Posted April 29, 2021

Going From Design to Production With CNC Milling

Programming a CNC milling machine for production


Modern prototyping methods and machinery allow manufacturers of new products to avoid errors and bring products to market more quickly than ever before. CNC (computer numerically controlled) machining processes increase efficiency by automating part production and prototyping, decreasing the time it takes to bring a part to market and reducing the chance of human error. CNC technology continues to lead innovation in the digitalization of the manufacturing sector. CNC machines include mills and lathes, also known as milling and turning. The decision to use one or both depends on a part’s design. This article will detail the process of going from design to production with CNC milling.

Prototyping with CNC Milling Machines

A CNC milling machine holds material in place with a mounted workholding within the machine. A machine tool then rotates and moves around it, sequentially removing material. A spindle holds the cutting tool, which spins at pre-set RPMs. Designed for precision, machine shops use CNC milling to manufacture parts in full-scale, intermediate, small-scale, or solo production runs using various materials. CNC milling techniques produce parts with tolerances ranging from +/- 0.001 inch (0.0254 mm) to +/- 0.005 inches (0.127 mm), though specific milling machines can reach tolerances of +/- 0.0005 inch (0.0127 mm). These tight tolerances make CNC mills particularly effective in many industries when manufacturing parts or prototypes. 

Milling Types

There are multiple ways to set up a CNC mill for machining operations. 

CNC mill setup includes: 

  • Angular milling involves angling the tool’s rotary axis toward the surface of the material. 
  • Face milling requires that the rotary axis is perpendicular to the worked material’s surface; this process uses tools with more teeth than other milling processes while those teeth directly in contact with the material perform finishing work. 
  • Form milling creates components without flat surfaces, and machines that use this technique can manage multiple tools to shape the material to the required curve. 
  • Gang milling employs two or more cutters—usually of varying sizes, shapes or widths—to perform cutting operations simultaneously, producing intricately designed components more quickly than other methods. 
  • Gear cutting involves producing teeth for gears with rolled gear cutters, which come in various pitch sizes and shapes depending on the number of teeth needed. 
  • Plain milling (also called surface or slab milling) involves cutting tools that use a rotary axis that lies parallel to the surface of the material, commonly used to create flat surfaces. 
  • Profile milling uses the machine tool to cut a path along angled or vertical surfaces by employing specific cutting tools and milling equipment working perpendicular or parallel to the surface. 
  • Straddle milling refers to milling methods where a machine cuts two or more parallel workpiece surfaces singularly, employing two cutters on the same machine, arranged to mill both sides simultaneously from either side of the material. 

Because of their versatility, CNC milling machines can conduct other machining processes to bore, drill, ream, or tap material as well. All of this is possible because of the advanced software machinists use to program tool paths.

Design Software Capabilities

Making custom parts on CNC machines starts first with the CAD (computer-aided design) models of the part provided by the customer. Specialized software generates the machine G-code that will direct the tool paths of the mills and lathes. This software works together with CAM (computer-aided manufacturing) systems to generate the G-code—done on a separate computer workstation. Once generated, a programmer will load the G-code into the appropriate mill or lathe and instruct the machine where and how fast to move the tools and workpiece to cut the material down to the requisite shape.

Modern CNC machines have multiple capabilities built into them, including advanced user interfaces that allow for easy interaction between the operator and the machine. Older machine software was comparatively complex, with many features tending to be underutilized. Gaining proficiency required extensive user training or developing familiarity with the machines over time.

In addition to these advances in CNC machine technology, there are other cutting-edge software systems in today’s modern machine shop. These are the measuring and reporting systems that monitor the part dimensions and tool usage of the CNC machines. This data is reported back through the network of the shop into the software system that generates the G-code from the customer’s CAD models. Smart learning systems like these refine the tool paths programmed into the machine's G-codes, improving the overall efficiency and quality of parts.

Materials

Both milling and turning machines are compatible with a wide range of materials. The main difference is in how the material is machined. Modern CNC machines’ ability to work metals, plastics, and composites makes them extraordinarily adaptable. CNC milling machines can machine almost any material, but the most common material is metal. Because of the technology’s flexibility, CNC machine shops can often order a particular alloy or material if necessary. A qualified machine shop will help determine the machinability of a design’s chosen material.

Understanding & Using CNC Milling Machine Tools

Depending on how tools move determines CNC milling tool paths and the number of axes involved, machinists classify them as continuous 5-axis, 5-axis-indexed, and 3-axis machining, which accommodate approach vectors for complex geometry from any angle. Tools fit into spindles, allowing machines to perform cuts and otherwise shape workpieces while also automatically changing inserts when needed. 

CNC milling involves both drilling and cutting, using cylindrically shaped cutting tools that rotate rapidly. A workholding precisely aligns and positions the workpiece, and tools move along a linear axis to remove material. Milling machines use rotary cutters to remove material. The two most common cutters are end mills and face mills. Face mills perform horizontal cutting, while end mills use both the ends and the sides to cut.

Most commonly used types of CNC milling tools include: 

  • ball heads
  • bull heads 
  • drills 
  • fact cutters 
  • flat heads
  • slot cutters 

Along the center axis, drills and other cutting tools can shape material geometrically. Drills also make holes. To create cavities, grooves, or walls, operators can use ball, bull, or flat heads, with each head’s geometry allowing the machine to shape the workpiece’s features. Slot cutters have smaller diameters than their cutting edges, which can cut T-slots and undercuts. With bigger diameters, face milling cutters subtract material from large, level surfaces to produce clean and flat surfaces in fewer passes. 

After milling, a part gets a custom surface finish. For going from design to production with CNC milling, one should first find a qualified machine shop.

Finding the Right Custom Milling Services for Precision Parts

Finding a reliable CNC machine shop that offers custom milling services for parts requires that the customer understand some machining basics. Although, a machine shop can help determine whether milling or turning is appropriate for a design. Sometimes a design will utilize both processes. Different machine shops offer various advantages for a given application.

When choosing a CNC machine shop, consider these things:

  • Ensure they have a compliant quality management system (QMS) that demonstrates its capabilities to provide products and services that meet regulatory and customer requirements. At a minimum, shops should be ISO 9001 compliant, though the IATF 16949 standard complements this. 
  • Look at whether their engineering department follows DFM protocols (Design for Manufacturing or Design for Manufacturability), which increases efficiency.
  • Industry experience, particularly with custom parts, ensures the company can better identify and fix any issues.
  • Positive feedback from satisfied customers indicates quality and good customer service.
  • A good reputation for quality and precision, often resulting from being in business for a while.
  • Transparency in communications. 

As custom CNC machining services require a high level of expertise, investigating testimonials and reviews from previous clients helps ensure their aptitude and confirms their reputation. 

If you’re looking for custom milling services for parts, look to Plethora. With our years of experience in CNC milling and proprietary software, we provide our customers with an advantage over competitors. Call us at 415-726-2256 to see what we can do for you, or go directly to Quote My Part to get started today. 

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the-plethora-team

The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: Design, Manufacturing, finishing, CNC machining, Quality, Prototyping, manufacturing trends, CNC milling

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