Thermoforming
Thermoforming is the process of creating a form from a flat sheet by combinations of heat and pressure, which first soften the sheet and then form the sheet into some three-dimensional shape. This is one of the simplest, more economical plastic forming processes. There are numerous variations of this process. There are three types of thermoforming: roll-fed, sheet-fed and in-line.

Thermoforming offers many distinct advantages over other shaping methods: lower tool mold cost that is one-tenth that of injection molding, the use of water cooled aluminum tools providing surface temperature control, simplified formation of laminates containing layers of different materials and higher production /throughput capabilities.

Thermoforming provides significant time and labor savings when producing large parts in smaller quanities. Design through final product (art-to-part time) is substantially reduced when using thermoforming. Other important benefits are low machine cost and short delivery time.

Compared to injection molding, thermoforming uses significantly less energy in order to form parts, often using sheets of different color and thickness for each part, resulting in lower mold costs and shorter lead times. The process also produces more stress-free products that resist cracking and is often the most cost-effective method to form large parts.

Thermoforming's disadvantages include the need to use more expensive plastic sheet rather than resins in pellet form, the required trimming operation, and the related problems of scrap storage.

For more information, please contact Mike, at Ultra Acrylics, Inc.

The poor thermal conductivity of plastics requires that care is taken to prevent the area being machined from getting too hot. The type of tool, depth of cut, rate of feed and coolant flow may have to be adjusted. If a coolant is used, make sure it does not chemically attack the plastic.

Check the supplier literature for recommendations on the types of tools and speeds to be used with a specific material.

Tolerances
Many designers will arbitrarily put a +/-.005 in tolerance on a part if it is to be machined. Quiz the designer to determine if the tolerances can be increased. Look at a ruler to visualize the size of the tolerance and think about the tools available to make the cut. Work with the designer to specify the tolerances really needed to make his part work and discuss what can actually be produced with the equipment available.

For more information, contact Mike at Acrylics, Inc.

Annealing is the baking of a material, without melting or distorting the part, to relax the internal stresses. The internal stresses are usually caused by uneven cooling. This means that the outside of the part cools much faster than the inside when the blank is made. This uneven cooling can also cause variations in the properties from the outside to the inside.

In today's challenging marketplace, the fabrication of plastic materials can add value for your customers. Following is an overview of the various fabrication techniques for stock shapes.

Machinability
Plastic stock shapes may be easily machined. However, the tool geometry and speed must be adjusted for optimum performance with a special material. The tolerances for machining plastics usually should be larger than those applied to metals. The tolerances must be larger because of thermal expansion and the shape changing from the relaxation of internal stresses within the material. In critical applications, it may be necesssary to premachine the part slightly oversize and stress relieve or anneal the part before taking the final cuts.