SELECTION OF A CUTTING TOOL IN AN FMS USING EXPERT SYSTEM

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Moses O’Connor’
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1 CHAPTER - 6 SELECTION OF A CUTTING TOOL IN AN FMS USING EXPERT SYSTEM 6.1 INTRODUCTION A flexible manufacturing system [I901 is highly automated GT machine cell, consists of a group of processing workstations, inter connected by an automated material handling and storage system, and controlled by a distributed computer system. The reason FMS is called flexible is that capable of processing a variety of different part styles simultaneously at the various work stations, and mix of part styles and quantities of production can be adjusted in response to changing demand pattern. The FMS is most suited for the mid variety, mid volume production range. An FMS relies on the principles of group technology. No manufacturing system can be completely flexible. There are limits to the range of parts or products that can be made in an FMS. An FMS is designed to produce parts with in a defined range of styles, sizes and processes. An FMS is capable of producing a single part family or limited range of part family. The three capabilities that a manufacturing system must posses to be flexible (1) The ability to identify and distinguish among the different part or product styles processed by the system. (2) Quick change over of operating instructions, and (3) Quick changeover of physical setup. Flexibility is an attribute that applies to both manual and automated systems.

2 There are several basic components of an FMS (1) Workstations (2) Material handling and storage system, and (3) Computer Control System. In addition, even though an FMS is highly automated, (4) People are required to manage and operate the system. A typical FMS Computer control System consists of a central computer and microcomputer controlling the individual machines and other components. The central computer coordinates the activities of the components to achieve smooth overall operation of the system. Various functions performed by the FMS computer control system are workstations control, distribution of control instructions to workstations, production control, traffic control, shuttle control, work piece monitoring, tool control performance monitoring and reportin 4' and diagnostics. \v\ -7- In a maching system, cutting tools are required tooling has become one of the C r\ hindrances to effff kerformance of FMS. Tool control is concerned with managing two aspects of cutting tools. K Tool Location: This involves keeping tracf of the cutting tools at each workstation. If one or more tools required to process a particular work piece is not present at the workstation that is specified in the parts routing, the tool control subsystems takes one or both of the following actions (a) Determines whether an alternative workstation that has required tool is available and/or (b) Notifies the operator responsible for tooling in the system that the tool storage unit at the station must be loaded with the required cutter. 4j- Tool Life Monitoring: In this aspects of tool control, a tool life is specified to the computer for each cutting tool in the FMS. A record of the maching time usage is

3 maintained for each of the tools, and when the cumulative machining time reaches the specified life of the tool, the operator is notified that a tool replacement is needed. Tooling management is one of most essential aspects of an effective flexible manufacturing system. Implementation of an effective tooling management system will reduce tool cost and inventory, decrease machine down time and improve the quality of parts being produced. In addition, proper tooling management is important because machine down time often results from tooling related problems. Moreover, the cost for the perishable and durable tooling in an FMS may be greater than labour and raw material combined. Losses due to operator error, damaged tools, over stocking and under stocking of tooling, loss or misplaced, under used inserts, and poor quality can be avoided through the use of modem tooling management methods. Tool management can increase the productivity. It aims to optimize the use of all tools -whether for a cutting, forming, are very special purpose in a plant. The objective of tool management efforts is to minimize tool change times and tooling. ' inventory. A simple method to keep a watch on tools in a cell is elapsed in cut. The elapsed time is compared with tool life based on speed, feed, work piece and tool materials and so forth. The tool lives are entered and stored at the each machine tool in the cell. ---z X CUTTING TOOLS The demand of the manufacturing industry in the recent years have led to the development of impressed machine tools, cutting tools and production process. The

4 cutting tool is one of the important elements in realizing the full potential out of any metal cutting operation. All the cutting tools used in metal cutting can be classified as single point tools and multipoint tools. The cutting tools that are having only one cutting edge are called single point tools, where as the cutting tools that are having more than one cutting edge are called as multipoint cutting tools. The cutting tools can also be classified as based on their motion, they are linear motion tools, rotary motion tools and linear & rotary tools. The performance of a cutting tool material for a given application depends on wear resistance, hot hardness and toughness. Wear resistance and toughness are two characteristics, which are interdependent, the gain of one resulting in the loss of the other. The commonly used cutting materials are high carbon steel, high speed steel, cemented carbides, cast alloys, cemented oxides or ceramics and diamonds. Tool life is defined as the time elapsed between two successive grindings of the tool. During this period the tools cut efficiently and effectively. The tool life is w effected by many factors. They are machicg variables i.e., speed, feed and depth of cut, type of cutting such as continuous and intermittent cutting tool geometry, tool bar' material, maching conditions such as temperature of work and tool, type of cutting fluid used and properties of material being cut.

