Have you considered spray contact cement, as in a canister & gun setup? I'm not a huge fan of it for most woodworking applications, but for hardboard to hardboard it might work out. Success depends on a few variables, mostly around if one side of the sandwich will be absorbing more moisture than the other, but if you could test it out it might be a quick way to cut clamp time by a ton.
Yep, contact cement isn't the right answer for that application. Heat is your friend if you want to decrease cycle time while using epoxy, but your sub 30 minute target will be tough to achieve. Heat is your friend: electric blankets over and under molds, tenting the mold off and putting oil filled portable radiant heaters, anything you can do to trap the heat inside will help some, but my experience is that the faster the epoxy cure time, the more flexible it is, so you might see some springback.
Another option to explore is powdered plastic resin cured with RF. The guerilla method would be to vacuum bag your parts to the mold and shoot it with a wood welder. PPR glue usually has a 5-10 minute full cure time under RF.
Is this a one time project or an ongoing product. If it is ongoing I would use IR heaters. Not something you buy in home depot to heat your house but industrial units like Infratech. Depending on your moulds you might was to use vacuum because it is easy to heat through.
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