When I’m visiting CNC operations around the country, shop managers often start our conversations like this, “Labor is killing us. We can’t find enough good operators and we’re losing some of our experienced operators to competitors. What are my options?” The manager often goes on to describe operational issues related to labor that are typical in high-mix CNC manufacturing. This article describes automation options for CNC shops, specifically focusing on those processing parts in CNC milling machines with batch sizes between 10 and 1,000 pieces.
Lean manufacturing principles are key to a successful high-mix part CNC manufacturing operation. Although lean manufacturing espouses many principles, the most important for high-mix manufacturing is elimination of over production. A lean manufacturing environment must be successful at producing many different kinds of parts in small quantities at a low cost. To do that, two things must be done well: low new-part-introduction costs and short part setup times.
Historically, automation has implied high new-part-introduction costs and long setup times. If the cost to introduce a new part to automated processing is high, shops are inclined either not to automate the part or try to recover those costs by increasing volumes. If the setup time is high, the batch costs are increased and there is incentive to produce more parts per batch. To successfully introduce automation to high-mix manufacturing, low new-part-introduction costs and part changeover times must be maintained while, at the same time, reducing the total labor required in the high-mix CNC manufacturing operation.
Pallet Loaders versus Part Loaders
In general, there are two types of automation solutions for CNC milling applications: part loaders and pallet loaders. With a part loader, the operator stages the raw material in front of the automation and the automation loads the parts into and out of the CNC. With a pallet loader, the operator secures each piece of raw material to a pallet, and the automation loads the pallet into the CNC and unloads the pallet when the CNC is finished. Examples of pallet loaders include horizontal machining centers and vertical machining centers that incorporate a pallet changer.
Examples of part loaders include the Halter CNC Load Assistant and the VersaBuilt VBX-160 (pictured). When comparing a pallet loader to a part loader, the setup time needed to changeover the automation and CNC workholding must be considered. For pallet loaders, setup time is a function of how much time it takes to changeover each pallet for the new part multiplied by the number of pallets in the automation system used to make the part. For part loaders, changeover time is dependent on the type of part loading system, but could include time for changing CNC fixturing, replacing robot gripper fingers, in-feed and out-feed changeover, re-grip station changeover and pick point calibration touchup.
Automation does not eliminate operator labor, automation reduces operator labor. Both part loaders and pallet loaders increase operator efficiency by reducing wasted motion. An operator tending three CNC machines will spend a significant amount of time walking between each machine, opening and closing a CNC door for each part. Automation allows operators to work with parts in batches where they can be focused with less wasted motion and, generally, fewer opportunities for distractions. Automation provides operators with flexibility to better plan their activities by significantly increasing the time between tending tasks. This results in better equipment utilization and reduced operator labor requirements.
When it comes to the labor required to load and unload the parts to be processed, part loaders usually require less operator labor than pallet loaders. To tend a part loader, the operator places a batch of parts in the part loader and then unloads a batch of completed parts. With a pallet loader, the operator indexes each pallet to an operator station then fixtures each part to a vise or other fixture on the pallet. Per part tending time is typically 10 to 20 seconds for a part loader and between one and 5 minutes for a pallet loader.
Lights-Out Manufacturing: The Ultimate Goal, Right?
The goal of most automation projects is to reduce the dependence on operator labor and to reduce costs. Both of those goals can typically be achieved without running lights-out. The primary goals of running lights-out are increased production capacity and equipment utilization. The savings from running lights-out can be significant, but should not stop a shop from considering automation if reduced labor and operational costs can still be achieved.
Many different factors affect the ability to run lights-out, including the type of automation equipment, average cycle time, average batch size and infeed/outfeed capacity. However, for many companies, successful lights-out manufacturing will initially be limited by internal process constraints, not the type of automation equipment chosen. For example, if your facility depends on an operator checking every third part for surface finish and dimensional tolerances to make good parts, it will not run successfully without an operator to manage the process. On the other hand, if your facility relies primarily on maintaining and measuring the CNC process to make good parts (think tool life management, regular preventative maintenance schedule and in process probing), it is already on its way to successful lightsout manufacturing.
Running lights-out is not to be confused with lowest labor required or lowest cost of production. If you choose an automation system that runs lights-out, but has substantially higher new-part-introduction costs and/or high setup costs, any savings or increased productivity from lights-out manufacturing can easily be wiped out.
Fully Automated or Half Automated?
