What Is the Step-by-Step Process of Making Rubber Prototypes?

Pre-Production: Define Requirements and Plan Design

Before you make anything, you need to know exactly what the prototype must do. Rubber parts serve specific functions, and your testing goals determine material and process choices.

Clarify Core Requirements

Rubber prototypes validate three main types of performance. Be clear about which matter for your part.

Hardness matters: Rubber hardness is measured on the Shore scale. Typical ranges are 30 to 70 Shore A. Softer rubbers seal better but wear faster. Harder rubbers last longer but require more force to compress.

Design 3D Models with Rubber-Specific Rules

Rubber shrinks as it cures. Your CAD model must account for this or your parts will come out undersized.

Shrinkage rate:

• Silicone: approximately 3% shrinkage
• Polyurethane: approximately 2% shrinkage
• Natural rubber: variable, typically 2% to 5%

If you need a final part that is 100mm long, model it at 103mm for silicone. Measure a test sample first to confirm actual shrinkage with your specific material and process.

Thickness and chamfers:

• Keep wall thickness between 0.5mm and 5mm. Thinner parts tear easily. Thicker parts take longer to cure and may develop internal voids.
• Add 0.5mm to 1mm chamfers on sharp edges. A silicone shock pad with 0.8mm chamfers survived 50 compression cycles. A sharp-edged version cracked after 50 presses.

Anti-slip patterns and holes:

• Mark texture areas clearly in your CAD. Grid patterns 0.5mm deep improve grip significantly.
• For assembly holes, model them slightly undersized. Rubber stretches, so a 2mm hole will accept a 2.5mm pin if needed.

Split Complex Parts

If your part has undercuts, thin walls, or sharp curves, consider splitting it into sections. Each section gets its own simpler mold, which reduces demolding problems and trapped air.

Example: A curved silicone earbud tip is split into the ear tip and the body. Two small molds produce better results than one large mold with complex geometry.

Mold Making: Choose the Right Method

Rubber prototypes need molds. You have two main options, depending on precision needs and quantity.

Practical tip: Start with a 3D-printed mold for your first one to five prototypes. Test the design. When you are confident, invest in a CNC mold for larger batches.

Molding Process: Select Based on Rubber Type and Part Size

Three common processes cover most rubber prototype needs. Match the process to your material and application.

Liquid Silicone Injection Molding (LSR)

This process is for high-precision parts made from liquid silicone.

How it works:

• Mix liquid silicone Part A and Part B in equal parts.
• Inject the mixture into a heated mold at 150°C to 200°C.
• Cure for 5 to 15 minutes depending on thickness.
• Demold and trim excess material.

Advantages: High precision for small parts, excellent elasticity, no post-curing needed.

Best for: Transparent medical parts like infusion tube fittings. High-precision seals for electronics.

Solid Rubber Pressing

This process uses pre-cut rubber sheets and pressure to form parts.

How it works:

• Cut rubber sheets to approximate shape.
• Heat sheets to 120°C to 180°C to soften.
• Press into the mold with 10 to 20 MPa pressure.
• Cool for 10 to 20 minutes, then demold.

Advantages: Low cost, fast for large parts, works with aging-resistant materials like EPDM.

Best for: Sealing strips and door gaskets. Large shock-absorbing pads.

Polyurethane Casting

This process uses liquid polyurethane that cures at room temperature or with mild heat.

How it works:

• Mix resin and hardener in equal parts.
• Degas under vacuum to remove air bubbles.
• Pour slowly into the mold to avoid trapping air.
• Cure at room temperature for 24 hours or 80°C for 2 hours.

Advantages: Mimics rubber flexibility well. Perfect for overmolding onto metal or plastic cores.

Best for: Overmolded grips where rubber bonds to a rigid handle. Prototypes with metal inserts.

Process Selection Guide

Post-Processing: Refine and Enhance Quality

Rubber parts almost always need some finishing after demolding.

Basic Trimming and Deburring

Use a sharp blade to remove flash—the thin layer of rubber that seeps between mold halves. For small parts like silicone earbuds, use tweezers to peel fine burrs. Avoid sanding soft rubber; it damages the surface.

Secondary Vulcanization for Silicone

Bake silicone prototypes at 150°C to 200°C for two to four hours. This improves temperature resistance by about 30% and extends lifespan by 50%.

Real example: A silicone automotive seal after secondary vulcanization withstood 150°C for 1,000 hours without hardening. An untreated version failed at 500 hours.

Surface Treatment

Add finishes that improve function or appearance.

• Anti-slip coating: Spray epoxy-based paint on grips to increase friction. Reduces slip by 60% on wet surfaces.
• Silk screen printing: Add logos, hardness ratings, or warning text.
• Material bonding: Use rubber-specific adhesives to attach rubber to metal or plastic.

How to write a spec that gets priced correctly

A drawing is a contract. If it leaves a number open, the shop fills that number in with its own default. The default is rarely the one you had in mind. Put these five lines on every RFQ and most of the back-and-forth disappears before it starts.

• A model you are willing to freeze for the build
• The question the prototype must answer
• Process and material that can answer it
• Tolerance on the features under test
• How many iterations you have budgeted

The point is not paperwork. Each line removes a decision the shop would otherwise make for you. A complete RFQ comes back priced. An incomplete one comes back guessed.

