Summary
Highlights
Dr. Tony Schmitz introduces machining as a subtractive process involving material removal using a defined cutting edge to produce parts with specific dimensions and surface finish. Advantages include good dimensional accuracy, creation of internal features, sharp edges, post-heat treatment finishing, good surface finish, and cost-effectiveness for small batch sizes.
Material is removed in the form of chips, sheared away by the cutting edge. The process involves significant deformation as the work material slides along the tool's rake face. Chips can be continuous, serrated, or discontinuous. A phenomenon called 'built-up edge' (BUE) occurs when work material sticks to the tool surface due to high pressure and heat, which can damage the tool and increase surface roughness. Cutting fluids can mitigate BUE.
Machining requires force to shear material. Key forces include cutting force (FC) in the direction of cutting speed and thrust force (FT) perpendicular to it. These combine into a resultant force (R). Other force representations include shear force along the shear plane and friction/normal forces along the rake face. Power, the product of force and velocity, is also required. Specific energy (Ks) indicates the energy needed per unit volume of material removed, varying with material and tool combination.
Power input generates significant heat, with high temperatures at the tool-chip interface. Cutting tools experience high forces, temperatures, and cutting speeds, leading to wear over time on both the rake and flank faces. Tool wear rate increases with cutting speed and temperature.
Tool wear rate depends on tool material (e.g., high-speed steel, carbide), coatings (e.g., titanium nitride for low friction and high hardness), and cutting fluids. Cutting fluids cool the tool and chip decrease friction, extend tool life, reduce cutting forces, wash away chips, and protect against corrosion. Various types of cutting fluids exist, including oils, emulsions, and synthetics.
Turning involves a rotating workpiece and a tool moving past it to create round shapes. A lathe, with a headstock, spindle, tool post, cross-slide, carriage, and tailstock, facilitates these operations. Common turning operations include straight turning (rough and finish), taper turning, contour turning (often CNC), forming, chamfering, and grooving. Parameters for turning include depth of cut, feed per revolution, spindle speed, average diameter, and cutting speed. Tool geometry, including rake angles and nose radius, is crucial.
Milling uses a rotating cutting tool that moves relative to a stationary workpiece. Vertical milling machines have a vertical spindle, while horizontal machines have a horizontal spindle. Milling machines typically feature X, Y, and Z axes for movement. CNC (Computer Numerically Controlled) milling machines are common, allowing automated and precise contouring. The video demonstrates face milling and end milling operations. Advanced configurations include 4-axis (adding a rotary axis) and 5-axis machines (adding two rotary axes), providing greater degrees of freedom for complex geometries. Examples of 5-axis configurations (AB, AC, BC) are presented.