FAQ - Advantage Plastics of New York, Inc.

A. Production molds are generally made of cast aluminum. Molds made of wood or epoxy are also used, but they usually don't do well in the long haul. They offer poor heat transfer and require much more maintenance than aluminum.

A. When a part is formed it must be cooled to the sheets set temperature before it can be safely removed from the mold. This prevents part warpage and maintains dimensional stability. Forced air from cooling fans provides part cooling from the outside of the part. The aluminum mold with embedded water lines provide cooling from inside the sheet. The heat from the sheet transfers through the mold and into the water. The temperature of the water is usually set to about the set temperature of the material being formed. Therefore, the mold temperature, sheet temperature, and cycle time of the machine will be consistent throughout the run. Using other mold materials other than aluminum will keep this from happening. Wood and epoxy mold temperatures will keep increasing during the run causing inconsistent cycle times.... and inconsistently formed parts.

A. Thermoforming is more than just cutting a piece of wood into the shape of the object you want and having a casting made. Several points must be considered. First is the aluminum shrinkage during the casting process. Then there is the material shrinkage during the forming process. Depending on the material it can be from .003" to .025" per inch. In other words a mold that is 20" long can produce a part that is 19.5" long. Another consideration before building a pattern is the secondary finishing operations. Many times there needs to be locators formed into the sheet, dimples for drilling, add-ons to aid in web control and general ease of forming. These are all determined on a part to part basis. Don't feel insulted if you build a pattern and you are told it won't work. The best thing is to leave it to the forming professionals. In the long run it will be cheaper.

A. Absolutely! Remember, we have to form and finish it. We have to make it our business to know the sheet extrusion process as it pertains to formable sheet. We know that stress in a sheet has to be controlled, after all, the forming process of thermoplastic sheet is to relieve the stress with heat and re-stress the sheet in the formed state. We know that a deviation in the die gap of an extruder of 10% or more is going to cause us severe heating problems. We know that unbalanced draw rates between the extrusion rate and the chrome roll and rates from the chrome roll and rubber rolls will cause problems. There are other considerations, too, such as UV additives, grain preference, fire retardency,impact strength, etc.

Q. I have heard that injection molded parts are cheaper than vacuum formed parts, why should I use vacuum forming?

A. There is a point where injection molded parts are cheaper. Lets look at a typical part piece price. We have created a table that shows the quantity, piece price for thermoformed parts and piece price for injection molded parts. In this example the thermoformed tool is $3,500.00 delivered in 6 weeks, and the injection tool is $22,500.00 delivered in 20 weeks.

QUANTITY	FORMED,EA.	INJECTION,EA.
500	11.55	46.47
1000	7.70	23.82
2000	5.80	12.50
5000	4.70	5.70
10000	4.30	3.43
20000	4.08	2.30

The above chart is for information only and should not be considered as a quote or an estimate from Advantage Plastics. The figures in the chart are from information found in seminar handouts provided by the McConnell Co.