Plastic Machining with CMS' Innovative CNC Solutions
There are countless types of plastics available, making it one of the most widely used materials in the world. Plastics are usually derived from petrochemicals, impervious to water and, depending on the application, can be substituted for a wide range of traditional materials such as wood, stone, glass, metal, and so forth.
Plastics are generally less expensive than metals, and many varieties offer comparable strength with significantly lighter weight. Commonly machined plastics include polypropylene, PVC, acrylic, vinyl, nylon, ABS, Torlon, Ultem, and Nomex. Plastic materials, including advanced engineering plastics, are very easy to process with the use of the right equipment. Plastic is readily cut, drilled, milled, and otherwise machined.
There's a increasing variety of "plastic" materials for different applications and uses, but the following represent a important selection of the most popular ones for thermoforming purposes—
- Acrylonitrile Butadiene Styrene -ABS
- Flame Retardant ABS - FRABS
- High Impact Polystyrene - HIPS
- High Molecular Weight Polyethylene - HMWPE
- Thermoplastic Olefin - TPO
- Thermoplastic Elastomers - TPE
- Thermoplastic Polyurethane - TPU
- Polypropylene - PP
- Polycarbonate - PC
- Amorphous Polyethylene Terephthalate - PETG
- Acrylic - PMMA
- Poly Vinyl Chloride - PVC
Physical/Chemical Properties of Plastics
Plastics are classified as of two types: those that are "thermoplastic" and those that are "thermosetting polymers". During processing thermoplastics do not undergo a chemical change when heated and can be even be remolded again. PVC is a good example of such a thermoplastic material. Thermosetting polymers, on the other hand, can only melt and be formed but once. Following that process they remain solid. The thermosetting process involves a chemical reaction which can not be reversed.
Plastic materials may be made from synthetic, semi-synthetic, or natural materials. Most plastics are manufactured from petrochemicals, but plastics made from plant materials (called bioplastics) are increasingly common.
Because there are so many different types of plastic, the physical properties of the material can vary considerably. Hardness, density, and resistance to heat, solvents, oxidation, and other factors are affected by the organic chemistry of the polymer.
Plastic materials, including advanced engineering plastics, are very easy to process with the use of the right equipment. Plastic is readily cut, drilled, milled, and otherwise machined. However, because of the varying physical characteristics of different types of plastic, certain factors must be accounted for.
Plastics are comparatively much softer than metals, as well as having greater elasticity. These properties can make it difficult to maintain tight tolerances during and after machining.
Plastics also have much lower softening/melting temperatures and greater thermal expansion rates than metals. A mist or full-flood cutting system can be used to reduce the heat generated in machining and minimize the effects of high temperatures.
Machining plastic can produce a large amount of dust and swarf. A full-flood cutting system, or one with dust extraction capabilities, can help eliminate particles from the machining environment.
Modern automobile dashboards are made with more engineered plastics than ever before, from individual components to complete panels. There are dozens of parts involved, all of which must match exact dimensional specifications to provide proper fit and function. CMSNA’s advanced CNC technology provides the multi-axis capabilities, high speed, accuracy, reliability, and rapid tool changeover automakers need for the start-to-finish cutting and machining of dashboards and related components...
Thermoformed plastic parts are widely used in home and building construction. Everything from shower stalls to vent covers to lighting components falls into this category. CMSNA’s CNC machining centers provide the versatility and flexibility needed to quickly and accurately produce these essential and wide-ranging parts...
There are countless products which owe their existence today to the countless types of thermoformable plastic materials currently available. Making thermoformed plastic products a large part of an enormus market. Plastics are generally less expensive than metals, and many varieties offer comparable strength with significantly lighter weight. Commonly machined plastics include polypropylene, PVC, acrylic, vinyl, nylon, ABS, Torlon, Ultem, and Nomex...
Plastic Machining on a Fiat Instrument Panel
Because thermoformed parts like this often involve a lot of contoured surface area, the job of holding and machining these parts by vacuum can be difficult. The Athena shown here features a highly functional, automatic part holding system. The operator places the part on the fixture’s saddle, where it is held in place via a CNC-controlled, pneumatically activated upper hold-down. The hold-down is cushioned to ensure secure holding without marring the part’s surface.
The part is easily referenced in the saddle. All areas to be trimmed are left open for access by the 5 axis trimming head, and the secure holding of the part makes for high quality edge trimming and faster cutting.
The system’s 5 axis trimming spindle includes an automatic tool changer. For this task, it has been filled with extended length tool holders to reach all cutting locations, which, on this part, are all close to the edge of the holding fixture.
A second tool change is carried out toward the end of the cycle to execute a fine inletting operation. This demonstrates Athena's ability to carry out fine, delicate work requirements as well as the everyday demands of production.
Trimming a car top carrier with a double spindle head
Athena, the entry point in CMS range of CNC machining centers for plastic, is shown here equipped with a special holding fixture which adjusts to the various sizes of a thermoformed car top carrier line of product.
In addition, Athena is provided with a special double spindle head which allows for one of these to be an ATC unit, while holding a saw blade mounted on a shaft in the other spindle. The double spindle revolver makes fast work of tool changing, while the ATC unit provides flexibility for the range of routing tools for trimming and slot work that may be required.
The first work shown is that of drilling holes, some of which are interpolated to obtain a larger diameter hole, without the need of changing tools, and cutting a slot in the car top carrier shell.
The second work takes place with the rotating of the head to a vertical position, which brings the saw blade in to work. The blade makes a fast trim cut all the way around the car top carrier to separate it from the flashing, which will become scrap.
Trimming thermoformed wheel cover
This video shows the trimming work on a thermoformed wheel cover. The thermoformed part will yield two components when the process is finished.
The holding fixture for the part is mounted on a standard table and incorporates vacuum to hold it in place during the machining work.
The work involves machining slots, drilling holes, cutting openings, and finally changing out the router bit for a saw blade to make the separation cuts which yield the two finished components in the end.
The 5-axis head makes fast work of all the cuts while continuing to be "normal" to the surface, whether during routing or sawing and its ample work envelope makes jobs of various sizes uncomplicated.
Surfacing high density foam model
The video shows a project being carried out by CMS Plastic's division CNC machine Athena for the finishing surfacing work on a model. The material is a high density polyurethane (PU) of 10 pounds/cu ft.
The complete project involves roughing passes which have already taken place, so that the excess material has first been removed from the block.
In his phase of the work, Athena is carrying out the finish surfacing passes using a "ball end" mill with a small step-over so that the resulting surface will be a smooth and ready for the next step.