Image Credit: CMF Industries | The Federal Group | 3 Dimensional Services Group

 

Computer numeric controlled (CNC) machining services use fast, repeatable, and programmable machines to manufacturer parts quickly and efficiently. CNC machines use CNC controllers to consistently perform complex cuts which would be too difficult or time-consuming to produce manually. Companies and individuals without precision machining tools and repeatable part production capabilities can save time and money by utilizing these services rather than undertaking the manufacturing process themselves.

 

In short, CNC machines offer these benefits:

  • Fewer mistakes caused by human error
  • Consistency and repeatability
  • Precision and accuracy
  • Fast production
  • Reduced waste
  • Reduced operator/labor costs

How CNC Machining Works

Modern CNC machining services are automated using computer-aided design (CAD) and computer-aided manufacturing (CAM) software. For simple designs, a CNC machine programmer will input the program commands for the cutting machine by hand. For more involved designs, a CAD  or CAM drawing of the part is generated and is integrated into the system. Alternatively, coordinate measuring machines (CMMs) can be used to physcially map the object to the system. Once the part design is in the system, software automatically generates and programs the steps necessary for the machine to form the product. During operation, the machine follows this programming to precisely shape the part from a workpiece of a specified size. The operation can be repeated any number of times, allowing for the fast generation of nearly identical parts.

 

Here is an example of a CNC milling machine cutting a face out of metal:

 

Video Credit: leehound

 

Early CNC machining processes took time to program and were best used only in high production (high volume) tasks. But today's complex tools and software allow for direct export from a computer generated model to a machining program. This results in a quick turn-around, making even low volume work practical and affordable.

 

CNC Equipment

There are a number of devices which are used in CNC machining.

 

  • Mills, routers, or milling machines are cutting machines which shape solid (typically stationary) workpieces using a movable and rotatable cutting tool. Milling machines can perform anything from simple keyway cutting to complex contouring tasks, and come in either vertical or horizontal orientations. 

 

 

 

 

 

 

 

Image Credit: Fabricating and Metalworking

  • Lathes are machines that cut cylindrical workpieces by rotating them at fast speeds against a stationary cutting tool. Because the cutting action on a lathe is uniform, they can only make symmetrical cuts. Lathes have direct application to making parts such as shafts and bushings.

 

 

 

 

 

 

Image Credit: Little Machine Shop

  • Grinders or grinding machines are tools used to grind down parts using abrasive wheels as cutting tools. They are commonly used for high accuracy surface finishing, but can also be used for grinding larger volumes of metal depending on the application. They are typically the easiest type of CNC machine to work with.

 

 

 

 

  • Electrical discharge machines (EDMs) remove and form material using an electrical discharge (spark machining, die sinking, or wire erosion). These machines typically work with hard metals which are much more difficult to machine via other methods.

 

 

 

 

 

 

 

 

Image Credit: K&K Productivity Solutions, Inc.

  • Water/abrasive jet machines use abrasives propelled in a high velocity gas or water to cut workpieces. They are designed to cut and shape heat-sensitive, brittle, thin, or hard materials, and can form intricate shapes.

 

 

 

 

 

 

 

Image Credit: Waterjetcuttingworld

 

Capabilities

When searching for the right CNC machining service, the company's capabilities must first be sufficient to produce the customer's product or parts.

 

Techniques

A CNC machining service's capabilities (i.e. what parts it can make and of what quality) will depend most prominently on the type of cutting techniques it can perform.

  • Drilling - drilling holes in a part or workpiece.
  • Milling - cutting and forming using a milling or other cutting machine.
  • Turning - reducing the diameter and shaping of a workpiece using a lathe.
  • Broaching - planning or shaping process to enlarge, shape, or smooth a bored or drilled hole, and remove material between adjacent holes.
  • Deep hole drilling- drilling and boring of deep holes using trepanning, gun drilling, ejector drilling, and other similar methods.
  • Etching / chemical milling - treatment of a prepared metal surface with acid or other chemical reagent to remove select material for intricate design needs.
  • Honing - use of abrasive stones or silicon-carbide slips to obtain a specified finish or dimensional tolerance.
  • Jig boring - process involving centering, drilling, reaming, counter boring, contouring, through-boring, and step-boring.
  • Laser machining - use of a laser for precise material removal, including drilling, cutting, grooving, marking, and scribing.
  • Screw machining - turning process for rapid and accurate production of duplicate parts from various materials.
  • Swiss machining - screw machining process used when high-finish, close-tolerance bearing surfaces are required on small shafts. Provides a higher quality product than a ground finish.
  • Electrode/wire EDM - use of an EDM to cut hard, high density materials when physical machining would cause excessive wear.
  • Water / abrasive jet machining - cutting method involving a pressurized fluid stream (gas or liquid) containing abrasive particles. Designed for precise machining of heat-sensitive, brittle, or hard materials.
  • Superabrasive machining- use of grinding wheels made from extra hard materials (e.g. diamond, borazon) resulting in close tolerance and less tool wear.

