CNC MACHINING INDUSTRY GUIDE

Introduction: CNC Machining Solutions

There’s no simple way to describe the benefits of high-quality, precision machining and its importance in today’s economy.

Just about any industry that relies on precision machined parts uses CNC machining services to create custom machined parts from raw materials, fabrications, or castings into individual components.

CNC machining, or computer numerical control machining, is a type of precision machining that’s automated, enabling high accuracy and extreme precision. Not only can CNC machining attain a degree of complexity and intricacy that traditional precision machining technology can’t, it’s also cost-effective, especially when producing complex parts.

Make a CNC Machine Shop Work for You

• Long gone are the days of people working levers, handling products excessively, and pushing buttons. The computer components of CNC machines are now the “live operator,” manipulating the cutting tools and shaping the material.
• Industries that benefit from CNC machining include metalworking, automotive, aerospace, agriculture, construction, power generation, marine, transportation, and more. And, the types of CNC machines vary as much as the industries they benefit.
• Extreme precision demands CNC machining. While conventional machining is acceptable for some industries, others require position tolerances of +/- .001” or tighter. And often, tens of thousands of identical parts are needed, which is impossible without CNC’s repeatability.

CNC Machine Shop Services

Standard CNC machining processes may include the following machining techniques:

• Milling — bringing a rotating cutting tool into contact with a stationary workpiece
• Turning — rotating a workpiece to contact a cutting tool; lathes are common
• Drilling — bringing a rotating cutting tool into contact with a workpiece to create a hole
• Boring — removing material to form a precise inner cavity within a workpiece
• Broaching — removing material with a series of shallow cuts
• Sawing — cutting a narrow slit in a workpiece using a saw blade

In addition to advanced machining, a CNC machine shop may provide additional services that elevate a project:

• Project Management — start-to-finish expertise (design to production) to ensure project scope, cost, quality, and schedule best meet customer needs
• Procurement — source material and provide experienced advice for the best possible solution
• Quality Control — control plans, failure modes effects analysis (FMEA), production part approval process (PPAP), supplier quality engineering, and production audits ensure parts meet customer requirements
• Engineering — a capable engineering team that leads production process design, tool selection and custom design, CNC programming, and fixture design/build provides flexibility, shortens lead times, and enhances quality

Machine Shop Comparison: Precision vs CNC

• Precision machining involves removing material from a workpiece, or blank, to produce a part while maintaining tight tolerances. This is typically done by removing layers of material using milling machines, by turning, or using electrical discharge machining.
• Custom CNC machine work, a type of precision machining, is automated, enabling high accuracy and extreme precision (tolerances can be in the single-digit micron range). Not only can CNC machining attain a degree of complexity and customization that traditional precision machining technology can’t, it’s also efficient and cost-effective
• It’s really no contest. Higher production quality. Reliable consistency. Customization. Superior accuracy. Increased efficiency. Reduced labor costs. It’s no wonder that CNC machine shops boast better part performance and happier workforces.

The Machines of CNC Machining

• CNC machining centers are a significant investment, and machine shops leverage the industry’s best-in-class equipment and technologies to be competitive. As you’ve read, CNC machines are capable of making “precision parts.” However, when a CNC machine shop wants to make highly complex, ultra-high-precision parts, it requires advanced machinery, engineering, and proven processes to do it consistently and efficiently.

• Types of CNC machines vary greatly. Most perform one or more of the services mentioned above. Typical range of motion includes 3, 4, 3+2, and full 5 axis.
  • Milling Machine
    • Vertical
    • Horizontal
  • Turning Machine (Lathe)
  • Mill-Turning

Vertical vs Horizontal CNC Machines

There are two main spindle orientations in CNC machining. In vertical CNC machines, the spindle axis, which is called the z-axis, is oriented vertically. In a C-column configuration, the spindle travels in this direction, and the table which holds the workpiece moves in both x and y horizontal directions. Vertical machines are perfect for projects milled from one side, such as covers and brackets.

