Programming of CNC Machines. Ken Evans
BASICS
1.Recognize the importance of Safety when working with CNC Machines.
2.Become familiar with Tool and Work holding methods for CNC Machining.
3.Learn how to calculate proper Feeds and Speeds for CNC Machining.
4.Learn how to plan for CNC programming by using Process Planning Documents.
5.Become familiar with Coordinate Systems and their use in CNC Programming
6.Learn terminology and acronyms associated with the CNC Basics.
7.To learn the ABC’s of CNC program format.
As you begin to learn about CNC Programming, it is important to first become aware of and learn how to practice safe working habits. You should not operate any machine without first understanding the basic safety procedures necessary to protect yourself and others from injury, and the equipment from damage. Most CNC machines are provided with a number of safety devices (door interlocks, etc.), to protect personnel and equipment from injury or damage. However, operators should not rely solely on these safety devices, but should operate the machine only after reading and fully understanding the Safety Precautions and Basic Operating Procedures outlined in the maintenance and operation manuals provided with the equipment. The following are some Do’s and Don’ts that should be practiced when working with CNC Machines.
Safety Rules for NC and CNC Machines
Do’s:
•Wear safety glasses and safety shoes at all times.
•Know how to stop the machine under emergency conditions.
•Keep the surrounding area well lighted, dry and free from obstructions.
•Keep hands out of the path of moving parts during machining operations.
•All setup procedures and loading or unloading of workpieces must be performed with the spindle stopped.
•Follow recommended safety policies and procedures when operating machinery, handling parts or tooling, and when lifting.
•Machine guards should be in position during operation.
•Wrenches, tools and parts should be kept away from the machine’s moving parts.
•Make sure fixtures and workpieces are securely clamped before starting the machine.
•Cutting tools should be inspected for wear or damage prior to use.
Don’ts:
•Never operate a machine until properly instructed in its use.
•Never wear neckties, loose fitting long sleeves, wristwatches, rings, gloves or unrestrained long hair, when operating any machine.
•Never attempt to remove metal chips with hands or fingers.
•Never direct compressed air at yourself or others.
•Never operate an NC/CNC machine without first consulting the specific operator manual for the machine.
•Never place hands near a revolving spindle.
•Electrical cabinet doors are to be opened only by qualified personnel for maintenance purposes.
A large investment has been made to purchase CNC equipment. It is very important to recognize the need for proper maintenance and a general upkeep of these machines. At the beginning of each opportunity to work on any Turning or Machining Center, verify that all lubrication reservoirs are properly filled with the correct oils. The recommended oils are listed in the operation or maintenance manuals typically provided with the equipment. Sometimes there is a placard (plate) with a diagram of the machine and numbered locations for lubrication and the oil type is found on the machine. Most modern CNC machines have sensors that will not allow operation of the machine when the Way or Spindle oil levels are too low. Pneumatic (air) pressures need to be at a specified level and regulated properly. If the pressure is too low, some machine functions will not operate until the pressure is restored to normal. The standard air pressure setting is listed in Pounds per Square Inch (PSI) and a pressure regulator is commonly located at the rear of the machine. Refer to the operator or maintenance manuals for recommended maintenance activities.
Coolant Reservoir
The Coolant tank level should be checked and adjusted as needed prior to use. A site glass is normally mounted on the tank for easy viewing. Use an acceptable water-soluble coolant mix, synthetic coolant or cutting oil. Periodically the coolant tank should be cleaned and refilled. And last but not the least important is the cleanliness of the work-table, tools and area. Be sure to clean off any metal chips and remove any nicks or burrs on the clamping or mating surfaces. Always clean the machine after use.
Daily Maintenance Activities
Do’s:
•Verify that all lubrication reservoirs are filled.
•Verify air pressure level by examining the regulator on the machine.
•Check the chip pan and coolant level and clean or fill, as needed.
•Make sure that automatic chip removal equipment is operational when the machine is cutting metal.
•Be sure that the worktable and all mating surfaces are clean and free from nicks or burrs.
•Check to see that the Chuck pressure setting is adequate for clamping the work to be machined.
•Clean up the machine at the end of use with a wet/dry vacuum or wash machine guards with coolant to remove chips from the working envelope.
Most new CNC machines are equipped with guards that envelope the worktable. The guards protect the Ways and sensitive micro-switches installed as limit switches for table movement. Guards also help keep the surrounding floor space clean but there is still the task of chip disposal. Some larger production machines incorporate a chip conveyor, which carries the chips to a drum on the floor on either side of the machine for easy removal. Even with these features, there is still a need for chip cleanup inside the working envelope at least once a day. If chips are allowed to gather within the guards, they will eventually find their way around the guards that protect the machine Ways. Over time, some of the chips might become embedded into the Ways and cause irreparable damage. Another problem that may occur as the chips collect, they bunch up and are pushed into contact with the micro-switches. This contact stops the machine from working since the switches send a signal to the control that indicates table travel limit has been exceeded. This message prevents the machine from operating until the chips are removed. If chips get within the guards around the micro-switches, it is necessary to remove those guards and clean. If this extent of cleaning becomes necessary the Machine should be turned off and a Lock-Out/Tag-Out should be incorporated to prevent injury. Remember, it is essential to replace the guards after cleanup.
It is very important to do a thorough machine cleanup when many chips are present. The exterior of the machine usually will only need wiping down with a clean rag. You can cleanup the Ways and the working envelope without damaging the machine by using coolant to wash the machine table and the guards free of chips. Another effective cleaning method is to use a wet/dry vacuum to pick up the chips. Along with the chip conveyor system, these two methods have proven hard to beat.
One cleanup method that is not recommended is to use compressed air to blow away the chips. It is appropriate to use compressed air to remove chips and coolant from the workpiece itself or work holding fixtures such as a vise. The problem