Silicone Prototype Manufacturing: DFM, Tooling Options and Pilot Production

Silicone prototyping is not simply about producing a soft part that looks like the final product. A useful prototype must answer specific engineering questions: Does the geometry assemble correctly? Does the material provide the required flexibility? Can the part seal, bond, stretch or withstand repeated use? Can the design be molded consistently at production volume?

The right prototyping method depends on the development stage. A 3D-printed elastomer may be suitable for checking shape and ergonomics, while functional testing may require the actual production silicone. Final validation and pilot production normally require a production-intent molding process.

This guide explains silicone design for manufacturability, prototype tooling options and the steps required to move from early samples to controlled pilot production.

Start by Defining the Purpose of the Prototype

Before selecting a process or requesting a quotation, determine what the prototype must prove.

Appearance Prototype

An appearance prototype evaluates:

• Overall shape
• Size and proportions
• Color direction
• Struttura superficiale
• Button position
• User handling
• Assembly space

The material does not always need to match production silicone.

Fit and Assembly Prototype

A fit prototype checks:

• Interface with plastic or metal components
• Hole and shaft alignment
• Compression in a housing
• Cable and connector routing
• Posizione di inserimento
• Snap or mechanical retention
• Assembly sequence
• Clearance and interference

Dimensional accuracy may be more important than exact material properties at this stage.

Functional Prototype

A functional prototype evaluates:

• Prestazioni di tenuta
• Tactile force
• Forza di estrazione
• Resistenza allo strappo
• Valve opening pressure
• Portata
• Flessibilità
• Conduttività elettrica
• Bond strength
• Repeated-use performance

The closer the prototype material and process are to production, the more useful the results will be.

Production-Equivalent Prototype

A production-equivalent prototype uses:

• The intended silicone grade
• Production-intent tooling
• Similar molding temperature and pressure
• Defined curing or post-curing
• Intended inserts or substrates
• Production inspection methods
• Representative secondary operations

These samples are often required before pilot production, reliability testing or regulatory validation.

Choose the Silicone Process Before Finalizing the Design

“Silicone” covers several materials and molding methods. The design should match the intended production process.

Liquid Silicone Rubber Injection Molding

LSR is supplied as two components that are metered, mixed and injected into a heated mold.

Lo stampaggio a iniezione di LSR è indicato per:

• High-volume parts
• Thin walls
• Complex details
• Medical and baby-care components
• Valves and membranes
• Guarnizioni e guarnizioni di tenuta
• Silicone-to-plastic overmolding
• Produzione automatizzata

LSR has low processing viscosity and can fill very small gaps, which makes precise parting lines and controlled mold construction especially important. Dow’s LSR processing guide covers material behavior, mold design, flashing, curing and demolding as connected process variables. (Dow LSR injection molding guide)

High-Consistency Rubber Molding

HCR is a solid, gum-like silicone that may be processed by:

• Stampaggio a compressione
• Stampaggio a trasferimento
• Stampaggio a iniezione
• Extrusion

Compression molding is often suitable for:

• Guarnizioni
• Tastiere
• Simple seals
• Larger components
• Lower-volume parts
• Prototype and bridge production

Prototype compression tooling may be simpler than a fully automated LSR injection mold, but part consistency and flash control still depend on compound placement, pressure, temperature and cure time.

RTV Silicone Casting

Room-temperature-vulcanizing silicone can be mixed and poured or dispensed into a mold.

RTV casting is useful for:

• Early functional samples
• Very low quantities
• Soft-touch prototypes
• Large or simple components
• Evaluating hardness
• Encapsulation concepts

However, cast RTV silicone may not reproduce the exact properties, shrinkage, surface condition or production behavior of injection-molded LSR.

Additive Manufacturing

Silicone 3D printing and soft elastomer printing can produce complex shapes without conventional tooling.

Additive prototypes may help evaluate:

• Form and appearance
• Ergonomia
• Internal channels
• Design alternatives
• Assembly space
• Early-stage user testing

The printed material may have different tear strength, elongation, surface finish, compression set and chemical resistance from molded production silicone. It should not automatically be treated as a production-equivalent sample.

SIMTEC lists additive manufacturing, CNC machining, casting and pilot pre-production as different prototype routes, each with its own advantages and limitations. (SIMTEC prototype process options)

Silicone DFM: Key Design Considerations

Design for manufacturability should begin before prototype tooling is ordered.

1. Material Grade and Hardness

The RFQ should identify more than “silicone rubber.”

