A. Wolfenden

Bio: A. Wolfenden is an academic researcher. The author has contributed to research in topics: Chip formation. The author has an hindex of 1, co-authored 1 publications receiving 11 citations.

Role of lead in free-machining brass

Abstract: The role of lead in free-machining brass has been studied by calculating the temperatures formed in the primary and secondary shear zones of chip formation and by examining, in a scanning electron microscope, the structure of chips from cutting experiments. The calculations show that the temperatures in the primary zone do not exceed 200°C for workpiece speeds up to 200mmin−l. The discontinuous chip segments are formed as ductile fracture occurs along a shear instability in the primary zone. Scanning electron microscopical observations of the cuplets on the free surface of the chips suggest that voids occur at the lead inclusions so that the void–sheet mechanism of crack propagation gives rise to the discontinuous chip. A possible cause of void initiation at the lead inclusions is discussed. In the chip/tool contact region the major function of the lead is to provide layers of low shear strength within the secondary shear zone. Lead is also drawn out of the many voids to be deposited on the tool ...

A review of the machinability of copper-base alloys

Abstract: Machining is widely used as the final shaping operation, and contributes significantly to the cost, of a manufactured product. As a result, it has been of paramount importance to develop easily “machinable” alloys with minimal sacrifice of other properties, to reduce the associated fabrication costs. Until now, leaded brasses have been the industry standard for “free-machining” copper-base alloys. However, health concerns about the use of lead in alloys, especially in plumbing applications, will restrict their use. This has created a need for an alternative free-machining copper-based alloy, without lead. MTL/CANMET has been involved in establishing such an alloy. The project was partially funded by the International Copper Association (ICA), and this review was undertaken to assist this effort to understand and summarize the data and concepts of the metal cutting process, assessment of machinability, and the metallurgical factors that contribute to an alloy's machinability, from the standpoint of copper-base alloys.

The effect of lead on the friction and machining of brass

Abstract: Experiments have been carried out on two αβ-brass alloys of similar zinc content, one containing 2·9% lead and the other being lead free. The experiments were of three types: (i) metal-cutting experiments, (ii) sliding friction experiments and (iii) mechanical-property measurements. The effect of lead was found to be very marked in all three cases. In metal machining, the lead addition caused the rake-face friction force to be reduced by a factor of about 5. Similarly, the coefficient of friction in sliding experiments, using an unlubricated steel hall, was reduced from 0·62 without lead to 0·32 with lead. Chip fracture was found to occur at larger depths of cut when machining the leaded alloy. This feature is related to a large reduction in ductility when lead is present. In a torsion test the shear strain to fracture was reduced by a factor of approximately 3 and a similar reduction was found for the fracture energy in a three-point notched bend test. The results of tensile tests showed that th...

Behaviour of Cu-Zn alloys in high speed shear tests and in chip formation processes

Abstract: In order to assess the material behaviour of brass during metal cutting processes, dynamic shear tests are carried out with effective strain rates between 1 × 10−3 and 2 × 105 s−1. The high strain rates are realized in hat-shaped shear specimens using a split Hopkinson compression-bar configuration. Different α- and α/β-brasses with and without lead are tested in annealed and strain-hardened condition. In the range of high stain rate, the material behaviour is governed mainly by two contrary effects: first, the adiabatic character behaviour of the high-speed deformation process, which promotes deformation localization; and second, the increased strain-rate sensitivity, which has a stabilizing effect on the deformation process and reduces the strain concentration. Both the effective strain at fracture and the deformation work per unit volume are considered as indicators for the formation of continuous chips during metal cutting. Beyond 104 s−1, both values are approximately proportional to the strain rate. The dependence of chip fragmentation on main cutting parameters is explained by these functions.

Effects of wetting on the compression creep behaviour of metals containing low melting intergranular phases

Abstract: The creep behaviour of several metallic alloys containing low melting intergranular phases has been characterized in experiments performed in uniaxial compression. The alloys included Al-3% Bi-0.35% Ti, Al-8.4% Sn, Al-33% Sn, and Cu-10% Bi. By performing creep tests above and below the melting point, it was found that melting of the intergranular phase has virtually no effect on the creep behaviour of the first three materials (the aluminium alloys); they creep in a manner very similar to that of pure aluminium, and generally behave as if no second phase were present at all. On the other hand, significant changes in behaviour occur in the Cu-10% Bi alloy. Melting of the intergranular phase both enhances the rate of creep and promotes tertiary creep and failure. The creep characteristics of the materials are discussed in terms of the wetting of the liquid phase on the solid grain boundaries and the fractional area of the boundary occupied by the liquid. It is suggested that a significant portion of the grain boundary area, in excess of 70%, must be wet before the liquid influences the compression creep behaviour in a significant way.

Creep behaviour of leaded brass

Abstract: The creep behaviour of Cu–36wt.% Zn alloys containing 2.5 wt.% of lead has been investigated. Constant tensile stress creep experiments were carried out in the temperature range from 523 to 823 K and under constant stresses from 5 to 250 MPa. Scanning electron microscopy and energy dispersive X-ray analysis were performed on crept as well as uncrept parts of the specimens in order to examine the mechanisms of creep deformation in leaded brass. Attention has been paid to the role of lead on the creep behaviour of brass, the influence of temperature on creep curves, the stress sensitivity parameter and apparent activation energy of creep. The creep data obtained are examined by several methods of conventional analysis of steady-state creep.