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What is CNC Machining of PVC?

Author: Yaozu Deng
Published on: 2023-09-08

CNC machining of PVC (Polyvinyl Chloride) represents a significant advancement in the manufacturing industry. CNC machines use computer-controlled tools to shape PVC into various components.” 

Polyvinyl Chloride, commonly known as PVC, is one of the most widely used synthetic plastics. It is a versatile material with unique properties, which makes it valuable in various industries, from automotive to healthcare. PVC is known for its durability, affordability, and resistance to environmental elements. Additionally, it can be made into rigid or flexible forms, making it suitable for a vast array of applications.

Now, Let’s discuss What is CNC Machining of PVC?  and its different intricacies.

 

What is PVC Plastic?

Polyvinyl Chloride, commonly known as PVC, is one of the world’s most widely used synthetic polymers. It is a type of plastic made from vinyl chloride monomers (VCM). PVC was first synthesized in 1872, but it was not until 1926 that Waldo Semon and the B.F. Goodrich Company developed a method to make it flexible and suitable for commercial applications.

PVC sheets

Structure of PVC

PVC is a thermoplastic which can be softened by heating and hardened by cooling. This property makes it suitable for molding into different shapes. The molecular structure of PVC consists of two carbon atoms, three hydrogen atoms, and one chlorine atom arranged in a vinyl structure. The vinyl chloride monomers are polymerized to form polyvinyl chloride (PVC) resin.

Structure of V.C. and PVC

The polymerization process involves using a catalyst and heat to initiate a reaction that links the monomers to form a polymer chain.

  • Molecular Formula: (C2H3Cl)n
  • Monomer: Vinyl Chloride Monomer (VCM)
  • Polymerization: The process of linking monomers together to form a polymer chain.

Production of PVC

The production of PVC involves the following steps:

  1. Show of Vinyl Chloride Monomer (VCM): Ethylene and chlorine gas are combined to produce ethylene dichloride (EDC), which is then cracked to produce vinyl chloride monomer (VCM).
  2. Polymerization: The VCM is polymerized to form PVC resin. This can be done using different methods, such as suspension polymerization, emulsion polymerization, or bulk polymerization.
  3. Compounding: The PVC resin is mixed with other additives, such as stabilizers, lubricants, plasticizers, and pigments, to produce the final PVC compound.
  4. Processing: The PVC compound is then processed into the desired form, such as sheets, pipes, or profiles, using various methods such as extrusion, injection molding, or blow molding.

Furthermore, various additives are used in PVC to enhance its properties and make it suitable for specific applications:

Table: Common Additives Used in PVC

Additive Function Examples
Stabilizers Prevent degradation of PVC Lead, tin, calcium-zinc compounds
Plasticizers Make the PVC flexible Phthalates, adipates, trimellitates
Lubricants Reduce friction Paraffin waxes, metal soaps
Pigments Give colour to PVC Titanium dioxide, carbon black

 

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What Are the Different Types of PVC?

PVC is a versatile material that can used in CNC machining for many applications. There are primarily two basic forms of PVC: rigid PVC (un-plasticized PVC or uPVC) and flexible PVC (plasticized PVC). However, these can be further categorized based on their properties and applications.

Rigid PVC (uPVC)

Rigid PVC, or uPVC, boasts high tensile strength and exceptional chemical resistance. Its low water absorption and excellent electrical insulation make it ideal for construction. Used in pipes, window frames, and doors, uPVC is also prevalent in electrical insulations and medical devices. Its self-extinguishing properties ensure safety, making it suitable for containers, tubing, and other medical equipment.

Flexible PVC

Flexible PVC distinguishes itself with its adaptability and resistance to fire and water. It maintains good chemical resistance and electrical insulating properties. This type of PVC is popular in cable insulation and sheathing. 

Chlorinated PVC (CPVC)

First, What is CPVC? It stands out with higher heat resistance compared to uPVC and retains good chemical resistance. Its flame retardancy and mechanical strength are notable. Primarily, CPVC is used in hot and cold water pipes. It’s also essential in industrial piping systems and fire sprinkler systems, showcasing its versatility.

High Impact PVC

High-impact PVC is one of the most common materials for CNC machining. It is renowned for its resistance to impact and weather conditions. Alongside its chemical resistance, it’s a durable choice. The common applications of high-impact PVC include window profiles, signs, and displays. This type of PVC is also crucial in the automotive sector, highlighting its wide-ranging utility.

What Are the Properties of PVC Plastic?

