Shaped Tube Electrolytic Machining

Nisarg Shah (11BIE021)Dhruv Patel (11BIE024)Rajat Patel (11BIE025)

Electrochemical Machining

• Electrochemical machining (ECM) is a Non-traditional machining process that relies on the removal of work piece atoms by electrochemical dissolution.

• The machining current passes through the electrolytic solution that fills the gap between an anodic work piece and a preshaped cathodictool.

• The electrolyte removes the dissolution products, such as metal hydroxides, heat, and gas bubbles, generated in the interelectrodegap.

• Shaped tube electrolytic machining (STEM) is based on the dissolution process when an electric potential difference is imposed between the anodic work piece and a cathodic tool.

• Because of the presence of this electric field the electrolyte, often a sulphuric acid, causes the anode surface to be removed.

• After the metal ions are dissolved in the solution, they are removed by the electrolyte flow the tool is a conducting cylinder with an insulating coating on the outside and is moved toward the work piece at a certain feed rate while a voltage is applied across the machining gap. In this way a cylindrically shaped hole is obtained.

Introduction

S.T.E.M

• STEM is, therefore, a modified variation of the ECM that uses acidic electrolytes.

• The process is capable of producing small holes with diameters of 0.76 to 1.62 mm and a depth-to-diameter ratio of 180:1 in electrically conductive materials.

• It is difficult to machine such small holes using normal ECM as the insoluble precipitates produced obstructs the flow path of the electrolyte.

Process Parameters

• Electrolyte: Type: Sulphuric, Nitric and Hydrochloric Acids

Concentration: 10–25% weight in water

Temperature: 38°C (sulphuric acid) and 21°C (others)

Pressure: 275–500 kPa

• Voltage:Forwar0d: 8–14 V

Reverse: 0.1–1 times the forward

• Time:Forward: 5–7 s

Reverse: 25–77 ms

• Feed rate: 0.75–3 mm/min

Process Capabilities

• Hole size: 0.5-6mm diameter at an aspect ratio of 150

• Hole tolerances: 0.5-mm diameter ± 0.050mm

1.5-mm diameter ± 0.075 mm

60-mm diameter ± 0.100 mm

Hole Depth ±0.050 mm

Advantages

• The depth-to-diameter ratio can be as high as 300.

• A large number of holes (up to 200) can be drilled in the same run.

• Nonparallel holes can be machined.

• Blind holes can be drilled.

• No recast layer or metallurgical defects are produced.

• Shaped and curved holes as well as slots can be produced.

Limitations

• The process is used for corrosion-resistant metals.

• STEM is slow if single holes are to be drilled.

• A special workplace and environment are required when handling acid.

• Hazardous waste is generated.

• Complex machining and tooling systems are required.

Applications

• Because the process uses acid electrolytes, its use is limited to drilling holes in stainless steel or other corrosion-resistant materials in jet engines and gas turbine parts such as:

• Turbine blade cooling holes.

• Fuel nozzles.

• Any holes where EDM recast is not desirable.

• Starting holes for wire EDM.

• Drilling holes for corrosion-resistant metals of low conventional machinability.

• Drilling oil passages in bearings where EDM causes cracks.

Thank You!!..