CNC Machining Centers Are Key to Production Efficiency

03/04/2020 | Matt Oswald

Efficiency is king in production manufacturing. CNC machines are a major tool for automating production of mechanical parts to increase throughput with consistent quality. CNC machine centers play a critical role in machine shop’s efficiency. 

This article explains five major advantages of CNC machine centers. It’s a great overview offering some experienced insights. 

Performance

Speed. How fast are CNC machines? The maximum feed and rapid rates can exceed 2,300 inches per minute (ipm); faster than three feet per second. A fast speed reduces cycle times in tasks, such as moving the spindle home for changing tools and then positioning the cutting tool precisely where it needs be prior to cutting.

Cutting feeds can exceed 300 ipm, with the machine repeatedly locating all features and doing so within a fraction of a millimeter. Cutting feed depends on several factors, such as part material, tool, path, and depth of cut. This quick 5-inches-per-second feed is ballpark for face-milling aluminum.

Precision. CNC machines, due to their design and construction, can cut as precise as 0.001”. That is splitting hairs. Literally, cutting at about 1/4 the width of a human hair. Plus, it’s accomplished with speed. 

Repeatability. Running from a program, a CNC machine reliably repeats all process steps over and over, part to part without skipping a step. The program controls the machining process with consistency and precision. As far as day-to-day operations, repeatability is more about the rigidity of the part and work holding, tooling wearing down, and not typically the machine’s performance.

Flexibility

Programmable. The basic operation of CNC machining is clear-cut. The machine is programmed to process the part using different tools. Engineers may use a visual 3D computer-aided design and manufacturing (CAD/CAM) software tool to program the machining process. For example we use MasterCAM which is common in CNC machining. CAM outputs g-code which runs on the CNC machine. Our programs are downloaded to and sent back from a machine remotely, by engineers or production.

Adaptable by Setup. The process of switching over a machine to run a new part is called setup. Fixtures hold parts in the machine for processing. Fixtures are designed for each part, and they are interchangeable. Tools are also interchangeable like fixtures. A set of cutting tools chosen to produce each part optimally. Tools, fixtures, and programs are changed over at the start of a new job. This makes CNC machines flexible to produce different parts.  Another level of flexibility comes from having many machines of the same type, since any of these machines can be setup to run a given part. 

Sizes and Types. CNC Machines come in different types and sizes. For example, a lathe spins the part and the cutter is fixed, which is great for making cylindrical parts. Whereas in mill the tool rotates to cut. CNC machines use standard pallet sizes on which the fixture sits; for example 500 mm X 500 mm. While machines and pallets are smaller or larger, they’re very similar from a programming and operations perspective. There typically is a best-fit machine for parts range from small to large. 

Automation

Automatic Changers.The machine can change tools using an automatic tool changer (ATC). The program controls tooling and process. The machine can start cutting features with a face mill, and when finished with this tool automatically change to another tool, like a drill.

Similarly, many CNC machines include two pallets that are exchanged with an automatic pallet changer (APC). One pallet is accessible by the operator (for loading, unloading, processing, etc.) while the other is in the cutting area. This improves spindle utilization, as the machine can cut while the operator processes, unloads, and loads parts.

Hydraulic Fixtures. Hydraulics systems are often incorporated to clamp, unclamp and support the part. Parts are clamped in the exact same sequence, with the same pressure with the push of button. This improves repeatability, consistency, and loading efficiency needed in production machining.

Uptime Features. Material waste, chips and shavings are removed automatically by a conveyor, and coolant is separated for reuse.

The machine tracks tool wear and use. The tool monitor alerts an operator when a tool should be replaced, increase up-time by staying in front of issues by running to the expected tool life. 

Standardizing Setups. The CNC setup process can be formalized to yield consistent manual changeovers. A setup checklist defines every step, covering fixtures, programs, tools, and first article. While not “automated,” formalizing the manual process ensures consistency.

Adaptability

Tool Capacity. Standard tool capacity is typically around 20 to 60 tools, depending on the machine type, but this can be extended to 100, 200, or more if the part is complicated. A larger tool matrix (240+ tools) can also be used when running multiple parts with varying features, which eliminates the need to switchover tools.

Pallet Automation. A pallet pool system moves pallets in and out of the CNC machine, allowing for multiple parts/pallets to be run while eliminating the manual setup repetition. Each part can be set up manually once and then autonomously changed over.

Different Spindles. High-torque spindles are beneficial for cutting iron and hard materials. High-speed spindles provide for maximum material removal rates and best surface finish. Matching the spindle to the need is critical to maximizing efficiency.

Tool Breakage Sensors. These sensors touch the tool to measure and check length. If the tool is short, it is likely broken. The tool needs to be checked, changed, and the part also needs to be checked. Stecker Machine include these sensors as standard in horizontal CNC machine centers, because of the ability to detect tool failures in process. This keeps quality point of control to the current in process part and prevent unnoticed production defects. 

High-Pressure Coolant. Added to machines to run certain tools, high pressure coolant helps create more consistent cutting. We often add Chip-blasters, which create high pressure coolant flow which also helps remove chips, or waste, from a part.

Gantries and Robots. To further automate processing of parts, additional equipment can be added to a CNC machine. Gantries and robots can be interfaced to lift, load, and further process parts. Typical applications include moving, loading, and unloading parts from CNC fixtures to and from dunnages or conveyors.

Probing. Probes are often used in setup, but can also be used during a part production to offset a program as well as check the part. For example, if machining tolerances are hard to control from work holding alone, a casting feature can be found precisely by probing. Then cutting program can be offset against the probe measurement.

Supply Base

Legacy and Evolution. In general, CNC machines have decades of history and reputation for being reliable. We've run machines for up to two decades without major issues. CNC machines keep advancing, with suppliers regularly introducing new features. A current technology push is adding more machine monitoring and remote diagnostics.

Market Competition.The CNC machine market is very competitive, with multiple, high-quality machines. CNC Machine manufacturers push each other to keep improving and adding features while holding costs down.

Manufacturing Partnerships. Typically, a machine shop develops strong partnerships with suppliers, who get to know a shop’s core needs and business model. When unique automation or machine customization demands arise, suppliers are often ready to offer solutions, helping that shop grow to better serve customers’ needs.

If you’re not sure your machining supplier offers the most CNC machining benefits for efficient and consistent production (and improve your relationship), contact us with a request for quote (RFQ) or questions. See if your partnership is providing extra benefits, sets you apart, and makes your life better.

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