Specificare:

• LSR, HCR or RTV
• Shore hardness
• Colore
• Sistema di cura
• Trasparenza
• Tear-strength requirement
• Compression-set requirement
• Conductive or insulating grade
• Food-contact or medical requirement
• Self-bonding capability
• Flame-retardant requirement
• Post-curing requirement

Two silicone grades with the same Shore hardness may behave differently during molding, demolding and functional testing.

2. Wall Thickness

Silicone can fill thin sections, but molding and demolding become more difficult as walls become thinner.

Very thin areas may:

• Tear during demolding
• Fold during handling
• Cure differently from thick areas
• Create measurement difficulties
• Require additional mold support
• Deform under packaging or assembly loads

Extremely thick areas may require longer cure time and can affect production cycle time.

Use gradual transitions where possible instead of abrupt changes between thick and thin sections.

3. Parting-Line Position

The mold parting line should be identified during DFM because it can leave a visible witness line or residual flash.

Avoid placing the parting line on:

• Critical sealing lands
• Optical areas
• Skin-contact edges
• Valve slits
• Electrical contact surfaces
• Adhesive bonding zones
• Precision assembly interfaces

If the parting line cannot be moved, the drawing should define the permitted flash and mismatch.

4. Gate Position

The gate controls how silicone enters the cavity.

Gate location can affect:

• Filling balance
• Air entrapment
• Knit lines
• Gate vestige
• Cosmetic appearance
• Trim requirements
• Local stress
• Flow around inserts
• Multi-cavity consistency

The gate should normally be located away from critical cosmetic or functional areas unless the geometry requires otherwise.

5. Venting

Air must escape as silicone fills the cavity.

Una ventilazione inadeguata può causare:

• Short shots
• Aria intrappolata
• Difetti superficiali
• Incomplete thin features
• Weak areas
• Irregular filling

Vents must release air without becoming uncontrolled flash paths.

6. Draft and Demolding

Silicone flexibility allows some parts to demold around undercuts, but flexibility does not eliminate demolding risk.

The DFM review should consider:

• Undercut depth
• Stretch during removal
• Tear-sensitive corners
• Core length
• Struttura superficiale
• Vacuum retention
• Membrane sottili
• Orientamento dei pezzi
• Manual or automated demolding

A part that can be removed once during a tooling trial may still be unsuitable for stable high-volume automation.

7. Radii and Tear Prevention

Sharp internal corners can concentrate stress during demolding and use.

Add suitable radii around:

• Holes
• Slot
• Linguette da strappare
• Tethers
• Membrane transitions
• Inserisci i bordi
• Uscite dei cavi
• Mechanical locking features

The radius should be designed according to wall thickness and available space.

8. Dimensional Tolerances

Silicone parts are flexible and shrink after molding. Applying tight tolerances to every dimension increases tooling and inspection cost without necessarily improving function.

Divide dimensions into:

• Critical functional dimensions
• Assembly dimensions
• Sealing dimensions
• Cosmetic dimensions
• Reference dimensions

The inspection method must also be considered. A conventional caliper can compress a soft silicone part and produce misleading results.

SIMTEC notes that prototype testing with the intended material can help establish realistic shrinkage values before final tool dimensions are fixed. (SIMTEC LSR design guidance)

9. Inserts and Overmolding

For silicone-to-plastic or silicone-to-metal components, provide complete substrate information.

Tra i fattori importanti figurano:

• Exact plastic resin or metal grade
• Insert tolerance
• Finitura superficiale
• Coating or plating
• Moisture condition
• Resistenza al calore
• Posizionamento dell'inserto
• Mechanical locking features
• Primer or plasma treatment
• Self-bonding LSR compatibility

Prototype inserts should be manufactured using a process and material condition representative of production.

10. Surface Finish and Appearance

Define whether the silicone surface should be:

• Polished
• Matte
• Lightly textured
• Optical
• Trasparente
• Traslucido
• Glossy
• Coated
• Printed
• Laser marked

Texture can influence release, appearance, cleaning and bonding. The prototype process may not reproduce the final production texture exactly.

Prototype Tooling Options

1. Cast Prototype Molds

A master pattern is produced using CNC machining or 3D printing. A secondary mold is then used to cast RTV silicone parts.

