Basic Knowledge of Machine Tools

A machine tool is a machine that processes metal or other material blanks or workpieces to obtain the required geometric shape, dimensional accuracy, and surface quality.

1. Definition of Machine Tool

A machine tool is a machine that processes metal or other material blanks or workpieces to obtain the required geometric shape, dimensional accuracy, and surface quality.

Parts of mechanical products are usually processed by machine tools. A machine tool is a machine that manufactures machines and can also manufacture machine tools themselves. This is the main feature that distinguishes machine tools from other machines. Therefore, machine tools are also called mother machines or tool machines.

2. Classification of Machine Tools

Metal cutting machine tools, mainly used for metal cutting processing;

Woodworking machine tools, used for cutting wood;

Special processing machine tools, which use physical, chemical, and other methods for special processing of workpieces;

Forging machinery. In a narrow sense, machine tools refer only to the most widely used and numerous metal cutting machine tools.

1. Metal cutting machine tools can be divided into various types according to different classification methods.

1.1 According to processing methods or objects, they can be divided into lathes, drilling machines, boring machines, grinding machines, gear processing machine tools, thread processing machine tools, spline processing machine tools, milling machines, planers, slotting machines, broaching machines, special processing machine tools, sawing machines, and scribing machines. Each category is further divided into groups based on structure or processing objects, and each group is subdivided into types.

1.2 According to the size of the workpiece and the weight of the machine tool, they can be divided into instrument machine tools, small and medium-sized machine tools, large machine tools, heavy machine tools, and super heavy machine tools;

1.3 According to processing accuracy, they can be divided into ordinary precision machine tools, precision machine tools, and high-precision machine tools;

1.4 According to the degree of automation, they can be divided into manually operated machine tools, semi-automatic machine tools, and automatic machine tools;

1.5 According to the automatic control method of the machine tool, they can be divided into copying machine tools, program-controlled machine tools, numerical control machine tools, adaptive control machine tools, machining centers, and flexible manufacturing systems;

1.6 According to the applicable scope of the machine tool, they can be divided into general-purpose, specialized, and dedicated machine tools.

1.7 Among dedicated machine tools, there is a type called combined machine tools, which are automatic or semi-automatic machine tools composed of standard general-purpose components combined with a small number of special components designed according to the specific shape or processing technology of the workpiece.

1.8 For the processing of one or several parts, a series of machine tools are arranged in sequence according to the process steps, equipped with automatic loading and unloading devices and automatic workpiece transfer devices between machine tools. Such a group of machine tools is called an automatic cutting processing production line.

1.9 A flexible manufacturing system consists of a group of numerical control machine tools and other automated process equipment, controlled by electronic computers, capable of automatically processing workpieces with different processes and adapting to multi-variety production.

Machine tools are the basic production equipment of the machinery industry. Their variety, quality, and processing efficiency directly affect the production technology level and economic benefits of other mechanical products. Therefore, the modernization level and scale of the machine tool industry, as well as the quantity and quality of machine tools owned, are important indicators of a country's industrial development.

3. A Brief History of Machine Tool Development

The earliest prototype of the machine tool appeared more than two thousand years ago with the wooden lathe. During operation, the foot pedal tightened a loop at the lower end of a rope, using the elasticity of a branch to rotate the workpiece driven by the rope. Shells or stone pieces were used as cutting tools, moving along slats to cut the workpiece. The elastic rod lathe of the Middle Ages still used this principle.

In the 15th century, due to the need for making clocks and weapons, thread lathes and gear processing machine tools used by watchmakers appeared, as well as water-powered cannon boring machines. Around 1500, the Italian Leonardo da Vinci drew conceptual sketches of lathes, boring machines, thread processing machine tools, and internal cylindrical grinding machines, which already included new mechanisms such as cranks, flywheels, tailstocks, and bearings. The Chinese Ming Dynasty publication "Tiangong Kaiwu" also recorded the structure of grinding machines, using foot pedals to rotate iron discs, combined with sand and water to cut jade.

The Industrial Revolution in the 18th century promoted the development of machine tools. In 1774, the Englishman Wilkinson invented a relatively precise cannon boring machine. The following year, the cylinder bored by this machine met the requirements of Watt's steam engine. To bore larger cylinders, he manufactured a waterwheel-driven cylinder boring machine in 1776, promoting the development of the steam engine. From then on, machine tools began to be driven by steam engines through overhead shafts.

