Machining components using CNC electro-discharge machines
Overview
This standard identifies the competences you need to operate Computer Numerical Control (CNC) electrical discharge machines, such as spark erosion, tape erosion and wire erosion machines, in accordance with approved procedures. You will take charge of the prepared machine and check that it is ready for the machining operations to be performed. This will involve checking that all the required components and consumables are present and that the machine has been approved for production. In operating the machine, you will be expected to follow the correct procedures for calling up the operating program, dealing with any error messages, and executing the program activities safely and correctly.
The components produced will have a number of different features, including such things as flat, tapered and angled faces, internal and external profiles, parallel and tapered slots and steps, parallel and tapered holes which are linearly or circularly pitched, and special profiles such as convex or concave. You will be required to continuously monitor the machining operations, making any necessary adjustments to machine parameters, in line with your permitted authority. Meeting production targets will be an important issue and your production records must show consistent and satisfactory performance.
Your responsibilities will require you to comply with organisational policy and procedures for the activities undertaken, and to report any problems with the equipment, tooling, program, materials or activities that you cannot personally resolve, or are outside your permitted authority, to the relevant people. You will be expected to work to instructions, taking personal responsibility for your own actions and for the quality and accuracy of the work that you produce.
Your underpinning knowledge will be sufficient to provide a good understanding of your work, and will enable you to adopt an informed approach to applying CNC electrical discharge procedures. You will have an understanding of the CNC electrical discharge machining process, and its application, and will know about the equipment, tooling, materials and consumables, in adequate depth to provide a sound background to the machine operation and for carrying out the activities to the required specification.
You will understand the safety precautions required when working with the CNC electro-discharge machine and its associated tools and equipment. You will be required to demonstrate safe working practices throughout, and will understand the responsibility you owe to yourself and others in the workplace.
Setting up of the machine, its tooling and associated workholding devices, are the subjects of other standards.
Performance criteria
You must be able to:
- work safely at all times, complying with health and safety and other relevant regulations, directives and guidelines
- confirm that the equipment is set up and ready for operation
- follow the defined procedures for starting and running the operating system
- deal promptly and effectively with error messages or equipment faults that are within your control and report those that cannot be solved
- monitor the computer process and ensure that the production output is to the required specification
- produce machined components
- complete the required production documentation
- shut down the equipment to a safe condition on conclusion of the activities
Knowledge and Understanding
You need to know and understand:
- how to work safely at all times, complying with health and safety and other relevant regulations, directives and guidelines
- the safety mechanisms on the machine, and the procedures for checking that they are operating correctly
- how to start and stop the machine in both normal and emergency situations
- the importance of wearing the appropriate protective clothing (PPE) and equipment, and of keeping the work area clean and tidy
- the hazards associated with the electro-discharge machining operations and how to minimise them and reduce any risks
- the application of a range of CNC electrical discharge machines such as spark erosion and wire erosion machines
- how to extract and use information from engineering drawings or data and related specifications (to include symbols and conventions to appropriate standards) in relation to work undertaken
- how to interpret first and third angle drawings, imperial and metric systems of measurement, workpiece reference points and system of tolerancing
- how to interpret the visual display and understand the various messages displayed
- the function of error messages, and what to do when an error message is displayed
- how to find the correct restart point in the program when the machine has been stopped before completion of the program
- the operation of the various hand and automatic modes of machine control
- how to operate the machine, using single block run, full program run and feed/speed override controls
- why you would conduct a full dry run and single block run
- how to make adjustments to the program operating parameters to take account of electrode wear
- how to set and secure the workpiece to the machine table/workholding device; the effects of clamping the workpiece; and how material removal can cause warping/distortion of the finished workpiece
- the various types of electrodes/wire used, and how they are located and secured to the machine head, tool cartridge and tool magazine
- the safe and correct handling and storage of tooling
- how to check that the electrode/wire is in a serviceable condition, and the effects that worn tooling will have on the workpiece surface finish and tolerances
- the procedures for dressing and reshaping electrodes, and the equipment to be used
- the problems that can occur with electrical discharge activities, and how these can be overcome
- the application of dielectric and ionised fluids with regard to different materials being machined
- the quality control procedures used, inspection checks to be carried out, and the equipment that is used
- where to obtain component drawings, eroding data, specifications and/or job instructions required for the components being machined
- the extent of your own responsibility and to whom you should report if you have problems that you cannot resolve
Scope/range
Scope Performance
1. Carry out all of the following during the machining activities:
- obtain and use the appropriate documentation
- adhere to procedures or systems in place for risk assessment, personal protective equipment and other relevant safety regulations and procedures to realise a safe system of work
- check that the operating program is at the correct start point
- ensure that machine guards are in place and correctly adjusted
- ensure that materials/components are correctly positioned and held securely without distortion
- check that the electrode or wire is in place and is in usable condition
- ensure that the dielectric fluid is at an appropriate level
- ensure that the workpiece is clear of the tooling before starting the machine
- use safe working practices and start up procedures at all times
- adjust machine settings, as required, to maintain the required accuracy
- leave the work area and machine in a safe and appropriate condition on completion of the activities
2. Operate one of the following CNC electrical discharge machines:
- CNC wire erosion machine
- CNC spark erosion machine
3. Produce machined components which combine different operations, and cover ten of the following:
- flat faces
- external profiles
- holes on pitch circles
- angular faces
- internal profiles
- linear holes (rows, angles)
- tapered faces
- enclosed slots/recesses
- special profiles (such as concave, convex)
- parallel faces
- open ended slots/recesses
- faces square to each other
- tapered holes
- parallel and tapered steps/slots/shoulders
- engraving
- circular/curved profiles (internal or external)
- threads
- other special forms or activities
4. Machine components made from one of the following types of material:
- ferrous
- non-ferrous
5. Carry out the necessary checks during production for accuracy of five of the following:
- dimensions
- parallelism
- squareness
- profile
- position
- angle/taper
- surface texture
6. Produce components within all of the following quality and accuracy standards, as applicable to the operations performed:
- dimensional tolerance as identified in relevant standard
- flatness and squareness 0.001" per inch or 0.025mm per 25mm
- components to be free from false starts and sharp edges
- angles within +/- 0.25 degree
- machined holes within H8
- surface finish 32 µin; 0.8µm; 18VDI