The process begins with machining a mold from materials like steel or sand to replicate the intended part's shape and attributes. Permanent molds are more frequently employed than sand molds due to their greater productivity potential. This mold is carefully sealed to prevent any undesired air ingress. Before molten metal enters the mold, certain pre-casting processes may be performed. The mold might be preheated to prevent thermal shock, and fluxes could be employed to clean its surface and prevent oxidation. To eliminate trapped gasses, degassing procedures may also be carried out before casting. Once these preliminary steps are complete, the metal is elevated to a temperature surpassing its melting point within a furnace. Subsequently, the molten metal is conveyed to a holding furnace (crucible) responsible for sustaining the temperature and eliminating any impurities present in the metal. The furnace is then pressurized. The molten metal enters the mold cavity steadily. This controlled process is characterized by a lack of turbulence due to the low applied pressure. Before solidification begins, air within the mold is allowed to escape through strategically placed vents.

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During the cooling phase, the molten metal gradually solidifies, conforming precisely to the shape of the mold cavity. Throughout this process, the applied pressure is maintained to fill any potential shrinkage pockets and guarantee that all intricate details of the mold are fully replicated by the solidifying metal. Once the metal has sufficiently cooled and solidified, the mold is opened, and the resulting casting is carefully removed. Depending on the complexity of the part, further processes such as trimming, machining, and finishing may be conducted to achieve the desired final product.

Steps in the Low-Pressure Casting Process

A detailed breakdown of each step involved in the low-pressure casting production cycle is discussed below:

1. Melt Metal Alloy in Furnace and Bring to Casting Temperature

The production cycle to make a low-pressure die casting part begins by melting the desired metal alloy in a furnace. Heating continues until it reaches the appropriate temperature for casting. Determining this casting temperature is a critical step and involves considering various factors to ensure the quality and integrity of the final part.

One key factor that influences the casting temperature is the melting point of the specific alloy composition being used. Different alloys have distinct melting points, and reaching this temperature ensures that the alloy is fully molten and ready for casting.

2. Transfer Molten Metal to Holding Furnace Below Mold

Once the liquid metal is brought to the right temperature, it's transferred to a holding furnace positioned beneath the mold. This holding furnace helps maintain the molten metal at the required temperature and ensures a continuous supply of material for the casting process.

3. Force Molten Metal Through Riser Tube into Mold by Applying Low Pressure

The molten metal is then forced through a refractory tube, or sprue, using low pressure. The pressure applied is usually significantly lower than in other casting methods, typically below 0.8 bars. The controlled low pressure in low-pressure casting and the slowness of the process facilitate a smooth and controlled flow upward through the riser and into the mold cavity via the mold's base. This pressure is typically sustained throughout the solidification stage to guarantee a thorough filling of the mold.

4. Let Metal Solidify Under Constant Pressure in Die Cavity

The molten metal begins to cool as it enters the mold but it only starts to solidify when it gets down to the liquidus temperature. The solidification process takes place under constant pressure, which ensures complete filling of the mold as the metal cools and contracts, or shrinks. This controlled solidification reduces the formation of defects and ensures a uniform structure within the cast component.

5. Release Pressure and Recycle Remaining Molten Metal

After the metal has solidified within the mold cavity, the pressure is released. Any remaining molten metal is then typically collected and recycled for future use, minimizing material waste.

6. Cool Mold for Easy Casting Removal

The mold, now containing the solidified cast component, is allowed to cool down. Cooling helps in the solidification process completion and enhances the overall integrity of the cast part. Once sufficiently cooled, the mold is opened, and the finished casting is removed. 

Metals Used in Low-Pressure Casting

The low-pressure casting process can be used to cast a variety of metals. Among the metals commonly cast using low-pressure casting are:

1. Magnesium

Magnesium alloys are often used in applications where light weight and high strength-to-weight ratios are crucial. These alloys find applications in industries such as: aerospace, automotive, and electronics. In the automotive industry, magnesium components are used to reduce the overall weight of vehicles, enhancing fuel efficiency and reducing emissions. For example, gearbox casings and steering components made from magnesium alloys contribute to lighter and more efficient automobiles.

