RTV Vacuum Casting vs LSR Molding

If you are choosing a prototype path, an RTV vacuum-cast cavity and an LSR shot are not interchangeable samples unless you only care about outline. On this site the product is the RTV mold: photos, sketch, or CAD, then a 3D-printed pattern, often a temporary silicone flip, a resin production mother, then batch RTV you dump food, wax, resin, or PU into. MOQ 20 pieces per design. Prototype usually 3-7 business days after CAD lock. Free DFM. CAD revision about USD 50 when we edit your 3D.

RTV vacuum casting is a geometry printer with a rubber tool: mix platinum or tin, pull a vacuum around -0.095 MPa / 28-29 inHg, pour, then cast. LSR molding is a small version of a molded-part process: a printed or aluminum injection cavity, heat, platinum liquid silicone under clamp, usually a cold-runner. Some catalogs call either stack "soft tooling." We keep that phrase as an industry aside. It is not the H1 and it is not the object. Using LSR to "prove" a chocolate tray is how you buy heaters you will never use. Using RTV to "prove" LSR flash is how fit samples pass and production parts miss.

Two objects called a silicone prototype

RTV vacuum casting (this site). Pattern, often a flip, resin production mother, then a rubber tool. You cast dumps into that tool. Cycle is manual. Platinum RTV shrink is typically about 0.1-0.3% after a full cure. The dump shrink is whatever you poured. Flash is a function of how you split the rubber, not of a steel shutoff. Mix 1:1 or 10:1. Shore 10A-20A skin plus a jacket / mother-mold support shell when the sheet would sag about 0.5-1.5 mm.

LSR molding (finished-part sample). You cut or print a cavity. You heat it. You inject an LSR grade. The article is a vulcanized part. Flash is a metal shutoff problem. Shrink is the LSR heat-cured band (about 2-3%), not the RTV tool's. Finished LSR parts are an HTV product RFQ here. We will not write an LSR part PO onto a RUUIPON mold letterhead.

Soft tooling as an industry aside

Buyers paste "LSR soft tooling" into an RFQ because a rapid-prototype shop used that label for aluminum or printed injection cavities. The useful split is still object, not nickname: are you buying a pour cavity, or a vulcanized part? If the sample is a handheld mold or a food tray, RTV is the product. If the sample is a gasket that must compress in a groove at 50A after post-cure, RTV is a costume - quote a parts OEM.

Common mix-up: life-testing a poured dump as LSR data

Casting a silicone article in an RTV mold can get you near a target Shore A. It does not get you LSR flow, knit, or post-cure shrink. Do not send that part to a life-test and call it production data. ISO 3302-1 might class either article. It is a drawing class, not a process.

When RTV vacuum casting is the right sample

Use it when the question is shape, assembly choreography, a photo, or a production food/resin mold:

• Undercut-heavy models you are not ready to slide-steel
• Fit checks where a 0.1-0.3 mm argument is acceptable
• Color and form reviews before anyone should freeze a resin production mother
• Quantities where an LSR pail and a press setup would be theatre
• Trays that are the product (gummy, chocolate, ice) and will stay craft-cast

Tin-cure RTV is cheaper and more forgiving of dirty printed patterns. It ages and shrinks more. Platinum holds size better in the rack and inhibits on uncured resin prints. Neither chemistry is LSR.

When LSR molding is the right sample

Use it when the question is the part process you will live with - flash a customer will measure, gate witness, post-cured shrink into a housing, a true LSR grade, a regulatory packet on that compound. Aluminum 1-cavity is the usual vehicle. That is not a custom RTV mold PO. Send the HTV product RFQ or LSR-tool RFQ (ask us) as an HTV product RFQ here, or ask us for a high-volume LSR tool.

The fork that changes the buy

Ask: what decision will this sample authorize?

Typical shop values

Reference values only. Confirm material-specific limits against the supplier’s technical data and agree project acceptance criteria before production.

Worked example: 18 mm bear chin

A confectioner argued RTV vs "just shoot LSR." Worst feature: 18 mm bear chin return. One RTV coupon in 10A-20A platinum after the pattern / flip / resin-mother path; ten peels, no nick. One LSR shot in a crude aluminum cavity of the same outline did not dump pectin and did not answer peel of the mold. The RTV sample authorized the tray. The LSR shot was a mood board for a toy nobody asked for.

Stay on this page / skip this page

Stay when you need to pick the sample that authorizes a pour-cavity PO, or when someone mailed "LSR soft tooling" and you still dump chocolate.

Skip if you already know the shippable object is a vulcanized LSR part - do not buy another RTV loop to prove flash; open an HTV product or mold RFQ here, or ask us if you need a high-volume LSR cold-runner tool. Skip if you already know the object is a chocolate tray and only need cavity Shore - this comparison is done.

We will not quote LSR molding to prove a chocolate tray. We will not life-test a poured silicone dump as LSR data. We will not raise Shore A first to "make it more like LSR."

Related: how RTV molds are made, RTV vs steel by volume, custom RTV molds, contact.

Send the worst feature and the dump material. We will say which sample authorizes the PO you actually want. [email protected] · +86 135 3006 2969.

FAQ

Can a vacuum-cast PU part prove LSR flash and shrink? No. RTV copies shape at room temperature with rubber-split flash. LSR molding is a hot cavity, metal shutoff, and heat-cured platinum shrink.

When is RTV vacuum casting the right sample? When the question is shape, a photo, or a production food/resin mold. Tin tools forgive dirty prints and age more; platinum holds size and inhibits on uncured resin.

When must I spend on aluminum LSR instead of another RTV loop? When the sample must authorize flash on a part, whether a thin fin fills in LSR, post-cure shrink into a housing, or a regulatory packet on that LSR grade. Handheld molds and chocolate trays do not need that. Finished LSR parts are an HTV product or mold RFQ here, or a different LSR-tool RFQ - ask us.

Is a silicone part poured in an RTV mold production LSR data? It can near a target Shore A. It does not give LSR flow, knit, or post-cure shrink.

Why not title this page LSR soft tooling? Soft tooling is a catalog nickname that smears a pour cavity and a printed injection cavity into one phrase. The H1 is RTV vacuum casting vs LSR molding so the object stays honest.