Based on previous studies, to increase the productivity and to reduce the grinding cost, there are three proposed solutions including using optimum lubricating-cooling condition, optimum
Trang 1A INTRODUCTION OF DISSERTATION
1 Dissertation title
Optimization on determination of dressing parameters, lubricant conditions and exchanged grinding wheel diameter in internal cylindrical grinding process
2 Rationale of the study
Nowadays, according to the great development of technologies, machining processes have to satisfy more and more requirements of mechanical products for quality as well as productivity In reality, among machining processes, grinding is commonly used to obtain the high quality
of surface finish Especially, it predominates in machining annealed products with high hardness, high strength It accounts for about 20-25% of the total expenditures for mechanical parts in industries Because of these reasons, improvement of grinding performance and reduction of machining expenditure while remaining accuracy requirement have been interested in researchers
In comparison with other type of grinding, internal cylindrical grinding process is implemented in difficult conditions and tight spaces For that reason, it is more difficult to study the process of internal grinding Therefore, the research of the internal grinding process is less interested by scientists than studying external grinding or surface grinding
In order to improve the internal grinding performance, many solutions have been proposed such as using high standard grinding wheels (diamond
or CBN wheel), high speed grinding and optimizing grinding process parameters (cutting, dressing and lubricant parameters) Among these solutions, optimization of grinding process parameters has been considered
in many studies
90CrSi is steel alloy with high mechanic strength and abrasion resistance It is commonly applied to make molds, low speed cutting tools and machine parts required high durable and abrasion resistance In medical factories in the North of Vietnam, this type of steel is often used for making tablet punches and dies
Although, internal grinding process has been used in finished step for making tablet dies, its quality and productivity are still low Therefore, the
Trang 2results of this dissertation will provide suitable suggestions to improve the efficiency of the internal grinding process when making these parts
Based on previous studies, to increase the productivity and to reduce the grinding cost, there are three proposed solutions including using optimum lubricating-cooling condition, optimum dressing condition and using optimum exchanged grinding wheel diameter
3 Research objects
This study focuses on the internal grinding process for annealed 90CrSi steel alloy
4 Research aims and objectives
The aim of this study is to improve internal grinding process to reduce grinding cost and surface roughness and increase productivity
5 Research methodology
The proposed methodology is combined both theoretical and experimental studies
Theoretical study: internal grinding technologies and grinding cost
calculation are analyzed and synthesized
Experimental study: the influence of lubricating-cooling parameters,
dressing parameters and exchanged grinding wheel diameter on the internal grinding cost analyzed and optimized based in experiments
6 Research contents
Overview of internal grinding technologies; Study on effect of lubricating-cooling parameter, dressing parameter on surface roughness and grinding productivity; Study on the calculation model of internal grinding cost and the influences of grinding process on grinding cost; Determination
of optimal exchanged grinding wheel diameter
Trang 3The lubricating-cooling parameters and dressing parameters have been analyzed and optimized based on grinding experiments of 90CrSi steel alloy
8 Dissertation structure
The dissertation includes the following parts: Introduction, 5 chapters, conclusions and appendix
Chapter 1: Overview of internal grinding process
Chapter 2: The model of efficiency improvement of internal grinding process and experimental system
Chapter 3: Experimental study on influence of lubricating-cooling parameter in internal grinding process
Chapter 4: Experimental study on influence of dressing parameter in internal grinding process
Chapter5: Determination of optimal exchanged grinding wheel diameter
9 Significances
Science significances
This dissertation has studied the influence of lubricating-cooling parameters and dressing parameters on the surface roughness as well as the grinding productivity when internal grinding 90CrSi steel alloy The model
of grinding cost has been developed relating to the proposed formula of the optimal exchanged grinding wheel diameter This research has provided a significant contribution in the reduction of grinding cost that is one of interested research directions in internal grinding process
Reality significances
