Optimising Time Cycle And Machine Productive Time

Update:17-09-2021
Summary:

  No matter what cost-saving ideas are introduced in th […]

  No matter what cost-saving ideas are introduced in the injection molding of plastic parts, the time period of the final machine and the speed at which it can produce good saleable molds are the criteria for profitability. Unfortunately, an operator or installer who does not fully understand the workings of the machine will try to grab odd seconds everywhere in the time period, usually reaching a stage, either producing a defective mold, or working in multiple impressions, one or two The impression is not working properly.

 

  Continuing to produce defective molds, for example, eight impressions of one impression, will soon reduce profitability to a very low level, and even cause the machine to run at a loss. Not only must one-eighth of the production loss be considered, but also the cost of the materials used, the cost of separating bad molds, and the cost of re-granulating waste. Also consider possible wear of the mold, such as flashing, or deformation of the mold when a cavity is not filled. The latter approach will make the mold lock out of balance.

 

  It is necessary to set a very strict machine time period. Some molding companies do this by locking the timer after setting the timer. This may have disadvantages, because as long as there are slight changes, the operator needs to call a setter (maybe urgently hired elsewhere) to make adjustments. The use of electronic sensing and feedback devices can ultimately minimize the need for manual adjustments, but it may always be necessary for a properly trained operator or installer to "fine-tune" the machine to obtain the best output.

 

  The shortest time for each element is determined by the capabilities of the machine or the characteristics of the material being molded. However, the machine function is between these main elements, which may result in time loss.

 

  First consider the locking of the mold to prepare for injection. This must be done quickly and gently. The speed is controlled by a flow control valve in the hydraulic fluid pipeline, and the mold protection is controlled by a micro switch. High pressure is allowed to be applied for locking only when the mold parts are almost in contact. If the settings are not accurate, the mold may take longer to close, and valuable time will be wasted.

 

  The next stage is injection. The shortest time for injection is determined by the rate at which the hydraulic pump supplies fluid or the rate determined by the nature of the material being molded and the configuration of the mold. However, injection cannot be performed before the cylinder nozzle is in contact with the mold runner bushing.

 

  If the machine is designed such that the closing of the mold will send a signal to move the cylinder trolley forward, if the trolley moves slowly and the distance exceeds the necessary distance, it may waste time. (Some machines have very slow motion hydraulic cylinders to move the trolley in order to avoid damage to the mold runner bushings and nozzles.) There will be a slight time delay at each stage of the machine operation, but a good setter would expect this The delay, caused by the inertia of the solenoid valve in the hydraulic system, will be fine-tuned accordingly.

 

  If the machine is running with a fracture, that is, the nozzle exits from the sprue sleeve of the mold after each injection, the cart should be allowed to move to a minimum to reduce the time loss before injection. The actual time when the gate fracture occurs overlaps with the beginning of cooling or mold opening.

 

  Unless a longer plunger residence time is required, such as in the flow molding of thick sections of certain materials or the molding of thick sections of nylon and acrylic resin, the screw/plunger should immediately start to spin or plasticize its direction when it reaches the end point. Forward stroke. Especially when high-speed injection is performed through a properly designed gate, since the gate will freeze immediately and the injection will stop, it is almost meaningless to maintain a long plunger residence time. The spin time should not be longer than the additional cooling time required, and this is rarely the case in normal molding practice. At the end of rotation or cooling, whichever is later, there is a mold opening signal

 

  The same standard applies to mold opening and mold closing, and the quality of the metal is controlled during its movement to minimize damage to the machine. During the mold opening process, the molded part will be demolded. When using a mechanical system, when the mold is opened, the ejector rod hits the stopper or pin fixed on the fuselage, and the ejector mechanism is activated. At this stage, the pressure plate moving too fast will cause poor machine vibration, excessive wear of the ejector system, and eventual failure of the machine or mold. The drive gear needs to be finely set to achieve speed with minimal strain. One advantage of hydraulic or pneumatic ejector systems is that they can be set to operate with very little vibration and can be timed so that the ejector movement is completed and the mold is ready to fall from the mold at the moment the mold is fully opened .

 

  Before starting the clamping operation, time must be allowed for the molded product to leave the mold. On all fully automatic machines, a delay switch is installed to provide an appropriate "pause" before the signal to restart the cycle-usually, the pause timer or interval timer is set to allow longer than necessary time.

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