In 1797, the Englishman Maudslay created a lathe driven by a screw to move the tool post, enabling mechanical feed and thread cutting. This was a major structural change in machine tools. Maudslay is therefore known as the "Father of the British Machine Tool Industry."

In the 19th century, driven by the textile, power, transportation machinery, and armaments industries, various types of machine tools appeared one after another. In 1817, the Englishman Roberts created the gantry planer; in 1818, the American Whitney made the horizontal milling machine; in 1876, the United States produced the universal external cylindrical grinding machine; in 1835 and 1897, the gear hobbing machine and gear shaping machine were invented respectively.

With the invention of the electric motor, machine tools began to use centralized electric motor drive, and later widely adopted individual electric motor drives. In the early 20th century, to process workpieces, fixtures, and thread processing tools with higher precision, coordinate boring machines and thread grinding machines were successively created. To meet the needs of mass production in industries such as automobiles and bearings, various automatic machine tools, copying machine tools, combined machine tools, and automatic production lines were developed.

With the development of electronic technology, the United States developed the first numerical control machine tool in 1952; in 1958, it developed a machining center capable of automatic tool changing for multi-process machining. Since then, with the development and application of electronic and computer technologies, machine tools have undergone significant changes in drive methods, control systems, and structural functions.

4. Operation of Machine Tools

The cutting processing of machine tools is realized by the relative motion between the cutting tool and the workpiece. This motion can be divided into surface generating motion and auxiliary motion.

Surface forming motion is the motion that enables the workpiece to obtain the required surface shape and size. It includes the main motion, feed motion, and cutting-in motion. The main motion is the primary motion that removes excess material from the workpiece blank. It can be the rotational motion of the workpiece (such as turning), linear motion (such as planing on a gantry planer), or the rotational motion of the tool (such as milling and drilling) or linear motion (such as slotting and broaching). The feed motion is the relative movement between the tool and the part of the workpiece to be machined, allowing the cutting to continue, such as the movement of the tool post slide along the machine guide rail during external turning. The cutting-in motion is the motion that makes the tool cut into the workpiece surface to a certain depth, removing a certain thickness of material in each cutting stroke, such as the transverse cutting-in motion of the small tool post during external turning.

Auxiliary motions mainly include rapid approach and retraction of the tool or workpiece, adjustment of machine tool components' positions, workpiece indexing, tool post indexing, material feeding, starting, speed changing, reversing, stopping, and automatic tool changing motions.

Various machine tools are generally composed of the following basic parts: supporting components used to install and support other parts and the workpiece, bearing their weight and cutting forces, such as the bed and column; speed-changing mechanisms used to change the speed of the main motion; feed mechanisms used to change the feed amount; spindle box for installing the machine tool spindle; tool post and tool magazine; control and operation systems; lubrication system; cooling system.

Machine tool auxiliary devices include loading and unloading devices, manipulators, industrial robots, and other additional devices, as well as machine tool accessories such as chucks, suction cups, spring collets, vises, rotary tables, and indexing heads.

The indicators for evaluating the technical performance of machine tools ultimately boil down to machining accuracy and production efficiency. Machining accuracy includes the dimensional accuracy, shape accuracy, positional accuracy, surface quality of the machined workpiece, and the machine tool's accuracy retention. Production efficiency involves cutting processing time and auxiliary time, as well as the degree of automation and operational reliability of the machine tool. These indicators depend on the static characteristics of the machine tool, such as static geometric accuracy and rigidity, and are more related to the dynamic characteristics, such as motion accuracy, dynamic rigidity, thermal deformation, and noise.

5. Future Development Trends of Machine Tools

The future development trends of machine tools are:

Further application of computer technology, new servo drive components, new technologies such as gratings and optical fibers, simplifying mechanical structures, improving and expanding the functions of automated work, enabling machine tools to adapt to inclusion in flexible manufacturing systems;

Increasing the speed of the power main motion and feed motion, correspondingly improving the dynamic and static rigidity of the structure to meet the needs of new types of cutting tools, and improving cutting efficiency;

Improving machining accuracy and developing ultra-precision machining machine tools to meet the needs of emerging industries such as electronics, machinery, and aerospace; developing special processing machine tools to adapt to the machining of difficult-to-process metal materials and other new industrial materials.

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