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Injection molding and urethane casting, each with its own merits, are like two stars on the manufacturing stage, with their own uniqueness, together to build a rich and colorful production world.
Injection molding, as a powerful means of large-scale production of plastic products, occupies an important position in the manufacturing industry with its amazing high precision and ultra-high production efficiency, and can be described as a leader in the industry. Urethane casting, on the other hand, is known for its high degree of flexibility and perfect suitability for small batch production, in contrast to injection molding.
Next, this article delves into the mysteries of these twomolding methods, carefully dissecting the differences between them, and showing the benefits of each and the wide range of applications. Through all-round comparison and analysis, we will illuminate the direction for you on the road of choice in the manufacturing industry, and help you find the technical path that best meets your own manufacturing needs.
What is urethane casting?
Urethane casting, also known as vacuum casting, is an extremely practical manufacturing process. Put simply, the liquid polyurethane is carefully poured into the mold, and then the liquid urethane gradually hardens to the desired shape of the part.
This approach is particularly effective when prototyping, low-volume production, and manufacturing parts that require the highest level of detail.Urethane casting is popular because it enables the rapid production of high-quality, beautifully detailed parts at a relatively low cost without the high cost of tooling.
What is Injection Molding?
Injection molding is a common manufacturing processthat uses thermoplastic or thermoset materials to produce a variety of products with the help of injection molding machines. The process is roughly as follows: the material is heated to a molten state, and then the molten material is quickly injected into a pre-prepared mold that is the shape of the product we want. After the material has cooled, open the mold and the molded product will be automatically ejected.
Injection molding is known for its high precision and efficiency, and has excellent performance in the production of various products, such as common plastic toys, precision medical equipment, and automotive parts, etc., can be completed by injection molding process.
Comparison: Urethane Casting vs. Injection Molding
Although both methods fill a mold cavity with plastic,there are some differences between urethane casting and injection molding. Let’s check them out.
| Features | Urethane casting | Injection molding |
| Mould tools | Silicone rubber molds are used | Use hardened steel or aluminum molds |
| Material selection | Thermoset polyurethanes are commonly used | Suitable for thermoplastics such as ABS, polypropylene, TPU, etc |
| Throughput | Best for small batches | Best for large quantities |
| Tolerance | The average tolerance is about 0.01 inches | Achieve tight tolerances (up to 0.005 inch) |
| Wall thickness | The permissible wall thickness is 1 mm to 5 mm | Produces consistent wall thicknesses (0.5 mm to 4 mm) |
| Undercut | Easier to adapt to undercuts | Complex undercut die design |
| Apply | Suitable for small part volumes and rapid prototyping | Ideal for high-volume production |
| Delivery time | Shorter lead times facilitate rapid prototyping | Longer lead times, especially for complex designs |
| Cost | Low tooling cost, suitable for small to medium batch production | The cost of tooling is high, and high-volume production is cost-effective |
Example: A small business needs to produce automotive interior parts
Let's say a small automotive parts manufacturer is planning to produce a new type of automotive interior parts. This interior part has special requirements that require a soft touch, good abrasion resistance and scratch resistance. Manufacturers are presented with two production processes to choose from: urethane casting and injection molding. Below, let's take a closer look at the start-up costs of the two processes.
Anatomy of start-up costs for urethane casting
- Mold cost:This manufacturerdecided to adopt silicone molds for urethane casting. After some market research and communication with suppliers, the cost of making such a set of silicone molds is about $1,000. Compared with some other complex molds, this price is relatively acceptable for small businesses.
- Production preparation:One of the majoradvantages of silicone moldsis the short production cycle. Manufacturers do not need to spend a lot of time preparing for additional production conditions, such as the construction of a clean room. Soon, after the mold is made, it can be put into production directly, which greatly shortens the preparation time.
- Total start-up cost estimate:Combined with tooling costs and negligible production preparation expenses, the total start-up cost of polyurethane casting is at a relatively low level. This is an attractive option for small businesses with limited funds.
Start-up cost analysis for injection molding
- Tooling costs:If a manufacturer chooses theinjection molding process, a steel mold must be developed. The cost of developing a steel mold for the production of automotive interior parts is not cheap, about $30,000. This is a significant difference compared to the cost of silicone molds used in polyurethane casting.
- Production scale requirements:The injection molding process has a characteristic, only when the production quantity reaches more than 5000 pieces, can the mold cost be effectively amortized, so that the cost of a single product can be reduced to a reasonable range. But for the small manufacturer, the initial volume of orders was nowhere near that scale. This means that in the early production process, the cost of the tooling will put a huge cost pressure on each product.
- Hidden cost considerations:In addition to the high tooling costs, there is also an overlookedhidden cost of injection molding: the need to build an ISO Class 8 clean room. After calculation, it will cost about $160,000 to build such a dust-free workshop. This is undoubtedly a heavy burden for small businesses.
- Total start-up cost assessment:The total start-up cost of injection molding is much higher than that of polyurethane casting, taking into account factors such as mold cost, cost pressure caused by production scale not meeting expectations, and construction cost of dust-free workshop.
