John S. Agapiou

Calculation of main cutting edge forces and torque for drills with arbitrary point geometries

Abstract A model for calculating main cutting edge torque, thrust, and radial force distributions for drilling gray cast iron with solid carbide and carbide-tipped drills is described. Unlike previous models, this model is applicable to arbitrary point geometries and includes radial forces due to point asymmetry. A general parametric method for characterizing complex point geometries is first described. Using this method, together with empirical cutting force models from end cutting tests, torque, thrust, and radial force calculations are carried out for ten representative drills covering a range of available geometries. Calculated and measured torque values agree to within the repeatability of the measurements. Calculated thrust force values are reasonable, but are significantly lower than measured values in most cases, since chisel edge contributions are not included. Calculated radial forces for an asymmetric drill agree with limited measured values to within twice the repeatability of the measurements. Future work on chisel edge contributions, temperature calculations, and force calculations for interrupted holes is briefly discussed.

On the determination of thermal phenomena during drilling—Part II. Comparison of experimental and analytical twist drill temperature distributions

Abstract The analytical models, developed in Part I of this paper, for estimating the temperature distributions along the cutting edge and on the clearance face of a twist drill are evaluated using an experimental technique that measures average drill flank temperatures. While the transient model tends to overestimate the values of the average flank temperatures, especially during drilling to a one diameter hole depth, the temperatures predicted from the steady state model agree reasonably well with the experimental results. The difference between the analytical and experimental results varied with the physical and thermal properties of the powder metallurgy work materials used in this experiment. The analytical drill temperature distribution models are also compared with others found in the literature.

A methodology to measure joint stiffness parameters for toolholder-spindle interfaces*

This paper introduces a methodology to evaluate and compare machine tool toolholder-spindle interfaces based on experimental and analytical finite element analysis results. This paper illustrates that the results generated from bench tests (an approach previously used for comparing different sets of interfaces) to characterize toolholder-spindle interfaces do not represent properly the interfaces in a machine tool spindle. The proposed methodology can help standardize the tests and/or the joint parameters required for evaluating, comparing, and selecting toolholder-spindle interfaces by modeling the machine tool spindle itself.

Sequence of operations optimization in single-stage multifunctional systems

Abstract The problem of optimizing a traditional or high-speed single-stage multifunctional numerically-controlled machine is investigated. In current practice, the parameters of the sequence for part machining processing, cutting conditions, and tool magazine organization are defined manually by a machine programmer or operator. These parameters are usually conservative and away from their optimal values. The machine should, however, maximize the throughput without cost penalty. In this paper, mathematical machining models combined with heuristic optimization algorithms (which determine the optimum values of the aforementioned parameters) are proposed to solve this problem. The optimum tool magazine organization for large batch or mass production systems minimizes the tool change time and maximizes the time between tool magazine reloadings. The optimization scheme can be utilized for modeling and simulation purposes in metal cutting environments where numerical control (NC)_equipment or flexible manufacturing systems (FMSs) are used. This work is therefore directed toward the development of an expert-system-based automated part machining process planner and tool magazine organizer. Its goal is to reduce the use of skilled human interaction. The proposed approach and its advantages are finally illustrated through an application example.

Machining Quality Analysis of an Engine Cylinder Head Using Finite Element Methods

Abstract Structural analysis is routinely used to design parts but less frequently used to design manufacturing processes. Structural analysis should be used in process design for many parts because loads experienced during manufacture exceed service loads. Application of these analyses has been limited due to lack of validation results for realistically complex parts against extensive sets of data. This paper describes structural analysis results for the manufacture of an aluminum engine cylinder head. Three specific error sources are modeled using finite element analysis (FEA): (1) cylinder head deckface distortion due to clamping forces, (2) deckface (or part) distortion due to a pressing in of seats and guides, and (3) seat and guide distortion due to clamping forces. A compliant fixture and contact-based boundary conditions are used for the clamping analysis using ABAQUS/Standard for the FEA modeling. The valve seat and guide insertion is modeled as a shrink-fit operation using the contact-pair approach, which greatly simplifies the numerical problem with satisfactory precision. The roundness and concentricity are computed for a variety of press-fit interference conditions covering the range of variation expected within the tolerance bands of the powder metal inserts and the pre-bored holes. Computed results from all studies agree well with direct CMM measurements and laboratory validation data.

