Melt Expansion refers to the fact that all plastics expand when they are melted--the same weight of a given material takes up more space. The exact degree to which the volume expands is unique to each plastic material. Said another way, a plastic's solid density is greater than its melt density. Melt Front is the location of the leading edge of flow as material is filling a mould. The location of the melt front is constantly changing with time. Melt Temperature is the actual temperature of the material at a given mould location during processing. The melt temperature is constantly changing. It varies with time and will not be the same at different locations in the mould. Mould Cooling describes the process by which the melt temperature of the material is reduced to the point where parts can be removed from the mould. Mould Packing is the process of delivering an additional amount of material to the mould which has already been filled with melted material. The packing portion of the shot compensates for the amount of volumetric shrinkage that will take place when the filling portion of the shot cools and solidifies. Mould Temperature refers to the surface temperature of the mould as measured by a contact pyrometer. While it is considered to be a single number for control purposes, mould temperature usually varies with location over the surface of the mould. Moulding Cycle is the series of steps that result in the machine producing a part. The cycle is usually described by breaking it down into four separate phases. The amount of time that it takes to complete one trip through the cycle is called the cycle time. No Flow Temperature is the temperature at which the viscosity of a material is so high that it effectively cannot be made to flow. Orientation is the change in shape that plastic molecules can undergo when they are made to flow. Optimum Conditions are the machine settings you use that will allow the mould to be filled with the lowest pressure drop and produce parts with the least amount of residual stress. Polymer Structure describes the composition and makeup of a given thermoplastic material from fundamental elements. Pressure describes how the net effect of force is distributed when it is applied over a specific area. Pressure is defined as the force per unit area. For injection moulding purposes, it is normally reported in units of psi or MPa. Pressure Drop is the loss in pressure that occurs when the material is pushed into a section of the mould during the filling phase. Pressure drop is reported in the same units as pressure, normally psi or MPa.