U N I T 2 MATERIAL REMOVAL PROCESSES This Unit examines the features of various machine tools. You will learn about milling, drilling, grinding and turning machines. A. INTRODUCTION TO MACHINE TOOLS 1 Read the following text and choose the main topic of each paragraph from the list below. Par. 1: a. Main machine tools Par. 2: b. Lubrification Par. 3: c. Classification of machine tools Par. 4: d. Definition of machine tool Par. 5: e. Characteristics of cutting-tool materials Par. 1 The term machine tool refers to any stationary power-driven machine that is used to shape or form parts made of metal or other materials. The shaping is carried out in four general ways: (1) by cutting excess material from the part; (2) by shearing the material; (3) by squeezing metallic parts into the desired shape; and (4) by applying electricity, ultrasound, or corrosive chemicals to the material. The fourth category covers modern machine tools and processes for machining ultra-hard metals not machinable by older methods. Par. 2 Machine tools can be classified under three main categories: conventional chip-making machine tools, presses, unconventional machine tools. Conventional chip-making tools shape the work-piece by cutting away the unwanted portion in the form of chips. Presses employ a number of different shaping processes such as forging, pressing or drawing. Unconventional machine tools use electrical, chemical or sonic energy, light or superheated gases to shape the materials. Par. 3 Machine tools that form parts by removing metal chips from a work-piece include lathes, shapers and planers, drilling machines, milling machines, grinders and power saws. The cold forming of metal parts, such as cooking utensils, automobile bodies and similar items, is done on punch presses, while the hot forming of white-hot blanks into appropriately shaped dies is done on forging presses. 114