From this case, it is clear that the startingcost of urethane castingis significantly lower than that of injection molding. For this small auto parts manufacturer, choosing polyurethane casting can not only effectively reduce the operating cost and alleviate the financial pressure, but also start production faster and meet market demand in a timely manner with its short preparation time.
How Do Material Options Differ?
Material selection is a crucial consideration when discussing urethane castingversus injection molding. Here are the main differences between the two molding processes in terms of material selection:
| Project | Urethane casting | Injection molding |
|---|---|---|
| Material Limitations | Only room-temperature curing resin, tensile strength ≤ 80 MPa, engineering plastics cannot be used | There are no obvious restrictions, and high-strength materials such as glass fiber reinforced nylon are supported, and FDA food-grade certified materials can be used |
| Material advantages | Good feel and texture effect, suitable for small batch production | A wide range of material options support high-strength materials and can be directly used with FDA food-grade approved materials |
From the perspective of material selection,urethane casting and injection molding have their own advantages. Urethane casting is suitable for those production projects that have special requirements for product feel and texture, and the output is not large. With a wide range of material options, especially for high-strength materials and FDA food-grade approved materials, injection molding is uniquely positioned to create products that are subject to high loads or come into contact with food. Therefore, when choosing a molding process, manufacturers must fully consider the actual needs of the product and the characteristics of various materials to make the most appropriate decision.
Case: An electronics company needs to customize a mobile phone protective case
Suppose an electronics manufacturer intends to manufacture a series of custom-made phone cases in production quantities of up to 100 pieces. In order to meet the market demand, the manufacturer decided to distribute orders for its products to different suppliers for processing. In view of the urgent needs of the market, the customer urged us to deliver the goods as soon as possible. The manufacturer decided to go with the production method of urethane cast cores. Manufacturers have two main production options: the casting of urethane and the injection molding process.
Compare the time of delivery
Urethane is used for casting
The manufacturing process of silicone mold:According to the common practice of the industry, the production of silicone mold covers multiple steps such as vacuum deaeration and curing, and the whole process takes about 48 hours.
The time required to make a polyurethane casting individual piece includes pouring, curing and manual post-processing, and the entire process takes about 20 minutes per piece.
There are a total of 100 products, and their manufacturing cycle is: 20 minutes/piece× 100 pieces=2000 minutes=33.33 hours, which takes about 1.4 days.
The total lead time is as follows: the production time of the silicone mold plus the production time of a single piece is equal to 48 hours plus 1.4 days, which is about 3.8 days.
Lead times for injection molding
1.Steel mold production cycle:
The key part of injection molding is to make steel molds. You know, steel molds are not something that can be done casually, it has to be done with the help ofCNC machining technology. The process can take anywhere from 4 to 8 weeks, depending on the complexity of the mold. For example, if the internal structure of the mold is particularly complex, with various fine lines and special shapes, it will take more time to carve; Or the mold size is very large, and the operation difficulty increases during processing, and the time consumption will be correspondingly longer. Here, let's assume that the processing time is 6 weeks, which translates to 42 days. During these 42 days, the machine masters will carefully operate theCNC equipment, grinding and carving the steel into a mold that meets the requirements, little by little, and there is no room for sloppiness in each process.
2.Single-part production time
Once the mould has been made, the subsequent production of the one-piece product becomes extremely efficient. The injection molding adopts a fully automated production mode, and the whole process is like a precision running assembly line. Typically, it takes about 30 seconds to produce a product. Imagine that the plastic raw material is quickly injected into the steel mold under high temperature and pressure, and after a short cooling and shaping, a product is freshly baked. If there is an order for 100 products, let's calculate the total production time, multiply 30 seconds by 100 pieces, get 3000 seconds, and then convert that time to hours, which is 0.83 hours. Compared to the 42 days it took to make the steel mold, that 0.83 hours is simply negligible.
Total Lead Time
In general, the total lead time for injection molding is mainly determined by the CNC machining time of the steel mold. Because the production time of a single piece is so short, the impact on the overall delivery time is negligible. So, the total lead time for injection molding is the CNC machining time for the mold plus the negligible production time per part, which is 42 days
| Molding process | Mold making time | Single-piece production time | Total delivery time |
|---|---|---|---|
| Polyurethane casting | 48 hours | 20 minutes/piece | About 3.8 days |
| Injection molding | 4-8 weeks (assuming 6 weeks) | 30 seconds/piece | 42 days |
What Are the Precision Gaps?
Whendiscussing the accuracy gap between urethane casting and injection molding, we can conduct a detailed analysis from two aspects: tolerance comparison and surface quality.
Tolerance comparison
| Molding process | Tolerance range | Influencing factors |
|---|---|---|
| Polyurethane casting | ±0.3mm | Affected by the deformation of the silicone mold |
| Injection molding | ±0.05mm | ISO 2768-m compliant |
Surface
| Molding process | Surface | Follow-up processing |
|---|---|---|
| Polyurethane casting | Hand polishing is required | Add $8 per piece cost |
| Injection molding | Can directly reach Ra 1.6μm | No additional processing is required |
Comprehensive analysis
There are significant differences between urethane casting and injection molding in terms of precision and surface quality. The precision of urethane casting is relatively low, the tolerance range is large, and thesurface quality needs to be polished by hand;The injection molding has a high precision, a small tolerance range, and the surface quality can directly reach Ra 1.6μm.