2. Aluminum

Aluminum and its alloys are widely processed using the low-pressure casting method. In fact, they dominate all other metal choices in low-pressure casting. Aluminum's versatility, lightweight nature, and excellent corrosion resistance make it a popular choice for various industries, including automotive, aerospace, and consumer goods. In consumer goods, such as laptops and smartphones, aluminum casings provide a balance between durability and aesthetic appeal

3. Copper

Copper is less common than other metals on the list because of its higher melting point which demands more energy and time to melt. Copper's high thermal conductivity, while advantageous in applications, can lead to mold cracking and thermal stress during rapid cooling, necessitating specialized mold designs. Oxidation susceptibility at elevated temperatures requires protective measures to maintain cast part quality. Additionally, copper alloys exhibit lower fluidity, potentially affecting mold filling in intricate designs. 

Overall, copper alloys are valued for their electrical and thermal conductivity, making them suitable for applications in electronics and telecommunications. The electronics industry use it for heat sinks, connectors, and various electrical components that require efficient heat dissipation.

4. Zinc

Zinc alloys are often selected for die casting applications because their properties make them easy to work with: excellent fluidity, low melting point, and dimensional stability. These alloys are used in applications having intricate shapes, for decorative pieces, and for hardware. A notable application is in the production of door handles and hardware, where zinc alloys can be intricately cast into detailed designs while maintaining durability and corrosion resistance.

Applications of Low-Pressure Casting

Low-pressure casting is mainly used for the manufacture of complex, high-quality components. These include aluminum alloy engine blocks and suspension components for cars, cylinder heads, aluminum wheels, heat sinks for electronic components, pump housings, impellers, and even golf club heads. LP casting is suitable wherever complex geometry and intricate designs need to be produced.

What Industries Use Low-Pressure Casting Products?

Low-pressure (LP) casting stands as a favored manufacturing technique across various industries, notably automotive and aerospace. The adoption of this method is driven by its economic viability and the assurance of producing high-quality products. The automotive industry uses LP casting for components such as wheels and cylinder heads. Along with the aerospace industry, this is where LP casting is most widely used. Tennis rackets and bicycle frames can be made using LP casting. Certain components for washing machines, vacuum cleaners, and cooking equipment are also made using LP casting. Various components found in industrial machinery are made using LP casting, including: impellers, pump housings, and gearbox casings.

What Is the Quality of Low-Pressure Casting Products?

Low-pressure casting is known for its ability to yield superior castings with enhanced strength and dimensional accuracy (+/-0.005 inch for the first inch and then +/-0.003 for each additional inch). This is due to the precise control of the mold filling, which results in reduced porosity and oxide formation and consequently ensures a low defect rate and homogeneous mechanical properties throughout the cast product. 

Lifespan of Low-Pressure Casting Products

Die cast molds are expected to last between 80,000 and 100,000 casting cycles. When low-pressure casting is performed with proper techniques and attention to detail, the resulting products can have a long and reliable lifespan. The carefully regulated and uniform flow of metal, combined with reduced turbulence of the casting process often leads to parts with good mechanical properties and reduced porosity, contributing to their durability. However, the lifespan of low-pressure casting products can vary widely based on multiple factors. These include: the type of material used, the quality of the casting process, the design and engineering of the product, the specific application and conditions in which the product is used, and the level of maintenance and care provided throughout its service life. 

Advantages of Low-Pressure Casting

Low-pressure die casting (LPDC) offers a host of advantages, as listed below:

1. Exhibits high accuracy as a result of maintaining low pressure during solidification. 
2. Minimizes inclusions from oxidation or trapped slag.
3. Introduces molten metal to the mold without turbulence. Avoiding churning and splashing the liquid metal helps to avoid oxide formation, which, in turn, leads to a lower level of unwanted inclusions in the final casting. 
4. Produces castings with minimal porosity by employing low pressure.
5. The regulated flow and solidification of metal enhance the mechanical attributes of the castings.
6. Controlled mold filling results in fewer casting flaws and consequently, less material discarded as scrap. 
7. Can accommodate a diverse array of non-ferrous alloys, such as: magnesium, aluminum, and zinc.

Disadvantages of Low-Pressure Casting

While the low-pressure die-casting process is renowned for its dimensional accuracy, it does also have some drawbacks:

1. Takes longer to fill a given mold shape than other casting processes, such as high-pressure die casting. 
2. The potential for erosion within the aluminum casting form primarily emerges from the interaction between the molten metal and metal components of the equipment. This phenomenon of erosion typically affects components such as the crucible and riser. While erosion of the aluminum casting itself is not a common issue, localized erosion might occur in areas of high turbulence, such as near the entry point or other critical regions of the mold. 
3. Requires a minimum wall thickness of around 3 mm.
4. Although low-pressure casting typically demands less energy than certain alternative casting methods, such as high-pressure die casting and sand casting, it does exceed the energy consumption of more straightforward techniques such as gravity casting. 
5. Substantial upfront financial commitment to procure specialized equipment and tooling. The expenses encompass the acquisition of the low-pressure casting machine, mold preparation, and additional ancillary equipment. 
6. The systems that control casting metal temperature and application of pressure for mold filling require skilled operators with appropriate training.

