Custom injection molding means the tool exists for your part and nobody else's, so you are buying a capital asset and a production service at the same time. Those are two different purchases with two different risks, and the contracts that go wrong are almost always the ones that treated them as one line on an invoice.
What is inside a tooling quote
Design of the tool, the steel or aluminium itself, cutting and electrode work, the hot runner or cold runner system, any side actions or lifters for undercuts, polishing or texturing, assembly, and the sampling that produces first articles. A quote that gives one number for all of that is not wrong, but ask for the split, because it shows where a design change would land.
Tool life and steel choice
Aluminium tools are cheap and quick and suit low volumes and bridge production. Pre hardened steel covers most mid volume work. Hardened tool steel is for high volume and abrasive filled resins. Specify the expected life in parts rather than in years, because that is the number the toolmaker can actually design to, and it decides half of the price.
Who owns the tool, and where does it live
If you paid for the tool, say in writing that you own it, that it may be moved on request, and what condition it is handed over in. Tools are routinely maintained by the moulder running them, so also agree who pays for wear, who pays for damage, and what records of shots and maintenance you are entitled to see.
Getting a part price you can plan with
Ask for the part price at several annual volumes and at several order sizes, because machine scheduling and material purchasing both depend on them. Ask what resin price basis the quote uses and how changes are passed through. And confirm what the price includes: degating, inspection, packaging and any secondary operation are frequently quoted separately.
Questions people ask about custom injection molding
What makes moulding custom rather than standard?
The tool. A custom moulder cuts a cavity for your geometry, so the part is unique to you and so is the capital cost behind it.
How long does a custom tool take?
Simple aluminium tools can sample in a few weeks. Multi cavity hardened steel tools with side actions take considerably longer, and the sampling and adjustment cycle afterwards is part of the schedule.
Can I move my tool to another moulder?
If you own it, yes, subject to whatever the contract says. Expect a requalification: a tool run on a different machine with different cooling will need its process developed again.
Should I pay for a multi cavity tool up front?
Only if the volume is real. A single cavity tool that is later replaced by a multi cavity one is a common and sensible path, and it puts the big spend after the demand is proven.