Our Technical Program
Best-in-class Machining of Engineered MaterialsSpeaker - Mike Finn - Tech-Solve, Cincinnatti, OH
Best-in-class machining frequently involves designing the material for machining
Some of the factors that influence the machinability of a material are: (1) Physical Properties, (2) Mechanical Properties, (3) Composition and (4) Microstructure. With the advent of Higher Machining speeds in fully automated equipment more cratering has been seen, and also the use of newer "biodegradable" cutting fluids has a negative impact. In the area of Mechanical Properties, and increase in "toughness" (with a decrease in machinability) has been seen with the use of new microalloy systems. In the area of microstructure, some types of precipitation in grain boundries can actually improve machinability. Abrasive particles of greater than 20 micro-meters degrade machinability, and thermal conductivity of materials also has a significant influence.
The term machinability itself is difficult to quantify. It contains components such as: Productivity, Quality, Tolerances, Cutting Tool life, Surface Roughness, and Chip removal. With fully automated machining centers, long consistent chips are a problem, and machines may have to be stopped to remove ratsnests of such chips. A broken chip is more desirable.
In carbon steels machinability is found to improve up to about 0.4 C. Above that value cementite in grain boundaries tends to hurt machinability. Free carbides also have a negative effect.
The machining process itself also effects machinability. With milling there is no time to reach any sort of thermal equilibrium, while with turning the thermal state at the cut is much more predictable.
Several small amount additives to alloys have been found to be beneficial to machining. These include MnS, Pb, Bi, Te, and Si. For high speed machining certain oxides also help such as CaO, SiO2, and Al2O3. Even hard Ferrite, and course Pearlite can have a beneficial effect.
In one project undertaken by Tech-Solve the machinability of Ti6Al4V was found to improve significantly when the initial surface was ground, as compare to a shot blasted and pickeled finish. Also Heat-treatment to a higher strength value was beneficial.
In another evaluation it was found the type of resin added to steel powders effects the machinability of the item made from the powders.
High Speed machining tends to create more crater wear on the rake face of the cutting tool. Under high speed conditions lead does not lubricate effectively and a chemical corrosion occurs facilitated by welding and a temperature rise as the crater. The addition of oxides such as CaO, Al2O3 and SiO2 actually become "glassy viscous barriers" to such cavitation and therefore improve machinability. HfN coating of tungsten carbide cutting tools has also been found to reduce corrosion cavitation.
In a project involving the milling of A359/SiC/20p-T6 Al material it was found that the SiC was extremely abrasive to the cutting tool. In this case the use of much higher cutting speeds with conductive diamond film on the tooling was found to significantly reduce this tool wear.
In a project involving AA380 aluminum Si particles were found in a fan clutch. Adding some Ca to the alloy was able to increase machining throughput 10 fold.
An example of an improvement through process change involves tapping AA-A346 T6 Aluminum alloy. In this case changing from a cutting tap to a carbide "form tap" caused a dramatic improvement.
Currently Tech-Solve is utilizing a "Part-Cost Reduction Software" which simulates many machining conditions. A typical project involves three phases. Phase 1) involves optimizing machinability, selecting machining actions, Intergation of the workpiece properties, Integrating best-in-class tooling settings, and performing a cost analysis all assisted by software. Phase 2) is the design process which involves testing and validating the strategy. Phase 3) is to deliver the report, assist in start-up of the new strategy, and monitor for continued improvement.