The output of traditional setup planning approaches is limited and insufficient for upstream process planning activity such as fixture planning. Most existing layout planning systems deal with the conceptual design phase of fixtures by selecting reference features.
Process Planning
In view of the importance of process planning for the manufacture of a part, the present thesis investigates process planning, in particular to automate setup planning for the machining of prismatic parts. Some examples of generative process planning systems are EXCAP (Expert Computer-Aided Process-Planning) [Davis and Darbyshire, 1984], PROPLAN (Prosesbeplanner) [Philips et al., 1984], CUTTECH (Cutting Technology) [Barkocy and Zdeblick, 1984], SIPP (Semi Intelligent Process Planning) [Nau and Chang, 1985], HI-MAPP (Hierarchical and Intelligent Manufacturing Automatic Process Planner) [Berenji and Khoshnevis, 1986], and QTC (Quick Turnaround Cell) [Kanumury and Chang, 1991].
Setup Planning in Machining Process
Although efforts to automate configuration planning have been underway since the 1980s, it is still a complex task. Nevertheless, the ultimate goal of automating setup planning is to achieve the desired quality of the final product at the lowest possible production costs and with minimal production time.
Constraints to be considered in Setup Planning
- Tolerance Requirements
- Tool Approach Direction (TAD) of a Feature
- Feature Interaction and Precedence Constraints
- Fixturing Constraints
- Datum and Reference Constraints
- Constraints of Good Manufacturing Practice
The reference and reference requirements lead to the restrictions that reference/reference features must be edited before the related feature. Because other features are located and sized with respect to reference/reference features, reference/reference features must be edited first.
Broad Objectives of the Thesis
Organization of the Thesis
In Chapter 3, a brief background knowledge of expert systems and the CLIPS expert system is presented, followed by a description of the various modules of the configuration planning expert system. The knowledge gathered from the experimental study is incorporated in the form of IF–THEN rules into the configuration planning expert system to set the data surface roughness to achieve a certain tolerance.
Introduction
In this chapter, an overview of available literature in the field of essay planning is presented in different sections. In Section 2.4, summary of literature review is presented and challenging issues in essay planning are discussed.
Traditional Approaches of Setup Planning
Decision Tree, decision Table and GT based Approaches
The algorithm for implementing a decision tree can be written in any of the procedural programming languages such as FORTRAN, PASCAL, C, etc. Opitz GT codes are used for providing input information about the parts, machine tools and cutting tools.
Algorithmic and Graph Theoritic Approaches
The criteria taken into account for the arrangement planning are TAD, tolerance relationships, priority relationships and orientation of the features. 1996] developed a setup planning system with an emphasis on achieving specified tolerances of the features present in the part.
Approaches based on Artificial Intelligence and Soft Computing
Expert System based Approaches
The authors developed an expert system to generate setups and operation sequencing for machining prismatic parts. Ferreira and Liu [1988] developed a rule-based expert system for automatic workpiece orientation generation for a prismatic part machining setup.
Artificial Neural Network (ANN) based Approaches
Both rotating and prismatic Rotating Rotating Rotating Both rotating and prismatic Prismatic Prismatic Prismatic Prismatic Prismatic. Rotating Prismatic Prismatic Rotating Prismatic Prismatic Prismatic Prismatic Prismatic Prismatic Both rotating and prismatic Prismatic Rotating Prismatic.
Application of Evolutionary Algorithms
To simulate the natural survival of the fittest process, the best chromosomes exchange information (via crossover or mutation operators) to produce offspring chromosomes. Some PSO and ACO-based setting design and process design efforts are discussed below.
Fuzzy Logic based Approaches
2005] used a hybrid of fuzzy set theory and Hopfield neural network for configuration planning of prismatic parts. A fuzzy set theory-based approach to configuration planning is presented considering TAD, tolerance requirements, precedence relationships, manufacturing cost, and good manufacturing practice.
