Zero setup time means a CNC machine consistently goes from job to job with no time in change-over. This can be difficult to achieve for most applications. While it may be possible to achieve zero setup time, it’s probably not feasible. That is, you may find ways to achieve zero setup time but not be able to justify the cost of implementing them.
Some machines and applications make it easier to achieve zero setup time than others. For example, I know of more than one company that uses bar-fed CNC turning centers that can go from one job to the next mid bar. They accomplish this with a series of custom macro call statements in the main program—one for each job being run. Each consecutive job is required to use the same cutting tools and bar sizes because one machine is dedicated to each bar size. The first part of the next production run comes out seconds after the last part of the previous production run.
Unfortunately, it isn’t so simple for most machines. Achieving zero setup time requires a great deal of engineering and willingness to spend money to implement the engineering ideas.
Keep in mind that we’re talking about zero setup time for the machine tool. That is, you may be able to achieve—or come close to achieving—zero setup time by doing many of the setup-related tasks offline, while the machine is producing. For example, many horizontal machining centers are part of a flexible manufacturing system—able to go from one job to the next in the time it takes to swap out a pallet. To achieve this, however, several people might be working to keep setups and workpieces loaded on pallets and cutting tools placed in the machine’s automatic tool changer magazine.
Again, you may not be able to justify what it takes to achieve zero setup time. However, with a little ingenuity, you may be able to justify the elimination of some setup-related tasks. By eliminating a given task, or moving it offline, you will reduce the time a machine is down between production runs by the amount of time it takes to perform the task during setup. This might be justifiable even if it takes longer to perform the task offline because machine downtime will be reduced.
Consider this list of tasks related to performing setups on a typical CNC machining center:
• Gather everything needed for the next setup.
• Tear down and put away the previous setup.
• Clean the machine.
• Set up the workholding.
• Measure program zero.
• Enter program zero assigning fixture offsets.
• Assemble cutting tools.
• Measure cutting tool lengths.
• Enter tool length compensation offsets.
• Measure milling cutter diameters (if cutter radius compensation is being used).
• Enter cutter radius compensation offsets.
• Load the program.
• Dry-run the new program.
• Machine the first workpiece.
• Inspect, make adjustments as necessary.
• Repeat until workpiece passes inspection.
• Save the program if it has been modified.
Your list of setup tasks may vary, but write them down for people to study. You may wish to be more detailed, listing every sub-task within each major heading. Invite anyone involved with making setups to study the list. What can be eliminated? Try to come up with at least one way, regardless of how far-fetched it may sound, to eliminate every task on your list.
For example, many companies have eliminated tasks related to measuring program zero and entering program-zero assignment values into fixture offsets by making qualified setups. If the program-zero point position does not change from one time the job is run to the next, the program-zero assignment values can be recorded for future use, eliminating the need to re-measure them every time the setup is made. Also, by including G10 commands with program-zero assignment values, the task of entering fixture offsets is also eliminated.
Here are some other ideas for eliminating tasks for machining center setups:
• Gathering: Can you store the most commonly needed components at the machine?
• Tear down/clean the machine: Can you run jobs that require the same workholding and cutting tools consecutively?
• Workholding setup: Is your machine table large enough to keep commonly used workholding devices permanently mounted on the table?
• Measure program zero, enter fixture offsets: Can you make qualified setups?
• Assemble, measure and enter offsets for cutting tools: Do you have a core group of commonly needed cutting tools that can be set up and ready for use at all times?
• Load the program: Do you have a DNC system that enables programs to be loaded and saved from the machine? Can your programs be loaded while the machine is running?
• Dry run: How effective is your offline program verification system?