When you request a custom silicone part, the material name alone is not enough to judge the quotation. The forming route controls the tool investment, first-sample accuracy, and whether the finished part keeps its shape in service. This guide walks through the silicone manufacturing process from compound preparation to final inspection, so you can compare the process plan before approving production.
The Process Starts With The Part, Not The Machine
Before silicone is mixed, the drawing has to answer a more useful question than “Which machine do you use?” It needs to show how the part will work after installation. Stable recovery matters most for a thin sealing lip. Along a long profile, cross-section consistency controls the fit. For a food-contact sheet, documented compound control and a cleanable surface matter just as much.
Even within one silicone family, a change in approved hardness or cure system can alter the finished result. For a custom silicone rubber profile, a clear cross-section drawing is often more valuable than a product photo. It lets you review the profile before tooling and spot installation risks early.
Confirm these points before selecting the route:
- Part geometry and critical tolerances
- Working temperature and contact media
- Required hardness, color, surface, and certification
- Annual volume, first order quantity, and sampling plan
These details decide whether a process is practical. They also prevent a common mistake: choosing a material by name and only discovering after tooling that the process cannot hold the required geometry.
Step 1: Choose The Silicone Form And Cure System
Silicone does not arrive at the factory in one universal form. The form of the raw material determines how it can be metered, shaped, and cured.
HCR Or HTV Silicone
High-consistency rubber is a solid, dough-like silicone compound. It is prepared, shaped, and then cured with heat. HCR is a practical starting point for continuous products and molded parts.
Its strength is flexibility in part size and process choice. Its limitation is that batch preparation and mold filling have to stay consistent. If those controls drift, a long strip may show hardness changes along its length or a molded seal may vary in compression.
LSR Or Liquid Silicone Rubber
Liquid silicone rubber is supplied as a two-component liquid system. The components are metered, mixed, and injected into a heated mold. LSR is attractive for complex details and thin sections. It becomes especially practical when the production volume justifies automated molding.
The liquid form does not remove the need for design work. The gate and vent layout must match the flow path, or a complex part may not fill evenly. That can leave a visible defect or a weak section even when the LSR itself is suitable.
RTV Silicone
Room-temperature-vulcanizing silicone is normally selected for applied or in-place curing rather than high-volume molded production. It can be useful when a part is too large for a conventional mold. It should not be treated as a direct replacement for an HCR or LSR grade without checking the required mechanical and production performance.
The practical distinction is simple: HCR and LSR are common routes for repeatable manufactured parts, while RTV is more often chosen when the silicone must be applied or cured at the installation site.
Step 2: Build A Compound That Can Survive The Application
Material selection is not finished when the word “silicone” appears on a quotation. The compound still has to be matched to the part function and working environment. The review then covers the approved hardness and any reinforcement or contact requirement that can affect performance.
Two compounds can use the same silicone polymer and still behave differently. The filler system and cure package can change the finished part’s density, moldability, and compression recovery.
This matters most in products that look simple. A flat silicone gasket may have only one outline, yet a small change in thickness or hardness can change the bolt load required to seal it. A silicone hose can pass an appearance check while failing when it is bent repeatedly. A colored profile can meet the drawing but show surface defects when the pigment is not dispersed evenly.
What To Confirm In The Compound Review
| Requirement | What It Affects | What To Confirm Before Production |
| Hardness | Compression force and installation fit | Target Shore range and test method |
| Cure system | Cure speed, by-products, and post-cure needs | Platinum, peroxide, or another approved system |
| Color | Appearance and brand consistency | Color standard, sample approval, and batch control |
| Reinforcement | Tear strength and dimensional stability | Fiber or insert type and placement |
| Contact requirement | Compliance and cleaning behavior | Food, medical, electrical, or other applicable specification |
We do not treat “silicone grade” as a complete technical specification. You still need the operating conditions and the part function before the compound can be judged properly.
Step 3: Mix, Meter, And Keep The Batch Consistent
For HCR production, compounding turns the base silicone and approved ingredients into a workable material with a controlled cure response. The important output is not a long list of machines. It is a batch that behaves predictably when it reaches the mold, die, or calender.