Polyvinyl chloride is a versatile material with a wide range of properties that make it suitable for various applications. Let’s discuss the properties of PVC in detail, including its mechanical, thermal, electrical, and chemical properties with a detailed table.

  • Tensile Strength (MPa): Rigid PVC (uPVC) has a higher tensile strength (40-80) compared to flexible PVC (15-30), influenced by type and formulation.
  • Impact Strength (kJ/m²): PVC offers good impact resistance, enhanced in high-impact PVC. Standard PVC ranges from 2-20, while flexible types are 2-10.
  • Flexural Strength (MPa): uPVC shows higher flexural strength (60-90) than flexible PVC (20-40), dependent on type and formulation.
  • Hardness (Shore D): uPVC is harder and more rigid (70-85) due to no plasticizers, while flexible PVC is softer (55-70).
  • Elongation at Break (%): uPVC has a lower elongation at break (20-50) compared to flexible PVC (100-300), varying by type.
  • Melting Temperature (°C): PVC’s melting temperature is relatively low, with uPVC at 160-210°C and flexible PVC at 150-200°C.
  • Glass Transition Temperature (°C): uPVC’s glass transition temperature is around 80°C, slightly lower for flexible PVC (60-80) due to plasticizers.
  • Thermal Expansion (10^-5/°C): PVC has a low coefficient of thermal expansion (uPVC: 5-8, flexible PVC: 6-9), ensuring dimensional stability.
  • Thermal Conductivity (W/mK): PVC, both uPVC and flexible types, exhibits low thermal conductivity, making it an effective insulator (uPVC: 0.16-0.24, flexible PVC: 0.14-0.22).
  • Electrical Properties – Dielectric Constant: PVC has a low dielectric constant (3-4), suitable for electrical insulation in both uPVC and flexible PVC.
  • Dielectric Strength (kV/mm): High dielectric strength in PVC (uPVC: 40-60, flexible PVC: 20-40) allows it to withstand high voltage without breakdown.
  • Volume Resistivity (Ω.cm): PVC’s high volume resistivity (uPVC: 10^15-10^16, flexible PVC: 10^13-10^15) makes it an excellent electrical insulator.
  • Chemical Resistance: PVC, both uPVC and flexible, shows excellent resistance to most acids, bases, and salts, but not to aromatic hydrocarbons, ketones, and chlorinated solvents.
  • Water Absorption (%): PVC has low water absorption, making it suitable for water-resistant applications (uPVC: 0.1-0.5, flexible PVC: 0.2-0.6).

Source

The PVC CNC Machining  Considerations 

CNC machining is a subtractive manufacturing process where computer-controlled machine tools are used to remove material from a workpiece to create a finished part. PVC is one of the many materials that can be processed using CNC machining. However, due to its specific properties, several considerations must be taken into account.

Material Characteristics

Firstly, understanding the material characteristics of PVC is crucial for successful CNC machining. PVC is relatively soft compared to metals, but it is harder and less flexible than many other plastics. This affects the machining parameters, such as feed rate and cutting speed.

  • Rigid PVC (uPVC) has high tensile strength, chemical resistance, low water absorption, good electrical insulating properties, and is self-extinguishing.
  • Flexible PVC has good flexibility, chemical resistance, and electrical insulating properties, and is resistant to fire and water.
  • Chlorinated PVC (CPVC) has higher heat resistance than uPVC, good chemical resistance, flame retardancy, and mechanical strength.
  • High-impact PVC has high-impact resistance, good chemical resistance, and good weather ability.

Tool Selection

Tool selection is another crucial aspect of CNC machining of PVC. Since PVC is a softer material, sharp tools with a high rake angle are recommended. This helps in producing a smooth surface finish and reduces the chances of the material melting or deforming during machining. Additionally, using tools with a larger diameter can help in minimizing tool deflection.

Cooling and Lubrication

PVC has a relatively low melting temperature, which makes it susceptible to heat buildup during machining. Therefore, proper cooling and lubrication are essential to prevent the material from melting or deforming. However, traditional coolants and lubricants are not recommended for PVC machining as they can cause the material to swell or degrade. Instead, compressed air or a special plastic cutting fluid can be used to dissipate the heat generated during machining.

Feed Rate and Cutting Speed

The feed rate and cutting speed must be carefully selected to avoid excessive heat buildup and material deformation. A slow feed rate and high cutting speed are generally recommended for PVC machining. However, it is always advisable to perform a test cut to determine the optimal parameters for the specific type of PVC being machined.

