Electric Discharge Machining (EDM) is a machining method suitable for repair and maintenance operations in nuclear power plants. Crack removal and material sampling are two common operations where EDM is used in the nuclear power industry. Each crack removal or material sampling operation is unique, a new EDM-tool is therefore designed for every operation. This, together with the fact that the electrode used in the EDM-tool usually wears out before the crack is removed or the sample has been collected, is the foundation of this thesis. The objective was to develop one or several concepts of a modular EDM-tool with the ability to change electrode at repair location. This to shorten the development time for EDM-tools and the time for electrode change during an EDM operation. The concepts would be developed to the extent that a prototype could be manufactured and tested. The result is in accordance to the objective with one fully developed concept ready for manufacturing. It has not yet been manufactured, and therefore not been tested. There are still some sections of the tool that needs to be verified, for example the electric supply to the electrode. The concept consists of; a slim EDM-tool with the ability to lock the rotating electrode shaft, compact dielectric fluid- and electric-supply, hydraulic actuator with belt drive and an electrode magazine with place for 3 electrodes. Keywords: Nuclear, EDM, Electric Discharge Machining, Product development, Crack removal / Electric Discharge Machining (EDM) är en avverkningsmetod lämplig för reparations- och underhållsarbete i kärnkraftverk. Sprickbortagning och materialprovtagning är två vanliga operationer som utförs med hjälp av EDM inom kärnkraftsindustrin. Varje sprickbortagningsoch materialprovtagnings operation är unik, därför utvecklas ett nytt EDM-verktyg inför varje operation. Detta tillsammans med det faktum att elektroden som används i EDM-verktyget ofta slits ned innan sprickan har avverkats eller provet har tagits ligger till grund för detta examensarbete. Målet var att utveckla ett eller flera koncept av modulära EDM-verktyg med möjligheten att byta elektrod på plats där aktuell reparation utförs. Detta för att korta ned utvecklingstiden för nya EDM-verktyg och minska tiden för reparations och underhållsarbeten. Koncepten skulle utvecklas så långt att en prototyp kunde tillverkas och testas. Resultatet är i linje med målet, ett välutvecklat koncept som är redo för tillverkning och testning. Det har än så länge inte blivit tillverkat och således inte testats. Konceptet består av ett smalt EDM-verktyg med möjlighet att låsa elektrodrotationen, kompakt dielektrikum- och ström-tillförsel, hydraulisk aktuator med kuggremsdrift och ett elektrodmagasin med plats för 3 elektroder. Nyckelord: Kärnkraft, EDM, Electric Discharge Machining, Produktutveckling, Sprickborttagning

Fir tree root forms are one way to retain turbine blades in turbine disks. These features are ruled surfaces that span the entire thickness of the disk and are usually machined by broaching. With increasing use of new heat resistant and difficult-to-machine materials, mechanical machining methods exhibit severe problems with tool wear and surface integrity. To mitigate these problems, thermal material removal processes such as Wire Electrical Discharge Machining (WEDM) are being considered in the aerospace industry. Developments in turbine design have led to a root form geometry in the form of an arc across the thickness of the disk in order to decrease the contact stress by increasing the contact area between blade and disk. A curved surface such as this cannot be produced by conventional WEDM as it is not a ruled surface. A novel WEDM process is being developed where an arc shaped curve is formed from an axially moving wire to allow for the production of such curved surfaces. / Thesis / Master of Applied Science (MASc) / Turbine blades are attached to turbine disks with specially shaped, straight slots called Fir Tree Root Forms (FTRF) that can be cut with broaching tools. Broaches wear out quickly because the disk is made of very difficult to cut material and the aerospace industry is starting to use Wire Electric Discharge Machining (WEDM), instead of broaching, to cut these slots since it can easily cut the material used. New turbine disk designs have curved slots, which can not be cut with a straight broach or wire, and a new process is therefore being developed which uses an arc-shaped wire to cut the desired curved shapes.

The aim of this master's thesis is experimental electric discharge sinking of special materials for the aerospace industry. The first part is a general overview regarding the technology of electric discharge machining with emphasis on electric discharge sinking. Following this is a practical part devoted to the electric discharge sinking of the Nimonic 263 material with a copper tool electrode with a subsequent evaluation of surface and subsurface changes in this material. The wear of the tool electrode is also examined with the conclusion highlighting combination of machined material and tool electrode material behave in different working conditions and how the surface layer of machined material is affected.

The diploma thesis Rationalization technology of production tools is divided into two parts. The first part is focused on injection molding of plastic materials and analysis current status of production injection tools. The second part contains proposal of rationalization steps in the production process and evaluation of rationalization.

Wire Electric Discharge Machining (wire-EDM) is a non-traditional machining process. Controlled electric sparks are successively used to vaporize part of a workpiece along a programmed path in order to machine a desired part. Because there is no tool that comes in direct contact with the workpiece, it is possible to machine thin, delicate parts. This thesis was designed to observe and analyze the differences in cutting capabilities for a conventional wire-EDM machine when cutting thin-walled sections from five commonly used metals utilizing a variation of roughing and finishing passes. The five metals that were used in this study are: Aluminum 6061 T6, Yellow Brass SS360, 420 Stainless Steel, D2 Tool Steel at 25 to 30 RC, and D2 Tool Steel at 60 to 65 RC. The thin-walled sections were constrained on each end by the parent material to which they remained attached, and they ranged in thickness from 0.05 millimeters (0.002 inches) increasing incrementally by 0.05 millimeters (0.002 inches) until they reached a thickness of 0.30 millimeters (0.012 inches). A Sodick AQ325L wire-EDM machine was employed to perform the machining. It was observed that differences exist in the capabilities of cutting thin-walled sections from the five different metals. This could be both observed visually through inspection and statistically through the analysis of each data set obtained by measuring the resultant thickness of each section. It was also observed that differences exist for the same material while utilizing the variations of cutting parameters: a roughing with no finishing passes, a roughing with one finishing pass, and a roughing with three finishing passes. Thus both the material properties and the cutting parameters play a significant role in determining the capability of cutting thin-walled sections with a wire-EDM machine.

Electric Discharge Machining (EDM) is a process for eroding and removing material by transient action of electric sparks on electrically conductive materials immersed in a dielectric liquid and separated by a small gap. A spark-eroded surface is a surface with matt appearance and random distribution of overlapping craters. It is mechanically hard and stressed close to ultimate tensile strength of the material and sometimes covered with a network of micro cracks. The violent nature of the process leads a unique structure on the machined surface and generates residual stresses due mainly to the non-homogeneity of heat flow and metallurgical transformations. An extensive experimental study is presented to explore the surface and sub-surface characteristics together with the residual stresses induced by the process. Layer removal method is used to measure the residual stress profile in function of depth beneath. A finite element based model is proposed to determine residual stresses and compared with the experimental results. The residual stress pattern is found to be unchanged with respect to machining parameters. Thus, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found as a special form of Gauss Distribution, which is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location that is represented by three constant coefficients. In each case, agreement with the proposed form is established with experimental results. Results have shown that these coefficients have a power functional dependency with respect to released energy.

This thesis deals with technology of electric discharge machining with emphasis on application of the principle of material removal on wire cut electric discharge machine. The main part is concentrated on wire cut electric discharge machining in terms of a small tool making shop. The goal of the thesis is to create a wire cut electric discharge machining workplace in the company with a focus on the production of cutting tools. The thesis defines requirements for each component of cutting tools and strategies for their machining. Machining of model part and subsequent technical - economic evaluation is included in the final part.