Introduction
There are several liquid silicone molding key tips in manufacturing process, in order to guarantee its perfect performance for projects with high volume, efficiency and tolerance. Determining the ideal liquid silicone rubber material and fabrication process is the most crucial step in silicone parts production. In addition, we also need to consider quantities, leading time, budgets, design features, future design changes, market success and other numerous variables.
Liquid silicone rubber is becoming the preferred materials for increasing application over traditional silicone rubber. Its excellent physiological properties make it a foothold in many industries. Such as high thermal stability, intricate geometries production and shorter cycle time.
How is Liquid Silicone Molding Different?
Liquid silicone molding is different from thermoplastics molding. Its cycle time will only take 3 to 10 seconds, while thermoplastics molding and solidification will take 10 to 90 seconds or more. There are some specific attributes in liquid silicone molding:
- Complex geometries: liquid silicone has low viscosity, it can flow into complex and thin features easily.
- Automation: liquid silicone molding is easy to transform into automated process with fewer worker.
- Safety improvement: operators can remove molded silicone parts by conveyor, chute, or robot in the mold area.
- Easy preparation: there is no milling or mixing process for the base rubber preparation.
Liquid silicone is an essential material in automotive, construction, medical, electrical and electronic industries. However, liquid silicone molding requires professional machinery and intricate tooling design, production development and expertise.
Here are liquid silicone molding tips as following to improve your success in liquid silicone projects.
Budget Plan for Liquid Silicone Molding Project
Budget plan is the most critical step in product development. The key to create an efficient budget is aligning with company strategic and long-term objective. Otherwise, it is also efficient to outsource the development to an experienced silicone molding company.
Once you estimate an overall budget, there are 3 main points you should consider:
Upfront Cost
Molding design: all preparations before products for sale.
Product design: all costs for silicone parts production, like silicone raw materials, tooling, equipment, shipping, delivery and package.
Production Setup
This item includes preparation cost for production run. Such as waste in refine and test process. For mass-production, we should prepare for production volume of 10,000 or more.
Production Cost
Silicone component cost: the incremental cost for more items’ production. Such as silicone raw materials, machining time cost, operator cost, post-production finishing.
- Assembly cost: normally manual or machines cost in assembly process.
- Quality control: the sample testing process for quality assurance.
Budget plan provides an estimate cost of products development based on prior experience, this will result in overestimate or underestimate of total costs. Therefore, you need to cooperate with silicone molding companies with excellent experiences, in order to avoid dramatic budget adjustments.
Liquid Silicone Material Selection
Liquid silicone molding technology apply a two-part compound materials, the compound A with catalyst, and the compound B with cross-liker. The cross-linker can convert raw liquid silicone into products with mechanical stability. Therefore, the liquid silicone material is ready-to-use compounds, we also can add color and additives to increase appearance and machinery performance.
Both liquid silicone compound A&B have translucent or slight opaque appearance. The normal catalyst of platinum curing agent can trigger the cross-linking reaction at room temperature. Furthermore, the compound A also contains inhibitors to slow down curing process below a certain temperature. Once above specific temperature, cross-linking will occur rapidly and freely.
Different LSR Types & Grades
Product developers and designers can select different grades and types of liquid silicone (LSR).
- Different liquid silicone rubber (LSR) can provide final silicone products with different surface texture, such as dry, slippery, or rubber, wet.
- Normal LSR materials have durometer range from 20 to 80.
As general-purpose liquid silicone rubber is only best for normal applications with basic physical properties. Therefore, we can apply fillers and additives to increase LSR resistance of heat, oil and other solvents, reinforce raw and cured liquid silicone properties. In order to stretch low-temperature capabilities of LSR, we can add phenyl units to mixture compounds. Furthermore, pyrogenic or precipitated silica, carbon black can be added to reinforce the silicone network. Finally, non-reinforcing filler like stabilizer are added into the mixture to optimize heat and resistance to different media.
