26 NONTRADITIONAL MACHINING AND THERMAL
26.1 Why are the nontraditional material removal processes important? Answer. Reasons for importance of are nontraditional material removal processes (1) the need to shape new metal alloys and non-metals that are difficult to machine by conventional processes; (2) the requirement of unusual and complex workpart geometries; and (3) the need to avoid surface damage which is often associated with conventional machining. 26.2 There are four categories of nontraditional machining processes, based on principal energy form. Name the four categories. Answer. The four categories are (1) mechanical, but not including conventional machining; (2) electrical; (3) thermal; and (4) chemical. 26.3 How does the ultrasonic machining process work? Answer. In ultrasonic machining, abrasives contained in a slurry are driven at high velocity against the work by a tool vibrating at low amplitude and high frequency. The tool oscillates in a direction perpendicular to the work surface, and is fed slowly into the work, so that the shape of the tool is formed in the part. The abrasives, impinging against the work surface, perform the chip removal. 26.4 Describe the water jet cutting process. Answer. Water jet cutting uses a high-pressure, high-velocity stream of water directed at the work surface to cut the work. 26.5 What is the difference between water jet cutting, abrasive water jet cutting, and abrasive jet cutting? Answer. WJC cuts with a narrow, high velocity water stream; AWJC adds abrasive grits to the water stream; and AJM cuts with abrasive particles that have been added to a high velocity air stream. 26.6 26.7 Name the three main types of electrochemical machining. Answer. The three types are electrochemical machining, deburring, and grinding. Identify the significant disadvantages of electrochemical machining. Answer. Disadvantages of ECM include (1) cost of electrical power to operate the process, and (2) cost of disposal of electrolyte sludge. 26.8 How does increasing discharge current affect metal removal rate and surface finish in electric discharge machining? Answer. As discharge current increases, metal removal rate increases and surface finish is degraded. 26.9 What is meant by the term overcut in electric discharge machining? Answer. Overcut refers to the gap between the electrode (tool) in EDM on each side of the tool and the machined hole, cavity, or kerf (in wire EDM). 26.10 Identify two major disadvantages of plasma arc cutting.
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Solutions for Fundamentals of Modern Manufacturing, 3/e (published by Wiley) © MPGroover 2007
Answer. Two disadvantages of PAC are (1) rough surface on cut edge and (2) metallurgical damage to cut surface. 26.11 What are some of the fuels used in oxyfuel cutting. Answer. Principal fuels are acetylene, MAPP (methylacetylene-propadiene), propylene, propane, and natural gas. 26.12 26.13 Name the four principal steps in chemical machining. Answer. The four steps are (1) cleaning, (2) masking, (3) etching, and (4) demasking. What are the three methods of performing the masking step in chemical machining. Answer. The three masking methods are (1) cut and peel, (2) screen resist, and (3) photographic resist. 26.14 What is a photoresist in chemical machining? Answer. A photoresist is a masking material that is sensitive to light. When exposed, it chemically transforms and can be removed from the surface of the work,...