Yuqian #8 - Production Control Strategies

Question 1

What are the four most common production control strategies?

Answer 1

1. Push Systems
2. Pull Systems
3. Pond-draining Systems
4. Focusing on Bottlenecks (drum, buffer, rope)

Question 2

Push Systems are on of the four types of production control strategies. How do they work?

Answer 2

Information about customers, suppliers, and production is used to determine when batches of each item should come out of each stage of production

Question 3

Pull Systems are one of the four types of production control strategies. Explain how they work

Answer 3

Look only at next stage of production and determine what is needed there, and produce only that item. We essentially make nothing until there is demand.

Question 4

What is the difference between a Push System and a Pull System?

Answer 4

Push: Inventory is pushed to the consumer of the good. Production is scheduled and based on our best projections of what the market wants.

Pull: Inventory is pulled from the producer by the consumer. Production of a good is initiated by the person or organisation who consumes the good.

Question 5

Compare Push Systems and Pull Systems in terms of lot size, inventory size, waste, management, and communication

Answer 5

Lot size: larger for Push Systems

Inventory size: larger for Push Systems

Waste: greater for Push Systems

Management: management by sight in Pull Systems, management by firefighting in Push Systems

Communication: better for Pull Systems

Question 6

Pond Draining Systems are on of the four types of production control strategies. How do they work? What is the main disadvangage associated with this?

Answer 6

There is emphasis on holding inventories of materials to support production with little information flow through the system. As the inventory level falls, orders are made for replenishment.

May lead to excessive inventories and is inflexible in ability to respond to customer needs

Question 7

Focusing on Bottlenecks is one of the four main production control strategies. How does this work?

Answer 7

Bottlenecks impede production since they have less capacity than upstream/downstream stages, so work arrives faster than it completed. This strategy focusses on preventing these bottlenecks from occurring

Question 8

What is meant by ‘drum-buffer-rope’?

Answer 8

This is a manufacturing execution methodology focussing on bottlenecks. The meaning of each term is:

Drum: Bottleneck, beating to set the pace of production

Buffer: Inventory, placed in front of drum/bottleneck to ensure it is always kept busy (determines throughput)

Rope: Communication signal, tells upstream processes when they should begin production

Question 9

What are the three main types of Pull Systems?

Answer 9

1. Just in Time manufacturing
2. Lean manufacturing
3. Kanban control systems

Question 10

What is TaktTime? Why do we need a definition for this?

Answer 10

TaktTime is ratio of the net available time to the required production volume to meet customer demand.

The time needed to complete work on each station must be less than TaktTime in order for production to be completed within allotted time.

Question 11

There is a total of 8 hours in a shift, with 30 minutes for lunch, 30 minutes for breaks, 10 minutes for a team briefing, and 10 minutes for basic maintenance checks. If we must produce 400 units per day, what is the TaktTime?

Answer 11

Net available time = 480 - 30 - 30 - 10 - 10 = 400 minutes

TaktTime = 400 minutes / 400 units = 1 minute

To keep up with demand, we must produce a unit every minute

Question 12

Just in Time manufacturing is one of the three main Pull Systems. What is it? What is the main goal?

Answer 12

JIT manufacturing attempts to deliver right amount of product at right time. The main goal is to reduce work-in-process inventories (WIP = materials that have been partially completed through production process)

Question 13

What are the classic Push and Pull Systems, and what do they mean?

Answer 13

Classic Push System: Material Requirement Planning (MRP), which computes production schedules for all levels based on demand forecasts.

Classic Pull System: Just in Time (JIT) manufacturing, whereby production at one level only happens when initiated by a request from the higher level (units pulled through system by request)

Question 14

What is the main advantage of Material Requirement Planning (classic Push System) over Just in Time Manufacturing (classic Pull System) and vice versa?

Answer 14

Advantage of MRP: takes forecasts for end product demand into account

Advantage of JIT: reduces inventories to a minimum. Side benefits include increases in quality and plant efficiency.

Question 15

What are three advantages and two disadvantages of Just in Time Manufacturing?

Answer 15

Advantages: decreased inventory costs, improved efficiency, and reveals quality problems via immediate feedback

Disadvantages: may increase worker idle time and decrease throughput rate

Question 16

What are three advantages and three disadvantages of Material Requirement Planning?

Answer 16

Advantages: can lead to economies of scale, allows managers to plan/control things, and results in intricate knowledge of production times and product flow

Disadvantages: large inventories, large waste, requires care to maintain effective product flow

Question 17

Kanban Systems are one of the three main types of Pull Systems. What are they?

Answer 17

Kanban Systems are used to manage the supply of components by means of instruction cards that are shared along the production line. They help to communicate the need to replenish or produce a component or item.

Question 18

Kanban Systems are typically two-card systems. What are the two cards usually used, and what do they mean?

Answer 18

Production: contains a comprehensive list of everything the part requires in order to be completed.

Conveyance: used to signal when a part is ready to move from one part of the production process to another.

Question 19

What is the equation used to determine the required number of Kanban cards in a system?

Answer 19

Question 20

Calculate the number of Kanban cards

Answer 20

Question 21

What are CONWIP systems? How do they work?

Answer 21

Constant work-in-process (Pull System) - as a batch of jobs is completed and leaves the facility, a signal is sent to release the next order. The order comes from the backlog list, which is based on demand forecasts.

Question 22

What are the implications of having too large or too small an amount of work-in-process (WIP) in a CONWIP system? How do we determine the optimal value for WIP?

Answer 22

Too large: long lead times and excess WIP

Too small: idle workstations and reduced output

Need to identify bottleneck station, then gradually increase WIP until the input queue before the bottleneck is rarely empty

Question 23

What are three advantages of CONWIP systems compared to Kanban systems?

Answer 23

1. Immediately react to increases in demand
2. Don’t require setup and maintenance of Kanban cards
3. Maintain constant levels of inventory while reacting to highly variable part mix demand

Question 24

What are three disadvantages of CONWIP systems compared to Kanban Systems?

Answer 24

1. Require maintenance of backlog list
2. Require ample storage space
3. Unwanted WIP may “clog up” system as demand changes over time - need to periodically “cleanse” system of excess WIP