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Cairo University Conference on mechanical design and production
Conference Report 27-29 December 1979, Cairo, Egypt
Cairo University Conference on Mechanical Design and Production During the three day technical sessions of this Conference, some 120 papers were presented and circulated. Those pertinent to Precision Engineering are reported below.
Accuracy and surface finish Rashed et al. z presented the results of experimental investigations and relevant numerical computations of the accuracy of dimensions and form of the free surfaces of press-fitted brass cylinders. With initial out-ofroundness of fitted cylinders, the authors used finite element analysis to determine deformations emanating at the free surfaces of the assembly. Good agreement was shown to exist between experimental results and numerically computed values. EI-Fayoumi 2 proposed a method for obtaining the optimal limit gauge design with the help of a computer, design parameters considered comprising the ratio of limit gauge tolerance to production tolerance and relative dispositions of these tolerance zones. A computer simulation model was built to evaluate gauge performance either by means of gauging deficiency or by the extent of accepted lot. In a study conducted by Moshref 3 on the mechanics of the turning process using self-propelled rotary tools, the effect of this cutting technique on surface roughness was carefully examined. A comparison was made between surface roughness values attained with rotary turning tools, with those obtained when using conventional cemented-carbide single-point cutting tools. Experimental results show that the use of the rotary tool leads to lower surface deterioration of the workpiece. The relationship between surface roughness and the conditions of turning, tool geometry and tool setting angle, as studied by Damir et al. 4 , was shown to be seriously influenced by the error incurred in the tool setting angle.
232
Surface roughness was found to increase with increase in plane approach angle. Roughness values were also shown to be linearly proportional to feed. While cutting speed was found, by the authors, to exert no remarkable influence on surface roughness for non-ferrous metals, an increase in cutting speed, for ferrous metals, would lead to lower roughness values. In an attempt to study the factors controlling surface roughness of spark-machined components, Ghabrial and Ebeid s proposed the relationship: R a = n U ~/~ C 'h in which R a represents the centre line average value, n a constant, U the breakdown voltage and C the capacity of the condenser. This was verified experimentally using different sparkerosion machines and various materials for tool and workpiece. Kassem and Shosha 6 conducted a theoretical investigation into the dynamic performance of a hydraulic copying mechanism incorporating a four nozzle flapper valve. They solved the governing equations for the case in which the cutting forces are negligibly small, ie for some finishing operations. It is concluded, in this work, that both accuracy and speed of response improve with increase in supply pressure and diameter ratio of flapper nozzles, also with the reduction of friction in the guide ways. In dealing with the design aspects for axial piston pumps, Beswarick 7 put forward a more precise method for estimating dynamic forces in the pump and contact stress levels at piston and cylinder bore interface. With minimum leakage and viscous drag losses taken as merit function, the author devised a chart for determining the optimum diametral piston clearance. In a paper by Elfar, EI-Mahdy and Eleiche 8, a simple and accurate
technique was developed for mounting resistance wire strain gauges in a denture base with a view to measuring and recording forces at the tissuedenture base interface. Salient merits of the technique were outlined.
Production Processes In dealing with billet production technology, Das and Basily 9 discussed the various aspects of high speed cropping in which high speeds result in a dramatic improvement in billet quality, thus resulting in billets of excellent geometrical form associated with close tolerances of weight and minimum metallurgical defects. Equipment required for the production of such superior billets was also reviewed at length. Experience gained with installations for bar sizes below some 30 mm diameter was claimed to be totally satisfactory.