Best for:

• Very small quantities
• Early design evaluation
• Large soft parts
• Low-cost concept validation
• Multiple design iterations

Vantaggi:

• Low initial investment
• Fast design changes
• No injection molding machine required
• Useful for checking form and basic function

Limiti:

• Limited mold life
• Lower dimensional consistency
• Manual mixing and pouring variation
• Air-bubble risk
• Not always production-grade material
• Different shrinkage from injection molding
• Limited representation of production flash and gate conditions

2. 3D-Printed Prototype Molds

A mold may be printed from a suitable polymer and used for casting or selected low-temperature molding trials.

Best for:

• Early geometry checks
• Very low quantities
• Rapid design iterations
• Simple casting trials

Limiti:

• Limited temperature and pressure resistance
• Surface layers may transfer to the part
• Short tool life
• Potential cure inhibition
• Difficult flash control
• Generally unsuitable for production-equivalent LSR injection molding

Compatibility between the printed mold material and silicone cure system must be tested.

3. Single-Cavity Compression Tooling

A simple metal compression mold can produce prototypes using HCR or suitable silicone compounds.

Best for:

• Guarnizioni
• Plugs
• Tastiere
• Copertine
• Seals
• Simple consumer products
• Small pilot quantities

Vantaggi:

• Uses real silicone compounds
• Lower complexity than automated injection tooling
• Supports functional testing
• Can produce representative surface finishes
• Suitable for moderate prototype quantities

Limiti:

• More manual processing
• Greater flash and trimming requirements
• Compound placement can affect consistency
• Cycle time is less representative of automated production
• Difficult for very thin or highly complex geometries

4. Prototype LSR Injection Tooling

A prototype LSR tool may use a single cavity, simplified runner system and standardized mold base.

Best for:

• Functional LSR prototypes
• Thin-walled parts
• Valves and membranes
• Componenti medicali
• Overmolded assemblies
• Near-production testing
• Pilot runs

Vantaggi:

• Uses production-intent LSR
• Provides representative curing and shrinkage
• Supports meaningful leak, force and durability tests
• Produces repeatable parts
• Helps identify production molding risks

Limiti:

• Higher cost than casting
• Requires LSR molding equipment
• Tool changes take time
• Simplified tooling may not reproduce final automation
• Single-cavity data may not predict multi-cavity balance

5. Aluminum Rapid Tooling

Aluminum is easier to machine than hardened steel and can reduce initial tooling lead time.

Protolabs describes aluminum molds as a rapid route for producing LSR parts during development and approval stages. (Protolabs rapid LSR molding)

Best for:

• Prototype injection molding
• Bridge production
• Moderate part quantities
• Convalida del progetto
• Early customer samples

Vantaggi:

• Faster machining
• Lower initial tooling cost
• Easier modification
• Suitable for many pilot applications

Limiti:

• Shorter life than hardened production steel
• Greater risk of wear in critical shutoffs
• May not suit very tight flash requirements
• Not ideal for every optical or highly automated part
• Tool life depends heavily on geometry and process

Aluminum tooling capability varies by supplier, part design and silicone process. It should be confirmed before the material is specified.

6. Soft-Steel or Modular Insert Tooling

Machined steel cavity inserts can be installed in a reusable mold base.

Best for:

• Production-intent prototypes
• Parts requiring controlled shutoffs
• Pilot production
• Future design changes
• Projects expected to scale

Vantaggi:

• Better wear resistance
• More representative of production tooling
• Replaceable cavity inserts
• Improved flash control
• Supports controlled pilot runs

Limiti:

• Higher initial cost than basic casting tools
• Longer machining time
• Modifications may be more expensive
• Mold-base compatibility must be planned

7. Full Production Tooling

A production mold may include:

• Cavità multiple
• Cold-runner system
• Automated demolding
• Caricamento in corso
• Ispezione visiva
• In-mold sensors
• Secondary operations
• Robot handling
• Cavity traceability

It provides the lowest unit cost at high volume but requires the highest initial investment and the most complete design validation.

Tooling Comparison

Tooling Route	Typical Development Stage	Material Accuracy	Repeatability	Relative Investment
Cast prototype mold	Concept and early function	Low to medium	Basso	Lowest
3D-printed mold	Early iteration	Low to medium	Basso	Basso
Compression prototype tool	Functional prototype	Da medio ad alto	Medio	Low to medium
Prototype LSR injection tool	Functional validation	Alto	Alto	Medio
Aluminum rapid tool	Prototype and bridge production	Alto	Alto	Medio
Modular steel insert tool	Pilot and scale-up	Alto	Alto	Da medio ad alto
Full production tool	Serial production	Highest	Highest	Highest

Prototype Tooling Should Anticipate Production

A low-cost prototype tool is most valuable when it answers questions that affect production tooling.