Summary of Literature Review and Challenging Issues
However, this aspect is not given due importance in the deployment planning approach found in the literature. Fuzzy set theory is used in various attempts at arrangement planning, as can be seen from the literature review.
Scope and Objectives of the Present Work
An important aspect that emerges from the literature review on facility planning is that most research efforts regarding uncertainty have focused on uncertainty in the workplace. A methodology for updating the knowledge base of the installation planning system: The adaptability of the installation plans to a changing production environment is an important issue.
Introduction
A Background of Expert Systems
An expert system shell is a software system where the developer must build the knowledge base. Some examples of expert system shells are EMMYCIN (Empty MYCIN), EXSYS (Expert System Shell), CLIPS (C Language Integrated Production System), ART (Automated Reasoning Tool), G2, LEVEL5, etc. [Nikolopoulos, 1997].
CLIPS: An Expert System Shell
In the present work, the CLIPS expert system shell is used to develop the configuration planning expert system. At the time of execution of the expert system program, the following steps should be performed.
Development of the Setup Planning Expert System
- Database
- Machining Feature Information
- Machining Operation Information
- Mathematical Functions and Other Required Information
- Knowledge-base
- Generation of Machining Precedence Constraints
- Setup Formation
- Machining Operation Sequencing Within a Setup
- Datum Selection for Each Setup
- Fixuring Information Generation Module
- Provision for Uncertainty and Feedback
- The Inference Engine
- The User Interface
The following section explains the format for representing input data to the expert system. The parent/nesting function must be processed before the child/nesting function. e), the two pockets only have area interaction in the form of a common face.
Summary
After developing the expert system program, it is important to validate its operation in various parts. Accordingly, the effectiveness of the developed expert system for layout planning is confirmed in various parts.
Introduction
A Background of Fuzzy Sets
- Mathematical Definition of Fuzzy Sets
- Determination of Membership Functions
- Fuzzy Set Operations
- Fuzzy Arithmetic
- Linguistic Variables and Hedges
Assigning appropriate values to membership degrees and constructing the membership function is one of the most challenging tasks of fuzzy set theory. A prominent branch of fuzzy set theory is fuzzy arithmetic, which deals with fuzzy numbers.
Strategy for Uncertainty Management in the Knowledge-base
Uncertainty in the Feature Precedence Relations
If the value of µc is high, there will be a greater chance of burr formation of significant size and therefore preferential relationship will be required. However, the actual drilling process must be monitored on the job floor to check for burr formation.
Uncertainty in the Datum Selection
If µgt, µgsa, and µgsq are the individual fuzzy membership degrees for good tolerance ratio, good surface, and good surface quality for a particular datum candidate plot, then the total plot membership score is given by . One of the requirements can be "very good tolerance ratio", "good surface" and "good surface quality".
Strategy for Adaptive Learning and Updating the Knowledge-base
Assume that the value of the general membership rate µc for pitting (from Equation 4.15) is µ1 (which is low) for a particular combination of material, tool, and feed rate that indicates no pitting will form. During the actual drilling process, it is found that there is formation of considerable size scratch and the observed value of the degree of membership is determined as μ2.
A Methodology for Fine Tuning the Membership Grades Assigned by
Problem definition
The success of a fuzzy-set-based method depends on the accurate assignment of membership grades as well as the use of an appropriate fuzzy-set-theoretic operation to obtain an overall membership grade. In Eq (4.18), however, the fuzzy input and output variables are related through an appropriate fuzzy set-theoretic operator f, and the output is obtained in a single step by performing operation f on the input variables µi (i=1 to n).
Fine Tuning the Membership Grades
For an acceptable solution, the minimum level of accuracy and deviation from the expert's judgment must be satisfactory. A solution with very poor/poor quality, either in terms of accuracy criterion or in terms of deviation from the expert's judgment criterion, is not acceptable.
Application of the Proposed Methodology to Burr Height
- Experimental Work
- Application of the Proposed Methodology
Burr heights for different feed rates when drilling a mild steel workpiece Feed rate Maximum burr height (mm). Burr heights for different feed rates when drilling a cast iron workpiece Feed rate Maximum burr height (mm).