Cosmetic Appearance of final silicone parts are important to designers, the common additive for LSR coloring compounds are consist of three chemical ingredients: pigments, carrier resins, and dispersants. All these ingredients must carry evenly in the mixture. Typically, we add color at the prior point to static or dynamic mixing equipment. The pigment is in paste or liquid form, it is custom formulated by metered equipment to blend into silicone mixture with specific percentage. In order to obtain desired color.
Self-adhesive Liquid Silicone
The new grade self-adhesive liquid silicone can bond to common thermoplastics without a primer step. This allows in-mold bonding of liquid silicone rubber to thermoplastic components. Therefore, we can add precise LSR on thermoplastics directly without any additional hold-place. This provides several benefits:
- No thickness addition on final molded parts.
- Economical with less material usage.
- Smaller miniature parts size.
Self-adhesive liquid silicone provides sufficient initial bond strength once remove from the molds. Its bond strength will increase to the peak value over time.
Liquid Silicone Design and Molding Tips
In liquid silicone molding, we cannot just focus on silicone parts design without tooling design considerations. We must design the best tooling to satisfy project requirement of dimensions and cavity geometries. Furthermore, align all these demands with limited mold space.
Once we select the perfect liquid silicone material for final products, we need to determine the following elements:
Determine Molding Process
Which molding process is applied to mold the liquid silicone parts? This will impact the final geometries significantly. We can realize that some silicone components work will in horizontal or automation LSR molding process, while others work better with vertical molding process or manual process. The complexity of components geometry is depending on molds size and injection molding machine size.
Decide Components De-mold
It is critical to achieve the easiest de-molding method in design process. As silicone has natural tackiness, it is difficult to remove, especially for high undercut components. Therefore, we need to consider undercut and wall thickness features carefully in design process.
Cold Runner System
In liquid silicone molding, the cold runner system allows direct gating without material waste. It consists of water-cooled nozzles in mold, and feed liquid silicone materials into each cavity. The liquid silicone material doesn’t cure within the cold nozzles.
Select The Gates
Once we decide the cold runner system, we can choose the typical gate styles of pin, submarine. For special design, we also can apply other gate types of edge band or ring.
The Best Gate Location
In material filling process, it is ideal to fill cavity from the thickest area of components. The gate location should never interfere with the assembly or action of final products.
The high pressure in liquid silicone molding result in double-sided design of molds. Although liquid silicone molding has some similarities to thermoplastic injection molding, there are still some critical differences. Only experienced engineers can understand these nuances, such as LSR mold heating, proper vent, surface finish and proper molds maintaining.
Liquid Silicone Molding Timelines and Benchmarks
In order to guarantee success of liquid silicone molding, we should plan detail timeline, and define major or minor benchmarks. Then track and monitor the progression of key activities and dates in the project.
- Design and engineering: convert concepts into virtual prototype by CAD and CAM software, evaluate design from multiple angles and make adjustments.
- Prototyping and model making: produce prototypes to emulate size, shape and cosmetic of final silicone parts. Then analyze parts properties and performance with actual samples for detail adjustment.
- Mold building: once finalize design process, start molds fabrication.
Notices of Liquid Silicone Prototypes
Prototyping is one of the most critical stages in product development, efficient prototyping will provide competitive edge in silicone molded components and assembly.
- At first, it will provide a clear and comprehensive understanding of final silicone parts in every aspect. This will cover all considerations for new successful production in tight time constraints.
- Secondly, the fabrication of prototypes in liquid silicone molding will save both time and money. We can evaluate silicone products form, fitness and functionality before tooling.
- Finally, we must get the right prototypes to continue further production without any issue.
Liquid Silicone Molding Manufacturer Selection
Liquid silicone molding is able to take enterprise operation and production into a new height level. However, it is challenging to find an experienced liquid silicone molding company. When choosing a liquid silicone molding company, you should search for a vendor with proven core competition in Liquid Silicone Rubber (LSR), LSR over-molding, and LSR 2-shot molding. Miwo is an experienced company in silicone product development and production. We prove invaluable cooperation with every stage of the project, including product design, mold design, molding process.
