Operating ExpenseTurnover (T)T = Throughput / Inventory
25 Theory of Constraints: TOC Concepts End of Part II
26 Adapted from:Schragenheim, Eli “The Theory of Constraints”, Lionheart Publishing, 1998.THE THEORY OF CONSTRAINTS: Making Process Decisions Under Conditions of Limited Resources, Capacities, or Demand -