Low-Pressure Casting Cost

Generally, low-pressure casting can be more cost-effective than some other casting methods, like high-pressure die casting, due to its reduced need for extensive tooling and its ability to produce high-quality castings with less porosity. While it still necessitates essential components like furnaces, liquid metal transfer systems, molds, and controls for temperature and pressure, LPDC does not need complex and costly die shot equipment and associated maintenance. The cost of low-pressure casting machines typically falls in the range of $30,000 to $50,000. Piece price of the cast products can range anywhere from as low as $1 to several thousand dollars. However, the exact cost would depend on the unique circumstances of each casting project. It's recommended to obtain quotes from casting service providers or manufacturers to get a more accurate estimate based on your specific requirements. 

Differences Between Low-Pressure Casting and High-Pressure Casting

Low-pressure casting and high-pressure casting are two distinct methods employed in metal casting. The main difference is that  low-pressure casting is generally conducted at pressures  below 0.8 bar, ranging up to 1 bar in some cases. High-pressure casting, on the other hand, involves significantly elevated pressures, frequently exceeding bars. 

The mechanical strength of the resulting cast parts is another point of difference. Components manufactured using low-pressure casting demonstrate elevated strength characteristics owing to their extended solidification duration accompanied by consistent pressure application. This combination of factors facilitates the formation of a more refined microstructure within the cast material, contributing to increased strength. On the other hand, components produced through high-pressure casting also possess commendable strength attributes; however, they encounter challenges in reaching the equivalent strength levels achieved by their low-pressure counterparts.

Desired part thickness plays a significant role in choosing between the two methods. Low-pressure casting excels in producing thick parts, yet is ill-suited for thin-walled components (less than 3 mm). On the other hand, high-pressure casting is useful for making thin-walled parts (down to 0.40 mm).

Summary

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Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry&#;s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

Buyer&#;s Guide: Selecting a Qualified Injection Molding Partner

In cases where budget and delivery problems occurred in a plastic injection molding project, it&#;s often true that these problems could have been prevented during the partner selection process. These problems include:

Compromised quality

Unpredictable lead and delivery times

Gaps in capability 

There are a number of qualities that plastic injection molding manufacturers can demonstrate to show that they are best qualified to avoid these problems.

Quality

Customers seeking a plastic injection molding partner can ask for a number of assurances about the quality of the work. Injection molding providers can prove their ability to meet quality standards by showing potential customers that they have:

Adequate traceability from resin raw material to the finished product

Quality certifications and protocols that are needed for your industry segment

The ability to track scrap to achieve a quality KPI

A robust molding process that is approved during the mold-building process

An excellent quality inspection lab (team)

Industry 4.0 technology that monitors the injection molding process on all machines live on the production floor

Demonstrated success in the market

Timeliness

A qualified partner should have a process for communicating timelines that involves an initial agreement between customer and manufacturer about timelines and expectations. Procurement challenges do occur, but advance planning reduces these challenges. In plastics, procurement of raw materials (resins and compounds) can take 6 to 16 weeks or more, depending on disruptions in the supply chain like weather-related disasters and global events.

Injection molders also meet expectations of timeliness through transparency in their forecast of the entire process and through supply chain management practices. Some specific ways they achieve on-time delivery include:

Providing mold design, fabrication, qualification, and production in-house: Providing these services in-house cuts down dramatically on the time that would be required to have the project transported and processed elsewhere.

Using Kanban (just-in-time) shipping technology to track and maintain inventory levels.

Using Quick Response Manufacturing (QRM) work cells: Studies have shown that the physical time of manufacturing the product is only 5-12% of the total lead time in a project. Using the

Quick Response Manufacturing (QRM)

system, manufacturers can optimally manage time, organizational structure, system dynamics, and time-based management principles in all parts of the organization. 

Using blanket purchase orders rather than waiting for a new P.O. in cases where purchases are recurring or when changes need to be made in dollar amounts, quantities, goods and services, and/or the maximum order. 

Capability

Does the partner you are considering have the production capabilities for your project? 

