What is Machinability of Materials

Machinability is the ability to remove the material with moderate force and is best measured by the amount of power required for cutting, resulting in a smoother surface finish and less wear and tear on equipment. 

A good polish can be achieved in some machine operations, while fine-grained metals are more difficult. As discussed in the next topic, engineers must identify solutions to improve machinability without compromising quality.

Machinability Is Hard To Predict

Predicting hardness is difficult as it is determined primarily by the specific features of the workpiece, its context, and its physical characteristics. However, engineers heavily rely on these two factors:

1. The conditions of the work materials, such as grain size, microstructure, chemical composition, hardness, yield strength, tensile strength, and heat treatment
2. The physical attributes, such as its elasticity modulus, thermal expansion coefficient, thermal conductivity, and hardness

Factors That Influence the Machinability Rating

Hard materials have the disadvantage of low machinability, as they use more power heat and wear more tools. Comparing tools in the same category can be done easily with this machinability rating chart. Below are features to consider when evaluating machinability:

Chemical Composition and Crystal Structure

The crystal structure and arrangement of atoms inside crystal grains determine how easy it is to remove material from a crystal. The crystal structure is altered by heat treatment, work-hardening, and fabrication, making the metal more difficult to fabricate. Metal machinability is influenced by its chemical composition; adding carbon increases its strength but makes it more challenging to produce.

Tool Material

Choosing a cutting tool with the correct hardness for the job is crucial, and the most important factors to consider are toughness and wear resistance. High-speed steel comes in two varieties, i.e., M and T (Molybdenum and Tungsten), outperforming carbon steel. Tungsten carbide tool bits are a longer-lasting choice, although they are fragile.

Tool Geometry

Tool design has a significant impact on machining. To produce a clean, trouble-free cut, a specific angle must be maintained for the rake face, clearing faces, and chip breakers. 

Feed Rate

The feed rate refers to how quickly a drill bit moves into the job or how quickly the tool moves automatically during drilling.

Speeds

Cutting speed is the most important factor in extending tool life, and the cutting speed must be adjusted to match the material's machinability. A quick cutting speed may provide a perfect finish at first, but it comes at the cost of severe tool wear, making accurate proportions difficult to maintain.

Cutting Depth

The amount of material in contact with the tool determines the depth of the cut. When carbon is added to the metal, its strength increases, but producing it becomes more complex.

The Rigidity of the Machine

A machine that is not steady will deliver poor results even if everything else is perfect. Among the design considerations for machines, this is what might impact accuracy:

• Drives using a ball screw
• The design of the clamping mechanism
• Powerful spindle
• The machine's total weight and toughness
• The bearings' quality

Machinability of Common Materials

Steels

Steel's machinability is heavily influenced by its carbon concentration. High carbon steels are difficult to process because they are strong and may include carbides, whereas steel contains carbides that abrade the cutting instrument. In contrast, low-carbon steels present a problem because they are overly soft. Steels with low carbon content are "gummy" and adhere to cutting tools, causing a built-up edge and reducing tool life. 

Stainless Steel

Due to the harder, gummier, and quicker hardening of stainless steel, they are more difficult to machine than conventional carbon steels. Steel could be easier to cut by slightly hardening it to reduce its gumminess because of sulfur and phosphorus.

Aluminum

Aluminum is a straightforward material to work with. On the other hand, the softer grades produce a built-up edge, resulting in poor surface quality. Good machinability requires fast cutting speeds, high rake angles, and high relief angles.

Thermoplastics

Because of their low heat conductivity, thermoplastics are difficult to manufacture. This generates heat in the cutting zone, which shortens the tool's life and melts the plastic locally.

Composites

In composites, the poor heat conductivity of the plastic resin is combined with a stiff or abrasive ceramic matrix, resulting in the least machinability.

Choosing SCTools means you can always expect a superior finish because our machining experience is unmatched. Our latest technologies give you access to a wide range of machine tool options with a wide range of features and benefits.

If you have any questions about carbide cutting tools, end mills, drills, etc. be sure to reach out to us @ sctools.co/Home or call us at (877)737-0987. We help you machine better!