Where practical, prototype tooling should evaluate:

• Intended parting line
• Gate location
• Venting strategy
• Demolding direction
• Critical tolerances
• Finitura superficiale
• Posizionamento dell'inserto
• Flash-sensitive areas
• Secondary operations
• Inspection datums

If the prototype uses a completely different gate, parting line or molding process, some results may not transfer to production.

From CAD to Pilot Production

Stage 1: Requirements Review

Conferma:

• Applicazione
• Materiale
• Quantità
• Critical dimensions
• Prestazioni meccaniche
• Sealing requirements
• Requisiti normativi
• Test conditions
• Production target

Stage 2: DFM Review

The supplier reviews:

• Spessore della parete
• Linea di separazione
• Gate and vent locations
• Sottotagli
• Sformatura
• Flash limits
• Tolerances
• Inserts
• Surface requirements

Design changes should be completed before cutting metal where possible.

Stage 3: Prototype Tooling

The tool is manufactured and inspected. Critical mold dimensions and surfaces are checked before the first trial.

Stage 4: Initial Tool Trial

Initial samples are evaluated for:

• Complete filling
• Flash
• Air entrapment
• Stesura
• Sformatura
• Condizioni della superficie
• Dimensioni
• Gate vestige
• Posizione di inserimento

The first trial should identify tooling and process issues, not serve as an automatic production approval.

Stage 5: Tool Correction and Second Trial

The mold or process may be adjusted based on initial results.

Changes may include:

• Vent depth
• Gate geometry
• Shutoff surfaces
• Cavity dimensions
• Finitura superficiale
• Insert fixture
• Condizioni di cura
• Injection settings

Stage 6: First Article Inspection

The first article report should focus on dimensions and functions that affect assembly or performance.

Inspection may include:

• Dimensional report
• Verifica dei materiali
• Durezza
• Colore
• Visual condition
• Flash
• Peso
• Functional test results
• Inserisci la località
• Bond strength
• Leak rate
• Force-displacement data

Stage 7: Pilot Production

Pilot production uses a controlled batch to evaluate whether the process can repeatedly produce acceptable parts.

A pilot run should verify:

• Material handling
• Metering and mixing
• Temperatura dello stampo
• Injection stability
• Tempo di indurimento
• Cavity balance
• Sformatura
• Rifinitura
• Post-indurimento
• Pulizia
• Inspection
• Confezione
• Tracciabilità

SIMTEC describes pilot production as a way to generate near-production-quality LSR parts and transfer lessons into the final production process. (SIMTEC pilot LSR production)

What Pilot Production Should Prove

A pilot run should answer four questions.

1. Is the Design Functional?

Testing may include:

• Leakage
• Compression
• Forza di estrazione
• Actuation force
• Portata
• Resistenza allo strappo
• Assemblaggio
• Bonding
• Electrical resistance
• User handling

2. Is the Molding Process Stable?

Recensione:

• Shot-to-shot variation
• Cure consistency
• Flash stability
• Cavity differences
• Material ratio
• Tempo di ciclo
• Scrap rate
• Demolding reliability

3. Can the Part Be Inspected Reliably?

Conferma:

• Measurement fixtures
• Metodo di ispezione
• Sampling plan
• Critical dimensions
• Visual standards
• Functional test equipment
• Calibrated reference parts

4. Can the Part Be Manufactured at the Target Cost?

Record:

• Tempo di ciclo
• Labor content
• Consumo di materiale
• Scrap
• Trimming time
• Secondary operations
• Inspection time
• Costo dell'imballaggio

Critical-to-Quality Characteristics

Not every dimension needs extensive pilot data. Focus on characteristics that affect safety, assembly, sealing or customer use.

Tra gli esempi figurano:

• Sealing diameter
• Spessore della membrana
• Valve slit
• Inserisci la località
• Bond strength
• Forza di estrazione
• Actuation force
• Contact resistance
• Leak rate
• Contaminazione superficiale
• Flash at a critical edge

Capability calculations should only be used when the process is stable and sufficient representative data are available.

Production-Intent Testing

Pilot samples should be tested under expected service conditions.

Testing may include:

• Temperature aging
• Cicli termici
• Umidità
• Esposizione a sostanze chimiche
• Water immersion
• Esposizione ai raggi UV
• Sterilizzazione
• Deformazione residua da compressione
• Cicli di fatica
• Repeated assembly
• Packaging and shipping simulation

Early prototype results should not replace validation using production-intent materials and processes.

