Extrusion is a manufacturing process is a continuous (producing indefinitely long material) or semi-continuous (producing many short pieces) metal or plastic process used to create long objects of a fixed open or closed, cross-sectional profile. The material, in the form of a feed stock billet (large cross section of raw material) is pushed with high pressure forces and/or drawn through a die (mold) of the desired profile shape.  Hollow sections are created by placing a plug or piercing mandrel inside of the die. Plastics materials are hot drawn while others metal materials may be cold drawn through a die. 

       The feedstock may be forced through the die by various methods. A single or twin screw auger, powered by an electric motor, or a ram, driven by hydraulic pressure (for steel alloys and titanium alloys for example), oil pressure (for aluminum), or other specialized processes for the production of many simultaneous streams or coextrusion of the materials.  Cold drawn metals - like aluminum require extremely high extrusion - materials push force pressures into the die to create the friction and heat to plasticize the metal forming the continuous profile at other end.  Extrusion is also the first step in the process of extrusion and spheronization, a commonly used process in the pharmaceutical and food industry.  Commonly extruded materials include metals, polymers, ceramics and food.

Plastic extrusion is common for both rigid materials such as PVC pipe and vinyl siding for buildings.  Working with Innerface Architectural signs,  Mr. Whiteside was one of the first Industrial Designer's, leading a project for Rupert/Jensen & Associates (formally of Atlanta) is to develop an all plastic, modular post and panel sign system.  Project involved working with Mobay® Engineering Materials conducting and FEA analysis and GE®  Plastics Division to specify the extrusion materials that would meet the challenging environmental performance requirements.  Final extrusion material choice was GE Geloy® material giving the necessary mechanical strength and weatherability, with an interlocking sleeve extrusion and modular panel size.  (See Sign Light)

      
Extruded Plastic Post & Panel Sign System
Innerface® Sign Systems, GA

Impact Extrusion commonly used to make collapsible tubes such as toothpaste tubes, cans from soft materials such as aluminum, lead, tin.  Usually a small shot of solid material is placed in the die and is impacted by a ram, which causes materials cold flow up the sides of the ram creating a deep well with thin wall sides.

Hydrostatic extrusion  is a form of impact extrusion which uses a fluid hydrostatic pressure instead of a mechanical ram. Applications is best for making parts out of harder materials such as Molybdenum, Tungsten that are relatively difficult to extrude using normal extrusion methods.

Calendering  is where wide sheets of material are extruded then finished by calendering, a finishing process applied to textiles, paper, steel and plastic.  During calendering rolls of the material are passed between several pairs of heated rollers, to reduce thickness and give a shiny surface. (Example: Extruded PVC sheet)   In paper and plastic, luster or reflective shine increases when the degree of heat and pressure is increased. Calendering is applied to fabrics including cotton, many linens and silks, and various man-made fabrics