by Denise Sullivan Denise Sullivan No Comments

CNC Machining Basics

cnc machining

Computer Numerical Control (CNC) machining is a manufacturing process that uses pre-programmed computer software to dictate the movement of the tools and machines. It allows devices such as lathes, mills, and grinders to cut three-dimensional objects.

To understand CNC machining, we are going through a basic overview of CNC machining, including terminology, how they work, and the advantages and limitations of a CNC machine.

Terminology

Understanding the terminology associated with CNC machining is the first step to understanding CNC machining. CNC stands for computer numerical control. A computer and CAM software are used to animate, control, and observe the motions of the machine using digital data. 

CAM stands for computer-aided machine or manufacturing. It uses different software programs to generate tool paths and NC code for a CNC-operated machine based on data from 3D computer models. CAM only uses CAD to generate code for the device to follow. 

CNC machines could be robots, sheet metal stamping machines, lasers, grinders, lathes, water jet cutters, or welders. The computer controlling these machines is often an onboard controller. However,  the controller may also be an external PC.

How Do CNC Machines Work

CNC machines cut a desired piece based on what is programmed into the system. Therefore, it begins with designing the component. This step is necessary to establish the dimensions and features of the finished product.

Often the component design takes place in a CAD-CAM package. It allows the flow to continue through the program without going through file translation. Suppose they are not in the same package or software package. Then the CAD models will have to be imported into the CAM software.

Designing the component using CAD software allows you to construct the real piece and see what it looks like on the screen. The program is a code generator for the CNC machine that compiles coordinates to direct the cutting head during the manufacturing process. 

The final step in CNC machining is to choose the proper parameters. These include:

  • Voltage
  • Cutting speed
  • RPMS

The software will choose how the parts are arranged and oriented in relation to the raw materials. The part shape and tooling influence the configuration of the other parameters and equipment used.

Open and Closed Loop CNC Machining

CNC machining takes place in either an open-loop or closed-loop system. Open and closed-loop refer to the control process of the system. The position of the piece is determined by the type of system used.

The signal runs in a single direction between the CNC and the motor in an open-loop system. This system uses stepper motors, but the use of stepper motors doesn’t necessarily indicate an open system.  This system is commonly used when the forces and speeds are minimal.

In an open system, once the motor is in place, the controller has no feedback. That means unless a limit switch is tripped, the controller runs the operation as if there are no errors. 

A closed-loop system allows the controller to receive feedback. Because the controller can receive feedback, the controller can rectify irregularities and correct errors when necessary. There are two types of closed-loop systems. With the first type, the return signal feeds directly into the controller. The other type returns the signal feedback to the PC running the program.

A closed-loop system is necessary to ensure speed and consistency. It is the ideal choice for accuracy in creating a part. However, because there are more working parts, they have more components that can fail and be harder to tune.

CNC Machining Advantages

There are many advantages of using CNC machining for part manufacturing. For one, it is an excellent method for producing multiple parts that are identical to one another. If you need upwards of 100 parts, CNC-machined parts are more cost-effective than 3D printing.

CNC machining creates precision pieces. With a tolerance of +/- 0.127mm, machined parts come down to +/- 0.005mm. The equipment can produce them quickly. 

CNC machines can be used with various materials. Alloys such as zinc and magnesium are standard materials. In addition, aluminum, steel, brass, and titanium are common choices.

Limitations

While CNC machining has many advantages, the process has several limitations. One of them is using older machines to perform this process. CNC machines require a system that can perform demanding tasks. As a result, older computers and devices may not be able to handle the tasks.

Another limitation is that most CNC controllers may be constrained by only comprehending circular arcs and straight-line motions. Archs are often allowed on the main XYZ planes. However, some parts require a five-plane rotation that some controllers can’t comprehend. 

Conclusion

CNC machining is a significant advancement in manufacturing with the aid of computer technology that will give you accurate parts. It is a quicker and more efficient way to produce parts. 

PVDF is used extensively in pumps, valves, fittings, and pipes
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

The Basics of PVDF

Kynar PVDF (property of Arkema) is a high purity polymer that combines extreme-temperature performance, easy manufacturability, and durability in some of the harshest environments. 

What is PVDF?

PVDF (polyvinylidene difluoride or polyvinyl fluoride) is a fluorinated thermoplastic resin that is classified as a specialty polymer whose brand names include Kynar (Arkema), KF (Kureha), and Solef or Hylar (Solvay). This engineering polymer can often be found in environments that involve high purity, hot acid, extremely high temperatures, and/or radiation. 

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Injection Molding of Fluoropolymers
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Injection Molding of Fluoropolymers: What You Need to Know

Injection Molded Parts

Fluoropolymers are used in multiple industries, including aerospace, transportation, chemical and petrochemical processing, pharmaceutical, medical, telecommunications, and electronics where they are used for seals, gaskets, bushings, bearings, hoses, tubing, wiring, and even fiber optic cladding. There are multiple ways to manufacture parts and components made from fluoropolymers, and injection molding is one of them.

What Are Fluoropolymers?

Fluoropolymers, as the name no doubt implies, are polymers that are based on bonding between fluorine and carbon. The first fluoropolymer was PTFE (polytetrafluoroethylene), which is perhaps better known by its trade name Teflon. Other common fluoropolymers include ETFE (ethylene tetrafluoroethylene), PFA (perfluoroalkoxy alkane), PVDF (polyvinylidene fluoride), PVF (perfluoralkoxy), FEP (fluorinated ethylene propylene), and ECTFE (ethylene chlorotrifluoroethylene).

They are popular materials because of their properties that include resistance to high temperatures, chemical attacks, and electrical current. They are also low friction, non-toxic, exhibit minimal aging and leaching of chemicals, and non-stick. In addition, many fluoropolymers are biocompatible, making them ideal for medical applications.

Injection Molding Process

Injection molding is a manufacturing method for thermoplastic materials where the plastics are heated almost to their melting point and then fed into aluminum or steel molds at extremely high pressures using a powerful screw mechanism. There are several benefits to injection molding:

  • Can handle high-volume production
  • Labor costs are relatively low
  • Products highly accurate parts that can meet tight tolerances
  • Consistent results
  • Supports fairly complex designs with fine details
  • Produces an excellent surface finish
  • In many instances, the scrap can be recycled

The major cost involved in injection molding is the tooling: to achieve good results, the molds must be high-quality and well designed. However, molds can be configured to make multiple parts at one time with minimal post-processing.

Note that injection molding can be used to manufacture otherwise challenging components, including thin-walled parts. The feasible envelope for parts can typically range from 0.01 in³ to 80 ft³ (depending on the fabricators’ capabilities) and can achieve tight tolerances and smooth surfaces.

Injection Molding Fluoropolymers

While fluoropolymers can be challenging to injection mold, the process is not impossible for most materials. Some of the best fluoropolymers for injection molding include PFA and FEP, which are both melt-processable. Additional consideration may have to be given to the tooling for molding fluoropolymers, including a hot runner system to keep the polymer flowing easily as it moves through the mold. 

PTFE, however, is challenging to injection mold because even when heated above its melting point because it simply will not flow like other thermoplastic polymers. It does soften, but not enough to make injection molding possible. Fortunately, there are several other options when it comes to manufacturing with PTFE, including machining, compression molding, cold extrusion, and isostatic pressing.   

Conclusion

Fluoropolymers are widely used in many different industries and applications. If you are looking for an effective way to reliably manufacture components using a fluoropolymer, injection molding may be an excellent option.

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