INTRODUCTION

As a greater demand for a larger variety of products grows, and the increase in global competition for world markets increases, the efficiency in design, production, and delivery becomes critical for the survival of manufacturing firms.  Flexibility has become the key ingredient for success and has been possible largely due to advances in computer technology.  In this module we will begin with a broad overview of the functions of CAD, CAM, and Manufacturing followed by the comparison of production systems, and finally, an introduction to programmable automation.  This topic will be the focus for the remaining class meetings and will deal primarily with control at the machine and workstation level.

Production Systems Overview:   In its basic form, a production process is simply  a system that converts raw materials into useful products.  Usually the system approach is either changing the properties of a raw material or combining different components to make a final product that is acceptable to the customer.  However the manufacturing cycle, coordination of data, and system control can become complex across different types of production systems.

Two main factors must be established before a firm can gain significant ground in picking up a share of the market and remaining competitive.  Efficiency and Flexibility.  In other words,  the raw materials must be available in time (theoretically no sooner or no later than needed) and flexibility to rapidly change production from one product to another must be in place.  The greatest influence in how these factors come about in the integration of computers for design (CAD)  manufacturing, (CAM) and control (e.g. CNC and PLC). CAD to CAM to Manufacturing.  The basic functions are shown below:  

CAD

 Engineering Documentation  Process Requirements  Material Requirements & FEA  Testing and Simulation

  CAM

Production Engineering    Tool Design

   NC/Control    Process Planning    GT Planning

Manufacturing Engineering     Scheduling and Control     Production Planning

Quality Engineering     Process Capability     Reliability

                                                                                                                                                              MANUFACTURING Fabrication Assembly Quality Assurance Production and System Control

PRODUCTION SYSTEMS

Production systems are classified by the arrangement of departments and processing within manufacturing facilities.  While many variations can exist, typically there are three major classifications including:  1) Job Shop,  2)Batch Production, and 3) Mass Production.  A brief overview along with advantages and disadvantages will be presented.

Job Shop.  This type of system is highly customized and produces many different types of products, with very low volume for a given product.  A variety of general purpose equipment is used in this environment.  Generally speaking, a high degree of skill is required of operators. Machines are typically grouped by type and is referred to as process layout.

A job shop can produce a wide variety of products however, scheduling becomes very difficult to manage from a flow stand point.   To give an example of how things can get complicated in a hurry,  consider   m number of parts being routed through n number of machines.  Suppose there are 4 different parts that must be routed through 8 machines.  The possible sequences of routing becomes mn  or 4 8 = 65,536 possible sequences.  It is quite easy to see how this can be a scheduling nightmare.

Batch Production.  When products are manufactured in limited quantities, it is referred to as batch production.  This type of system is more suited for intermediate size quantities, but those that are not sufficient to warrant a dedicated production line per product.  Typically the production capacity is greater than the demand, and products are produced then stored in inventory.   Safety stock levels are generated to meet the current and future demand, then production is switched to the next item to be produced to meet scheduling demand.   Production equipment and processing machines in a batch environment are more specialized than the job shop. However; the skill level required is decreased.  Varying levels of automation exist, and typically machines are arranged in a manner to conform to the products.  This type of layout is called product layout.

Mass Production.  The mass production system is strictly for high volume and virtually no flexibility.  A production line or even an entire plant is dedicated to producing only one product.  Hard automation is employed since no changeover is required.  Mass production is capital intensive and requires specialized tooling, jigs, and fixtures.  A high and constant demand is a must for mass production to pay for the capital invested.  Work is moved between stations, and the production line is balanced to maximize the rate of production.  Labor skills are reduced to a minimum, making work on an assembly line repetitious.  Thus the workstations are good candidates for automation.  Two common terms associated with mass production are assembly line and flow line.    In assembly line production systems workstations are sequential, and parts are usually moved using conveyors or high speed material handling equipment.  Flow line production is usually associated with processes that are continuous such as paper, petro-chemicals or continuous casting steel mills.    

 FMS.  Across all manufactured goods, batch production is by far the most prevalent.  It has been estimated that 95% of all manufactured goods are produced in lot sizes less than an average of 50 parts.  Obviously processes layout cannot accommodate high volume, and mass production is not capable of quick changeover.  Therefore, cellular or flexible manufacturing systems are require.  In this type of system, machines are arranged in a manner to accommodate a "family" of parts within a given group.  This is called group technology.  By processing similar parts through a cell, set-up times are reduced and throughput times improved.  Duplication of equipment and tooling is also reduced.

The diagram shown below illustrates a comparison of job shop, FMS and transfer lines with respect to volume and flexibility.

PROGRAMMABLE AUTOMATION

With increased competition and the need for flexibility,  automation has become a major factor in the success of many manufacturing firms.  Two common types of automation at the "workstation" level are CNC and PLC controls.  We will look at the basics of how CNC machines are controlled in this module, and continue with PLC in module 8.

CNC.  Computer Numerical Control has it's roots all the way back to the Jacquard Loom.  However it was in the late 1950's that numerical controlled machines tools found their way into American industry.  The most prevalent application of CNC is in metal cutting in processes such as the the following:

Milling Drilling Boring Turning Grinding Sawing EDM