电火花加工
维基百科，自由的百科全书
电火花加工又称放电加工，是特种加工技术的一种。
电火花加工可以用来加工传统切削方法难以加工的超硬材料和复杂形状的工件，但是仅限于导电的材料。
电火花加工可以在诸如钛、工具钢和碳钢等难加工金属上加工复杂的型腔或者轮廓。
电火花加工原理是，在导电的工具电极和工件之间加上周期性快速变化电场，通过脉冲放电产生的局部高温使工件表面金属熔化、气化，从而蚀除金属。因此几乎不需要有切削力的存在。
电火花加工在模具制造业应用最广。
這種加工方式的機器有：
- 模具電浸切割機：在火水混合液（介電質）中由金屬極端放出高壓電流，將置放下方的工件以產生的高熱切開。
- 線切割機：在去離子水（ Deionized water ，超純水？） 中利用幼細金屬絲通電所產生的火花切割工件。
目录 |
[编辑] 歷史
1943年，兩位俄國科學家（Dr. B.R. Lazarenko 及 Dr. N.I. Lazarenko ）改良了放電加工製程。
日本牧野（Makino）公司在1980年發明第一台數值控制放電加工機。
[编辑] 優點
放電加工具有以下的優點
- 可以製造傳統切削加工機所無法生產的特殊形狀製品。
- 加工堅硬的材料也可以有好的公差精度。
- 傳統加工機的切削力可能會損壞小型的工件，但放電加工沒有此情形。
[编辑] 缺點
放電加工具有以下的缺點
- 不能加工非導體（已經有技術可以加工陶瓷材料）。
- 加工速度緩慢。
- 加工直角較為困難。
[编辑] 線切割
In wire electrical discharge machining (WEDM), or wire-cut EDM, a thin single-strand metal wire, usually brass, is fed through the workpiece, typically occurring submerged in a tank of dielectric fluid. This process is used to cut plates as thick as 300mm and to make punches, tools,and dies from hard metals that are too difficult to machine this other methods. The wire, which is constantly fed from a spool, is held between upper and lower diamond guides. The guides move in the x–y plane, usually being CNC controlled and on almost all modern machines the upper guide can also move independently in the z–u–v axis, giving rise to the ability to cut tapered and transitioning shapes (circle on the bottom square at the top for example) and can control axis movements in x–y–u–v–i–j–k–l–. This gives the wire-cut EDM the ability to be programmed to cut very intricate and delicate shapes. The wire is controlled by upper and lower diamond guides that are usually accurate to 0.004 mm, and can have a cutting path or kerf as small as 0.12 mm using Ø 0.1 mm wire, though the average cutting kerf that achieves the best economic cost and machining time is 0.335 mm using Ø 0.25 brass wire. The reason that the cutting width is greater than the width of the wire is because sparking also occurs from the sides of the wire to the work piece, causing erosion. This "overcut" is necessary, predictable, and easily compensated for. Spools of wire are typically very long. For example, an 8 kg spool of 0.25 mm wire is just over 19 kilometers long. Today, the smallest wire diameter is 20 micrometres and the geometry precision is not far from +/- 1 micrometre. The wire-cut process uses water as its dielectric with the water's resistivity and other electrical properties carefully controlled by filters and de-ionizer units. The water also serves the very critical purpose of flushing the cut debris away from the cutting zone. Flushing is an important determining factor in the maximum feed rate available in a given material thickness, and poor flushing situations necessitate the reduction of the feed rate.
隨著更嚴格的公差，多軸線切割加工中心機新增許多功能。像是多條線同時切割兩個部份、控制線的磨損、斷線時自動穿線、優化加工步驟。
線切割常用於需要低殘留應力的地方，由於線切割幾乎沒有存在切削力，所以不會對材料增加應力。也幾乎不會影響材料的機械性能。
