Preparing for Lights-Out Production
As manufacturers face the challenges of reducing cost-per-part while meeting quality and delivery demands, adding a workerless third shift is a tantalizing possibility. It’s also a bit scary.
The vision of barstock automatically loading into unattended turning machines and pumping out parts overnight can seem like a dream come true. However, ceding total control of production to unmanned machines and worrying about everything that could go wrong is the stuff of nightmares. In fact, one machine shop owner confided that he couldn’t sleep the first night he ran lights-out production. “I kept thinking about everything that could go wrong and finally went to the shop at 3 a.m. Everything was working perfectly. Now I can sleep at night.”
How can a shop owner prevent sleepless nights and live the dream? It’s a matter of defining the goals, thinking through the entire production scheme, selecting the right equipment and documenting the process.
It Starts with the Parts
For most manufacturers, the reason for implementing lights-out is to reduce overall production costs. If the company already has work cells that largely operate unattended during the day, the temptation is to simply set up a run at the end of a shift, turn out the lights and let the magic happen. However, it’s often not as simple as that. With no one in the facility to monitor the cell, it’s critical to eliminate potential problems that would require intervention.
The first consideration should be the types of parts that will run. For a single part or a family of parts from one diameter of barstock (something for which Swiss-type machines are well suited), loading a bar feeder with material can allow the job to run all night. The length of the part will help determine how many parts can be produced.
However, for multiple parts from various diameters of barstock, the number of parts that can be produced overnight is limited because nobody will be there to manage the change-over from one material to the next. An alternative process such as using a single diameter bar for multiple applications may provide the solution.
For example, if parts are typically made from both ⁷/8- and 1-inch diameter barstock, standardizing on 1-inch bars will increase the volume of parts that can be produced overnight. Obviously, this also increases machining time, tool usage and material costs a bit, but may well be worth it to make more parts unattended. This strategy may not be effective for expensive materials, such as titanium.
Typically, production programs are designed to optimize cycle time and throughput. Running lights out, however, may require modifying part programs to ensure uninterrupted operation. For example, reducing spindle speed or tweaking the cutting approach may reduce tool wear, and because no operator is available to replace worn or broken tools, extending tool life enables the machine to make more parts overnight. The material used also impacts tool life. Depending on the application, aluminum or brass may yield 20,000 parts per cutting edge while hardened steel, such as heat-treated AISI 4140, may only yield about 500 parts per edge.
Regardless if the job involves running a single part all night on a Swiss-type machine or multiple parts on a fixed headstock turning machine, it is critical to consider every aspect of the process that could impede production.
CNC turning machine. The heart of a lights-out work cell is the turning machine or machining center. Overnight operation requires a machine that is capable of continuous, unattended operation. Reliability is the chief concern, and this leans heavily on the stability and rigidity of the machine’s construction.
Other considerations are advanced interconnectivity that allows the machine tool and peripherals to share complex, bi-directional data; a part scheduler program; adequate coolant capacity and chip evacuation; and sufficient tooling stations.
Bar feeding. Second only to the machine tool itself, an automatic bar feeder is essential for lights-out production. Like the turning machine, the bar feeder must have the strength and reliability to continuously load barstock and provide material support necessary for optimal spindle speeds. It must also have the capacity to hold enough barstock to produce the required part volume.
If the production run includes a variety of parts to be made from the same diameter barstock, the bar feeder must be able to automatically change over from one program to the next. With LNS bar feeders, this can be accomplished by communications between the machine tool scheduling program and the bar feeder’s Part Library. When it’s time to change programs, the turning machine tells the bar feeder what part it wants to make next, and the bar feeder calls up the corresponding program from the Part Library, which then loads the appropriate parameters and automatically adjusts itself accordingly.
This interconnectivity, which can be facilitated via the LNS e-Connect communications system, provides another important benefit when running multiple part programs overnight. The bar feeder continuously keeps track of material usage and communicates the information to the turning machine’s master schedule. The machine tool can then compare the lengths of the various parts to be run with the available material. If the material is adequate to complete the required part run, and the total quantity has not been produced, it does so. If not, it determines the length of the remnant and selects another part from the schedule that it can make using the remaining barstock. Both the machine tool and the bar feeder automatically adjust themselves to optimize material usage. When this cycle is complete, the master scheduler selects the next part program, the turning machine and bar feeder make the appropriate adjustments, a new bar is loaded and production continues.
