This document discusses shaped tube electrolytic machining (STEM), which is a variation of electrochemical machining (ECM) that can produce small holes with high depth-to-diameter ratios in electrically conductive materials. STEM uses a cathodic tool in the shape of a conducting cylinder with an insulating coating to drill holes in an anodic workpiece when an electric potential is applied through an electrolyte, typically an acid. The document outlines the STEM process, parameters including electrolytes, voltage, time and feed rate, capabilities including hole size and tolerances, advantages, limitations, and applications for drilling cooling holes in parts like turbine blades.

1. Shaped Tube Electrolytic
Machining
Nisarg Shah (11BIE021)
Dhruv Patel (11BIE024)
Rajat Patel (11BIE025)

2. 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 cathodic
tool.
• The electrolyte removes the dissolution products, such as metal
hydroxides, heat, and gas bubbles, generated in the interelectrode
gap.

5. • 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

6. S.T.E.M

7. • 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.

8. 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

9. 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

10. 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.

11. 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.

12. 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.

13. Thank You!!..