Number of Axes

The number of axes is the number of planes that a CNC machine can work on. More involved machines can manipulate the cutting tool and the workpiece in more planes to perform more complex and intricate cutting. Machining capabilities can range from 2-axis to 5-axis.

 

    

Milling machine axes: 3-axis (left) and 5-axis (right) - Image Credit: Sandvik Coromant

 

Specialty Machining Techniques

Certain CNC machining services are designed to manufacturer specific types of products or parts for a specific industry. Specializations include:

  • Gears
  • Jigs and fixtures
  • Cast parts
  • Forged parts
  • Extruded parts

Materials Serviced

Machining services may only be able to handle certain types of materials depending on the capabilities of the equipment and the intrinsic properties of the machining services. For example, most standard milling machines and lathes could not adequately handle metals with high hardness without excessive wear of the cutting tools. Temperatures-sensitive materials would also limit the applications of many standard machining processes which generate high heat from friction.

 

Part Dimensions

A service provider may only be able to machine parts of a certain range of sizes, since machining equipment must be able to adequately fit the workpiece and make size appropriate cuts. These capacity ranges are specified based on diameter and length.

 

Secondary Treatment

After machining, manufacturing services typically provide secondary operations for further treatment of the part(s) or product(s).

  • Anodizing -   Anodizing is a galvanic finishing process well suited to aluminum and its alloys.  Anodized finishes can be hard for wear applications, or can include corrosion-resistant properties. The finishes are available in a wide variety of colors.
  • Black oxide -   Black oxide is applied as an anti-corrosion treatment for a variety of steels.
  • Electroplating - Electroplating is a finishing process often used for materials such as brass, bronze, and copper. A wide variety of colors and textures can be achieved.
  • Heat treating / stress relieving- Heat treating is a broad category of processes used to treat metals (e.g., annealing, passivation, hardening, etc.). Stress relieving is used to relieve residual stresses imposed during the stamping process.
  • Lapping / polishing -   Lapping and polishing processes use abrasive materials to smooth, polish, and brighten surfaces.
  • Painting / powder coating -   Painting and powder coating apply decorative and/or protective finishes. Typically, coatings are thicker than plating or anodizing operations.
  • Welding - Welding joins parts by melting and reforming a bond between materials, with or without additional filler metal.

Additional Services

CNC machining services may provide a number of additional services on top of the actual part production.

  • Assembly services - Suppliers assemble components of products/parts for the customer.
  • CAD / CAM support - Suppliers can receive solid-model files electronically and/or use those files for part creation. Consult the supplier for details on computer aided design (CAD) software, computer aided manufacturing (CAM) software, and support capabilities.
  • Design assistance - Supplier can assist with concepts, manufacturing costs, manufacturing techniques and material considerations. Suppliers may also be able to assist in upgrading or redesigning, re-evaluating or modernizing existing products to increase performance and/or reduce manufacturing costs.
  • Just-in-time delivery - Suppliers have just-in-time (JIT) manufacturing capabilities of components in order to reduce the need for inventory maintenance.
  • Prototype services - Suppliers can build a small quantity of representative parts for use in presentations and functional testing.
  • Reverse engineering - Suppliers can reverse-engineer a part to provide replication or duplication services. 

Other Considerations

Once all of the service criteria for part production have been met, factors such as cost and location need to be added to the equation.

 

Cost

The cost of a service is important to consider in any application. Quotes (cost estimates) for orders or services are given to the customer after he or she provides the supplier with a description of the job requirements. Cost typically correlates to the time spent producing the product and the expense of the materials used (when purchased by the service company). Additional costs include transportation or shipment costs of the parts once they have been made.

 

Location

The location of the service provider is important to consider both for logistical reasons and expenses. Operations located farther away from the customer will have higher associated shipping costs. In addition, there may be additional logistical complications when dealing with suppliers from different countries.

 

References

 

CNC Concepts, Inc. - What Is CNC?

 

Technology Student - CNC Work - An Introduction

Read user Insights about CNC Machining Services

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