What actually drives the price

Buyers usually push on material because it is the line they can see. In practice the material is rarely the biggest number on a quote. These five lines decide most of it:

• process choice
• part size and feature count
• material
• finish and fit checks
• number of iterations

Ask for the quote split by line. A supplier who cannot break it down is guessing, and you will pay for the guess. The line you can usually renegotiate is the tolerance band, not the raw material.

Problems you will meet, and the fix

Every process has a failure mode it prefers. The same four show up again and again on this kind of work, and none of them are mysteries once you know what to look for.

• A prototype that is too good and hides a production problem
• A prototype that is too rough to test the real question
• Material chosen for speed rather than for the test
• No measurement plan, so the result is an opinion

Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order. Write the check into the purchase order so nobody has to remember it.

What to check on the first article

The first article is the cheapest inspection you will ever buy. Use it properly and the rest of the run becomes boring, which is exactly what you want.

• Every dimension on the drawing, with the measured value written beside it.
• The material certificate, matched to the heat or lot number on the parts.
• The finish against the sample you approved, under the same light.
• Fit against the mating part, assembled rather than measured.
• Packaging, because parts that arrive damaged were never in tolerance.

Check in this order: datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise. Keep the report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.

How to compare two quotes fairly

Two numbers are not comparable unless the scope matches. Line them up before you decide, because a low number with three gaps is not a low number.

Same drawing, same material, same finish, same inspection. Anything else is a different job wearing the same part number. Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps.

Ask each supplier to state their assumptions in writing. The one who does is usually the one who has run the process before.

Scaling from one part to a batch

The first part teaches you the process. The hundredth teaches you the process cost.

Watch three things as volume grows: setup amortisation, tool wear, and how much hand work the finish still needs. If the unit price barely moves between ten and a hundred, the cost sits in material or in hand work, not in setup. Ask which, because only one of them is negotiable.

Lead time behaves the same way. A one-off is scheduled around other jobs. A repeat order is scheduled around your forecast. Give the shop a forecast and the lead time gets shorter, not longer.

How to read a supplier's quote

A quote is a short document with a long shadow. Four things in it decide whether the job runs smoothly, and only one of them is the price.

• The scope line. It should name the process, the material and the finish, not just the part.
• The tolerance basis. General tolerance or the drawing, and which standard it follows.
• The exclusions. Tooling, freight, certificates and inspection are the usual omissions.
• The validity date. Material prices move, and an open-ended quote is a promise nobody can keep.

Read the exclusions before you read the total. A quote that leaves out tooling is not cheaper. It is a quote for a different job.

What to send with the first order

The first order sets the pattern for every order after it. Send a complete package once and the shop files it, and the second order takes a fraction of the time.

• A STEP or native model plus a PDF drawing carrying the same revision letter.
• The material callout by standard number, not by trade name.
• The finish and the exact faces it applies to.
• Any test the part must pass: fit, seal, drop, salt spray, dielectric.
• A contact who can answer a question inside one working day.

Then write down what was agreed. An email that confirms the material, the finish and the date is worth more than a longer purchase order that leaves them open.

When this is the wrong choice

A good supplier tells you when the process does not fit. These are the cases where we say so.

• The volume is so low that setup costs more than the parts are worth.
• The tolerance is tighter than the process can hold without a second operation.
• The geometry cannot be made without a tool feature that will not pay back.
• The material you need is not available in the form the process requires.
• The schedule is shorter than the tooling or setup time, and nobody has said so yet.

None of these are refusals. They are reasons to look at a different route, and the earlier that conversation happens the cheaper it is. The most expensive mistake in manufacturing is a process chosen before the question was understood.

Planning the ramp from prototype to production

The gap between one good part and a thousand identical ones is a plan, not a machine. Three decisions close it.

First, freeze the design. Every change after tooling starts is a re-cut, and re-cuts are where schedules go. Second, decide the inspection level. A prototype is checked by eye; a production part is checked against a report. Third, agree the change process in writing, including who pays for it.

Write the ramp down as dates and owners, not as intentions. A ramp plan with three names and three dates is worth more than a page of good intentions.

Testing and Optimization: Validate Performance and Fix Issues

Test your prototype against the requirements you defined at the start.

Key Test Items

Solve Common Defects

Making rubber prototypes requires a different approach than plastic or metal. You must account for shrinkage in your CAD model. You need molds, which means choosing between fast 3D-printed molds for early iterations and precision CNC molds for larger batches. The molding process—LSR, solid pressing, or polyurethane casting—depends on your material and part geometry. Post-processing refines the part, and testing confirms it meets requirements. Rubber prototypes reward attention to detail. Small adjustments like adding a 2-degree draft angle or adjusting shrinkage compensation can turn a frustrating process into a reliable one.

Our solution for Step-by-Step Process

YiguProto runs rapid prototyping in house, from a single prototype to a production batch. We quote the process, the material and the finish as separate lines, so you can see where the money goes instead of arguing with one number.

Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the features that will not hold tolerance on the process you picked.

Every order ships with an inspection report on the features you call out. If a part misses, we make it again. Ready to price a part? Start with a free quote and DFM review, or read more about our rapid prototyping. You can also talk to an engineer before you commit to a drawing.

FAQ about Step-by-Step Process

The short version

Step-by-Step Process rewards the buyer who reads the data sheet and the drawing together. Pick the option for the property that matters, not for the price per kilo.

Tighten only what mates. Test a sample before the run. Then let the process do the rest.