CHAPTER 5 APPLICATION OF WEB-ENABLED KNOWLEDGE BASE SYSTEM

Transcription

1 97 CHAPTER 5 APPLICATION OF WEB-ENABLED KNOWLEDGE BASE SYSTEM 5.1 SELECTION OF APPROPRIATE NON-TRADITIONAL MACHINING PROCESSES The selection and ranking procedure for the developed web-enabled knowledge base system was tested on 12 Non-Traditional Machining Processes (NTMPs) (nine basic and three derived). Basic NTMPs include three of the mechanical energy type, one of the electrochemical energy type, one of the chemical energy type, and four of the thermal energy types. The nine basic and three derived NTMPs are: Abrasive Jet Machining (AJM) Water Jet Machining (WJM) and Ultrasonic Machining (USM) Electro-chemical Machining (ECM) Chemical Machining (CHM) Electrical Discharge Machining (EDM) Electron Beam Machining (EBM) Laser Beam Machining (LBM) Plasma Arc Machining (PAM) Electro-chemical Grinding (ECG) Electro-chemical Honing (ECH) and Wire Electrical Discharge Machining (WEDM).

2 98 The structure of the developed web-enabled system enables the user to remove unsuitable NTMPs and obtain a narrowed down list of NTMPs, and then to rank them according to their suitability for the desired application. The logical flow diagram of the selection procedure is given in Figure 5.1. It is necessary to know the nature of application to select the suitable Non- Trraditional Machining Process (NTMP). A NTMP can be used very efficiently for a particular application, but changes in the application type and requirement attributes can reduce the efficiency significantly. Therefore, the selection approach must start with a clear identification (description) of the application by the manufacturing personnel. The user has to identify the desired application in terms of workpiece material, shape application and technical (functional), cost and material removal rate requirements to initiate the selection procedure. 5.2 GRADES AND VALUES ASSIGNED Table 5.1 shows the Grades and values assigned for the entries in the tables such as Material Application (Table 5.2), Shape Application (Table 5.3), and Process Economy (Table 5.4).The individual grades of process parameters and total grades for suitable NTMPs are calculated based on the values assigned in Table 5.1. Table 5.1 Grades and value assigned for Material Application, Shape Application, and Process Economy attributes Sl.No Material and Shape Application Process Economy Grade Value assigned Grade Value assigned 1 Good 3 Very Low 0 2 Fair 2 Low 1 3 Poor 1 Medium 2 4 Very Poor 0 High 3 5 Not Applicable * Very High 4 *- disqualify the processes

3 Verify user authenticity Figure 5.1 Logical Flow diagram of WEKBS 99

4 CLASSICAL APPROACH OF NON-TRADITIONAL MACHINING PROCESS SELECTION The selection of an appropriate NTMP to machine a specific material requires, firstly, profound knowledge regarding the applicability, capability, economy, and related effects of the concerned process. An NTMP that is highly capable of machining a specific material may not be economical enough in its operation. Still, other such conflicting situations may also arise. Therefore, sometimes, the decision maker(s) has to make a compromise between several criteria to select the NTMP for a particular condition. In other words, the decision maker(s) needs to set the priority values as to which criteria should be given more importance than the others. The complexity of the problem increases multi-fold when the considered criteria have other subcriteria whose priority values are also to be evaluated. The ultimate step involves the comparison of the available alternative NTMPs with respect to those criteria and sub-criteria. The selection process, therefore, demands sound reasoning power from the point of view of the decision maker(s).the major criteria or attributes that play vital roles in the selection of the NTMPs, as traditionally being considered, are as follows: Workpiece Materials The applicability of the processes with respect to various materials is taken care of under this criterion. It determines how often an NTMP can be used for a specific material. This criterion is of prime importance, as it will have a major role to play in the selection of the most suitable NTMPs. The following materials are taken into consideration in the proposed system: 1. Aluminum 2. Steel 3. Super alloys

5 Titanium 5. Refractories 6. Plastics 7. Ceramics and 8. Glass Table 5.2 shows suitability levels of NTMPs for different types of workpiece material, based on experience, data collected from industries dealing with NTMPs and reference (Mitsubishi 2008 and Pandey 1988). The non-applicable NTMPs are directly eliminated from the list of candidate NTMPs to be ranked Shape Applications Under the shape application criteria, various shapes that can be generated by the available NTMPs are considered. This criterion also plays a vital role in the selection of the NTMP, as the type of the required shape to be generated will obviously dictate the selection procedure. In the manufacturing field, NTMPs are used in four areas: 1. machining shaped blind cavities, 2. producing through profiles (profiles or holes that penetrate the workpiece entirely), 3. cutting operations, and 4. surface finishing operations. Non-Traditional Machining Processes are often applied when complicated blind cavities are machined into hard or brittle workpieces that are difficult to shape by conventional methods. Shaped tools are used in producing complex two- and three-dimensional blind cavities. USM, ECM,