Another factor in reducing labor is whether the automation equipment is capable of processing each part “complete” without further operation intervention. Most parts require at least two operations, in other words, the part needs to be fixtured in two different orientations to complete the part. Some automation equipment is capable of performing both operations and other automation equipment can process only one operation before operator intervention is required. Although some part loaders can be configured for processing both sides of a part, pallet loaders are inherently limited to processing a single operation at a time. Automation that can process a part complete will usually reduce tending labor by more than half.
One of the primary advantages of a pallet loader is that there is no need to develop a part picking process. The automation system of a pallet loader is delivered pre-integrated and tested, ready to load the same thing every time: a pallet. A part loader requires a part picking process to be developed for every part introduced to the system. Historically, developing a part picking process for each part introduced for automation was a high-cost proposition handed off to automation engineers. The new generation of part loaders has significantly reduced the engineering burden of new part introduction so that an average shop can easily create their own reliable part picking processes.
Robotic Part Loaders: A Growing Choice in Automation
For many years, the general consensus was that robotic part loaders were for single-part, high-volume applications only. The reason? We couldn’t go out and buy robotic part loaders as ready-to-run products; they were fully-custom engineered systems. Several important technology advancements have changed that situation and there are now robotic part loading options that are not only viable for automating mixed-part manufacturing, but may be superior to traditional choices such as pallet loaders.
A robot-in-a-box is a new category of part loaders that has emerged over the past several years. The robot-in-a-box is an attempt to bring the substantial labor savings of per-part tending of a part loader to the high-mix CNC manufacturing market. To do this, robot-in-a-box vendors have standardized many, historically custom, aspects of robotic part loaders. Standardizations include caging and safety systems, part infeed and outfeed, robot programming and CNC integration. Robot-in-a-box products are typically configured with two grippers and easy-to-adjust and easy-to-change gripper fingers.
One of the ways robot-in-a-box vendors have been successful at achieving low new-part-introduction costs and short setup times is to process a single operation at a time. By avoiding the first-operation-to-second-operation transfer, new-part-introduction design steps are eliminated and setup times are reduced when using traditional robot grippers.
Robot-in-a-Box with MultiGrip
MultiGrip is a new automation workholding technology designed specifically for the automation of high-mix CNC manufacturing and available in the VersaBuilt VBX-160. MultiGrip combines the robot gripper and CNC vise jaws into an integrated system that combines some of the best features of a pallet loader with a part loader. By eliminating robot gripper fingers, MultiGrip further reduces new-part-introduction design steps and setup time versus robot-in-a-box systems using traditional robot grippers. Another advantage of MultiGrip is that it is able to process multiple operations without operator intervention, reducing operator labor costs over other robot-in-a-box solutions.
What’s the Best Option for My Shop?
Consider a CNC manufacturer with 100 part numbers, an average batch size of 100 pieces and part cycle time of 20 minutes (10 minutes per operation). Compare an HMC to a VMC tended by a VersaBuilt VBX-160 MultiGrip system with the following assumptions:
• 2 pallets, 4-sided tombstones, 2 double-activating vises per tombstone face, total of 16 vises
• Capacity of 32 (8” x 8”) parts per load
• $350 per set of quick-change vise jaws
• 10 minutes setup time per vise
• 2 minutes per part operator tending time
• 2 MultiGrip vises
• Capacity for 52 (8” x 8”) parts per load
• $400 per set of two-operation MutliGrip vise jaws
• 2 minutes setup time to load MultiGrip jaws and enter job information
• 15 seconds per part operator-tending time
The following information shows that the part loader has significant advantages over the pallet loader in both fixturingcosts and per order labor costs.
Fixturing costs for 100 part numbers Operator labor per 100 part order (hours) Max. unattended run time (hours)
HMC: $560,000 6.00 5.33
VBX-160: $40,000 0.45 17.33
Just a few short years ago, multiple-pallet HMCs were the only choice when it came to automating high-mix CNC manufacturing. Through technology advancements, robotic part loaders have not only become a viable solution, for many CNC shops they represent the optimal option for automating high-mix manufacturing.
Related Glossary Terms
Checking measuring instruments and devices against a master set to ensure that, over time, they have remained dimensionally stable and nominally accurate.
Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.
- computer numerical control ( CNC)
computer numerical control ( CNC)
Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.
Device, often made in-house, that holds a specific workpiece. See jig; modular fixturing.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- lean manufacturing
Companywide culture of continuous improvement, waste reduction and minimal inventory as practiced by individuals in every aspect of the business.
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.