Plastic Machining Services Selection GuidePlastic Machining Services Selection GuidePlastic Machining Services Selection Guide

Image Credit: Delmar Company | General Plastics Manufacturing Co. | WS Hampshire, Inc.

 

Plastic machining services fashion or fabricate finished parts and components out of various plastic and thermoplastic stock materials. These services are utilized by companies that lack the proper equipment for manufacturing plastic parts in-house.

 

Machining Capabilities

Plastic Machining Services Selection GuidePlastic machining services may utilize a number of machining approaches that are favorable for working with plastics. Because plastics have lower hardness and melting temperatures than metals, not all metal machining processes are optimal for manufacturing plastics. Specifically, plastic machinists need to keep in mind a number of key differences between plastics and metals:

 

  • Thermal expansion with plastics is up to 10 times greater than with metals.
  • Plastics do not cool as fast as metals, so localized overheating needs to be avoided.
  • Softening (and melting) temperatures of plastics are much lower than metals.
  • Plastics are much more elastic than metals.

 

Image Credit: Precision Machining

 

Shops that specialize in plastic machining have optimized their fixtures, tool materials, angles, speeds, and feed rates based on these principles for achieving the best results. The most common plastic machining processes used are drilling, milling, and turning.

  • Drilling may encompass a number of different methods used to drill holes in parts.
  • Milling is a versatile machining process that can perform many different types of cuts on a workpiece.
  • Turning describes machining processes performed on a lathe, where a cutting tool is applied parallel to a workpiece being rotated continuously.
    • Screw machining is an automatic turning process used for the fast and accurate production of small- to medium- sized parts.
    • Swiss screw machining is a type screw machining used for producing high-finish, close-tolerance bearing surfaces on parts with small shafts.

Plastic Turning. Video Credit: CNC Woodturning

 

Some other, more specialized processes include abrasive flow/jet machining and laser machining:

  • Abrasive flow/jet machining processes direct jets of water or air containing abrasives at the material to be machined. The cutting action is a grinding process which results in a very small width of cut, allowing for precise machining.

Waterjet cutting. Video Credit: FedTech, Inc.

  • Laser machining is a material removal process accomplished by laser / material interaction.

Secondary Operations

Plastic machining shops may offer additional treatment operations for plastic parts after they are machined.

  • Plastic annealing or stress relieving is used to relieve residual stresses imposed during machining, welding, forming or other manufacturing processes. Residual stress can later cause curling, warping or cracking of the component.
  • Painting or coating adds decorative or protective finishes to the part.
  • Polishing operations are performed by using heat or flame, chemical, vapor or mechanical processes. Polishing and buffing processes are used to smooth and brighten plastic surfaces. Polished, clear plastic is important in products that require transparency (e.g., windows, guards, and optical components).
    • Mechanical polishing buffs parts or components with abrasive compounds, abrasive slurries, or fine-grit fixed-abrasives such as fining pads or film-backed coated abrasives. Mechanical methods can be applied to both thermoset and thermoplastic parts.
    • Flame-polishing melts a thin surface layer, and is used with both thermoplastics and glasses. Often, chemical and vapor-polishing methods involve proprietary technologies
  • Welding joins parts by melting and reforming a bond between materials, with or without using additional filler material.

Service Capabilities

Machine shops may offer a number of additional capabilities that correspond to the plastic machining services they provide.

  • CAD / CAM support - Service companies often have the ability to take computer-model design files electronically and use them for part creation. Clients should consult the suppliers for details on the computer aided design (CAD) and/or computer aided manufacturing (CAM) software they use and support.
  • Design assistance - The supplier may offer assistance 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.
  • Prototype services - Shops may provide services for building small quantities of representative parts for use in presentations and functional testing.
  • Low volume production - Shops may specify that they offer low volume production, meaning they can cost-effectively produce low quantities of parts for their clients.
  • High volume production - Shops may specify that they are capable of high volume production, meaning they are able to produce large quantities of parts in a reasonable time.
  • Reverse engineering - Some plastic machining shops can offer reverse-engineering of parts in order to provide part replication or duplication services. 

Other Considerations

The costs associated with a machine shop's services, along with the shop's location, are important to consider in the selection process.

 

Cost

The service cost is important to consider in any application. Quotes (cost estimates) for part manufacturing orders are given to the customer after he or she provides the shop with the part specifications or a description of the requirements. Cost typically correlates to the time spent producing the product and the expense of the plastic 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 shop is important to consider both for logistical reasons and expenses. Operations located farther away from the customer will have higher associated shipping costs, especially for large production volumes. In addition, there may be additional logistical complications when dealing with suppliers from different countries.

 

References

 

Guide to Plastics Machining - Boedeker Plastics, Inc.


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