In short, your partner must have the equipment to perform the job, provide facilities that are modern and well maintained, and have a plant designed for efficient workflow with flexible manufacturing systems. They should perform process monitoring, scientific injection molding, and decoupled molding to ensure that the best manufacturing process is performed.

Your partner should have demonstrated success in designing and fabricating injection molds. They should be equipped with both horizontal and vertical molding presses, depending on your project needs. In addition, they should offer the highest level of standards for certification and decoupled molding processes. 

 

Finally, the financial health of the company is an essential indicator of capability. A potential partner should be able to demonstrate proven success in overseeing operations, such as forecasting into the next quarter, and conducting inventory forecasts. A financially healthy partner not only has all of the equipment, processes, and personnel to complete your job, but has the capacity to acquire assets that will make your job run with optimal quality and efficiency.

 

Case Study: Finding the Right Injection Molding Partner Solves 3 Key Challenges

Additional reading:
How Does Epoxy Coated Wire Mesh Price Impact Your Project Costs?
4 Tips to Choose an Aluminum Oxide Flap Disc

Want more information on low pressure overmolding services? Feel free to contact us.

&#;We were looking to find a partner that could support our company&#;s entry into the biopharmaceutical market and also a partner that met all of the technical requirements for manufacturing molded parts for that market.&#; &#; Pharmaceutical Executive

Technical Challenges

A pharmaceutical company was seeking a partner to support entry into the biopharmaceutical market. They engaged a procurement specialist to research vendors. &#;We were looking to find a partner that met all of the technical requirements for manufacturing molded parts for that market,&#; an executive reports.

This company had the following criteria:

Molded parts needed to be manufactured in an ISO Class & Clean Room.

The supplier needed to be certified for manufacturing to the ISO Medical Devices Standard.

The molding tools needed to be manufactured in the United States.

Design Challenges

The customer was seeking to stay with their total budget for three tools with multiple variations of the parts. This presented a significant budget hurdle, but Crescent Industries met the challenge by building injection molding tool sets with removable cavities that would utilize their Master Frame bases to house their tools during production runs. 

Timing Challenges

The supplier needed to support a schedule to design and fabricate tooling and produce initial injection-molded parts with a quick turnaround. The solution to this problem was 

Working with a partner that could design and fabricate in-house

Working with a partner that manufactured tools in the United States to avoid long transportation line times and the risk of shipping delays.

Best Buying Guide for an Injection Moulding and other Mouldings

 

Best Buying Guide for an Injection Moulding and other Mouldings

 

Generally, a repetitive manufacturing or production of a plastic products includes moulds. Moulding is a process of production by shaping liquid or plastic raw material using a rigid frame called a mould. It is most typically used in mass-production methods where a likewise part is being created thousands or millions of times in a continuous succession. In the present manufacturing units injection moulding is the cost effective, when compared to other types of Mouldings.

Types of Moludings

&#; Blow moulding
&#; Compression moulding
&#; Injection moulding
&#; Matrix moulding
&#; Transfer moulding
&#; Rotational moulding or spin casting

 

Blow Moulding:

A manufacturing process by which hollow plastic pieces are formed and can be joined together. It is also used for producing glass bottles or other hollow shapes. There are three types of blow moulding they are extrusion blow moulding, injection blow moulding, and injection stretch blow moulding. The blow moulding begins with melting down the plastic and moulding it into a parison or, in the case of injection and injection stretch blow moulding, a pre-form. A parison is a plastic tube-piece with a hole through which compressed air can pass. The parison is clamped to a mould and air is blown into it. The air fills the molten plastic to the walls of the mould making a hollow space in the middle. It is removed after the plastic gets cooled.

Compression Moulding:

Compression moulding is a general process used for both thermoplastic and thermo set to frame materials. Compression moulding is performed by placing the plastic material in a mould and produced by heat and pressure. The heat and pressure will harden the material and then it can be removed.

Injection Moulding:

Injection moulding is a production process for producing parts by injecting molten matter into a mould. Injection moulding can be made with a host of materials mainly metals, glasses, elastomers, pastries, and most commonly thermoplastic and thermosetting polymers. This technology is also used in 3D printing. Extrusion moulding is most similar to the injection moulding.

Types of Injection Moldings:

&#; Thermoplastic injection molding
&#; Over molding
&#; Insert molding
&#; Cold runner
&#; Hot runner
&#; Injection blow moulding

Matrix Moulding:

Matrix moulding is a technique often used during moulding. The assembled disposition first creates the rigid outer shell or flask, then introduce the softer and more fluid moulding material within the shell and the prototype. This process is often used for complicated shapes using composites such as glass and ceramic.