Summary
Fine-tuning the initial expert's estimates improved the performance of the burr height prediction methodology. It is noted that fine-tuning the initial expert's estimates of membership degrees of fuzzy variables improves the performance of the system.
Introduction
2001] studied the effect of workpiece surface roughness and reference point on locating accuracy in a multi-station machining process. Deiab and Elbestawi [2005] presented the results of an experimental investigation of the tribological condition of the contact surface of the workpiece and the fixture, taking into account the surface roughness of the workpiece, the fixture, the normal load and the material of the workpiece.
Experimental Procedure
The basic surface of the workpiece A was machined in a vertical milling machine by changing the process parameters to obtain different roughness values of the attachment point. The coordinate values of the points on the top page give an idea of the parallelism tolerance.
Observations
Observations on Parallelism
However, as the datum roughness becomes higher (Ra = 4.86 µm), the differences in the Z-coordinate values decrease significantly. Further increase in datum roughness to Ra of 5.43 µm and 6.35 µm shows that the differences in the Z coordinate values decrease with increasing surface roughness.
Observations on Perpendicularity
Here again, the changes in the Z coordinate values are smaller in the case of the base with high roughness of 6.35 µm compared to the base with low roughness values of 2.15 µm and 0.85 µm. In all cases, the datum with the highest surface roughness of 6.35 µm provided the smallest parallelism tolerance.
Statistical Analysis of the Experimental Results
- Parallelism
- Perpendicularity
Let xH and xL be the mean maximum parallelism tolerance for the highest and lowest datum roughness cases, respectively. The conclusion can be drawn at the 95% confidence interval that there is a significant difference in parallelism tolerance for cases with low and high datum roughness.
A Theoritical Model for Explaining the Observations
After processing the upper surface, the height difference between points 1 and 2 is given by Since (δ2 −δ1) is negative, the difference in magnitude in the heights of the upper surface in the case of the rough reference point is reduced compared to the smooth rigid reference point.
Experimental Verification of the Proposed Theoretical Model
Experiments in a Universal Testing Machine
Similar experiments on perspex revealed that deflections with a rough base are greater by 0.24 mm and 0.25 mm than with a smooth base. In the present work, the approximate data is able to deviate the workpiece approximately on the order of 0.2 mm and compensate for the inherent machine error, de.
Experiments on Workpiece Supported on a Rubber Pad
It is stated that if the desired parallelism tolerance (μp) is within 0.09–0.17 mm, there are two options for selecting the reference surface roughness (μRa). The process parameters must be selected by the process planner to achieve the given surface roughness.
Summary
Introduction
In addition to configuration planning information, the system can now provide the following output: (i) fuzzy recommended cutting/feed depth, (ii) fuzzy machining and clamping forces, (iii) approximate optimal location and layout of clamps and (iv) sizes of locators and clamps. The device designer can further optimize the installation plan by receiving input from the configuration planning module.
The Architecture of the Fixturing Information Generation Module
- Setups, Operation Sequence and Datum Selection Module A
- Machining Force Calculation Module B
- Locator and Clamp Layout Optimization Module C
- Workpiece-Fixture Contact Module D
- Locator and Clamp Design Module E
Therefore, the angular displacement ψ at a distance y from the free end of the cutter is given by . It is assumed that the stiffness of the locators and clamps is higher than the stiffness of the workpiece.
The Methodology for Generating Fixturing and Process Related
The following strategy is developed to find the maximum value of radius of curvature R%max. The radius of curvature of the spherical locator button RL is determined taking into account the onset of yielding in the workpiece material.
An Example End Milling Process
Young's modulus of elasticity for the workpiece, clamp and locating materials may vary by ±5%. The radius of curvature of the spherical locator knob, RL comes to be 24 mm from equation (6.17).
Summary
Example Parts
Example Part 1
Example Part 2
Example Part 3
Summary
Conclusions
Contributions of the Research Work
Scope for Future Work