Whether to choose a 12-foot or short-loader bar feeder for lights-out operation depends on the specific applications. In many cases, a 12-foot bar feeder is preferable because it holds a larger amount of material and has only one remnant per 12-foot bar. Short loaders can be used for overnight production of parts with certain requirements, such as when running parts with long cycle times, and when using profiled material or bars that are not perfectly straight. Also, in conjunction with a shaped spindle liner and custom workholding, short loaders can run a variety of extruded shapes as well as square and rectangular bars, allowing the machining of parts that would previously be milled.
Regardless of which type of bar feeder best suits the application, it must have the ability to continuously load barstock of the required diameter without misfeeds. Otherwise, production will grind to a halt.
Unloading parts. What goes in must come out, albeit in a more refined form. The standard parts catcher may be perfectly adequate to handle the output, depending on the size and quantity of parts produced overnight. If not, options are available such as the LNS Blaze Air vacuum unloader, which uses suction to unload parts as long as 48 inches and deposit them into its storage tray. Blaze Air is primarily used with twin-spindle or subspindle machines with through-hole to remove the part through the back of the secondary spindle when both ends have been machined. It can also be used on single-spindle machines in many cases.
Another approach is to add a robotic arm to remove parts from the unloader tray or parts catcher and place them in containers. With recent advances in both touch and vision sensing capabilities, robots can locate and move large, long or small parts to appropriate receptacles.
Chip management. A buildup of chips can compromise the cutting area and create a bottleneck that slows or stops production, and fines can clog and damage coolant pumps. Tooling used for lights-out production must adequately break up chips to prevent bird nests of stringy chips that can break tooling and produce bad parts.
Receptacles that can’t contain the volume of chips created overnight can also cause backups. For lights-out production to run smoothly, the chip conveyor must be capable of handling all types and sizes of chips, as well as adequately filtering coolant. LNS SFcompact chip conveyor, for example, uses a self-cleaning filtering system to remove particles as small as 50 microns. For lights-out production using several workstations, another option is a 3D chip conveyor that moves chips from multiple machines through a piping system to central repositories either within or outside the factory.
Preventive maintenance. Even the most reliable machinery requires routine maintenance. When it comes to lights-out production, keeping the machine tools and all peripheral equipment in optimum condition is a must. When a work cell goes down during the day, operators may be able to move production to another workstation, but a breakdown during lights-out stops production altogether. That’s why it’s important to have a preventive maintenance schedule in place and to buy equipment from an OEM that keeps an adequate inventory of replacement parts on hand plus has a staff of readily available service technicians.
Remote monitoring. If nobody is around to address the failure of a work cell, a number of production problems can arise. LNS bar feeders constantly monitor the work cell and, via a built-in web server, can instantly send email trouble alerts if necessary. Standard machine status information messages that the system transmits include Availability, Mode, Machine State, Alarm State, Alarm ID and Alarm Description.
Analytical data. In addition to the machine status information for remote monitoring, other data is available for use in refining operations and quantifying results. This data includes production information such as part number, part diameter, part length, production volume and remaining parts; machine data including machine type, machine SN and PLC SN; and statistics for total cycles and total time in automatic mode.
These data provide essential information used within Industry 4.0, MTConnect and the Industrial Internet of Things (IIoT). The e-Connect system can also work with proprietary machine tool data systems and provides customized data reporting, as requested.
Documentation. Because lights-out requires a lot of pre-planning, once the process is perfected, it is wise to codify the plan, including specific instructions on how to set up the work cell for overnight production. This may include procedures for checking fluid levels, tool life monitors and ensuring adequate tooling is in place for extended, unattended operation. This document will be both a reference for current machine operators and a learning tool for new hires.
For an informed decision for determining if lights-out is a good fit, a shop should consider the above points, then compare notes with other manufacturers who have implemented successful overnight, unattended production. Equipment suppliers who have established proven lights-out knowledge and experience can help lay the groundwork for a successful operation.
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