Strippers Stroke

If thick-walled tubes with small inside diameters, such as hollow copx)er bars for stud bolts, are to be extruded from the same container, tools with a pointed mandrel, as per sketch b, are employed. The operation is the same as that described above. The stripper stroke is somewhat longer, because the advance motion of the mandrel in this case is shorter than that in sketch a by the length of the mandrel point projecting over the dummy-block. 

The impact extrusion process is used to produce open-ended collapsible tubes from softer metals such as tin and lead. When aluminium is used, it work-hardens during the forming process and the resultant tubes must be annealed to regain flexibility. Alternatively aluminium tubes may be left in their work-hardened state as rigid containers. Impact extrusion is a particularly useful process to produce containers with a high length to diameter ratio, e.g. up to 7 1. A slug of the metal to be formed is held in a female die and is struck by a punch which has the same form as that of the inside of the ultimate container. Upon impact the metal flows up the outside of the punch. A stripper plate then removes the extruded container on its return stroke. 

A fixed stripper. Fig. 16.8, is used when the work material is in the form of strip, fed across the top of the die. The stripper in this case is a flat plate screwed to the top of the die and contains a hole through which the punch passes. When the punch is on the upward return stroke, the plate prevents the material from lifting and strips it off the punch. 

The effect of such stripper cylinders can also be attained by eliminating the distance between the surfaces c and d and providing a flexible stroke limiting device on the columns of the piercer device, the power of which must, however, be greater than that of the piercer, or by arranging the stops in such a way as to provide for their respective position to be adjusted or to be changed by means of spacers quickly. 

Step II Stroke of the stripper rings 7 and 8, to get space for the elastic strip-off ... 

Standard system for small parts During opening stroke in direction of demoulding. Ejeetion with pins, sleeves or stripper plate Various mechanical, hydraulic, pneumatic, manual, machine stop, lifting cylinder, cam, pivot, inclined plane, thrust plate Mouldings without undercuts... 

Direction of ejection towards movable side, stripping is used but usually for circular parts only During opening stroke pull in direetion of demoulding, ejeetion with stripper plate Mechanical, hydraulic, pneumatic, stripper bolt, lifting cylinder, pin-link chain Cup-like mouldings wiA internal gate... 

Demoulding of parts with local undercuts (slide mould) During opening stroke thrust in direetion of demoulding, ejection with pins, sleeves or stripper plate after release of undercut Mechanical, cam pins, slide mechanism Flat parts with external undercuts (threads)... 

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