Push and Pull

University Of Windsor

INDUSTRIAL & MANUFACTURING SYSTEMS ENGINEERING

Course Name - Production Systems Analysis

Course # 91-413

Pull and Push Systems: An In-depth Look

By:

Jegapiragasam Jyapiraharan 100 799 376

Mohanty Abhishek 101 421 155

Farsed Ibrahim 100 646 715

Yan Zhang 100 995 363

ABSTRACT

This report examines the different production planning methods being used in the current manufacturing environment. The report focuses on Push and Pull systems. The report discusses the advantages and disadvantages of each method and also looks at JIT and MRP as examples of Pull and Push systems respectively. The report also discusses two real world scenarios where these systems have been implemented successfully. In conclusion this report discusses Hybrid systems that have been gaining popularity.

Table of Contents

Abstract Page 2

Table of Contents Page 3

Introduction Page 4

Pull systems Page 5

Advantages and Disadvantages Page 8

JIT Page 10

JIT - A case study Page 10

Push Systems Page 13

MRP Page 13

Advantages and Disadvantages Page 17

MRP - A case Study Page 20

Hybrid Systems Page 26

Conclusion Page 28

References Page 29

INTRODUCTION

Push and pull systems determine when and where to move material in a production process. A push system is characterized by a make to stock environment and a pull system is characterized by a make to order. An appropriate system that would cater to the requirements of the company has to be selected. A distinction is made between push and pull production systems based on the trigger point. The push system is based on customer orders, while a pull system is based on forecasts. In short, push systems can be compared with MRP systems that utilize past information to forecast the future customer demands. In the case of a pull system the difference between the safety stock point and the state of current inventory is similar to just-in-time which controls the order quantities. The fluctuations in inventory levels in a push system are affected by forecasting errors, while the fluctuations in customer demand affect the pull system. Most of the production problems can be solved by using an appropriate push and or pull system. It is evident that neither one is always better than the other. In fact, a hybrid approach is more superior, depending upon the manufacturing system. The main objective of a hybrid system is to combine the best features of both worlds, rather than differentiating between the two.

PULL SYSTEMS

Pull systems were pioneered by American grocery stores. Grocery Stores only replace their shelves with products that are demanded or consumed by their customers. To make this possible, the grocer used FIFO and just in time delivery. The grocer also had to engage in continuous communication with suppliers as well as customers. In simple terms, a pull system is a method of controlling the flow of resources by only replacing materials that have already been consumed. An easy way to visualise a pull system is to think of a vending machine. The vending machine company only replenishes the exact amount that has been consumed by the consumers.

A key concept is the production of small lots in standard sizes to replenish only the consumed inventory. Forecasts are also a key aspect of Pull systems. In pull systems the forecast values are used to turn cycle time into a target inventory level. In pull systems buffer inventories are determined by multiplying cycle times by the daily forecasts. This ensures optimal level of buffer inventory.

There are three distinctive types of pull systems. These can be categorised as -

1. Supermarket Pull System - In a supermarket pull system, each process simply produces to replenish what has been consumed. Each process has its own supermarket, as material is pulled from the supermarket by a downstream customer; information is sent upstream authorizing the upstream process to commence production. The advantage of this system is that products can be produced and shipped in a short amount of time and the management and kaizen of each production cell is relatively simple.

2. Sequential pull system - Sequential Pull Systems are also called B-type pull systems and are used when there are too many part numbers to hold a separate inventory or supermarket for each. Products are made to order and the entire inventory is minimized. The production control department schedules the production of each part by using a Heijunka board. A First In First Out production sequence is maintained for each product. This type of pull system requires a lesser amount of inventory and produces a lot less waste than Supermarket pull systems, but it also requires high process stability, short lead time and a strong management to function correctly.

3. Mixed Supermarket and Sequential Pull systems - In this kind of pull system, supermarket and sequential pull systems are used side by side. A mix system maybe used when small number of part numbers account for majority of the production volume and a large mix of part number form maybe 20% of the production volume. In mix system it is really difficult to balance the work load and implement kaizen activities; therefore it requires a great amount of discipline to work with a mixed system.

The objectives of a pull system are -

1. Control and balance the flow of material and resources.

2. Eliminate material wastage.