Suggestion:
- High requirements for precision and surface quality:It is recommended to choose the injection molding process to meet the high precision and high surface quality requirements of the product.
- Low requirements for precision and surface quality:Urethane casting may be a viable optionwhen the production volume is not large and the lead time is urgent, but care needs to be taken to control the impact of mold deformation on accuracy and consider the increased cost of manual polishing.
In practical applications, manufacturers should comprehensively consider the selection of the appropriate molding process according to the specific needs of the product, production conditions and economics.
How to Choose Based on Volume?
Production quantity is an important consideration when choosing between urethane casting and injection molding. The following is an analysis of how to choose the appropriate molding process based on production quantity:
Comparison of urethane casting and injection molding in production quantity
| Molding process | Mold making time and cost | Production time and cost per piece | Suitable production quantities |
|---|---|---|---|
| Urethane casting | The mold making time is short (about 48 hours) and the cost is relatively low | The production time of a single piece is long (about 20 minutes/piece), and the cost increases with the increase of quantity | It is suitable for small batch production, and the production quantity varies from a few to several hundred |
| Injection molding | The mold production time is long (4-8 weeks) and the cost is high | The production time per piece is extremely short (approx. 30 seconds/piece) and the cost is significantly reduced as the number increases | It is suitable for high-volume production, and the production quantity usually reaches more than thousands of pieces |
Recommendations for selecting a molding process based on the production quantity
Small batch production (e.g. dozens to hundreds):
Choosing a urethane casting:
- Advantages: The mold production time is short, the cost is relatively low, and it can quickly respond to market demand.
- Precautions: Because the silicone mold is easy to deform, which may affect the dimensional accuracy and surface quality, the mold needs to be checked and replaced regularly.
Injection molding is not recommended:
Reason: The mold takes a long time to make, the cost is high, and it is not cost-effective for small batch production.
High-volume production (e.g. more than thousands of pieces):
Choosing Injection Molding:
- Advantages: Although the mold making time is long and the cost is high, the production time of a single piece is extremely short, and the cost is significantly reduced with the increase of quantity, which is suitable for mass production.
- Precautions: It is necessary to ensure the accuracy and stability of the mold to ensure the dimensional accuracy and surface quality of the product.
Urethane casting is not recommended:
Reason: The production time of a single piece is long, and the cost increases with the increase of quantity, which is not suitable for mass production.
Summary
There are significant differences between urethane casting and injection molding in terms of material properties,molding principles, process, product performance and application areas. When choosing a processing method, it is necessary to comprehensively consider factors such as the specific requirements of the product, production scale and economic cost. With the continuous advancement of technology and continuous optimization of processes, it is believed that urethane casting and injection molding will show their unique advantages and application value in more fields.
Disclaimer
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FAQs
1.What is the difference between casting and injection molding?
The difference between casting and injection molding is: casting is to pour liquid or semi-solid materials into a mold for cooling and curing molding, which is suitable for a variety of materials but the process is complex and the production efficiency is low, and the product accuracy and surface quality may not be as good as injection molding; Injection molding is to inject the molten plastic into the mold through high pressure to cool and solidify the mold, mainly suitable for plastics, with high process efficiency, automatic production, accurate product size, good surface quality, suitable for large-scale, standardized product production.
2.What are the disadvantages of urethane casting?
The disadvantages of urethane casting mainly include: the cost of the mold is high and the life is limited, which is not suitable for mass production; The silicone mold is easy to deform, resulting in unstable product dimensional accuracy; The surface quality of the product may not be as good as that of injection molding and requires additional treatment; At the same time, the performance of urethane materials may be reduced in high temperature or strong polar solvents, strong acid and alkali media, and the use scenarios are limited.
3.Can you inject polyurethane molds?
Yes, it is possible to inject polyurethane molds. Polyurethane (TPU) is a commonly used injection molding material with good abrasion resistance, oil resistance, low temperature resistance and elasticity. Injection molding polyurethane molds can realize automated production, improve production efficiency, and ensure the dimensional accuracy and surface quality of products. However, it should be noted that injection molding polyurethane molds require the use of specialized injection molding machines and molds, and the mold manufacturing cost is high.
4.What is Polyurethane Molding?
Polyurethane molding is a molding process that processes polyurethane materials into the desired shape and size. The polyurethane molding process includes a variety of methods such as injection molding, casting molding, reaction injection molding (RIMPU), etc. Among them, injection molding is one of the most commonly used methods, which involves injecting a molten polyurethane material into a mold, cooling and curing, and then demolding to obtain a finished product. Polyurethane molded products are widely used in automobiles, electronics, medical, sports equipment and other fields because of their good physical properties and processing properties.
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