CNC Operators Help Grow Your Business

Simply put, a CNC machine operator transforms metal castings into working machined parts. Sounds easy, but it requires a unique mix of brains and hands-on attention to shape a metal casting into a part that meets exact specifications.

Responsibilities of a CNC Machine Operator

• Dilligence is vital for CNC machine operators because they’re constantly refocusing between different tasks: loading, unloading, deburring and inspecting parts, and changing tools. All tasks need to be completed thoroughly and timely.

Specific responsibilities include:

• Gathering supplies for each day’s work
• Communicating with other operators (usually about a machine or part quality)
• Checking loading instructions for a part
• Loading/unloading finished parts
• Deburring parts
• Monitoring tooling

• Quality control warrants a separate mention here. An eye for detail is one of the top traits of a high-end CNC machine operator. All parts are deburred — removing sharp edges and any small metal pieces still attached to the part after machining. Parts are sampled for in-process audits. Part dimensions are checked using different measuring tools: caliper, bore gage, pin gage, thread gage, depth gage, and both ID and OD micrometers. Parts are inspected by quality assurance on a Coordinate Measuring Machine (CMM) to verify all dimensions and positions are in tolerance.

An operator also listens to the machine during use, paying attention to anything that sounds different than normal and hearing the machine’s alarm for tool life being met. Want to see what else a CNC operator does? Review our blog, Day in the Life: What Does a CNC Operator Do?

What Training Does a CNC Operator Complete?

• Internal training for operators naturally happens within a machine shop as experienced operators pass along real-world knowledge and processes to new employees. Successful training takes a drive to learn and diligence to properly run machines.

CNC machinists can become operators of any number of machines, from a CNC lathe to a CNC robotic cell to many others (see “Types of CNC machines” mentioned above).

• External training can be gained at a local technical school or community college that offers classes in math, 3D design, blueprint reading, and specialized CNC machinist training.

The Importance of Casting

• Casting simplifies the process of forming a metal into a product. It eliminates the need for many parts to be put together; instead, molten metal is poured into a mold, and the cast is one solid piece.
  
  
• In metal manufacturing, cast parts straight from the mold most often require machining to be ready to use. Many mechanical features require machining to add characteristics that casting alone cannot do. CNC machine shops work parts to ensure they meet various specifications (shape, design, accuracy, etc.).

There are three methods of casting that are more common and cost-efficient than others:

1. Sand casting is the most versatile casting method for producing many products. A pressed pattern into fine sand forms the mold into which the metal is poured. Sand casting is a more expensive piece price process than die casting (see below), however it’s more economical for intricate designs, small quantities, and large castings. Because iron can’t be put under high pressure, sand is its only casting option.
   
   
2. Die casting forces molten metal into a steel die/mold, creating precisely formed parts (holding tighter tolerances) that require less machining and finishing. Die casting is often used for high-volume production because it’s faster. Die casting means a significant increase in the cost of steel tooling, however the right investment in tooling upfront results in a lower overall piece price.
   
   
3. Mold casting (permanent or semi-permanent) flows metal into the mold using gravity or low-pressure, as opposed to high-pressure die casting. Compared to other methods, permanent mold castings can often be stronger. Semi-permanent mold casting places sand cores in the mold to create internal passageways that are removed by burn/shake out. Tooling is more expensive than sand but less than die casting tooling.

• A cast part is considered “complex” if it’s large (and usually heavy, too…over 70 pounds), needs unique fixturing, has a tight tolerance, consists of a challenging material, or is difficult to control for pressure testing.
• Close relationships with foundries help CNC machine shops control part costs and quality, reduce timelines, and make changes smoothly, especially prior to production when changes aren’t cost-prohibitive. Often the lowest total cost requires balancing costs of casting and machining. For example, removing cast stock may reduce machining but increase fallout from porosity.

Finding a CNC Machine Shop that Offers DfM

You may have seen this stat: 80% of the cost to manufacture a product is determined in the design stage. Modern designers use design for manufacturing (DfM) guidelines to reduce costs while simplifying how a product is produced, reducing design rework, and maintaining overall quality. DFM is the merging of product design and its production method and can apply to designing parts or components.