Uneven dispersion can create local hardness changes. Poor temperature control can narrow the processing window. Contamination can inhibit curing or produce visible defects. Those problems may later appear as unstable dimensions or incomplete curing.
LSR uses a different control point. Its two components must be metered at the correct ratio and protected from contamination before they enter the mixing and injection system. A small dosing error can change cure behavior across the entire shot, so traceability and ratio control matter more than a supplier’s general statement that the material is “high quality.”
For purchasing, the useful questions are straightforward:
- Can the batch be traced from raw material to finished lot?
- Is the approved color or hardness sample retained for comparison?
- How is the compound protected from contamination before forming?
You are not only buying silicone. You are buying repeatability across the production order.
Step 4: Select The Forming Process For The Part And Volume
The forming method should follow the geometry and production plan. A process that is economical for a thick, simple pad may be inefficient for a thin multi-cavity component. A route that works for a continuous strip will not automatically work for a three-dimensional gasket with inserts.
Process Decision Table
The figures below are planning references, not fixed quotations. Geometry and the approved specification can move the actual range. Use the table to choose a route for the first discussion, then confirm the numbers against the drawing.
| Part Requirement | Suitable Route | Typical Volume Reference | Tooling Cost Reference | Main Risk To Review |
| Prototype, simple shape, or large molded part | HCR compression molding | 50–5,000 pcs/year | US$200–$1,500 | Flash, voids, and uneven charge placement |
| Complex 3D geometry and repeat production | LSR injection molding | 10,000+ pcs/year | US$1,500–$6,000 | Venting, gate marks, air traps, and flash |
| Inserts, reinforced parts, or detailed HCR geometry | Transfer molding | 1,000–10,000 pcs/year | US$800–$3,000 | Insert alignment and trapped air |
| Continuous tube, cord, or profile | Silicone extrusion | Long continuous runs | US$500–$2,000 die reference | Die swell, dimensional drift, and cure consistency |
| Flat sheet or coated fabric | Calendering or coating | Continuous sheet demand | Project-specific line setup | Thickness variation and adhesion |
| Large component or in-place cure | RTV application or casting | Low-volume work | Project-specific tooling | Cure depth, surface contamination, and long cycle time |
Compression Molding
The operator places a measured HCR charge into the mold, closes the heated tool, and applies pressure until the material fills the cavity and cures. Compression molding is often practical for a large or relatively simple silicone part when the volume does not justify a more automated route.
The part’s result depends heavily on charge weight and placement. Too little material can leave an incomplete edge. Too much can increase flash and trimming work. A drawing should identify the critical sealing surface rather than treating every dimension as equally important.
LSR Injection Molding
The two liquid components are metered and mixed before entering a closed heated mold. This process suits repeat production with complex details, thin sections, and consistent part-to-part output.
The most useful review is not simply cycle time. Gate and vent design must protect the visible surface, while the cavity must fill evenly enough to protect a thin lip during demolding. A small cosmetic defect may be acceptable on an internal seal but unacceptable on a medical or consumer-facing component.
Transfer Molding
Transfer molding places the HCR charge in a transfer pot and pushes it through a runner system into a closed cavity. It is useful when the part is too detailed for a simple compression charge or when inserts and reinforced areas need better positioning.
The closed cavity can improve consistency, but it does not solve poor insert preparation. If an insert moves during filling, the final part may have an uneven wall or a sealing surface that no longer matches the assembly drawing.
Extrusion
Extrusion is used when the silicone part has a continuous cross-section, such as a long sealing profile. The die controls the shape while the cure system stabilizes it through the production line.
For a profile, the first sample should be checked at several points along its length. A profile that looks correct at the beginning of a coil can drift later if die temperature, line speed, or cure stability changes. The same concern applies to silicone rubber strips, especially when the strip will be cut to length and installed in a frame.
Calendering And Coating 
Calendering creates a continuous silicone sheet with controlled thickness. Coating applies silicone to a carrier such as fabric or another substrate. These routes are relevant to flat sheets and coated carriers.
