Buyers of machines or tools often do not take advantage of the unique situation in the purchase process when the parts have been completed by the vendor. At this point the purchaser has paid a down payment of between 15% to 40% and the bulk of the purchase price is due on shipment. The vendor on the other hand has spent more than 90% of his total cost eagerly awaiting the next payment. It is therefore in the vendor's best interest to ship as soon as possible. However, the buyer has to release the shipment and this gives him the upper hand.
I recommend to do an acceptance test against written specifications in the vendor's factory no matter whether the vendor is in the US, Europe, or Asia. The exact details are negotiable but it always involves running the machine or tool for a number of hours without operator intervention. If material is being melted the minimum time should be 6 hours with 24 hours a reasonable maximum. For stretch blow machines 3 to 12 hours maximum is sufficient. This will allow close inspection of machine/tool functions over time and reveal deficiencies. Sample parts should be taken every 30 to 60 minutes depending on the test length. Statistical Process Analysis should be performed on the samples with a minimum cpk of 1.2 to 1.33 for dimensions under observation. For bottles and preforms this would be neck dimensions, weight, perpendicularity, diameters, length, and visual defects.
Before samples can be taken the machine has to settle out. If material is being melted this may take up to 3 hours whereas stretch blow machines will setlle in 30 minutes or so. Technicians of the vendor should judge that and tell the buyer when the first samples can be taken. If the cavitation is 10 for example a 12-hour test with 30 minutes sample intervals would result in 250 samples. To test all the different variable may be too cumbersome and time-consuming. An alternative method is the first and last sample inspection whereby the samples taken after the warm-up period are compared to the last samples taken. In this case tolerances for each attribute to be measured need to be agreed upon and both sets of samples have to fall within them.
If problems arise the vendor will do everything possible to quickly resolve the issues and the buyer will have a machine/tool arriving in the plant that has been fully tested. Necessary changes are done much quicker in the vendor's facility compared to fixing them on the buyer's floor with delays in spare parts and personnel availability.
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