6 102 CHM and EDM are the NTMPs used in this type of application. In this study, cylindrical blind hole opening and pocketing operations are included as `blind cavity operations (Table 5.3). Other applications of NTMPs include producing through holes and profiles that are difficult to produce conventionally because of material hardness or hole geometry. In these applications, shaped tools penetrate the workpiece (USM, ECM, EDM), or a stream (electron beam in EBM, abrasive jet in AJM, laser beam in LBM, plasma in PAM) is directed at the workpiece to produce through holes or profiles. In this system, cylindrical hole and through cavity (including all types of profile except the cylindrical one) opening operations are given as `cylindrical through hole and `through cavity operations (Table 5.3). In cutting operations, the objective of the application is to cut or slit sections of the materials. Examples are cutting sections from hard materials with complex geometry. AJM, WJM, WEDM, EBM, LBM and PAM are NTMPs that are applied in this type of application. In this system, shallow and deep through cutting operations are included (Table 5.3). Finishing operations remove small quantities of material from the workpiece surface. Grinding, cleaning, polishing, removing recast, threading, deburring, radiusing and honing are typical finishing operations. An example of the use of an NTMP in this area is the application of AJM to workpieces containing passageways that are considered to be inaccessible with conventional deburring and polishing tools. AJM, WJM, ECM, ECG, ECH and LBM are typical NTMPs used as finishing operations in industry today. In this system, grinding, deburring and threading are included as finishing operations (Table 5.3). In addition to the above-mentioned shape applications, NTMPs are also used to produce complex external shapes, such as the ECM process for gas turbine blades, and in CHM of aircraft parts.

7 103 The NTMPs and shape applications categorized in Table 5.3 can be further improved or extended for the special application requirements of the manufacturer. The various shape features that can be generated by the NTMPs are summarized as below: (a) Holes: (i) Precision (small holes having a diameter in the range of mm) (ii) Standard: (a) L/D<20 (b) L/D>20 where L/D = length/diameter = slenderness ratio (b) Through cavities: (i) Precision (ii) Standard (c) Surfacing: (i) Double contouring (ii) Surface of revolution (d) Through cutting: (i) Shallow (ii) Deep Elimination of NTMPs on the basis of shape Application Table 5.3 helps the user to find the feasible NTMPs for the selected shape application. In Table 5.3, columns correspond to shape applications and rows correspond to NTMPs. In Table 5.3, if a non-traditional process has the capability of performing a particular shape application, a suitable grade value (Table 5.1) is assigned; otherwise `0 is assigned. An NTMP is accepted as a feasible alternative if a grade value other than 0 appears in the corresponding shape application column.

8 Table 5.2 Workpiece material suitability levels of NTMPs for WEKBS NTMPs Aluminium Steel Metals and Alloys Super alloy Titanium Refractory Material Non-metals Ceramics Plastics Glass USM poor fair poor fair good good fair good AJM fair fair good fair good good fair good ECM fair good good fair fair NA NA NA CHM good good fair fair poor poor poor fair EDM fair good good good good NA NA NA EBM fair fair fair fair poor good fair fair LBM fair fair fair fair poor good fair fair PAM good good good fair poor NA NA NA WEDM fair good good good good NA NA NA ECG poor good good fair good NA NA NA ECH poor good good fair good NA NA NA WJM fair fair good fair good good fair good 104

9 Cost Considerations in identification of suitable NTMPs Machining cost is an important attribute in determination of the suitable NTMPs. The machining cost comprises tooling and fixture, power consumption and tool wear costs. Tooling and fixture costs include workpiece holding and adjustment costs. The power consumption is principally the cost of electricity used directly in material removal (as in ECM, EDM, WEDM) or indirectly in driving pumps, compressors, electric motors, heating units, beam generators, etc. The cost of liquids (electrolytes, dielectrics, chemicals, acid solutions, etc.) or gases used or consumed during the process is included in the power consumption cost. Tool wear cost includes the entire tool and tool replacement costs due to wear of the tool or related parts (such as electrode, wire and nozzle wear). The suitability of an NTMP improves as the required tooling cost, the process power consumption and the tool wear rate (or relative tool wear) decrease. A qualitative scale is developed to rate the machining cost level of NTMPs (Table 5.4). Table 5.4 shows ratings assigned for cost levels of NTMPs in tooling and fixture, power consumption and tool wear costs. Development of a generalized cost formula, which gives a precise machining cost score for each NTMP based on tooling and fixture, power consumption and tool wear cost elements, is very difficult. In some proprocesses the power consumption cost and tooling cost are the critical costs, as in ECM, whereas in some processes tooling and fixture cost and tool wear cost are the critical costs, as in EDM. The weights of machining cost elements in Table 5.4 are approximate and based on experience, data collected from local industries dealing with NTMPs and reference (Mitsubishi 2008 and Pandey 1988) Process Capability Attributes of NTMPs The process capability criteria mainly concerns with the ability of the NTMPs to achieve the desired material removal rate, tolerance, surface