Clamping and Work-holding

PVC is a relatively flexible material, especially in its flexible form. Therefore, proper clamping and work-holding are essential to prevent the material from moving or deforming during machining. It is recommended to use soft jaws or fixtures with a soft lining to avoid damaging the material. Also, the clamping force should be evenly distributed and not too high to avoid deforming the material.

Machining Strategies

PVC CNC machining

Different machining strategies can be employed when CNC machining PVC. For example, climb milling can be used to produce a better surface finish and reduce tool wear. However, conventional milling may be preferred in some cases to avoid excessive force on the workpiece. Additionally, using a smaller stepover and a larger step-down can help in producing a smoother surface finish.

Surface Finish and Post-Processing

PVC usually produces a good surface finish when machined properly. However, if a smoother surface is required, post-processing techniques such as sanding or polishing can be used. Additionally, PVC can be glued, welded, or mechanically fastened if required.

Click here to download:  CPVC Plastics and Its Properties 

 

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What Are the Common Tools for PVC Machining? 

PVC is a relatively soft and easy-to-machine material. However, it is important to select the appropriate tools for PVC machining to ensure a good surface finish and to prolong tool life. Here are some common tools used for PVC machining:

Tools for PVC CNC machining

  • End Mills: End mills are the most common cutting tools used for PVC machining. Solid carbide end mills are recommended for PVC machining as they offer better wear resistance and longer tool life.
  • Drill Bits: Solid carbide drill bits are recommended for drilling holes in PVC as they offer better wear resistance and longer tool life.
  • Router Bits: Router bits are used for edge finishing and surface smoothing. Solid carbide router bits are recommended for PVC machining as they offer better wear resistance and longer tool life.
  • Taps and Dies: Taps and dies are used for threading PVC parts. High-speed steel (HSS) taps and dies are commonly used for PVC machining as they offer a good balance between wear resistance and cost.
  • Saw Blades: Saw blades are used for cutting PVC sheets and rods. Carbide-tipped saw blades are recommended for PVC machining as they offer better wear resistance and longer tool life.

Table: Common Tools for PVC Machining

Tool Material Application
End Mills Solid Carbide General Machining
Drill Bits Solid Carbide Drilling holes
Router Bits Solid Carbide Edge finishing and surface smoothing
Taps and Dies High-Speed Steel (HSS) Threading
Saw Blades Carbide-Tipped Cutting sheets and rods

 

Applications of CNC Machined PVC Parts

CNC machined PVC part

PVC, being a versatile and cost-effective material, is widely used in various industries and applications. CNC machining of PVC parts allows for precise and complex components to be produced quickly and accurately. Here are some common applications of CNC-machined PVC parts:

  • Electrical: Due to its excellent electrical insulating properties, PVC is commonly used for electrical conduits, boxes, and insulations. CNC machining allows for the production of intricate electrical components with high precision.
  • Medical: PVC is used for various medical devices such as containers, tubing, and other medical equipment. CNC machining ensures the production of medical components with tight tolerances and high precision.
  • Automotive: PVC is used in the automotive industry for various components such as dashboards, interior trim, and cable insulation. CNC-machined PVC parts ensure a high level of precision and consistency.
  • Signage and Displays: PVC is commonly used for signs and displays due to its lightweight, durability, and ease of machining. CNC machining allows for the production of complex signs and displays with intricate details.
  • Industrial Piping Systems: PVC is widely used for industrial piping systems due to its chemical resistance and durability. CNC-machined PVC parts are used for pipes, valves, and fittings.

 

How Much Does CNC Machining of PVC Cost?

The cost of CNC machining PVC components varies widely based on several factors. First and foremost, the size and complexity of the part play a significant role. Larger or more complex parts require more material and longer machining times, which increases costs. Additionally, the machining method(CNC milling, CNC turning, or another technique) also influences the price. Different methods have varying levels of efficiency and precision, impacting both the cost and the suitability for specific designs.

Another critical factor is the level of accuracy required. Higher precision demands more sophisticated equipment and skilled labor, which can escalate costs. The finish of the PVC part, such as smoothness or texturing, can also affect the price. More intricate finishing processes require additional time and resources. Lastly, the quantity of parts ordered plays a role. Bulk orders can often reduce the cost per unit due to economies of scale, whereas custom or small-batch production may be relatively more expensive.

Real-World Cost Estimation Example

Consider a company needing custom PVC parts for a medical device. The parts are cylindrical, with dimensions of 50mm in diameter and 100mm in length. The chosen machining method is precision CNC milling, requiring a high degree of accuracy (±0.01mm) and a smooth finish to ensure compatibility with other device components.

