CustomPartNet
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August 6, 2026
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Updated August 6, 2026
Before you narrow down a supplier list, it helps to know the numbers behind your part. Tonnage requirements, cooling behavior, and material properties all influence which suppliers can actually run your job, and at what cost. Browse our supplier network to compare injection molders by press size, material capability, and location, then use the calculators below to double check your own numbers before you request quotes.
Most buyers researching injection molding focus on part cost. But three numbers, clamping force, cooling time, and thermal diffusivity, actually determine whether a mold and machine combination will work at all. They govern how big a press you need, how long each cycle runs, and how a given resin behaves as it solidifies. CustomPartNet offers a free calculator for each one, and together they give you a quick, practical view of the physics your supplier is managing on the shop floor.
What it does: Calculates the tonnage needed to hold a mold shut during injection, based on cavity pressure and the projected area of the part (including any runners in that cavity).
Why it matters: During injection, molten plastic pushes outward on the mold with enough force to separate the two halves if the clamping unit isn't strong enough. Undersized clamping force lets the mold "breathe" open slightly, which shows up as flash along the parting line and can lead to short shots or dimensional drift. Oversized clamping force isn't dangerous, but it usually means you're quoting a bigger, more expensive machine than the job requires.
How buyers use it: Estimate the tonnage your part needs before you talk to a supplier, so you can ask the right question upfront: does your press lineup cover this range? A part that needs 150 tons run on a shop with only 500 and 1,000 ton presses may end up costing more than it should, simply because there's no efficient machine match.
Try the Clamping Force Calculator →
What it does: Estimates the theoretical cooling time for a part based on the plastic's thermal diffusivity and the part's maximum wall thickness.
Why it matters: Cooling is almost always the longest stage of the injection molding cycle, often accounting for more than half of total cycle time. Pull a part out too soon and it can warp, sink, or distort as it finishes solidifying outside the mold. Cooling time scales with the square of wall thickness, so a part that's twice as thick doesn't just cool twice as slowly, it cools roughly four times as slowly. That relationship is easy to underestimate when you're specifying wall sections on a drawing.
How buyers use it: Run a few wall thickness options through the calculator before finalizing a design. Shaving even half a millimeter off an oversized wall section can meaningfully shorten cycle time and lower your per-part cost at volume.
Try the Cooling Time Calculator →
What it does: Calculates or looks up the thermal diffusivity of a material, the rate at which heat moves through it, which feeds directly into the cooling time calculation above.
Why it matters: Not all plastics cool at the same rate, even at the same wall thickness. Semi-crystalline resins like nylon and POM often need different cooling strategies than amorphous resins like ABS or polycarbonate, partly because of how their thermal properties differ. Thermal diffusivity is one of the values that explains why swapping resins on an existing tool can shift your cycle time and mold temperature setpoints, even when the part geometry stays identical.
How buyers use it: If you're comparing two candidate materials for a part, check their thermal diffusivity values side by side. A resin with lower diffusivity will generally need longer cooling or a more aggressive cooling channel layout in the mold, both of which affect tooling design and cycle cost.
Try the Thermal Diffusivity Calculator →
Clamping force, cooling time, and thermal diffusivity answer questions about the mold and the material. But before a supplier can even quote your job, they need to know whether their machine's injection unit can deliver enough material in one shot. CustomPartNet doesn't currently host a dedicated shot weight calculator, so for that step we point buyers to Improve Your Injection Molding's Shot Weight and Injection Capacity Calculator, which converts a machine's rated injection capacity (usually specified in general purpose polystyrene) into an equivalent shot weight for your actual resin. Pairing that number with the clamping force estimate above gives you a solid, machine-agnostic picture of what press size your part actually needs.
Say you're sourcing a mid-size housing in ABS with a 0.100" nominal wall. Run the wall thickness and ABS's thermal diffusivity through the cooling time calculator to get an expected cooling stage length. Take the part's projected area and expected cavity pressure into the clamping force calculator to get a tonnage estimate. Then check that tonnage against the shot weight your part requires, using the injection capacity calculator, to confirm you're not over- or under-utilizing the barrel. With those three numbers in hand, you can talk to suppliers about press size, cycle time, and cost with real data instead of guesswork, and you'll spot mismatches (like a part that needs a bigger press than its shot size would suggest) before they cost you a quote cycle.
Not necessarily. Generic property values for common resins like ABS, PP, or nylon will get you a reasonable estimate. For a final tooling decision, ask your supplier to confirm properties for the specific grade they plan to run, since additives and fillers can shift thermal diffusivity and shrinkage.
Knowing your part's required tonnage lets you evaluate suppliers before committing, not after. It also helps you catch problems early, like a part that's borderline for a given press, before tooling is cut.
It's a solid starting estimate, but real cooling time also depends on mold temperature control, cooling channel design, and how efficiently heat is pulled out of the steel. Suppliers typically refine this number during mold design and initial trials.
Yes. Running the same geometry through the cooling time and clamping force calculators with different material properties is a fast way to see how a material swap affects cycle time and machine requirements before you commit to a resin.
Generally yes, since cycle time is a major driver of per-part cost in injection molding. But it's not the only factor. Multi-cavity tooling, automation, and material cost all interact with cooling time to determine final part economics.
Cooling time scales with the square of wall thickness, not linearly. That's why designers are encouraged to keep wall sections as thin and uniform as the part's strength requirements allow.
Our supplier network includes injection molders who can review your part file, confirm machine compatibility, and refine these estimates based on their actual equipment and process data.
Use the calculators above to understand your part's clamping force, cooling time, and shot weight requirements, then connect with suppliers who have the right press size and material experience for your project.
Get Quotes Now → or Register for a Free Account → to save calculator results, build supplier shortlists, and manage RFQs.