Look for the 5 Areas of Emphasis in DfM

1. Process — Implementing DFM early in the process is key because as design progresses, changes become more and more expensive and difficult to implement.
2. Design — Challenging the design (by all stakeholders) helps ensure it’s optimized and simplified, which reduces the time and inventory required to make the product.
3. Material — Reviewing a material’s cost, physical properties, and machining properties promotes a wise choice (adequate physical properties but not overkill, for instance).
4. Environment — Scrutinizing the physical environment can help reduce the number of assembly operations required, so setup time drops as workflow improves.
5. Compliance/Testing — Testing and checking compliance are critical. An alignment error can damage parts and/or equipment, hurt productivity, or shut things down.

Demand These DfM Services
(and Enjoy Their Benefits)

• Partnering on the front end allows expertise and manufacturing knowledge to enhance the process while reducing potentially costly engineering design changes.
• A build process efficiency review ensures that product design and its method of production are scrutinized, making the process simpler and more cost-effective.

• In-house design team and fixture building provides the opportunity for expedited designs and tooling with very short lead times.

• Input on casting and machining designs prior to launch, including design review and Advanced product quality planning (APQP), saves money and increases agility during development.

• Prototype services allow for timely review of both cast and machine tools, which helps rapid prototype delivery.

• In-house robotics and PLC programming provide confidence that efficiency, repeatability, and flexibility are maximized from start to finish, whether its repetitive tasks or quality control.

Trends in CNC Machining

Computer-Aided Manufacturing (CAM)

• Software, such as MasterCam, helps program a part’s manufacturing by inserting a 3D computer-aided design (CAD) model into a virtual setup. Next, tool sets are added and operations are designed and simulated.

• Advanced collision detection mitigates this risk as well as improves part machining thanks to the simulation. This is especially beneficial as multi-axis machining becomes more common (see below).

• Tribal knowledge can be built into the CAM software, so years of experience is shared and used.

• Machinists can access instructions that incorporate a CNC machine’s platform, tool specifications, and best pathing, leading to less downtime and increased production.

Increase in Multi-Axis and Multi-Function CNC Machining Centers

• 5-axis and multi-function CNC machining centers add simultaneous control of a workpiece’s A-axis rotation in addition to and its XYZ motion and B rotation. Multi-function machines integrate functions like turning and milling.

• Combining operations is one benefit of more axes and multi-function machines, which means the labor cost per part is decreased. The number of operation steps (with potential for operator error) is reduced as is scrap. Eliminating re-fixturing improves accuracy.
• Machines can be upgraded with interchangeable rotary tables. A 3-axis machining center converts to a 3+2-axis machine by adding tilt and rotation of the workpiece. Or a machine can have dedicated, pre-installed rotary axes.
• Better CAM software inspires 5-axis machining centers by optimizing the use of guiding curves for tool pathing, which improves live-contouring material removal.

Robots

• Robots work alongside humans (not “instead” of them), and improve operator productivity by taking on repetitive work like loading and unloading.

• Reducing human error, which also improves daily production output, complements the improvements in tooling options and fixturing also realized with robots.

• Programming robots is straightforward, meaning they’re “taught” motions and behavior as a sequence of points and functions. For instance, an operator jogs a robot’s arm throughout an operation, teaching the points, and then the robot repeats it over and over. Operations can update robots to adjust to changes and issues without relying on engineering.
• Collaborative robots, or cobots, are new technology that work alongside operations and can assist in a simple task as well as a multi-functional manufacturing environment.

Industrial Internet of Things (IIOT)

• A software dashboard gathers and reports on incoming data from any number of operations within the industrial internet of things, or IIOT. Machines output data, which is used for monitoring/scheduling work and other software-augmented suggestions. One tool is CNC machine integration with Enterprise Resource Planning (ERP) software.
• Trends can be identified to help apply resources for effectively to improve operations. Also, any action taken can be measured and improved upon.
• Preventative maintenance improves with IIOC input, too, as predictive models plan for scheduled downtime.