Design and performance of metal cutting tools Wear and machining performance of coated versus uncoated tools was discussed in three papers by Abdel Aziz 1°, Shabaik 11 and Naiem 12 . Coated cemented carbides were found to lead to an exponential increase in metal cutting productivity as the life of the coated tool may well attain 3 to 5 times that of the uncoated tool. In the first paper wear mechanisms in titanium coated cemented carbides were carefully studied, while cutting performance of coated tools was examined in the paper by Shabaik 11, who has also conducted flank and crater wear measurements. Improvement in tool life was evaluated for the various coatings considered. In his study of machinability comparison for various coated and uncoated carbide tools, Naiem ~2 used the 'response surface technique' with a view to obtaining meaningful results (ie within required confidence limits) with minimum consumption of tools and materials
PRECISION ENGINEERING
and with minimum expenditure of time. He came to the conclusion that coated tools display the best performance and the longest life, and that the response surface technique is a very efficient and economic method for the assessment of tool life. Etheridge 13 developed a theoretical treatment, including computer programmes, for the accurate determination of rake face geometry for a large helically fluted form cutter for generating the steam face of turbine blades. This treatment is also capable of predicting the rake angle in the true normal, base normal and transverse planes. In their approach to developing an optimal design of multiedge cutting tools, Osman and Latinovic 14 derived a multivariable non-linear objective function which they modified to an unconstrained type with bounded decision variables. A numerical, direct search method, accelerated in distance, was selected to minimise the objective function. Preliminary experimental evidence of the overall performance of the designed tools comprising tool guidance, hole size control, hole straightness, chip formation and tool stability was provided. The multi-edge tools were shown to be capable of undergoing relatively high feed rates. For precision boring, Attia Is proposed a procedure for maintaining the required accuracy by controlling variations in the deflection of the boring bar as caused by variations of workpiece material hardness and variations in the depth of cut. Boring bar deflection variations were restricted, in this procedure, to a certain percentage of bore tolerance. The effect of various machining parameters on cutting forces and power consumption was studied experimentally for the thread turning operation by Riad and Dawood 16. Parameters considered include cutting speed, number of cuts, contact length and feed criterion. Experimental results pave the way to achieve optimum conditions for thread machining.
servo-controlled tool feed mechanism with a view to controlling the electrolysing current during machining. With this servo-mechanism together with the use of a drooping-characteristic dc power supply, the authors claim that it was possible to control the drilling process and to reduce tool damage, due to occasional short circuits and sparks, to a minimum. Precision of the electrochemical drilling process, as dictated by side gap, was investigated by Ebeid Is who developed a radial gap equation which takes into consideration both tool rotational geometry and tool size. Test results show closer agreement with the proposed gap equations. The ratio of side to frontal gaps at the tool face was found to be a function of voltage-feed rate ratio in contradistinction to the constant value used in previous work. An attempt to obtain precise and reproducible results in an electrolytic sinking machine was reported by EI-Dardiry 19. Circular holes, as produced with a rotary tool, while displaying significant reduction in the out-of-roundness feature, suffer,
Electrochemical
9. Das M.K. and Basily B.B. High Speed Crop-
machining
An electrochemical drilling machine, designed and built by Riad and AbdelMawgoud 17 was equipped with a
PRECISION ENGINEERING
however, from an increase in oversize. The out-of-roundness is shown to decrease with higher rotational speeds and lower rates of feed (down to 16#m in the test versus 120/~m with a non-rotating tool). Rashed et alfl ° proposed a control device capable of maintaining the electrolysing current at a constant value in an electrolytic sin.king process. This feature is highly desirable to obtain high machining quality combined with close machining tolerances. The servomotor of the control device has been identified as a second order transfer function and the error measurement circuit was modelled by a constant parameter. It is claimed that the proposed control device attains stable conditions fast enough to control the process under internal and external disturbing influences. Owing to its fairly low overshoot, it is recommended to use this control system with a relatively low loop gain.
G.S.A. Shawki Department of Mechanical Design and Production, Faculty of Engineering, Cairo University, Cairo, Egypt
References 1. Rashed A.F., Damir M.N.H. and Wail H.M.
