Semi-finished products Plastic granules Special compounds

MachiningDimensional stabilityBecause of a high strain coefficient, it is advisable tomake a dimensional control when the room temperatureis reached. The chosen plastic manufacturingtolerances have to be bigger than the metals´ ones.Similar attention must be paid to the dimensionalchanges induced by the temperature. These can differ,respect the metals’ ones, by a factor of 10. Dimensionallyprecise parts should be made of low-stresssemi-finished product (see “Post heat treatment”).Sometimes these parts should be annealed beforethe production. If a big and uneven chip removal isrequired, we recommend, taking into considerationthe tolerance desired, to make a rough adjustment ofthe workpiece, and wait 24-hour relaxation storingor make an intermediate annealing process, beforebeginning the final machining. Please notice, that byannealing or 24-hour relaxation storing a shrinkageof the workpieces and a corresponding oversize mustbe scheduled.ClampingWhen the workpiece is clamped, its warping due toan excessive clamping pressure must be avoided. Furthermorealso a long-term clamping must be avoided,because the workpiece could have a dimensional variationand thus a reduction of the clamping pressure.Workpieces can be fastened by vacuum chuck technologyor with double-sided tapes.Machining errorInternal stress and an additional imperfect machining,can lead to the formation of tears or to successivedimensional variations. Usually, the reasons are:– use of worn tools, that generates, additional to theinternal stress, other machining stress– production of strong cross-section variations andsharp edges, which concentrates the internal tensionon small areas– large chip removal, could lead the part to thebreak, through a sudden internal stress balancedisturbance and a warping speed increment.Rupture due to large chip removalPrevention of tears during machiningSome of the ZEDEX ® high performance plastics,need to be warmed up and machined, when they arestill warm. Hints are in the table 3 on the next page.Vacuum clampling devicesZEDEX ® basic types ZEDEX ® families Post heattreatmentMachiningShippingoverviewSterilizationChemicalresistance25