Plastics Molding & Manufacturing/Operator Roles

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A machine operator is by far the most important of all the various components that come together to make up the injection-molding process. The injection moulding machine can be fine-tuned and monitored to run flawlessly from cycle to cycle. BUT the operator is the only component with the capacity to actually think, and therefore can adjust his or her activities whenever needed from cycle to cycle. This attribute can be extremely beneficial to an employer because the operator can make on-the-spot observations regarding how well (or poorly) a job is running.

Focus on the operator role

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Operator must make sure that every cycle is run exactly the same as every other cycle by operation of the machine gate. For the semi-auto machine, the gate is simply a large sliding door that the operator opens at the end of a cycle to remove plastic parts, and then closes to begin the next cycle. On some machine,the gate opens automatically but it still must be closed by the operator. The timing of opening and closing the gate controls the consistency of the cycle. The operator must make sure that the opening and closing activities take exactly the same amount of time each cycle. A difference of as little as 1 second from cycle to cycle can make a difference of $10,000 or more a year in lost revenue to a company.

Inspection of Parts

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Operator had little things to do when a molding job is running well. But in reality this is not the case. For instance, the molded part may not drop off the ejector pins when the mold opens or there may be a small amount of flash present on the molded part. This requires operator action to identify the errors and quickly corrects them. Even when the job is running almost perfectly, the operator must visually inspect the parts to make sure there are no defects. It is important to understand one major economic fact. Someone pays for every part molded, whether good or bad. The customer pays for good parts, the molding company pays for bad parts. It is imperative that bad parts be discovered quickly so corrective adjustments can be made to the machine settings. It is the responsibility of the operator to make those discoveries and immediately notify the supervisor to make changes to the settings. Regardless of whom are making the change, it must be recorded. This record should include pertinent information such as what change was made; what happened to require the change; the result of the change; and shift information including operator, supervisor, time, and date.

Inspection of Mold

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Operator must understand that mold is an expensive but necessary tool. The cost for one mold can be from tens of thousands of dollars to hundreds of thousands. Molds also takes from a few weeks to many months to be built. Some forms of damage may actually ruin an entire mold to the point of requiring total replacement. So, again, it is important to understand that damage to a mold is costly in terms of time and production that is lost while the mold is out of commission. Usually the customer is paying for building the original mold but the molding company pays for mold repairs.

Inspection of Machine

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A molding machine consists of many parts that must work together. If any parts breaks down, the machine will not operate properly and may produce defective products, causing damage to the mold and become a safety hazard that can cause injury.

Housekeeping ( 5S )

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Proper housekeeping at the operator’s workstation is important for at least two reasons.

The first is safety. If items are left lying around where they do not belong, or if tools are not replaced in the proper area, there are high chances untowards incidents such as someone may inadvertently be cut with a trimming knife, or trip over a cables on the floor,may occur.

The second is contamination. This is the second most common cause of defects in molded parts (second only to moisture, which is also a form of contamination). These defects can be caused by potato chip salt getting into the plastic material before it reaches the hopper, or by empty soda cans carelessly deposited in material containers by people who thought they were trash barrels. It can even be caused by touching freshly molded plastic parts with hands that are oily or otherwise dirty.


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The final area of responsibility for the operator to be concerned with is attitude. At times, the job of operating a molding machine can seem boring and tiresome. The job is mostly repetitive, and sometimes the operator feels that no one is paying attention to him or her. In a good productive company, this is not the case. Actually, the company wants to listen to the operator because it is aware that the operator knows better than anyone else how well or poorly a job is running and how to improve the efficiency or productivity of a job.