Operating CNC grinding machines
Overview
This standard identifies the competences you need to carry out grinding operations, in accordance with approved procedures, using Computer Numerical Control (CNC) machines, such as universal grinding machines, gear grinding machines, thread grinding machines, ring grinding machines and grinding machining centres. You will confirm with the machine setter that the machine is ready for the operations to be performed and that all the required components/materials and consumables are available. 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.
You will be expected to produce a range of components that combine a number of different features, such as ground plain diameters, external screw threads, stepped diameters, flat faces and shoulders, chamfers, special forms, internal and external profiles, tapered diameters and faces, grooves/undercuts, parallel and tapered bores.
You will be required to operate the CNC machine in line with safe working practices and approved procedures, to continuously monitor the machining operations and, where necessary, make minor adjustments or seek the help of the setter to make the required adjustments, in order to ensure that the work output is to the required quality and accuracy. 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 machining activities undertaken, and to report any problems with the machining activities that you cannot personally resolve, or are outside your permitted authority, to the relevant people. You will be expected to work to instructions, with a minimum of supervision, taking personal responsibility for your actions and for the quality and accuracy of the work that you produce.
Your underpinning knowledge will be sufficient to provide a sound basis for your work, and will enable you to adopt an informed approach to applying machining procedures. You will have an understanding of the CNC grinding process used, and its application, and will know about the equipment, materials and consumables in adequate depth to provide a sound background for carrying out the activities to the required specification.
You will understand the safety precautions required when working with the machine, 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 programming, tooling and associated workholding devices, is the subject of another standard and is the responsibility of the machine-tool setter.
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 machining 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
- operate the machine to produce machined components
- monitor the computer process and ensure that the production output is to the required specification
- 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:
- the safe working practices and procedures to be followed whilst operating CNC grinding machines
- the safety mechanisms on the CNC grinding machine, and the procedure for checking that they function correctly
- how to stop the CNC grinding machine in both normal and emergency situations, and the procedure for restarting after an emergency
- the hazards associated with working on CNC grinding machines (such as moving machinery, automatic machine operation, sparks/airborne particles, bursting grinding wheels), and how to minimise them and reduce any risk
- the personal protective equipment (PPE) to be worn, and where this can be obtained
- the importance of keeping the work area clean and tidy
- the operation of the various hand and automatic modes of machine control (such as program operating and control buttons)
- how to use 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
- where to obtain the component drawings, specifications and/or job instructions required for the components to be machined
- how to extract and use information from engineering drawings or data and related specifications (to include symbols and conventions to appropriate BS, ISO or BSEN standards) in relation to work undertaken
- how to use imperial and metric systems of measurement
- the main features of the CNC grinding machine, and the accessories that can be used
- the various CNC grinding operations that can be performed, and the methods and equipment used
- how to handle and store grinding wheels safely and correctly
- the application of roughing and finishing cuts, and the effect on wheel life, surface finish and dimensional accuracy
- the application of cutting fluids with regard to a range of different materials
- the effects of clamping the work piece in a chuck/work holding device, and how this can cause distortion in the finished components
- how to recognise CNC grinding machining faults, and identify when adjustments need to be made
- the quality control procedures used, inspection checks to be carried out, and the equipment that will need to be used
- the problems that can occur with the CNC grinding activities, and how these can be overcome
- the extent of your own authority and to whom you should report if you have problems that you cannot resolve
Scope/range
Scope Performance
1. Confirm that the machine is ready for operation by checking all of the following:
- obtain and use the appropriate documentation (such as job instructions, drawings, quality control documentation)
- adhere to procedures or systems in place for risk assessment, COSHH, personal protective equipment and other relevant safety regulations and procedures to realise a safe system of work
- confirm with the machine setter that the machine is ready for production
- where appropriate, seek any necessary instruction/training on the operation of the machine
- ensure that machine guards are in place and are correctly adjusted
- hold components securely, without distortion
- check that the operating program is at the correct start point and the workpiece is clear of the machine spindle
- follow the defined operating procedures and apply safe working practices and procedures at all times
- ensure that machine settings are adjusted as and when required (either by yourself or the setter) to maintain the required accuracy
- ensure that the components produced meet the required specification for quality and 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 grinding machines:
- CNC universal grinder
- CNC gear grinder
- CNC thread grinder
- CNC grinding machining centre
- other specific CNC grinding machine
3. Produce ground components which cover four of the following, as applicable to the machine type used:
- plain diameters
- internal and external profiles
- parallel bores
- stepped diameters
- eccentric diameters
- tapered bores
- tapered diameters
- external screw threads
- involutes and helical forms
- flat faces and shoulders
- chamfers and radii
- curvic couplings
- special forms (such as concave, convex)
- internal/external undercuts/bearing tracks
4. Machine one type of material from the following:
- ferrous
- non-ferrous
- non-metallic
5. Use appropriate gauges or instruments to carry out the necessary checks for accuracy, during production, of three of the following:
- dimensions
- profile
- surface texture
- ovality/lobing
- parallelism
- concentricity
- angle/taper
- hole size
- squareness
- thread form
6. Produce component with dimensional accuracy, form and surface texture within all of the following quality and accuracy standards as is applicable to the operations performed:
- dimensional tolerance equivalent to BS EN 20286 or BS 1916 Grade 7
- flatness and squareness within 0.0005" per inch or 0.0125mm per 25mm
- angles within +/- 0.5 degree
- surface finish 16 µin or 0.8 µm
- ground bores/holes within H8
- screw threads BS medium fit