Thickness is the first check, but not the only one. The surface must remain consistent, and the silicone must bond to the carrier without weak areas. A sheet that is technically within thickness tolerance can still fail in use if its surface finish or adhesion is unsuitable for the assembly.
Step 5: Cure The Silicone And Stabilize Its Performance
Silicone becomes a usable elastomer when its molecular chains form a cross-linked network. A simple way to understand curing is to imagine bridges connecting loose polymer chains. Once enough bridges form, the material holds its shape and recovers after deformation instead of flowing like an uncured compound.
Shrinkage is a mold-design input, not a final inspection afterthought. As a planning reference, LSR is often reviewed around 2.0–4.0% and HCR around 3.0–5.0%. The exact value changes with the approved grade and section design, so confirm it before cutting the mold. Using the wrong value can make an entire batch miss its dimensional target.
The cure schedule has to match the selected silicone system and part geometry. A thick section may cure differently from a thin lip, and a deep cavity may need more attention to heat transfer than a flat sheet. An under-cured part can remain weak or tacky, while excessive heat can damage the surface or reduce the intended performance.
Some HCR and LSR systems also require post-curing. A common planning reference is 180–200°C for 2–4 hours in a forced-air oven, but the exact schedule must follow the compound and part geometry. Post-curing may reduce residual volatiles or stabilize the finished material; it is not an automatic step for every silicone product. For food-contact or medical applications, confirm the chosen grade and cure schedule against the applicable project specification before approval.
For food, medical, or high-cleanliness applications, curing and post-curing affect more than hardness. They can influence odor and extractables, which is why the approval plan should state the cleanliness requirement before mass production.
Step 6: Deflash, Finish, And Prepare The Part For Assembly
After molding or extrusion, silicone parts may need edge finishing or assembly work. The correct finish depends on where the part will be installed.
For a gasket, a small amount of flash on the non-sealing edge may be removable, while flash on the sealing land can change the compression path. With an extruded profile, a poor splice can matter more than a small surface mark because the joint may open during installation. On a sheet, clean cutting and edge control may decide whether the part fits the fixture without tearing.
The inspection method should follow the functional surface. Do not approve a silicone part only because its color and general shape look correct. Mark the areas that seal against the mating assembly, carry compression, or remain visible after installation.
Step 7: Inspect The Properties That Matter In Use
Silicone inspection should connect the test to the failure the test is meant to prevent. A test list without an acceptance purpose does not help you compare two production lots.
| Property Or Check | Why It Matters | Common Reference |
| Hardness | Confirms compression and fit behavior | ASTM D2240 or ISO 48-4, as applicable |
| Tensile strength and elongation | Shows how the material behaves under stretch | ASTM D412 or ISO 37 |
| Compression set | Indicates recovery after long compression | ASTM D395 or ISO 815-1 |
| Tear strength | Helps evaluate edges, notches, and thin sections | ASTM D624 |
| Dimensions and flash | Protects installation and sealing fit | Approved drawing and sample |
| Color and surface | Controls visible appearance and batch consistency | Approved color or master sample |
The correct reference depends on the specification and test laboratory. Your drawing, material approval, and inspection record should describe the same part. A hardness result cannot compensate for the wrong thickness, and a visually clean part cannot prove compression recovery.
We recommend reviewing the complete inspection plan through the project’s quality assurance process and confirming any special performance testing through the research and testing resources.
A Few Manufacturing Problems That Are Easy To Miss
Defects Usually Point Back To A Process Decision
Short shots often mean the charge, gate, or filling path was not matched to the cavity. Flow marks can appear when the material front cools or cures unevenly. Mold sticking usually needs a review of release conditions and draft. Hardness variation is more likely to come from inconsistent mixing or cure control than from the name “silicone” alone. Each defect should be traced to its location and production record before changing the compound.
Design Warning: Do not copy an HCR mold design directly into an LSR project. The material flow, shrinkage behavior, gating, and venting requirements can be different.
Procurement Warning: A thinner wall does not automatically mean a lower-cost part. Thin sealing lips may require tighter LSR tooling control and can create more scrap during sampling.