This study has determined solutions to improve the internal grinding efficiency to increase the grinding productivity and the reduction of the grinding cost when grinding 90CrSi tool steel The results of this study can
be applied for internal grinding tablet dies
Trang 4B DISSERATION OUTLINES CHAPTER 1 OVERVIEW OF INTERNAL GRINDING PROCESSS 1.1 Internal grinding process: grinding schema, grinding shaft, position and role of internal grinding in machining process
1.2 Properties of internal grinding process
- The properties of internal grinding process are grinding chord length lk, grinding depth az, equivalent grinding wheel diameter Dtd, shaving removal process of grinding grains, grinding productivity, grinding forces
- Wear of grinding wheel
- Grinding wheel life and method to determine it
- Surface roughness
- Topography of grinding wheel and method to measure Topography
1.3 Literature of internal grinding process
This section focuses on researches relating to the influences of lubricating-cooling, grinding and dressing parameter on the ground surface
in the internal grinding process In addition, the models to determine grinding cost such as Tarasow – Shaw, Field and Ebbrells – Rowe are reviewed and analyzed
1.4 Proposal solution to improve grinding efficiency
- Determination of appropriate lubricating-cooling conditions;
- Determination of optimal dressing parameters;
- Determination of optimal grinding wheel life (optimal exchanged grinding wheel diameter)
CHAPTER 2 MODEL TO IMPROVE THE EFFICIENCY OF INTERNAL GRINDING PROCESS AND DEVELOPMENT OF
EXPERIMENTAL SYSTEM 2.1 Model to improve the efficiency of internal grinding process
Normally, researches focus on the technical efficiency of the grinding process to improve the accuracy and the ground surface quality; reduce force, heat, vibration or increase productivity In order to solve both directions, the dissertation develops a model to improve the efficiency of the internal cylindrical grinding process This model has been proposed
Trang 5including three parts to increase accuracy and machining surface quality and reduce grinding cost in internal cylindrical grinding process
Part 1: Input parameters
Internal grinding process is complex under the influences of many input parameters These input parameters can be classified into five groups including: grinding machines and cutting parameters; workpieces; grinding wheels; dressing technologies and lubricating-cooling technologies Among these five input groups, some significant groups can be chosen to be studied
Figure 1 Model to improve the efficiency of internal grinding process
Part 2: Solutions to improve the efficiency of internal grinding process Three solutions to improve the efficiency of internal grinding process including finding optimal lubricating-cooling parameters to reduce surface roughness and increase the grinding wheel life; finding optimal the dressing parameters to increase the grinding wheel life and the grinding productivity; finding the optimal grinding wheel life to reduce the grinding cost These models will be presents in next chapter respectively
Part 3: The quality of the grinding process is increased and technical requirements are ensured, productivity is increased and grinding cost is decreased All of the input lubricating-cooling parameters and dressing parameters affect the surface roughness
Trang 6Based on these arguments, it can provide a model to improve the efficiency of the internal grinding process as shown in Figure 1
Three solutions are proposed for studying to improve the efficiency of the process when internal cylindrical grinding small holes Among these solutions, the application of the optimal grinding wheel life (exchanged grinding wheel diameter) has not been considered in previous researches Figure 2 presents the relationship between the grinding wheel life (L), grinding cost (Cgw,p) and cost of machine, labor and management (Cmt,p) in internal grinding process for one product
Figure 2 The relationship between the grinding wheel life and grinding
cost
The longer the grinding wheel life, the lower the cost of grinding wheel
is In contrast, the cost for machines, labors and management linearly increases with the machining time The total machining cost for a part includes the expenditures of grinding wheel, machines, labors and management In Figure 2, a certain optimal grinding wheel life always exists
Trang 72 This study has proposed a model to improve the efficiency of internal grinding process including: determinations of the appropriate lubricating-cooling parameters, the optimal dressing parameters and the optimal exchanged grinding wheel diameter These solutions will be presented in next chapters of this dissertation
3 An experimental system has been developed to meet the requirements
of experimental research
CHAPTER 3 EXPERIMENTAL STUDY ON INFLUENCE OF LUBRICATING-COOLING PARAMETER IN INTERNAL
GRINDING PROCESS 3.1 Effect of cooling parameters on surface roughness
Cooling flood is the most commonly used in grinding hole Therefore, in this study, finding optimal coolant parameters is one of the directions to improve the grinding efficiency