Common Prototype Manufacturing Problems

Problem	Likely Cause	Recommended Action
Prototype fits but production part does not	Different material or shrinkage	Use production-grade material and update tool dimensions
Part tears during demolding	Sharp corner, deep undercut or thin wall	Add radii or revise demolding direction
Flash eccessivo	Tool gap, excessive shot or worn shutoff	Review tooling fit and process settings
Part is tacky	Insufficient cure or incorrect mixing	Verify temperature, cure time and mix ratio
Air bubbles or voids	Poor venting or casting technique	Improve venting, vacuum or filling method
Hardness differs from requirement	Incorrect material or cure condition	Confirm grade, mixing and test method
Insert moves during molding	Weak fixture or excessive injection force	Improve insert location and support
Pilot cycle is too slow	Tool or demolding process is not optimized	Review automation and cure conditions
Dimensions vary between samples	Unstable process or measurement deformation	Stabilize molding and use proper fixtures
Surface appearance is inconsistent	Tool finish, release or contamination	Standardize mold and handling conditions

Cost Drivers for Silicone Prototypes

Prototype cost is influenced by:

• Part size
• Geometry complexity
• Number of cavities
• Sottotagli
• Finitura superficiale
• Flash requirement
• Grado del materiale
• Insert molding
• Self-bonding requirements
• Tool material
• Required quantity
• Tolleranza
• Secondary operations
• Inspection documents
• Test funzionali
• Cleanroom requirements

The cheapest prototype method is not always the most economical choice. A low-fidelity sample that cannot answer the required engineering questions may delay the project and increase the cost of later tooling changes.

Silicone Prototype RFQ Checklist

Provide:

• Disegno 2D
• File CAD 3D
• Prototype purpose
• Required quantity
• Target production volume
• LSR, HCR or RTV preference
• Grado del materiale
• Shore hardness
• Colore
• Critical dimensions
• Flash limits
• Finitura superficiale
• Insert or substrate drawings
• Requisiti di incollaggio
• Functional test requirements
• Esposizione ambientale
• Post-curing requirements
• Requisiti normativi
• Inspection documents
• Target pilot-production date

Also identify whether the prototype must match the final production material and process.

Conclusione

Successful silicone prototyping begins by defining what the prototype must prove.

Early appearance and fit checks may use additive manufacturing or cast silicone. Functional testing often requires real silicone compounds and controlled prototype tooling. Production-equivalent validation typically requires compression molding or LSR injection molding using production-intent materials, gates, parting lines and curing conditions.

A structured DFM review reduces tooling changes by addressing wall thickness, parting lines, gates, vents, tolerances, undercuts, inserts and inspection methods before mold construction. Pilot production then confirms that the design, tooling, molding process, secondary operations and quality controls can operate together consistently.

FHY Silicone supports silicone product DFM, prototype tooling, LSR molding, compression molding, overmolding and pilot production. Send us your CAD files, material requirements, prototype quantity and target production volume for a manufacturability review.

Domande frequenti

Which process is best for a silicone prototype?

It depends on the purpose. Casting or 3D printing may be suitable for appearance and fit, while functional or production-equivalent testing usually requires molded production-grade silicone.

Can a 3D-printed soft part replace an LSR prototype?

Not always. Printed elastomers may differ from LSR in tear strength, elongation, compression set, surface finish and chemical resistance.

Is prototype tooling always discarded?

No. Aluminum or modular insert tooling may sometimes support pilot or bridge production. Tool life and future use should be agreed before manufacturing.

Should the prototype use the final production material?

Use the production material when testing sealing, bonding, chemical resistance, sterilization, compression set or long-term mechanical performance.

What is pilot production?

Pilot production is a controlled pre-production batch used to verify process stability, part quality, inspection methods, secondary operations and packaging before serial manufacturing.

How many parts are needed for a pilot run?

There is no universal quantity. It depends on process complexity, testing requirements, number of cavities and the amount of data needed to evaluate repeatability.

What is the difference between a prototype tool and a production tool?

Prototype tooling usually emphasizes speed, lower cost and design flexibility. Production tooling emphasizes long life, automation, multiple cavities and consistent high-volume output.

Can prototype samples be used for regulatory testing?

Only when the material, tooling, manufacturing process and documentation meet the project’s validation requirements. This should be confirmed with the customer’s regulatory and quality teams.