Cost-Saving Direction: For a large flat gasket with a relatively loose tolerance, sheet conversion and die cutting may be more economical than a dedicated compression mold. Confirm the comparison using the finished part cost, not only the tooling fee.
A Silicone Part Can Look Fine And Still Seal Poorly
Appearance inspection will not reveal every compression problem. If the cure response or wall thickness is unstable, the part may lose recovery after installation even though its color and outline are acceptable.
The Correct Material Can Still Fail In The Wrong Process
An LSR grade may be technically suitable but poorly matched to a compression tool. An HCR grade may be appropriate for a profile but difficult to use for a thin, highly detailed part. The process and material have to be approved together.
A Food-Grade Claim Does Not Finish The Review
You still need to confirm how the part contacts the product and how it will be cleaned. For food-processing projects, compare the compound and production controls with the relevant food grade silicone rubber sheet requirements instead of approving a generic “food-safe” statement.
Typical Process-Selection Scenario
For a low-volume, large gasket, compression molding may keep the initial tool investment reasonable. A thin, detailed component with repeat demand may justify LSR injection because automated metering and cavity filling can improve consistency. The right choice is determined by the drawing and production plan, not by the lowest tooling number shown in an initial quote.
FAQ
Can HCR And LSR Silicone Use The Same Mold?
Sometimes, but you should not assume the mold can transfer directly from one material form to the other. LSR relies on flow and injection behavior that differs from a preformed HCR charge. Review the mold design and demolding method before changing the material form.
Which Silicone Manufacturing Process Is Best For A Large, Simple Part?
Compression molding is often a practical starting point for a large or simple part when the production volume does not justify a more automated route. Wall thickness and annual quantity still need review before the route is fixed.
Does Every Silicone Product Need Post-Curing?
No. Post-curing depends on the silicone compound and the end-use requirement. Some applications use it to reduce residual volatiles or stabilize performance, while other parts may not require the same treatment. Ask for the recommended cure and post-cure conditions for the exact grade being quoted.
Why Do Silicone Parts Develop Flash Or Air Bubbles?
Flash is commonly related to mold alignment, excessive material, or pressure escaping at the parting line. Air bubbles require a separate review of venting and cavity filling. Confirm the cause from the defect location and process record instead of changing the compound blindly.
What Should You Send For A Silicone Manufacturing Quote?
Start with the drawing or sample, then state the part’s function and expected quantity. Add the working conditions that could affect the process route. If the part is a profile, include a cross-section drawing and cut-length requirement.
What Is The Typical Shrinkage Rate For LSR And HCR Silicone?
As an early design reference, LSR is often reviewed around 2.0–4.0% and HCR around 3.0–5.0%. The approved compound’s data should control the mold design because hardness, wall thickness, and cure temperature can move the actual result.
Can Silicone Be Overmolded Onto Metal Or Plastic Inserts?
Yes, when the insert material, surface preparation, retention geometry, and cure system are compatible. The insert drawing should show the bonding or mechanical-locking area before the mold is designed.
How Long Does Silicone Tooling Usually Last?
Tool life depends on the tool material, cycle conditions, geometry, maintenance, and production volume. A general number without those inputs is not reliable, so ask for a tool-life estimate based on the actual mold and planned cycles.
Is Extrusion Cheaper Than Injection Molding For Long Silicone Seals?
Extrusion can be more economical when the part has a continuous cross-section and will be supplied in long runs. Injection is more suitable when the part needs a closed three-dimensional geometry. Compare the die or mold with the finished-part operations before deciding on price.
What Certifications Can Apply To Food-Grade Silicone Parts?
The applicable requirement depends on the product and destination market. Common references include FDA 21 CFR 177.2600, LFGB, and project-specific hygiene or extractables testing. Confirm the exact certificate and test scope for the compound and finished part being quoted.
Choose The Process Before You Commit To The Tool
Silicone manufacturing is not one single molding operation. Each material form and forming route solves a different production problem. When you send Weprofab your drawing, working conditions, and quantity, our team can review the process route and inspection requirements before quotation. Send your detailed silicone part requirements for a practical manufacturing review.