10 106 finish, etc. The following are the various sub-criteria as considered under these criteria: (a) Material removal rate (b) Tolerance (c) Surface finish (d) Surface damage depth (e) Corner radii The Web page for Editing Shape Applications, Process Capabilities, and Process Economy in the Expert Module for the developed WEKBS is shown in Figure 5.2. Updated process capabilities of NTMPs based on experience, data collected from local industries dealing with NTMPs, and reference (Mitsubishi 2008 and Pandey 1988) are summarized in Table Effects on equipment This criteria is mainly associated with the effects of the NTMPs while generating a particular shape feature on a given material. Though it is clear that this criteria is not as critical as the others, it is still important, as it takes care of the environmental effect, tool effect, contamination, etc. of the NTMP itself. The sub-criteria under these criteria are as follows: (a) Tool wear (b) Machining contamination (c) Safety (d) Toxicity

11 Table 5.3 Shape Application suitability levels of NTMPs for WEKBS Process Precision small holes Standard Diameter <.025 mm Diameter >.025 mm Holes Through cavities Surfacing Through cutting L/D <20 L/D >20 Precision Standard Double contouring Surface of revolution Shallow USM NA NA good poor good good poor NA poor NA AJM NA NA fair poor poor fair NA NA good NA ECM NA NA good good fair good good fair good good CHM fair fair NA NA poor fair NA NA good NA EDM NA NA good fair good good fair NA poor NA EBM good good fair poor poor poor NA NA NA NA LBM good good fair poor poor poor NA NA good fair PAM NA NA fair NA poor poor NA poor good good WEDM NA NA fair fair good good NA NA good good ECG NA NA good good fair good good fair good NA ECH NA NA good good fair good good fair good NA WJM NA NA fair poor poor fair NA NA good NA Deep 107

12 108 Table 5.4 Cost Considerations of the various NTMPs for WEKBS Process Capital cost Tooling cost Power consumption cost Material removal rate efficiency Tool wear USM low low low high medium AJM very low low low high low ECM very high medium medium low very low CHM medium low high* medium very low EDM medium high low high high EBM high low low very high very low LBM low low very low very high very low PAM very low low very low very low very low WEDM medium low low high high ECG medium medium medium low low ECH medium medium medium low low WJM very low low low high low * indicates cost of chemicals

13 109 Figure 5.2 Web page for Editing Shape Applications, Process Capabilities, and Process Economy in the Expert Module

14 Table 5.5 Process Capability levels of Various NTMPs for WEKBS (Continued) Process Part material Tolerance (mm) EDM E.C pr po. ECM E.C pr po. AJM WJM E.N.C.& R E.N.C. & N.M. surface finish (CLA) (µm) 1.0 pr. 0.3po. 1.0 pr. 0.1 po pr. 0.4 pr. 0.1 po pr (AWJM) WEDM E.C (positioning accuracy) surface damage µm corner radii mm 20 (T.D.) 0.1pr po. N.T.D. 0.2pr po. taper (mm/mm) hole dia (mm) width of cut (mm) overcut (mm) (ESD) N.T.D. 0.1 po N.A pr. N.T.D. 1.5 pr N.A pr. 0.3 po. ECH E.C pr. 0.5 pr. 0.1 po. 20 (T.D.) (poss.) N.A pr po. NA NA NA NA NA Max. depth to dia. Ratio Btl., Brittles: C.D, Chemical Damage: E.C., Electrically Conductive: E.N.C., Electrically Non-Conductive: M, Metals: M.D, Mechanical Damage: N.A, Not Applicable: N.M, Non-Metal: N.T.D, No Thermal Damage: R, Refractories: T.D, Thermal Damage: ESD, Electro Stream Drilling: AWJM, Abrasive Water Jet Machining: AECG, Abrasive Electro Chemical Grinding: pr., practical: po., possible 110

