A Step-by-Step Guide to CNC Automation

- continued with Steps 5 through 8

5. Workflow Through the Shop

Workflow is somewhat related to the Job Planning discussed earlier. Can the workpieces be moved from machine to machine around the shop in an organized manner? Is it possible to locate a particular workpiece that is currently in production on the shop floor? Are the machines on the shop floor arranged in a logical manner that matches the production process or are they placed wherever they fit in the shop at the time they were purchased. These are the issues to be addressed to streamline the workflow of a part.

Due to the standardization required by adding an automation cell to a shop, "fudge factors" which have been a fact of life in most shops can no longer be tolerated. Each part must be produced to exact tolerances for it to fit into the overall process. This consistency in part production that is required when implementing an automation system goes hand in hand with the ISO quality standards being implemented by so many shops.

6. Palletization and Presetting

The modern tooling and palletization system is the key that allows us to use automation principles in a tool or mold building environment where no two parts may be the same. They provide a standard interface to the machine tool while offering flexibility in workpiece mounting (see photo on the right). The latest versions of these "automation ready" systems that are available today enable workpieces to be mounted to fixtures or pallets outside of the machine tool and then brought into the machine (with .000080" repeatability) and located without wasting precious machining time for part pickup in the machine. The investment made in tooling is offset by the improved accuracy and consistency of setup and increased machining time available. The “return on investment” period for these systems can be as little as 3 months due to the gains in machining time they offer.

It is also important to pick the tooling system that best meets your needs. Multiple tooling systems can be utilized in the shop if the workpiece must be removed from the tooling system during production (i.e., one system used for milling and raw material prep before heat treat and another used for EDM and grinding after heat treat). You don’t send the workpiece out to be heat treated while it is still mounted on the tooling system! In this case, provisions need to be made for remounting and locating the workpiece onto the second system when the parts return to the shop. (An example of a tooling system that can be used for both milling and die sinking EDM is shown to the right).

There are two basic options for offline workpiece presetting. The first and most common is the mechanical presetting station (shown below in the photo on the right) based on the tooling system chosen for the cell. This type of station allows the parts to be clamped and aligned parallel to the machine axes eliminating the need to spend time leveling and aligning the work in the machine. The part must still be located in the machine tool with the measure functions of the machine since this type of presetting station does not have the capability to locate the workpiece in reference to the tooling. Standard reference locations for part pickup can be implemented to allow the use of automated pickup cycles in the machine.

The second option involves the use of a Coordinate Measuring Machine (CMM) as a presetter (shown in the photo to the right). In this case, the part alignment can be set to match the machine axes and part measurement data can also be taken in reference to the tooling system. Once this is done, the data can be passed directly to the system or machine tool control via a serial or network link. Multiple part setups per pallet are also possible as multiple start locations can be measured and stored in the system. Electrode offsets for die-sinking EDM applications may also be obtained using this technique. Time spent on workpiece setup is done only once when the workpiece is placed on the tooling system. The cost savings is recouped every time you move the workpiece to another machine tool using the tooling system. Since the tooling repeats to a very close tolerance, the zero point is automatically set each time you clamp the pallet to a machine table.

The use of an automation-ready tooling system also allows the operator to stop a job, remove it from the machine, and then return it to the machine later for completion without losing any of the setup or machining time already invested in the part. This flexibility makes the shop more responsive to customer demands without sacrificing productivity.

7. Automatic Loading and Unloading

There are two basic types of automation systems that can be applied to today’s CNC equipment.

The first is a one-machine / one-robot approach where the machine is the master and the robot or pallet changer is the slave. The handling system is usually a self-contained unit consisting of a pallet magazine, a pallet manipulator or robot, and an integrated safety system. These stand-alone units can be placed next to an existing machine tool to create a one-machine cell.

The system is usually controlled by a program in the machine tool. The program has codes that call for the part to be changed out after the cutting cycle is finished. Each part in the pallet changer is loaded, machined, and returned to the magazine when it is finished. This procedure continues until all of the parts in the magazine are completed. At this point an operator is required to unload the magazine, reload it with new work, and set up the new programs in the machine tool for the next run.

The advantage of this type of system is that they are simple to understand and run. They are also less expensive to implement. The disadvantages are that they require greater human intervention and they lack some flexibility in that a workpiece is dedicated to a particular machine tool. If the machine tool stops due to a problem, all the remaining workpieces in that system will not be completed.

The larger multiple machine systems can use one robot to support multiple machine tools. The workpieces are stored in a central storage magazine and can be loaded into any machine tool that is available. Since this is a large-scale system, it requires a software-based cell controller to maintain and orchestrate the movement of work in the cell. In this configuration if a machine tool goes down for maintenance or a service problem, the work can be routed to any other machine in the system for production since it is not tied to a particular machine tool. This offers greater flexibility in scheduling and a fault tolerance to guarantee that a given workpiece will be completed on time.

8. System Integration and Options

When an automated system is added to a shop there are several integration issues that can improve its impact on productivity. While most people focus on the hardware aspects of a system (such as the machine tool, the robot, etc.) some of the most important features lie in the software side of the system. This is part of the system that deals with process information. Without a quality cell management system to monitor and direct the flow of work the system can be rendered useless like a CNC machine tool without a NC program. Key software features include:

1. A Pallet ID system to identify a workpiece as it moves around the shop floor. This type of system consists of a reading head mounted on the presetting station and on the robot and a set of ID chips; one mounted on each pallet in the cell. With these ID chips the pallet is identified by the system when a part is loaded on it and then checked before the robot loads it into the machine to prevent a part from being machined with the wrong program or tool.
2. A central database that stores all of the information on work currently in the cell. This allows the operator to get up-to-the-minute information on the status of a job. This information can also be passed to the company’s business systems to update information on delivery schedules, job costing, etc. With this information available, sales personnel can get up-to-the-minute info on the status of a customer’s job in the shop via the company’s network.
3. A user-friendly operator console that allows the user to monitor the system and perform system functions such as adding new jobs and scheduling the order of work to be machined.

Each of these software components combined with the automation hardware will give the company an up-to-the-minute picture of the work being processed.

In Conclusion…

Remember that for an automated system to function in a job shop environment the entire shop must be committed to making it work and all of the possible bottlenecks must be addressed.

Another important point is to purchase new technology in quantities that can be quickly absorbed and implemented into your shop’s production.

The Key Benefits of Automation are …

• Maximizing the machining hours on each CNC machine.
• Allowing for quick change between jobs and even the possibility of pulling a job to handle emergency situations without loss of accuracy or setup time.
• Improving customer response time.
• Reducing stress on the operator to get the work completed.
• Improving profitability of the company.

The Key Things to Remember are …

• Get all individuals involved to understand the system concept.
• Review the current job planning and workflow through the shop.
• Select and implement the proper tooling system for use in each machining department.
• Initiate off-line presetting, possibly including a CMM to be used as a presetting station and as an in-process inspection device.
• And Follow the 8-Step Process!

“CNC automation is not something you can purchase,
but a process that you apply to your shop!”