11 .Shabaik A.H. Machining Performance of
The Effect of Initial Out-of-Roundness of Press-fitted Cylinders on their Accuracy
High-Speed Steel Tools with Superhard Coatings
2. El-Fayoumi S.M. Computer-Aided Limit Gauge Design 3. Moshref s.c. A Study of Rotary Turning Tool and its Effect on Surface Roughness 4. Damir M.N., Shouckry A.S. and Saleh S.
Surface Roughness Related to Machining Conditions 5. Ghabrial S,R. and Ebeid S.J. Finish Factor
for Spark Erosion Machining 6. Kassem S. and Shosha M. Dynamic Performance of a Hydraulic Tracer with
Four-Nozzles Flapper Valve 7. BeswarickW.J. Contributions to the Design of Axial Piston Pumps for Hydrostatic Transmission 8. Elfar M.M., EI-Mahdy A.S. and Eleiche
A.M. A New Method for Mounting Electronic Wire Strain Gaugesin Denture Base to Record Forces Transmitted to the Underlying Tissue ping: A New Technology for Billet Production 10 Abdel Aziz M.M. Wear Behaviour of
Coated Carbide Cutting Tools
12. Naiem A.F. Machinability Comparison for Various Coated and Uncoated Carbide Tools 13. Etheridge R.A. Technical Determination
of the Rake Face Geometry of a Large Helically Fluted Form Cutter 14.Osman M.O.M. and Latinovic Optimal Design of Multi-Edge Cutting Tools for BTA Deep-Hole Machining 15.Attia H.A. Planning the SuccessiveCuts in Precision Boring for Batch Production 16.Riad M.S,M. and Dawood O.M. Variables
Affecting Thread Machining 17. Riad S.M. and AbdeI-Mawgoud B.M.
Electrochemical Drilling of Steel and Cemented Carbide Tips 18. Ebeid S.J. Side Gap Estimation in Electrochemical Drilling 19. EI-Dardiry M.A. On the Performance of an Electrolytic Sinking Machine 20. Rashed A.F., Soliman S.M., Abuelnasr B.M. and EI-Mehdawi ~.H. Modelling,
Identification and Analog Computer Simulation of a Proposed Control Device for Electrolytic Sinking Process
233
Cairo University Conference on Mechanical Design and Production During the three day technical sessions of this Conference, some 120 papers were presented and circulated. Those pertinent to Precision Engineering are reported below.
Accuracy and surface finish Rashed et al. z presented the results of experimental investigations and relevant numerical computations of the accuracy of dimensions and form of the free surfaces of press-fitted brass cylinders. With initial out-ofroundness of fitted cylinders, the authors used finite element analysis to determine deformations emanating at the free surfaces of the assembly. Good agreement was shown to exist between experimental results and numerically computed values. EI-Fayoumi 2 proposed a method for obtaining the optimal limit gauge design with the help of a computer, design parameters considered comprising the ratio of limit gauge tolerance to production tolerance and relative dispositions of these tolerance zones. A computer simulation model was built to evaluate gauge performance either by means of gauging deficiency or by the extent of accepted lot. In a study conducted by Moshref 3 on the mechanics of the turning process using self-propelled rotary tools, the effect of this cutting technique on surface roughness was carefully examined. A comparison was made between surface roughness values attained with rotary turning tools, with those obtained when using conventional cemented-carbide single-point cutting tools. Experimental results show that the use of the rotary tool leads to lower surface deterioration of the workpiece. The relationship between surface roughness and the conditions of turning, tool geometry and tool setting angle, as studied by Damir et al. 4 , was shown to be seriously influenced by the error incurred in the tool setting angle.