5 formulae. The relation between the cutting speed and tool life is given by Taylor F 4 Where V = Cutting sp d in mlmin T = Tool life in minutes n = An index closely related to the cutting tool material. = 0.1 to 0.5 for H.S.S. = 0.2 to 0.4 for tungsten carbide tool = 0.4 to 0.6 for ceramic tool. c = Constant. In general a parabolic decreases in tool life, as cuang speed is increaseds The effect of feed and depth of cut on tool life is given by the formula Where V = Cutting speed in mlmin. T = Tool life in minutes F = feed in mmfmin. A case study for the selection of cutting tool based on type of operation, cutting tool material, tool geometry and operation in an FMS using expert system is presented in 6.3

6 6.3 PROBLEM DESCRIPTION IN FMS The five part types can be machined by the system. Each part has a processing time and predetermined sequence of operation. The problem is described by four parameters namely (i) (ii) (iii) Tool magazine capacity. Cutting tool quantity. Used tool life. (iv) Processing time. 0-e The pr~blem~selection of a cutting tool to be used on real time control of FMS is based on these four parameters. FMS consider in this problem is hypothetical system for machining of five similar components of a part family. The system consists of two machining centers arranged in two parallel rows and interconnected by the automatic material handling system. They are automatic loading & unloading centers.

7 The five parts can be machined by the system as shown in figure 4.1. Part-I Facing. Turning, Stepped Turning Facing, Turning, Stepped Turning Threading Facing, Turning, tapering , -. Facing, Turning, tapering, threading Facing, Indexing, Tooth cutting, Drilling a hole Slot cutting for Fig.6.1. Five similar parts in a part family

8 Each part has a process time and predetermined sequence of operation. Sequence of operations for these five parts is given below in Tale I. 6.4 The steps to develop the knowledge based system for selection of cutting tool in FMS A good knowledge based system needs a good knowledge. This must be acquired, structured and represented. The knowledge can be acquired from various sources. The knowledge engineering is the process of obtaining knowledge from experts, organizing it in a usable is applied.+l'r b.4 <,...i.. h w tnis kmmk@-~ applied i.e., the building a knowledge based system. The process of building a knowledge based system for selection of cutting tool in an FMS, is divided into four steps [l91]. I STEP-I : Knowledge base for selection of machining center based on operation. The operations performed in each machines center is given table 2. Based on operation we use two types of machining centers. (1) Turning Centre (Lathe Centre) (2) Milling Centre

9 - S.No MACHINING CENTRES Turning Centres Milling Centres Table 2. - OPERATIONS Facing, Turning, Stepped turning, Tapering, threading. Facing, Indexing, Tooth cutting, Drilling a hole, slot cutting for key way. STEP-I1 : Knowledge base for selection of cutting tool material based on work -i?k.'z> piece material and type of cut and cutting is as shown in table 3. 2 STEP-111 : Selection of tool geometry based on operation and cutting tool material as shown in Table 4. Table 4. MATERIAL FACING TURNING MILLING DRILLING Hi& Carbon Steel GF 1, GF2, GF3 GTI, GT2, GT3 OM], GM2, GM3 OD], GDZ, OD3 High speed Steel GF4, GF5, GF6 GT4, GT5, GT6 GM4, GM5. GM6 GD4, GD5,GD6 Cemented Carbide GF7, GF8, GF9 GT7, GT8, GT9 GM7, GM8, GM9 GD7. GD8, GD9 Ceramics GFIO, GFI 1, GF12 GTIO, GTI I, GT12 GMIO, GMI I, GM12 GDIO, GDII, GDl2 Diamond GF13,GF14, GF15 GT13,GTl4,GT15 GM13,GM14,GMI5 GD13.GD14. GDlS STEP-IV : Decision rule : Select the tool whose remaining life is greater than and nearer the operation time.

10 6.5 SAMPLE TEST 1. What is the machining center for turning? A) Result : Lathe Centre 2. What is the cutting tool material based on work piece material, speed, feed, depth of cut and operation? A) Result : High carbon steel 3. What are the geometry of High carbon steel for operation turning? A) Result : GT1, GT2, GT3 (Select GTI ) 4. What are the numbers of cutting tools of Cieometry GTl? A) 4 5. What are the details of four cutting tools of geometry? A) Tool 1 : (i) A) 180 (ii) A) 120 (iii) A) 60 Tool 2: What is the tool life? What is the accumulated usage tool life? The remaining life is? (i) What is the tool life? A) 180 (ii)what is the accumulated usage tool life? A) 30 (iii) A) 150 The remaining life is?

11 Tool 3: (i) What is the tool life? A) 180 (ii) What is the accumulated usage tool life? A) 20 (iii) The remaining life is? A) 160 Tool 4: (i) What is the tool life? A) 180 (ii) What is the accumulated usage tool life? A) 160 (iii) The remaining life is? A) What is the operation time? A) 152 Result : Tool An except system is developed for the selection of a cutting tool in an FMS --- based on type of operations, cutting tool, work material, tool geometry and the operations time.

Workshop Practice TA 102 Lec 6 & 7 :Theory of Metal Cutting. By Prof.A.Chandrashekhar

Workshop Practice TA 102 Lec 6 & 7 :Theory of Metal Cutting By Prof.A.Chandrashekhar Theory of Metal cutting INTRODUCTION: The process of manufacturing a component by removing the unwanted material using