Breakdown of Cost

  • Material Cost: For high-quality PVC, the cost is approximately $5 per kilogram. Given the size of the part and the density of PVC (around 1.38 g/cm³), each part weighs approximately 0.3 kg. So, the material cost per part is around $1.5
  • Machining Time: Precision milling of such parts might take about 30 minutes per piece. Assuming an hourly rate of $40 for CNC machine operation, the machining cost per part is $20.
  • Setup Cost: For a custom job, the setup cost includes programming the CNC machine and preparing the tools. This one-time cost can be around $200, which, when amortized over a batch of 1000 parts, adds $0.2 per part.
  • Finishing Cost: A smooth finish requires additional processing, such as sanding and polishing. This might add $2 per part.
  • Quality Assurance: High-precision parts, especially for medical applications, require thorough quality checks. This can add another $4 per part.
  • Packaging and Shipping: Depending on the destination, packaging and shipping can cost approximately $2 per part.

Summing these costs, the total estimated cost per part is $29.7. However, it is important to note that costs can vary significantly based on the supplier, geographic location, and current market conditions. For example, China’s PVC CNC machining services are more cost-effective than the USA/Europe or other regions. 

Related: A Cost-Effective Approach: Six Ways to Reduce the Manufacturing Cost of Plastic Parts 

 

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Prolean’s Plastic Machining Services: Accuracy and Perfection

In a world where plastic components are integral to various industries, it’s essential to choose a service provider with the expertise and experience to deliver high-quality parts. Prolean offers specialized plastic machining services that cater to a wide array of needs. Whether it is PVC or any other plastic material, Prolean can machine it precisely according to your specifications.

PVC

Apart from CNC machining, Prolean also offers services such as plastic welding, injection molding,  bending, and assembly. This means that you can get a complete solution for your plastic component needs, from initial machining to final assembly. Prolean ensures that each step of the process is conducted with the highest standards of quality and precision.

CNC Machining Service

If you need high-quality, precision-machined plastic components, our plastic machining services are the ideal choice. With their expertise, state-of-the-art technology, and commitment to customer satisfaction, Prolean is the partner you can trust for all your plastic machining needs.

 

Summing Up 

Polyvinyl Chloride (PVC) is one of the most widely used plastics worldwide, thanks to its versatility, durability, and cost-effectiveness. Its properties, such as high tensile strength, chemical resistance, low water absorption, and good electrical insulating properties, make it suitable for a variety of applications, from construction materials and electrical insulations to medical devices and automotive parts.

The ability to modify PVC by adding plasticizers, impact modifiers, or by chlorination, enables the creation of materials with tailored properties for specific applications. However, it is crucial to consider the environmental impact and safety concerns associated with PVC, as it releases toxic fumes when burned.

Overall, PVC is a crucial material that contributes significantly to various industries. Its machining considerations and applications underscore its importance and utility in today’s world.

 

FAQs

What is PVC?

PVC, or Polyvinyl Chloride, is a type of thermoplastic made by polymerizing vinyl chloride monomers.

What are the different types of PVC?

PVC comes in two basic forms: rigid (uPVC) and flexible. uPVC does not contain any plasticizers, making it rigid and strong, while flexible PVC contains plasticizers to make it more flexible and soft.

What are the properties of PVC?

PVC has good mechanical strength, chemical resistance, thermal insulation, and electrical insulation properties. It is also biocompatible and does not support combustion.

What are the applications of PVC?

PVC is used in various applications, including construction (pipes, window frames, siding), medical devices (blood bags, tubing), electrical insulation (cables, conduits), and packaging (bottles, food packaging).

What are the considerations for CNC machining of PVC?

CNC machining of PVC requires special considerations due to its low melting point, softness, and potential release of chlorine gas when heated. It is essential to use low cutting speeds and tool temperatures, sharp tools with high rake angles and low lead angles, and proper ventilation and safety precautions.

How can Prolean’s Plastic Machining Services help with my PVC machining needs?

Prolean’s Plastic Machining Services offers expert guidance, state-of-the-art CNC machines, and skilled technicians to provide precise, high-quality PVC parts for your application. Our team can advise on the best machining practices for PVC and help optimize your design for manufacturability.

 

Resources 

1. Titow, W. V. (1990). PVC Plastics: Properties, Processing, and Applications. Springer Dordrecht. https://doi.org/10.1007/978-94-011-3834-5

2. AZO Materials. (2001). Unplasticised Polyvinyl Chloride – Unplasticised PVC – UPVC. Retrieved from https://www.azom.com/article.aspx?ArticleID=770

 

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