Bo Lindström

Present Situation and Future Trends in Modelling of Machining Operations Progress Report of the CIRP Working Group ‘Modelling of Machining Operations’

Abstract In 1995 CIRP STC “Cutting” started a working group “Modelling of Machining Operations” with the aim of stimulating the development of models capable of predicting quantitatively the performance of metal cutting operations which will be better adapted to the needs of the metal cutting industry in the future. This paper has the character of a progress report. It presents the aims of the working group and the results obtained up to now. The aim is not to review extensively what has been done in the past. It is basically a critical assessment of the present state-of-the-art of the wide and complex field of modelling and simulation of metal cutting operations based on information obtained from the members of the working group, from consultation in industry, study of relevant literature and discussions at meetings of the working group whit the aim to stimulate and pilot future developments. For this purpose much attention is given to a discussion of desirable and possible future developments and planned new activities.

Monitoring and Adaptive Control of Cutting Process by Means of Motor Power and Current Measurements

Summary This study is carried out to establish the feasibility of motor power and current measurements for ACO, ACC and monitoring. The dynamics of measured power and current signals from the spindle and feed motors of an NC lathe and a machining center is investigated to establish the response of power and current variations due to tool wear, tool breakage and vibrations. An extensive investigation of two commercially available adaptive control systems (based on motor current measurement) - one on an NC lathe and the other on a machining center is conducted with the aim of exploring practical aspects when employing such systems in workshop environment.

The role of tool-chip contact length in metal cutting

Abstract This research work is concentrated on a detailed analysis of the role of tool-chip contact length in the cutting process. The work has been carried out as a series of tests in order to map different factors affecting the contact length as well as factors affected by the contact length when turning conventional construction steel using carbide tools (coated and uncoated). The tests have been performed using production cutting data for three-dimensional cutting. The work includes mapping of the relationship between contact length and cutting data, work material, coating material, cutting forces, flank wear, and tool temperature. The results from the above-mentioned relationships have been used in a graphical solution, according to the Rowe and Spick model, to clarify the effect of tool-chip contact length, cutting data and coating material on the rate of the total work done through its effect on the shear-plane angle.

The effect of restricted contact length on tool performance

Abstract An experimental analysis has been carried out as serial tests with the aim of making a thorough study of the relationship between tool-chip contact length, tool life (flank wear) and tool temperature. A series of tools with restricted contact lengths (0.2–1.3 mm) have been used to machine carbon steel using different cutting data. The test result shows that reducing the contact length from the natural length will reduce the flank wear, but if the contact length is too heavily restricted, tool wear will increase rapidly. The test result also shows that a reduction of the contact length from its natural size to one smaller than the adhesion zone (zone1) leads to a displacement of the point of maximum temperature towards the cutting edge, which results in fast growing flank wear and plastic deformation of the cutting edge. The results are used to determine why the capacity of the same tools differs with different restricted contact lengths.

A statistical model for prediction of tool life as a basis for economical optimization of the cutting process

Summary The paper is dedicated to the implementation of statistical optimization of the cutting process by identification and prediction of the tool condition and lifetime. A statistical model is presented which uses ideas from the theory of reliability and statistical quality control. Since the model is consistent with the Taylor equation, it can easily utilize existing information about relations between cutting data and tool life. A control strategy, which is based on the model, is put forward. Results from experimental tests of the statistical model and of the influence on the wear rate due to feed variations as well as of the performance of the control algorithm are presented.

Cutting Data Field Analysis and Predictions — Part 1: Straight Taylor Slopes

Summary This paper deals with mathematical models for tool life relationships needed for Adaptive Control Optimization. Based on extended Taylor relationships, analysis of available industrial cutting data fields have been performed using a software package giving the mathematical variables needed for the accurate mathematical description of the entire cutting data field. The program is described and the possibilities to give reliable extended outing data predictions is showed. Furthermore, the meaning of some of the obtained constants are discussed as is the use of these predictions in an ACO turning system and the future developments of the model.

Measurements of the Segmentation Frequency in the Chip Formation Process

Measurements of the Segmentation Frequency in the Chip Formation Process This investigation has showed that the relationship between the chip formation process and the dynamic cutting forces in the shear zone is probably one of the most essential features of the cutting process. In the cutting tests conventional accelerometers and a special new cutting force sensor have been used. Also metalographic samples from the chips have been studied. By comparing the information from the transducers and the metalographic samples, extended experiments and tests have showed that this method can be very useful for the basic understanding of the mechanisms of the cutting process. Also flank wear and tool damage propagation can be measured by this method. The results in this work are discussed and described in the paper. Also the possibilities of in-process measurements for adaptive control are discussed.

Advanced process monitoring—a major step towards adaptive control

Adaptive Control (AC) of machine tools requires many kinds of measured input data. The more information about the complex metal cutting process that can be obtained, the better the process can be ...

A simple concept to achieve a rational chip form

Abstract A thorough study of the relationship between the tool chip contact length and the chip thickness ratio has been carried out. A series of tools with restricted contact lengths (0.2–1.3 mm) have been used to turn carbon steel (SS 1572-03), using different cutting data. The test results show that the relationship between the natural and the restricted contact length can be introduced as a control factor, K. By using this factor as a function of feed, the chip form can be classified as under-controlled, controlled or over-controlled . The test results also show that the control factor can be used in a simple module in the preparation process to ensure a rational chip form during the cutting process. The control factor as a function of feed can also be used as a short-time test method to establish the rational chip breaking area of the chip former groove.

Investigations in the Static and Dynamic Performances of Different End Mill Locking Systems

Four of the existing locking systems for end mills have been tested in order to establish their static and dynamic performances. The tests were performed on threaded shank ends (Clarkson type) flattered shank and mounting screw (Weldon type) and two different types of collet chucks. On the latter types of chucks the force needed to pull out the tools were measured using a special test rig making it possible to apply both torque and axial force with additional impulse forces simulating a real cutting situation. The static stiffness of the different systems were also measured. In order to establish the dynamic stability of the different systems, relative damping was measured. These test were compared to a direct mounted end mill. It was found that besides differences in static and dynamic performance, the condition of the surfaces in the locking system and the amount of torque applied during upsetting is an important factor.