232
Surface roughness was found to increase with increase in plane approach angle. Roughness values were also shown to be linearly proportional to feed. While cutting speed was found, by the authors, to exert no remarkable influence on surface roughness for non-ferrous metals, an increase in cutting speed, for ferrous metals, would lead to lower roughness values. In an attempt to study the factors controlling surface roughness of spark-machined components, Ghabrial and Ebeid s proposed the relationship: R a = n U ~/~ C 'h in which R a represents the centre line average value, n a constant, U the breakdown voltage and C the capacity of the condenser. This was verified experimentally using different sparkerosion machines and various materials for tool and workpiece. Kassem and Shosha 6 conducted a theoretical investigation into the dynamic performance of a hydraulic copying mechanism incorporating a four nozzle flapper valve. They solved the governing equations for the case in which the cutting forces are negligibly small, ie for some finishing operations. It is concluded, in this work, that both accuracy and speed of response improve with increase in supply pressure and diameter ratio of flapper nozzles, also with the reduction of friction in the guide ways. In dealing with the design aspects for axial piston pumps, Beswarick 7 put forward a more precise method for estimating dynamic forces in the pump and contact stress levels at piston and cylinder bore interface. With minimum leakage and viscous drag losses taken as merit function, the author devised a chart for determining the optimum diametral piston clearance. In a paper by Elfar, EI-Mahdy and Eleiche 8, a simple and accurate
technique was developed for mounting resistance wire strain gauges in a denture base with a view to measuring and recording forces at the tissuedenture base interface. Salient merits of the technique were outlined.
Production Processes In dealing with billet production technology, Das and Basily 9 discussed the various aspects of high speed cropping in which high speeds result in a dramatic improvement in billet quality, thus resulting in billets of excellent geometrical form associated with close tolerances of weight and minimum metallurgical defects. Equipment required for the production of such superior billets was also reviewed at length. Experience gained with installations for bar sizes below some 30 mm diameter was claimed to be totally satisfactory.
Design and performance of metal cutting tools Wear and machining performance of coated versus uncoated tools was discussed in three papers by Abdel Aziz 1°, Shabaik 11 and Naiem 12 . Coated cemented carbides were found to lead to an exponential increase in metal cutting productivity as the life of the coated tool may well attain 3 to 5 times that of the uncoated tool. In the first paper wear mechanisms in titanium coated cemented carbides were carefully studied, while cutting performance of coated tools was examined in the paper by Shabaik 11, who has also conducted flank and crater wear measurements. Improvement in tool life was evaluated for the various coatings considered. In his study of machinability comparison for various coated and uncoated carbide tools, Naiem ~2 used the 'response surface technique' with a view to obtaining meaningful results (ie within required confidence limits) with minimum consumption of tools and materials
PRECISION ENGINEERING
and with minimum expenditure of time. He came to the conclusion that coated tools display the best performance and the longest life, and that the response surface technique is a very efficient and economic method for the assessment of tool life. Etheridge 13 developed a theoretical treatment, including computer programmes, for the accurate determination of rake face geometry for a large helically fluted form cutter for generating the steam face of turbine blades. This treatment is also capable of predicting the rake angle in the true normal, base normal and transverse planes. In their approach to developing an optimal design of multiedge cutting tools, Osman and Latinovic 14 derived a multivariable non-linear objective function which they modified to an unconstrained type with bounded decision variables. A numerical, direct search method, accelerated in distance, was selected to minimise the objective function. Preliminary experimental evidence of the overall performance of the designed tools comprising tool guidance, hole size control, hole straightness, chip formation and tool stability was provided. The multi-edge tools were shown to be capable of undergoing relatively high feed rates. For precision boring, Attia Is proposed a procedure for maintaining the required accuracy by controlling variations in the deflection of the boring bar as caused by variations of workpiece material hardness and variations in the depth of cut. Boring bar deflection variations were restricted, in this procedure, to a certain percentage of bore tolerance. The effect of various machining parameters on cutting forces and power consumption was studied experimentally for the thread turning operation by Riad and Dawood 16. Parameters considered include cutting speed, number of cuts, contact length and feed criterion. Experimental results pave the way to achieve optimum conditions for thread machining.