Modeling the HSK toolholder-spindle interface

The HSK toolholder-spindle connection was developed to overcome shortcomings of the 7/24 steep-taper interface, especially at higher speeds. However, the HSK system was standardized quickly, without detailed evaluation based on operational experience. Several issues concerning the reliability, maintainability, and safety of the interface have been raised within the international engineering community. This study was undertaken to analytically investigate factors which influence the performance and limitations of the HSK toolholder system. Finite Element Models were created to analyze the effects of varying toolholder and spindle taper geometry, axial spindle taper length, drawbar/ clamping load, spindle speed, applied bending load, and applied torsional load on HSK toolholders. Outputs considered include taper-to-taper contact pressures, taper-to-taper clearances, minimum drawbar forces, interface stiffnesses, and stresses in the toolholder. Static deflections at the end of the holder predicted by the models agreed well with measured values. The results showed that the interface stiffness and load-carrying capability are significantly affected by taper mismatch and dimensional variations, and that stresses in the toolholder near the drive slots can be quite high, leading to potential fatigue issues for smaller toolholders subjected to frequent clamping-unclamping cycles (e.g., in high volume applications). The results can be used to specify minimum toolholder material properties for critical applications, as well as drawbar design and spindle/ toolholder gaging guidelines to increase system reliability and maintainability.

Optical method for inspecting surface defects inside a small bore

Most automotive powertrain parts made of castings have surface defects such as pores. However, detecting pores inside small diameter bores is a challenge because of the limited dimensional accessibility. Adding to this difficulty is the auto industrys desire to conduct the porosity inspection in-line, i.e. within the machining production cycle time of a part. A technique or equipment that meets these requirements currently does not exist. In order to meet these demands, it is necessary to develop an entire new methodology to inspect the inner surface of small diameter bores. This paper presents an innovative methodology to inspect the porosity of the inner surface of small bores and to provide their characteristics such as size and location. A prototype measurement system was built and tested in the lab. Experimental results showed the proposed method to be reliable and consistent.

Assuring the Day-to-Day Accuracy of Coordinate Measuring Machines—A Comparison of Tools and Procedures

Abstract The continual use of coordinate measuring machines (CMMs) in high-volume manufacturing has led to several applied standards. With the ever-increasing emphasis on quality, annual certification of conformity by a qualified outside calibration service is no longer adequate. An artifact can be used in an interim testing plan to evaluate machine performance between certifications. The objective of this paper is to evaluate the design of artifacts, evaluate the analytical procedure to estimate certain characteristics of CMM performance, and evaluate the artifacts’ repeatability and accuracy measurements. The capability of two traceable artifacts (one 2-D and one 3-D design) and a machine checking gage were assessed. The results indicate that an artifact can be used for interim performance evaluation but not for calibration or certification.

ESTIMATING THE STATIC STIFFNESS FOR A SPINDLE-TOOLHOLDER-TOOLING SYSTEM

This article focuses on static analysis to integrate the necessary components for the design of spindle-toolholder-tooling systems; the modeling and analysis of the systems is based on a mathematical model using a systematic approach for evaluating the static deflection at the cutting point. The analysis addresses the deflection of most of the components in the system including the spindle shaft, front and rear bearings, toolholder, cutting tool and their corresponding spindle-toolholder and toolholder-tool interfaces modeled with linear (radial) and rotational (tilting) springs. The effects of design parameters on the static performance of these systems are analyzed in order to assess the contribution and the influence of the individual system components. Computations and experimental results show that improvements can be made in the system by adjusting the aforementioned parameters. The proposed strategy is to iteratively predict the tool deflection at the tool tip using the analytical model based on the superposition appoach. The model is simple and it provides tremendous assistance to an engineer to select the proper toolholder and tool for minimum deflection.

Modeling Machining Errors on a Transfer Line to Predict Quality

Abstract This paper introduces a methodology for predicting part quality based on the expected and measured process variations (geometric, static, and dynamic errors). Part quality in terms of dimensional (location), orientation, form, and profile tolerances can be predicted using a “stream of variation model” in a multistation machining system (serial, parallel, or hybrid) and validated on an engine cylinder head. The understanding gained from an application of this methodology to a machined component can help achieve substantial part-quality and process improvements.