Table of Contents

1. General Overview

Although a near net shape process, products manufactured via powder metallurgy often require secondary machining operations. The papers presented in this chapter highlight the particularities and differences that exist between the machining of PM products and wrought materials.

Machining of Powder Metallurgy Materials
Machinability Improvements of P/M Steels
The Importance of Machinability in the Processing of P/M Parts

2. Machining & Machinability

The improvement of the machinability of PM components requires an understanding of the effect of the process parameters on the response of the material being cut. Different machining operations imply different metal flow patterns and dissimilar chip formation mechanisms. Thus, the quantitative characterization of machinability constitutes the basis from which the optimization work can start. The papers assembled in this chapter cover the vast majority of the machining operations used to shape PM products as well as techniques to characterize their machining performances.

The Machinability of P/M Materials as Determined by Drilling Tests
Machining-A Discussion of Some Variables
Influence of Machining Parameters on the Machinability of Sintered Steels
Prediction and Modeling of Surface Finish in Drilling of P/M Parts
Test Bench for the Routine Evaluation of Machinability of Powder Metallurgy Materials
Lapping of P/M Materials
Cutting Data Recommendations for Turning Various PM Materials Using Different Tool Grade and Geometry Selections
Characterization of Machinability of Sintered Steels During Drilling Operations
Turning of Warm Compacted High Density P/M Steels in the As-sintered Condition
Primary Variables Affecting Tool PCBN Tool Life During the Machining of Ferrous P/M Parts
Residual Stress Measurements in Machined P/M Steel

3. Improving Machinability

The papers presented in this chapter focus on novel strategies that can be used to improve the machining response of PM products. Green machining and retained graphite are two of those strategies that generate a lot of interest in the PM community. It is our belief that the future of PM machining will be marked by an increase in the number of new machining approaches such as those highlighted in this section.

A New Improvement in the Machinability of P/M Steel due to Retained Graphite Particles
Speed and Feed Optimization in Drilling of As-compacted P/M Parts
Machinability Evaluation of Selected High Green Strength P/M Materials
Tensile, Machinability and Fatigue Properties of Pre-alloyed Free Cutting Steel Powders
Finish-turning of Hardened Powder Metallurgy Steel Using Cryogenic Cooling

4. Specific Alloy Systems

One of the major fields of research on the improvement of the machinability of PM products deals with the optimization of the microstructure to enhance machinability while keeping the mechanical properties of the parts intact. Indeed, since the properties of a part are dictated by its microstructure, it only seems logical to work on this aspect in conjunction with the optimization of the parameters of the different machining processes. The papers presented in this section discuss the machining performances of a broad spectrum of PM materials from sinter-hardenable steels to brass, tool steels, stainless steels, etc.

The Effect of Microstructure on the Machinability of an MPIF FC-0208 Copper Steel
Machinability of Highly Alloyed Powder Metallurgical Tool Steels
Effects of Various Machinability Additives on the Corrosion Resistance of P/M 316L Stainless Steel
Machinability of Sintered Stainless Steel 316L
Continuing Work on Machinability of Brass P/M Parts
Machining Non-leaded Brass
Machinability of Powder Metallurgy Materials
Effect of Porosity on the Machinability of P/M 304L Stainless Steel
Turning and Drilling of Parts Made from Sinter Hardenable Steel Powders

5. Stability of Machining Aids

In continuity with the previous chapter, the following articles focus on the usage of chemical compounds intentionally added to the microstructure of PM systems to enhance their response to metal cutting. By far, manganese sulphide particles are the favored machinability enhancers. This is highlighted by the relatively large number of papers published on the subject. The criteria that were used to select the articles that are presented in this chapter were based on the novelty of the results presented as well as the quantitative methods that were used to obtain them.

The Influence of Furnace Atmospheres on the Chemistry of Additives to Powders Made for Improved Machinability
250MSA Resulfurized High Green Strength Steel Powder
Effect of Sulphur Content on Machinability of Forged Specimens Made of Water-atomized Steel Powders Pre-alloyed with MnS
Shelf Life of MnS Powder and MnS Containing Mixes
Sulphur-free Iron Powder Machinable Grade
Enhanced Machinability and Oxidation Resistance with MnS Containing Additions of Iron
Optimization of Pre-alloyed MnS Steel Powders for Improved Machinability

6. Case Studies in Machinability

Case studies are always difficult to find in the PM literature because they generally constitute a strategic advantage that companies, understandably, are unwilling to disseminate. Nevertheless, the two examples that are presented in the following section are of very high quality. Interestingly, they both stem from applications related to the automotive industry. They certainly constitute one more proof that the machining of PM components is something feasible technically and economically even on a large scale.

Machinability and Performance of Precision Powder Forged Connecting Rods
P/M Valve Seat Insert Material with Improved Machinability