15 Table 5.5 Process Capability levels of Various NTMPs for WEKBS Process USM Part material EN.C.&E.C Tolerance (mm) pr (poss.) surface finish (CLA) 0.5 pr. 0.2 po. CHM E.C.&R 0.08 po. 2.0 pr. LBM E.C. & E.N.C pr po. 0.5 po. 1.0 pr 0.4 po. PAM E.C. 1.0 pr. 80 pr. EBM M& NM 0.03 pr po. ECG E.C pr po. 50 po. (µm) surface damage µm N.T.D. 25 (M.D.) N.T.D; 5 (C.D.) 5 pr. N.T.D. 0.3 pr. 0.1 po. corner radii mm taper (mm/mm) hole dia (mm) width of cut (mm) overcut (mm) po pr N.A 3 80 (T.D.) 0.25 po N.A (T.D.) 4 pr N.A (M.D.) pr N.A po. NA NA NA NA NA Max. depth to Btl., Brittles: C.D, Chemical Damage: E.C., Electrically Conductive: E.N.C., Electrically Non-Conductive: M, Metals: M.D, Mechanical Damage: N.A, Not Applicable: N.M, Non-Metal: N.T.D, No Thermal Damage: R, Refractories: T.D, Thermal Damage: ESD, Electro Stream Drilling: AWJM, Abrasive Water Jet Machining: AECG, Abrasive Electro Chemical Grinding: pr., practical: po., possible dia. Ratio 111

16 CALCULATION OF TOTAL GRADE Weighted property indices approach is followed for calculating the individual grades of process parameters and total grades for NTMPs short listed as most suitable. The following is the sequence of operation to calculate the Total grade for NTMPs displayed in the selection list: 1. First of all, Program checks for input entry from Input web page. Cost input is checked, and then the selected Cost input is converted into grade values for all the processes for the selected Cost input (Table 5.4). 2. Shape application input is checked, and then the input is converted into grade values for all the processes for the selected Shape application input (Table 5.3). 3. Material Application input is checked, and then the input is converted into grade values for all the processes for the selected Material Application input (Table 5.2). 4. Process capability input, Tolerance is checked (Table 5.5). Weightage calculation for the input Tolerance is determined. 5. Process capability input, Surface finish input is checked (Table 5.5). Weightage calculation for the input Surface finish is determined. 6. Process capability input, Max.Surface damage input is checked (Table 5.5). Weightage calculation for the input Max.Surface damage is determined.

17 Process capability input, Corner radii input is checked (Table 5.5). Weightage calculation for the input Corner radii is determined. 8. Process capability input, Taper input is checked. Weightage calculation for the input Taper is determined (Table 5.5). 9. Process capability input, Width of cut input is checked. Weightage calculation for the input Width of cut is determined. 10. Process capability input, Over cut input is checked. Weightage calculation for the input Over cut is determined (Table 5.5). 11. Process capability input, Max.Depth to diameter ratio input is checked. Weightage calculation for the input Max.Depth to diameter ratio is determined (Table 5.5). 12. The Total grade for the selected processes (by excluding the disqualified processes) is calculated after getting the grade values for the inputs such as Material Application, Shape Application and Process Economy, and weightages for the process capability inputs such as Tolerance, Surface finish, Corner radii, Taper, Width of cut, Overcut and Max.Depth to diameter ratio. Individual Grades for Material Application, Shape Application, Process Capabilities, and Process economy are found out though SQL query. 13. Result is made ready to send to the browser from the server. Dynamic display table is created using XHTML. Final result is displayed through Output web page.

18 114 To calculate the total grade, the values stored in the data tables are collected from the User Module through The four data tables used in the developed WEKBS are: 1. Material Application 2. Shape Application 3. Process Capabilities and 4. Process Economy. 5.5 SUMMARY In this study a web-enabled machining process selection system for NTMPs has been developed. Using the developed system, any users can select appropriate NTMP which meets their requirements on material type, shape application, process capability and process economy. It also helps engineers to examine the appropriateness of selected tools and machines, and to understand sophisticated machining problems. Design engineers who are geographically separated but well connected by the internet can make use of this system to realize selection of NTMPs for a given limiting requirements. This web-enabled system for selection of NTMPs can cut down the cost, enhance the product quality and decrease the product lead time considerably. Web technology has immense potential to develop a collaborative design and manufacturing environment. It simplifies the sharing of process knowledge and provides intelligent decision making in a collaborative way through the internet. Results of this study are presented as case studies, the input and output web pages, analysis, observation of the case studies are presented in detail in Chapter 6.