Transfer Moulding:

Transfer moulding is a production process where cast material is forced into a mould. It is different from compression moulding where mould is enclosed rather than open to the fill plunger emerging in higher dimensional endurance and less environmental impact. Compared to injection moulding, transfer moulding uses higher forces to uniformly fill the mould hole. This allows reinforcing fibre moulds to be more completely saturated by resin. This can reduce machine costs and time dependency. The transfer process may have a slower fill rate than injection moulding processes.

Rotational moulding or Spin casting:

Rotational Molding involves a roasted hollow mould which is filled with a shot weight of the material. It is then slowly rotated such that the softened material would disperse and hold to the walls of the mould. In order to maintain the quality throughout the material, the mould is continuously rotated to avoid the deformation while cooling. The improvements made in process control within plastic powders have resulted in a vital increase in this method. Spin casting also involves in a similar type of moulding. It has a disc shaped rotating plate where the rubber is moulded in to a required shape.

Best Buying Guide of an Injection Mould

&#; Ensure your production demand meets the injection mould.
&#; The metal used in a mould should meet your production.
&#; Mould base size, shot size, tonnage, platen size, tie bar spacing, ejector stroke strength, stability and performance helps in maintain the product quality with low production cost.
&#; Should also have a glance at energy efficiency
&#; What will be the design of the mould?
&#; What will be the cost borne to manufacturer a part or product
&#; what will be the volume of the product?

Guidelines of Choosing Best Injection Mold Supplier:

&#; Before you place your first order to a new plastic injection mould find whose is the best supplier and why?
&#; Need to be very careful about the choice you make on the manufacturer.
&#; Firstly you need to know what your needs are. Discuss it with the mould suppliers about the requirements, you should be clear what the steel and mould base be used, and whether hot nozzle included or not, request the details as specific as possible.
&#; Know about the companies quality control and what are their quality assurances.
&#; Compare the cost variations
&#; Look forward for the services and previous feedback on their service.
&#; Top Suppliers of Injection Moulding and Other Moulding Types

6 Tips to Consider When Purchasing Injection Molds

When purchasing an injection mold, attention to detail throughout the effort is critical to long-term success and stress-free manufacturing. Some mold design aspects should be considered as early as the start of the product development effort. Others begin when the tool order is placed.  The project manager&#;s main goal in this process is to keep the customer happy without creating problems for manufacturing.

 

Here are six tips to consider when buying an injection mold:

 

Part design is the most important aspect of long-term molding success.  You don&#;t want to quickly approve a plastic part design only to find out later that it is plagued with features that are not friendly to injection molding.  Real design creativity comes from minds that can find attractive solutions that considers manufacturing process limitations.  The best outcomes occur when the part designer, mold maker and injection molder work together collaboratively.

 

Proper risk management, effective communication and realistic timelines are critical to production success. Anticipating potential issues and budgeting for them during the planning stages will help the project stay on schedule and close to budget. For example, planning and communicating for a possible mold re-cut to bring plastic features into the appropriate tolerance range after the initial mold sampling. 

 

Consider cost savings on tooling wisely. No amount of savings is worthwhile if it compromises the ability to maintain the condition of the mold, has the potential to affect part quality, or complicate start-up and daily production.  Relatively small tooling savings will be dwarfed by the cost of scrap, drain of resources, lost time and repair activities, so carefully consider how cost savings can impact overall efficiency.

 

Take your time with the mold design review.  This is your chance to get it right before it is too late.  The focus should be on mold filling, cooling, and ejection attributes.  Simulation data and documented prior experience should justify most of the decisions.  When it comes to ejection, ask yourself why the part would remain on the tool&#;s ejection side in every cycle and be convinced it can be removed without damage.

 

Standardize mold features to save time and money.  Make sure you supply the mold maker with standards for clamp slots, lift bars and connection sizes. You also need to provide location preferences for utilities including air, water, oil electric, etc.  Otherwise the mold might need replumbing when it arrives or if it is moved to other machines.

 

Check in with the shop floor and quality groups before a new tool arrives. This is the time to ensure your team has what they need to hang the mold efficiently and measure the parts.  Some items to review are the number of ports on water manifolds, availability of controllers for hot runners and coolant, heater cables and plugs, fittings, hoses, bolts, lifting straps, etc.

 

 

 

Are you interested in learning more about custom low pressure overmolding solutions? Contact us today to secure an expert consultation!