servo-controlled tool feed mechanism with a view to controlling the electrolysing current during machining. With this servo-mechanism together with the use of a drooping-characteristic dc power supply, the authors claim that it was possible to control the drilling process and to reduce tool damage, due to occasional short circuits and sparks, to a minimum. Precision of the electrochemical drilling process, as dictated by side gap, was investigated by Ebeid Is who developed a radial gap equation which takes into consideration both tool rotational geometry and tool size. Test results show closer agreement with the proposed gap equations. The ratio of side to frontal gaps at the tool face was found to be a function of voltage-feed rate ratio in contradistinction to the constant value used in previous work. An attempt to obtain precise and reproducible results in an electrolytic sinking machine was reported by EI-Dardiry 19. Circular holes, as produced with a rotary tool, while displaying significant reduction in the out-of-roundness feature, suffer,
Electrochemical
9. Das M.K. and Basily B.B. High Speed Crop-
machining
An electrochemical drilling machine, designed and built by Riad and AbdelMawgoud 17 was equipped with a
PRECISION ENGINEERING
however, from an increase in oversize. The out-of-roundness is shown to decrease with higher rotational speeds and lower rates of feed (down to 16#m in the test versus 120/~m with a non-rotating tool). Rashed et alfl ° proposed a control device capable of maintaining the electrolysing current at a constant value in an electrolytic sin.king process. This feature is highly desirable to obtain high machining quality combined with close machining tolerances. The servomotor of the control device has been identified as a second order transfer function and the error measurement circuit was modelled by a constant parameter. It is claimed that the proposed control device attains stable conditions fast enough to control the process under internal and external disturbing influences. Owing to its fairly low overshoot, it is recommended to use this control system with a relatively low loop gain.
G.S.A. Shawki Department of Mechanical Design and Production, Faculty of Engineering, Cairo University, Cairo, Egypt
References 1. Rashed A.F., Damir M.N.H. and Wail H.M.
11 .Shabaik A.H. Machining Performance of
The Effect of Initial Out-of-Roundness of Press-fitted Cylinders on their Accuracy
High-Speed Steel Tools with Superhard Coatings
2. El-Fayoumi S.M. Computer-Aided Limit Gauge Design 3. Moshref s.c. A Study of Rotary Turning Tool and its Effect on Surface Roughness 4. Damir M.N., Shouckry A.S. and Saleh S.
Surface Roughness Related to Machining Conditions 5. Ghabrial S,R. and Ebeid S.J. Finish Factor
for Spark Erosion Machining 6. Kassem S. and Shosha M. Dynamic Performance of a Hydraulic Tracer with
Four-Nozzles Flapper Valve 7. BeswarickW.J. Contributions to the Design of Axial Piston Pumps for Hydrostatic Transmission 8. Elfar M.M., EI-Mahdy A.S. and Eleiche
A.M. A New Method for Mounting Electronic Wire Strain Gaugesin Denture Base to Record Forces Transmitted to the Underlying Tissue ping: A New Technology for Billet Production 10 Abdel Aziz M.M. Wear Behaviour of
Coated Carbide Cutting Tools
12. Naiem A.F. Machinability Comparison for Various Coated and Uncoated Carbide Tools 13. Etheridge R.A. Technical Determination
of the Rake Face Geometry of a Large Helically Fluted Form Cutter 14.Osman M.O.M. and Latinovic Optimal Design of Multi-Edge Cutting Tools for BTA Deep-Hole Machining 15.Attia H.A. Planning the SuccessiveCuts in Precision Boring for Batch Production 16.Riad M.S,M. and Dawood O.M. Variables
Affecting Thread Machining 17. Riad S.M. and AbdeI-Mawgoud B.M.
Electrochemical Drilling of Steel and Cemented Carbide Tips 18. Ebeid S.J. Side Gap Estimation in Electrochemical Drilling 19. EI-Dardiry M.A. On the Performance of an Electrolytic Sinking Machine 20. Rashed A.F., Soliman S.M., Abuelnasr B.M. and EI-Mehdawi ~.H. Modelling,
Identification and Analog Computer Simulation of a Proposed Control Device for Electrolytic Sinking Process
233