3.1.1 Experiment and results/ Experimental results
a Caltex Aquatex 3180 oil
Table 1 Experimental results for Caltex Aquatex 3180 oil
No Points
Ra (µm) Flow
Trang 8The regression coefficients present the effect level of the flow rate, the concentration parameters and their interaction on the objective function Ra They all have influence on the surface roughness, thus the regression function is a quadratic function as below:
Y = 1,048 - 0,229x1 – 0,133x2 + 0,033x12 + 0,030x2 - 0,010x1x2 (1) When this parameter increases, the roughness Ra decreases to minimal value because friction is reduced However, if the contribution is too high, the coolant is concentrated and then amount of chips sticking on the workpiece surface is increased As a result, the surface roughness Ra is increased Similarly, the flow rate also affects on the roughness Ra There is
an optimal flow rate to obtain a minimum roughness Ra Increasing the flow rate, more coolant is in the cutting area and then the roughness Ra is reduced However, the space of internal grinding is limited by the gring wheel dimension, increasing the flow rate does not increase amount of the coolant in cutting area In addition, increasing the flow rate increases the concentraion of the coolant in the cutting area and also increases the chips
on the workpiece surafce That is an interaction effect between two parameters on the roughness Ra
Figure 3 Regression surface of Ra for Caltex Aquatex 3180 oil
b Emulsion
Trang 9Table 2 Experimental results for Emulsion oil
Ra (µm) Flow
Results and Discussions
Using Minitab software, analyzing the experiment results, we obtained the regression equation:
Y= 0,218 – 0,006x1+0,038x2 - 0,016x1x2 + 0,016x12 + 0,004x2 (2)
Figure 4 Regression surface of Ra for Emulsion oil
Trang 10In figure 4, when the flow rate is low, the concentration strongly affects
to the roughness value Increasing the concentration, surface roughness
increase When flow rate equal 4 l/min, the roughness value is almost
constant for all concentration value In general, the more Emulsion oil will increase the surface roughness This is because Emulsion solution is high density, makes it difficult to escape chips and clean the machining surface
3.1.2 Optimization of the concentration and the flow rate
a Caltex Aquatex 3180 oil
Using response surface method, the relation between the concentration and the flow rate with the roughness Ra is shown From the optimization plot, there exists an optimal set of these parameters to obtain a minimum roughness Ra The solution of the optimal parameters are shown, the minimal roughness Ra is 0.4102µm with the concentration of 3.907% and
the flow rate of 2.864 (l/min)
b Emulsion oil
Similarly, we can determine the optimal cooling parameters when using
Emulsion oil solution The flow rate value is 1,38 l/min and the
concentration value is 2,37% The minimum of surface roughness Ramin = 0,3 µm
3.2 Conclusion of chapter 3
This chapter focuses on experimental study on influence of 2 types (Caltex Aquatex 3180 and Emulsion), lubricating-cooling parameter to surface roughness in internal grinding process This study results show that:
- When grinding and using Emulsion oil solution, surface roughness is better than using Caltex Aquatex 3180 oil solution
- The optimal Aquatex 3180, Emulsion oil solution lubricating-cooling parameter with was determined
+ With Aquatex 3180 oil solution: the flow rate is 2,86 l/min and the
concentration is 3,91%
+ With Emulsion solution: the flow rate is 1,38 l/min and the
concentration is 2,37%
Trang 11CHAPTER 4 EXPERIMENTAL STUDY ON INFLUENCE OF DRESSING PARAMETER IN INTERNAL GRINDING PROCESS 4.1 Experimental setup
Table 3 Dressing parameters and their values at different levels
Using Minitab, the experiment setup was design The experiment with the six dressing parameters including the dressing feed rate, the coarse dressing depth, the coarse dressing times, the fine dressing depth, the fine dressing times and the dressing number without depth of cut was conducted using Taguchi method Table 2 shows the dressing parameters and their values at different levels As it can be seen from the table, five three-level dressing parameters and one six-level dressing parameter are established for the experiment The L18 (53x16) was used for the experiment work
Trang 124.2 Effect of dressing parameter to surface roughness (Ra) and material remove rate (MRR) in internal grinding
4.2.1 Experiment results and single-objective optimization
a, Influence of dressing parameter to Ra
From the analysis of variance – ANOVA, it is clearly seen that the feeding dressing times has the largest effect on surface roughness Ra, The other parameters, which have the effect on Ra, sequence: coarse dressing depth, coarse dressing times, fine dressing depth, fine dressing times and dressing feed rate
Table 4 The effect of dressing parameters on Ra at their levels
Level CK t tho n tho t tinh n tinh S sd