Turning, Milling, Grinding & Electroerosion Machining
Item 15: Turning
Introduction to Turning
Turning is a machining operation that shapes rotating workpieces using a cutting tool. Lathes are machine tools designed for turning operations. These machines mount cutting tools, often referred to as knives, to perform various turning processes.
Types of Lathes
Lathes are categorized based on their technical characteristics and the type of work they perform:
- Parallel Lathes: Used for horizontally placed workpieces.
- Vertical Lathes: Designed for heavy and difficult-to-handle parts.
- Turret Lathes: Used for working parts with large diameters and short lengths.
- Revolver Lathes: Suitable for series production.
- Precision Lathes: Used for small workpieces requiring high accuracy.
The most commonly used type is the parallel lathe, which consists of a bed, headstock, tailstock, carriage, and cross slide.
Turning Operations
- Cylindrical Turning (Cilindratge): Gives the workpiece a specific diameter.
- Facing (Escairament): Reduces the length of a piece to the given dimensions.
- Parting (Rarunatge): Creates a cut perpendicular to the workpiece’s axis.
- Cutting Off (Reaped): Divides the workpiece into two pieces with a perpendicular cut.
- Threading (Roscatge): Creates a screw thread on the surface.
Key Turning Parameters
Fundamental parameters to consider include the angle of incidence, angle of departure, and angle of cut.
Milling
Introduction to Milling
Milling is a machining operation that uses rotating cutting tools called milling cutters to remove material from a workpiece. Milling machines are machine tools designed to hold and rotate these cutters.
Types of Milling Machines
Milling machines are classified as horizontal, vertical, and universal (a combination of horizontal and vertical). The most important components of a milling machine include the base, column, spindle, knee, saddle, and table.
Milling Cutters
Milling cutters are categorized based on several factors:
- Number of Cuts: Can have 1, 2, or 3 cutting edges.
- Mode of Fixation: Can have cylindrical or conical shanks with smooth or threaded holes.
- Method of Work: Different cutters are designed for specific tasks.
- Shape: Cutters come in various shapes.
Milling Operations
Basic milling operations involve setting up the workpiece, determining the type of work, establishing the kinematic conditions, and starting the machine.
Milling Process
The milling cutter rotates at high speed while the workpiece moves linearly towards the cutter. Contact between the cutter and workpiece removes a layer of material, creating the desired shape.
Applications of Milling
Milling machines can perform various tasks, including surface planing, slotting, mortising, cam milling, gear cutting, and creating geometric figures.
Grinding
Introduction to Grinding
Grinding is a machining process that removes material using abrasive grains on a tool called a grinding wheel. This operation is used for finishing flat surfaces and machining parts.
Grinding Machines
The most common grinding machine is the universal cylindrical grinder, which consists of a bed, table, work head, wheel head, and tailstock.
Abrasive Materials
Abrasive materials used in grinding wheels can be natural or artificial.
Binders
Binders hold the abrasive grains together. Common binders include vitrified, resinoid, rubber, and silicate.
Grinding Wheel Hardness
Grinding wheels are classified by hardness, ranging from soft (grains separate easily) to hard (grains do not separate easily).
Grinding Operations
Factors to consider in grinding operations include the type of grinding wheel, working speed, rotation speed, depth of cut, and feed rate.
Basic Grinding Operations
- Surface Grinding
- External Cylindrical Grinding
- Internal Cylindrical Grinding
- Profile Grinding
Electroerosion
Introduction to Electroerosion
Electroerosion is a metal machining process that uses electrical discharges to remove material. It is suitable for metals that are difficult to machine using conventional methods.
Advantages of Electroerosion
- Works on hard-to-machine metals.
- Enables automated production of complex shapes and profiles.
Numerically Controlled (NC) Machines
Introduction to NC Machines
NC machines are automated machines controlled by a computer program. The program provides two types of instructions:
- Dimensional Information: Specifies the toolpath.
- Technological Information: Defines the machining conditions.
Advantages of NC Machines
- Automated part loading and unloading.
- Automated assembly.
- Reduced transmission elements.
- Integrated quality control.
- Improved chip evacuation and coolant control.
- Enhanced safety features.
Safety Rules
Turning
- Rotating parts must be guarded.
- Use protective screens and chip guards.
- Remove chips with hooks.
- Maintain sharp cutting tools.
- Keep the work area clean.
Milling
- Rotating parts must be guarded.
- Regularly collect chips.
- Maintain sharp cutters.
- Keep the work area clean.
Grinding
- Rotating parts must be guarded.
- Use safety glasses.
- Do not exceed the peripheral speed.
- Keep the work area clean.